Hinge Axis II. History

. Mandibular movementsWe can view the face in the frontal, sagittal, and horizontal planes. The mandible rotates in each of the three planes around an axis. This axis can be stationary or moving .Movement occurs in the horizontal plane when the mandible moves into a lateral excursion. The center of rotation is the vertical axis extending through the rotating condyle.The mandible also rotates around the sagittal axis when the orbiting side drops down during a lateral excursion.In the sagittal plane the mandible makes a purely rotational opening and closing border movement around the Transverse Horizontal Axis.Quick summary of mandibular movementIII. How do we define hinge axis today?Transverse Horizontal Axis: An imaginary line around which the mandible may rotate. (GPT-6)This rotation averages about 12o or 18-25mm of incisal opening according to Rahn, and occurs during centric relation.How do we define centric relation: The relation of the maxilla to the mandible when the condyles are in the uppermost and rearmost position in the glenoid fossae. This position may not be able to be recorded in the presence of dysfunction of the masticatory system. IV. Is there any controversy concerning hinge axis?Of course there is. It has been present since 1921. Controversy has arisen over the presence of a single axis, the methods used to locate the axis, the method and validity of recording the positions on the skin for future reference, and the relation of the terminal hinge position to the position of centric relation.On with the controversy?Does a single axis exist? (a line needs only two points and therefore anatomic symmetry of the condyles is not necessary) So why was there a controversy?Page says "Lack of training in the basic sciences lies behind the plausible but groundless arguments against (hinge axis)"Page says again " A condyle rotates; therefore, any argument against its doing so around rotational centers or a hinge axes is an argument against the truth."Can a single point in the condyle be located and can it be transferred to the articulator? Page says no! So what is Page's opinion on hinge axis? (Intracondylar or Intercondylar, Two arcs of rotation)Is Page right? Does each condyle have its own axis of rotation? Does it matter?Granger says something else! What does Granger say? (Intercondylar, Why?)Can one arc result from compound mandibular movements?V. Four theories of the location or existence of the hinge axis.1. Absolute location of the axisThe hinge axis is a component of every masticatory movement and can not be disregarded. If the hinge axis of the articulator is not the same as the hinge axis of the patient then the mechanical reproduction of jaw motions are impossible.

2. Arbitrary location of the axisThe value of actually locating the exact hinge axis is not worth the effort. This group fails to recognize that if the hinge axis of the articulator does not coincide with the hinge axis of the patient, the paths of closure will not be the same.3. Nonbelievers in the transverse axis locationThis group does not believe the hinge axis can be accurately located or believes other movements are involved and can not be reproduced by an articulator simulating one axis; therefore, an arbitrary axis is just as good.4. Split axis theoryThis group believes there are two axis of rotation ( one in each condyle) and they parallel each other. What did Arthur E. Aull find out about the hinge axis? Who's study supported him?1. The horizontal axis is a hypothetical line connecting the two horizontal rotation centers of the two condyles of the mandible.2. There is one hinge location!3. Beard and Clayton reproduced a 1967 study by Trapozzano and Lazzari that obtained evidence to the contrary of Aull. Beard and Clayton found there is only one hinge axis!VI. What is the significance of a hinge axis mounting?Remember the purpose of the articulator is to reproduce on a mechanical instrument the relationship of the teeth as they come together in the mouth.The hinge axis provides the means of transferring the patient to the lab to construct the restorations. It must be considered. What else must be considered.?Can a simple protrusive registration accurately allow the settings of an articulator to resemble the movement of the mandible? ( No way Jose!!)So locating the hinge axis is just one step in attempting to reproduce mandibular movement. It is however very important because all movement starts at the axis and returns there. See above drawing. Draw some mandibular movements if anyone desires.Review.Why is it important to know about the hinge axis or to determine where it is located.?What will happen to the arc of closure if the hinge axis is mistakenly placed anterior, posterior, superior, or inferior the true hinge axis?How does this pure hinge movement affect dentistry? (Arc of closure)Is the path of closure the same as the arc of closure? (No) The path results from closing rotation and a gliding path.VII. Does everyone believe that the mandible closes on an axis?What, Who said so? What did they do and how did they reach their conclusions? Shanahan and Leff in 1962 and Ferrario, et al. in 1996VIII. Locating the axisHow accurate are individuals in locating a true hinge axis?- Kurth and Feinstein said within 2 mm when restricting opening to ¾ inch at the incisal pin.- Borgh and Posselt said within 1.5 mm when a 10 degree arc was used and within 1.0 mm when a 15 degree arc was used.

- Lauritzen and Wolford were able to achieve an accuracy of 0.2 mm when using a 10 degree arc of movement.What are some methods of locating a true hinge axis?Observing the motion of a stylus on an axis bow, as created by jaw movements, in relation to a flag fixed over the patients axis area. When the stylus no longer translates but rotates then the point is accepted.Geometric principles can also be used to aid in locating the point as described by Getz3. Gunderson and Parker described a technique similar in thought to Getz.How accurate is an arbitrarily selected axis?Scallhorn found that 95% of the axis points located 13 mm anterior to the posterior margin of the tragus on the tragus-canthus line to be within a 5 mm radius of the kinematically located axis.Beyron found that approximately 87% of the located points were within a 5 mm radius of the arbitrary points.Lauritizen and Bodner found only 33% of the true axis points to be located with in a 5 mm radius of the arbitrary points. Teteruck and Lundeen found similar results.Walker found that 20% of the true axis points were located within 5 mm from the arbitrarily selected point.Palik, Nelson, and White found that the earpiece face-bow related the maxillary cast to the hinge axis only 50% of the time. 92% of the time the arbitrary axis was located anterior to the terminal hinge axis.What are some methods of arbitrarily selecting an axis?Schlosser described palpating the condyles as the patient opens. He also described drawing a 25 mm line from the upper margin of the external auditory meatus to the outer canthus of the eye. At a point 13 mm in front of the tensed anterior margin of the meatus a line is drawn crossing the first line at right angles.Brandrup-Wognsen described a point on a line extending from the tragus to the lateral angle of the eye, a point is marked at about 12 mm in front of the posterior margin of the most prominent point of the tragus.Prothero recommends placing a Richy condyle marker in the external auditory meatus then placing a ruler from the top of the marker to the outer canthus of the eye and drawing a line. The condyle marker is then rotated to make a line 13 mm from the anterior side of the metal part of the marker.Weinberg recommended adjusting the face bow pins to a point 11 to 13 mm anterior on a reference line drawn from the middle and posterior border of the tragus of the ear to the corner of the eye.What does Simpson have to say about arbitrary mandibular hinge axis location?Use a point on Camper's line 10 mm from the superior border of the tragus!IX. Does the mandible flex and why do we care?Yes it does. This response is a function of the mechanical properties of the bone as well as the type, magnitude, direction, and point of application of the force.The later pteygoid muscle is most frequently cited as inducing mandibular flexure.- What are the clinical implications of the mandible flexing?- Producing an inaccurate cast if flexure occurs during impressions

- Producing an inaccurate maxillo-mandibular relationship if flexure occurs during a CR registration- Mandibular flexure may influence stress on abutment teeth- Adduction of the mandible may effect the ultimate stability of a lower dentureWhat width changes were seen in various mandibular positions and manipulations in the Gates and Nichols article?Opening 0-0.3 mm decreased value in arch widthProtrusion 0.1-0.5 mm decreased value in arch widthHorizontal retruding force 0.11 mm increased value in arch widthTherefore the amount of mandibular arch width change during impression making can be minimized by preventing any protrusive movement and /or opening beyond 20 mm.

- Abstracts -03-001. Page, H.L. Some confusing concepts in articulation. D Digest 64: 71-76, 1958.Purpose: The purpose of the article is to discuss issues on articulation an encourage criticism.Discussion: Criticism has been expressed about the terminology of new principles, as being too "complicated". It is claimed that publication has been of no value for the average dentist since they will not bother to read the difficult material. Therefore the task is left to teachers and leaders to absorb the new concepts and to infiltrate the new philosophies into clinical practice.     As a profession we should awaken to the fact that something is wrong with our teaching and practice. Probably some confusion arises because of the great variety and complexity of methods and material offered, but more probably it is that information given to them is incorrect and founded upon wrong concepts. Confusion also arises from the fact that there are as many ways to solve a problem of jaw relations and occlusions as there are dentist.No one questions that the condyles are asymmetrically sized, shaped, and positioned.No one can argue that the condyles are joined at the symphysis and not by any connective tissue mechanism running through the head from condyle to condyle.Shift of the mandible in function- is not merely a " bodily side shift of the mandible in lateral excursion" as described by Granger, it is a bodily shift of the mandible in vertical function with each condyle moving in any one or in all three dimensions.Importance given to the Bennett movement- Granger also endows the Bennett movements with extraordinary powers. It determines the form and position of the sulci and marginal ridges. The power movement as the muscles on the working side contract. It determines the direction of stress on the supporting structures and therefore whether the cusps are pathologic or physiologic. If the Bennett movement is so important , it would be helpful to know more about it.Cause of movement claimed- Granger also considers a Bennett movement to be limited to a bodily side-to-side shift of the mandible occurring only during lateral excursions. He states that the limitation of movement against the inner curbing of the glenoid fossa determines the Bennett movement.Explanation of movement required- an unsupported statement cannot be accepted as a scientific fact . A condyle, "balancing" or otherwise, does not ride the "inner curbing" or any other part of a fossa under its own power, for it is the mobile part of a universal joint. Yet, no explanation is given to show how a " balancing" condyle can maintain unaided so firm a contact with the bone ceiling and above and medial to it that forces the working side of the head to move outward. In the absence of a valid explanation, what becomes of those powers of the Bennett movement?

Many hinge-axes exist- there are at least twelve hinge-axes in every head; three in each temporomandibular joint and three in each mandibular angle. Only the three in each joint require consideration: (1) the transverse hinge-axes that govern jaw rotation in the sagittal plane (opening and closing), (2) the vertical hinge-axes that govern jaw rotation in the horizontal plane (side-to-side), and (3) the sagittal hinge-axes that govern jaw rotation in the transverse plane (jaw rocking). 03-002. Preston, J. D. A reassessment of the mandibular transverse horizontal axis theory. J Prosthet Dent 41: 605-613, 1979.Purpose: to briefly review the history and development of the theory and practice of the transverse horizontal axis location, its applications and some controversies that have surrounded its use.Discussion and Conclusions: A single transverse horizontal axis can usually appear to be located. (within the limits of accuracy of operators, equipment and patients.)- When a kinematic axis is located, this is a worthwhile clinical procedure to transfer the arc of rotation in the sagittal plane from patient to the articulator- No one has proved or disproved the presence of colinear or noncolinear condyle arcs.- The right angle-non right angle concept is misleading and generally not indicated for use.- Anatomic asymmetries of the axis transfer procedure may result in cast dislocations that produce undesirable changes in esthetic tooth positions.- The single transverse horizontal axis exists as fact in articulating instruments and as a theory in the human craniomandibular complex.- The term "transverse horizontal mandibular axis" ("hinge axis") should be used instead of "condylar or intercondylar" axis.03-003. Granger, E. R. Clinical Significance of the Hinge Axis Mounting. DCNA,   Mar 1959:205-213. Discussion: The relationship of the teeth as they come together is determined by the relation of the condyle to the glenoid fossa. The hinge axis governs the art of closure in every contacting position of the teeth. The rotation of the asymmetrical condyles and the asymmetrical mandible, is guided by the form of the surface on the meniscus.The purpose of an articulator is to reproduce on a mechanical instrument the relations of the teeth as they come together in the mouth. The hinge axis provides the means of transferring the patient to the laboratory bench. Locating the hinge axis and reproducing the protrusive path (anterior slant and curvature of the condylar path) and lateral paths (Bennett movement) allows all combinations of movements to be made. To locate the hinge axis with a hinge bow, a clutch is mounted on the mandibular teeth. The chin is dropped open with pure hinge motion while a stylus records the position opposite the condyle. No gliding of the condyle should be allowed. The hinge axis must be located in the most posterior superior position of the condyle which is centric relation. The point of the stylus will reach the stationery point and the patient can be tattooed for future reference. Mounting the cast on the articulator can be accomplished by using the hinge bow as a transfer or face bow. The Frankfurt Plane is used to relate the face bow instead of the ala-tragus plane. Method of choice to register the paths of motion of the axis is the pantograph. Stone check bites may be used for edentulous patients. Wax check bites are worthless.

The hinge axis determines the arc of closure in every contacting position of the teeth. The path of closure is different from each open position of the mandible to tooth contact. This path results from the closing rotation combined with a gliding path of the axis. 03-004. Aull, Arthur E. A study of the transverse axis. J Pros Dent 13:469-479, 1963.Purpose: To demonstrate the fallacy of the hinge axis theory.Materials and Methods: The hinge axis was to be located using extra long arms and four flags and styluses. The extra two flags were placed 4 to 5 inches outside the inner flags. A hole was drilled were the hinge axis was located and a light was shown through the hole to see if there was one line.Results: One line was produced.Conclusion: There are four main schools of thought regarding hinge axis theory. Group 1. Absolute location of the hinge axis. These people believe the hinge axis is a component of every masticatory movement of the mandible and cannot be disregarded.Group 2. Arbitrary location of the axis. These people believe the hinge axis is of some value, but not worth the effort to locate.Group 3. Nonbelievers of the transverse axis theory. They believe the hinge axis is theoretical, but not practical.Group 4. Split-axis rotation. They believe in the transograph theory. That each condyle has its own center of rotation. i.e. two axes that parallel each other.Aull's study disproved the transograph theory03-005. Shanahan, T EJ and Leff, A. Mandibular and articulator movements. Part III. The Mandibular Axis Dilemma. J Prosthet Dent 12: 292-297, 1962.Purpose: Sustained protrusionTo observe mandibular movements to confirm or deny the presence of an axis in the region of the condyles.Methods & Materials: Photographic records were made of the normal opening and closing movements of the mandible from both side and front.     Lights were placed to lower and upper incisors and side and view records of the movements of the lights were obtained by placing the camera at the side of the face and a mirror in front of the subject at an angle of 45 degrees to the camera.Observations & Recordings: Observing the mandibular movements from the front, the mandible did not open and close on an axis; from the side, the rotation center of the pseudo arc was not in the region of the condyle. These two views of opening and closing movements were not tracings of axis movements and therefore did not support the mandibular axis theory. From the side there was no evidence of rotation about a mandibular axis in the region of the condyle with a concomitant anterior translation. Bilateral Deviation: It was evident from the light  that the mandible may deviate to the right or left during opening and closing movements.Chewing Tests Fox Axis Determination: A subject chewed a piece of hard cracker three times to explore the possibility of the presence of mandibular axis during the mastication of food. None of the movements showed evidence of a natural mandibular axis.Artificial Mandibular Axis: The term artificial mandibular axis designates an axis that is the result of forcing the mandible backward. This axis cannot be found during normal physiologic mandibular movements. An artificial mandibular axis can be produced in one of two ways: the patient may voluntarily retrude the mandible as far as possible during the opening and closing movements, or the dentist can apply firm, backward pressure to the chin during movements.

Conclusion: The authors concluded that an artificially produced mandibular axis, jaw movement, jaw position is not a normal physiologic movement.     There was no evidence of rotation about a mandibular axis in the region of the condyles with concomitant anterior translation in these studies of the opening, closing, and masticating movements.03-006. Schalhorn, R. G. A study of the arbitrary center and kinematic center of rotation for facebow mounting. J Prosthet Dent 7: 162-169, 1957.Purpose: Discuss certain advantages of the face bow when used properly, and its merits in prosthetic dentistry.Discussion: The kinematic face bow is expensive, and a rather lengthy and difficult procedure.     If the advantages are enough to offset the disadvantages, then by all means, its general use should be established. It has been stated by Arstad Thor, in his study on mandibular movements, that an error of 5mm from the hinge axis results in an error of only 0.2 mm, in the articulator, the molar of the lower jaw model will have contact with its antagonist 0.2 mesial or distal to the intraoral occlusal position of the molar after a corresponding mandibular movement of 2mm. Because of this 5mm tolerance with the resultant negligible error, many feel that it is not necessary to determine the axis accurately.Materials & Methods:1. Seventy dental students with normal occlusion and at least 28 teeth were selected for the study.2. Alginate impressions and study casts were made. Large undercut areas were filled with Tenax wax, and a splint was molded over the teeth with self-curing acrylic resin. 3. The face-bow was embedded in the resin splint while plastic, and the acrylic resin was allowed to cure. The fork was then removed from the cast. The splint was then trimmed.4. The patient was then instructed to practice opening and closing the mandible in centric relationship through and arc of about 10mm at the incisor region.5. Marks were placed over the condylar area, and a line was drawn from the center of the tragus to the outer canthus of the eye. On this line, the arbitrary axis was plotted 13 mm. Anterior to the posterior margin of the tragus, and the tape was identified by the side and the number of the determination.6. The fork was then fastened to the splint and the Hanau model H face-bow attached to the fork. By a process of trial and error, the axis was plotted and marked on each type.7. Rechecking was done for reproducibility, and of the 30 or more actual cross-checks, only one such check was more than 1.5 mm from the original plotting. In most cases, the error of reproducibility was at a radius of less than 1 mm from the original plotting.Conclusion:1. In over 95 % of the subjects with normal jaw relationships, the kinematic center lies within a radius of 5mm from the arbitrary center, which is considered by Arstad and others to be within the limits of negligible error.2. The arbitrary axis of rotation as set by Snow, Gilmer, Hanau, Gysi and others, of 13mm, anterior to the tragus on the trageal-canthus line comes very close to an average determined axis on individual with normal jaw relationships.3. The author agrees with other authors that determining the kinematic center of rotation is not nearly as important as obtaining proper centric and vertical records.

03-007.  Lauritzen, A. G., and Bodner, G. H. Variations in location of arbitrary and true hinge axis points. J Prosthet Dent 11: 224-229, 1961.Purpose: to determine the variations in the location of the true hinge axis points from the location of the hinge axis points determined by arbitrary means.Materials & Methods: a technique for easy and accurate location of the true hinge axis was developed by researchers of the Lauritzen Research Group. This technique included a special tray (anterior portion of a rim lock tray) secured to the mandible utilizing alginate impression material. The hinge axis point was located utilizing readings from the hinge axis locator . ( 1 cm. square of millimeter graph paper was attached to the skin in an area anterior to the tragus of the ear. The above method was utilized on fifty patients, thus locating 100 true hinge axis points.Conclusions: The study found that in locating true hinge axis points, 67% were from 5 to 13 mm. away from the arbitrarily marked hinged points (using surface landmarks).This means that arbitrary marking of the hinge axis may result in inaccurate mounting of casts to an articulator, and occlusal discrepancies if the centric relation record is made with separation between the upper and lower teeth. Therefore, the accurate location of the true hinge axis points is recommended by the authors.03-008.  Walker, P. M. Discrepancies Between Arbitrary and True Hinge Axis. J Prosthet Dent 43:279-285, 1980.Purpose: Analysis of a clinical study to determine if there exists an anatomic average measurement to use for arbitrary hinge axis point locations.Methods & Materials: 222 undergraduates had their true anatomic hinge axis point locations determined using a Denar hinge axis locator. Each had a full complement of teeth. The reference line chosen was tragus-canthus line. These points were compared with a 12mm anterior reference and 5mm inferior arbitrary axis point locations. Results: No consensus for arbitrary hinge axis location existed. Most of the locations will give a 6mm or more error with a minimum of 5mm expected. The largest percentage of locations will be inferior to the tragus-canthus line at the superior border of the tragus of ear. Very few people had the same true axis point located on both sides of the face.Conclusion: Any chosen arbitrary location would not reliably represent the true anatomic hinge axis. 03-009. Beard, C.C.  and Clayton, J.A. Studies on the validity of the terminal hinge axis. J Prosthet Dent 46:185-191, 1981.Purpose: To determine whether the results of Trapozzano and Lazzari's study would have been different had they used a different recording apparatus.Materials and Methods: Hinge axes were located by drawing arcs on the paper rather than just visualizing the stylus. Results: One not multiple hinge axes were located.Conclusion: The Trapozzano and Lazzari study showed multiple hinge axes but with the use of drawing arcs on paper this study showed only one hinge axis.03-010. Gates, G.N. and Nicholls, J. I. Evaluation of mandibular arch width change. J Prosthet Dent 46(4):385-392,1981.Purpose: To evaluate width changes of the mandibular arch at various mandibular positions and manipulations so that dentists can minimize problems during dental treatment.Materials & Methods: A light sensing photo-diode (Pin-SC/4D, United Detector Technology, Inc, Santa Monica, CA) a light detector source (In-sight light, American Midwest, Des Plaines,

Ill) and a 0.020 inch plastic fiberoptic strand (Edmonds Scientific Supply, Barrington, NJ)to transmit the light to the photodiode surface. To compare arch width changes with mandibular opening or protrusion, a linear variable differential transformer (LVDT) mounted extraorally measured millimeters of opening, protrusion while the photodiode measured mandibular arch width changes. The device was attached to the mandibular teeth with minimal force to reduce mobility by natural teeth.Ten men between 20 and 50 years of age who had a full complement of natural teeth with no evidence of periodontitis were evaluated. The data measured provided the following comparisons:  a.  opening, protrusion, and sustained opening and protrusion, vs. arch width change  b.  arch width change vs. mandibular manipulation using chin point guidance  c.  arch width change vs. maximal biting forces in the cuspid/ first premolar locations both unilaterally and bilaterally  d.  subjects were premedicated with Banthine tablets to decrease salivary flow  e.  five sustained max protrusions, openings , and five continuous mand. manipulations  f.  after each movement passive or resting states were recorded to return to "zero" driftsConclusion:   a.  The width of the mandible is influenced by intrinsic and extrinsic forces.  b.  Maximal opening, protrusion, and biting forces cause the mandible to decrease in arch width.  c.  A horizontal retruding force on the mandible caused an increase in arch width  d.  The amount of mandibular arch width change during impression making can be minimized by preventing any protrusive movement and/or opening beyond 20 mm.03-011. Simpson, J.W. , Hesby, R.A. , Pfeifer, D.L. and Pelleu, G.B. Arbitrary mandibular hinge axis locations. J Prosthet Dent 51: 819-822, 1984.Purpose: Compare the location of selected arbitrary hinge axis points and an experimental arbitrary axis point with the kinematic axis.Materials & Methods: 1. Fifty subjects 19-60 years old, with acceptable occlusion and no clinical signs of TMJ dysfunction were selected.2. TMJ INSTRUMENT HINGE axis flags were positioned on the face slightly anterior to the tragus of the ear.3. Five arbitrary axis points were recorded on graph paper:  (a) Beyron’s point was located 13mm anterior to the posterior margin of the tragus of the ear on a line from the center of the tragus to the outer canthus of the eye.  (b) Gysi’s point was located 10mm anterior to the posterior margin of the tragus on a line from the center of the tragus to the outer canthus of the eye.  (c) Bergstrom’s point was marked 11 mm anterior to the posterior margin of the tragus on a line parallel to and 7 mm below the Frankfort horizontal plane.  (d) Teteruck and Lundeen’s point was located 13 mm anterior to the tragus on a line from the base of the tragus to the outer canthus of the ear.  (e) The experimental arbitrary point selected was placed 10mm anterior to the superior border of the tragus on Camper’s line. (Camper’s line connects the superior border of the tragus and the inferior border of the ala of the nose).

4. The Almore mandibular hinge axis locator was used to locate the kinematic axis.5. The true axis point was recorded on the same graph paper as the arbitrary axis points. The % of arbitrary axis points that fell within 5mm of the kinematic axis was calculated for each point, the distance between each point and the kinematic axis was measured.Discussion: 1. The study shows that 78% of experimental axis points were located within 5mm of the kinematic axis. Arstad and Weinberg reported that a 5 mm error in locating the mandibular hinge axis results in a negligible occlusal error of 0.2 mm at the second molar.2. 80% of the kinematic axis points were located below a reference line drawn from the superior border of the tragus to the outer canthus of the ear, and posterior to a point 12 mm anterior to the superior border of the tragus on the same reference line.3. An experimental arbitrary axis point was located below Walker’s reference line and closer to the superior border of the tragus.4. The experimental point was located on Camper’s line, 10 mm anterior to the superior border of the tragus.Conclusion: 1. In a review of the hinge axis theory, Preston stated that a superior-inferior error in axis location results in a larger discrepancy than an error in anterior-posterior location. Beyron, Gysi and Bergstrom showed an inferior-anterior tendency.2. The arbitrary points of Beyron, Gysi, and Bergstrom showed directional tendencies, whereas the experimental arbitrary points were evenly distributed around the kinematic axis, and closely and consistently approximated the kinematic axis.3. The clinical use of a point on Camper’s line, 10 mm from the superior border of the tragus, results in a more accurate transfer of the maxillary cast to the articulator.03-012.  Gordon, S.R., Stoffer, W.M. and Connor, S.A.  Location of the terminal hinge axis and its effect on the second molar cusp position. J Prosthet Dent 60:553-559, 1988Purpose: to mathematically calculate the amount of cusp height and mesiodistal error at the second molar, resulting from locations 5 and 8mm (anterior, superior, posterior and inferior) to the kinematically located hinge axis. The maxillomandibular relationships were measured by interdental records of 3 to 6mm thick at the incisal region.Methods & Materials: Calculations were based on the following:  a.  a distance from the midpoint of the hinge axis to the mandibular incisal edges of 87.9 mm calculated from       Bonwill’s triangle.  b.  the Balkwill angle equals 18 degrees  c.  cusp inclines in a mesiodistal direction equal 30 degrees  d.  5-8 mm erroneous locations of the hinge axis (anterior, superior, posterior, and inferior), as stated above  e.  jaw relation records of 3 and 6 mm thick at the incisors, measured along the arc of closureSummary/ Conclusions: from the criteria stated above, the errors in cusp height at the second molar ranged from 0.15 mm open space to 0.4 mm excess height. The mesiodistal error ranged from 0.51 mm toward the distal to 0.52 mm to the mesial.

the CR record should be recorded at a vertical dimension close to the planned vertical dimension of occlusion

locating the kinematic hinge point prior to extensive treatment for dentulous patients results in a better occlusion and also saves time

when no change in vertical dimension (hence kinematic hinge point is not applicable) other techniques may be used

03-013. Palik, J. F., Nelson, D. R. and White, J. T. Accuracy of an Ear Piece Face-bow. J Prosthet Dent 53:800-804, 1985.Purpose: To record variations between the kinematic axis and earpiece determined axis and measure the magnitude and direction between the two points on selected subjects. Also, to evaluate the significance of the difference between the kinematic axis and the earpiece determined axis and the repeatability of the ear face-bow method statistically.Methods: The earpiece facebow used the external auditory meati and the inferior orbital rim as reference points, while the kinematic facebow used the terminal hinge axis and the inferior orbital rim as reference. Points.Kinematic location of terminal hinge axis: The area of the true hinge axis was located by palpating the subject’s condyles during opening and closing of the mandible. A clutch tray was affixed to the mandibular teeth with Impregnum. With the mandible in centric relation the axis points were tattooed on the skin. A bitefork was adapted o the occlusal surfaces of the maxillary teeth with black modeling compound. The bitefork was used for both kinematic and arbitrary facebow recordings. Modified Plexiglas disks were positioned on the lateral aspect of each of the condylar element of the articulator parallel to the sagittal plane. On each disk a graph circle was placed with the 0,0 coordinate point coinciding with the horizontal and vertical line intersection to simulate a x-y graph. The subject’s identification, side of articulator (r or L ) and anteroposterior positions were identified on the graph circles.Location of arbitrary hinge axis: The same bitefork previously used with the kinematic facebow was repositioned intraorally on the maxillary occlusal surface and stabilized with finger pressure. The Hanau earpiece facebow was attached to the bitefork and the ear rods adjusted in the subject’s external auditory meati until pressure was equally distributed bilaterally.Results: Most arbitrary axis locations were anterior and inferior to the true hinge axis. 56 % of the arbitrary axis locations were anterior an inferior to the terminal hinge axis, while 36% were anterior and superior to the terminal hinge axis. ONLY 50% of the arbitrary hinge axes were within a 5mm radius of the true hinge axis, while 89% were within a 6-mm radius.Discussion: In comparison studies of variations between arbitrary axis and the kinematic axis, results varied from 20% to 95% of the arbitrary hinge axis points, falling within a 5 mm radius of the true hinge axis point. This study compared favorably with that o Lauritzen and Bodner and firmly supported Teteruck and Lundeen. However, it did not support the findings of Beyron and Schallhorn. The statistical analysis demonstrated that the earpiece facebow is not statistically reliable or repeatable. This does not suggest that it is unsuitable clinically. The nylon earpiece should be modified to increase repeatability.Summary: This investigation demonstrated a significant statistical difference between the arbitrary axis located with an ear-bow and the terminal hinge axis. Additional study is needed to determine the practical value of the arbitrary facebow and to pursue modifications to improve its accuracy.Conclusions:  1.  The earpiece facebow related the maxilla to the hinge axis with the 5mm acceptable range 50% of the time.  2.  The earpiece facebow recorded the arbitrary hinge axis anterior to the terminal hinge axis

92% of the time.  3.  The earpiece facebow measurement in this study was not statistically repeatable.

 - Summary of Authors and Concepts – 

Page. Many hinge axes existPreston. Arc may result from compound movementsGranger. There is only one position of the hinge axis.Aull. Only one hinge axis.Shanahan. Study of natural motion does not show a hinge axisSchallhorn. 95% of patients true axis is within 5mm of the arbitrary hinge Axis (13 mm anterior to the tragus on the tragus- canthus line.Lauritzen and Bodner. 33% of a patients true hinge axes are within 5 mm of the patients true axis.Walker. 20% were within 5mmBeard and Clayton. One hinge axisGates and Nichols. The width of the mandible changes due to intrinsic and extrinsic forces.Simpson. Use a point 10mm from the superior border of the tragus on Camper's line for an arbitrary hinge axis. 78% within 5 mm.Gordon. Keep your centric relation record thin.Palik. Hanau ear bow. 50% within 5mm Hinge axis was located anteriorGetz. Geometric location of the hinge axisGunderson and Parker. Geometric location againFerrario. Pure rotation did not occur.

Section 04: Hinge Axis II(Handout)

Terms:Centric relation - the maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective disks with the complex in the anterior-superior position against the shapes of the articular eminences.Centric occlusion - the occlusion of opposing teeth when the mandible is in centric relation. This may or may not coincide with the maximum intercuspation position.Terminal hinge position = Retruded contact position - that guided occlusal relationship occurring at the most retruded position of the condyles in the joint cavities. A position that may be more retruded than the centric relation position. Maximum intercuspation - the complete intercuspation of the opposing teeth independent of the condylar position.Border movements - mandibular movement at the limits dictated by anatomic structures, as viewed in a given plane. Rotation - the movement of a rigid body in which the parts move in circular paths with their centers on a fixed line called the axis of rotation.Translation - that motion of a rigid body in which a straight line passing through any two points always remains parallel to its initial position.Hinge axis = Terminal hinge axis = Transverse axis = Transverse horizontal axis =

Transverse hinge axis - an imaginary line around which the mandible may rotate within the sagittal plane.Hinge axis point = posterior reference points - two points, located one on each side of the face in the area of the transverse horizontal axis, which together with an anterior reference point, establish the horizontal reference plane.Kinematic face-bow - (Hinge bow) face-bow with adjustable caliper ends used to locate the transverse horizontal axis of the mandible.Arbitrary face-bow - a device used to arbitrarily relate the maxillary cast to the condylar elements of an articulator. The position of the transverse horizontal axis is estimated on the face before using this device.Average axis face-bow - a face-bow that relates the maxillary teeth to the average location of the transverse horizontal axis.HISTORICAL PERSPECTIVE - Winstanley, R. B. The hinge axis: A review of the literature. In this review we can try to answer the following questions:1. Can the mandible open/close as a hinge in the sagittal plane? Is it normal?2. Should the axis be located when carrying out restorative procedures?3. If located, how accurate is it? Where is it located?Campion (1902-1905) - No one axis, but a complex one. First rotation, then down and forward. Bennett (1908) No single fixed center of rotation, constantly shifting in sagittal plane. Mandible can rotate, translate. Criticized for working on himself; no general conclusions.Gysi (1910) Treatise on History of Articulators. "Condyles not truly rotational points, but fixed guides of the mandible in its movements." "The mandible opens/closes and rotates on another rotational center which has no influence in the setting up of the teeth on articulators. Therefore, need not be considered in the construction of an articulator.Needles (1923) agrees with Bennett: hinge joint + sliding joint. 1927 used heads of condyles as reference point for axis on articulators which can open considerably without error in the occlusion. 1924 relation with prosthodontic dentistry: no center of rotation in temporomandibular joint itself. Instantaneous and constantly shifting centers.Wadsworth (1925) Anatomist's view: first movement around transverse axis through condyles which remain seated in fossae. 2nd movement on eminentia.Stansbery (1928) Dubious about face-bows and adjustable articulators. Plain line hinge articulator was just as effective. Hall (1929) Gave credit to Balkwill for recognizing mandibular movements which were hinge like and forward and back in the fossae. Quoted Luce: "Condyle is not the center of rotation." McLean (1937) Hinge portion of joint is the great equalizer for disharmonies between the gnathodynamic factors of occlusion. Inherently the place where vertical dimension of occlusion is controlled. In denture construction:- Hinge axis Premature contact on patient- Denture interocclusal alteration done in mouth or by using a hinge-axis articulator.McCollum (1939) Publishes a very important series of articles on restorative remedies. Leading advocate of the hinge-axis theory: "Amount of gliding depends on size of pin, but center of action is an imaginary axis through center of pin." External landmarks are of little use. Noted variation between sides of same individual (asymmetry).     Rotation occurs during 0.5 inch at incisors for most people, some can open 1 inch.Stuart (1939) Complemented the work of McCollum. Together pioneer Gnathology theory:-3D location of rotational centers

-Hinge axis location as a point-Border movements are to be recorded-Movements are reproduced on articulators-Delayed canine guidance-Point vs. Area contact-Condylar guidance dominantHigley (1940) Discussed development, adaptive changes in the joints, muscles influencing movement, and movement patterns of the mandible and condyle.With Logan (1941) Showed that as the mandible dropped from occlusion 15 mm, there was retrusive movement of the chin point, and the head of the condyle dropped progressively.     With an opening of 10 mm, 95% of cases showed a forward shift of the head of the condyle. When the mandible was opened 15 mm, all subjects showed a forward movement of the condyle.McLean (1944) Stated: " the diagnosis of pathological occlusion depended on the fact that the final phase of jaw closure was pure hinge movement."Oldies but GoldiesBrandstad (1950) The adjustable articulator was as important in oral diagnosis as the microscope was in pathological or bacteriological investigation. (Gnathological society)Kurth and Feintein (1951) Investigated the determination of hinge-axis mathematically. They concluded that because of all the variables (perception, anatomy, physiology, patient ability to follow instructions, prejudices of operator) it was unlikely that the hinge-axis could be located accuratelyEberle (1951) Hinge axis movement was a component of every motion of the mandible, and mechanically more important than the inclination of glenoid fossa.Lauritzen (1951) discussed the physiology of the TMJ. He thought articulation would be understood more easily if the joint were regarded as two separate joints. The only movement which could take place in the 'menisco-condylar' part of the joint was opening and closing - a purely rotational movement. In all patients, the anterior teeth could be separated by at least 12 mm in the rotational hinge relation. *Lauritzen and Wofford (1961) - Hinge axis location on an experimental basis - To study the accuracy of hinge axis location techniques. A special device was designed to test the hinge axis location at 5, 10, 15 degrees of movement. Five subject groups each with different experience levels were tested. Results: Training led to better scores; interest played a strong part in accuracy attained; physical characteristics (e.g. visual acuity) had an effect on the results; subjects who used loupes were more accurate. Conclusion: with 10 degrees of opening experienced clinicians are able to locate a hinge axis to 0.2 mm area.Sloane (1951) Denture fabrication - Axis is a demonstrable biomechanical fact.Clapp (1952) Amer. pupil of Gysi. Agreed with Gysi, that a number of axes existed for opening movements of the mandible which are located outside the mandible. The infrahyoid muscles open straight vs. external pterygoids.Granger (1952) Centric relation is the only position where hinge axis is common to both mandible and maxilla.Craddock & Symmons (1952) Small opening, the axis passes through condyles; on wider opening axis becomes displaced downward. Accurate determination is of academic interest because it is found within a few mm of assumed center of condyle.Posselt (1952) Hinge opening is obtained if patient is in passive, or trained active motion. He

could not prove this movement was habitual. Hinge-axis opening = 20 mm.Page (1952) praised McCollum's hinge bow as "one of the most important contributions to dental service."Lucia (1953) Simple rotation on the lower surface of meniscus could happen at any point along the condylar path. The correct transfer of casts to the articulator is of tremendous importance. Without a hinge-axis transfer he thought it impossible to diagnose an occlusal problem because the teeth on the models would not meet in the same way as they would in the mouth.Brandrup-Wognsen (1953) Discussed the theory and history of face-bows. Quoted Beyron who demonstrated that the axis of movement of the mandible did not always pass through the centers of the condyles. Complicated forms of registration were rarely necessary for practical work.Granger (1954) The mandible is capable of an infinite variety of paths of movement; one condyle could be undergoing only rotational movement while the other condyle was both rotating and gliding, or both could be rotating and gliding simultaneously.     It was only in the retruded relation that the condyle could make pure rotatory movements without gliding. This position was centric relation. He pointed out that the split hinge-axis theory was not possible. Successful treatment depended upon the correct orientation of the teeth to each other and to the hinge-axis.Sicher (1954) Terminal hinge-axis is the most retruded position of the mandible that the individual can assume under the action of his mandibular musculature and is, therefore, an unstrained position.Thompson (1954) was concerned with full mouth reconstruction of the natural dentition. He described the importance of recreating the same hinge-axis relationship on the articulator as it is in the patient's mouth.Page (1955) criticized the report of the official Nomenclature Committee Meeting of 1952 for its definition and explanation of hinge opening position. He said that it was a misconception and had failed to recognize that none of the groups who used kinematic location of the hinge-axis considered this a significant component of mandibular opening. These groups stressed that the important mandibular movement to be recorded was functional hinge closing. Page also stated that the jaw relaxed with the condyles dropping into the hammock and capsular ligaments. (Compare with Eberle's view)Collett (1955) There is no agreement on the existence of the hinge-axis. The recording of the opening axis and the transference of it to an articulator were of considerable value in the diagnosis and treatment of occlusal malfunction.Kornfield (1955) The location of the hinge-axis was the basis of all articulator transfer. Incorrectly articulated casts would lead to restorations that would not meet in the mouth, unverifiable CR registration, cusps harmony would not match the arc of closure, any change in the VDO would produce disharmonies.Levao (1955) Mandibular movements were a combination of rotation and translational movements different from habitual opening and closing movements and this could be clearly seen in his diagram of the envelope of sagittal rotation.Trapozzano (1955) Hinge-axis represented a border movement that could be recorded repeatedly with unfailing accuracy.Cohen (1956) He used McCollum's Gnathoscope and Gnathograph to prove the existence of mandibular hinge-axis within the range of vertical dimension used.Beck and Morrison (1956) Non-arcon type articulator can record beginning and end points of mandibular movement. Arcon type can reproduce mandibular movements in between.?

Nevakari (1956) With cephalometric studies found it impossible to determine whether the movement actually occurred around a stationary axis of whether it was complex (rotational and translational) taking place at different times.Schallhorn (1957) Compared the advantages and disadvantages of arbitrary versus kinematic hinge-axis location for face-bow transfer. In over 95% of individuals with normal jaw relationships the kinematic center was found within 5 mm radius from the arbitrary center. This was within the limits of negligible error.*Posselt (1957) Terminal hinge movement of the mandible.       To analyze terminal hinge movement, up to 20 mm of hinge opening by checking the relation of the axis points to the condyles and by recording the shift of the kinematically established hinge axis. The results show that the median section of the terminal hinge axis lay within the outlines of the condyles, and that three different experimental methods, which gave fairly similar results, suggest that the terminal hinge movement can be regarded as rotation around an axis passing through the condyles.Trapozzano (1957) Transograph - disagreed with theory and practice because mandible would have to bend or have to be broken.Borgh & Posselt (1958) Confirmation of inherent inaccuracies in hinge-axis recording.*Sheppard (1958) The effect of hinge axis clutches on condyle position.     He found that clutches immediately altered the closed position of the condyles in most of the joints studied and could also limit the extent of condylar movement. Therefore, hinge axis recordings of functional condylar movement may have an inaccurate starting and record abnormal behavior of the condyle.Beck (1957) Compared the four following axes of rotation:   (1) Bergstrom's axis: 10 mm anterior to center of auditory meatus and 7 mm below Frankfort plane.   (2) Gysi's arbitrary axis: on line from upper border of ext. aud. meatus to canthus of the eye, 13 mm ant of margin of meatus.   (3) Beyron's arbitrary axis: 13 mm ant. to post. margin of tragus, on tragus-canthus line.   (4) Kinematic axis (McCollum)The Bergstrom points were most favorable with the kinematic points, within radius of 5 mm.Next came Beyron's axis points, while the Gysi points showed a greater difference from the kinematic points.*Beck (1959) A critical evaluation of the arcon concept of articulation - Bergstom Arcon vs. the Hanau H. Conclusion: no conclusive evidence could be recorded from duplicate dentures which were constructed on the arcon and the condylar type instruments.*Weinberg (1959) The transverse hinge axis: Real or imaginary? (Engineering principle)Some highlights:Gnathologists - one THA common to both condyles; tattooingTransographics - different THA for each condyleHanau - anatomic average; exact duplication impossibleArcon/Non-arcon reversal of relationship would not change guidanceHe also:

described the hinge-axis described geometrical and clinical methods for finding it described its use

determined whether there were one or two transverse hinge-axes discussed the mandibular movement pattern for the opening and closing movements gave clinical evidence of the transverse hinge-axis determined if pin point accuracy in the location of the transverse hinge-axis was

necessary, and related these factors to clinical practice.

*Trapozzano and Lazzari (1961) A study of hinge axis determination. To investigate whether there is a terminal hinge axis, and whether or not only one exists. 52% of the subjects showed more than one hinge axis point. These findings indicate that, since multiple condylar hinge axis points were located, the high degree of infallibility attributed to hinge axis points may be seriously questioned.* Boucher (1961) Limiting factors in posterior movement of mandibular condyles.Does the capsular ligaments of the TMJ limit the posterior movements of the mandible?Measurements of gothic arch tracings done before and after severing the TMJ and capsular ligaments were identical, indicating that they are not responsible for limiting posterior border movement of the mandible.* Regli and Kelly (1967) The phenomenon of decreased mandibular arch width in opening movements.     Does the cross-arch distance change in mandibular opening? The deformation of the mandible (0.03 mm inter-bicuspid, 0.09 mm inter-molar) that occurs during opening is of clinical significance and could affect the fit of an RPD or FPD. Impressions should not be taken in a wide open mandible, and rigidly joining the lower teeth in a cross-arch manner is questionable. Further investigation is indicated.* Gonzalez (1968) Evaluation of planes of reference for orienting maxillary casts on articulators. (Dentures)     Using lateral cephalogram tracings (21 patients) of the Frankfort horizontal plane running from the right and left porion and the orbitale, the arbitrary condylar axis (Beyron), the maxillary residual ridge plane, the tip of the incisal edge of the left maxillary central incisor, and the crest of the mesiobuccal cusp of the left maxillary molar. None of the three planes of reference were parallel to the Frankfort horizontal; the maxillary residual ridge plane was the closest to being parallel, but was the most variable. The distance of condylar axis to the Frankfort horizontal plane was the least variable and measured 7.1 mm, which is in accord with Bergstrom's findings. The points of reference on the articulators, condylar axis rods and the orbital indicators were at the same level. The mean angle between the plane of occlusion and the Frankfort plane was -9 degrees for the group of 21 patients.     To compensate for the error in the location of reference points on the articulator the orbital pointer on the facebow can be placed 7 mm below the orbitale on the patient. Another method would be to place the the pointer 7 mm above the indicator on the articulator during the transfer.*Winstanley (1979) Hinge axis location on the articulator.     To see how accurately the center of sagittal rotation of an articulator could be determined when using clinical methods. This study would give an indication of the minimum errors which could be expected to occur before clinical methods are taken into account.     The best results were obtained when using a microdot pattern flag than a plain record, and when anterior opening was 15 mm instead of 10 mm. Errors were found to occur up to a diameter of 2.4 mm . Greatest inaccuracy was when location was 1.2 mm in front and 1.0 mm below true center. More inaccuracy occurred in the horizontal direction than vertical.

* Gordon (1984) Location of the terminal hinge axis and its effect on the second molar cusp position.     Incorrect location of the terminal hinge axis of 5 and 8 mm to the anterior, posterior, superior,and inferior was examined. With jaw relation records 3 and 6 mm thick at the incisors, the errors in cusp height at the second molar ranged from 0.15 mm open space to 0.4 mm excess height. The mesiodistal error ranged from 0.51 mm distally to 0.52 mm mesially. Conclusions:1. The centric jaw relation record should be recorded at a vertical dimension close to the planned vertical dimension of occlusion. Keep the CR record thin. 2. Location of a kinematic hinge point prior to treatment for dentulous patients who require extensive treatment saves time and results in a more satisfactory occlusion.3. Techniques that do not require a change of vertical dimension on the articulator are useful when a kinematic hinge axis is not applicable.4. The difficulty of accurately refining a balanced occlusion in the mouth where complete dentures with anatomic teeth have been used, supports the use of nonanatomic teeth.*Palik (1985) Accuracy of an ear piece face bow. This is a popular arbitrary method.     (Walker found only 20% within 5 mm of true location, 60% were 6 mm or more. Schallhorn found 95% to be within 5 mm of true hinge axis).     18 randomly selected patients were used. The validity of the Hanau ear-bow to transfer an arbitrary hinge axis to a Hanau 158-3 Arcon articulator was compared with the Hanau kinematic face-bow. Results: only 50% of the arbitrary hinge axes were within a 5 mm radius of the true hinge axis, while 89% were within a 6 mm radius. The discrepancy was significant in the anteroposterior direction but not in the superior-inferior direction.      92% of the clinically located THA were posterior to the ear-bow position. Therefore this method is not statistically reliable.* Gunderson (1987) An alternative technique for location of the hinge axis.    Use of intersecting lines to locate the hinge axis on graph paper then transferred to patient seems to be as time consuming as using a kinematic face-bow.*Getz (1988) Application of a geometric principle for locating the mandibular hinge axis through the use of a double recording stylus.Theorem #1. A line drawn through the center of a circle perpendicular to a chord meets it as its midpoint and bisects the arcs determined by the chord;theorem #2. The line joining the center of a circle to the midpoint of a chord is perpendicular to the chord.Using a modified Satellite Bow with double recording styli at a distance of 2 to 4 inches from the estimated axis area, 12 determinations on 2 subjects were made. It was possible to define the axis point between 0.1 to 1.0 mm.* Pitchford (1991) A reevaluation of the axis-orbitale plane and the use of orbitale in a facebow transfer record.     The use of a facebow in conjunction with the orbitale as the anterior reference point frequently results in an overly steep anterioposterior angulation of the occlusal plane.     It is the vertical relationship which may result in esthetic failures, balancing side occlusal errors in complete dentures, and nonworking occlusal interferences in fixed restorations.     A correction of 7 mm is concurs with other authors (Gonzales, Kingery, Nowlin, Stade).     This study noted that the use of the porion-orbitale plane was originally adopted at an anthropologic congress in Frankfort, Germany, in 1882. Later, the axis-orbitale plane was used as a reference by the early designers of articulators and facebows. In 1955 the Research Report

by McCollum and Stuart solidified this concept by stating that the axis-orbitale plane is horizontal or nearly so when the body is erect. The Glossary of Prosthodontic Terms made this concept a fact. Use of the orbitale as the anterior reference point, will place the maxillary central incisors an average distance of 54 mm below the condylar plane. In 1866 Balkwill found the incisal edges of mandibular teeth to be 35 mm below the condylar plane, while the results of this study place the incisal edges of the maxillary teeth 36 mm below the condylar plane.1. Frankfort plane nor axis-orbitale plane is parallel to the reference horizontal in the esthetic reference position. The use of either of these planes will place the maxillary cast too low in the articulator.2. Esthetic reference position places orbitale 18.5 mm higher than the axis, axis-orbitale plane will form a 13 degree angle with reference horizontal. Orbitale averages 11.45 mm higher than the porion in the esthetic reference position, and the Frankfort plane will form an angle of 8 degrees to the horizontal reference.3. In the esthetic reference position the incisal edge of the maxillary central incisors will be 36 mm below the condylar plane. Minor alterations of the facebow, orbitale indicator, or the position of the pointer will allow an average value transfer of the esthetic reference position to the articulator.* Nairin (1994) The position and function of the mandibular hinge axis.     Beyron's point was used for this study. Ten patients who were having routine orthopantomograms (OPG) were used. The hinge axis point was marked on the side of the face with a 'O' about 5 mm in diameter. Lateral skull radiographs of ten other subjects were also studied.Results: the average hinge axis is seen to lie over the condylar neck rather than the head of the condyle. The mandibular axis of hinge like movement is located automatically in the region of the neck of the mandibular condyle and not in the condyle itself. This conclusion is supported by the anatomy of the joint with particular reference to the TM ligament.'In the final analysis, the true value of our individual work can be measured only by the degree of fineness with which we practice the art of dentistry rather than by the particular school of thought to which we adhere.' Weinberg (1959)  

- Abstracts –04-001. Weinberg, L. The transverse hinge axis: Real or imaginary? J Prosthet Dent 9:775-787, 1959.04-002. Posselt, U. Terminal hinge movement of the mandible.   7:787-797, 1957.04-003. Trapozzano and Lazzari. A study of hinge axis determination. J Prosthet Dent 11:858-863, 1961.04-004. Boucher, L. J. Limiting factors in posterior movement of mandibular condyles. J Prosthet Dent 11:23-25, 1961.04-005. Winstanley, R. B. The hinge-axis: A review of the literature. J Oral Rehabil 12:135-159, 1985.04-006. Winstanley, R. B. Hinge axis location on the articulator. J Prosthet Dent 42:135-144, 1979.04-007. Beck, H. 0. A critical evaluation of the arcon concept of articulation. J Prosthet Dent 9:409-421, 1959.

04-008. Sheppard, I. M. The effect of hinge axis clutches on condyle position. J Prosthet Dent 8:260-263, 1958. 04-009. Lauritzen, A.G., and Wofford, L. Hinge Axis Location on an Experimental Basis. J Prosthet Dent 11:1059-1067; 1961.Purpose: Measurable errors in the occlusal surfaces are produced when the position of the articulator hinge axis does not coincide with the patient's anatomical hinge axis. Subject: The article examines the ability of the practitioner to accurately locate the hinge axis.Methods and materials: A special experimental apparatus was designed and constructed to measure experimental accuracy at recording hinge axis. A number of operators of varied experience made five attempts at registering hinge axis with a range of movement varying from 5 to 15 degrees. A total of 190 measurements were made.Results: 1. Training and experience led to better results2. Poor vision led to more difficulties3. Binocular loupes led to more accurate results4. For experienced practitioners, 10 or 15 degrees of movement produced more than 95% of locations within 0.2 mm. With only 5 degrees of movement, accurate location was more difficult.Conclusion: A ten degree range of movement is sufficient for hinge axis location, and in the experienced operator can attain 0.2mm accuracy.04-010. Regli, C. P. and Kelly, E. K. The phenomenon of decreased mandibular arch width in opening movements. J Prosthet Dent 17:49-53, 1967.Missing abstract .......04-011.Missing abstract .......04-012. Gordon, S.R. et al. Location of the terminal hinge axis and it’s effect on second molar cusp position. J Prosthet Dent 52:99-105, 1984.Missing abstract .......04-013. Palik, J. F. Accuracy of an earpiece face-bow. J Prosthet Dent 53:800-804, 1985.Previous studies are conflicting:Walker - 20% of true axis were within 5 mm of the arbitrary location situated 13 mm anterior to the tragus. 60 % were 6 mm or more.Schallhorn - 95 % of true hinge axis were within 5 mm radius of an arbitrary axis.Materials and methods:Hanau No 158-3 arcon articulatorPlexiglas disks were used on the articulator record the exact point of the terminal hinge axis on the articulator. Self adhesive TMJ graph circle placed on the plexiglas.Hanau No. 159-4 earpiece facebow.Earbow record repeated 4 times.Results:1. Arbitrary axis were, anterior and inferior to true hinge axis 56% and anterior and superior 36%. anterior 92 % of the time. 2. Only 50% were within a 5 mm radius of the true hinge axis.

3. 89% were within a 6 mm radius.4. The arbitrary axis located with the ear face-bow was significantly different from the true axis in an anteroposterior direction but not in a superior-inferior direction.     The earpiece face-bow was not repeatable.Discussion:No inference should be made that the earpiece facebow does not possess a practical clinical value. However there is no consensus that the earbow approximates the terminal hinge axis within the acceptable range.2. Modifications are needed in the condylar compensators of the arbitrary facebow to increase its accuracy. This study suggests that the arbitrary location of the terminal hinge axis incorporated into the condylar compensators of this ear-bow is misleading, because 92% of the clinically located terminal hinge axes were posterior to the ear-bow position. This suggested that the arbitrary hinge axis should be located less than 13 mm from the external auditory meati.04-014. Getz, E.H. et al. Application of a geometric principle for locating the mandibular hinge axis through the use of a double recording stylus. J Prosthet Dent 60:553-559, 1988.Missing abstract .......04-015. Pitchford, J.H. A reevaluation of the axis-orbital plane and the use of orbitale in a facebow transfer record. J Prosthet Dent 66:349-55, 1991.Missing abstract .......04-016. Nairin R.I. The Position and Function of the mandibular Hinge Axis. Aust Prosthodont J  8:19-22, 1994. Purpose: To relate the average hinge axis position to the mandibular condyle.Method: Hinge axis location chosen for this study was Beyron's point, 13 mm anterior to the posterior border of the tragus of the ear, on a line between the mid-posterior margin of the tragus and the outer canthus of the eye. In any single case, the hinge axis location, empirical or average will probably lie within the same circle of about 5 mm diameter (Beyron 1942, Schallhorn 1957, Weinberg 1961, Brandrup-Wognsen 1953). Walker (1980) found that 80% of 444 point locations were below the tragus-canthus line running to the superior border of the tragus. Lauritzen and Bodner (1961) came to the same conclusion. The average point will be within +/-2.5 mm.Subjects. Ten patients who were having routine orthopantomograms (OPG) for clinical purposes were used. The average hinge axis point was marked on the side of the face with a lead letter 'O' about 5 mm in diameter.     Lateral skull radiographs of ten other subjects were also studied. Landmarks were traced on the ten lateral skull radiographs.Results: The average hinge axis point as denoted by the marker appears to lie over the anterior border of the condylar neck more than 1 cm from the center of the shadow of the condylar head. A similar situation holds on the other side. In a series of ten OPGs no variation from this appearance was observed.Discussion: In this study the average hinge axis point is seen to lie over the condylar neck rather than the condylar head on both sides of 10 orthopantomograms, on ten lateral skull radiographs of different subjects and on a skull extrapolation. This coincidence must reduce the possibility that these appearances are due to radiographic distortion. The view that the hinge axis lies within the condyle appears to arise from an unjustified and untested assumption or from experimental error, e.g. the use of tomograms in which almost nothing clear can be seen, or by the use of geometrical extrapolations from mandibular tracings made at points remote from the condyle. It

remains to postulate a mechanism for the hinge movement compatible with its anatomical position. The temporomandibular, or lateral, ligament is a substantial thickening of the capsule and when under tension will provide an area of restricted mobility for the mandible. Such ligamentous tension will be present when the hinge-axis is located and it seems reasonable to suppose that it provides the fulcrum for the hinge like movement. Obviously any opening movement around an axis through the condyle would require further lengthening of the already tense and unstretchable ligament.Conclusion: The mandibular axis of hinge like movement is located automatically in the region of the neck of the mandibular condyle and not in the condyle itself. This conclusion is supported by the anatomy of the joint with particular reference to the temporomandibular ligament. 04-017. Gonzales, J.B., Kingery, R.H. Evaluation of planes of reference for orienting maxillary casts on articulators. JADA 76:329-36, 1968.Missing abstract .......04-018. Gunderson, R. B. and Parker, M. H. An alternative technique for location of the hinge axis. J Prosthet Dent 58:448-450, 1987.Missing abstract .......

Section 05: Eccentric Movements(Handout)

 Definitions:      1. eccentric: adj. 1. not having the same center 2. deviating from a circular path 3, located elsewherethan at the geometric center 4. any position of the mandible other than that which is normal position.     2. border movement: mandibular movement at the limits dictated by anatomic structures, as viewed in a given plane      3. laterotrusion: n. condylar movement on the working side in the horizontal plane. This term may beused in combination with terms describing condylar movement in other planes, for example laterodetrusion, lateroprotrusion, lateroretrusion, and laterosurtrusion. (also called Bennett's movement).     4. laterodetrusion n. lateral and downward movement of the condyle on the working side.     5. laterosurtrusion n. lateral and upward movement of the condyle on the working side.     6. lateroretrusion n. a lateral and backward movement of the condyle on the working side.     7. lateroprotrusion n. a protrusive movement of the mandibular condyle in which there is a lateral component.     8. mandibular translation the translatory (medio-lateral) movement of the mandible when viewed in the frontal plane. While this has not been demonstrated to occur as an immediate horizontal movement when viewed in the frontal plane, it could theoretically occur in an essentially pure translatory form in the earlypart of the motion or in combination with rotation in the latter part of the motion or both. (mandibular lateral translation also called Bennett's side shift).     a. immediate mandibular lateral translation the translatory portion of lateral movement in which the nonworking side condyle moves essentially straight and medially as it leaves the centric relation position.

     b. early mandibular lateral translation the translatory portion of lateral movement in which the greatest portion occurs early in the forward movement of the nonworking side condyle as it leaves centric relation.     c. progressive mandibular lateral translation 1. the translatory portion of mandibular movement when viewed in a specified body plane 2. the translatory portion of mandibular movement as viewed in a specific body plane that occurs at a rate or amount that is directly proportional to the forward movement of the nonworking condyle.     9. Bennett angle obs. the angle formed between the sagittal plane and the average path of the advancing condyle as viewed in the horizontal plane during lateral mandibular movements (GPT-4).    10. Fischer angle eponym for the angle formed by the intersection of the protrusive and nonworking condylar paths as viewed in the sagittal plane.    11. pantograph n. 1. an instrument used for copying a planar figure to any desired scale in dentistry, an instrument used to graphically record in one or more planes paths of mandibular movement and to provide information for the programming of an articulator.    12. pantographic tracing a graphic record of mandibular movement in three planes as registered by the styli on the recording tables of a pantograph; tracings of mandibular movement recorded on plates in the horizontal and sagittal planes.History:      Bonwill- described a 4 inch triangle between mandibular incisors and each condyle. Also proposed         a concept of bilateral balanced occlusion.     Balkwill – discovered that during lateral jaw movement, the translating condyle moved medially.     VonSpee- observed that the occlusal plane of the teeth followed a curve in the sagittal plane.         (curve of Spee).     Christensen (1901)  – observed the opening of posterior teeth in mandibular protrusion.     Bennett (1908) – described immediate side shift (Bennett movement).     Gysi (1910)  – develops one of first articulators to allow for Balkwill-Bennett movements.      Monson (1916) – develops spherical theory, one of first three dimensional occlusal concepts.     Hanau (1921) – advocated bilateral balanced occlusion with eccentric mandibular movements.     Pankey-Mann (1920’s) – amalgamation of Monson theory and Meyer functionally generated          path to obtain bilateral balance. Pankey-Mann-Schuyler eliminated balancing side contacts,

         emphasized incisal guidance, and proposed long centric.     McCollum (1920’s) – Gnathology – study mandibular movement:         1. Propose colinear hinge axis,         2. Develop pantographic recording of three dimensional envelope of motion         3. Maximum intercuspation of teeth when condyles are in hinge position         4. Bilateral balance with eccentric jaw movement.Movement of the Mandible:     1. Posselt examined mandibular movement using a Gnatho-Thesiometer to measure the mandibular position of natural teeth. Recordings were made of both habitual and extreme

positions with opposing teeth in occlusion.        How were his measurements made?     What were his observations and conclusions?      2. Mandibular movement during chewing can vary greatly within the prescribed envelope. Gibbs, et.al. , performed a study of chewing and border movements of five subjects with good occlusion and two subjects with malocclusions. What did they observe about opening and closing strokes? Closing and opening strokes differed markedly. Opening strokes were typically anterior and medial to closing strokes.      Chewing movements were found to differ greatly until final closure, where a similarity was noted. Most chewing paths nearing final closure coincided or nearly coincided with the working-side lateral border path in both frontal and sagittal views.      The movement of the first molar on the working side had a small anterior component during closure. What does this indicate? Chewing function occurred in the lateral retrusive range until gliding tooth contact occurred. (Retrusive slides are seldom seen on the working side during chewing)      How did the working side movement compare to the non-working side? The non-working first molar closed from an anterior medial aspect and had a posterior component of movement.      What did they conclude regarding neuromuscular control and occlusal interferences?     How did this compare to what Clayton, et.al., found in their study of pantographic tracings of mandibular movements?      3. Condylar movement determines tooth occlusal patterns. Or do tooth occlusal patterns determine condylar movement? Aull described nine possible variations in the direction of the condylar path of the working (rotating) condyle. Describe these nine variations:     Which one did he fail to observe in his study of 50 patients(100 condyles)?      Did he find a symmetry in condylar inclinations? No, only one pair of 50 was symmetrical.      Side shift is the only condylar determinant that affects both the vertical and horizontal components of the posterior teeth. What general effect will an increase in laterotrusion have on occlusal morphology? shorter cusps, gentler cusp slopes, shallower, broader fossae.      Laterotrusion accompanied by an upward movement of the same condyle has what effect on thecusp length?     Laterotrusion accompanied by downward movement has what effect on cusp length?     As intercondylar distance is increased, what happens to the angle formed by the transverse and obliquepath of the cusp in its movements?      As laterotrusion increases, what happens to this angle?      Did Kurth agree with Aull's conclusions?     What did Levinson report regarding the nature of side shift in mandibular movement?      What impact would the presence of (or lack of) an immediate side shift have on articulator selection?      4. The clinical significance of lateral mandibular movements is controversial. What did Preiskel conclude?      What are some of the difficulties encountered in studying the lateral side shift of the mandible (as discussed by Simonet)     What were Hobo's conclusions regarding lateral side shift from the use of an electronic measuring system?

     5. Mandibular motion is produced by muscle activity. According to McCollum, is the path of mandibular movement determined primarily by the anatomy of the joint or the activity of the  musculature?     Would Gysi concur?     The masseter and temporalis muscles function to close and retrude the mandible. Do they contributeto lateral movements?      Which muscles are the most active participants in lateral movements?      What happens to the activity of the masseter and medial pterygoids in retruded contact position?      What did Santos, et.al. determine regarding the relationship between cusp steepness and forces generated? Recording mandibular movement:        1. Fabrication of an esthetic and functional restoration for the patient routinely requires the effective use of an appropriate articulator. One of the roles of the prosthodontist is to transfer information from the patient to the articulator in such a manner so that the articulator closely simulates mandibular movement to the degree required by the restoration. Attempts to record mandibular movement are as historical as the study of mandibular movement itself, and include a variety of intraoral and extraoral tracing mechanisms, as well as photographic, radiographic, electronic, and electromyographic studies.     Stuart describes the recording of mandibular movement. Which movements does he record, and how are they registered?     What is the significance of recording border movements? Border movements are constant enough in position, direction, and path as to be dependable and repeatable. When the true boundary movements are recorded and transferred, all other movements are automatically included in the circumscribed areas of movement.     Upon which issues do Boucher and Stuart agree? disagree?     2. According to Mongini and Capurso, what factors influence the tracing patterns of mandibular border movements?     What effect does an internal derangement have on tracings?     What effect does severe muscle tension have on tracings?     What can be done to help address the effect of severe muscle tension?     What effect did Theusner, et.al., observe regarding the tracings obtained from symptomatic patients?     Were these considered to be adaptive or pathologic changes?     3. Lundeen and Wirth recorded mandibular movement by engraving plastic blocks and photographing the engravings. Did they observe immediate side shift?     Was a greater side shift observed with firm lateral guidance of the body of the mandible by the dentist, or with passive guidance at the chin point?     Did the length of the central bearing screw affect the engravings?     4. Clayton, et.al. examined the effect of various factors on graphic tracings. What did they determine regarding the effect of changes in the occlusal vertical dimension?     Regarding changes in the central bearing guiding surface?     Regarding tooth guidance?

Summary:  The intricacies of mandibular movement, while intensely studied, discussed, and debated, are still fraught with uncertainties. Nevertheless, these questions should not deter the diligent practitioner from the pursuit of additional understanding and the effective restoration of his patients based upon the prevailing standard of care and evidence based decision making.

- Abstracts -05-001. Posselt, U. Movement areas of the mandible. J Prosthet Dent 7:375-385, 1957.Purpose: To elucidate the shape and dimension of the contact area of movement of the anterior measuring point, and of the points on the condyles. Individual variations were also studied.Literature Review: Hanau and Fischer described the shape of this contact movement area. Fischer described this contact movement area in dentulous subjects as " broken and more or less uneven". Fehr writes that the condyle movement area is larger for the left side than the right. Gysi and Fischer illustrate the areas of movement a rhomboid. Gysi carried out his investigations on edentulous persons. No investigations were on record at that tie concerning the contact area of movement of a point in the anterior part of the mandible or for the condyles.Materials & Methods: 5 people with almost complete dentitions were measured with a Gnatho-thesiometer. The positions of the measuring points (1 close to the infradentale and 2 in the middle of each condyle) were enlarged and traced on paper in the 3 planes at right angles. Stone models were made with the help of the drawings.Results/Discussion: The area of movement of a point on the anterior part of the mandible can be projected on a plane surface by graphic registration in both dentulous and edentulous subjects provided that any vertical cusp guidance has been eliminated. The triangle, which connects the three measuring points, corresponds to BONWILL’s Triangle.     Contact area of movement of the anterior measuring point: rhomboid shape but markedly asymmetric. In the vertical plane, different levels were noted and individual variations evident.     Areas of movement of the condylar points: the shapes in all 3 planes differed widely along with the extreme and in extreme positions.Summary/Conclusion: The areas of movement for three points on the mandible were recorded in the 3 planes with the aid of a Gnatho-thesiometer. The paths of movement cannot be measured with a Thesiometer. Lines can be drawn from one point to another and an approximation secured. The results of this investigation support observations from previous studies that differences exist between habitual and extreme positions.05-002. Aull, AE. Condylar determinants of occlusal patterns. J Prosthet Dent15:826-846,1965.      Condylar tracings from 50 patients were analyzed. A Stuart facebow, axis-orbital plane indicator, pantographic tracing device, and articulator were used. The following findings were obtained.     Condylar variation: Only one of the fifty pairs of condyles had bilateral symmetry. The average steepness for the right and left sides were 36.6O and 37.7O Intercondylar distance: The average distance is 55.5 mm. Range was 45 -70 mm Bennett movement: All had mandibular movement with a side shift.Summary of condylar determinants on occlusion by Aull:1. Increasing the steepness of the eminencies increases the requirements for steeper sloping cusp on the balancing side.2. Increasing the curvature of the eminencies has the same effect on the tracings as if the eminencies is increased.

3. As laterotrusion (side shift) is increased shorter cusp are required (mainly the balancing side is effected). If the rotating condyle also moves upward the working side cusps are more effected.4. Laterotrusion accompanied by downward movement requires longer cusps on both sides (mostly on working).5. As intercondylar distance is increased, the more acute the angle becomes between the transverse and oblique paths of the cusps points.6. Increase intercondylar distance, increase eminence slant, increase laterotrusion, the more obtuse the angle between the transverse and oblique paths of the cusps points.7. An immediate laterotrusion which equals a distributed laterotrusion will have a more blunt angle, and the balancing lines will diverge more in the central fossa.8. When the laterotrusive rotating condyle retrudes, the angle made between the working and balancing tracing is more obtuse than that made between the same type of tracings made with a protruding laterotrusive rotating condyle.9. As the slant or curvature of the eminencies is increased, the slant of the pure protrusive tracing is also increased.Kurth, LE. Discussion. J Pros Dent 15:847-849, 1965.Kurth said if you are not trying to achieve bilateral balanced occlusion there is no need for all the diagnostic tracings.05-003. Stuart, C. E. Accuracy in measuring functional dimensions and relations in oral prosthesis. J PROSTHET DENT 9: 220-236, 1959.Purpose: Discuss the use of the articulator as a diagnostic tool.Discussion: A. Purpose of the articulator     1. Record         a. Receive and register craniodental and maxillo-mandibular relations.         b. Receive and register the three dimensions of the oral organ.         c. Receive and register the axes of mandibular rotations.         d. Guide the dentist to incorporate all these factors into the prosthesis.         e. Store all the dimensional information .B. Anatomy and physiology of the articulator    1. It should be put together in such a way that it can be reproducible, without compromise. It should fit the   anatomy and physiology of the oral organ.C. Hinge axis     1. To provide a point in the third dimension, a line is extended from the hinge axis to the lower border of the orbit , to the right side of the nose and marked.D. Mandibular movement recorder     1. Two parts        a. Upper bow- holds vertical and horizontal recording plates in the condylar areas and carries writing styluses in the anterior crossbar.        b. Mandibular bow- carry vertical and horizontal styluses in the condylar areas and horizontal recording plates on the front bar.     2. The recorder has two styluses to write the Gothic arch tracing, two to write the effect of the anterior condylar glidings, and two to write the effects of the lateral condylar glidings.     3. Border movements are used because in such a simple movement as straight protrusion the patient seldom can make the same movement twice. The habitual positions vary according to

postures, health, muscular and nervous states. When they are transferred to the articulator they become boundary positions, and automatically all other movements are included in the circumscribed areas of movements.E. Condylar path tracings: The tracing is composed of two parts: a forwardly drawn tracing and a backward tracing. Each tracing in itself is made up of two parts joined at the point of centric relation as indicated by the stylus.     1. The two Gothic arch tracings show the effects of the lateral and anterior movements of the condyle, and they are influenced by any opening and closing.     2. The reverse tracing of each anterior condyle serves as an index of the upward or downward path direction of the outward rotating condyle. The reverse tracing of the Bennett line is an index of the backward or forward path direction of the outward moving rotating condyle.F. Magnetic styluses: Tracings are written by a frictionless ball-point stylus magnetically controlled, and preserved with adhesive cellophane. After the record lines are made and covered, the upper and lower face-bows are cemented together in centric relation with stone. G. Transfer of jaw relations: The recorded lines are used to set the articulator. The articulator consists of two main frames, and upper and a lower.     1. Upper frame- centered on the lower and maintained in centric relation by a spring-loaded arm. Carries all the cams that direct the gliding of the condyle mechanisms, the right and left glides for the sideshifts (the Bennett movements), and the right and left fossa cusps carry the eminentias under which the condyles glide.      2. Lower frame- carries the mechanical condyles and simulates the mandible. The cams, or guide controls of the mechanical condyles, when set, remain fixed in relation to the upper teeth and dental arch. The mechanical condyles and their axes remain fixed in relation to the lower teeth. Boucher, C.O. Discussion. J Prosthet Dent 9: 237-239, 1959. Purpose: Discussion by Dr. Charles E. Stuart.Discussion: Dr. Boucher states that any instrument that is adjusted solely by a series of these records can be absolutely correct only in the exact positions at which the records were made. He says that any movements made by the patient when the teeth are out of contact are of no importance to the arrangement of teeth. It is desirable to have any movements that may be made while the teeth are in contact reproduced on the articulator. This is necessary so the occluding surfaces of the teeth can be shaped in harmony with each other, in any position in which they came in contact. The articulator should approximate these movements of the mandible that may occur when teeth are in contact, this involves: (1) the correct relation of the two casts to the opening axis of the instrument, (2) the establishment of the correct centric relation, (3) the development of guiding surfaces in the mechanical counterparts of the TMJ so the casts may assume the same relations to each other that the denture foundations have to each other in the mouth while the teeth are in contact.     Dr. Boucher states that orientation of the face-bow and the cast to the arbitrary facial and cranial landmarks seems unnecessary, except for the convenience of observing the anterior teeth and the occlusal curvature on the articulator. The directions of the styluses should not be mistaken with the directions of the actual movements of the mandible. A posterior movement by the working side condyle is likely to be developed by the fact that the tracing is made as an extension of the horizontal axis of the mandible.    The use of magnetic styluses appears to be a problem, since there is a possibility of the weight of the recording device altering the normal position and movements of the mandible. This would

be difficult to demonstrate or prove.     The clutches must be cemented to the teeth during registrations, making it impossible for denture construction. This is important since the resiliency of the supporting tissues would likely produce errors in the registrations.Dr. Boucher emphasizes Dr. Stuarts suggestion of using an interocclusal record to mount the casts in centric relation, otherwise all other articulator adjustment would be incorrect05-004. Clayton, J. A., Kotowicz, W. E. and Zahler, J. M. Pantographic tracings of mandibular movements and occlusion. J Prosthet Dent 25:389-396, 1971.Purpose: To determine the relationship of functional movements (chewing) to the border tracings recorded by a pantograph.Methods & Materials: Clutches were fastened to the maxillary and mandibular teeth of four subjects so as not to interfere with tooth contacts during function. Border tracings were made from centric relation guided by the author and unguided tracings from centric occlusion. The subjects were then instructed to chew test foods: gum, uncooked carrots, and peanuts. These movements were recorded and compared to the initial sets of tracings. After the recordings were completed one patient had occlusal interferences removed and a second set of tracings made.Results: The functional movements contacted the border tracings frequently. The movements did not go beyond the border tracings. The chewing pattern was heaviest on the patients favored side. The tougher the consistency of the food the more the patient favored one side versus the other. The two subjects who had no occlusal interferences had a larger area of coverage than the two patients who had interferences. After removal of the interferences one of the subjects produced recordings that were closer to the border tracings.Conclusions: the authors conclude that subjects can function to the border tracings provided that no interferences are present which may deflect the functional movements away from the border tracings. They also conclude that occlusion in harmony with border tracings may be the most physiologic. These conclusions are pretty amazing considering the fact that there were only four subjects.05-005. Lundeen, H.C., Wirth, C.G. Condylar movement patterns engraved in plastic blocks. J Prosthet Dent 30:866-875, 1973.Purpose: To report findings of an investigation designed to test the reliability and reproducibility of a method of three-dimensional tracing of mandibular movements in plastic blocks.Methods & Materials: 50 patients without pain or limited mandibular movement utilized. All patients were premedicated with 0.4mg of atropine sulfate, 150mg sodium pentobarbital, and 50 mg meperidine as intravenous medication prior to recording session. Condylar movement patterns were recorded as three-dimensional engravings in clear plastic blocks using turbine air drills. The drills cut a pathway in the plastic block that corresponds to movements of the mandible. The blocks are attached to the upper bow of the recorder assembled on the patient’s transverse hinge axis and secured by locking the bows to the clutches with attachment tubes filled with plaster. The engravings of the condylar movement patterns made by the turbine air drills in the plastic blocks were photographically enlarged to permit comparisons between patients. Results: The protrusive pathways of 50 superimposed tracings of the recordings showed similarity of the right and left sides. At a point corresponding to 5mm of protrusive movement, the angle formed with the axis-orbital plane was a minimum of 25 degrees, a maximum of 65 to 75 degrees, with a median of approximately 40 degrees. The tracings of the lateral pathways were also similar on the right and left sides. At a point corresponding to 5mm of lateral

movement of the balancing condyle, the angle formed with the axis-orbital plane was a minimum of 25 degrees, a maximum of 75 degrees, with a median of 45 to 50 degrees. A superior view of the recordings showed the immediate side shift (Bennett movement) and the Bennett angle as two identifiable portions of the lateral movement. Once the immediate side shift had occurred, very little variation was seen in the rest of the movements for the different subjects.Conclusion: The results of the recordings of condylar movements of the 50 subjects were superimposed and compared in three views showing the protrusive and lateral pathways as well as the superior view of the immediate side shift. Similarities in the tracings were noted in all three views for the 50 subjects tested. The study was designed to compare the shapes of the lateral boundaries of condylar movement. No attempt was made to relate these characteristics to the occlusal relations of the teeth.05-006. Gibbs, C.H. et al. Chewing movements in relation to border movements at the first molar. J Prosthet Dent 46:308-322, 1981.Purpose: To identify movements during chewing which are characteristic of subjects with malocclusion.Materials & Methods: There were seven adults in this study, five with good occlusion and two with malocclusion. Data was collected with unilateral chewing of cheese, raisins, gum, carrots and peanuts. He jaw movements were measured with photo-optical transducers mounted between maxillary and mandibular facebows. Clutches were well designed and cemented to the facial surfaces of teeth (well below the chewing surfaces.)     The patient sat upright, with head unrestrained during the chewing recording. The data was processed by computer, and the overall accuracy was 0.125 mm.Results: In the first malocclusion, a 28 year old woman with minor posterior interferences, dysfunction symptoms (pain on palpation of lateral pterygoid muscle).     The first molar movement on the working side had a small anterior component during closure, indicating that chewing function occurred on the lateral retrusive range for chewing soft as well as hard food. Chewing closure movements occurred posterior to the lateral borders until tooth gliding occurred. Retrusive slides are seldom seen on the working side during chewing.In the second malocclusion, there was a 67 year old man with severe wear. His jaw motion was continuous as teeth slid over one another from working to non working side.Conclusions: In certain malocclusions, the neuromuscular system exerts fine control during chewing to avoid particular occlusal interferences. Present restorative procedures based on lateral border registration are applicable to functional chewing movements.      The region between the terminal hinge axis and the working-side lateral border path is seldom used and does not involve tooth contact. The harder the food , the more lateral and rearward the closing movement. In adults, opening is usually medial to the closing movement when viewed in the frontal plane.  05-007. Mongini, F. and Capurso, U. Factors influencing pantographic tracings of mandibular border movements. J Prosthet Dent 48:585-598, 1982.Purpose: To study how the characteristics of the pantographic tracings can be utilized as a diagnostic aid and to evaluate the influence of anatomic and neuromuscular factors on the tracing pattern.Methods and Materials: Three different studies were performed. The first study consisted of 50 patients all with the signs of dysfunction of the somatognathic system; the second study, 20 patients from the first group, underwent occlusal rehabilitation. The third study of 20 patients utilized 10 patients from the second study and underwent biofeedback induced muscle

relaxation. Temporomandibular joint radiographs, noises, condylar location and shape, patient tenderness and spasms, and mandibular movements were parameters considered. Two pantographs were made and evaluated for immediate side shift, sagittal displacement, deviation, restrictions and other abnormalities. Results: See article for pantographic tracings and correlation.Conclusion:

1. Articular and neuromuscular factors influence the tracing patterns of the mandibular border movements.

2. Internal derangement of the TMJ with the condylar disk incoordination leads to typical pantographic tracings. The shape of the condyle also affects the type of tracing.

3. Severe muscle tension leads to very irregular tracings and are dramatically improved after relaxation. An initial protrusion of the movement of the orbiting condyle probably accounts for the incoordination of the lateral pterygoid muscles.

4. Biofeedback therapy is a valuable therapeutic tool in dysfunctional patients. This confirms their value as a therapeutic tool in dysfunctional patients.

5. Improvements in the tracings after therapy may be equally due to the improvement of the articular situation or increased muscle relaxation and coordination.

05-008. Gibbs, C. H., Mahan, P. , Wilkinson, T.M. and Mauderli, A. EMG activity of the superior belly of the lateral pterygoid muscle in relation to other jaw muscles. J Prosthet Dent 51: 691-702, 1984.Purpose: The paper describes the activities of the superior lateral pterygoid (SLP) and the inferior lateral pterygoid (ILP) in relation to the masseter, temporal, anterior belly of the digastric and medial pterygoid muscles during some basic jaw positions and movements.Methods and Materials: Eleven subjects were monitored in individual sessions of about 3 hours duration.      The EMG activities of the SLP, ILP and medial pterygoid muscles were monitored using fine insulated wire electrodes inserted directly into the muscles. The masseter, temporal and digastric muscles were monitored by means of electrodes placed on the skin over the muscles.Results/Conclusions:      1. The EMG activity of the SLP was similar but not identical to the EMG activity of the anterior fibers of the temporal muscle. The SLP muscle was active in clenching, especially clenching in retruded contact. It was moderately active in ipsilateral movement and showed little activity in other basic jaw positions.      2. In contrast to the SLP muscle, ILP muscle was active in protrusive, opening and contralateral positions. It was minimally active during clenching in retruded contact, while the SLP muscle achieved its greatest EMG activity at this position.      3. The anterior fibers of the temporal muscle are active in elevating the mandibular condyles and mandible during clenching. They also assist the digastric muscles in retruding and posturing the mandible ipsilaterally.     4. The anterior belly of the digastric muscle depresses and retrudes the mandible. In protrusion it opposes the masseter and medial pterygoid muscles to keep the teeth separated while the ILP protrudes the mandible. It is active in isometric clenching, which stiffens it to protect the teeth in the event of an unexpected rapid closing movement such as fracture of brittle food.      5. The medial pterygoid and superficial masseter are strong elevators during clenching in the intercuspal position and assist in the protrusion of the mandible by the prevention of wide

opening. The medial pterygoid muscle is active during lateral movements as an agonist and antagonist, but its activity diminishes to a low level at the extreme ipsilateral position.     6. Activity of the elevating superficial fibers of the masseter and medial pterygoid muscles is greatly reduced in the retruded contact position. Perhaps this is a mechanism that protects the posterior band of the disc from injury by the condyle during bruxing and chewing.      7. Simultaneous EMG activity (cocontraction) of shortening and lengthening muscles is commonly involved in basic jaw movements and appears to be important for fine control, mandibular stability and stiffening of antagonistic muscles to provide protection in the event of unexpected rapid mandibular movement.  

5-009.  Levinson, E. The nature of side shift in lateral mandibular movement and its implications in clinical practice. J Prosthet Dent 52:91-98, 1984.Purpose: To investigate mandibular side shift.Materials and Methods: Skulls were examined, tracings from patients and a fully adjustable articulator were examined.Results: ISS would not occur if the condyles were fully seated.Conclusion: When using a one handed push back technique the centric relation position can be improperly recorded and an ISS can be evident. However this article supports Dawson that the immediate side shift does not occur when the condyle are fully seated. Therefore, a semiadjustable articulator is adequate for the laboratory phase of occlusal reconstruction.010. Simonet, P. Influence of TMJ dysfunction on Bennett movement as recorded by a modified pantograph. Part I: Literature review. J Prosthet Dent 46:437-442, 1981.Purpose: To review the literature regarding Bennett movement.Subject: Examining the importance of and difficulties encountered in studying Bennett movement (lateral side shift of the mandible), based on reviewing existing literature.Discussion: While Bennett is generally given credit for his description of lateral shift, credit should be shared with Ferrein (1748) , Bell (1831), and Ulrich (1896). Bennett used two incandescent light bulbs attached to the mandible, and using lenses, focused the images on the wall, where they were traced during mandibular motion.     In 1926, Gysi repeated Bennett's study, developed an articulator allowing some lateral component. He believed that incisal guidance was more important than condylar guidance in determining cusp inclination. Landa proposed no movement in the working condyle, but disregarded the role of the lateral pterygoids, which was studied by Sicher.     The important role of neuromusculature was presented by Boucher, Jacoby, and McMillan. The influence of TMJ dysfunction on neuromuscular activity and Bennett movement has been speculated in different studies. DePietro applied the concept of instantaneous centers of rotation to the movement. Mongini, comparing lateral polytomographics of the TMJ with pantographic tracings performed on subjects with TMJ dysfunction, found a significant relationship between condylar shapes and tracing patterns.      Credit for the development of the pantograph is given to the Gnathological Society. Cotte, in 1969 found that, although lateral movements could be registered, side shift of the mandible was minimal or absent. In 1978, Lundeen, using the same instrumentation, found an average shift of 0.75mm, with 80% shifting 1.5mm or less. Gibbs found average lateral movement was around 0.4mm. In 1979, Bellanti and Martin found only 13% demonstrated Bennett movement of more than 0.2mm.     Conclusion: This review points out the difficulties in studying lateral side shift, as well as

contradictory results from various investigations. It seems reasonable to conclude that 1) Bennett movement accompanies most lateral jaw movements, but the amount and timing varies between individuals, and may be influenced by muscle incoordination and TMJ dysfunction. 2) the axis around which all lateral movements occur may be oblique rather than vertical and perpendicular to the subject's hinge axis. Disagreement still exists regarding: 1) the immutability of its magnitude throughout occlusal therapy and 2) the possible relationship between TMJ dysfunction and Bennett movement05-011. Hobo, S. A kinematic investigation of mandibular border movement by means of an electronic measuring system. a. Part II: A study of the Bennett movement. J Prosthet Dent 52:642, 1984. Purpose: To analyze the motion of the working condyle during lateral movement of the mandible.Methods and Materials: Fifty adults from 20 to 50 years of age with an orthognathic maxillomandibular relationship and no apparent TMJ disorders were selected for evaluation of Bennett movement (lateral shift of the working condyle) kinematically via an electronic measuring device with an accuracy of + 0.06mm. Intraoral custom made clutches containing sensors recorded right and left border movements. Calculations made external to the TMJ at intervals of 52-58 mm from the mid-sagittal plane were compared to the computer-assisted electronic recordings made at the condylar axis. Results: Bennett movement is the lateral shift of the working condyle along the terminal hinge axis (transverse horizontal axis). The orbits of the working side on the horizontal and frontal planes were more effected as the distance from the mid-sagittal changed as compared to the orbits in the sagittal plane. When the distance was small, the working condyle moved forward and downward. When the distance was large, the working condyle moved backward and upward. When the distance from the mid-sagittal plane was an average of about 55mm, the condyle moved in a straight lateral direction.Conclusions: It was found that at orbits 55mm from the midpoint of the terminal hinge axis the orbits shift straight laterally on the terminal hinge axis and do not show any deviation in the sagittal plane. Based on these findings, it was believed that the Bennett movement was a straight lateral shift of the working condyle along the terminal hinge axis. It was stated that the previous reports that the working condyle rotates and translates in various directions, which created the impression that Bennett movement is complex, might have been caused by mislocation of the targets for measurement.05-011b. Hobo, S. A kinematic investigation of mandibular border movement by means of an electronic measuring system. Part III: Rotational center of lateral movement. J Prosthet Dent 52: 66-72, 1984.Purpose: To explain and illustrate the rotational center of the mandible.Methods and Materials: Fifty adults from 20 to 50 years of age with an orthognathic maxillomandibular relationship and no apparent TMJ disorders were studied. Terminal hinge reference points 12mm anterior to the external auditory meatus formed the posterior points of a plane whose anterior reference point was 43mm above the incisal edge of tooth #8. Maxillary and mandibular reference points were secured in acrylic resin Stuart clutches. Right- and left-lateral border movements of the 50 subjects were recorded and the average movement of the field of the intercondylar axis and the targets on the intercondylar axis 65mm from the midpoint was computed.Results: A converging point was identified on the working side where the field of motion

became a minute region approximately 0.3mm long in a vertical direction and 0.1mm wide in an anteroposterior direction in the sagittal plane. The converging point existed approximately 55mm from the midpoint of the terminal hinge axis. Conclusions: This converging point was at the point of intersection between the terminal hinge axis and the intercondylar axis, which appeared at the conclusion of the lateral movement. The net side-shift caused by translation of the mandible along the terminal hinge axis is equal in the nonworking and the working sides. A point approximately 55mm from the midpoint on the intercondylar axis is the kinematic rotational center of the mandible during lateral movement. 05-012. Preiskel, H.W. Lateral translatory movements of the mandible: Critical review of investigations. J Prosthet Dent 28: 46-57, 1972.Purpose: Discuss the movements executed by the condyle on the working side.Discussion: With wide opening and the jaw moving to the right, the working condyle moved in an almost direct lateral line. This has been termed the " Bennett movement". He only investigated his own jaw movement, his right side was larger than his left side, and he was missing the mandibular posteriors. Bennett was aware of the risks of drawing general conclusions from this.     The condyle is pear shaped when viewed from above, and the glenoid fossa is wedge shape with the lateral section opening out sharply. The medial section of the condyle was rigidly contained within bone, but the lateral aspect has freedom of movement. Fischer, a Swiss dentist, suggested that lateral mandibular movements occur about an axis inclined forward, inward, and medially, involving the working-side condyle in rotation in the frontal plane.     Sicher, points out that mandibular movements are described by muscle activity rather than by bone contacts or ligaments. He feels that the temporomandibular ligament limits mandibular displacement so that the condyles cannot brace themselves against the fossa.     The neurophysiology of this area is unclear, since the ligament contains nerve endings susceptible to stretching, but there may be an absence of muscle spindles in the external pterygoid muscle.     Photographic methods have found: (1) the pathway of the working side condyle on voluntary lateral sliding movements was different from that of lateral movements made with the teeth out of contact, (2) a direct lateral movement of the condyle was present in voluntary lateral movements of the mandible. This is one of the best designed experiments, however only two subjects were discussed.     Cinefluorographic studies show the absence of lateral translation. Electromyographic studies cannot differentiate between isotonic and isometric contractions, and no direct conclusions can be drawn by the action of individual muscles.     Tracing devises usually have a clutch, that may alter the centric occlusion and alter jaw movements. Lateral movements are assessed at an increased vertical dimension of occlusion. Some pantographs were unable to reproduce consistent results from one patient. Another pantograph was joined to an articulator and eccentric records were made. The line records were reproduced, but the differences in articulator settings were considerable. Isaacson modified McCollums recording device and found the Bennett movement near the vertical dimension of occlusion in all 26 patients examined.Conclusion: Lateral translatory movements of the human mandible have yet to be completely evaluated.05-013. McCollum, B. B. and Stuart, C. E. A Research Report. Scientific Press, South Pasadena, CA.

      See reference: 05-014. Santos, J., et al. Vectorial analysis of the static equilibrium of forces generated in the mandible in centric occlusion, group function and balanced occlusion relationships. J Prosthet Dent 65:557-567, 1991.Purpose: Mechanical analysis based on a static equilibrium of forces in an effort to support various and prevailing stomatognathic concepts of occlusal function.Materials & Methods: Two-dimensional mechanical models were designed to represent frontal projections of maxillomandibular relations focusing on only the coronal aspect of molars and both condyles. The objective was to ascertain the instantaneous static equilibrium of forces when different interocclusal eccentric relationships were imposed on these models. Templates representing a functional projection of the maxilla and the mandible were fabricated. The buccal and lingual occlusal inclines were assigned steeper angles on the right side than the left. The relationships were imposed on a centric occlusion position, a group function and a cross arch balanced occlusion relationship.Results & Discussion: All of the studies in this area have values and limitations influenced by the complexity of the biomechanical elements added to the artificially created models. Biologic systems demonstrate ranges of variability. Neuromuscular control may contribute to or override a condition of static equilibrium. For any load applied to a given body, there will be a reaction of equal intensity and direction, provided the force is exerted on a flat surface. When forces are applied against inclined surfaces they will be decomposed into vectors with different directions and magnitudes.      1. The concentration of forces generated in a stable centric occlusion produces less loading response in the joints.      2. The working side of the dentition accepts increased load and increased reaction in the contralateral balancing condyle in an observation of balanced occlusion.      3. The best approach for a uniform distribution of forces acting upon the masticatory position is erect cusps with similar angulations for both sides of the dental arches. When cusps are less steep, resultant forces in the dentition increase. Summary & Conclusions: This study, using a mechanical model, simulates a system in function and provides a vectorial analysis based on static equilibrium of forces generated in a mandible at 10 different positions(1 in centric and 9 in eccentric positions). Positions were in a balanced occlusion and in group function. The most revelant conclusion seems to be the findings that cusp inclines and condylar path inclination have a profound influence on the forces acting within the joints and dentition. 05-015. Theusner, J., et al. Axiographic tracings of temporomandibular joint movements. J Prosthet Dent 69:209-215, 1993. Purpose: To investigate the spatial patterns of condylar movements and to determine if they differ between individuals who are symptom-free and those who have subclinical symptoms. Also the biomechanics of the TMJ were documented by studying the range of condylar movements during maximum jaw movements.Materials & Methods: Forty-nine volunteers (24 men and 25 women) between 22 and 56 years were selected. The only criteria for their selection was that they were not in or seeking TMD therapy. On all 49 volunteers (symptomatic and asymptomatic), three dimensional condylar movements were recorded with a hinge axis tracing system axiograph during maximum opening , protrusion, and mediotrusion. Tracings that were displayed in sagittal and frontal planes were measured to evaluate the biomechanics of the TMJ.

Results & Conclusions: The only differences between the groups (symptomatic and asymptomatic) were in the right joint, recorded in the sagittal plane during maximal opening an the Bennett angle. The symptomatic group had a much longer condylar path. and a smaller Bennett angle compared with the asymptomatic group.These results were interpreted to be indication of adaptive morphologic instead of pathologic changes. The authors concluded that alterations in condylar tracings should be cautiously considered as an indicator of joint pathology.05-016. Clayton, J. A., Kotowicz, W. E. and Meyers, G. A. Graphic recordings of mandibular movements: Research criteria. J Prosthet Dent 25:287-298, 1971. Purpose:  To determine whether or not graphic tracings of mandibular movements could be affected by:     1. Changes in the VDO     2. Changes in the central bearing guidance surface     3. Tooth guidanceVertical Dimension Changes:  The orientation of the styli and recording table affected graphic tracings of mandibular movement when the VDO was changed. Cusps gliding on inclines involved changes in vertical dimension. Studies of mandibular movements should have the recording device oriented to the terminal hinge axis so that changes in vertical dimension do not cause different tracings. Inconsistencies previously recorded by other studies, could be due to mechanical errors in the positioning of the recording device.Central Bearing Surfaces, Shapes and Graphic Tracings:  The shape of the central bearing surface can affect graphic tracings depending on the angulation of the styli recording movement. Graphic tracings of mandibular movements recorded against different bearing surfaces will coincide if the styli is "zeroed." Graphic tracings will be different for each surface if the styli are angled backward or forward from the "zeroed" position.Tooth Guidance, Chewing and Graphic Tracings:  Unguided tracings made by the patient with the teeth in contact may not be true border tracings. Tooth interferences and muscles may deflect movement away from the border position. Border tracings should be guided when teeth are in contact, or a central bearing surface should be used to eliminate the influence of tooth interfernces and muscle conditioning on theses interferences. The position of the styli can affect the graphic recording of functional movements. the angle of the styli and the positions of the styli in relationship to the terminal hinge axis should be reported.Graphic Tracings v.s. Pantographic Tracings: Graphic tracings are recordings made on the patient from which conclusions are drawn about mandibular movements directly from the tracings. Pantographic tracings are recordings of mandibular movements from a patient that are transferred to an articulator and then conclusions are drawn after the movement of the casts on the instrument. 

Section 06: Incisal Guidance(Handout)

Definitions:Incisal guidance: 1. The influence of the contacting surfaces of the mandibular and maxillary teeth on mandibular movements. 2. The influence of the contacting surfaces of the guide pin and guide table on articulator movements. (GPT-6)Incisal guide angle: 1. Anatomically, the angle formed by the intersection of the plane of occlusion and a line within the sagittal plane determined by the incisal edges of the maxillary and

mandibular central incisors when the teeth are in maximum intercuspation. 2. On an articulator, that angle formed in the sagittal plane, between the plane of reference and the slope of the anterior guide table, as viewed in the sagittal plane. (GPT-6)Anterior guidance: 1. The influences of the contacting surfaces of the anterior teeth on tooth-limiting mandibular movements. 2. The influence of the contacting surfaces of the guide pin and the anterior guide table on articulator movements. 3. The fabrication of a relationship of the anterior teeth preventing posterior tooth contact in all eccentric mandibular movements. (GPT-6)Mutually protected articulation: An occlusal scheme in which the posterior teeth prevent excessive contact of the anterior teeth in maximum intercuspation, and the anterior teeth disengage the posterior teeth in all mandibular excursive movements. (GPT-6)Anterior protected articulation: A form of mutually protected articulation in which the vertical and horizontal overlap of the anterior teeth disengage the posterior teeth in all mandibular excursive movements. (GPT-6).Canine protected articulation, Canine guidance, Canine protection, A form of mutually protected articulation in which the vertical and horizontal overlap of the canine teeth disengage the posterior teeth in the excursive movements of the mandible. (GPT-6)Group function: multiple contact relations between the maxillary and mandibular teeth in lateral movements on the working side whereby simultaneous contacts of several teeth act as a group to distribute occlusal forces. (GPT-6).Anterior protected articulation, canine protected articulation, or group function.What do we use and why?D. Blake McAdam summarized some similarities and differences in his article.Similarities:Both must provide a multiple posterior contact with intercuspal position (centric occlusion) located either coincident with centric relation contact position or within 1mm of protrusion in a straight sagittal direction. Where these positions are not coincident they should be joined by continuous bilateral contact of pairs of teeth as described by Beyron or a flat area or "long centric" as described by Schuyler in 1969.There must be an absence of posterior contact during mediotrusion.There should be no posterior contact during anterior incision whenever the anatomic arrangement permits.There should be an anterior group-functional guidance during the protrusive movement accompanied by a posterior disclusion where the anatomic arrangement permits.Both schemes try to keep horizontal forces to a minimum although they accomplish the task differently.Differences:The manner in which the teeth function in laterotrusion.In canine guidance the horizontal forces are minimized by limiting the contact of the support cusp to their opposing fossa at or near their intercuspal position. All other lateral contacts are prevented by the steeper inclines of the canines. This results in the chewing stroke being more sagittal in a frontal view.

In group function the first contact is not made between the supporting cusp and opposing fossa, but instead at a lateral location followed by a slide to centric occlusion. This will exert some horizontal forces, but these forces can be minimized by the following:

Striking simultaneously as many working side contacts as possible. Reduce the angle of the incline so the resultant force is more along the long axis of the

tooth. Reduce friction by removing any roughness or irregularities. Slightly round the facial occlusal line angle.

A possible disadvantage for group functionWorking group function occurring on relatively steep inclines can be damaging since it may generate excessive horizontal loading. This situation is usually seen in the transition between a worn occlusion with canine guidance and an early group function type of occlusion.Tooth mobility in both types of occlusions? It would seem that with more horizontal forces present in group function the teeth would exhibit more mobility. However, O'leary, Shanley, and Drake found just the opposite. They found that teeth in a group function occlusion had less mobility than teeth in cuspid protected occlusion. Siebert found that canine protected occlusion is necessary to limit tooth mobility. Why all the differing findings??What is more common, Canine guidance or group function?Scaife and Holt examined 1200 young people and observed that most North Americans under the age of 25 had canine guidance either bilaterally or unilaterally. However, clinical observation suggest that most people over 40 years of age have group function guidance. Weinberg found only 19 of 100 people had cuspid protected occlusion.McAdam suggest that both occlusions are normal and a dentist restoring only a portion of an occlusion should not change the occlusal scheme. Obviously some qualifying remarks should be made with this statement now with the emergence of implant restorations.ImplantsJemt, Lundquist, and Hedegard looked at group function v. canine guidance in implant restored patients and found the chewing cycles to be consistent with patients having a natural dentition. (i.e. more vertical chewing in canine protection) How does this fit in with implant supported occlusion?What about parafunction v. masticatory movement of the mandible?Muscle ActivityWilliamsom and Lundquist discussed the effects of anterior guidance on the temporal and masseter muscles and found that posterior disclusion reduced the elevating activity of the temporal and masseter muscles. This also makes us think about parafunction v. masticatory movement when deciding on an occlusion.FMAWhat effect does the FMA have on occlusion in prosthodontics and what arguments can be made for each type of occlusion in high or low FMA patients. Did DePietro and Moergeli ever look at FMA related to canine guidance or group function?Occlusion

After reviewing some basic concepts about occlusion what type of occlusion does Reynolds suggest and why? This article was written one year prior to O'leary's.Schuyler wrote that incisal guidance equals or surpasses the temporomandibular joints in its influence upon the functional occlusion of the dentition. How does incisal guidance relate to condylar guidance.Kohno states the incisal path should equal the condylar path. When rotation of the condyle occurs; however, the incisal path may be increased, but not more than 25 degrees.Schuyler discussed incisal guidance in oral rehabilitation. He incorporated freedom of movement in centric occlusion be the addition of a pin in the anterior guide table.Schuyler lists his objective of an occlusal rehabilitation to be:

A static centric occlusion in harmony with the centric maxillomandibular relation. An even distribution of stress in centric occlusion over the maximum number of teeth. Lateral and anteroposterior freedom of movement in centric occlusion. Masticatory efficiency which involves uniform contact and an even distribution of stress

on eccentric functional tooth inclines which are coordinated with the incisal guidance and normal functional condylar movements.

Reduction of the buccolingual width of the occlusal surfaces of the teeth Reduction of the balancing incline contacts as a means for reducing a potentially

traumatogenic load on the structures supporting the dentition.Dawson discussed anterior guidance and firmly believes anterior guidance should be related to condylar guidance. Dawson does not believe in allowing the posterior teeth to share the load in eccentric movement stating "Even when anterior teeth are weakened by loss of supporting structure, it is preferable to have them carry the whole load during jaw excursions because by doing so we actually lessen the load on the anterior teeth because of reduction of elevator muscle contraction to only one actively contracting muscle on each side." His support for this statement may come from Williamson's article. Dawson states maximum comfort and stability may be achieved if the following criteria are met:

Stable holding contacts for each anterior tooth Centric relation contacts occurring simultaneously with equal intensity posterior tooth

contacts. Position and contour of anterior teeth in harmony with the envelope of function. Immediate disclusion of all posterior teeth the moment the mandible leaves centric

relation. Position and contour of all anterior in harmony with the neutral zone and lip closure path.

How does Dawson "Harmonize the Anterior Guidance" ? Lower anterior teeth reshaped and restored Posterior equilibrated Establish coordinated centric relation stops on all anterior teeth Extend centric stops forward at the same vertical to include light closure from the

postural rest position. Establish group function (of the anterior teeth)in straight protrusion. Establish ideal anterior stress distribution in lateral excursions.

After doing this Dawson will fabricate an anterior guide table.Cusp angle as the occlusal determinant

Hobo will fabricate two guide tables and use cusp angle instead of condylar path or incisal path as a basis for the occlusion. This differs from any other technique we have studied. How does he do this and what are the advantages? What is his reasoning?His steps are listed on the next page. His reasoning is cusp angle may be the most reliable factor to build an occlusion to. His basis for this is condylar guidance is influenced by occlusion, and therefore if you precisely simulate mandibular movement that is influenced by traumatic occlusion you will only duplicate that occlusion.Steps for the twin stage procedure:

A cast with a removable anterior segment is fabricated. Remove the anterior segment. Set the condylar path and incisal guide table to 25 degrees. Set the Bennett angle at 15

degrees and the lateral wings of the guide table to 10 degrees. Wax the posterior teeth to a balanced occlusion. This will produce a 25 degree cusp angle.

Adjust the condylar path to 40 degrees and the sagittal inclination of the anterior guide table to 45 degrees, adjust the lateral wings to 20 degrees and wax the anterior guidance.

A standard amount of disocclusion will be obtained on the molars and a physiologic anterior guidance will be fabricated.Hobo's limitationsSome limitations of this technique are if the condylar inclination of the patient is less than 16 degrees cuspal interferences will occur. (There is an 8% occurrence rate of condylar paths less than 16 degrees and Hobo states these interferences can be removed intraorally.)Hobo's contraindicationsThe twin stage procedure is contraindicated in the following cases:

Abnormal curve of Spee Abnormal curve of Wilson Abnormally rotated tooth Abnormally inclined tooth.

Helpful laboratory guideIf the anterior guidance is predetermined intraorally Clements describes an incisolingual index that will record the information for the lab tech to adapt wax or porcelain to. This technique was originally described by Fox.A matrix of acceptable provisional restorations is also helpful in contouring the facial esthetics.Basic review of anterior guidance and estheticsHeilein discusses how to establish anterior guidance. Incisal edge position is determined by phonetics and esthetics. His technique does not differ greatly from Dawson's.

Establish coordinated centric relation stops. Centric stops in a postural position must have the same vertical dimension as those for

centric relation. Refine protrusive excursions. Establish canine guidance in lateral border movements. Check lateral protrusive movements. Make sure there is a smooth transition to a cross over position.

- Abstracts –

06-001.  Scaife and Holt. Natural occurrence of cuspid guidance. J Prosthet Dent 22:225-229, 1969.Purpose: To examine the natural occurrence of cuspid guidance in eccentric positions.Materials and Methods: 1200 young men between the ages of 17 and 25 were examined. Subjects with multiple missing or carious teeth, missing maxillary first bicuspids or cuspids, or those who had restorations involving the occlusion of the maxillary or mandibular cuspids were not included in the study. An Angle classification was recorded for each subject. The presence or absence of gross wear facets was noted. The subject was instructed to close on their back teeth and side the teeth to protrusion, right and left laterotrusion. Contact was noted during the movements. Contact of the cuspids in centric occlusion was also noted.Results: The results are displayed in two tables.Conclusion: Cuspid protected occlusion in lateral movement was present bilaterally in 57% of the subjects, unilaterally in 16% and none in 26%. In protrusion, 99.4% lacked a cuspid protected occlusion. 91.5% had cuspid contact in centric occlusion.06-002. Schuyler, C. H. The function and importance of incisal guidance in oral rehabilitation.  J Prosthet Dent 13:1011-1030, 1963.abstract missing ........06-003. Anterior Guidance. Evaluation, Diagnosis, and Treatment of Occlusal Problems. C. V. Mosby, St Louis, 1974, Chapter 16, Anterior Guidance, pp. 146-165.     Posterior teeth that are not protected from lateral or protrusive stresses by the discluding effect of the anterior teeth will, in time, almost certainly be stressed or worn detrimentally.     The anterior teeth are all forward of the closing muscle power, so to exert stress on the anterior teeth, the mechanical result of the closing muscles would be like trying to crack a walnut by placing it at the tips of the handles of a nutcracker and squeezing the handles back at the hinge. This is the unique position of the resistance to stress that the anterior teeth enjoy by virtue of their relationship to the condylar fulcrum and the source of muscle power.     It is popular fallacy, that whatever path the condyles follow must be duplicated in the lingual surfaces of the upper anterior teeth so the lower anterior teeth can follow the same path. This is wrong. Condylar paths do not dictate anterior guidance, and there is no need or even advantage to try to make the anterior guidance duplicate condylar guidance. Advocates of such a concept have failed to recognize that the condyles can rotate as they move along their protrusive pathways. This allows the front end of the mandible to follow a completely different path without interfering with the condylar path.     Patients may have the same outer limits of motion, but each may have a different envelope of function. Even though condylar guidance is the same, the anterior teeth would have to be contoured differently for each patient.      Since functional movements occur within the envelope of motion borders, merely recording the outer limits of motion would not supply enough needed information for optimally restoring anterior teeth. The envelope of function that controls the anterior relationship must be treated as a separate entity.     Anterior guidance cannot be determined on an articulator regardless of how perfectly the condylar path is duplicated. It is a separate entity and must be determined in the mouth where the determinants of anterior tooth position can be observed in function.     Disclusion of all posterior teeth in eccentric jaw position reduces muscle contraction in two of the three elevator muscles.     The moment any posterior tooth comes into premature excursive contact, not only the anterior

guidance looses its capability for shutting off elevator muscle contraction, but also the elevator muscles are hyperactivated by the posterior contact.      Because of our new understanding of muscle responses to posterior disclusion, we no longer attempt to bring posterior teeth into working side group function to help weak anterior teeth. Even when anterior teeth are weakened by loss of supporting structure, it is preferable to have them carry the whole load during jaw excursions because by doing so we actually lessen the load on the anterior teeth because of the reduction in elevator muscle contraction to only one actively contracting muscle on each side. 6-004.  Hobo, S. Twin-tables Technique for Occlusal Rehabilitation: Part II - Clinical Procedures. J Prosthet Dent 66:471-477, 1991.      The deviation of the incisal path in an individual is less than that of the condylar path. The incisal path influences disocclusion at the second molar twice as much as that of the condylar path during a protrusive movement, three times as much on the non-working side and four times as much on the working side during lateral movement. The cusp angle is considered to be the most reliable reference for occlusion. The standard cusp angle values were determined to be 25 during protrusive movement, 15 on the working side, and 20 on the non-working side during lateral movement.      In order to provide disocclusion, the cusp angle should be shallower than the condylar path. To make a shallower cusp angle, it is necessary to produce balanced articulation so the cusp angle becomes parallel to the cusp path of a opposing teeth during eccentric movement. The twin stage procedure uses a cast with a removable anterior segment and fabricates the posterior teeth in a balanced occlusion. The anterior segment is replaced and anterior guidance is established.( 1mm during protrusive movement)     In Hobo’s article a description is given to create a custom incisal guide table, and a technique to simulate the protrusive movement on the articulator is detailed. In his text book, values have been determined and can be programmed into a semi-adjustable articulator.      Stage I: The sagittal condylar path inclination 25 ; Bennett angle 15 ; sagittal inclination of the incisal guide table 25 ; and the lateral wing angle 10 .The anterior segment of the maxillary and mandibular casts are removed using dowel pins and the casts are adjusted so they do not disclude during eccentric movements. Wax the occlusal morphology of the posterior teeth so the maxillary and mandibular teeth contact during eccentric movements (balanced articulation).      Stage II: The sagittal condylar path inclination 40 ; Bennett angle 15 ; sagittal inclination of the incisal guide table 45 ; and the lateral wing angle 20 .The anterior segment of the maxillary and mandibular casts is replaced. Wax the palatal contours of the maxillary anterior teeth so the incisors contact during protrusive movement, and the canines on the working side contact during a lateral movement. Anterior guidance is established and disclusion is produced.     If the sagittal condylar path of the patient is steeper than the articulator adjustment value (40 ), disclusion increases. If the path is less than 40 , then the amount of disclusion decreases. If the patient has less than 16 (only about an 8% occurrence rate), cuspal interferences will occur.     If the incisal path is more than 5 steeper than the condylar path, patients complain of discomfort( Mc Horris 1979).06-005. Reynolds, J. M. The organization of occlusion for natural teeth. J Prosthet Dent 26:56, 1971.abstract missing......

06-006. Heinlein, W. D. Anterior teeth: Esthetics and function. J Prosthet Dent 44:389-393, 1980.abstract missing.........06-007. Broderson, S. P.: Anterior Guidance-The Key to Successful Occlusal Treatment. J Prosthet Dent 39: 396-400, 1978.Purpose: To show that the relationship between the maxillary and mandibular anterior teeth is the most important factor in the restoration and maintenance of the ideal occlusion. Ideal in this case is characterized by minimal wear, a healthy periodontium and temporomandibular joint, and maintains a quiet neuromuscular mechanism.Materials & Methods: This literature review focused on the gnathologic approach for the treatment of anterior teeth by C. E. Stuart, who stated that the lingual surfaces of the maxillary anterior teeth are entirely controlled by condylar border movements, and the Pankey-Mann-Schuyler philosophy which stated that the lingual surfaces of anterior teeth are independent from condylar border movements and are dictated by a need for long centric.Results: The author discussed the determinants of anterior guidance as being:1. esthetics2. phonetics3. condylar border movements4. positional relationship of the maxillary and mandibular anterior teeth.Without the boundaries of the anterior teeth and the neuromuscular system the masticatory apparatus would destroy itself or muscle dysfunction would occur. The functions of anterior guidance are:1. to incise food2. to aid in speech3. to aid in esthetics4. to protect the posterior teeth, by directing the teeth together in centric occlusion so that the closing forces will be vertically directed onto the posterior teeth.The anterior teeth must also allow the Bennett movement to occur so that the final closure forces will be directed along the long axis of the posterior teeth. This is of particular importance for the restoration of the canines. As more Bennett movement is introduced and the angle of the eminence is reduced more lingual concave curvature is needed. In contrast a steep eminence will be in harmony with a small amount of lingual curvature.Discussion: Regardless of philosophical approach to restoring the dentition, anterior guidance must be developed to restore and maintain a healthy masticatory system. Diagnostic casts and wax-ups, protrusive registrations, pantographs, functionally generated paths, resin provisional restorations, all contribute to fabricating a final restoration which maintains the harmony between the anterior teeth and the condylar movements.Conclusion: Anterior guidance is an important component of occlusal treatment designed to protect the posterior teeth from eccentric forces, and allowing the posterior teeth to protect the anterior teeth by absorbing the vertical forces in centric position.06-008. DiPietro, G.J. Significance of the Frankfort-mandibular plane angle to Prosthodontics. J Prosthet Dent 36:624-635, 1976.     The FMA is an angle formed by the intersection of the Frankfort horizontal plane and the mandibular plane. Normal FMA ~25 plus or minus 5 degrees, high angle ~ 30 degrees or more (open bite skeletal patterns), and low angle ~ 20 degrees or less (closed bite skeletal patterns) and

not to be confused with open or closed bite dental patterns.     Clinically open bite skeletal type is associated with decreasing biting force and a low FMA (deep bite skeletal patterns) are associated with increased biting forces. "Sassouni" believed that with a deep bite molars are directly under the impact of the masticatory forces and that in the open bite patient the posterior vertical chain of muscles is arcuate, and the masseter is posterior to the molars and the premolars and therefore the patient had less powerful masticatory muscles.      In the attempt to increase VDO, it is contraindicated in the low FMA patient as they tend to return to their former occlusion. Additionally, these teeth are more susceptible to abrasion. A prime importance in deciding to render a patient edentulous with a low FMA is that the increased biting forces and resorption may further complicate stability and retention and may also result in fractured resin dentures.     With a high FMA, the glenoid fossa is situated superiorly and posteriorly and the low FMA patient, it is situated anteriorly and inferiorly. Constancy of the relationship between the position of the glenoid fossa and the FMA can be used in modifying the location of a particular arbitrary center of rotation ( Beyron, Bergstrom, and Gysi) for face bow mountings. Therefore using the Bergstrom point as a standard, the position of this arbitrary center can be modified superiorly and posteriorly for high FMA and anteriorly and inferiorly for low FMA. Additionally, the types of face bows using ear rods and anatomic averages can be modified to reflect the variation in position of the condyles as determined by the FMA.06-009. McAdam, D. B. Tooth loading and cuspal guidance in canine and group function occlusions.  J Prosthet Dent35:283-290, 1976. abstract missing ...........06-010.  Williamson and Lundquist, Anterior guidance: Its effect on electromyographic activity of the temporal and masseter muscles. J Prosthet Dent 49:816-823, 1983.Purpose: To determine the effect of anterior guidance or posterior contact in excursive movements on the temporal and masseter muscles.Materials and Methods: Five women were selected, four had previous symptoms of dysfunction or pain associated with the TMJ. Maxillary acrylic resin splints were made that allowed for anterior guidance. Surface electrodes from a Teca EMG unit were attached to the right and left temporal and masseter muscles. The subject was instructed to close firmly and maintain pressure against the splint while moving into right laterotrusion, back to retruded contact position, into left laterotrusion, back to retruded contact position, and the into protrusion. Recording were printed with a paper speed of 10 cm/sec and a microvoltage of 500 microvolts. After the recording were made the anterior guidance was eliminated from the splint and the recording were repeated. Results: The electromyogram strips are copied in the article. When the anterior guidance was eliminated from the splint more muscle activity was recorded.Conclusion: This study showed the elimination of posterior contacts will exhibit less muscle activity than an occlusion that allows posterior contacts. However; the altered splint allowed bilateral posterior contacts that are not consistent with group function and possibly less drastic results may have been obtained without balancing contacts.06-011. O'Leary, T. J., Shanley, D. B. and Drake, R. B. Tooth mobility in cuspid protected and group function occlusions. J Prosthet Dent 27:21-25, 1972.abstract missing .......

06-012. Jemt, T. , Lundquist, S. and Hedegard, B. Group function or canine protection. J Prosthet Dent 48;719-724, 1982.D’Amico - states that canine protection favors a vertical chewing pattern and prevents wear of teeth.Beyron - states group function, implies contact and stress on several teeth in lateral occlusion and indicates abrasion as a positive and inevitable adjustment.- Angle of departure was steeper than the approach angle, and these angles were slightly greater with group function than with canine protection.- Lateral displacement and total displacement of the mandible, was greater with group function.- Mandibular velocity was greater with group function.- Duration of chewing cycle was stable between the two.All results indicate that the chewing pattern may be influenced by the type of occlusion. 06-013.  Kohno and Nakano. The Measurement and Development of Anterior Guidance. J Prosthet Dent 57:620-625, 1987.Purpose: To describe a method of measuring condylar and incisal angles in developing a criteria for anterior guidance in clinical practice.Methods and Materials: 35 subjects were measured using a specific apparatus to record the jaw movements. A metal splint was attached to the lower teeth.      A facebow with three small light bulbs was used with cameras to record the path of jaw movements. Results: The average inclination of the incisal path was 46 . The average condylar path was 38.

Conclusion: The inclination of the incisal path should be equal to the inclination of the condylar path. The incisal path should not be more than 25 steeper than the condylar path. A jerky condylar movement will result from an incisal path that is flatter than the condylar path. If the incisal path is shallower than the condylar path, the condyle rotates in a reverse direction during protrusive movements. 06-014. Siebert, G. Recent results concerning physiological tooth movement and anterior guidance. Oral Health Rehabil 8:479-493, 1981. abstract missing .......06-015. Clements, William G. Predictable anterior determinants. J Prosthet Dent 49:40-45, 1983.Purpose: To describe a method to predictably fabricate anterior restorations.Materials and Methods: Author's description of a clinical and lab technique. Results: NoneConclusion: Prior to make the tooth preparations on the anterior teeth resin composite restorations are placed that will determine the size and shape of the final crowns. Diagnostic cast are made when the patient is comfortable and pleased with the resin composite restorations. Provisional restorations are made from this cast in the laboratory. At the following appointment the teeth are prepared and provisional restorations are placed. A face bow transfer and centric relation record are made at the next appointment. The provisional restorations are evaluated and an impression is made of the provisional restorations. A face bow transfer and centric relation record are made with the provisional restorations in place. A custom incisal guide table is fabricated from the articulated provisional and lower opposing cast to reconfirm the excursions in the completed restorations.

     When the case is forwarded to the laboratory an incisolingual index is fabricated. To fabricate the incisolingual index the maxillary cast with the provisional restorations is attached to the upper member of the articulator and a new mounting plate is attached to the lower member. Boxing wax is wrapped around the lower mounting plate one inch short of the maxillary cast. The cavity is filled with mounting stone and the exposed surface roughened to create undercuts. Lab putty is placed over the mounting stone, catalyst is placed on the maxillary cast to act as a separating medium. The centric lock is engaged and the articulator is then closed. The putty gives an index to which the wax pattern or porcelain can be compared with. 06-016. Kahnm, A. E. The importance of canine and anterior tooth positions in occlusion. J Prosthet Dent 37:397-410, 1977.abstract missing .....

Section 07: Articulators I - Overview(Handout)

I. Definition: A mechanical instrument that represents the temporomandibular joint and jaws, to which maxillary and mandibular cast may be attached to simulate some or all mandibular movements. (GPT-6)II. Classification:     A. The Glossary of Prosthodontic Terms classifies articulators into four classes.Class I. A simple holding instrument capable of accepting a single static registration. Vertical motion is possible.Class II. An instrument that permits horizontal as well as vertical motion but does not orient the motion to the temporomandibular joints.Class III. An instrument that simulates condylar pathways by using averages or mechanical equivalents for all or part of the motion.. These instruments allow for orientation of the cast relative to the joints and may be arcon or nonarcon instruments. (Arcon articulator - An articulator that maintains anatomic guidelines by the use of condylar analogs in the mandibular element and fossa assemblies in the maxillary element.)Class IV. An instrument that will accept three dimensional dynamic registrations. These instruments allow for orientation of the cast to the temporomandibular joints and replication of all mandibular movements. (GPT-6)     B.  Awni Rihani published an article in JPD in 1980 discussing the classification of articulators that appears to be the accepted terminology to date. A nonadjustable articulator can accept one or two of the following records: Face bow, centric jaw relation or protrusive record. A semi adjustable articulator can accept all three of those records.A fully adjustable articulator can accept the following five records: Face bow, centric jaw relation, protrusive, lateral records, and intercondylar distance record.

A class I articulator is a nonadjustable articulator. A class II or III articulator is a semiadjustable articulator. A class IV articulator is a fully adjustable articulator.

For a review of the previous names for classifying articulators review the Rihani article at J Pros Dent 43: 344-347, 1980.

III. Occlusion and occlusal theories in addition to mechanical theories drove the development of articulators. (J Pros 2:33-43, 1993)     A. Occlusion.  1. Bonwill 1858 Triangular theory of occlusion  2. Balkwill 1866 Translating jaw moved medially  3. Von Spee 1890 Occlusal plane of teeth follow a curve   4. Snow 1899 Facebow  5. Christensen 1901 Opening of posterior teeth in protrusion  6. Bennett 1908 Immediate side shift

  7. Gysi 1910Demonstrated use of incisal guide pin. One of the first to allow for side shift

  8. Monson 1916 Spherical theory of occlusion  9. Hall 1918 Conical theory 10.Hanau 1921 Rocking chair denture occlusion11.Stanbury 1929 Positional records Tripod.12.Meyer 30's Chew in technique13.Avery Brothers 1930 Anti-Monson Reverse curve of Wilson14.Pleasure 1930 Anti-Monson except 2nd molars in balance15.PMS 20's Eliminate balance, Incisal guidance important, Long centric16.Gnathology 20's Pantograph, need to reproduce mandibular movements17.Page 1950 Transographics. Page is dead and so is Transographics.

18.Gelb 1970Cranial Orthopedics. The condyles assume a certain shape based on mandibular movements.

IV. Basic anatomic principles and movements that need to be applied to articulators were discussed by Weinberg in 1963. He also discussed an outdated classification system.     A. The hypothetical patient.

Protrusive condylar inclination of 400 The 2nd molars located 50mm from the hinge axis in the horizontal plane and 32mm

below it. The incisal edge of the mandibular incisors is located 100mm from the hinge axis on the

horizontal plane and 32mm below it.     B. The basic elements of mandibular motion

Protrusion Incisal guidance Balancing condylar path Balancing cusp inclines Working condylar motion -- Basic types of working condylar motion

     C. Tooth contact dominates mandibular motion.     D. Two essential steps in a face bow mounting.

1. Hinge axis2. Anterior point of orientation

     E. Effects of raising or lower the occlusal plane and changing the condylar inclination have on tooth morphology.

V. Contributions of specific individuals     A. Bonwill

Philosophy of mastication Anatomy of the human jaws The Bonwill articulator The method of using Bonwill's articulator Significance of the equilateral triangle.

     B. GysiGysi used the gothic arch tracing and a tracing of the sagittal inclination of the condylar path.The average angle of the gothic arch is 1200 and the average sagittal inclination of the condyle is 300. The two condyle and incisor point determine interdigitation.In the edentulous patient the movement from incisive to protrusive is completely lost.Gysi does not regard lateral movements of the mandible important except in unusual cases and suggest an average condylar path of 150.The following four features are required of an articulator:

centric relation of the mandible control of lateral incisor point movements sagittal inclinations of the condylar path incisor path

Four methods of adapting the articulator The intra-oral checkbite method with plastic material The intra-oral checkbite method with plaster The extra-oral graphic method with the face-bow (Gysi prefers) The intra-oral dentographic method

A faulty cuspid relation is a frequent cause of denture displacement.The lateral incisor paths are more important than the condylar paths because the teeth lie closer to the incisor point and the lateral paths of the condyles are more difficult to reproduce.Use of a facebow is necessary to accurately place the cast on the articulator especially when the sagittal condylar path differs from the incisor path.Denture teeth should be placed over the ridge to insure stability and guard against tipping or dislodging of the dentures.Teeth should be set to conform to the alveolar ridge.     C. Monson The various phases of occlusion of the teeth in

The developing jaws The bones adjacent to the maxillary bones forming the masticating organs of man The segments or teeth mounted in this mechanism, forming the masticating members The normal construction of the human jaw Anatomical malformations of the mandibular mechanism The construction of crowns and bridge work

     D. HallHis role in the development of articulatorsHis love for Gysi 

VI. In today's dental schools we have different articulators for fixed v. removable restorations. What about in the "real world".

In dental school, the Whip-Mix and Denar are the most commonly used articulators used for fixed restorations while a Hanau model is more commonly used for removable. (Smith JPD 54:296-302, 1985)

Mohamed (JPD 36:319-325, 1976) found that 64% of practicing dentist used a hinge or simple articulator, 26% used a semi-adjustable, and 10% used a fully adjustable articulator.

Schweitzer found that he had equal amounts of success using different articulators. (JPD 45:492-498, 1981) 

Board QuestionsAlfred Gysi was the first to produce an articulator which could reproduce downward and forward movements.The first articulator to record downward and forward motion at the condyles was the Balkwill articulator.William Walker developed an adjustable articulator for individual mandibular movements, making registrations of the inclinations of individual condylar paths extraorally.The Fournet and Hageman articulators are examples utilizing the spherical theory.Instruments that encompass the "terminal orbital function" are the Gnathoscope, the Wadsworth articulator, the Transograph, the Denar D-5A, and the StuartGnatholator, Denar, and Stuart are fully adjustable articulatorsHanau, Whip-Mix, and Dentatus articulators are semi adjustable.The Whip-Mix, Hanau University, and Stuart are examples of articulators with adjustable intercondylar distance.Walker first recorded mandibular movement 

- Abstracts -07-001. Bonwill, W.G.A. The Scientific Articulation of the Human Teeth as Founded on Geometrical, Mathematical, and Mechanical Laws. Dent. Items of Interest, pp. 617-643, October 1899. In Vol. I., Classic Prosthodontic Articles. A.C.O.P., pp. 1-28.Theory of Mastication: Only one side of the jaw can function at a time. He relates how millstones are grooved to the left from the center of the stone and the upper stone is revolved to the right to allow clearing of the grain to the outside. He recommends using articulation rather than occlusion because it was a word of action.Anatomy of the Human Jaw: 95% of cases will have the upper teeth project over the lower, and the depth of overbite varies as the depth of the cusps of the bicuspids are deep or shallow. The ramus will be found to come upward and backward in relative proportion to the length of the cusps and the overbite.Tripod arrangement of the lower jaw forming an equilateral triangle from the center of one condyloid process to the other, four inches is average. From the condyloid process to the inferior centrals touch at the cutting edge is also four inches. It varies slightly, but not more than ¼ of an inch.

Ordinary brass articulators are joined as if the jaw was jointed at the pharynx. The cuspids to molars are in a straight line to enable them to keep the largest proportion of surface presented for mastication.Overbite or underbite will be in proportion to their depth and to the length of the cusps of the cuspids, bicuspids and molars. The length of the cusps on bicuspids will never be more than 1/8 inch off.Bonwill Articulator: As of 1858, the Bonwill Articulator corresponds to the shape and movements of the mechanism of the jaw. The base with its movements forms one part and the two bows another. It is made of 1/8 inch diameter brass wire. Method of Using the Articulator: Always model the upper wax (record base) first, judging the length of incisors and trial placement of anterior teeth for shade, shape, length and width. To articulate the lower cast, use a pair of dividers four inches apart with the center of the lower teeth at the median line just four inches from the condyles on either side. The first bicuspid should only have one cusp. A groove in the upper teeth should be placed nearer the buccal side, and for the lower on the lingual.      Proposes "bilateral balance" to equalize the pressure and action of the muscles on both sides or parts of the dental arches. The incisors never touch when the jaws are in lateral movement. One side of the mouth can be used at the same instant, leaving the other free to balance the other side at work.Significance of the Equilateral Triangle: The center of each condyle being the center of motion, rotating on one condyle only, the other describing the arc of a circle by moving in the glenoid cavity. Bonwill claims to have examined 4,000 dead jaws and at least 6,000 living jaws.      The size of the lower jaw must be 1/12 of the main circle drawn around the equilateral triangular jaw. The six incisors mean diameter, in line, measure the same as the two bicuspids and two molars on either side forming an equilateral triangle. 07-002a. Weinberg L. A. An evaluation of basic articulators and their concepts. Part I. Basic concepts. J Prosthet Dent 13, 622-644, 1963.Evaluation and associated concepts of articulators compared to that of a hypothetical patient and the clinical implications. The maxillary arch is the fixed base from which mandibular motion is recorded. The importance of facebow transfer and CR records to the starting position of mandibular motion is emphasized. The condyles and incisors are the three points used to study mandibular motion. Incisal guidance is the dominant determinant of mandibular motion due to it's mechanical leverage. Transfer of a kinematic axis requires the rods of the articulator are moved to meet the pins of the facebow for accuracy. Bennett Angle, Fischer Angle and Bennett movement are discussed.07-002b. Weinberg L. A. An evaluation of basic articulators and their concepts. Part II. Arbitrary, Positional, Semiadjustable Articulators. J Prosthet Dent 13, 644-663, 1963.Arbitrary: Monson's spherical Theory and the 8" sphere do not consider individual variations but has value in establishing a general curve of the occlusal plane.Positional: Stansbury Tripod of limited use, any change in VDO requires new records.Semiadjustable: Hanau Model H.Orientation of the Maxillary Cast

Anatomic average for hinge axis. Anterior point of reference can be the orbital pointer or by aligning the incisal edges of the teeth or the wax rim to the notch on the incisal pin.

CR record, the Gysi Gothic arch tracing is the most desirable. Interocclusal wax records or other records are acceptable.

Protrusive record gives condylar inclination Balancing Condylar motion- downward, mesial and forward. The protrusive is used for

the downward component . Bennett movement is determined by formula ( h/8 +12).Mathematical study of the Hanau Model H

Approximate Error at the second molar cusp height

Balancing

Working

Type of error

1. Anatomic average hinge axis .2 .2 ant/post2. Arbitrary anterior point of reference .2 .0 neg3. Straight condylar path    .2 .2 pos4. No Fischer angle .1 0.0 pos5. No individual working condylar motion .0 .8 neg

Arbitrary hinge axis CR record, Gothic arch desirable, wax records acceptable Protrusive record gives condylar indication and Bennett Angle Bennett movement of working condyle gives up, back and out movement only, can only

vary amount Condylar indication changed by arbitrary third point of reference Fischer angle unaccounted for Lack of adjustment of working condyle could cause negative error of.8mm

     The most significant error is produced by the lack of working condylar motion. Overall, most of the errors tend to cancel each other out rather than compound.. The error produced is often negative and tends to produce flatter cusps. The error in the working condylar guidance effects posterior teeth more than anterior teeth. Decreasing the Bennett angle of the opposite balancing condylar guidance produces more rotation and less lateral shift of the working condyle and , therefore increases posterior working cusp inclines.07-003. Celeza, F. V. An analysis of articulators. DCNA 23: 305-326, 1979.Purpose: Redefine the articulator.Discussion: An articulator is defined as a "mechanical device which represents the temporomandibular joints and jaw members, to which maxillary and mandibular casts may be attached". Many devices that are called articulators do not satisfy this definition. Some of these devices make no attempt to represent the TMJ ( facebow transfer) or their paths of motion (eccentric registrations).     Noneccentric movement articulators differ in the approach to the occlusal position.     The mandibular pathways are all curved and only one of these pathways can be registered. Eccentric movement articulators must all be oriented to the TMJ and therefore, require registrations of centric relation as a starting or reference position. The reason for using an instrument that allows eccentric movement is to minimize adjustments and preserve anatomical detail. The more adjustments required, the greater the loss of anatomical form, since all adjustments are subtractions only.

     When selecting an articulator for prosthodontic use, first determine what type of occlusal scheme is most desirable. If centric occlusion is to be used as the position of MIP, then only a registration of that position with the remaining teeth in contact should be taken. The working casts cannot be joint oriented because centric occlusion is not a border position. Therefore, the precise end point of centric occlusion must be maintained by the articulator.     If centric occlusion is going to be used as the position of MIP, it would be most advantageous to use a joint-oriented technique such as the face-bow transfer. In this way the endpoint (centric relation) can be preserved on the articulator with slight changes in vertical dimension. Eccentric pathways can be dynamically registered either graphically (pantographic method) or stereographically (engraving method), positionally registered (checkbite method), determined by the articulator (mechanical equivalents), or adjusted entirely on the patient.Classification of cast relators:1. Class I - simple holding instruments capable of accepting a single static registration. The eccentric movements permitted offer no advantage because they are not registered and are therefore inaccurate. The exception to this is the Subdivision C instrument. Class I instruments are suitable for crown and bridge, and operative instruments. Important features are positive stops and locks at the mounted position.

Subdivision A: vertical motion is possible. Ex: Corelator, Venticulator. Subdivision B: vertical motion is joint related. Ex: Centric Relator.

Class II - instruments that permit horizontal as well as vertical motion but do not orient the motion to the TMJ.

Subdivision A: eccentric motion is unrelated to patient motion. Ex: Gysi Simplex. Subdivision B: eccentric motion permitted is based on theories of arbitrary motion. Ex :

Shofu Handy II. Subdivision C: eccentric motion permitted is determined by the patient by using

engraving methods. Ex: Gnathic Relator.Class III: instruments that simulate condylar pathways by using averages or equivalents for all or part of the motion. They allow for joint orientation of the casts and may be arcon or nonarcon instruments. All the examples are arcon instruments, accept facebows, and have mounting plates for unlimited case load.These instruments can fulfill the requirements for complete denture construction.Desirable features would be good centric lock, progressive and immediate side shift controls, protrusive inclination, intercenter distance adjustment, a simple mounting procedure, a good sturdy design, and an arcon arrangement.

Subdivision A: accept static protrusive registrations. Ex: Hanau Arcon II. Subdivision B: accept static lateral protrusive registrations. Ex: Denar Mark II, Whip

Mix, Case Articulator Simulator, Panadent model P, Hanau Model 130-22, TMJ Mechanical Fossa Instrument.

Class IV: instruments that will accept three dimensional dynamic registrations.     These instruments allow for joint orientation of casts. These articulators are the instruments of choice for complete reconstructions. These instruments should hold adjustments, contain good centric locking mechanism, versatile incisal guide tables, and stable mounting features, and be precision engineered.

Subdivision A: the cams representing the condylar paths are formed by registrations engraved by the patient. Ex: TMJ.

Subdivision B: instruments that have condylar paths that can be angled and customized. Ex: Stuart Gnathological Computer, Denar Model 5A, Denar Model SE.

07-004. Hall, R. E. An analysis of the development of the articulator. JADA 17:3-51, 1930. In Vol II, Classic Prosthodontic Articles A.C.O.P., 1978, pp. 53-101.Purpose: To increase knowledge and understanding of the development of the articulator in an effort to end the controversy over 2D (gothic arch) vs 3D (anatomic) articulators.Discussion:A). Review history of development:-Gariot (1805): original invention; simple hinge-Snow: facebow(1st evidence of 3D relations)-Hayes: articulating caliper-Broomell: planes of orientation to plane of occlusion, ala-tragal-Evans(1840): given credit for the 2nd articulator-Cameron: the real 2nd contributor; 1D opening & closing movement-Bonwill (1858): father of anatomic/balanced occlusion, equilateral triangle-Walker (1896): real pioneer but Gysi took credit, varied axes of lateral movement, condyle path and rotation point theory adjustable condylar guidance, incisal guidance and Balkwill-Bennett movement were, only real changes prior to 3D-Hayes (1899): downward movement of the condyle-Luce (1911): incisal pin and support guide; 3D but plastic-Gysi (1910): Balkwill-Bennett movement; incisal guidance and pin-Hall: adjustable 3D anatomic articulator; universal mandibular movements, adjustable incisal guide-Gysi Trubyte and Wadsworth: components of all previous articulators-Hanau (1920): engineer; 2DB). Warring camps of Gysi(2D) and Hall(3D)2D: gothic arch tracing; cannot reproduce arcuate movement of the mandible and accurately check 3D bites3D: working condyle moves in all directions, no restraining hinge joint; automatic C). Other notable credits:Davis & Leuchenring: intercondylar width adjustment Monson: divider for determining basic curves disk locating center for projecting curves 07-005a. Donald L. Mitchell, DDS, MS, and Noel D. Wilkie, DDS. Articulators through the years. Part I. Up to 1940. J Prosthet Dent 39:330-338, 1978.A pictorial history of the articulators at the National Naval Dental Center is presented. All articulators in the article will be listed with a unique attribute noted.The Plaster Articulator. Plaster extensions off the distal portions of the cast articulated the cast together. Credited to Philip Pfaff of Berlin who was the dentist of Frederick the Great.The Barn Door Hinge. Heavy duty hinge modified by bending each arm 90 degrees to form a L-shaped upper and lower member.The Adaptable Barn Door Hinge. Has an anterior vertical stop. Usually a machine bolt.The Kerr Articulator. Hinge is on the same plane as the occlusal plane. Fixed protrusive and lateral movement.

The New Century Articulators. Snow in 1906. Rotational centers placed 4 inches apart.The Acme Articulator. Elaboration of the New Century articulators. Three different models to allow for three ranges of intercondylar distance.The Gysi Adaptable and Simplex. The adaptable was introduced in 1906 but was too technical and cost too much so the simplex was introduced in 1914. The condylar guidance was fixed at 330 and has a S-shaped curve in profile.The Bixby Attachment. A forerunner of the facebow in attempted to regulate the anteroposterior position of the cast on the articulator. (1894)The Maxillomandibular Instrument. Designed by Monson in 1918 based on the spherical theory. Average radius of the sphere was 4 inches but could be changed.The Stephan Articulator. Developed in 1921. Has a fixed condylar inclination and allows for an arbitrary lateral movement.The Hanau Model M Kinoscope. Early 1921. Four post. The Bennett angle is adjusted by changing the eccentric cone on the outboard post.The Homer Relator. Developed in 1923 by Joseph Homer. TMJ uses a similar principle in relating cast.The Wadsworth Articulator. Flag feature and an adjustable intercondylar distance.The Hanau Model H110. Designed to encompass mechanical averages.L= H/8 + 12The Hanau Model H110 Modified. Introduced the incisal guide table.The Hageman Balancer. 1920's. Based on the spherical theory of occlusion. Mandibular teeth constructed first.The Phillips Student Articulator (Model C). Developed around 1929. It's developer claimed it could follow any graphic record.The Stanbery Tripod Instrument. Reproduces positions not movements.The House Articulator. Developed in the 1920's. Rotary milling device. The Precision Coordinator. Developed in the early 1930's by Terrell. Curvilinear condylar guides.The Hanau Crown and bridge Articulator. Small articulator that can simulate working and balancing side excursions of 150 and protrusive of 300.The Phillips Occlusoscope. Phillips believed in only two (condylar) determinants of occlusion therefore the incisal pin rested on a flat plane. 07-005b.  Donald L. Mitchell, DDS, MS, and Noel D. Wilkie, DDS. Articulators through the years. Part II. From 1940. J Prosthet Dent 39:451-458, 1978.A pictorial history of the articulators at the National Naval Dental Center is presented. All articulators in the article will be listed with a unique attribute noted.The Stephan Articulator (Modified). 1940. Simple hinge joint with longer upper and lower members than the 1921 model and a fixed condylar path of 300.The Stephan Articulator Model P. An incisal pin and fixed 100 incisal guidance.The Fournet Articulator. No lateral movement.

The Johnson - Oglesby and Moyer Articulators. The Johnson - Oglesby instrument is a small, nonadjustable, flexible articulator developed around 1950. The upper member of the Moyer has a ball and socket adjustment. It is a mean value articulator.The Coble Articulator. A hinge articulator that maintains vertical dimension and centric relation but does not allow for functional movements. The Galetti Articulator. The cast are held mechanically without plaster.The Panky-Mann Articulator. Occlusal plane of the mandibular teeth are based on the Spherical theory.The Stuart Articulator. The settings are programmed by using pantographic tracings from the patient.The Hanau Model H2 Series. Increased the distance between the upper and lower member from 95mm to 110mm and added an orbital indicator to the upper member.The Dentatus ARL Articulator. Allows for the transfer of cast from one articulator to another while the same relationship is maintained.The Improved New Simplex Articulator. Average movements. Condylar inclination of 300. Bennett movement of 7.50. The incisal guide table adjust from 00 to 300.The Verticulator. Developed to be used with the functionally generated path technique and quadrant trays.The Ney Articulator. No locking device between upper and lower members. Varying intercondylar distances. Can use custom ground plastic inserts in the condylar elements.The Hanau Model 130-21 Articulator. One of the Hanau university series. Introduced in 1963. The Whip-Mix Articulator. A simplified version of Stuart's fully adjustable articulator. Can not be set to all positional records.The Simulator. A fully adjustable articulator that can be set from pantographic tracings, positional records, and other tracings.The Denar D4A Articulator. A fully adjustable articulator. Programmed from tracings made with a pneumatically controlled pantograph.The Dentatus ARO Articulator. A moveable arm that holds the mandibular cast allows for repositioning the mandibular cast without remounting. 07-006.  Mohamed, S.E., Schmidt, J.R. and Harrison, J.D. Articulators in Dental Education and Practice. J Prosthet Dent 36:319-325, 1976Discussion: Survey sent to 305 labs in the East Coast and in Illinois. They received a response from 106 laboratories. The survey results were interpreted to identify dentist’s use of articulators after training. Only a small percentage of students continued to use or prescribe articulators. Responses from 98 labs disclosed the type of articulators dentists were submitted : 64% were hinge or simple articulators, 26% were semi-adjustable articulators, and 10% were fully adjustable. The most common complaints of the lab technicians were poor registration records and poor impressions. They preferred that the dentist articulated the casts prior to referring them to the lab.      Authors thought it would be better to place emphasis on the selection of an articulator dependent upon the difficulty encountered with each patient, rather than learning to use one articulator - i.e. semi-adjustable.

07-007. Smith, D. Does one articulator meet the needs of both fixed and removable prosthodontics? J Prosthet Dent 54:296-302, 1985. Purpose: Survey of dental school's Fixed and Removable department as to the type of Articulatores required of their students.Methods: Surveys were sent to each dental school and their respective Fixed and Removable Departments.Conclusion: Fixed Departments preferred an articulator that allows separation of the maxillary and mandibular members and in Removable departments prefer those that do not.07-008.  Awni Rihani, DDS, MSc. Classification of articulator. J Prosthet Dent 43:344-347, 1980.Purpose: To discuss a classification system for articulators.Discussion: Articulators have been classified in several ways by several different people. Rihani suggest classifying articulators as nonadjustable, semiadjustable, or fully adjustable. This is based on the type of records they can accept.

A nonadjustable articulator can accept one or two of the following records: Face bow, centric jaw relation or protrusive record.

A semi adjustable articulator can accept all three of those records. A fully adjustable articulator can accept the following five records: Face bow, centric

jaw relation, protrusive, lateral records, and intercondylar distance record.07-009. Monson G. S. Occlusion as Applied to Crown and Bridge Work. J Nat Dent Assoc 7:399-413, 1920. In Vol II, Classic Prosthodontic Articles, A.C.O.P. pp. 1-15.Purpose: To achieve well balanced geometric proportions to the face and optimum function, one can relate all jaws to a sphere whose radius is approximately four inches . The center is equi-distant from the occlusal surface of the teeth and the center of each condyle.Discussion:First - The Developing JawThe function of mastication is essential in developing the normal jaw and the base of the cranium. Food and function play the key role in development and will create the ideal masticatory forces and facial form.Second - The Bones Adjacent to the Maxillary Bones Forming the Masticating Organs of ManThe total action of the muscles converge to a common center.Function of these muscles are the main factor in developing well balanced geometrically proportioned face.Third - The segments or Missing teeth Mounted in This Mechanism Forming the Masticating MembersNo matter what positions the mandible may take, the masticatory forces are directed down the long axis of the teeth. The center of the applied forces converge to a common radial point about four inches from the occlusal surfaces and the head of the condyles. Tooth attrition is the greatest disturbance to this geometric balance.Fourth - The Normal Construction of the JawThe normally constructed jaw will exhibit Bonwill's equilateral triangle. Lines from each corner of the triangle are drawn upward to form a pyramid. From that common point, radii can be drawn to each occlusal surface forming a sphere of eight inches in diameter.Fifth - Anatomical Malformations of the Mandibular Mechanism

Malformations are any deviation from the equilateral triangle of four inches. These will lead to improper function and poor development as well as contribute to possible obscure disorders according to the author.Sixth - The Construction of Crowns and Bridgework in Such a Manner As To Allow Freedom of Range of Occlusion, Producing the Harmonious Action and Permanent Health of the UnitsAll patients should be restored in accordance with the spherical pyramid of which Bonwill's triangle is the baseSummary: The dentist should provide more than just proper mastication with his restorations. His responsibility is to see that the proper facial and cranial dimensions are achieved. 07-010.  Alfred Gysi, DDS. Practical application of research results in denture construction. JADA 16:199-223, 1929.Several topics are discussed. Important bullets are listed below.

Gysi used the gothic arch tracing and a tracing of the sagittal inclination of the condylar path .

The average angle of the gothic arch is 1200 and the average sagittal inclination of the condyle is 300.

The two condyle and incisor point determine interdigitation. In the edentulous patient the movement from incisive to protrusive is completely lost. Gysi does not regard lateral movements of the mandible important except in unusual

cases and suggest an average condylar path of 150.The following four features are required of an articulator:

1. centric relation of the mandible2. control of lateral incisor point movements3. sagittal inclinations of the condylar path4. incisor path

Four methods of adapting the articulator1. The intra-oral checkbite method with plastic material2. The intra-oral checkbite method with plaster3. The extra-oral graphic method with the face-bow (Gysi prefers)4. The intra-oral dentographic method

A faulty cuspid relation is a frequent cause of denture displacement.The lateral incisor paths are more important than the condylar paths because the teeth lie closer to the incisor point and the lateral paths of the condyles are more difficult to reproduce.Use of a facebow is necessary to accurately place the cast on the articulator especially when the sagittal condylar path differs from the incisor path.Denture teeth should be placed over the ridge to insure stability and guard against tipping or dislodging of the dentures.Teeth should be set to conform to the alveolar ridge.07-011. Schweitzer, J.M. An evaluation of 50 years of reconstructive dentistry. Part II: Effectiveness. J Prosthet Dent 45: 492-498, 1981Purpose: Evaluation of reconstructive therapy for patients that were under observation for at least 10 years.Discussion:

A. Documentation    - Observations    - Patients must be receptive to the program.    - Record keeping.B. Prognosis    - Extent and type of disease, which may be systemic, local, or emotional.    - Etiology, which includes local environmental factors, some which may be correctable or not.    - Physical health and habits of the patient, the number and distribution of remaining teeth, and the health of the periodontium.    - Retention of questionable teeth, alteration in occlusal vertical dimension, and alteration of interocclusal distance.    - Problems created by uncooperative patients, inadequate home care, or failure to return for postoperative examination and therapy.    - Biological problems- postural changes induced by disease and aging which may alter the position of the mandible, malocclusion, growth anomaly, and systemic disease.C. Results    - The goal of reconstructive therapy is to provide the patient with an esthetic, functioning, stomatognathic system, in which the progress of degenerative disease is arrested or at least retarded.    - A large majority of the patients with good prognoses maintained good dental health.    - A lesser percentage of patients with fair or poor prognoses improved with time.    - Women held a slight advantage over men in maintaining good dental health.    - Age favored patients under 50 years when the prognosis was good.    - Increasing the vertical dimension of occlusion did not consistently influence the results.    - Prostheses in which working and balancing occlusion were produced for 27 patients failed to demonstrate superior results.    - For some patients, both an increased vertical dimension of occlusion and balancing occlusion was provided.    - The treatment plan included increasing vertical dimension of occlusion and establishing balanced occlusion. This was attained with fixed temporary prostheses, for a trial period.    - The patient adapted well to the increases vertical dimension of occlusion, and the permanent restorations were inserted 8 months later. The increased vertical dimension and balanced occlusion were included in the final restorations.Conclusion: Dental therapy must reject the concept of permanence. Mutilated dentitions may be restored to health and serve to create a nonpathogenic stomatognathic system for a satisfactory period.07-012. Becker C.M. and Kaiser D.A. Evolution of Occlusion and Occlusal Instruments. J Prosthod 2:33-43, 1993.Purpose: To review the historical origins and evolution of occlusal concepts.Materials & Methods: NoneResults: NoneDiscussion: Occlusal concepts proposed during the period of 1800 to 1930 (age of occlusal theories) were basically formulated for complete denture patients stressing bilateral balance. 1920-1940's Pankey, Mann, Schuyler and Gnathology were developing. The concepts of transographics, cranial orthopedics, and mandibular centricity (centric relation) are further discussed. Biologic occlusion is a flexible concept with the goal to achieve an occlusion that

functions and maintains health. Goals: 1. No interference between CR-MI. 2. No balancing contacts. 3. Cusp to fossa occlusal scheme. 4. A minimum of one contact per tooth. 5. Cuspid rise or group function. 6. No posterior contacts with protrusive jaw movements. 7. No cross tooth balancing contacts. 8. Eliminate all possible fremitus. 9. Obtain and maintain a neurological release. Conclusion: It is recommended to avoid occlusal therapy for individuals who appear to be functioning in health, even if their occlusal scheme does not fit a concept of optimum occlusion. When therapy is unavoidable it is suggested to treat within the guidelines of a biologic occlusion.

Section 08: Articulators II – SemiAdjustable(Handout)

Semiadjustable articulator: an articulator that allows adjustment to replicate average mandibular movements-called also Class III articulator (GPT-6)A Class III articulator, an instrument that simulates condylar pathways by using averages or mechanical equivalents for all or part of the motion. These instruments allow for orientation of the cast relative to the joints and may be arcon or nonarcon instruments. (GPT-6)The semiadjustable articulator has evolved to become the "workhorse" articulator in prosthodontics. In the first articulators seminar, history was reviewed and it was shown how sophisticated and complex articulators such as the Hanau Model M Kinoscope and the Stuarts articulator were simplified into the Hanau Model H110 series and Whip Mix articulators in common use today.To briefly review, Rihani developed a modern system based on adjustment capabilities of the articulators, and this has simplified the process. Table I Classification of articulators:

ARCON and NON ARCON articulators Bergstrom coined the term arcon from articulating condyle, this articulator has the condylar elements on the lower member of the articulator and the condylar path elements on the upper member. The non arcon or condylar articulator has the reverse sequence with the condylar element on the upper member of the articulator.The angle between the condylar inclination and the occlusal plane is fixed on the arcon, this is not so with the nonarcon articulator.What clinical implication does this difference have? What is Weinberg’s view about fabricating restorations on these articulators? In his investigations, what did Beck have to say about the advantages of the arcon articulator?In his classic article, Weinberg reviewed the use and mathematical study of the Hanau Model H Hanau stated the less realeff, the more the instrument would simulate mandibular movements.Use of the Model H (designed primarily for complete dentures)Orientation of the maxillary cast: anatomic average for the hinge axis, anterior point of reference can be orbital pointer, or lining up the incisal edges of teeth, or the wax rim to the notch on the incisal pinCentric relation record:"Gysi Gothic arch" tracing, interocclusal wax records acceptableProtrusive record: records condylar inclination (Christensen's method)Balancing condylar motion: motion is downward, forward and medial (medial or Bennett angle is determined by H/8 +12

Working condylar motion: the Hanau Model H has no individual accommodation, the intercondylar rod passes laterally through the working condylar ball. This produces an upward, backward and lateral motion. The Bennett movement varies only in amount rather than directionMathematical study of the Model H:The most significant error is produced by the lack of working condylar motion. Overall, many errors tended to cancel each other out.When comparing usage for complete dentures versus fixed prostheses, the negative error is due to the lack of working condylar guidance, which produce flatter posterior cusps.Compensation for this negative error can be done by decreasing the Bennett angle of the opposite balancing condylar guidance, which produces more rotation and less lateral shift of the working condyle in question, thus increasing the working cusp inclines. As stated in Rihani’s table of capabilities of articulators above there are distinct differences in the semi and fully adjustable articulators.Bellanti compared the capabilities of the semi and fully adjustable articulators.He stated the semiadjustable articulator (Whip-Mix) guides only the lateral component of the rotating condylar element, whereas the fully adjustable articulator (Denar 4A) may be set to simulate all components of mandibular movement.What were his criteria/findings and what is needed to reproduce the effects of mandibular movements with reasonable accuracy?From Bellanti’s first article it was noted that an immediate side shift (ISS) produced a large difference in the cusp pathways of the opposing dentition. If this ISS occurs in patients, an excessive amount of intraoral adjustment may be needed due to occlusal interferences..What percentage of the subjects in this study demonstrated an immediate side shift?IMMEDIATE SIDE SHIFT: defined as a mandibular side shift in which the orbiting condyle moves essentially straight medially as it leaves centric relation (Guichet)The ISS occurs at the beginning of lateral jaw movement, since the teeth are not, or only slightly separated when this movement occurs, the presence and degree of immediate side shift affects the shape of the occlusal surfaces of the teeth. (Aull) This must be considered, movement in all three planes along with the timing (4th dimension), when selecting an articulator, in recontouring the existing occlusal surfaces and developing the morphology of dental restorations.Wachtel and Curtis also addressed the immediate side shift in both their articles involving the limitations of semiadjustable articulators. The first did not provide for an ISS setting to the articulator, while the second article did so by providing patient lateral interocclusal records.The article noted that most semiadjustable articulators lack adjustments for the ISS, surdetrusion of the superior wall, proretrusion of the posterior wall, and the intercondylar distance. Also there is no provision for motion along curved pathways. What were the significant findings from these two articles? HANAU’S FORMULA – In 1930 Hanau introduced his formula (L = H/8 + 12)Used in the setting of the lateral condylar guidance, for Hanau and some other type of articulators. How accurate is this formula? What did Javid and Porter recommend when precise restorative procedures were indicated?In Taylors article how did he compensate for discrepancies when immediate shift was present? How did the intercondylar distance affect this?

(In Lundeen’s study with the plastic blocks and air turbine drills the average Bennett angle was found to be 7 ½ degrees)

FACEBOW TRANSFER (on the Hanau articulator)To review, the facebow measures the glenomaxillary relationship in three planes, this is anteroposteriorly, laterally and vertically. The anteroposterior and lateral positions are anatomically determined by their relationship to the maxilla and glenoid fossa.It is the vertical relationship, ie. the anterior reference point that is determined by several techniques. Weinberg stated that if the face-bow mounting is oriented 16mm too high on the articulator, a disclusion of 0.2mm will be noted on the balancing occlusal side.What did Lauciello find as the most accurate method to orient the maxillary cast to the articulator?HANAU‘S QUINT coordinates the ten main laws of articulation. It records the influence of one factor, governing the establishment of balanced articulation, one other factor, while the remaining factors remain unchanged. Each fifth of the quint represents a factor and the change is indicated with a heavily drawn arrow.Dr. Thielmann’s formula helps to visualize the interrelationships of the "Quint". Thielmanns Formula:    CG x IG = Balanced Occlusion CH x CC x OP  CONDYLAR GUIDANCEINCISAL GUIDANCECUSP HEIGHTCOMPENSATING CURVEOCCLUSAL PLANEARTICULATOR SELECTION FOR RESTORATIVE DENTISTRY (HOBO/SHILLINGBURG/WHITSETT)Although the semiadjustable articulator has its limitations as noted above, it is very popular because of its stability, durability and ease of manipulation.QUESTIONS TO CONSIDERWhat are the problems with using a small hinge articulator? (shorter radius of movement, steeper are of closure)How does the semiadjustable articulator decrease the errors noted above?Define positive error and negative error (Which is more beneficial for fixed/removable?)What are the sources of error when using a semi-adjustable articulator?

- Abstracts -08-001. Weinberg, LA. An evaluation of basic articulators and their concepts. Part II: Arbitrary, positional, and semiadjustable articulators. J Prosthet Dent 13:645-663,1963.- Only a summary of the semiadjustable is presented in this abstract.- Weinberg discussed the use and a mathematical study of the errors of the HanauUse of the Model H.- Orientation of the Maxillary cast: Anatomic average for the hinge axis. Anterior point of reference can be the orbital pointer or by aligning the incisal edges of the teeth or the wax rim to the notch on the incisal pin.

- Centric relation record: Hanau states the Gysi gothic arch tracing is the most admired method. Interocclusal wax records or other methods are acceptable.- Protrusive record: The condylar inclination of the patient is recorded by a protrusive record.- Balancing condylar motion: Is downward, forward, and mesial. The protrusive is used for the downward component. The medial or Bennett angle is determined by H/8 + 12.- Working condylar motion: The intercondylar rod passes laterally through the working condylar ball. This produces an upward, backward, and lateral motion. The Bennett movement varies only in amount rather than in direction.Mathematical study of the Hanau Model HApproximate error at the second molar cusp heightBalancing Workingtype of error1. Anatomic average hinge axis                 0.2 0.2 anterior-posterior2. Arbitrary anterior point of reference 0.2 0.0 Neg3. Straight condylar path                         0.2 0.2 Pos4. No Fischer angle                                 0.1 0.0 Pos5. No individual working condylar motion 0.0 0.8 Neg     The most significant error is produced by the lack of working condylar motion. Overall, most of the errors tend to cancel each other out rater than add up. The error produced is often negative and tends to produce flatter cusps. The error in the working condylar guidance affects posterior teeth more than anterior teeth. Decreasing the Bennett angle of the opposite balancing condylar guidance produces more rotation and less lateral shift of the working condyle and, therefore, increases posterior working cusp inclines.Overall: The instrument is of practical value and within the accuracy of the records used for complete dentures.08-002. Hobo, S., Shillingburg, H. T. and Whitsett, L. D. Articulator Selection for Restorative Dentistry. J Prosthet Dent 36:35-43, 1976.Discussion: Maximum intercuspation is a static position and would require only a simple hinge articulator. The mandible, however, is not a simple hinge and can rotate about axes in three planes. There are four types of occlusal interferences: centric occlusion interference, working occlusal interference, nonworking occlusal interference, and protrusive occlusal interference. Centric occlusal interference is an occlusal prematurity which causes the mandible to deflect forward and/or laterally and may lead to bruxism. Working occlusal interference occurs during a lateral mandibular movement on the side corresponding to the direction in which is moving. A nonworking occlusal interference occurs on the side opposite to the direction the mandible is moving. This is the most damaging interference and can disrupt normal function. The protrusive occlusal interference can prevent posterior teeth from being disoccluded by the incisors.      Errors in occlusal restorations can be classified into two categories - positive and negative. A positive error on the occlusal surface occurs when the articulator undercompensates for the mandibular movement causing a cusp tip or ridge that is too high. A negative error occurs when the articulator overcompensates for the mandibular movement and grooves are wider or cusp are more narrow. If contacts are maintained in centric relation, negative errors will result in a slightly flatter occlusal surface and can still be acceptable      A facebow transfers the distance between the hinge axis and the tooth being restored from the patient to the articulator. If the hinge axis is not kinematically located (arbitrary), the

interocclusal record must be made at the correct vertical dimension of occlusion. A small hinge articulator has a shorter radius of movement when closing in centric position. A tooth will travel a steeper arc of closure on a small articulator than in the mouth. A slight positive error occurs on the mesial incline of maxillary teeth and the distal incline of mandibular teeth on casts mounted on a small articulator and no increase in VDO. If the intercondylar distance of the articulator is greater than the mandible, the paths of movement will be distal to the ones in the mouth. If the condylar inclination on the articulator is set at a steeper angle than the patient, the restoration will have a positive error on the protrusive or nonworking side. A negative error occurs when the angle is less steep than the patient and will give greater clearance in excursive movements. A negative error is acceptable as long as centric occlusal contacts are maintained.      A nonadjustable articulator with a fixed condylar path is acceptable for single restorations. A shallow 20 fixed condylar inclination is desirable because the error will usually be a negative error. Multiple restorations or FPD’s can be fabricated on a semiadjustable articulator. A facebow transfer will minimize tooth hinge axis errors. The fully adjustable articulator is indicated for extensive treatment of the occlusion, significant side shift movements, and restoring lost vertical dimension of occlusion.  08-002. Hobo, S., Shillingburg, H. T. and Whitsett, L. D. Articulator Selection for Restorative Dentistry. J Prosthet Dent 36:35-43, 1976.This is a review article on selecting an articulator for restorative dentistry. The article looks at various aspects of using the various classes of articulators. The highlights include:Occlusal Interferences: There are four types of occlusal interferences: (1) in centric (2) in working (3) in nonworking and (4) in protrusive. The centric occlusal interference will cause the mandible to be deflected forward or laterally from the optimum mandibular position. A working side interference will occur on the facial aspect of the maxillary lingual cusps and on the lingual aspect of the mandible facial cusps. A nonworking side interference will occur on the lingual aspect of the maxillary facial cusps and the facial aspect of the mandibular lingual cusps. Protrusive occlusal interferences occur on the mesial aspect of mandibular centric holding cusps and on the distal aspect of the maxillary holding cusps.Positive vs. Negative Errors: By definition a positive error is one that occurs on the occlusal surface when the articulator undercompensates for the mandibular movement. What one will see on the restoration is a positive feature on the restoration where that feature should be smaller or nonexistent.     A negative error is when the articulator overcompensates for a mandibular movement. One will see a fossa or groove that is wider than ideal or a ridge or cusp that is narrower than normal.If contacts are maintained in CR, negative errors may be acceptable.Condylar Inclination and Occlusal Morphology: The steeper the condylar inclination the steeper the cuspal inclines and the occlusal morphology can be; the reverse is true with a flatter condylar inclination.Effect of Intercondylar Distance: - When the intercondylar distance on the articulator is greater than that of the mouth, the paths of movement on the articulator are slightly distal to the paths traced in the mouth.- When the intercondylar distance on the articulator is less than that of the mouth, the cusp paths traveled on the articulator will be slightly mesial to the paths traced in the mouth.

Summary: A fully adjustable articulator should be utilized in the following situations: extensive treatment in which opposing quadrants are being restored, for reconstruction of the entire mouth and patients with considerable side shift during lateral movement.08-003a. Neal D. Bellanti, DDS, MA. The significance of articulator capabilities Part I. Adjustable vs. semiadjustable articulators. JPD, Mar 1973.Orbiting condyle - moves medially, anteriorly, and inferiorly.Rotating condyle - moves laterally within the confines of a cone whose apex is at the terminal hinge position and whose axis lies on the terminal hinge axis. The direction of movement of the condyle within this cone is determined by the contours of the glenoid fossa. This movement in turn determines the cusp height, fossa depth, and ridge and groove direction on the occlusal surfaces of the prostheses.     The semiadjustable articulator guides only the lateral component of the rotating condylar movement, whereas the fully adjustable articulator may be set to simulate all components of mandibular movement.Purpose: measure the discrepancies that may exist in articulator capability due to incomplete movement simulation. The effects on cusp positions produced by variations of intercondylar width, the shape of the condylar housing, and the timing and direction of the side shift were ascertained.* Intercondylar Width:   The semiadjustable articulator is capable of three intercondylar width settings, with a 7mm interval between each two (48, 55, and 62mm. measured from the midline).     To determine the efficacy of the 7mm. interval, 48mm. was compared with one half of the interval to the next larger setting, or 51.5mm. Also, the largest possible setting, 62mm., was compared with the maximum patient width of 70mm. reported by Aull.Results - The variance in mesiodistal cusp tip position between the1) 48mm. and the 51.5mm. widths was:     .2mm on the working side      .2mm on the nonworking side   62mm. and the 70mm. widths was:     .2mm. on the working side     .5mm. on the nonworking sideConclusions - The 7mm. interval between the settings is adequate to provide clinical accuracy within a correctable range. However, the 62mm. or large, width is to narrow to accommodate all patients at a correctable discrepancy.The error incorporated at the wide extreme would require more than minimal intraoral adjustment at insertion.* Timing Of The Progressive Side Shift: To study the effect of the timing of the mediotrusion on the mesiodistal cusp position, the flat medial wall of the condylar fossa, the control, was compared with a maximum early side shift insert. Results - effect of the early progressive side shift on the mesiodistal cusp tip position was:      .1mm on the working side     .5mm on the nonworking side Conclusions - The variation is beyond the range of clinical acceptability for the nonworking side.The semiadjustable articulator is incapable of reproducing any variation in the timing of mediotrusion. The variation of the progressive mediotrusion timing would require substantial occlusal adjustment at insertion.Shape Of The Condylar Housing: The effect of the shape of the superior wall of the condylar

housing on the vertical cusp tip position was studied with the use of the flat insert as control and the 3/8 inch radius convex curvature insert as experimental. Results - The variance produced by a curved superior wall wasa .1mm. longer cusp on the working side anda .2mm. shorter cusp on the nonworking side. Conclusions - The effects of the superior wall shape are within a clinically correctable range.* Direction Of The Side Shift:  The effects of the directional components of the side shift on both vertical and mesiodistal cusp positions were studied with only the working side adjusted and again with both condylar housings adjusted. Control was simple laterotrusionResults - variations produced by altering the direction of the side shift are varied from 0 - .6mm change, with ranges of 1.2mm. mesiodistally and .5mm vertically.Conclusions - the variance of the total possible combinations at the settings measured is greater than could be controlled clinically.     The semiadjustable articulator is capable of only a simple laterotrusion.      In those patients with a backward or upward component in laterotrusion, the eccentric error would represent the variance proportional to the amount of backward or upward movement in the laterotrusion.     In those patients with a forward or downward component in laterotrusion, the error would represent the variance shown, proportional to the amount of forward or downward movement in laterotrusion.Occlusal adjustments cannot be considered minimal. * Immediate Side Shift:Results - Figures show changes ranging from 0 - 2.4mm, with ranges of 4.4mm mesiodistally and 1.7mm. vertically.Conclusions - The variance of the total possible combinations at the settings measured is greater than could be controlled clinically. Summary: An articulator with a wide range of intercondylar width adjustment and with adjustable posterior, medial, and superior fossa walls is needed to reproduce the effects of mandibular side shift with reasonable accuracy.08-003a. Neal D. Bellanti, DDS, MA. The significance of articulator capabilities Part I. Adjustable vs. semiadjustable articulators. J Prosthet Dent Mar 1973.Purpose: To compare the capabilities of adjustable and semiadjustable articulators.Subject: Comparisons were made between a Whip-mix semiadjustable and a Denar D4A fully adjustable articulators Methods and materials: Dental casts were articulated on the fully adjustable Denar, all posterior teeth were removed, styli were placed in the position of the mesiolingual cusp tip of the maxillary first molars, and recording tables parallel to the occlusal plane at the level of the central pit of the mandibular first molars. The adjustments of the semiadjustable articulator were simulated on the fully adjustable articulator by making only the adjustments available on the semiadjustable articulator. Examined were the intercondylar width, timing of the progressive side shift, shape of the condylar housing, direction of the side shift, and immediate side shift. Results/Conclusions: Intercondylar width: The semiadjustable articulator is capable of three settings: 48, 55, and 62mm measured from the midline. (A maximum patient width of 70mm was reported by Aull). For widths between 48 and 62mm, discrepancies of .2mm were measured on the working and non working side, which was considered a correctable discrepancy. However at the maximum of 70mm, a .5mm discrepancy was measured on the nonworking side, considered

to be in excess of a correctable discrepancy. Timing of the progressive side shift: an early progressive side shift produced an error of .5mm on the nonworking side, considered to be beyond the range of acceptability.Shape of the condylar housing: A curved superior wall produced a .1mm longer working cusp and a .2mm shorter nonworking cusp, considered clinically acceptable.Direction of the side shift: Variations produced by altering the direction of side shift varied from 0 to .6mm, with a range of 1.2mm mesiodistally and .5mm vertically. This variance was considered to be greater than could be controlled clinically.Immediate side shift: Changes ranged from 0 to 2.4mm, with ranges of 4.4mm mesiodistally and 1.7mm vertically. (Note that these measurements were recorded with a setting of 2mm side shift added.) Conclusion: The error produced by the use of a semiadjustable articulator may result in a need for more than minimal eccentric occlusal adjustment or uncontrolled amounts of disocclusion of fixed prostheses. An articulator with a wide range of intercondylar width adjustment and with adjustable posterior medial and superior fossa walls is needed to reproduce the effects of mandibular side shift with reasonable accuracy. 08-003b. Neal D. Bellanti, DDS, MA. The significance of articulator capability. Part II: The prevalence of immediate side shift. Sep 1979, Vol 42, Num 3, pp255-256.Purpose: To determine the prevalence and extent of immediate side shift of the mandible in a sample population.Results: 24 of 80 (30%), demonstrated an immediate side shift with a mean length of .3mm. Six subjects presented immediate side shifts bilaterally and eighteen subjects unilaterally.The presence of immediate side shift of the mandible increases the potential for working and nonworking side tooth contacts. Although the mean length of the immediate side shift was found to be .3mm, only 13% demonstrated an immediate side shift greater than .2mm. With such a low prevalence, it is possible that intraoral adjustment could eliminate the undesirable occlusal contacts more easily than use of a more complex articulator system. Observing for the presence of these interferences immediately adjacent to the centric relation contacts is especially important.Conclusion: the prevalence and degree of immediate side shift do not indicate that a fully adjustable articulator is required for all patients.08-003b. Neal D. Bellanti, DDS, MA. The significance of articulator capability. Part II: The prevalence of immediate side shift. Sep 1979, Vol 42, Num 3, pp255-256.Purpose: In Part I, 1973, it was asserted that a semi adjustable.articulator may produce a significant error when used to fabricate fixed prostheses for a patient with immediate side shift. This article addresses the prevalence of immediate side shift in a sample population.Subject: Eighty subjects evenly divided into four groups: men 15-30, men over 30, women 15-30, women over 30 Methods and materials: Acrylic resin clutches fabricated, hinge axis located, a pantographic tracing made and verified by repetition for each patient. Results: 24 of 80 (30%) demonstrated an immediate side shift with a mean length of 0.3mm. Six subjects presented immediate side shift bilaterally and eighteen subjects unilaterally. Conclusion: The prevalence and degree of immediate side shift do not indicate that a fully adjustable articulator is required for all patients. The decision to use or not use a fully adjustable articulator must remain an individual one, based on a careful analysis of the patient's movements.

08-004. Hanau RL. Articulation Defined, Analyzed and Formulated. JADA 13:1694-1709, 1926.Purpose: To discuss Hanau’s theoretical basis for the laws that govern balanced articulation in the fabrication of satisfactory dentures, and the concept of Hanau’s Quint. Discussion: Articulation is the change from one occlusion to another occlusion while the masticatory surfaces maintain contact. The maintenance of balanced contact of the masticatory surfaces is designated as balanced articulation.      Hanau further defines variations on the original definition of articulation to explain the many combinations of interarch relationships and denture designs, namely:Natural- is physiologicUnnatural- is not conforming to accepted physiologic requirementsAnatomic- infers the articulation of natural dentures in the mouthProsthetic- infers the articulation of prosthetic dentures in the mouth individual occlusions being associated with analogous jaw relationsSemiprosthetic- is not always associated with like jaw relationsOrdinary- is always balanced within admitted resilient limitsMalarticulation- lacks balanceMixed- balanced only during part of masticatory strokeUnbalanced- balanced is interrupted or lackingStrained- function while pressure is appliedUnstrained- function while pressure is not appliedBalanced anatomic- natural dentures in changing balanced occlusion associated to analogous jaw relations to other corresponding associationsBalanced prosthetic- prosthetic dentures in changing balanced occlusion associated to analogous jaw relations to other corresponding associations

Balanced Semiprosthetic- prosthetic dentures in changing balanced occlusion not always associated with analogous jaw relation to other corresponding associations, while the

masticatory surfaces maintain contact.HANAU’S QUINTEach fifth represents one of the five factors governing articulation. They are:Condylar Guidance- anteroposterior guidance – horizontal inclination – forward and downward excursion along protrusive guidance. - lateral guidance – sagittal inclination – forward, downward and inward excursion on the balancing side- lateral aberration – the lateral excursion on the working sideCompensating Curve- Tooth alignment is characterized as a horizontal, vertical, and frontal projection.Incisal Guidance     The mandibular incisors (including cuspids) may be considered as one large cusp having a curved ridge, and the maxillary incisors (including cuspids) considered as a large sulcus. Simplified, it is an ordinary cusp guidance with its protrusive and bilateral guiding surfaces.Relative Cusp Height

Includes the cusp guidance inclines for protrusive, lateral and balancing sides. The cusp height is only relative if it is compared with its "basal radius" which is the projection on the cusp base of the movement of a point directed along the incline from the base to the cusp summit.Position of Triangle of Orientation (Denture Position)The triangle of orientation is a plane through the central incisal contact point and the occlusal terminations of the second molar buccal grooves. These three points are the corners of the triangle of orientation, through there may be a plane of orientation.THE LAWS OF BALANCED ARTICULATIONArticulation is a purely mechanical function and must be explained by geometry, cinematics and mechanics. The Quint gives a combination of the most essential laws of articulation in convenient form. Each fifth represents a factor undergoing a change. The changes indicated are accompanied by heavy arrows. The light arrows in each fifth refer to the other factors. The direction of the light arrows indicates the sense in which to read the influence of a respective factor on the factor they identify.08-005. Weinberg, L. A. Arcon Principle in the Mechanism of Adjustable Articulation. J Prosthet Dent 13:263-268,1963.Purpose: To evaluate the condylar articulator with the Arcon articulator. An Arcon articulator has the condylar fixed to the upper member and the ball attached to the lower member. The condylar articulator (non-Arcon) has the condylar slot that keeps changing angulation to the upper member. The Arcon articulator has the condylar slot in a constant angulation to the maxillary dental arch.Methods and Materials: The protrusive and lateral records were placed on both types of instruments and readings were calculated mathematically. The non-Arcon (condylar type) articulator has a constant angulation of the condylar slot to the lower member. In protrusive movements, the angulation changes between the upper member and the condylar slot of the articulator. In the Arcon articulator, the upper member remains constant in relation to the condylar slot. In a protrusive movement, the angulation of the condylar slot changes to the lower member. Results: In protrusive position, both instruments measured the same. The balancing condylar positions were identical on both articulators. Bennett angle readings were different on the two instruments due to the mechanical method of producing the motion. The position of the balancing condyle and motion were identical on each instrument. Conclusion: Both the Arcon and non-Arcon articulators produce the same motion because condylar guidance is the result of the interaction of a condylar ball on an inclined plane. Reversing the relationship does not change the guidance produced. Only the numbers used to record the inclination are changed. Mathematical evidence proves that neither instrument has any specific advantage over the other. 08-005. Weinberg, L. A. Arcon Principle in the Mechanism of Adjustable Articulation. J Prosthet Dent 13:263-268,1963.Purpose: To evaluate the condylar articulator with the Arcon articulator. An Arcon articulator has the condylar fixed to the upper member and the ball attached to the lower member. The condylar articulator (non-Arcon) has the condylar slot that keeps changing angulation to the upper member. The Arcon articulator has the condylar slot in a constant angulation to the maxillary dental arch.Methods & Materials : The protrusive and lateral records were placed on both types of

instruments and readings were calculated mathematically. The non-Arcon (condylar type) articulator has a constant angulation of the condylar slot to the lower member. In protrusive movements, the angulation changes between the upper member and the condylar slot of the articulator. In the Arcon articulator, the upper member remains constant in relation to the condylar slot. In a protrusive movement, the angulation of the condylar slot changes to the lower member. Results : In protrusive position, both instruments measured the same. The balancing condylar positions were identical on both articulators. Bennett angle readings were different on the two instruments due to the mechanical method of producing the motion. The position of the balancing condyle and motion were identical on each instrument. Conclusion: Both the Arcon and non-Arcon articulators produce the same motion because condylar guidance is the result of the interaction of a condylar ball on an inclined plane. Reversing the relationship does not change the guidance produced. Only the numbers used to record the inclination are changed. Mathematical evidence proves that neither instrument has any specific advantage over the other. 08-006. Wagner,AG, and Rennels, KE. The effect of the articulator settings on the cusp inclines as measured by a coordinate measuring machine. J Prosthodon 2: 19-23,1993. Purpose: To learn the effect of various articulator settings on cusp inclines during working, nonworking and protrusive movements.Materials and Methods: a reference point of the maxillary first molar (mesiolingual cusp) was fixed to the upper member of the 96H2 Hanau articulator. A coordinate measuring machine (CMM) recorded the position of the reference point in centric relation, working, nonworking and protrusive. Articulator setting were changed (ie the condylar angles and anterior guide angles) for a total of 432 different cusp angles were measured at the first molar by the coordinate measuring machine.Results: The data collected was used to produce formulas, three formulas were produced, the working angle, nonworking angle and protrusive angle.     These formulas were used to calculate the working, nonworking and protrusive cusp angles produced as a result of 72 different articulator settings.Discussion&Conclusion: The Numerex coordinate measuring machine is useful in taking measurement of articulator movements. Further research is needed to determine the cusp angles of manufactured teeth, as then coordination could be made with the cusp angles of the teeth and the cusp inclines found from the articulator. In the future comparisons can also be made between articulators (ie arcon vs non-arcon) 08-007. Javid, N.S. and Porter, M.R. The importance of the Hanau formula in construction of complete dentures. J Prosthet Dent 34:397-404,1975.Purpose: To determine the accuracy of the Hanau formula for use in the construction of complete dentures.Materials and Methods: Six articulators (two Denar D4-A, two Whipmix and two Hanau model 130-28) were used. Maxillary and mandibular alginate impressions were made and duplicated for five patients. The Denar hinge axis facebow kit was used to transfer the upper cast of all patients to the articulators. The mandibular casts were articulated in maximum intercuspation. Protrusive and lateral interocclusal records were made for each patient. The horizontal and lateral condylar inclinations were adjusted on all articulators using the protrusive and lateral records. The adjustments were repeated twenty times for each articulator. The actual recording were compared to the values obtained by using Hanau’s formula.

Discussion: In studying the five patients, the difference of the means of the protrusive condylar guidance inclinations between the two Hanau articulators was 3 degrees on the right side (30.4 – 27.4 = 3) and 2.8 degrees on the left side (30.6 – 33.4 = 2.8). The range of means of the 20 readings of the protrusive condylar guidance of the Hanau articulator No. 1 for five patients was from 18 to 42 degrees on the right side and 22 to 42 degrees on the left side. This range for the Hanau articulator No. 2 was 22 to 36 degrees on the right side and 20 to 39 degrees on the left side. The range of the means in the five patients with the protrusive condylar guidance of the same articulators adjusted by lateral interocclusal records varied (1) from 22 to 32 degrees on the right side and from 26 to 41 degrees on the left side with the Hanau articulator No. 1 and (2) from 22 to 36 degrees on the right side and 20 to 39 degrees on the left side with the Hanau articulator No. 2. Significant differences in the means of condylar guidance readings existed in the Hanau articulators, when adjusted with the use of the records and the Hanau formula, in the readings of the right and left sides of the Hanau articulator No. 1 and in the left side of the Hanau articulator No. 2. Further study of the lateral condylar guidance of the same patients in the other articulators clearly indicated that the range of the lateral condylar guidance in different articulators varied from 0 to 50 degrees and the means of the five patients varied from 1 to 34 degrees. The range of means of lateral condylar guidances of the Hanau articulators adjusted by using the Hanau formula was only from 14 to 17 degrees. This small possibility of variation in the lateral condylar guidances will affect the balanced occlusion of the complete dentures when the are placed in the patient’s mouth, assuming a wider variation existed in the mouth. Conclusion: The range of means of lateral condylar guidances of Hanau articulators using the Hanau formula was small. This small possibility of variation in the lateral condylar guidance would suggest the use of lateral interocclusal records when precise restorative procedures are necessary08-008. Laucello, F.R. Anatomic comparison to arbitrary reference notch on Hanau articulators. J Prosthet Dent 40:676-681, 1978.Purpose: to determine the average orbitale-maxillary incisal edge distance and to compare this measurement to the incisal reference notch of the Hanau articulators.     The facebow registers the glenomaxillary relationship in three planes(anteroposteriorly, laterally, and vertically). The anteropostererior and lateral positions are determined by the anatomic relationship between the maxilla and the glenoid fossa. The vertical position , i.e., the anterior reference point, has been determined various techniques.     One recommended method of locating vertical position when using Hanau articulators is to elevate the maxillary cast while the facebow is still attached to the articulator until the maxillary incisal edges are aligned to the level of a groove on the incisal guide pin. This groove is 30 mm below the horizontal condylar plane ( a plane described by the center of the condylar spheres and the infraorbital indicator) and is called the "incisal reference notch". Unfortunately the location of this groove bears no relation to the anatomic anterior reference point (orbital). In other words, the 30 mm measurement is not calibrated to approximate the average distance between the orbital and the maxillary incisal edges. Literature review:Snow - recommended that the occlusal plane be parallel to Campers plane(ala-tragus line) and oriented to the articulator so that it is parallel to the maxillary and mandibular bows of the articulator.Gysi and Kohler - referred to "the prosthetic plane".     Recent investigators noted that the Frankfort horizontal plane(porion to orbital) is usually

parallel to the floor. It would seem logical to orient the maxillary cast to this plane so that the articulator would more accurately represent the patient. Clinically a maxillary cast is oriented to the Frankfort horizontal plane by using an infraorbital pointer that is attached to the facebow. The end of the pointer is placed at the lowest margin of the orbital rim. When transferred to the articulator, the end of the pointer is placed level with the condylar plane by utilizing the infraorbital indicator, thus orienting the maxillary cast to the (condylar) axis-orbital plane, which closely parallels the Frankfort horizontal plane. Thus the plane of occlusion, when viewed on the articulator, will be similar to that of the patient in an upright position.Gonzalez and Kingery disputed this concept. They determined cephalometrically that the Frankfort horizontal plane was not parallel to the axis-orbital plane. The condylar axis was 7.1 mm below the cephalometrically determined porion. They suggested compensating for this error by adjusting the orbital pointer 7 mm above the orbital indicator or by placing the orbital pointer 7 mm below the orbitale of the patient during the facebow transfer. This has been compensated for in part by selecting the infraorbital foramen instead of the orbitale as the anterior reference point.     An alternative to the use of the infraorbital pointer is the incisal reference notch on the Hanau incisal guide pin.     The Hanau XP-51 has an incisal pin reference notch which measures 51 mm from the condylar plane. It was thought that this arbitrary measurement might better approximate the average orbitale-maxillary incisal edge distance.Methods & Materials:- 60 patients of different sex, race, and age with complete natural dentition- Orbitale located by the point on the lower margin of the orbit which is directly below the pupil.- A bar was positioned intraorally, recording the incisal edges of the teeth in compound.- A Boley gauge was placed flush with the inferior surface of the bar, while the other arm was positioned level to the orbitale.Results: The average orbitale-maxillary incisal edge distance determined from the representative population use in the study was 53.99 mm.Discussion: According to Weinberg, if the facebow mounting is oriented 16 mm too high on the articulator, a disclusion of .2 mm will be noted on the balancing occlusal side. Manly states that complete denture patients can distinguish thicknesses down to.18 mm. Brill states complete denture patients can perceive objects at .6 mm.Results: Results show a significant difference between the average orbitale-maxillary incisal edge distance and the 30 mm incisal reference notch measurement on the Hanau incisal guide pin. The average difference was 24 mm.     Gonzalez and Kingery noted that the porion was 7.1 mm above the condylar axis point. Taking this information into consideration, the average determination of 54 mm was adjusted to 47 mm, thus more accurately paralleling the axis-orbital and Frankfort horizontal planes. Therefore if an incisal reference notch is to be used as a third point of orientation for the facebow, it should be calibrated 47 mm from the condylar plane. Therefore, it is suggested that using the orbital pointer when making the facebow transfer and adjusting the pointer 7 mm above the condylar plane of the articulator is the most accurate method of anatomically orienting the maxillary cast.Conclusion:1. The average orbitale-maxillary incisal edge distance for the representative population used in this study was found to be significantly greater than the 30 mm incisal reference notch on the

incisal guide pins of the Hanau articulators.     According to the present anatomic data, the incisal reference notch on Hanau articulators should be calibrated 47 mm below the condylar plane. 2. Due to the wide range of measurements recorded for the orbitale-maxillary incisal edge distance, it is suggested that the use of the orbital pointer when making the facebow transfer and adjusting the pointer 7 mm above the condylar plane of the articulator is the most accurate method of anatomically orienting the maxillary cast to the articulator.08-009. Taylor T D et al. Analysis of the lateral condylar adjustments of nonarcon semiadjustable articulators. J Prosthet Dent 54:140-143,1985.Purpose: A method to set the lateral condylar adjustment of the non arcon semiadjustable articulator to simulate border movements of the mandible more closely.Materials and methods: A Denar D5A fully adjustable articular was used as the simulated patient. Pantographic tracings were done using only the anterior horizontal tables and transferred to the semiadjustable articulator.Results: The semiadjustable articulator was able to duplicate the simulated patient tracings with a high degree of accuracy for the patient simulations without immediate side shift. It is suggested the semiadjustable articulator may be adjusted to simulate border movements more accurately by reducing the lateral condylar adjustment below the suggested range of 15-10 degrees. A single gothic arch tracing may be used to set the lateral adjustment or the articulator settings can be predicted by obtaining an intercondylar distance measurement with an arbitrary facebow. If ICD>=to 110 then lateral condylar adjustment should be set to 0 degrees. If<100 set to a slightly higher amount (8 degrees for ICD 100). If a more lateral cusp path is desired then set to 20-30 degrees.Conclusions: Immediate side shift cannot be simulated by a slot rack semiadjustable articulator. Significant errors in cusp position and groove orientation may result. The results indicate that the Hanau formula or an arbitrary setting of 150-10 degrees does not provide the most accurate articulator setting possible.08-010. Wachtel, HC and Curtis DA. Limitations of semiadjustable articulators. Part I: Straight line articulators without setting for immediate side shift. J Prosthet Dent 58:438-442,1987.Purpose: To measure the amount and direction of error at the first molar when using a semiadjustable articulator.Materials and methods: A Denar D5A articulator was used as a model for this study and programmed to simulate mandibular movements with the reported average values. Lateral and protrusive plaster records were made on the D5A and transferred to both the Hanau H2 and TMJ instruments and adjusted. A tracing was made on the D5A model articulator. The same tracing plate was transferred to one of the test articulators and a second line was scribed in the same plane. Tracings were completed in this manner for each of the tested articulators in each plane. The starting reference point of the tracings was the mesiolingual cusp tip of the upper first molar. Duplicate recordings were made with two different immediate side shift settings. The separation of lines in the recordings was measured 1 mm and 3 mm from the reference point in nonworking, working and protrusive movements.Results: The Hanau H2 and TMJ articulators demonstrated positive error in the frontal plane. A comparison of tracings demonstrated that errors increased significantly when immediate side shift was increased. Errors were greater in the horizontal than in the frontal plane. Negative error was recorded in the sagittal plane.

Conclusion: The semiadjustable articulators adjusted with interocclusal records but without rear wall, top wall, and intercondylar distance settings demonstrated limitations in all three planes of measurement.      To minimize the errors of straight line articulators in the horizontal plane, additional clearance should be made distal to the occlusal groove on mandibular teeth. For patients with less than 0.75mm of immediate side shift, chairside correction of the errors in the horizontal plane is possible. Errors in the sagittal plane were negative and small. The results demonstrated the need for incorporating immediate side shift into articular movements. 08-010. Wachtel, H C and Curtis, D A. Limitations of semiadjustable articulators Part I: Straight line articulators without setting for immediate side shift. J Prosthet Dent 58:438-442,1987.Purpose: Controversy exists concerning the complexity of the articulator to accurately simulate mandibular movements. This study measured the amount and direction of error at the first molar when using a semiadjustable articulator.Methods: A Denar D-5A was used. A 37 degree condylar inclination, an immediate side shift of 0.75mm, progressive side shift of 7.5 degrees condylar insert was used and intercondylar distance of 110 mm was used. Lateral and protrusive interocclusal records were used on the semiadjustable articulator. Casts were mounted on TMJ and Hanau H for comparison.Results: Frontal plane:  Errors increased significantly when ISS was increased from 0.75 mm to2mm. The greatest errors were in nonworking direction where 1 mm of error was recorded 3mm from the reference positionHorizontal plane: Errors were greater in horizontal than frontal plane, again highest in the nonworking direction where 2,2 mm of error was recorded 3mm from the reference position. Sagittal plane: Negative error in the sagittal plane was noted for the Hanau H-2 and TMJ articulators. Negative error measured 1mm from the reference position was 0.20 mm with Hanau and 0.30 mm with TMJ articulator.Conclusion: the average arbitrarily adjusted settings of a straight-line articulator should have a condylar inclination of 45 degrees and a progressive side shift of more than 30 degrees.- errors in the sagittal plane were negative and small- in the frontal and horizontal planes errors increased significantly when ISS was elevated from 0.75 mm to 2 mm.- the results demonstrated the need for incorporating ISS into articulator movements.08-011. Curtis, D A and Wachtel H C. Limitations of semiadjustable articulators with provision for immediate side shift. Part II. JPD 58:569-573, 1987.Purpose: This study determined the error when a semiadjustable articulator with a provision for setting ISS was used.Methods: Same as previous study with Denar D5 A and TMJ articulators.Conclusions:- adding ISS settings to a semiadjustable articulator significantly improved accuracy in the horizontal plane compared with fully adjustable articulator model- errors in the frontal plane emphasize the importance of the top wall setting.- when ISS is less than 0.75 mm both TMJ and Mark II articulators provide a satisfactory mechanical equivalent to mandibular movement.xsu po

08-011. Curtis, DA and Wachtel, HC  Limitations of semiadjustable articulators with provision for immediate side shift.  J Prosthet Dent 58: 569-573, 1987.Purpose: To determine the error when a semiadjustable articulator straight-line articulator with a provision for setting ISS (Immediate Side Shift) is used.Materials&Methods: A Denar D-5A articulator programmed with average values was used to simulate mandibular movements. Values were condylar inclination 37 degrees, ISS 0.75 mm, progressive side shift 7.5 degrees, condylar insert ¾ inch, and intercondylar distance 110 mm. The Mark II and TMJ articulators were used as a comparison, with the intercondylar distance set at 110 mm and flat guiding surfaces to represent condylar inclination. Duplicate maxillary and mandibular typodont casts were prepared, and the maxillary cast was secured to the articulators with an average face-bow setting. Lateral and protrusive interocclusal records were made in an edge to edge relationship on the Denar-5A and transferred to the other articulators. Acrylic resin plates (transferable) were fabricated for tracings made in the frontal, horizontal and sagittal planes at the first molar. Two tracings were made in each plane, first on the Denar D-5A, then the tracing was transferred to the articulator tested, and another line was scribed in the same plane. Recordings were made with an ISS of 0.75 mm and also at 2 mm, measurements were taken at 1 mm and 3 mm from the reference points.Results: In the frontal plane, both the Mark II and TMJ articulators showed a positive error (ie the articulator undercompensates resulting in positive adjustment when the restoration is transferred to the patient.) Errors increased appreciably when the sideshift was increased to 2 mm. In the horizontal and sagittal planes, both articulators showed minute error when compared with the model articulator. Discussion: This research supports work done by Gibbs, in that a patient with average Bennett movement (<.75 mm) and an acceptable anterior guidance, can have restorations made on semi-adjustable articulators with minimal eccentric interferences.     The addition of ISS provided greater accuracy in the horizontal plane on semiadjustable articulators, in the frontal plane, the error was due to the top wall (ie surtrusion-detrusion of the working condyle is not represented.)Conclusions: When ISS settings are added to the semiadjustable articulator improved accuracy in the horizontal plane, errors in the frontal plane were due to the top wall setting not being represented. When ISS is less than 0.75 mm both TMJ and Mark II articulators are satisfactory for mandibular movement, but when the ISS is 2 mm or more these articulators are unreliable for movement in the frontal plane at the first molar. 08-012. Beck, H.O., and Morrison, W.E. Investigation of an Arcon Articulator. J Prosthet Dent 6:359-372,1956.Purpose: To investigate the arcon articulator introduced by Bergstrom. Discussion: The new features introduced which vary from most condylar articulators are: 1. A face-bow registration which employs the Frankfort horizontal. 2. The axis equivalent guide, which is adjustable from 0 to 90 degrees, is fixed to the upper member of the arcon instrument and has a convex curvature of 0.022mm. The Bennett angle is fixed at 15 degrees.      The articulator is constructed so cases may be transferred from one articulator to another. The upper member is freed by locks so as not to distort the interocclusal record during setting the articulator. The centric position can be altered in a retrusive manner.      The facebow registration uses Frankfort horizontal which is an orientation of the external auditory meatus to the left orbitale on the patient. Some limitations may be the location of orbitale on the patient and the fact that the external auditory meatus in relation to the condyles

may vary greatly not only between patients, but in the same patient from right side to left.     Since the axis guide is fixed to the upper member the occlusal plane will maintain its relationship to the adjusted arcon indication in any position of the upper bow of the instrument. This relationship does not exist in the condylar articulator. This fact, according to the authors, results in an articulator that may better reproduce mandibular movement. One important fact to remember is the intercondylar distance must be accurate to gain the benefit of the arcon design, especially in lateral motion.

Section 08: Articulators III – Fully Adjustable(Handout)

Definitions: -articulator n: a mechanical instrument that represents the temporomandibular joints and jaws, to which maxillary and mandibular casts may be attached to simulate some or all mandibular movements-usage articulators are divisible into four classes Class I articulator: a simple holding instrument capable of accepting a single static registration. Vertical motion is possible - see NONADJUSTABLE A. Class II articulator: an instrument that permits horizontal as well as vertical motion but does not orient the motion to the temporomandibular joints. Class III articulator: an instrument that simulates condylar pathways by using averages or mechanical equivalents for all or part of the motion. These instruments allow for orientation of the casts relative to the joints and may be arcon or nonarcon instruments- see SEMI-ADJUSTABLE A. Class IV articulator: an instrument that will accept three dimensional dynamic registrations. These instruments allow for orientation of the casts to the temporomandibular joints and simulation of mandibular movements--see FULLY ADJUSTABLE A., FULLY ADJUSTABLE GNATHOLOGIC A.-fully adjustable articulator: an articulator that allows replication of three dimensional movement of recorded mandibular motion- called also Class IV articulator.-fully adjustable gnathologic articulator: an articulator that allows replication of three dimensional movement plus timing of recorded mandibular motion- called also Class IV articulator.Developmental History (of the fully adjustable articulator)What group was devoted to the study of the physiologic movement of the jaw and was instrumental in the development of the fully adjustable articulator? Gnathological Society of California (Contino, p68) Led by researchers such as McCollum, Stuart, and Stallard the gnathologists studied mandibular movement in three dimensions, and developed what we know as the pantograph. Great efforts were then directed to develop a sophisticated three-dimensional adjustable articulator that would accept and reproduce the measurements recorded by the pantograph.The Denar system was developed by Guichet. What was one of his purposes in developing this system? Guichet's efforts aimed to simplify the pantograph and bring gnathology into every dental office. Guichet also advocated overcompensation of the gnathologic instrument settings to provide increased disclusion. The development of the TMJ articulator, as discussed by Wipf, used a stereographic method of recording mandibular movement. This was actually a modification of an engraving method introduced to dentistry by Warnekros in 1892 and later taught by House and Needles. What two

elements of the system allow vertical dimension to be maintained during the recording procedures?A central bearing screw in the mandibular clutch and a central bearing plate in the maxillary clutch. (Wipf p 271) (for more information, see Becker and Kaiser, Evolution of Occlusion and Occlusal Instruments JPROSTH 1993; 2:33-43, included in Articulators I seminar)Characteristics of the fully adjustable articulator (see Weinberg)What are three essential requirements of a gnathologic system? To maintain the same relationship of the pantographs to the styli as the transfer is made from the patient to the instrument. 2. The instrument must be three-dimensionally able to accept the records. 3. The final casts must be articulated in exactly the same relationship to the motion recorded as it occurred in the patient. (Weinberg p1042) What features should we expect to find on the fully adjustable articulator? Adjustable intercondylar distance, horizontal and vertical condylar adjustments, either a curved or straight horizontal condylar guide, Bennett guide adjustment, and provision for Fischer's angle (Beck p630)Pantograph/Stereograph Utilized for the conveyance of information from the patient to the articulator.Definitions pantograph: an instrument used to graphically record in one or more planes, paths of mandibular movement and to provided information for the programming of an articulatorpantographic tracing: a graphic record of mandibular movement in three planes as registered by the styli on the recording tables of a pantograph; tracings of mandibular movement recorded on plates in the horizontal and sagittal planes.stereograph: n. an instrument that records mandibular movement in three planes. Engraving, milling, or burnishing the recording medium by means of styli, teeth, abrasive rims, or rotary instruments obtains the record. stereographic record an intraoral or extraoral recording of mandibular movement as viewed n three planes in which the registrations are obtained by engraving, milling, or burnishing the recording medium by means of studs, rotary instruments, styli, teeth, or abrasive rims.Is it always necessary to locate the kinematic hinge axis?Precise location of the hinge axis offers no advantage when centric relation is recorded at the vertical dimension of the restoration. If the treatment requires centric relation be recorded at other than the vertical dimension of the restoration, a kinematic hinge axis should be located. (Guichet p248-9, Weinberg p1044)What should be used for an anterior point of orientation (third point of reference)?The anterior point of orientation can be completely arbitrary in a three dimensional system of recording, but must be accurately and consistently used for orientation. (Weinberg p1044-45) Shields and Clayton investigated a possible relationship between TMJ and muscle dysfunction and the ability to reproduce pantographic border tracings, (which was quantified by means of a pantographic reproducibility index- PRI) What was their conclusion? The PRI can be an aid to the detection of TMJ dysfunction and muscular incoordination, and can be used to assess the severity of dysfunction.

Types of fully adjustable articulators Stuart (Stuart) Describe the relationship between the styli and recording tables for the pantograph used with the Stuart articulator. The recording styli are attached to the mandibular frame element, while the recording tables are attached to the maxillary element. Thus the recording styli move with the mandibular element, while the recording tables remain stationary.Denar (Guichet) Describe the relationship between the styli and recording tables for the pantograph used with the Denar articulator. The recording styli are attached to the maxillary frame element, while the recording tables are attached to the mandibular element (the reverse relationship compared to the Stuart) Thus the recording tables move while the styli remain stationary. TMJ (Wipf, Swanson) Four styli on maxillary clutch inscribe four "diamond shaped" tracings on acrylic added to mandibular clutch.Swanson describes a technique for fabrication of a complete denture on a TMJ articulator. What is used instead of clutches in the edentulous patient? The actual final maxillary and mandibular impressions. The TMJ clutch forming bite fork is used to make the recording platform on the tray of the mandibular impression, and the central bearing screw is attached. The four studs are placed in preplanned canine and molar areas on the maxillary impression tray, along with the central bearing plate. (p499-500) What are the advantages of using the TMJ articulator for complete dentures? What are the disadvantages?Selection of an articulator or Why use the fully adjustable instrument?Accuracy (Stuart, Weinberg)According to Stuart, what should be the goal of the fully adjustable articulator?It should be able to "reproduce" without compromise, the border and habitual physiologic movements of the patient. (Stuart p221) Which aspects of the movements of the rotating (working) condyle does Stuart indicate should be addressed?How far the condyle travels in its lateral movement, any upward, downward, forward or backward component, and the timing of the movement (Mandibular lateral translation) (Stuart p222-223)What did McCollum think about the importance of properly recording mandibular lateral translation (Bennett movement)?He felt that it had as much or probably more influence upon the articulating surfaces of the teeth than any other component of jaw movement (Weinberg p. 1038) What did Weinberg think? He indicates that a mathematical investigation supports this view. (Weinberg p. 1038).Reproducibility (Winstanley, Solberg)What did Winstanley's experiments conclude regarding the reproducibility of the adjustments of the Denar articulator? He found that most of the articulator adjustments were reproducible with a reasonable degree of accuracy. (p. 671) Which adjustments did he find were of questionable value? The rear wall and top wall adjustments (p671) Why? The tracings were short and large variations in the settings cause only small deviations of the styli, (p 666)

What effect did familiarity/experience with the technique have on reproducibility? Familiarity increased the accuracy in reproducing the settings. (p.671) What did Solberg and Clark find regarding the reproducibility of molded condylar controls using a stereographic recording system? They found that the error in the technique appeared to be within acceptable limits. (p. 527) What was the net effect of the error they observed? The error produced a slightly smaller horizontal condylar inclination than actually existed in the"patient" (p. 527)What effect did familiarity/experience with the technique have on reproducibility? The inexperienced dentist was capable of making acceptable registrations, but had some difficulty in registering maximum Bennett movement. (p. 527) Did they fabricate the condylar controls with a single mix of acrylic? No, they discarded the single mix technique in favor of the optional reline technique. (p. 526) Reliability (Beck)Beck examined whether an articulator (the Denar D5A and the Hanau 130-21) set to a subject's records either positional records (for the Hanau) or a pantographic tracing (for the Denar) accurately reproduced that subject's mandibular motion. A computerized jaw-motion sensing apparatus was used. What type of clutches were used? Ticonium. What did he conclude? Both the Denar D5A and the Hanau 130-21 adequately reproduced jaw motion for the 5 subjects tested.Variability (Coye)Coye studied the variability (between 7 different dentists) involved in setting a fully adjustable articulator to a pantographic tracing of known parameters. What did he use for a "patient"? A pantographic tracing was made from a fully adjustable articulator arbitrarily set to randomly chosen values (p 460-61) What were his findings? His analysis showed that there was a statistically significant difference in both the magnitude and variability of the error encountered, but the magnitude of that error was very small .(p464) What was the effect of these errors on the occlusal surfaces of the teeth? The error was found to be barely perceptible . (p.464) Potential sources of error (Javid, Manary) Javid used static protrusive and lateral interocclusal records to set the condylar guidance angles using two each of Denar D4A, Whip mix, and Hanau 130-28 articulators. What were his conclusions? A comparison of the mean difference of the means of the left and right protrusive condylar guidance readings showed no significant difference between the two Denar articulators, however, there was a significant difference in the Hanau and Whip mix articulators, on the left side only. He concludes the condylar guidances of the Denar are more stable than the Hanau or Whip mix.Manary examined the effectiveness of the TMJ articulator to reproduce the border movements of a patient model. What did he use for his "patient"? A Stuart articulator. What were his results? On the posterior vertical tables, both the right and left scribings were superior to the patient's (less steep). The right and left protrusive scribings were also consistently superior to the patient model. On the posterior horizontal tables, the right and left scribings were lateral to the patient model scribing (a decreased lateral condylar inclination-Bennett angle)

What effects would these differences have on restorations? Posterior restorations would have a reduced cusp height, and could have an error in cusp-groove orientation (a more acute angle formed by the orbiting and rotating paths of the mandibular molar). (p. 278-9) What did he find with regards to immediate mandibular lateral translation? The TMJ articulator simulated the "immediate side shift" of the patient. (p. 279) What was his conclusion? The small difference consistently observed between the pantographic scribings of the patient model and the TMJ articulator suggests that the TMJ system can have significant clinical application. (p. 280) SummaryThe choice of an articulator is dependent upon the patient's occlusal requirements, type of restoration(s) planned, and also the operator's philosophy, ability, and experience.

- Abstracts -09-001. Stuart, C. E. Accuracy in Measuring Functional Dimensions and Relations in Oral Prosthesis. J Prosthet Dent 9:220-236, 1959.Purpose: To describe the movements of the mandible and to emphasize the importance of reproducing those border and habitual movements with the articulator.Discussion: The articulator should suit the anatomy and physiology of the oral organ and not the converse. Movement in the temporomandibular joint can be described as occurring about three axes. The possible movements within the joint with respect to those axes are described. Of the rotating and gliding movements, the latter is the more important and should be faithfully reproduced in the articulator. The mechanics of a mandibular movement recorder, as well as the procedure for transferring the obtained information to an articulator, is described. The Stuart articulator is described and a basic explanation of it's set-up procedure is given.Conclusion: The use of the fully adjustable articulator is an accurate method of studying mandibular movement which "becomes a fascinating game". Understanding the masticatory system is basic to progressing in our learning in the field of dentistry.09-002. Guichet, N. E. The Denar System: Its Application in Everyday Dentistry. DCNA 23:243-257, 1979.I. Anatomical Considerations as they Relate to the Denar System: A brief discussion of the movements of the mandible is presented. How they can be reproduced on the Denar instrument is also presented. When restorations include the last few teeth in the arch, the author feels that the use of the Denar D5A and pantograph is time effective. Treatment sequencing is given for the use of the fully adjustable articulator in the rehabilitation of the posterior dentition.II. The Denar SystemA. Instrument systems

1. Pantograph2. Fully adjustable articulator (D5A)3. Laboratory Relator4. Field Inspection Gage5. Semi-adjustable articulator (Mark II)

B. Educational Programs1. Office Tutor2. Patient Tutor3. Protocol for Dentist-Laboratory Relations and Laboratory Support

09-003. Beck D. B. and Knap F. J. Reliability of Fully Adjustable Articulators using a Computerized Analysis. J Prosthet Dent 35:630-642, 1976.Purpose: The purpose of this study is:

a. to determine whether an articulator set to a subject's records, accurately reproduces that subject's mandibular motion

b. to compare the accuracy of an articulator set to positional records with one set to pantographic tracings.

Methods & Materials: Five subjects were examined, all of whom had either a full complement of natural teeth or fixed partial dentures. Using ticonium clutches and aluminum pin-and-plate assemblies, mandibular movements were evaluated with a digital computer. Additionally, casts were fabricated and articulated using a fully adjustable articulator with positional records (Hanau 130-21) and a fully adjustable articulator with pantographic tracings (Denar D5A). The computer sensor was attached to the articulators in the same manner as it was attached to the subjects. Data was collected and evaluated for each subject and each set of articulators.Results: At the 95% level, no significant difference was found between the data obtained from the subject-articulator or articulator-articulator comparisons. Conclusion:

1. Statistical analysis of the graphic data showed no significant difference between the Denar D5A and Hanau 130-21 articulators for the five subjects tested.

2. Both the Denar D5A and Hanau 130-21 articulators adequately reproduced mandibular movement for the five subjects tested.

09-004. Wipf, H. Pathways to Occlusion: TMJ Stereographic Analog and Mandibular Movement Indicator. DCNA 23: 243-257,1979.Purpose: TMJ technique article.     Is unique among fully adjustable articulators. It provides precise curvilinear paths of the TMJ articulator fossae elements.     Method for recording mandibular movement is known as the stereographic analog.     Material used to record the analog is autopolymerizing acrylic resin.     At the time the TMJ articulator was developed, there was only a few fully adjustable articulators available.Procedure:

1. Induce initial side shift - measured in millimeters using the tapered end of the TMJ ruler.2. One-fifth of a millimeter is measured for each millimeter of ingress. 3. Clutches fabricated indirectly or directly.

Similarities with pantographs:1. central bearing screw.2. clutches.3. terminal hinge and orbital reference point.

Dissimilarities with pantographs:1. recording styli are four in number and are fixed, the media is acrylic resin.2. pantographs are recorded extraorally3. pantographs have two vertical plates to record vertical changes whereas the vertical

controls of the stereographs are on the floor of all four analogs which are in a solid state.4. both systems record the horizontal records in four areas.

     The task of following and coordinating six lines for each of the two border and protrusive movements can be a considerable endeavor if precision is the goal. Each movement recorded is dependent on the ability to see all lines at once and hold them while the instruments are adjusted.     The lack of interpolation and eye and muscle coordination as well as the lack of numerous screws to adjust, make the stereograph a convenient and practical system of recording spatial movement.09-005. Javid, N. A comparative study of sagittal and lateral condylar paths in different articulators. J Prosthet Dent 31:130-136, 1974.Purpose: To determine the condylar guidance angles for protrusive and lateral progressive side shift in three different kinds of articulators.Methods & Materials: Two Denar D4-A, two Whip-Mix, and two Hanau model 130-28 articulators were used. Five patients whose kinematic axis have been located were used. Protrusive and lateral interocclusal records were made of acrylic. The protrusive and lateral condylar guidances of all six articulators were adjusted with both the protrusive and lateral interocclusal records. The procedure was repeated 20 times. Results: Use of the Denar articulators and comparison of the mean difference of the means of the left and right protrusive condylar guidance readings of two similar articulators showed there was no significant difference between the two Denar articulators. There was a significant difference with the Hanau and Whip-Mix articulators.Conclusion: The condylar guidances of the Denar articulator are more stable than the Hanau or Whip-Mix used in this study.09-006. Coyer, R. B. A Study of the Variability of Setting a Fully Adjustable Gnathologic Articulator to a Pantographic Tracing. J Prosthet Dent 37:460-465, 1977.Purpose: To determine the variability involved in setting a fully adjustable gnathologic articulator to a pantographic tracing of known parameters, thereby eliminating the problem of setting the articulator with incorrect information.Methods & Materials: A pantographic tracing was made on a fully adjustable gnathologic articulator. Patient tracing were not used. The instrument was arbitrarily set and tracings were made in the normal manner. Seven dentists were given the articulator and a still-mounted pantographic tracing and were asked to set the articulator. Seven sets of tracing were used. The original random settings were used as the standard and deviations determined.Results: Statistical significant difference was noted for the following settings:

Immediate side shift Progressive side shift Top wall

Operator consistency was compared by plotting the variable error and constant error for each operator for each tracing. Operators tended to set the articulator in excess of the original setting.Conclusions: There is an inherent system variability and that mechanical and operator errors were involved only in the actual setting of the instrument.09-007. Winstanley, R.B. Observations on the use of the Denar Pantograph and Articulator. J Prosthet Dent 38:660-672, 1977.Denar D4A and pantograph used to transfer settings to articulator. Participants attempted to duplicate settings by following the tracing.Results:

1. Most articulator adjustments were reproducible with a reasonable degree of accuracy but not to the extent one would hope.

2. Rear and top wall adjustments were very inaccurate, probably because the tracings were short and large variations in the setting caused only small deviations of the styli.

3. Familiarity improves results. 4. Reciprocal actions - when articulator adjusted to move one stylus, it may have a mutual

or reciprocal influence on other styli, should follow instructions in manual.09-008. Solberg, W.K. And Clark, G.T. Reproducibility of Molded Condylar Controls with an Intraoral Registration Method. Part I. Simulated Movement. J Prosthet Dent 32:520-528, 1974.An articulator with molded fossa boxes served as the patient, three dentists made 4 stereographic tracings and molded 4 fossa boxes each. The right condylar controls were compared in protrusion, latero and mediotrusion by a computerized measuring machine to the master condylar control.Results:

1. Error of stereographic technique is WNL.  2. Sagittal component of protrusion and mediotrusion resulted in a condylar inclination

which was slightly less than that of the patient (neg error).  3. More experience operators had less variation.

09-009. Weinberg, L.A. An Evaluation of Basic Articulators and their Concepts. Part IV. Fully Adjustable Articulators. J Prosthet Dent 13:645-663, 1963.Purpose: To discuss the principles that apply to fully adjustable articulators.Discussion: In the effort to create an articulator that will take into account the varying degrees of curvature of the articular eminence and the potential mandibular lateral translation, the fully adjustable articulator was designed. Records of centric relation, protrusive, right and left lateral border positions, and intermediate three-dimensional border paths of motion are used to set the articulator with the aid of a pantograph.      The pantograph is an enlarged tracing of mandibular movement obtained by fixing a writing plate to one jaw and a stylus to the other. The three-dimensional motion of the condyle can be reproduced by combining the information attained by the six plates of the pantograph. It is not necessary for the pantograph to be exactly oriented in each of the three planes of space but their arrangement must remain constant during the recording of mandibular movements. All tracings start at the terminal hinge axis and are recorded on these three pair of plates:Symphyseal pantograph- the typical Gothic arch tracing is produced. Sagittal pantograph- records the vertical components of movement. The protrusive and balancing paths traced form the Fischer angle. A short "backlash" tracing is the vertical component of the working condylar movement. This "backlash" is a projection of the axis of the mainly rotating working condyle as the tracing element is extended beyond the actual condyle. Inclined Horizontal pantograph- records of the horizontal components of motion. The Bennett angle is created by the protrusive and balancing tracings. The lateral component of the working condylar movement is represented by the backlash.The essential requirements for duplicating these motions are:

1. To maintain the same relationship of the pantograph to the styli and transferring it from the patient to the instrument.

2. The instrument must be three-dimensionally adjustable to accept records.

3. The final casts must be mounted in the exact relationship to the motion recorded as it occurred in the patient.

     An anterior point of orientation (usually the infraorbital point) can be completely arbitrary but once established must be consistent. Tattooing the patient is recommended to insure reproducibility. Condylar readings are not obtained from the instrument but are recorded in the tracings and transferred to the instrument. The curved condylar path eliminates the 0.4 mm error associated with rectilinear path articulators. The pantograph's recording of the Fischer angle can eliminate the 0.1 mm error produced in the second molar cusp height.      The gnathologic instrument conceptually produces no occlusal errors although discrepancies can occur. From day to day, however, ones facial muscles vary in the degree of tonus. Pressure on the central bearing point may cause a rock in the mandible and create deviations. The weight and bulk of the equipment can alter the reproduction of tracings as well as head position and respiration. There can also be inaccuracies with the materials used in record making, fabrication and cementation of the restoration. The author does not agree that all possible movements in between the border movements are automatically reproduced by the fully adjustable articulator as the patient tends to chose the most comfortable path of motion.Conclusion: Fully adjustable articulators are extremely accurate in duplicating the three-dimensional motion of the condyle. Semiadjustable articulators are adequate for complete denture construction and their settings are based on clinical averages. The most serious error that is created by semiadjustable articulators is a space between the posterior teeth during lateral excursions on the working side due to negative error. Fully adjustable articulators can reduce the amount of intraoral corrections to be made and will accept all non-pathologic records.09-009. Weinberg, L. A. An Evaluation Of Basic Articulators And Their Concepts. Part IV. Fully Adjustable Articulators. J Prosthet Dent 13:645-663, 1963.Purpose: To discuss the principles that apply to fully adjustable articulators.Concept: Three-Dimensional Pantographs       Three-dimensional motion can be reproduced if simultaneous pantographs are obtained containing the three planes of space. To reproduce the original motion, the pantographs must be in the same relationship to each other and to the styli on the instrument as they were on the patient. Simultaneous tracing of these pantographs on the instrument effectively recreates the motion.     It is not necessary for the pantographs to be exactly oriented in each of the three planes of space. However, their arrangement must contain the three planes of space and remain constant during the recording and during the reproduction of the motion.Contents of each tracing     Each writing table contains the tracings of the three border movements starting from the terminal hinge position. These movements are represented characteristically on all six pantographs.Symphyseal Pantograph - The typical Gothic arch (needlepoint) tracing is produced.Sagittal Pantograph - records the vertical components of condylar motion. During eccentric condylar movements it traces the protrusive path, the balancing path, and forms the Fisher angle in between these two paths. The short curved line, resembling a "backlash," is the tracing of the vertical component of the working condylar movement.Inclined Horizontal Pantographs - record the horizontal components of condylar motion. The Bennett angle is recorded by the angle between the protrusive and the balancing condylar tracings. The lateral component of the working condylar motion is again represented by a short

curved "backlash" tracing.Method:The gnathologic system of duplicating motion has three essential requirements:

To maintain the same relationship of the pantographs to the styli as the transfer is made from the patient to the instrument.

The instrument must be three dimensionally adjustable to accept the records. The final casts must be mounted in exactly the same relationship to the motion recorded

as it occurred in the patient.Instrument settings:

Protrusive Inclination - Condylar slots of the appropriate radius are placed on the condylar ball and the inclination is adjusted so that the styli trace the same protrusive path on the instrument as has been recorded on the patient.

Intercondylar Distance - The symphyseal pantographs capture the vertical axis of each working condyle. The condylar mechanism is adjusted sideways until the styli trace the lateral border movement along both symphyseal pantographs.

Balancing condylar motion - is adjusted by combining the individual condylar path curvature, vertical angulation, and Bennett angle obtained from the pantographs.

Working condylar motion - Bennett shift, if any, is recorded by the horizontal pantographs and transferred to the Bennett guide in the midline of the instrument. The Bennett guide can be shaped by grinding if necessary. The condylar rod can be adjusted to any angulation in all three planes permitting individual working condylar motion away from the original hinge axis line to its eccentric position.

Face-bow - The hinge axis and infraorbital tattoos allow the casts to be remounted at any future time without repeating the procedure, unless specifically desired.

Arbitrary Location of the Anterior Point of Orientation - Three -dimensional motion, as recorded in the pantographs, is fixed in relation to the two jaws and transferred in total to the instrument. No error is produced by the arbitrary orientation of the plane of occlusion.

Curved Condylar Path - The .4mm condylar error associated with a straight condylar mechanism is eliminated.

Balancing Condylar Movement - Fischer angle is recorded in the pantographs and used for the adjustment of the instrument. This eliminates the .1mm error produced at the second molar cusp height when the protrusive inclination is used for the balancing inclination.

Working Condylar Movements - On a theoretical basis, no mathematical error is produced at the cusp level.

Summary: A gnathologic instrument in which three-dimensional pantographs are used is extremely accurate in duplicating three-dimensional motion. Theoretically, no occlusal error is produced.     Factors of muscle tone, pressure of the central bearing point, head position, respiration and weight of the instruments attached to the jaws should be kept in mind in relation to the above conclusion.09-010.  Shields, Clayton, and Sindledecker. Using pantographic tracings to detect TMJ and muscle dysfunctions. J Prosthet Dent 39:80-87, 1978.Purpose: To determine if a relationship existed between clinical findings and uncoordinated mandibular movements.

Methods & Materials: Forty-six subjects with varying degrees of dysfunction were examined. HDI (Helkimo dysfunction index) and pantographic tracings were completed on the patients. The degree of reproducibility was scored for the tracings (PRI). The scores are as follows:

00-10 Reproducible 11-16 Slightly reproducible 17-30 Moderately reproducible 31-+ Severely nonreproducible

The subjects were divided into groups according to there clinical symptoms and further divided based on the state of occlusion.Results: The PRI detected differences between the group with moderate dysfunction and the groups with no dysfunction. Subjects with poor occlusion had slightly higher PRI scores.Conclusion: The PRI can aid in detecting TMJ dysfunction. 09-011. Manary, D AND Holland, G. Evaluation of Mandibular Movement Recording and Programming Procedures for a Molded Condylar Control Articulator System. J Prosthet Dent 52:275-280, 1984.Purpose: To analyze the effectiveness of the TMJ articulator to reproduce the border movements of a patient model.Materials & Methods: Stuart articulator was programmed to serve as a laboratory model for a patient. A Stuart pantograph was attached and pantographed 20 times by one operator. The scribings were photographed and then compared with the scribings from a programmed TMJ articulator. Results: All centric relation points were the same on the 20 sets of fossae and the patient model. On the posterior vertical tables, the TMJ orbiting and protrusive paths were consistently superior to (less steep than) the patient model scribings. Conclusion: The error associated with the development of the TMJ stereograph and custom fossae resulted in a decrease in steepness of the articular eminentia. The immediate side-shift is simulated by the TMJ stereograph and fossae formation. The horizontal orbiting path of the programmed TMJ articulator was consistently lateral to the orbiting path of the patient model (decreased Bennett angle). The horizontal rotating path of the programmed TMJ articulator was consistently medial to the rotating path of the patient model (retruded laterotrusive). As the operator gained experience, the TMJ articulator more closely simulated all the movements of the patient model. The small difference consistently observed between the pantographic scribings of the patient model and the TMJ articulator suggests that the TMJ system can have significant clinical application.09-012. Swanson, K. H. Complete Denture Using the TMJ Articulator. J Prosthet Dent 41:497-506, 1979.Purpose: To review a technique for use of the TMJ articulator in the fabrication of a complete denture.Methods & Materials: House's technique is reviewed and the TMJ technique described:

1. A Face-bow mounting of the maxillary cast, an arbitrary axis can be used, but a kinematic hinge is preferred.

2. Secure accurate impressions with custom acrylic trays. A flat metal plated secured to the maxillary tray. Trays trimmed to correct extension, border molded and refined with a wash of silicone impression material.

3. Plane of mandibular occlusion on which to make the mandibular movement recording is planned. This is done by putting both impressions in the mouth, and the mandibular handle reduced so that as the patient closes the jaws the handle on the mandibular tray will stop closure, and by adjusting the handle a preliminary vertical dimension of occlusion can be determined.

4. The TMJ clutch forming bite fork is used to make the recording platform on the tray of the mandibular impression.

5. Central bearing screw is placed on the convex side in one of the two holes in the bite fork.

6. Autopolymerizing acrylic is placed around the central a bearing screw, at putty stage the portion of the bite fork around the central bearing screw is covered to the size of the mandibular impression tray and brought to place on the tray side of the mandibular impression.

7. Another mix of autopolymerizing resin, four studs are placed in the preplanned canine and molar areas on the maxillary impression tray.

8. Impressions with attachments are tried in the mouth and the central bearing point adjusted to support established VDO.

9. After patient has been trained to make excursive movements the surface of the maxillary tray and studs are lubricated. TMJ resin is made and a pat placed on the mandibular platform in each area where the studs will move.

10. Mandibular impression is placed in the mouth and the patient instructed to close on the central bearing screw and instructed to move in the previously rehearsed mandibular movements.

11. The impressions are removed, and some of the material is removed around each recording, the central bearing screw is lowered about an eighth to a quarter of a turn, pathways lubricated, and record reinserted. Patient ask to refine tracings with cutting studs.

12. When recording is satisfactory, a face-bow is made. It is made with the four studs in modeling compound.

13. Impressions are poured in artificial stone, and are not removed until they have been mounted on the articulator.

14. Maxillary is mounted via the face-bow. The mandibular is related by attaching the recordings together with modeling compound with the four studs in their respective points of the four Gothic arch recordings. Incisal guidance pin is set at zero.

15. TMJ fossa and tray acrylic is placed in each fossa box, the controls are molded.  09-013. Contino, R.M. and Stallard, H. Instruments Essential for Obtaining Data Needed in Making a Functional Diagnosis of the Human Mouth. J Prosthet Dent 7:66-77, 1957.Purpose: A discussion of knowledge and instrumentation needed for acquiring and implementing data in making a functional diagnosis of the mouth.Summary: - Basic condyle motions- limited to 2 kinds of movement/rotation and sliding; in many combinations which make all mandibular movements possible- Condyle slidings- 2 types of condyle sliding movements:1) fore and rear, 2) outward and inward/Bennett movement- Pure anatomical information- hinge-sliding joint/ginglymoarthrodial joint; capsule- bandage of tissue surrounding the condyle and the disc; lateral pterygoid muscle- attaches to the disc; no

retracting muscles are directly attached to the condyle- Significance of joint anatomy- a) the maxilla: temporal suspension of the joint, the eminences, mandibular fossa and the upper compartments of the joints; b) the mandible: lower compartments of the joints, the meniscuses, the condyles, the lower synovial cavities, the lower portions of the capsules and the condylar axes- Expectations of an articulator- the individual expression of the condylar movements of the patient; McCollum- condylar slots; Stuart- discarded the horizontal axis for a functional axle, grinding of the cams for Bennett timing, replaceable eminences for various condyle paths, articulator to accept data found by jaw writing instruments- History of jaw writings- Goldberg- too complex; Snow- facebow, Harlan- modified the facebow by fastening it to the lower teeth; the mandibular clutch; the maxillary clutch and facebow; Gnathologic society's greatest contribution- the pattern of condyle movements is fixed and independent of teeth and muscles; Gysi was unable to do this- writing device not rigidly fastened, writing card not always fixed in the same place and dissimilar starting points - Inadequacies of interocclusal records- at best, they can only register the end position of a path- Adaption of face-bows to write jaw motions- MacQueen, Stuart and Wightman;jaw writing device- tridimensional caliper, consisting of a maxillary frame to hold the record flags and a mandibular frame to carry the writing points that can be used to determine the dimensional relation of the teeth and jaws to the cams and axes of the joint movements. Purpose- produce data from which the dentist can determine and locate the centric axis position of the opening-closing action of the mandible, establish the slant and curvature of the condyle paths, set and direct the amount and direction of the Bennett pathsFunctional diagnosis- can only be made by studying the relationship of the jaws, the interrelations of the opposing teeth and the relation between the dental factors and the condyle factors of articulation as they are revealed when dental casts are mounted on a duplicating instrument

Section 10: Centric Relation(Handout)

Definitions:Centric Relation (CR): the maxillomandibular relation in which the condyles articulate with the thinnest avascular portion of their respective discs with the complex in the anterior-superior position against the shapes of the articular eminences. This position is independent of tooth contact. This position is clinically discernible when the mandible is directed superiorly and anteriorly. It is restricted to a purely rotary movement about the transverse horizontal axis.Deprogrammer: various types of devices or materials used to alter the proprioceptive mechanism during mandibular closure.Maximum Intercuspation (MI): the complete intercuspation of the opposing teeth independent of condylar position.Anatomy influence on Centric Relation:1. Atwood states that there are two basic concepts of CR.    a. anatomic concept - the most posterior border position is established by ligaments.     b. pathophysiologic concept - the most posterior unrestrained jaw relationship (not a border position)       established by muscle action.

    The posterior limit of the mandible is established by structures anterior and lateral to the condyles (lateral pterygoid and temporomandibular ligament) rather than posterior to them. The temporomandibular ligaments contain proprioceptive nerve endings, susceptible to stretching, leading to inhibition of the retrusive muscles (temporalis and digastrics), and stimulation of the protrusive antagonist muscles (lateral pterygoids).The term "unrestrained " relates to no undo force causing distortion of the tissues.Does reproducibility assure correctness? _________ 2. Moss stated that:   a. CR is a nonfunctional position that is not habitual or common.   b. Are the functional surfaces of the TMJ capable of adaptation over long periods of  time? _______    c. When would these changes occur? ___________   d. The dynamically fluctuant state of the neuromuscular apparatus makes it reasonably certain that       variation in CR position can exist. Ex. Pain caused by a high restoration.    e. As mandibular function begins, and muscles contract, the functioning joint surfaces are brought       into a compressive articulation and the condylar heads are not in CR.  3. What is Levy’s dynamic concept of centric relation?      a. A quasi-fixed position of temporary duration which exists in a state of equilibrium established by         the neuromusculature and ligaments.     b. Does this mean that the TMJ and musculature can adapt by remodeling to the newly acquired         intercuspation?     c. According to Levy, does this mean that a fixed retruded positional concept can lead to unnecessary         treatment?  Dawson stated that in CR:     a. Proper alignment of the condyle disk assembly is required and the condyles should be against the        eminentia.    b. The medial pole plays the predominant stop of upward movement of the condyle.     c. The muscles surrounding the joint pull the condyle disk assembly firmly against the eminentia.    d. Elevator muscles (temporalis, masseter, and medial pterygoid) pull superiorly.    e. The medial pterygoid pulls the medial pole of the condyle into the buttressed part of the glenoid         fossa. The medial pole of the condyle braced against the glenoid fossa can have no posterior        movement without moving inferiorly.    f. The anterior pole of the condyle rests against the eminence and prevents forward movement.    g. The medial pole of the condyle (superior-anterior) seated in CR can make a rotary movement.         The lateral pole of the condyle can translate during opening and closing of the mandible while in         CR due to angulation. This anatomy allows occlusal relationship records to be taken at

varying        vertical dimensions of occlusion as long as the correct horizontal axes are recorded.    h. Lateral pterygoid muscles resist the elevator muscles and deviate the mandible to avoid occlusal        interference’s.    i. Centric relation is a functional position and relates to the muscle harmony of the patient.     j. Occlusal interference’s to the uppermost centric relation position mean that the lateral pterygoids        must deviate the mandible to conform to the maximum occlusal position and they cannot deviate       to that position without serving as a holding muscle against the elevator muscles. This can progress       into a clenching pattern, and incoordinated musculature.    k. Bilateral manipulation is the method preferred to determine optimum TMJ condyle position.

        Where are the fingers placed for this method? ____________________________________5. According to Gilboe, is it possible to place the condyle in a position so posterior that the condyle-disk assembly is no longer in contact with the eminence? _____ If an internal derangement exists, the most posterior position could be pathologic. With an anteriorly displaced disk, the condylar articular surface bears on the posterior band of the intra-articular tissue. If restored in this position, can an iatrogenically induced derangement of the TMJ occur? _____ Does reproducability imply desirability? __________Restorative services should be postponed until CR has been established and confirmed by the absence of symptoms.Centric Relation, Why is it important?CR is a bone to bone position and MI is a tooth to tooth position.CR is the only clinically repeatable (verifiable) jaw relation. It is the logical position to fabricate a prosthesis.CR and MI are coincidental in only 10% of the population. The discrepancies between CR and MI can be observed on articulated study casts.When is it needed? An accurate CR recording should be made to reduce time spent making intraoral adjustments at delivery. Applicable situations include:    a. MI not clearly defined due to restored dentition.    b. Changing VDO    c. Occlusal scheme - group function rather than mutual protection.    d. TMJ disorder patients with occlusal discrepancies as part of the etiology of the TMD.    e. Angles’ class II patients requiring freedom to move from CR to a pseudo - class I (protrusive)        position.    f. When the number of artificial teeth out number the natural teeth. Systems for recording Centric Relation: Static Recording ( interocclusal check bite) - teeth or supporting tissues as predominant factors. Oldest and most commonly used method used today. CR recording should always be verified against a second recording. There should be no tooth contact through the CR records. If contact

occurs, undetected mandibular translation may occur due to deflective contacts or neuromuscular avoidance mechanism. When a slide to MI is present, the first contacts in CR are usually the most posterior teeth, and the molars can act as a fulcrum to cause the condyles to move down and backward initially and then forward as the teeth slide into MI.Graphic Recording - intraoral or extraoral Gothic arch tracings.Physiological / Functional Recording - usually recorded on wax rims or wax cones during unguided / unassisted patient movement.Cephalometric Recording - cephalometric radiography to determine optimal position of the condyles. Impractical and seldom used. Deprogrammer: Deprogramming devices are used to eliminate muscle engrams, prevent the activation of the neuromuscular avoidance mechanism, and allow the mandible to more easily achieve the CR position. While the concept of using deprogramming devices to record CR is widely accepted, controversy and variation in technique abound. Current literature tends toward agreement that deprogramming takes about 30 minutes. More time (several hours or overnight) does not provide benefit. Some of the major techniques include:1. Bite on cotton roles: used with chin point guidance. This was the norm when the definition of CR was the most retruded position.2. Lucia jig: a Duralay jig was made indirectly and fitted during deprogramming, adjusted with a slight incline until a gothic arch tracing was demonstrated with articulating paper. The CR record is made with a hard material on a wax wafer and the patient closed firmly onto the jig. The criticism of this technique today revolves around the incline of the jig and the choice of wax to make the record. Elastomeric materials were not available.3. Leaf gauge: this device was very popular in the seventies and eighties. The patient closed into a thick gauge and leaves were removed until the teeth were minimally separated in what was assumed to be CR. The record was made with the leaf gauge in place. Drawbacks included the incline of the leaf gauge may force the condyles posterior. Williamson recommended less biting force to allow the physiologic placement of the condyles in the glenoid fossa.4. Anterior flat plane: essentially a Lucia jig, but without any inclines. Used in the power centric recording. Recording techniques:Chin-point guidance: not recommended due to the posterior displacement and stress on the bilaminar zone.Bimanual technique (Dawson): patient is deprogrammed using an anterior device or leaf gauge. Fingers are at right angles with upward pressure, thumbs on chin with downward pressure. Manipulate into pure hinge movement (romancing the mandible). This technique is accurate and has support in the literature. It can also be technique sensitive. The operator must be careful not to over-manipulate the patient and place the condyles in a more posterior position.What does McKee say about this technique?McKee stated that the most important criteria for CR is the complete release of the inferior lateral pterygoid muscle during jaw closure. If not released, the condylar position will be inferior.Single-handed technique: same as the bimanual but with one hand, fingers at the angles and the base of the thumb at the chin. The free hand is used to place the recording medium. Many say that it is not as accurate as bimanual manipulation.

4. Myotronics: not very popular today. Electrodes measure muscle activity. Records are difficult to verify and are anterior to CR compared to other techniques. What does Jankelson say about the neuromuscular aspects of occlusion? Unassisted free closure by the patient (swallowing, pull tongue back): no anterior deprogrammer. Records tend to be anterior to repeatable CR compared to bimanual guidance.6. Unassisted free closure by patient (with anterior deprogrammer): What did Campos find?7. Power Centric (Roth): this excellent technique is a modification of Lucia’s original work. A flat plane anterior deprogrammer (to prevent activating the neuromuscular avoidance mechanism) is combined with free closure by the patient to eliminate operator induced error. The use of the flat plane allows the elevator muscles (masseter and temporalis) to seat the condyles in a superior anterior position. The anterior deprogrammer is made without indentations to register the mandibular incisal edges. The original technique, used a two piece wax bite. More stable registration materials like acrylic resins can be used for the deprogrammer and an elastomeric recording material.    a. The patient is fitted with the anterior deprogrammer so the teeth are minimally separated.   b. During the deprogramming the patient is taught to move into CR without assistance.   c. The recording material is introduced posteriorly and the patient exerts firm anterior biting pressure on the      deprogrammer in the CR position while the material sets. Hickey stated that artificial teeth will contact in CR when the proprioception of natural teeth is absent. Three methods of recording CR are discussed:   a. Physiologic technique - swallowing procedures and chew in records. Problems - movement of rims on the       tissues, patient not reaching the most retruded position as he chews side to side, and resistance of the       material may result in a lack of consistency in the mandibular position.   b. Graphic indication of mandibular position – intraoral or extraoral tracing devices. Problems - supported by       movable tissues, discrepancy in opposing ridge size or position. Direct interocclusal records - made by interposing recording medium between occlusal rims. Recommended by Hickey because of its simplicity. Problem - Accuracy dependent on clinical judgement by the dentist.Recording Materials: CR recording should always be verified against a second recording.Careful trimming of the interocclusal recording material is critical because the soft tissue is recorded in a compressed state. The stone casts record the soft tissue in an uncompressed state. The two areas that must be trimmed are the gingival tissues of the maxillary teeth (palatal) and the distal tissue of the terminal maxillary tooth. Waxes: Hard baseplate or reinforced (Aluwax, Coprawax): Many variations in technique. The material is generally considered too unstable and inaccurate for CR (ok if used immediately, must be no proprioception, must harden quickly, Ex. Delar wax.), but can be used successfully for static (positional) lateral checkbites.Compound (modeling plastic): accurate but are technique sensitive. Need to have uniform softening to prevent uneven pressure while recording CR.

Plaster and ZOE: accurate and stable but difficult and messy to use.Elastomeric (Stat BR, Blu Mousse, etc.): stable, easy to use and acceptable accuracy. Several variations in technique. Widely accepted as the current norm. Factors that affect Centric Relation records: The resiliency of the supporting tissues.The stability of the recording bases.The TMJ and associated neuromuscular mechanisms.The character of the pressure applied in making the recording.The technique used in making the recording and the associated recording devices used.The skill of the dentist.The health and cooperation of the dentist.The maxillomandibular relationship.Character and size of the residual alveolar arch.The size and position of the tongue.What did Kingery say about problems associated with CR?1. Requirements:    a. Record correct horizontal relationship    b. Equal vertical contact of arches2. Errors:     a. Positional - incorrect horizontal and vertical contact, excessive pressure on closing.    b. Technical - poor rims, pin moved, processing errors. How are the errors manifested clinically?Vertical - _______________________________________________________________Horizontal - _____________________________________________________________Recording     a. Extraoral and intraoral tracing - use a central bearing point to establish equal contact.    b. Direct check bite - occluding surfaces must not touch. Recording medium must be soft.    c. Functional recording = chew in - gothic arch tracing made with pressure - be careful with displaceable        tissue.Shafagh found what about CR and diurnal variance?.What is his suggestion ? Guichet:- How does the SCM muscle affect jaw position? - Can a dentist reprogram the musculature and condylar position?- What is the protective reflex? - How is equilibration related to jaw separation? Williamson - What does he say biting hard does to the condyles?- What does he say about forcefully retruding the mandible vs. a physiologic position using the anterior guidance technique? - The temporalis has more influence on CR than the masseter when an anterior guidance appliance is used (Williamson).Campos - what did he say about recording positions of CR in upright or supine positions? Which one is better? Did they have a difference in reproducability?

Articulation: 1. The choice of the articulator is dependent on the intended occlusal scheme (group function, mutually protected) to be developed, the complexity of the restoration. 2. Semi-adjustable articulators are commonly used, along with arbitrary facebows.3. CR records should be less than 3 mm to minimize the arc of closure errors.4. The degree of sophistication chosen will be negated if accurate centric relation records are not obtained and excessive intraoral adjustments -may be required.Prosthesis fabricated in centric relation or centric occlusion:Lucia recommended that centric occlusion should be built to occur at centric relation. Regardless of whether we believe that centric occlusion should be slightly anterior to this terminal hinge position, thisis the only constant, repeatable position that can be used to check the work as we proceed.What does he say about proprioceptive impulses?Glickman evaluated a patient with full mouth restorations and placed one set fabricated in CR and the other in CO.  What did he find?Serrano used a corrective occlusion prosthesis to try to improve the reproducability of CR. What didhe find after the three month period?Wood used an interim prosthesis to allow for easier CR recording later. What did he recommend? Conclusion:1. The definition of CR has evolved over the years and with greater understanding of mandibular movement, it may change again. As the definition changed, the techniques for recording it often changed or were modified. Other modifications in technique are associated with the improved materials.2. CR is an area, a small area.3. In the 1950’s "the most retruded relationship of the mandible to the maxilla when the condyles are in their most posterior unstrained positions in the glenoid fossa from which lateral movements can be made, at any degree of jaw separation". The chin point push back technique was popular.In the 1980’s "RUM" the rearmost uppermost and midmost position. Dawson and others pointed out that clinicians tended to emphasize the rearmost aspect and, with manipulation by the operator, the patient recording could actually end up posterior to CR. Chin point guidance was followed by the bimanual guided technique, both with and without anterior deprogramming.The clinician should select a technique and material for recording centric relation position based on the patient’s presentation, proposed treatment, and the clinicians personal philosophy.References:Kapur An evaluation of CR records obtained by various techniques. JPD 7:770, 1957.Yurkstas, Factors affecting CR records in edentulous mouths. JPD 14:1055, 1964.Meyers, CR records - historical review JPD 47:141, 1982.Wipf, Pathways to Occlusion: TMJ Stereographic Analog and mandibular movement Indicator. DCNA 23:271, 1979.

Guichet, Initial reference, procedures for occlusal treatment, Anaheim, 1969, Denar Corp.Millstein, determination of the accuracy of wax interocclusal registration. Part II JPD 29:40, 1073.Kinderknecht, The effect of a deprogrammer on the position of the terminal transverse horizontal axis of the mandible. JPD 63:123, 1992.Lucia, Technique for recording CR. JPD 14: 492, 1964.Long, Locating CR with a Leaf gauge. JPD 29:608, 1973.Dawson, temporomandibular joint pain-dysfunction problems can be solved . JPD 29:100. 1073.Wood, Reproducibility of CR bite registration technique. Angle Orthod 1994; 64(3):211.Schalhorn, A study of the arbitrary center of rotation and kinematic center of rotation for facebow mounting. JPD 7:162, 1957. 

- Abstracts -10-001. Atwood, D.A. A critique of research of the posterior limit of the mandibular position. J Prosthet Dent 20:21-36, 1968.Purpose: To discuss the concept of centric relation and evaluate past, current, and need for future research.Discussion: There are two basic concepts of CR. The anatomic concept which states a most posterior border position established by ligaments. The pathophysiologic concept states that CR is the most posterior unstrained jaw relationship not a border position and is established by muscle action. CR is important as a reference position for the restoration of occlusion due to it being relatively reproducible. But reproducibility does not assure physiologic desirability or correctness. A number of clinical and specific problem studies are reviewed.Conclusion: Posterior limit of the mandible at VDO is established by structures anterior and lateral to the condyles rather than posterior to them.(lateral pterygoid and temporomandibular ligament) The temporomandibular ligaments contain proprioceptive nerve endings susceptible to stretching leading to inhibition of the retrusive muscles(temporalis and digastrics), and stimulation of the protrusive antagonist muscles (lateral pterygoids).The need for a large variety of future studies is called for.10-002. Moss, M.L. A functional cranial analysis of centric relation. DCNA 19:431-442, 1975.Purpose: This article is a review of the information as to the anatomy of the TMJ and its relationship to Centric position. The following conclusions have been made:  1. In biomechanical terms the centric relation is a nonfunctional position.  2. Over relatively long periods of time, the morphology of all functional surfaces of the TMJ is capable of significant adaptive alterations. These are normal compensatory responses of skeletal units to the prior alterations of functional matrices.  3. In much shorter time periods, the dynamically fluctuant state of the neuromuscular apparatus makes it reasonably certain that intra-individual variation in condylar positions can exist.10-003. Levy, PH. Clinical implications of mandibular repositioning and the concept of an alterable centric relation. DCNA 19:543-570, 1975.Summary of important points:- Early attempts to obtain repeatable positions in treating denture patients resulted in a fixed retruded position being standard for centric relation. This concept was later used for dentate patients. Levy feels this is incorrect. The mandible repostures to a more favorable position to

establish a new balance and equilibrium. The condyle and fossa remodel and adapt to this position.- The joints assume their position as a result of the intercuspation of the teeth, jaws, and neuromusculature. - Form follows function.10-003.  Levy, P.H. Clinical implications of mandibular repositioning and the concept of an alterable centric relation. DCNA 19:543-570, 1975.Discussion: A fixed retruded positional concept is traced to early complete denture attempts to obtain duplicable bites. This concept, later gained acceptance as a physiologic entity for patients with teeth. Static centric relation, ultimately lead to entirely reproducible systems involving all mandibular movements. An interpretation of centric relation as fixed or static has become the common cornerstone for virtually subspecialties in dentistry. According to Levy, a fixed retruded positional concept has lead to unnecessary treatment in certain orthodontic cases and rehabilitation cases as related to extractions and surgical jaw repositioning.      Reposturing the mandible to a clinically favorable " as if " position determined by the anatomic factors present is an integral aspect of the reconstruction procedure. Control of the situation requires that the newly acquired intercuspation be definitely keyed to allow the patients' musculature to establish a new balance and equilibrium and time for the condyles and their fossae to readapt and remodel their relationship.      Temporomandibular articulation has a wide range of adaptability and remodeling capacity. The joints assume their position as a result of interplay of intercuspation of teeth , jaws and neuromusculature. A dynamic concept of centric relation is presented as a quasi-fixed position of temporary duration which exists in a state of equilibrium established by the neuromusculature and ligaments. Adoption of this concept allows for a diagnosis and treatment which is rational in theory and workable in fact. 10-004.  Jankelson, B. Neuromuscular aspects of occlusion: Effect of occlusal position on the physiology and dysfunction of the mandibular musculature. DCNA 23:157-1688, 1975.     Mechanical measurement performed under conditions for registering condylar (border) occlusion does not establish whether the repetitiveness is occurring under muscularly relaxed or muscularly strained conditions. The presence of mechanical devises, such as clutches, central bearings, or pantographs, which have been used to measure border positions, elicit a neuromuscular response by their very presence.     Transcutaneous electrical neural stimulation (TENS) is firmly established in physical medicine as a most effective, physiologically rational means of relaxing specific areas of the musculature. The Myo-monitor was designed to adapt TENS specifically to the requirements for the relaxation and control of the complex of muscles involved in mandibular function. This is accomplished by the application of mild, time-spaced programmed stimuli through the fifth and seventh nerves.Tracings in this study showed:1. Chewing and swallowing were done at, or in the vicinity of, centric occlusion and that no chewing strokes or swallows went to centric relation.2. Pathways between centric occlusion and centric relation is seldom a symmetric posterior movement, but involves changes in all dimensions.3. The muscle tension generated on retrusion from centric occlusion to centric relation gives further support to the findings that centric relation represents a neuromuscularly strained position. (Note: Definition of C.R. used: Rearmost, uppermost, midmost position)

4. Centric occlusion, apparently by feedback to proprioceptors, is the dictator and controller of the posture and the skeletal relationship of the mandible to the skull. When centric occlusion does not coincide with the neuromuscular position, proprioceptive feedback from the malpositioned centric occlusion dictates and maintains strained muscle accommodation, and an accommodative trajectory of closure. The result is mandible dysfunction characteristic of craniomandibular syndrome.5. Myocentric occlusion often coincides with centric occlusion, but in no instance was myocentric occlusion found to coincide with centric relation.6. Registration of myocentric occlusion is achieved by isotonic muscle contraction that originates from rest position.Note: This author lists only 3 references, all of which are himself.This article is nothing more than an advertisement for the Myo-monitor.10-005. Dawson, P.E. Optimum TMJ condylar position in clinical practice. Int J Perio Rest Dent 3:11-31, 1985.Purpose: To discuss, in length, the optimum condylar position in clinical practice.Conclusion: Definition of C.R.: When the properly aligned condyle-disk assemblies are in the most superior position against the eminentia, irrespective of tooth position or vertical dimension.     C.R. is a horizontal relationship of mandible to maxilla.     The most important point in regard to condyle-fossa relationship has been grossly ignored, and that is the role that the medial pole plays as the predominant stop of upward movement of the condyle.     When we have occlusal interferences to the uppermost centric relation position, it means that the lateral pterygoids must deviate the mandible to conform to the maximum occlusal position, and they cannot deviate to that position without also serving as a holding muscle against the elevator muscles. If this progresses into a clenching pattern, we are going to then have hypermyotonia and incoordinated musculature. What we are really after is a totally harmonious relationship of functional harmony.Bilateral manipulation is the method preferred to determine optimum TMJ condyle position.10-006. Kingery, R.H. A review of some problems associated with centric relation. J Prosthet Dent 2:307-319, 1952.Purpose: To discuss four problems associated with centric relation:Methods/Problems discussed:

1. What is required: Problem of requirements include the position of the horizontal relationship of the mandible to the maxilla with equalization of vertical contact, is known as centric relation, or the most retruded unstrained positions of the heads of the condyles in the glenoid fossa, at any degree of jaw separation, from which lateral jaw movements can be made. We do not "take" centric relation, we "record" centric relation.

2. Errors: There are two classes of error. Positional errors caused by operator error in recording horizontal or vertical relationship, excessive closing pressures and changes in supporting area. Technical errors may be caused by ill fitting occlusion rims, indiscriminate opening or closing of the occluding device or articulator, slight shifting of teeth in final wax set-up to the permanent base material.

3. How errors manifest: Loss of retention particularly in the mandibular denture, irritation on the crest of the lower ridge (localized ulcer usually hyperemic) in a premature contact, premature contact of one or several teeth on one side.

4. Recording centric relation: This author feels that too many operators are prone to accept without question CR recordings without questions. Five methods are discussed.

1. Graphic recording: Referred to as arrow point tracing and represents the movement of the mandible on one plane. The resultant graph will be take the form of a V. the point refers only to the anteroposterior jaw relation and must be registered with equalized vertical pressure. Error can be made by the amount of pressure applied by the patient and displacing the supporting tissue. Stansbery brought out a method to check the correctness of the position of the central bearing point.

2. Extraoral procedure: the gothic arch tracing is developed extraorally, allowing full view at all times. Plaster injected between the occlusion rims and central bearing point is used as a recording medium. Allows one to detect any jaw movement from the apex of the arch tracing and avoids locking a patients jaw in a certain position.

3. Intraoral procedure: Gothic arch developed while the central bearing point is locked at the apex of the tracing and plaster is injected between the occlusion rims and central bearing point as the recording medium.

4. Direct check bite method: Most common material is wax. (wax distorts) Secured on occluding surfaces and made with equalized pressure.

5. Functional recording method: Frequently call a chew-in, allows the patient to indicate the position of CR by functional movement. Accomplished by abrasive material, wax, or studs placed on the occlusal rims.

Summery: Many methods are acceptable. The purpose of this paper is to stimulate more thought on the problems of recording CR.10-007. Wood, G.W. Centric relation and the treatment position in rehabilitating occlusions: A physiologic approach. Part I: Developing optimum mandibular posture. J Prosthet Dent 59:647-651, 1988.Purpose: The article discussed a physiological clinical approach to developing optimum mandibular posture and clinical methods of recording this posture when rehabilitating complete occlusions.Methods & Materials: NoneResults: NoneDiscussion: The purpose of occlusal orthopedic therapy is to give tissues a functional opportunity to approach their optimum physiologic health. the prosthesis should provide a firm nondeflective occlusion.      Fabricating occlusal orthopedic interim prosthesis: Make acrylic provisional restorations that provide optimum occlusion at the proper vertical dimension. Periodic adjustments will be necessary. This will allow for an easier recording later.     Three methods discussed to determine CR are free arcing by the patient, resisted arcing with patient bracing, and manipulated arcing with dentist bracing.10-008.  Hickey, J.A. Centric relation, a must for complete dentures. DCNA Nov 1964:587-600.Complete dentures have no means of attaching to it bony support so, to maintain stability, it is necessary for the opposing teeth to meet evenly on both sides of the arch within the normal functional range. CR is the only position within the functional range that even contacts can be established and therefor, it is a must for complete dentures. To eliminate error in a fabricated

denture, CR records must be made at the exact VDO desired and accurately transferred to the articulator. Reasons to construct a complete denture in CR are:1. CR is the only position that can be routinely repeated and reproduced in an edentulous patient.2. Mounting the casts in CR eliminates the problem of determining how far anteriorly to this most retruded position centric occlusion should be established.3. CR must be recorded to permit accurate adjustment of the condylar guidance of the articulator for eccentric movements.4. Opposing artificial teeth will likely contact in CR when the proprioception of the natural teeth is absent.5. An accurate CR record orients the lower cast in the correct relationship to the opening axis of the articulator.The author discusses three methods of recording centric relation.The physiologic technique includes swallowing procedures and chew-in records. Movement of the rims on the supporting tissue, the patient not reaching the most retruded mandibular position as he chews side to side and resistance of the material used often result in a lack of consistency in the mandibular position. The graphic indication of mandibular position is recorded using intraoral and extraoral tracing devices. The recording elements being supported by movable tissues and any discrepancy in opposing ridge size or position can result in erroneous records.Direct interocclusal records are made by an interposing recording medium between occlusal rims. The author prefers this method because of it's simplicity and lack of mechanical devices. He warns that accuracy is dependent on clinical judgement by the dentist and cooperation between the dentist and patient.10-009. Glickman, et. Al. Telemetric comparison of centric relation and centric occlusion reconstruction. J Prosthet Dent 31:527-582, 1975.Purpose: To study a completely reconstructed natural dentition under actual function to determine whether CR or CO relationships are used during chewing and swallowing.Discussion: Two full mouth restorations were made for a patient, one fabricated with casts set in intercuspation and the other with casts in CR. Telemetry tests were conducted to determine how each set-up affected the tooth contact patterns during function. No significant change in the frequency of contacts and glides occurred after placing either reconstruction except after three weeks of wearing the set-up built in CR. The findings indicated that adjusting to an occlusion set in CR does not readily happen in the three week testing period. The patient tended to function in the existing CO position. The author concludes that the use of the terminal hinge axis in oral rehabilitation is subject to question because the patient will not function in this position.     The distance between CR and CO is variable and unpredictable so the use of the terminal hinge as a reference point is also questionable. CR is tolerated in complete denture set-ups because the proprioception of the PDL does not exist anymore.10-010. Shafagh I, Yoder JL, Thayer KE. Diurnal variance of centric relation position. J Prosthet Dent 34:574-582, 1975.Purpose: To investigate diurnal changes in centric position within a period of one day.Materials/Methods: Ten men and three women with Angle Class 1 occlusions, ranging in age from 20 to 30 years of age, with no evidence of systemic or physiologic dysfunction and normal TMJs. Centric relation was repeatedly recorded for thirteen patients at 9:00 a.m., 3:00 p.m., and 9:00 p.m. on a single day. Denar model D4A articulator was used with a kinematic facebow at

each appointment for consistency. The dentist used the chin point guidance technique for positioning the mandible using an anterior programmer, also called " anterior stop" or "anterior jig". To avoid subject fatigue the entire procedure was done in approximately 25-minute appointments separated by 5-½ hours rest.Results/Discussion: Various positions of the condyles observed on sagittal tables could be attributed to 1) nonadjustability of the intersagittal distance of the instrument to the intercondylar distance of each subject; 2) the inability of the patients musculature to allow a pure hinge movement; 3) diurnal variance in the TMJ; 4) variations in location the hinge-axis and transferring it to the articulator; 5) invalidity of the stationary hinge-axis theory.Conclusions: On the basis of the analysis of the data collected in this experiment, the following conclusions were made:     1. Centric relation was repeatable for a few patients but in most there was variation. The greatest variation         was in the superoinferior direction. There was no time of minimum variability.     2. In many patients the condyles were in their most anteroinferior position in the morning and in their most         superoposterior position in the evening. This may indicate that there is a diurnal pattern in the position of         centric relation possibly related to fluid content in the joint.     3. Depending on one's definition of centric relation, one time of day may be favored over another due to diurnal         bias. If the most retruded and superior position of the condyles is desired, the evening seems to be a better         time for making CR records.     4. Freedom to move to some degree around a clinically determined centric relation position may have merit          as a treatment philosophy.10-011. Gilboe, DR. Centric relation as the treatment position. J Prosthet Dent 50:685-689, 1983.Purpose: To analyze the morphology of the TMJ not as a bone to bone mechanism, but as a bone to tissue to bone mechanism. Materials & Methods: NoneResults: NoneDiscussion: The position of the disc id important in centric relation as the middle zone or central bearing area has no vascularity or innervation and therefore is adapted to accept pressure.Centric relation redefined: The most superior position of the mandibular condyles with the central bearing area of the disc in contact with the articular surface of the condyle and the articular eminence. This position may not always be possible to obtain due to anterior dislocation of the disc.10-012.  Williamson E.H., et al. Centric relation: A comparison of muscle determined position and operator guidance. Am J Ortho 77:133-145.Purpose: 1. To determine the direction and magnitude of shifts in condylar position when an interocclusal record is formed by biting hard or easy on a leaf gauge using ZOE as compared to the use of a wax interocclusal record.2. To determine whether the temporal or the masseter muscles are most active in seating the

condyles in centric relation when a leaf gauge is used.Methods & Materials: The sample consisted of fifteen adults, 21-35 years of age. The Vericheck instrument was used to compare the condylar position when different interocclusal records were made using three separate techniques of recording centric relation.1. Hard bite on the leaf gauge for 5 min.2. Bite "half as hard" as technique #13. Bite into pink wax while guided by the operator.Electromyographic recordings were concomitantly made.Conclusion: 1. Biting hard tends to cause the condyles to be forced posteriorly and away from the articulating surface of the eminence.2. Biting easy with the leaf gauge allow the physiologic placement of the condyles in the glenoid fossa.3. The temporalis muscles have more influence upon centric relation condylar position than the masseter muscles.10-013.  Serrano, P.T. and Nicholls, J.I.  Centric Relation Change During Therapy with Occlusal Prostheses. J Prosthet Dent 51:97-105, 1984.Purpose: 1. To evaluate the change in location of centric relation with time2. To discover if CR stabilizes within a period of 3 months in patients undergoing corrective occlusion prosthesis therapyMaterials & Methods: Eleven patients, 25-48 years of age, were selected.#1 A modified Lucia jig was made for each patient. The patient's jaw was gently guided to close until contact was made with the anterior jig/ZOE recording medium. Casts were fabricated and mounted using the ZOE record. #2 A corrective occlusion prosthesis were fabricated and inserted. Records were made after 1,3,7,14,30,and 90 days.Reference points were established on the mounted casts and measurements made.Results: 1. Corrective occlusion prosthesis therapy did not improve the reproducibility of centric relation in asymptomatic patients. 2. Centric relation is not one position but is a range of positions.3. The range of CR variation is greater laterally than antero-posteriorly.10-014. Lucia, V.0. Centric relation - theory and practice. J Prosthet Dent 10:849-856, 1960.Purpose: To locate a "center" that will enable us to reproduce the patient's movements on a suitable articulator and execute our work more intelligently and with grater ease.Principles & Belief’s: 1. There is one hinge axis.2. By the use of twin Gothic arch tracings in the horizontal plane, it is possible to locate the centers of lateral movement and can be duplicated on an articulator that has an adjustable intercondylar distance.3. Centers of rotation are made of two components, the center of vertical motion and the center of lateral motion, one in the same center, one in each condyle.4. Proprioceptive impulses are responsible for the awareness of the position of the mandible in space, natural reflex acts of the mandible are to close in a lateral or lateral protruded position.

Therefore the patient must be deceived by keeping the teeth apart. The patient must be trained and guided to execute the terminal hinge action.5. Lucia method to record an interocclusal record to mount the lower cast to the articulator using Tenax wax, Sure-Set wax and Aluwax.6. It is necessary to transfer the centers of lateral motion to an articulator if the other movements have been reproduced, this is accomplished by the use of twin Gothic arch tracings on a suitable articulator which can be adjusted for intercondylar width.Summary & Conclusion: 1. By having the centric relation of the mandible to the maxillae properly related on an articulator, the dentist can develop the centric occlusion accurately according to his own specifications.2. Functional movements must seat the condyle in the terminal hinge position, Centric occlusion should be built to occur at centric relation.3. Regardless of whether we believe that centric occlusion should be slightly anterior to this terminal hinge position, this is the only constant, repeatable position that can be used to check the work as we proceed. 10-015a. Guichet, N F. Biological laws governing functions of muscles that move the mandible. J Prosthet Dent 37:648-656, 1977.Purpose: To clarify if occlusal contacts cause specific responses in particular muscle groups and if there are precise laws which quantify the responses of the muscles to a particular occlusal contact pattern.Materials & Methods:  Description of how to formulate a study based on clinical observations. No subjects described other than three generalized groups of study hypothesis to support clinical observations.Clinical Observations: The reciprocal muscle response induced in the SCM muscle by functions of the lateral pterygoid muscle to advance the condyle can be demonstrated by grasping the belly of the right SCM and pull in a lateral direction; by pressing at the opposite side of the mandible at the premolar site a response is felt at the SCM.     Lateral pterygoids will be in chronic contraction for the patient who has an occlusal condition that programs both condyles to be maintained in an advanced position so that the teeth can fit in MI. Chronic muscle contraction will be felt in both SCM muscles which results in chronic pain in the back of the head and neck.     Just as the occlusion programs functions to locate the mandible in the horizontal plane, the occlusion will also program muscle functions to locate the mandible in the vertical plane.      A deflective contact in CR on the mesial incline of the lingual cusp of the maxillary right second molar causes pain in the right lateral pterygoid muscle (commonly diagnosed as earache) and in the right SCM (neck pain) or right occipital region at the attachment of the SCM (pain on back of the head). Occlusal contacts can program responses in the muscles that move the mandible and reciprocal responses in their antagonists to produce symptoms frequently diagnosed as " referred pain". Summary: Many factors other than proprioception originating from occlusal contacts of teeth program jaw position and the functions of the muscles that move the mandible. Once this is understood, an accurate diagnosis can select the course of patient treatment.10-015b. Niles F. Guichet, D.D.S. Biologic laws governing functions of muscles that move the mandible. Part II. Condylar position. J Prosthet Dent 38:35-41, 1977.

Purpose: specific muscle responses programmed by specific types of occlusal contacts, based on clinical observation of modified muscle responses related directly to occlusal treatment procedures.     The direction of the resultant force vector to the occlusal loading determined proprioceptively, governs functions of the muscles that move the mandible.     If occluding forces are applied parallel to the long axis of the tooth, the tooth has maximum load bearing ability without proprioceptive sensors signaling for inhibition of the application of the load. If the applied forces are not in the direction of the long axis of the tooth upon application of a relatively minor load, certain periodontal ligaments will be stresses to their physiologic limits, initiating a proprioceptive signal to inhibit further application of the load.     There is a physiological limit to the amount of stress which the periodontal fiber can withstand.     In order to prevent damage during chewing, periodontal ligaments are equipped with the proprioceptive mechanism This signal induces a protective muscle response such as an opening reflex or inhibited movement. Condylar position:  Condylar positions of the mandible at rest as it moves to maximum intercuspation are programmed by the occlusal scheme.     The ability of the dentist to modify the occlusion and reprogram the condylar position and muscle response is easily demonstrated clinically in occlusal treatment procedures.     When clutches are removed, the teeth do not fit together properly. After several jaw closures the muscles reprogrammed the condylar position to complement the prevailing occlusion. This phenomenon illustrates the potential of the dentist to almost instantly reprogram the musculature and condylar position by occlusal treatment.      The ability of the occlusion to program condylar position accounts for the patient’s repeated ability to avoid damage.     Patients avoid occlusal contact on prematurities.     The challenge in obtaining an accurate centric relation record is not so much one of obtaining an indexing registration of the mandibular teeth to the maxillary teeth as it is one of how to relieve stress in the muscles or reprogram them so they will allow the condyles to seek and retain the position of centric relation. 10-015c. Niles F. Guichet, D.D.S. Biologic laws governing functions of muscles that move the mandible. Part III: Speed of closure - manipulation of the mandible. J Prosthet Dent 38:174-179, 1977.Purpose: To study the effects of occlusal contacts on the muscles that move the mandibleDiscussion: This is the third part of a series that deals with how specific muscle responses are programmed by specific types of occlusal contacts. The article reviews a model to facilitate in developing jaw-manipulation skills.     There are four "independent personalities" in this scenario, the dentist, the patient, the patients protective reflexes, and the gnathostomatic system.     Basically, when the dentist approaches the patient to make a CR registration the patient "braces" (protective reflexes) for a potential damaging premature occlusal contact.     Hence, there is a there is a programmed muscular response to brace the condyles in the most physiologic or protected mandibular position in consideration of the existing occlusal condition.     The author compares the deflective occlusal contact to an irritation. As an analogy, if a patient had an extremely sore wrist, the doctor must approach the area slowly and carefully so as not to induce a protective reflex in a patient. This is in contrast to a patient with a vaguely sore, chronic

wrist pain. Here the doctor could approach the sore part with greater speed before a protective reflex would be initiated.     The same situation is true with teeth, with respect to the speed the dentist can forcibly arc the mandible in CR, as deflective occlusal contacts are removed in occlusal equilibration.Three examples are given for centric prematurities on the lingual cusp of a first molar, cuspal inclines of a second molar, and on steep inclines on the posterior segments of dental arches, the last example with occlusal contact on steep inclines is the most difficult to manipulate the mandible into centric relation. This is because since the vector of force is contrary to the long axis of the tooth, the ability of the tooth to tolerate an occlusal contact in CR is limited. 10-015d. Niles F. Guichet, D.D.S. Biologic laws governing functions of muscles that move the mandible. Part IV: Degree of jaw separation and potential for maximum jaw separation. J Prosthet Dent 38:301-310, 1977.Purpose: To emphasize that there definite principles by which muscles respond to occlusal contacts.Discussion: This the fourth and last part to a series on the biological laws governing functions of muscles that move the mandible.     The article discusses how a patient will also exhibit a "protective reflex" to the hinge opening of the mandible depending on the occlusal prematurity in centric relation.     The distance that the patients mandible can be depressed from occlusal contact before the patients musculature inhibits further opening (protective reflex) is termed the physiologic zone of jaw manipulation. This is a protective reflex in the patients musculature, designed to prevent damage to the tooth that first makes occlusal contact in closure at that condylar position.     The more equilibrated the patient is , the higher the physiologic zone, ie there is a neuromuscular release and the mandible moves without interference from the muscle.      An example here is a premolar with a deflective occlusal contact will allow only 200 stress bearing units which is the physiologic limit load of that tooth. This would be equal to 2mm.     In a dentition that had a full complement of teeth, with four posterior teeth that had simultaneous contact, there would be 1300 stress bearing units which would equal to 13mm of the physiologic zone of jaw manipulation.     The physiologic zone is also decreased by the loss of periodontal ligament and the drifting of teeth.     A single anterior restoration may cause a deflective occlusal contact when the mandible is in CR thus programming the retractor muscles (posterior belly of the temporal and digastric) to function and protect the tooth from trauma. In some clinical situations, a wax programmer may be used to promote simultaneous even contact of the anterior teeth (this relaxes the elevator and depressor muscles of the mandible) and facilitate a more accurate centric relation record.     In clinical situations, an anterior jig may be used to disengage premature posterior tooth contacts, which cause splinting of the condyles by lateral pterygoid muscles.Conclusion: Neuromuscular release of the mandible may be accomplished by equilibration of the natural occlusion, orthodontics, restorative procedures, or surgery. Most of the time it is a combination of these procedures. The criteria for success is not the method utilized, but the neuromuscular response to the treatment.

Section 11: Centric Relation Recording Methods(Handout)

Centric relation – The maxillomandibular relation in which the condyles articulate with the thinnest avascular portion of their respective discs with the complex in the anterior superior position against the shapes of the articular eminences. This position is independent of tooth contact. This position is clinically discernable when the mandible is directed superiorly and anteriorly. It is restricted to a purely rotary movement about the transverse horizontal axis.Deprogrammer –Various types of devices or materials used to alter the proprioceptive mechanism during mandibular closure.Myocentric – the position to which the muscles carry the mandible if no deflective factors exist on the teeth or occlusion rims. Myocentric position is recorded automatically, without manipulation of the mandible by the dentist or voluntary closure by the patient, by the use of an electronic device called the Jankelson Myo-Monitor.Interocclusal Record Materials.1.  Accuracy of baseplate wax, SS White and Hygienic:      Millstein (1973), described effects of initial heating temp - 121, 126, 131, initial closing pressure - 102 psi, 136, 172, storage environment - cold water at 12 degrees C, tap water at 25 degrees C, air cooling at 25 degrees C and storage time - 2, 6, 48 hours on accuracy of recordings made with baseplate wax. What were the results of each? - 102 psi were statistically significant causing increased vertical displacement.- Initial temp variation was significant for Hygienic wax vertical displacement increased at 121 degrees and with double-thickness of wax. - Water storage produced greater vertical and rotational changes than air.- Water storage produced the greatest change and air cooling the least.- Effects of time were inconsistent. No one storage time is preferred. 2.  Effects of dimensional change of gypsum materials described by Roraff:- Least expansion - yellow stone with slurry .0017"- Most expansion - impression plaster .0056"- Shim stock .0005"- Double mount to minimize the mounting discrepancy caused by linear expansion.3.  Vertical interocclusal error produced by:- Zinc-oxide eugenol paste - (Super Bite) resulted in open cast relationships.- Aluwax - most variable and least reliable.- Silicone putty - least error- Polyether - least errorElastomeric’s showed a decrease in vertical with a thicker record and an increase with a thinner record that were statistically significant but perhaps not clinically important.4.  Fattore evaluated the accuracy of recording materials:- Two thicknesses of base plate wax - wax rarely registers accurate incisal forms- Reinforced wax- The waxes were consistently unreliable.- Zinc oxide eugenol paste - difficult to modify, dehydrates, cracks, rarely used twice, flash may prevent accurate seating of the casts - second in accuracy.- Polyether - may cause casts to open, "spring".- Polyether with a carrier - second in accuracy.- Polyether without a carrier - most accurate

Distortion occurred more frequently in a vertical direction, followed by an anterio posterior direction.5.  Gysi listed four methods of "adapting" the articulator:- plastic material - wax or compound.- plaster- extra-oral graphic method with face-bow- intra-oral dentographic method (after Luce)- Plastic led to great error. Compound cooled more rapidly were it was thin. - An error of 25 degrees was made on the sagittal condylar path.- Plaster was practicable.- Extra-oral - most reliable for CR, 5 degrees in the condylar path. 6.  Balthazar-Hart (1981) examined the accuracy of:- Zinc oxide eugenol paste - Eugenol-free-zinc oxide paste- Silicone putty- Polyether registration materialWhile these materials are similar to impression materials, they have been modified to give them different handling characteristics.- Eugenol free zinc oxide paste exhibited no statistically significant difference in dimensions.- With polyether, silicone, and zinc oxide eugenol paste there was a statistical difference between the die and the samples at the immediate reading and throughout the experiment for 168 hours.- Polyether showed the least difference and zinc oxide eugenol paste the greatest.- All dimensional changes were negative except for ZOE during the first hour.- All were less than .02 % after the first hour.Recording Methods.1.  What were the methods that Kantor compared in 1973?     a.  Swallowing or free closure.  Patient was told to swallow and hold, manual guidance was totally avoided.     b.  Chin point guidance     c.  Chin point guidance with anterior jig.  To erase the proprioceptive patterns of habitual tooth contact. A wax wafer carries the metallic oxide paste.      d.  Bilateral manipulation.  They emphasize the importance of superior placement of the condyles. Little effort is utilized in gaining a posterior placement. The technique employs a specific superior guidance by the dentists finger position. At the same time downward pressure with the thumb attempts to seat the condyles in their most superior position. An attempt is made to obtain an arcing motion of the mandible in its most superior position. They suggest that a posterior guidance from the operator may move the condyles inferiorly.     i. Free closure or the Myo-monitor produced greatest variability for registering CR. Created the most protrusive positions.      ii. Bilateral manipulation greatest replicability in 85 % of patients.      iii. Chin point guidance with anterior jig gave the most posteriorly placed records. Created the most retrusive records. The deconditioning effect of the jig may allow the condyle to retrude where it is influenced by the posterior slope of the fossa, causing an inferior drop. Condylar drop may be associate with records made by this method.      iv. Chin point guidance showed less consistency than bilateral manipulation.          Variability results:

          Swallowing .4 mm          Myomonitor .38 mm          Chin point guidance .14 mm          Chin point guidance with a jig .07 mm          Bilateral manipulation .05 mm CR can be located by any one of many techniques, however there is variability in the results obtained by any technique.Does reproducability mean that it is correct? Not according to Atwood.2.  Kapur evaluated CR techniques in 1957. He found that intraoral tracing and extraoral tracing were more consistent as compared to the wax registration method.- "Flabby"ridges caused less consistency for the intra and extraoral methods.- Wax showed the most consistency on flabby ridges.The mean deviation in mm of all three methods approached .2-.4mm, which is barely perceptible clinically.3. Reproducibility of CR in three dimensions was evaluated by Hobo in 1985.      Techniques evaluated were :       Unguided closure       Chin point guidance       Bilateral manipulation      a. .2-.3 mm of maximum condylar displacement was recorded by the three centric relation registration methods.     b. Bilateral manipulation showed most consistent reproducability.- Condylar positions obtained by bilateral manipulation and guided closure were similar anteroposteriorly and superoinferiorly.- Unguided closure revealed appreciable lateral displacement, which indicates that muscular position is less reproducible laterally, and condylar displacement can be expected.- Chin point guidance placed on the condyle may result in harmful effect on the bilaminar zone, and inferior displacement may cause an occlusal discrepancy.4.  Comparison of articulator mountings to MRI was done in 1993.- The articulator analysis of CO and CR is statistically replicable.- Condylar concentricity was observed in half of the sample and remained constant in the other half in retruded, CO, and CR. Therefore the diagnosis of health on the basis of concentricity is not supported by the present data.- 13 % demonstrated anteriorly displaced discs that were not influenced by posterior condyle placement. - The concept of treating to CR as a preventive measure to improve disc-to-condyle relationships was not supported by this study.III. Technique and Materials 1. Lucia Jig for recording CR 1964. - To eliminate patient engram, reflex closure determined and guided by the teeth. The proprioceptive mechanism determines the path of mandibular closure.- Importance for periodontally involved teeth? Unless CO occurs when the mandible is in CR there will be strain on the periodontal tissues from a fulcrum effect on the teeth instead of the condyle.- Split cast to verify CR.

- Split cast to verify hinge axis using different VDO’s.- Train the patient to hinge in upper rearmost position.- Do not let the teeth touch. - Scribe a gothic arch on the jig.- Wax wafer 2.  Gothic arch apex relation to dentist assisted CR:- Many argue that the posterior position of the mandible locate with firm pressure by the thumb on the mandible may be less variable than the Gothic arch apex and thus be more reliable as a reference position for occlusion.- Myers in 1980 found no evidence to support the contention.3.  Woelfel leaf gauge (1986):- A thin flexible wafer is customized. Used with its leaf gauge it helps to guide the mandible superiorly and posteriorly and to maintain the desired minimum vertical opening.- The system uses a thin .15-.32 anatomically shaped partially perforated card laminated on both sides with .0015 inch Mylar. Each wafer has a combination slot handle for holding a new disposable leaf gauge. The slot tab, when bent down provides the necessary vertical separation for the wafer posteriorly in addition to the amount provided by the leaf gauge. The recording material of choice is polyether, next is zinc oxide-eugenol paste. - The leaf gauge of minimum incisor separation is necessary to prevent posterior tooth contact and negate an adaptive closure pattern (engram).The patient will close in the back and hold the leaf gauge firmly. The gauge is centered at a 45 degree posterior upward slope. For centric registration procedures, the vertical dimension should be opened by the leaf gauge 2-4 leaves beyond the first premature tooth contact. The leaf gauge assembly is positioned in the mouth and the dentist guides the mandible until the lower incisor engages the tab on the wafer beneath the leaf gauge. The paper leaf gauge is narrower and more solid than the plastic leaf gauge and thus forms a better anterior leg of the tripod with the two condyles on patient guided terminal hinge closures.Advantages: economical, anatomically designed, accurate, easy to use, disposable.4.  Ziebert in 1984 described a technique for stabilized baseplate interocclusal records for partially edentulous arches with prepared teeth.- Make an impression of the prepared teeth.- Cover the preps with putty on the lingual and incisal to give 1-2 m of relief, cover ridges with foil.- Resin is adapted over the teeth (1-2 mm over the facial surfaces of the anterior teeth) and ridges. - Apply adhesive to the ridge areas of the resin and reline the ridges of the baseplate on the working cast.- Reline the part of the resin that covers the teeth intraorally with bite registration paste. This will provide a stable recording base.- Adjust the occlusal rim to contact the opposing arch evenly at the anticipated VDO. - Make the vertical and CR record with wax or registration paste on the occlusal surface of the baseplate.- Protrusive and lateral records can also be made. 5.  Christensen described preserving a centric stop for interocclusal records particularly when the distal abutment is the last tooth in the arch. The author relates the working casts at the proper VDO by using a distal tooth as a vertical stop. Around the selected centric stop, leave an island

of enamel. Prepare the tooth with the enamel left on the cusp tip. Index the island with a 34 bur. Make final impression. Remove the enamel island. - Articulate the casts with the island.- Remove the island from the die.- Fabricate the unit.IV. Muscle Action and Tissue effects on CR. 1.  Lundeen studied the effect of muscle action on CR records in 1974.- First method involved using manual chin guidance to position the mandible in the terminal hinge position with both heavy and light contractions of the muscles to seat the condyles superiorly.- Second method employed the Myo-Monitor to stimulate muscle contractions. - Records were compared using the Buhnergraph.      3 records were compared:i.  Metal reinforced Aluwax, anterior stop chilled in ice water, posterior softened at 105 degrees. Imprints made in softened wax. This was classified as a heavy type of muscle contraction.ii.  Acrylic resin jig was made, apex of gothic arch tracing was identified. Fiberglass mesh frame with ZOE impression paste was used to complete the record. The muscle exertion was fairly light.iii.  Resin material was used to record the imprints, while the Myo-Monitor unit stimulated rhythmic contractions.- Aluwax showed the greatest number of superior condylar positions.- Acrylic jig CR was inferior to Aluwax by .5 mm on the left and .4 mm on the right. These were the closest to the hinge axis of the articulator. - Myo-Monitor were least consistent. They were inferior to Aluwax 1.75 mm on the left and 2.25 mm on the right.The differences between # 1 and 2 were due to the muscle contraction. - A technique with heavy contraction seems better. However there is some indication that the condyles may not remain in their most superior position following reconstruction. Celenza in 1972 found that a small movement space may recur as a result of tissue changes within the joint. This indicates that a physiologic constant may exist between the occlusion and the condyle-to-fossa relationship which will re-establish itself following the use of the most superior condylar position to reconstruct the patient’s occlusion.- Gibbs pointed out in 1971 that the condyles may not function as pressure bearing joints in the healthy dentition and introduced the concept of a tooth supported joint. They also suggest that damage to joints can follow the loss of posterior teeth, this could indicate that minimum muscular activity may be more physiologic. 2.  Strohaver in 1972 compared articulator mountings made with CR and Myocentric position records.- Methods for making CR records were selected for comparison.- Forceful guidance, ZOE paste, Lucia - Forceful guidance, wax- Voluntary retrusion, impression plaster- Forceful guidance by dentist, acrylic resin, Stewart jig- Myo-Monitor, imprint plastic- Hand articulation

Method 1 was least variable, most posterosuperior.Hand articulation for mounting the mandibular cast was least variable.Myocentric were the most variable articulator mountings of the six methods, and produced the most anteroinferior (protruded) relationships of the mandibular cast to the axis of the articulator.3.  Latta, in 1992 studied the influence of circadian periodicity on reproducibility of CR records for edentulous patients. Normal changes such as those resulting from circadian periodicity, have been demonstrated to affect the fit of complete dentures. These same rhythmic changes also affect CR records made for edentulous patients. Patients were divided into three groups and the dentures remounted twice on the same day. Twice in the morning - Twice in the afternoon- Once in the morning and once in the afternoon.- Compound was used for the record.The mean change for the AM group was .57 mm, PM group was .675 mm, and for the AM-PM group .932 mm.The circadian periodicity significantly affected CR records, suggesting that the denture fabrication process should include procedures to accommodate this phenomenon. Treating patients in the middle of the day will dilute the effect of circadian variations but is impractical. Providing occlusal freedom is a possible solution.

- Abstracts –11-001. Millstein, P.L. Determination of the accuracy of wax interocclusal registration. Part II. J Prosthet Dent 29: 40-45, 1973.Purpose: To study the effects of initial heating temperature, initial closing pressure, storage environment, and storage time on the accuracy of recordings made with single and double thickness samples of pink baseplate wax.Methods & Materials: Two different brands of pink baseplate wax were tested, S.S. White no. 9 and Hygienic extra-tough baseplate wax. One thousand two hundred samples were fabricated on upper and lower dentulous casts. The following factors were varied throughout the experiment: 1. Thickness, 2. Initial heating temperature, 121, 126, and 132 F, 3. Closing pressure, 102, 136, and 172 psi, 4. Storage environment, cold water, room temperature water and air, 5. Storage time and 6. Seating pressure. Both rotational and vertical displacement was measured.Results: Complete closure was never achieved regardless of the pressures used. The higher the closing pressure the less vertical displacement. Double thickness wax yielded a greater displacement than single thickness wax when lower pressures were used. Storage in water led to greater rotational displacement. S.S. white wax No. 9 offered less resistance to closure than Hygienic wax. The effects of varying storage times were inconsistent.Conclusions: Exact reproduction of the original wax registration was never achieved. The use of pink baseplate wax as an interocclusal registration will always result in some error.11-002. Roraff, A.R., and Stansberry, B.E., Errors caused by dimensional change in mounting material. J Prosthet Dent 28:247-252, 1972.Purpose: To investigate the effect of dimensional change of gypsum mounting materials on the accuracy of articulated casts.Methods and materials: A dental articulator was modified by adding custom mounting plates with a dial micrometer fixed to the lower plate. Mounting materials tested were Velmix (vacuum mixed), yellow stone (vacuum mixed), impression plaster (hand mixed), yellow stone and 80cc slurry water, (hand mixed), laboratory plaster (hand mixed), yellow stone (hand mixed), and

yellow stone and 70cc slurry water (hand mixed). A thickness of 37.5 mm of material was used. Ten samples of each of the seven combinations of materials were measured. Results: The mean linear expansion measured varied from 0.0056 inch with impression plaster to 0.0017 inch using 80cc thick empirical slurry. Expressed as a percentage, this ranged from 0.11% to 0.38%. Conclusion: Compared to the thickness of 0.0005 inch shim stock, the expansion could be critical. It is suggested by Kingery and Brewer that a two step procedure for articulation be utilized: first, by initially leaving a small thin space between the cast and mounting material, then by filling the space with a second mix after the first mix has set. The reduced quantity of material will not produce as much change in the relationship between the casts as a larger amount of material would.11-003. Lucia, V. O. A technique for recording centric relation. J Prosthet Dent 14:492-505, 1964.Problem: The mechanical procedures necessary to relate the mandible to the maxillae present the problem. There is not a single ideal material that we can place between the teeth that would allow the patient to close in a perfect terminal hinge position. This is especially true in patients with strong engrams.Purpose: To present a technique for recording centric relation.Materials & Method: Critical steps in the technique are described.1. Locate the centers of rotation, (a) hinge axis, and (b) centers of lateral rotation.2. Prepare the upper cast for the split-cast technique.3. Relate the prepared upper cast to the centers of rotation by means of a facebow transfer.4. Form the wax wafer tray.5. Construct and adjust the centric relation jig in order to interrupt the reflex action of the muscles and permit a normal closure of the jaws.6. Check the wafer and jig to make sure there is no tooth impingement against the wax wafer.7. Make the interocclusal centric relation records.8. Trim the interocclusal records with a curved tissue shears having serrations on one blade.9. Replace the records in the mouth to eliminate any possible distortion of them.10. Relate the lower cast to the upper cast by means of the interocclusal record and attach the cast to the articulator.11. Check the accuracy of the mounting by using the second and third interocclusal records and observing the fit of the parts of the split cast.Conclusion: This method has enabled us to consistently and accurately check one centric relation record against another. The important difference between this procedure and others where anterior stops have been used is that the adjustment of the DuraLay jig is responsible for training the patient to place his mandible in the centric relation. No special skill is required to carry out the procedure, and it can be accomplished by any dentist.11-004. A Study of Interocclusal Record Materials. Mullick, SC et al. J Prosthet Dent 46:304-307, 1981.Purpose: To determine the vertical assembly error in articulating dentulous casts on an articulator as affected by three parameters (materials, the distance between the prepared and opposing teeth, and operator variability)Materials and Methods: Alginate impressions from a patient having a complete dentition were poured in stone and articulated to an articulator using a facebow and mounting rings. Full crown preparations were simulated on all posterior teeth except the upper left dental arch. The

articulator, used for making the interocclusal registration, eliminated patient variability. The materials used were Super Bite, Aluwax, Input (silicone putty), Coltoflax silicone putty, Reprosil (silicone putty), Flexane silicone putty, and Ramitec (a polyether)     For all materials, the first measurements were made with the articulator closed before removal of the record. The upper member of the articulator was disassembled, the interocclusal records were trimmed, and the articulator base with the lower cast and assembly was returned to the measuring stand for second measurements.     Three operators repeated the tests (10 times) for every material on both the right and left sides. Two operators were experienced dentists and one was a dental student. Results and Discussion: The difference between the first and second readings, were errors that were due to material or operator variability,.      Aluwax (extremely open to closed relationships of the mounted casts)     Super Bite (extreme variability)     Elastomerics (easy to manipulate, little resistance to closure, accurate cast reproduction)     Both the Aluwax and the Super Bite were disqualified by Cochran’s Test from     the ANOVA due to extreme variabilities.Conclusions: Aluwax was the most variable and least reliable of all materials.Super Bite consistently resulted in open cast relationships. The five elastomers resulted in the least amount of errors. The two different thicknesses of elastomeric records resulted in statistically significant mounting discrepancies. The overall average showed that the inexperienced student performed as well as the two experienced dentists. 11-005. Lundeen, H.C. Centric relation records: The effect of muscle action. J Prosthet Dent 31:244-251, 1974.Purpose: To compare condylar positions obtained by two methods of making interocclusal centric relations records.Methods & Materials: Stone casts were fabricated for 8 dentate adults. Hinge-axis points were located and a hinge-axis facebow used to transfer records to Whip-mix articulator. The mand. cast was articulated with a CR record. The condylar posts of the mandibular frame of the articulator were replaced with a bar containing two pointer rods ( Buhnegraph). The pointed rods were collinear with the opening and closing axis dimples on the sides of the condylar housings and opposed graph paper on the outer surface of the condylar housing of the articulator. The axis point of the articulator was used as the basic reference position from which to orient and compare the three types of interocclusal records. The first method was the manual chin guidance. It was keyed by an anterior stop (wax or acrylic). Heavy (Aluwax/record "A") and light (acrylic resin jig-ZOE/record "B") muscle contractions were used to seat the condyles superiorly, while forming imprints of the posterior teeth in keyed records. The second method electrically stimulated muscle contractions using Myo-Monitor (record "C") and a resin recording medium between the opposing occlusal surfaces of the teeth. The tips of the pointer rods were marked on the graph paper with the record supported casts. Photographic enlargement was used to study the various recorded average condylar positions.Results:      the "A" records showed the greatest number of superior condylar positions.     The "B" records were located inferiorly to "A".     The "C" records were the least consistent.     The "B" records were closest to the hinge axis of the articulator.The difference between the condylar positions obtained with the "A" and the "B" records are

explained in terms of the magnitude of muscle contraction: ZOE requires several minutes to harden and it id difficult for the patient to maintain heavy muscle contraction throughout. If the treatment objective is to develop a new occlusal relationship to coincide with the most retruded and superior condylar position a centric relation technique employing heavy muscle contraction will be helpfulConclusion: The Buhnegrph device was shown to be an excellent method for comparing condylar positions obtained from various types of interocclusal records.   11-006a and b. Kantor, ME, Silverman, SI, and Garfinkel, L. Centric relation recording techniques. A comparative investigation. J Prosthet Dent 28:593-600, 1972. J Prosthet Dent 30:604-606, 1973.Purpose: To investigate the variability of centric jaw relation records obtained utilizing different clinically acceptable techniques that are currently (1972) in use.Discussion: (technique evaluation) Swallowing or free closure: Advocated by Shanahan. A preformed wax wafer was held in position against the maxillary teeth and the patient was instructed to "swallow and hold." Manual guidance was totally avoided. There was no contact between the dentist and the patient.     Chin-point guidance: Described by McCollum. Also advocated by Kornfeld, Thompson, Aull, and Sloan.     Chin-point guidance with anterior jig: Described by Lucia. He felt an inclined plane attached to the maxillary incisors would help to fully seat the condyles in their fossa and aid in record making. The anterior jig was made to separate the teeth minimally and , if possible, to erase the proprioceptive patterns of habitual tooth contact.     Bilateral manipulation: Used by those who adhere to the functionally generated path technique. They emphasized the placement of the condyles in a superior position. The technique employs a specific superior guidance to the mandible by the dentist fingers. At the same time, the dentist applies downward pressure with his thumbs, thereby attempting to seat the condyles in their most superior position. Little effort is made to gain a posterior placement. An attempt is made to obtain an arcing motion of the mandible in its most superior position.     Myomonitor: A technique which uses electrodes to provide impulses to the 5th cranial nerve, as well as to the mandibular division of the 4th cranial nerve.Materials and Methods: Fifteen subjects with complete dentitions and minimal dental restorations were selected for the study. Ages from 21 to 45. 12 men and 3 women. No patients had a removable prosthesis. Twenty-four centric relation records were made for each patient. Six record of each of the above techniques. Additional records were made using the myomonitor and evaluated. All records used a wax wafer with a metallic-oxide paste. Cast were made of each patient and articulated with a face bow record. Attached to the upper member was a fixed scribe which when lowered recorded a specific point on an interchangeable plate. The interchangeable plate would be transferred to a microscope and evaluation of the mark in an x and y axis was located at 25x. The six dots were joined to give an indication of the degree to which that specific guidance system was replicable and consistent with the others.Results: The results are expressed as a median variability for the amount the records deviated from their mean point. Swallowing records deviated 0.40mm. Chin-point guidance records deviated 0.14mm. Chin-point guidance with anterior jig records deviated 0.07mm. Bilateral manipulation records deviated 0.05mm. The myomonitor produced a variability of 0.38mm.Conclusion: Bilateral manipulation produced the smallest area of displacement of maxillomandibular relation records when compared to the other techniques tested. The most

protrusive records were made with the free-closure or myomonitor technique. The most retrusive records were made with the chin-point guidance with an anterior jig11-007. Kapur, K.K. and Yurkstas, A.A., An evaluation of centric relation records obtained by various techniques. J Prosthet Dent 7:770-785, 1957.Purpose: To examine various available methods of recording centric relation.Subject: Although several techniques are mentioned in the article, three are specifically evaluated for comparison purposes: 1) the intraoral tracing procedure (Hardy), 2) the wax registration procedure (Hanau), and 3) the extraoral tracing procedure (Stansbery) Methods and materials: A total of 31 patients were utilized. Three interocclusal records were made for each patient. Ridges were categorized as flat, well developed, or flabby. Registrations were compared on a recording tripod and variations were recorded on millimeter graph paper.Results: The intraoral tracing procedure produced the most consistent results. There was no statistically significant difference between the intraoral and extraoral tracing methods. The wax method seemed to be the least consistent. In patients with flabby ridges, the tracing procedures became less consistent as compared to good and flat ridges. The wax method showed the most consistency on flabby ridges.Conclusion: The mean deviation in millimeters of all three methods approached 0.2-0.4mm. This amount in the case of an edentulous patient is barely perceptible clinically.11-008. Myers, M. L. Centric relation records – historical review. J Prosthet Dent 47:141-145, 1982.Problem: Many prosthodontists feel that recording centric relation is the most difficult, yet the most important step in treating edentulous patients with complete dentures.Purpose: To review the philosophies and methods of recording centric relation.Materials and Methods: Historical review.Discussion: Centric relation is generally defined as the most retruded relation of the mandible to the maxillae when the condyles are in their most posterior unstrained position in the glenoid fossa from which lateral movements can be made, at any given degree of jaw separation. There are four categories of centric relation records: direct checkbite recordings, graphic recordings (intraoral and extraoral), functional recordings, and cephalometrics.

Direct Checkbite Interocclusal RecordingsPhillip Pfaff (1756): first to describe the imprecise "taking the bite" in wax. Also called mush, squash, biscuit bite. Christensen (1905): used impression wax.Greene (1910): mushbite of compound and plaster wash. Occlusal rims added later for stability. Had patients hold mouth open 10 seconds to fatigue muscles. Invented the "Pressometer".Brown (1954): recommended repeated closures into softened wax.Trapozzano: wax checkbite was the technique of choice for recording CR. Light pressure.Schuyler: modeling compound was preferable because it softened more evenly, cools slower and does not distort as much as wax. Light pressure. Verification of records.Payne, Hickey, and Boos: plaster is more accurate, less material needed, less pressure.Hanau: Realeff = resilient and like effect. Concern for equalization of pressure when recording the bite.Wright: of the four factors, resiliency of tissue, saliva film, fit of bases, and pressure, the dentist cannot control pressure. He therefore advocated zero pressure

Gysi: plaster is the only accurate material.Page: centric records were worthless the instant the surfaces are altered.

Graphic RecordingsBalkwill (1866): Gothic arch tracing. Hesse (1897): "needle point tracing". Gysi (1910): extraoral incisal tracer on maxillary rim traced onto the tracing plate attached to the mandibular rim.Phillips developed a plate for the upper rim and a tripoded ballbearing mounted on a jackscrew for the lower rim. The occlusal rims were removed and softened compound was inserted between the trial bases. This innovation was called the "central bearing point" which supposedly produced equalization of pressure on the edentulous ridge.Stansbery (1929) used a curved plate corresponding to Monson’s curve mounted on the upper rim. A central bearing screw was attached to a lower plate with a reverse-Monson curve. Plaster was used to form the centric registration.Hall (1929) used the Stansbery’s technique but substituted compound for the centric relation record. Hardy and Pleasure the intraoral tracer called the Coble Balancer.Robinson designed the Equilibrator with a hydraulic system and four bearing pistons.Silverman used the intraoral Gothic arch tracer to locate the biting point of a patient.Hanau conceded that Gysi tracing was satisfactory to check records, but that universal usage was not good. Tench stated that the Gysi tracing technique was the only means of recording CR. (5-degree error vs. 25-degree error of wax and compound).Criticism of Gothic arch tracings: equal pressure unattainable, shifting bases, difficult to see, too much patient cooperation needed, sore spots cause eccentric tracings.

Functional RecordingsGreene (1910) Wax occlusal rims and plaster index.Boos used the Gnathodynamometer to determine the vertical and horizontal position at which a maximum biting force could be produced. His Bimeter was mounted on the lower occlusion rim with a central bearing point against a plate on the upper occlusion rim. Plaster registrations were made.Shanahan placed cones of soft wax on the mandibular rim and had the patient swallow several times to record centric relation.

CephalometricsPyott and Schaeffer used cephalometric radiographs to record CR and VDO.This method never gained widespread usage.Conclusion: In the final analysis the skill of the dentist and the cooperation of the patient are probably the most important factors in securing an accurate centric relation record.11-009. Fattore, L. et al. Clinical evaluation of the accuracy of interocclusal recording materials. J Prosthet Dent 51: 152-157, 1984.Purpose: To determine the clinical accuracy of waxes, zinc oxide-eugenol, and polyether dental materials for recording interarch dental relationships. Materials and Methods: The study utilized thirty-one patients (25-30 years old) with a full complement of teeth. There were 17 women and 14 men, the criteria included also sparse restorative treatment and adequate occlusal stops, both posterior and anterior.Irreversible hydrocolloid impressions were made per arch and poured in stone. An arbitrary facebow was used, articulated to a Whip Mix articulator. The lower cast was hand articulated to

the upper cast in centric occlusion.Five types of interocclusal records were made of each patient, (1) baseplate wax (two thicknesses) (2) reinforced wax - Copruwax (3) ZOE paste - Kerr bite registration paste (4) modified, nonrigid polyether recording medium - Ramitec with a carrier (Coe Bite registration tray (5) polyether without a carrier.All measurement of the four recording mediums, were compared with that of the hand articulated full arch models in centric occlusion. The position of the hand-articulated mandibular casts with the maxillary casts were recorded on graph paper (using a Buhnergraph attachment that replaced the condylar spheres). This process was repeated when the interocclusal record was placed between the two casts. Measurements of the right and left condyles were recorded for each interocclusal record. Any measurements that deviated from the pre-established centric occlusion position in a vertical, anteroposterior, and declination-rotation direction were noted. The Buehnergraph could not accurately determine lateral movement.Results and Discussion: When waxes were compared with other recording mediums they were inferior, but still are popular due to cost and ease of manipulation.ZOE paste is reliable , but it dehydrates, cracks and tends to stick to teeth. (only a minimal amount of ZOE paste is advised)Polyether is an accurate interocclusal material. However, if improper technique is used, there is a "spring" to this material than can cause an error, ie. the casts to "open" in centric occlusion. Polyether should also be used sparingly avoid excess inaccuracies. Conclusions: The most accurate interocclusal recording medium was the polyether without a carrier. Next were the polyether and ZOE pastes with carriers, but this required a very disciplined technique. Recording waxes were consistently unreliable.Distortion occurred more frequently in a vertical direction, followed by an anteroposterior position11-010. Myers, M., Dziejma, R. and Goldberg, J. Relation of Gothic Arch Apex to Dentist-Assisted Centric Relation. J Prosthet Dent 44:78-81, 1980.Purpose: To compare centric relation position utilizing a gothic arch tracing and a patient unassisted recording versus a dentist-assisted recording. Methods & Materials: Twenty-two subjects between the ages of 20-30 had clutches fabricated to produce a gothic arch tracing at a specific vertical dimension of occlusion for each subject. Subjects were seated in a dental chair to orient Frankfort horizontal plane parallel to the floor. Three investigators measured recordings independently. Each subject had consecutive gothic arch tracings done on the first and seventh days. The unassisted recording was done first, and measurements were completed. The clutch plate was painted over with draftsmen fluid, the clutches were placed in the patient’s mouth, and the dentist-assisted the jaw movement posteriorly with thumb and forefinger on the patient’s jaw. Results: The dentist-assisted position was posterior to the unassisted position in 9 of 22 subjects on the first day and the seventh day. Out of the 9, only 4 subjects showed the dentist-assisted position posterior to the unassisted position on both days. The dentist position varied from the first to the seventh day in 20 out of 22 subjects. The unassisted position varied in all 22 patients. Results showed no statistically significant difference in the reliability of one method over another. Conclusion: No evidence to support the contention that the dentist-assisted jaw relation is more reproducible than the gothic arch apex tracing.

11-011. Strohaver, R. A Comparison of articulator mountings made with centric relations and myocentric position records. J Prosthet Dent 28: 379-390, 1972.Purpose: 1) To determine the precision of mandibular cast mountings made by several dentists utilizing four different techniques, 2) to determine whether consistent articulator mountings of a mandibular cast could be made using a myocentric position records using a Jenkelson myomonitor, 3) to evaluate the precision by which mandibular cast mountings could be made using the hand articulated maximum intercuspation method, 4) to compare the relative reproducibility of the jaw relationships produced on the articulator by each of these six methods.Materials and Methods: A single subject with healthy dentitions and a healthy masticatory system was used for the entire study. The subject’s hinge axis was located by using the Stuart head frame and reference plate assembly kit. An accurate set of impressions were made and casts were poured up in die stone. Holes were drilled into the cast and nine stainless steel rods were inserted as reference points for measuring. The rods were positioned so that when the casts were mounted the ends of the rods would form triangles in the frontal plane and the right and left sagittal planes. Five triangles were formed by the rods with each other and with the hinge axis on the articulator using this method. The maxillary cast was mounted to a Hanau OSU model 130-28 articulator by means of a kinematic facebow transfer. Four centric relation recording methods were used for relating the mandibular cast to the mounted maxillary cast. The first method (method Z) used a zinc oxide and eugenol paste as the recording material and also involved the use of a Lucia jig for use as an anterior deprogrammer. The second method (method W) used Aluwax reinforced with Ash’s metal. The Aluwax record used an anterior stop also made in Aluwax to prevent contact of teeth. The third method (method P) involved the use of impression plaster as the recording material and no forceful guidance of the mandible is used. Instead the patient is asked to pull his lower jaw back as far as he can and close into the recording material. The fourth method (method A) uses acrylic resin as the recording medium and the end of a tongue blade or Popsicle stick is inserted between the incisors as the subject closes into the recording material and the dentist pries slightly downward and backward to encourage posterior closing. Method M is the myocentric position which is made using the Jankelson myomonitor. Recording material is imprint plastic. The last method (method O) is hand articulation of the cast into maximum intercuspation. Method O was basically a control group for this study. Three guests (Dr. Huffman, Dr. Boucher, and Dr. Stuart) were invited to make a series of three records by each of the methods of centric relation records using these methods described and an additional series of three records using their preferred method: method Z for Dr Huffman, method P for Dr Boucher and method A for Dr Stuart. Casts were mounted and measurements were made. Results: Method Z produced the least variability in the mountings made. Method Z also produced the most posterior-superior relationship of the mandibular cast to the hinge axis. The least variable of all methods for mounting casts was method O. Myocentric (method M) produced the most variability of all mountings. Method M also produced the most anterior-inferior relationship of the mandibular cast to the hinge axis.Conclusion: the most retruded articulator mountings were also the most precise in this study. This retrusion involved forceful manipulation by the dentist.11-012. Gysi, A., DDS, Practical Application of Research Results in Denture Construction, JADA 16, pp.199-223, 1929.     If we are given the rotation points for the right and left lateral bites and the protrusive movement, we can determine by purely scientific methods(without sharks teeth), the size and

inclination of each facet of each tooth.What determines interdentation? The exact interdentation of the bicuspids and molars during the masticatory movements is determined by the movements of the three main points of the mandible, that is, the two condyles and the incisor point. Movements toward the right and left, when traced by the mandible on a recording plate, forms the gothic arch.     In the edentulous patient, the inclination of the incising or protrusive movement is entirely lost, whereas all other movements still exist as if natural teeth were present. We can vary this lost inclination at will on the articulator.     Any alteration of the height of the bite is a chair operation and not a laboratory operation. If the height of the bite is to be changed, it is better to do it at the chair, then to detach one cast from its support and reattach it in a new position, than to seek to change the bite by lengthening the incisor pin or by any other similar method.m    Relative importance of the movements:- The record of the lateral movements of the mandibular incisor point is the most important of all records of movements and the sagittal inclination of the condyle path is the next most important. It is sufficient if the articulator reproduces an average lateral condyle path of about 15 degrees.- We need not register the working movement of either condyle, because, in the horizontal plane, this is controlled by the balancing movement of the opposing condyle and the lateral movement of the incisor point.Four methods of adapting the articulator:     plastic material     plaster     extra-oral graphic method (with face-bow)     intra-oral dentographic method (after Luce)     Plastic material, wax or compound, led to great error. Compound cooled more rapidly where it was thin than where it was thick, and made unequal pressure on the bite rims.     An error of 25 degrees may be made.     Plaster material as a checkbite method is practicable.      The extra-oral method registers both the gothic arch and the sagittal condyle path inclinations. When the registering point is in the angle of the gothic arch, the mandible is in centric relation to the maxilla for this height of bite. This is considered the most reliable method of establishing centric relation.      The included angle of 120 degrees is the average. If the gothic arch is registered farther from the incisor point, the included angle will be greater. As intercondylar distance increases, the gothic arch angle gets smaller. The tracing will control the lateral movements of the incisor point, it will locate the axes for the lateral movements of the denture in approximately identical positions with the axes established by the natural dentition. After centric relation, this is perhaps the most important adjustment in denture construction.     A gothic arch of 100 degrees requires the formation of relatively steep facets on the teeth.     120 degrees requires facets with average inclinations.     140 degrees requires facets with less than average inclinations.     An error of 5 degrees may be made with this method.     Condyle path in relation to the occlusal plane varies from 0 to 50 degrees. In most cases it is about 30 degrees.      Bennett angle of 0, 12, and 24 degrees do not differ in the least in their cusp angulations. The errors that might result from differences in the inclination of this movement are smaller than the

unavoidable errors made during impression making and bite taking, setting up the teeth and the flasking and vulcanizing process. Therefore, we need not trouble ourselves, provided the articulator allows an average angle of 15 degrees.      The gothic arch variation, on the one side, is from about 50-70 degrees, a range of 20 degrees, while the condyle path may vary from 0-50 degrees.      The lateral movements of the incisor point are more important than are the lateral movements of the condyles, because they can be more accurately recorded and are more effective in adjusting the articulator. It is desirable that the articulator resemble the mandible in having lateral variability at the incisor point. The lateral variability at the condyles is not important.     Errors in the lateral incisor path are important than errors in the lateral condyle path. Second molars are about half-way between the incisor point and the condyles, so that practically all of the teeth lie in the half of the mandible adjacent to the incisor point and are strongly influenced by its lateral movements, while the condyles are so far away that they influence the lateral movements of the teeth little, and control by the incisor point renders that slight influence wholly negative.     The importance of mounting casts correctly:     The distance above or below the occlusal plane is less important than the distance from the intercondylar axis. To far forward will decrease the cusp height. To far backward will increase the cusp height. If the condyle path and incisor path are identical, it makes no difference where the casts are mounted, high, low, front or back.     We should not depart greatly from the sagittal inclination of the patient’s condyle path in the articulator if we desire good articulation. We must establish a much flatter sagittal inclination of the incisor path than the patient had with his natural teeth. There will be a wide divergence between these two path inclinations, and this necessitates the use of a face-bow. 11-013. Latta GH Jr., Influence of circadian periodicity on reproducibility of centric relation records for edentulous patients. J Prosthet Dent 1992 Nov;68(5):780-3.Purpose: To evaluate the effect of circadian periodicity on the reproducibility of centric relation records for edentulous patients.Materials and Methods: Complete dentures were made for 30 edentulous patients. The patients were divided into three groups and the dentures were remounted twice on the same day in a Denar Vericheck instrument.Discussion: The dentures for 10 patients were remounted twice in the morning (AM group), for 10 patients twice in the afternoon (PM group), and for 10 patients once in the morning and again in the afternoon (AM-PM group). Changes in position between the interocclusal records were measured on both the right and left horizontal X and Y axes and the sagittal Y and Z axes.Results: No significant changes were noted when horizontal versus sagittal or right versus left positions were compared, but significant changes were noted between the AM versus AM-PM time groups, and between the PM versus AM-PM time groups. The mean variability for the AM group was .577 mm, for the PM group was .675mm and for the AM/PM was .932mm. Conclusions: Circadian physiologic changes can have an effect on the fit of complete dentures and on the occlusion of complete dentures. The author suggests fabricating complete dentures during the middle of the day could help by averaging out theses circadian effects. It may not be practical, so another solution may be to include additional occlusal freedom to accommodate for this circadian change.11-014. Hobo, S. Reproducibility Of Mandibular Centricity In Three Dimensions. J Prosthet Dent 53: 649-654, 1985.

Purpose: To evaluate different techniques of condylar positioning and record the amount of displacement of the condyle in three dimensions with a newly developed electronic mandibular recording system.Methods & Materials: Ten adults with complete dentitions and minimal restorations and no history on TMD were selected as participants. A system for measuring the 3 dimensions of mandibular movement consisted of 3 dimensional optical sensors, a point light source, stainless steel upper and lower clutches, and altitude meter, and a microcomputer. The centric recording techniques used in this study were: 1. Unguided closure, 2. Chin-pointed guidance, and 3. Bilateral manipulation.     At least three measurements were produced with each technique, for a total of nine readings for each subject, and performed by one dentist.Results: The bilateral manipulation technique produced the most consistent data. There were statistical differences between chin-point guidance and unguided closure and bilateral manipulation. Conclusions: Approximately 0.2 to 0.3 mm of maximum condylar displacement was recorded by three centric relation record techniques. Bilateral manipulation showed the most consistent reproducibility and is recommended for centric relation records. Condylar position obtained by bilateral manipulation and unguided closure technique were similar anteroposteriorly and superoinferiorly . Unguided closure revealed appreciable lateral displacement, which indicates that muscular position is less reproducible laterally, and condylar displacement can be expected. Chin-point guidance placed the condyle posteriorly, inferiorly, and right-laterally and is not recommended.11-015. Woelfel, J. B. New Device for Accurately Recording Centric Relation. J Prosthet Dent 56:716-727, 1986.Purpose: To describe a new technique using the O. S. U. Woelfel Leaf Wafer.Methods & Materials: Centric relation is recorded using a thin, flexible perforated wafer with a thin mylar coating on both sides. A leaf gauge is used to provide minimum incisor separation necessary to prevent posterior tooth contact (to prevent an adaptive closure pattern or engram). An interocclusal recording material such as ZOE is placed on both sides of the wafer and the patient closes unassisted into CR position. The material can be trimmed and verified intraorally. The record should be used within 15 minutes to prevent dimensional changes with the recording material. Results: Advantages of a leaf gauge include: patient unassisted closure in CR, periodontal ligament proprioception is eliminated, and potentially negates patient’s engrams. Conclusion: Method is quick and easy for the patient and multiple records can be made. May be a concern that the recording is made with patient’s head tipped back and the leaf gauge is not a flat plane for the incisors to occlude against. Potential that the record obtained is not a superior anterior position. 11-016. Alexander, S. R., et al. Mandibular Condyle Position: A Comparison of Articulator Mountings and Magnetic Resonance Imaging. Am J Orthod Dentofacial Orthop 104:230-239, 1993.Purpose: Compared commonly used articulating mounting techniques and Magnetic Resonance Imaging (MRI) Methods & Materials: Twenty-eight men, 22-35years old with Class I occlusions and no history of TMD dysfunction. Records taken were: Manipulated Retruded position (RE), leaf gauge-generated Centric Relation (CR), Centric occlusion (CO), and MRI evaluated jaw positions and

anatomic relationships. The mandibular position indicator of the SAM articulator was used to determine reproducibility of CR. Results: The articulator analysis of CO and CR is statistically replicable. Condylar concentricity was observed in half of the sample and remained consistent in RE, CO, and CR. Of the sample 13% demonstrated anteriorly displaced disks that were not influenced by posterior condyle placement. The clinical concept of treating to CR as a preventive measure to improve disk-to-condyle relationships was not supported by this study.Conclusion: The data did not support distinct condylar positions for RE and CR and do not suggest CO and CR are coincident. MPI data failed to correlate statistically with MRI data possibly due to lack of sharp demarcation of cortical bone on the MRI reducing the accuracy of measurements. The premise that the leaf gauge established CR may not be accurate. 11-017. Ziebert, G J and Balthazart-Hart, Y. Stabilized base plate technique for interocclusal records. J Prosthet Dent 52: 606-608, 1984.Purpose: To present a technique of recording centric and eccentric jaw registrations that can be accurately transferred to the working cast.Materials and methods: The technique described was used for recording accurate maxillomandibular jaw relations intraorally at the predetermined VDO with the few remaining teeth of partially edentulous arches prepared. The materials and methods used were similar to a record base technique of recording VDO on partially dentate arches but with few minor modifications.Conclusion: The technique provides for accurately recording maxillomandibular relation when there are few teeth and interach stabilization is difficult to achieve.11-018. Christensen, L.C., Preserving a centric stop for interocclusal records. J Prosthet Dent 50:558-560, 1983.Purpose: A technique article describing a method of preserving existing centric stops to relate working casts for a fixed partial dentureSubject: A single patient presentation is made where the patient has the distal abutment for a fixed partial denture as the last tooth in the dental arch. Methods and materials: Preoperatively, centric stop(s) are marked with articulating paper. Index grooves are cut around the selected centric stop to leave an "island’ of enamel. Prepare the remainder of the tooth, indexing this island at the desired depth of preparation with an inverted cone bur. Make the final impression. Remove the enamel island, and deliver the provisional restoration. Articulate the master cast, then remove the "island" from the die. Fabricate the restoration in an appropriate conventional manner.Results: The patient’s centric stop is used as a guide to relate the working casts.Conclusion: The technique reduces the possibility of dimensional changes and inaccurate cast relationships often observed with conventional materials.11-019. Balthazar-Hart, Y. et al. Accuracy and dimensional stability of four interocclusal recording materials. J Prosthet Dent 45:586-591, 1981.Problem: Few studies have been made on four materials used to record maxillomandibular relationships. Purpose: To examine the accuracy and dimensional stability of zinc oxide-eugenol paste, eugenol free zinc oxide paste, silicone elastomer, and polyether elastomer in a controlled laboratory environment.Material and Methods: 5 samples of each material were studied. After mixing, the material was

carried to a Teflon die. The die was inverted onto a 2 x 2 inch square glass plate and covered with a polyethylene sheet. Hand pressure was applied for 5 seconds to express material. The die was submerged in a 32-degree water bath to simulate open mouth conditions. The dies and materials were separated and the 2 parallel line markers were measured at six different times.Results: The eugenol free-zinc oxide paste exhibited dimensional stability for the 168- hour period. Each batch of the polyether, silicone, and zinc oxide-eugenol paste exhibited a statistical difference between the die and its respective sample. Polyether was the second most accurate and stable material. 0.3% shrinkage after 24 hours. Zinc oxide-eugenol paste was the least accurate of the materials tested. Silicone putty is not recommended due to initial inaccuracy and because its rate of contraction precludes storage of the registration.Conclusion: The eugenol free zinc-oxide paste is the most accurate. The remaining three materials had a statistical difference between the die and the respective samples.

Section 12: Vertical Dimension(Handout)

1. DefinitionsA. Definition of Vertical Dimension Rest: The vertical dimension with the jaws in rest relation. Rest relation is the habitual postural position of the mandible to the maxillae when the patient is resting comfortably in the upright position and the condyles are in a neutral unstrained position in the glenoid fossa, with minimum tonic contraction of the mandibular musculature to maintain posture.B. Vertical dimension of occlusion: The vertical dimension of the face when the teeth on occlusal rims are in contact in centric relation. GPT-6: The distance measured between two points when occluding members are in contactC. Interocclusal distance: The distance between the occluding surfaces of the maxillary and mandibular teeth when the mandible is in its physiologic rest position. This can be determined by calculating the difference between the rest vertical dimension and the occlusal vertical dimension.D. Speaking space: The interocclusal space which exists between the posterior teeth when the patient is enunciating "S" sounds. It is not related to the interocclusal space of rest position. It represents the difference between the vertical dimension of occlusion and the clearance between the teeth when S sounds are spoken.Other terms: Closest speaking space, Physiologic rest position, Interocclusal rest space.2. Historical reviewa. Hunter – 1771: Stated that "In the lower jaw, as in all the joints in the body, when motion is carried to its greatest extent, in any direction, the muscles and ligaments are strained and the persons are made uneasy." Hunter also felt that the joints naturally fall when we sleep and the middle extremes of motion suggests that the muscles and ligaments are equally relaxed. Therefore the jaws are naturally and commonly not in contact nor are the condyles positioned as far back as they can go.b. Wallisch – 1906: First to define physiologic rest position of the mandible." That the position of the mandible wherein all muscle action is eliminated and the mandible is passively suspended. " c. Anatomists – early 1900’s: Believed that at birth the gums were contact and with eruption and alveolar growth the jaws were forced apart increasing the vertical dimension.3. Concepts: Constancy verses non-constancy

a. Niswonger – early 1930’s: First investigator to study the rest position of the mandible by recording measurements on patients. What was his theory?b. Brodie – utilized the Broadbent-Boltan cephalometer introduced by broadbent in 1931 and utilizes bony landmarks of the head. Brodie stated what?c. Thompson – believed that a balance of tension in the musculature, which suspends the mandible determines the rest position. What were his conclusions? d. Swerdlow – "A major failure in denture construction is the establishment of incorrect VDO." What did he observe that lead to this statement?e. Turner – stated that the "temptation to restore a youthful appearance by increasing vertical dimension must be resisted." Why? Variability of Rest Position: non-constancya. Harris and Hight – theory that the correct vertical opening in edentulous patients was debatable. Why was it debatable?b. Duncan and Williams – found a reduction in pre-extraction face height with the teeth in occlusion, as related to corresponding facial height after prosthetic treatment. What did they conclude from this?c. Coccaro and Lloyd- observed that the greatest reduction to be in the mid facial region in denture patients. What did they contribute this to?d. Atwood – one of the most extensive studies in the country. What was it? Why is vertical dimension important? 1. What is its significance in a dentate Patient? 2. What is the significance in an edentulous patient?3. What does it determine overall?Is there really a "loss"of vertical dimension? 1. Yes/NoWhat are the factors that may lead to the loss of vertical dimension?a. caries b. periodontal diseasec. attrition d. traumatice. iatrogenicIf there is a "loss" how do we evaluate it? (17 ways to evaluate Vertical dimension)a. Ceph – Brodie, Swerdlow, Thompson, Atwood, Tallgren, Silverman S., Coccarob. Electromyography – Feldman, Leupold, Weinberg,c. Gnathodynamometer - Prombonas d. Sorenson profile scale – Sorenson, Toolson and Smithe. Occlusal rims – Shanahan, Gattozzif. Wear – Turner, TallgrenHistorical Methodsa. Bimeter – Boos and Tueller (closing forces/power point)b. Tapping - Lytle and Timmer (proprioception-tactile sense)c. Jaw relator – Niswongerd. Standard of 3mm of IOD – Niswonger, Pleasure and GillisMore common

a. Pre-extraction records b. Physiologic rest positionc. Facial dimensions - Koisd. Open restMost commona. Phonetics – (S sound) Silverman M., Pound, (M sound) Wagner, Turrel ("emma" Mississippi) b. Swallowing – Gillis, Shanahan, Ismail and Georgec. Esthetics – Facial expression: look for relaxation around eyes and nares.Lip profile will hint at jaw relationship: Normal – (Class I) Lips even and slightly touchProtruded – (Class II) protruded mandible. Lips not touchingRetruded –(Class III) retruded mandible. Lips not touchingCan we feel confident that we have recaptured Vertical Dimensiona. Feedback from patientsb. Your impressionc. Cephalometrics – FMAd. Denture – wax rim stagee. Postural   Class I, II, III, differences in VDR: a. Variations in interocclusal rest spaceClass I 3-5 mmClass II > 5 mmClass III < 3 mmFMA normal 25 5 degreesa. FMA high – noncritical > 30 degreesb. FMA low – critical < 20 degrees Why is this so critical?How do you challenge Vertical dimension?a. stentsb. provisionalsc. duplicate dentures at altered VDOe. orthotics

- Abstracts -12-001. Swerdlow, H. Vertical dimension - literature review. J Prosthet Dent 15:241, 1965.abstract missing ......12-002. Turrell, A. J. W. Clinical assessment of vertical dimension. J Prosthet Dent 28:238-246, 1972.abstract missing .......12-003. Thompson, J. R. The rest position of the mandible and its significance to dental science. JADA 33:151-180, 1946.abstract missing .......12-004. Atwood, D. A. A critique of research of rest position of the mandible. J Prosthet Dent 16:848-854, 1966.abstract missing .......

12-005. Hickey, J. C., Williams, B. H. and Woelfel, J. B. Stability of mandibular rest position. J Prosthet Dent 11:566-572, 1961.abstract missing .......12-006. Lyons, M.F. An electromyographic study of masticatory muscle activity at increased vertical dimension in complete denture wearers.  J Prosthet Dent60:346-348, 1988.abstract missing .......12-007. Gattazi, J. G. Variations in mandibular rest positions with and without dentures in place. J Prosthet Dent  36:159, 1976.abstract missing .......12-008. Atwood, D. A. Cephalometric studies of the clinical rest position of the mandible. Part I. J Prosthet Dent 6:504-509, 1956.abstract missing .......12-009. Niswonger, M. E. Rest position of the mandible and centric relation. JADA 21:1572, 1934.abstract missing .......12-010. Tallgren, A. The continuing reduction of the residual alveolar ridges in complete denture wearers: A mixed longitudinal study covering 25 years. J Prosthet Dent 27:120-131, 1972.abstract missing .......12-011. Olsen, E. S. Vertical dimension of the face. DCNA 1964:611-622. abstract missing .......12-012. Weinberg, L. Vertical dimension: A research and clinical analysis. J Prosthet Dent 47:290-302, 1982.abstract missing .......12-013. Toolson, L. B. and Smith, D. E. Clinical measurement and evaluation of vertical dimension. J Prosthet Dent 47:236-241, 1982.abstract missing .......12-014. Silverman, S. I. Vertical dimension record: A three dimensional phenomenon. a. Part I:  J Prosthet Dent 53:420-425, 1985. b. Part II: J Prosthet Dent 53:573-577, 1985.abstract missing .......12-015. Atwood, D. A. Cephalometric studies of the clinical rest position of the mandible. a. Part II: J Prosthet Dent 7:544, 1957. abstract missing .......b. Part III: J Prosthet Dent 8:698, 1958.abstract missing .......016. Fayz, F., et al. Use of anterior teeth measurements in determining occlusal vertical dimension.  J Prosthet Dent 58:317-122, 1987.abstract missing .......

Section 13: Recording Vertical Dimension(Handout)

  Handout not yet available for this section

- Abstracts -13-001. Turrell, A. J. W. Clinical assessment of vertical dimension. J Prosthet Dent 28:238-246, 1972.Abstracts not yet available for this section13-002. Lytle, R. B. Vertical dimension of occlusion by the patient's neuromusculature. J Prosthet Dent 14:12, 1976.Abstracts not yet available for this section13-003. Silverman, M. M. Determination of vertical dimension by phonetics.   J Prosthet Dent 6:465, 1956.Abstracts not yet available for this section13-004. Boucher, L. J., et al. Can biting force be used as a criterion for registering vertical dimension? J Prosthet Dent 9:594, 1959.Abstracts not yet available for this section13-005. Ismail, Y. and Arthur, G. The consistency of the swallowing technique in determining occlusal vertical dimension in edentulous patients. J Prosthet Dent 19:230, 1968.Abstracts not yet available for this section13-006. Sheppard, I. M. and Sheppard, S. M. Vertical dimension measurements. J Prosthet Dent  34:269, 1975.Abstracts not yet available for this section13-007. Wagner, A. Comparison of four methods to determine rest position of the mandible. J Prosthet Dent 25:506, 1971.Abstracts not yet available for this section13-008. McGee, G. Use of facial measurements in determining vertical dimension. JADA 35:342, 1947.Abstracts not yet available for this section13-009. Ekfeldt, A. and Jemt, T. Interocclusal distance measurement comparing chin and tooth reference points. J Prosthet Dent 47:560-563, 1983.Abstracts not yet available for this section13-010. Silverman, S. I. Vertical dimension record: A three dimensional phenomenon. Part I. J Prosthet Dent 53:420-425, 1985.Abstracts not yet available for this section13-011. Silverman, M. M. Pre-extraction record to avoid premature aging of the denture patient.  J Prosthet Dent 5:465, 1955.Abstracts not yet available for this section13-012. Smith, D. The reliability of pre-extraction records for complete dentures. J Prosthet Dent 25:592, 1971.Abstracts not yet available for this section13-013. Boos, R. H. Intermaxillary relation established by biting power. JADA 27:1192, 1940.

Abstracts not yet available for this section13-014. Shanahan, T. E. Physiologic jaw relations and occlusion of complete dentures. J Prosthet Dent 5:319, 1955.Abstracts not yet available for this section13-015. Pound, E. Controlling anomalies of vertical dimension and speech. J Prosthet Dent 36:124, 1976.Abstracts not yet available for this section

Section 14: Functionally Generated Path(Handout)

Handout not yet available for this section- Abstracts -

14-001a. Meyer, FS. The generated path technique in reconstruction dentistry. Part I: Complete dentures J Prosthet Dent 9:354-366, 1959.Purpose: To describe a technique useful in complete denture construction.Materials and Methods: Author's experience and review of literature.Results: NoneConclusion: A technique was described,.- After making impressions and casts, make occlusion rims at the proper location.- Transfer the occlusion rims to a plain line articulator.- Make modeling compound occlusion rims.- Place soft carding wax on the rims and have the patient glide them together.- Remove the wax from the lower rim.- Pour stone into the maxillary wax and use the modeling compound on the lower rim for its base.- This lower stone path is what the upper teeth are set to and is in harmony with the condylar path.- The upper posterior teeth are set against the lower stone model.- The maxillary teeth are checked for esthetics.- The modeling compound on the lower rim is lowered 2mm below the upper incisors so there is no contact.- The compound on the lower rim is softened, the rim is placed in the mouth and the patient is instructed to protrude and retrude the mandible several times. Then when retruded the patient is asked to lightly close at the vertical dimension and make an imprint into the compound. - Cusps and Sulci analysis is performed. If the compound ridge is not high enough to contact the buccal cusp then the sulcus creating it is not deep enough and must be deepened.- Wax is then placed on the compound rims, softened and with a few lateral and protrusive movements the wax is formed.- Stone is poured into the wax and the teeth are set to the stone.- Balance will be obtained. 14-001b. Meyer, F. S. The generated path technique in reconstruction dentistry. Part II: Fixed partial dentures. J Prosthet Dent 9:432-440, 1959.Abstract not available at this time .......14-002. McCracken. Functional Occlusion in Removable Partial Denture Construction. J Prosthet Dent 8: 955-963, 1958.

     A method of establishing occlusion on the partial denture involves the generation of occlusal paths and the use of an occlusal template to which the denture teeth are occluded and by which they are modified to accept eccentric movements.     Should partial dentures be necessary in both arches, a choice must be made as to which denture is to be made first on a simple articulator mounting and which denture is to have the functional occlusal pattern.     By wearing and biting into a wax occlusion rim, a record is made of the opposing teeth in all extremes of jaw movement.     The occlusal path recorded will represent each tooth in its three dimensional aspect and although the cast poured against the record will resemble the opposing teeth, it will be much wider than the tooth which carved it because it represents a tooth in all extremes of movement. The recording of occlusal paths in this manner eliminates the problem of trying to reproduce mandibular movement on an instrument.     The occlusion on the partial denture will have more complete harmony with the opposing teeth and the remaining natural teeth by this method than can ever be obtained by adjustments in the mouth, because corrections to accommodate to voluntary movements does not mean complete freedom from occlusal disharmony in postural positions or during stress periods. Also it is very doubtful that any dentist can interpret articulation paper markings correctly without an occlusal analysis, which brings us to the need for a complicated instrument as the only alternative to this method.     It makes possible the obtaining of jaw relations under actual working conditions, with the new denture framework in its terminal position, the opposing teeth under function, and an opposing denture, if present, fully seated before jaw relations are recorded.     In some instances, it makes possible the recovery of lost vertical dimension, either bilaterally or unilaterally, where abnormal closure or mandibular rotation has occurred instead of recording and perpetuating an abnormal position which is correctable.     The occlusal registration must be converted to an occlusal template by filling the wax with hard stone. It is desirable that stone stops be used to maintain the vertical relation, rather than relying upon some adjustable part of the articulating instrument which might be changed accidentally. By the use of stone stops and by mounting both the denture cast and the template before separating them, a simple hinge or even a tripod instrument may be used, thereby eliminating the use of any but the simplest articulator. The jaw movements having been recorded and transferred to a template, eliminates the need for articulator adjustments.     Electroplating permits a metallic surface to be formed on the wax record with accuracy and with greater hardness than low-fusing metals     Electroforming with silver has proved to be the simplest and most satisfactory method. 14-003. Vig, R. G. A modified chew-in and functional impression technique.   J Prosthet Dent14:214-220, 1964.Abstract not available at this time .......14-004. Zimmerman, E. M. Modifications of the functionally generated path procedure. J Prosthet Dent 16:1119-1126, 1966.Abstract not available at this time .......14-005. Schnader, Y. E. Symposium on occlusion and function: The stone core intaglio in restorative dentistry. DCNA 25:493-510, 1981.Abstract not available at this time .......

14-006a. Dawson, P. E. Evaluation, Diagnosis, and Treatment of Occlusal Problems. Ch. 8.: The Plane of Occlusion. C.V. Mosby, St. Louis, 1974. pp. 190-205.Purpose: To establish the plane of occlusion with the Broadrick Occlusal Plane Analyzer and the P.M.S. technique. Material and Method: This descriptive text presented the requirements for proper occlusion i.e. anterior guidance, discluding posterior teeth in protrusion, disclusion of all teeth on the balancing side in lateral excursion. It also defined the following terms:1. Curve of Spee: anteroposterior curvature of the occlusal surfaces, beginning at the tip of the lower cuspid and following the buccal cusp tips of the bicuspids and molars and continuing to the anterior border of the ramus.2. Curve of Wilson: mediolateral curvature of the cusps as projected on the frontal plane expressed in both arches.Discussion: If the curve of Spee is too high in posterior the supporting tissues are prone to deleterious forces. If the curve of Spee is too low posteriorly it will not interfere with the basic requirements of protrusive and balancing side disclusion. It can create a poor esthetic and poor crown-root ratio on upper teeth. If the curve of Spee is too high or too low anteriorly the premolars can contact the upper cuspids in protrusive. Having the lower premolars much lower than the anteriors is unaesthetic.      The curve of Wilson deals with the mediolateral slant of posterior teeth in its relationship with the lateral anterior guidance angle. The steeper the lateral anterior guidance angle, the higher the lower lingual cusps may be on the opposite side.There are 3 practical methods for establishing an acceptable plane of occlusion:   1. Analysis on natural teeth through selective grinding   2. Analysis on models with fully adjustable instrumentation   3. Pankey-Mann-Schuyler method with the Broadrick Occlusal Plane AnalyzerConclusion: When the occlusal plane is predetermined prior to preparation of the teeth only the most minor occlusal adjustment should be necessary on the finished restoration.14-006b. Dawson, P. E. Evaluation, Diagnosis, and treatment of Occlusal Problems. Chapter 23: Functionally generated path techniques for recording border movements intraorally. C. V. Mosby, 1989, 410-433.Purpose: To review the technique for recording and utilizing the Functionally Generated Path technique (FGP). The chapter describes both the clinical and laboratory procedures. Subject: FGP procedures are described as a useful and accurate method to record all possible border pathways of the lower posterior teeth when preparing upper posterior teeth for restoration. Technique is described for maxillary full arch, single tooth, and quadrant restoration.Methods and materials: Brief technique summary for bilateral maxillary posterior preparations: 1) prepare teeth 2) alginate impression 3) extra hard baseplate wax base (or acrylic or cast base) fabricated to be stable cross-arch, adapted down around each tooth, but thin on prepared occlusal surface with no contact 4) functional wax softened and added to baseplate, enough to be impressed by about one third of each lower tooth. 5) patient guided through protrusive and all lateral excursions 6) wax chilled with ice water and a stone mix applied to wax in the mouth. 7) upper master die model articulated against FGP stone core. 8) Wax-up can be made against the functional model, made against an anatomic opposing cast and refined on the functional model, or castings fabricated from anatomic model and adjusted against the functional model. Variations are described for single tooth or quadrant preps.Results: 1) Group function is attained by adjusting the lingual inclines of the upper buccal cusps

to contact against the functional core. 2) Disclusion is attained when the inclines are taken out of contact with the functional core and only centric stops are retained. 3) Balancing contacts will be reproduced in functional core, therefore balancing side disclusion must be effected by reduction of the balancing inclines in restoration or wax pattern.Conclusions: 1) Anterior guidance and condylar movement determine border pathways of lower posterior teeth. By recording and reproducing all possible border pathways of the lower posterior teeth, in a functionally generated path, a method can be utilized for restoring upper posterior teeth 2) FGP procedures are not generally used on lower teeth. In lower teeth, functioning contacts on the buccal cusps and centric contact in the base of the fossae can be accomplished in less time consuming ways than FGP.Comments: The article provides a cookbook recipe for utilizing a FGP for accurately restoring occlusal contours. 14-007. Meyer, F. S. Construction of full dentures with balanced functional occlusion. J Prosthet Dent 4:440-445, 1954.14-008. Mann, AW and Panky, LD. Concepts of occlusion: The PM philosophy of occlusal rehabilitation. J Prosthet Dent 10:135-162, 1960.     The lower is rebuilt to an ideal occlusion using the PM instrument that allows for Bonwill's triangle and Monson's curve. The incisal guidance is then rebuilt by grinding or restoring the anterior teeth. The maxillary is then reconstructed using the FGP technique describer by Meyer.     The four prime objectives of oral rehabilitation are (1) optimum oral health, (2) functional efficiency, (3) mouth comfort, and (4) esthetics. 14-009. Mann, A. W. and Pankey, L. D. Oral rehabilitation. J Prosthet Dent 10:135-162, 1960.Abstract not available at this time .......14-010. Schuyler. An Evaluation Of Incisal Guidance And Its Influence In Restorative Dentistry. J Prosthet Dent 9: 374-378, 1959.      Complete occlusal coordination of the masticatory mechanism necessitates a coordination of posterior guiding tooth inclines with the two extreme guiding factors which are the incisal guidance and the unrestrained movement of the condyles in the glenoid fossae. Of these two extreme factors, the incisal guidance is the more influential factor due to its proximity to the occlusion and nonresiliency. There is a degree of resiliency of flexibility in the movement of the condyles in the glenoid fossae.     The controls of the lateral functional inclinations of the posterior teeth are the incisal guidance and the lateral movement of the condyles in the glenoid fossae, which is called Bennett movement.     A steep incisal guidance, or a locked or restricted relationship of the anterior teeth, or a functional abnormality of posterior tooth inclines may influence the direction and degree of the Bennett movement.     By building posterior occlusal contours to some irregular functional movements of the condyles, we may be perpetuating pathology of the joints.     The anterior movement of the condyles upon the articulating eminences of the glenoid fossae has little or no influence upon the functional relation of the posterior tooth surfaces on the working side. In complete oral rehabilitation, it has little or no influence upon the steepness of lateral working inclines of the teeth.     Incisal guidance and the forward movement of the condyles are the factors controlling

inclinations of the posterior teeth on both the balancing side and in the protrusive relationship.     In the evaluation of factors controlling posterior occlusal contours of the complete oral rehabilitation of the natural dentition, we must come to the conclusion that incisal guidance is the predominating factor. Therefore, the establishing of the anterior tooth relation, esthetics, and incisal guidance should be the first step in planning the oral rehabilitation. Posterior tooth surfaces are then formed to function in harmony with this guiding factor.     The reduction of horizontal stresses by a reduction of the steepness of posterior occlusal inclinations may be desirable. This necessitates a reduction of the lateral guiding inclines of the anterior teeth, these being the controlling factors to the inclines of the posterior teeth.     Schuyler - mount casts in the articulating instrument with a retruded, but unrestrained centric maxillomandibular relation record. After this relation record has been checked and proved and the instrument has been set to the recorded movements, the mandibular member of the instrument is advanced by placing a strip of tin foil of the desired thickness in front of the axis balls in the slot in the condylar guidances of the instrument. The thickness commonly used is .5 or.75 mm. The restorations on the teeth are finished and milled at this advanced position. Then the articulator is retruded to its normal position and the occlusal surfaces of the restorations are milled again to that position. This procedure provides a slight range of anteroposterior freedom for the mandible and a slight freedom in intercuspation. Complete dentures and complete oral rehabilitation are more readily tolerated when this freedom is built into the occlusion. 14-011a. Dawson,P.E. Evaluation, Diagnosis, and Treatment of Occlusal Problems. C.V., Mosby, St. Louis, 1974. Chapter 8, Pankey-Mann-Schuyler philosophy of complete occlusal rehabilitation, pp108-110.     The deviation of the incisal path in an individual is less than that of the condylar path. The incisal path influences disocclusion at the second molar twice as much as that of the condylar path during a protrusive movement, three times as much on the non-working side and four times as much on the working side during lateral movement. The cusp angle is considered to be the most reliable reference for occlusion. The standard cusp angle values were determined to be 25 during protrusive movement, 15 on the working side, and 20 on the non-working side during lateral movement.      In order to provide disocclusion, the cusp angle should be shallower than the condylar path. To make a shallower cusp angle, it is necessary to produce balanced articulation so the cusp angle becomes parallel to the cusp path of a opposing teeth during eccentric movement. The twin stage procedure uses a cast with a removable anterior segment and fabricates the posterior teeth in a balanced occlusion. The anterior segment is replaced and anterior guidance is established.( 1mm during protrusive movement)     In Hobo’s article a description is given to create a custom incisal guide table, and a technique to simulate the protrusive movement on the articulator is detailed. In his text book, values have been determined and can be programmed into a semi-adjustable articulator.      Stage I: The sagittal condylar path inclination 25 ; Bennett angle 15 ; sagittal inclination of the incisal guide table 25 ; and the lateral wing angle 10 .The anterior segment of the maxillary and mandibular casts are removed using dowel pins and the casts are adjusted so they do not disclude during eccentric movements. Wax the occlusal morphology of the posterior teeth so the maxillary and mandibular teeth contact during eccentric movements (balanced articulation).      Stage II: The sagittal condylar path inclination 40 ; Bennett angle 15 ; sagittal inclination of the incisal guide table 45 ; and the lateral wing angle 20 .The anterior segment of the maxillary and mandibular casts is replaced. Wax the palatal contours of the maxillary anterior teeth so the

incisors contact during protrusive movement, and the canines on the working side contact during a lateral movement. Anterior guidance is established and disclusion is produced.     If the sagittal condylar path of the patient is steeper than the articulator adjustment value (40 ), disclusion increases. If the path is less than 40 , then the amount of disclusion decreases. If the patient has less than 16 (only about an 8% occurrence rate), cuspal interferences will occur.     If the incisal path is more than 5 steeper than the condylar path, patients complain of discomfort (Mc Horris 1979).14-011b. Dawson, P. E. Evaluation, Diagnosis, and Treatment of Occlusal Problems. C. V., Mosby, St. Louis, 1974. b. Chapter 14, The plane of occlusion, pp 190-205.Abstract not available at this time .......14-011c. Dawson, P. E. Evaluation, Diagnosis, and Treatment of Occlusal Problems. C. V., Mosby, St. Louis, 1974. c. Chapter 15, Determining the type of posterior occlusal morphology, pp. 206-218. Abstract not available at this time .......