EVALUATION OF THE NEEDLE POINT TRACING AS A

METHOD FOR DETERMINING CENTRIC RELATION

MOHAMED A. EL-ARAMANY, B.Cq.D., MS.“, W. ARTHUR GEORGE, B.S., D.D.S.,“”

AND RUSSELL H. SCOTT, M.S., PH.D.“**

University of Pittsburgh, School of Dentistry, Pittsburgh, Pa.

S INCE THE TIME of its proposal by Gysi in 1910,’ the (Gothic arch) needle point tracing has been accepted as an accurate method of locating the centric

maxillomandibular relation at a given degree of jaw separati0n.l.I7 One group of investigators thought that the intercuspal position of the natural

teeth should coincide with the most retruded position or the apex of the arrow point tracing. 1s-23 They considered a lack of coincidence between these two positions to be nonphysiologic.

Other investigators considered centric relation of the mandible to be anter- ior to the apex of the tracing. 24-29 It was their belief that the apex of the tracing represented a retruded or strained position. They recommended a more anterior position which they called a “true” or “functional” relation. Many more such references in the literature provide additional concepts concerning the position of the condyles in the glenoid fossae when the mandible is positioned at the apex of the needle point tracing.

HYPOTHESES UNDERLYING THE DETERMINATION OF CENTRIC RELATION

There are various techniques for determining centric maxillomandibular re- lation. The hypotheses underlying these techniques can be derived from one of the following three theoretical positions of the condyles in the glenoid fossae:

1. Hinge axis theory, supported by a large number of writers who believe that by determining the posterior terminal hinge position the centric relation is established in all dimensions. 20-22,30-3? Others question the validity of the hinge axis theory.33-40

2. The rest position theory as suggested by Thompson,41 and supported by others,42-44 was taken as an aid in recording centric relation. Craddock43 postulated that when the mandible assumes the position of rest it is in centric relation.

Based on a thesis entitled “The Effect of Increasing Vertical Dimension on Centric Rela- tion,” submitted in partial fulfillment of the requirements for the Master of Science Degree in Prosthodontics, University of Pittsburgh, School of Dentistry.

*Lecturer, Department of Prosthodontics, Cairo University School of Dentistry, Cairo, Egypt. **Professor and Head, Department of Prosthodontics, University of Pittsburgh, School of

Dentistry, Pittsburgh, Pa. ***Assirtant Professor, Behavioral Sciences, University of Pittsburgh, School of Dentistry,

Pittsburgh, Pa.

1043

EL-ARAMANY, GEORGE, AND SCOTT J. Pros. Den. November-December. 1965

3. The most retruded unstrained position of the mandible.42~46~46 It is very difficult to determine when the position is strained or unstrained, since this de- pends upon the subjective judgment of the patient and the dentist. Many adherents of this theory recommended the needle point tracing as a “scientific” method for determining the centric relation in the horizontal plane. Other adherents of this theory state that the needle point tracing is not a reliable method for determining it 32,47

It should be noted that if the adjective “unstrained” were deleted from the third definition, it would be very close to the hinge axis theory. If the adjective remains, the definition closely resembles the second theory. In short, the following question may be raised concerning the position of centric relation: Is it a terminal position of the condyles in the glenoid fossae, or does it fall somewhere anterior to this position?

On examining Posselt’s4s figure (Fig. 1) , it may be noted that the intercuspal position does not coincide with the retruded contact position and that the rest position was not situated on the posterior border path. These were considered by Posselt to be intra-extreme positions whereas the advocates of the terminal hinge position determine the centric relation position on the posterior border path.

One of the unsolved problems is whether the opening movement of the man- dible starts with a pure hinge movement, or if translation of the condyles starts at the very beginning of the movement. If the hinge axis theory is correct, then the vertical dimension can be changed on the articulator without altering the centric relation record.

HYPOTHESES

The aim of this study was to investigate the relationship between the vertical relation and the centric relation, and to answer the following questions: (1) Is the centric relation, as determined by the needle point tracing, reproducible in the same individual within the same sitting at different degrees of jaw separation? (2) Does the centric position of the mandible deviate laterally from the midline with an increase in the jaw separation?

METHODS AND MATERIALS

The 10 subjects were male university students, aged 22 to 33 years (25.2 years average). The subjects had complete dentitions except subject 1, who had lost the lower right first bicuspid, and subject 9, who had lost the upper right first bicuspid. The third molars were not counted. The dentitions were apparently normal, and there were no symptoms of discomfort regarding the teeth, support- ing structures, or the temporomandibular articulation.

Impressions were made and casts formed of the maxillary and mandibular jaws of each subject. The center of the palate in the molar region of the maxillary cast was located by dividing the distance between the central fossae of the right and left maxillary first molars equally. The maxillary cast was orientated on a mount- ing plate, on which the center of the Hanau articulator was marked, so that the area between the upper central incisors and the line indicating the center of the arch in the molar area fell on the central line of the mounting plate (Fig. 2). The max-

Volume 15 Number 6 NEEDLE POINT TRACING FOR DETERMINING CENTRIC RELATION 1045

Fig. l.- The range of movement in the median plane, showing the habitual closing move- ment (h), rest position (r), retruded contact position (EC), occlusal (intercuspal) position (i), protruded contact position (P), hinge movement (H), and maximal open position (kf). Approxi- mately natural size. (Redrawn from Posselt, Ulf: J.A.D.A. 56:12, 1958.1

Fig. 2.-The maxillary cast is oriented on the mOUntiU&T Plate.

illary cast was then mounted in this position. The mandibular cast was mounted in the intercuspal position in relation to the upper cast.

Labial splints of acrylic resin were constructed for both the maxillary and mandibular jaws of each subject. The tissue-contacting surface of the splints was reduced, and a lining of soft acrylic resin was added to avoid excessive pressure on the soft tissues during wiring. The splints were tried in the mouth, and all occlusal interferences were eliminated.

A hole was drilled in the anterior horizontal plate of the maxillary component of the Hight tracer* just posterior to the tracing pin. A nut was soldered over the hole to allow for a screw to be fitted through it. The amount of vertical opening was adjusted and controlled by means of the screw. A plastic disc with a hole in the middle was mounted on the posterior horizontal plate of the tracer’s maxillary

*Hanau Engineering Company, Buffalo, N. Y.

EL-ARAMANY, GEORGE, AND SCOTT November-D.&e,%% %

component to permit the insertion of a marker through to the central line of the mounting plate (Fig. 3).

The maxillary component of this modified Hight tracer was oriented on the

maxillary splint so that the middle of the hole in the plastic disc, the bearing pin, and the tracing point fell on the extension of the central line of the mounting plate. This component was mounted parallel to the occlusal plane (Figs. 4 and 5).

Using cold curing resin, the mandibular component of the Hight tracer was attached to the splint parallel to the maxillary component. Holes were drilled through the splints in the region of the interdental spaces to permit the wiring of the splints to the teeth.

Smoked tracing papers were prepared to be attached on the tracing table with transparent tape. The splint was wired to the teeth in the anterior region and on both sides. Then the occlusion was checked for proper intercuspation and for pos- sible occlusal interference (Figs. 6, 7, and 8).

The distance between the two arms of the tracer was measured at the tracing point (Fig. 9). A nonsmoked tracing paper was taped to the tracing table and the subject was asked to close in the intercuspal position. Then the point of the tracing pin was used to mark a point on the paper (Fig. 10). This mark was called point “A.” A mark was made on the same tracing paper through the plastic disc, this point was designated as point “B.”

The jaw separation was increased to 4 mm. at the tracing point, and a smoked paper was fixed on top of the nonsmoked paper. Then the subject was instructed to move the mandible from side to side while keeping the bearing screw touching at all times. The apex of the needle point tracing was pierced through the smoked paper to the nonsmoked paper with a sharp probe (Fig. 11) . A new piece of smoked tracing paper was placed in position and the same process was repeated, using separations at the tracing point of 8, 12, 16, and 20 mm. The apexes of each of these tracings were transferred to the nonsmoked paper with the sharp stylus as before. This procedure was repeated five times on each subject during

Fig. 3.-The maxillary and mandibular arms of the Hight tracer after modification. Note the plastic disc on the maxillary arm (right).

ixzz ‘6” NEEDLE POINT TRACING FOR DETERMINING CENTRIC RELATION 1047

one sitting with the appliance wired in place throughout all five repetitions. The distance between the arms of the tracer was checked between repetitions to assure that the tracer was immobile in relation to the teeth. The same Hight tracer was used throughout the investigation, thus eliminating variance due to possible dif- ferences between tracers.

At the end of the investigation, there were five nonsmoked tracing papers for each subject. On each of these papers there were two marks, one, point “A,” in- dicating the position of the tracing point while the teeth were in the intercuspal position, the other, point “B,” indicating the central contact point as recorded through the center of the hole in the plastic disc. Each tracing paper also had five other holes representing the positions of the apexes of the five needle point trac- ings made at the different jaw separations (Fig. 12).

Fig. 4.-The maxillary component of the Hight tracer is oriented so that the needle point the tracer, the hole in the disc, and the central bearing screw fall on the midline.

of

Fig. B.-The maxillary and mandibular arms of the Hight tracer attached to the splints.

1048 EL-ARAMANY, GEORGE, AND SCOTT November-D&et ?%

Fig. 6.-The maxillary component of the Hight tracer is wired to the maxillary teeth. Note the hole in the plastic disc to be used for making the reference mark (I?) in Fig. 32.

Fig. 7.-Maxillary and mandibular components of the Hight tracer wired to their respective arches.

Fig. K-After the splints are wired to the teeth, the intercuspation of the teeth is checked to make certain that the teeth are in occlusion without interference from the resin clutches.

Volume 15 Number 6 NEEDLE POINT TRACING FOR DETERMINING CENTRIC RELATION 1049

Fig. 9.-Measuring the distance between the upper and lower arms of the Tracer.

Fig. IO.-The tracing pin is in place indicating the mark (A) and the marker through the disc indicates mark (B).

Fig. Il.-The hole is made through the tracing paper at the apex of the needle point tracing to transfer its position to the nonsmoked paper below.

1050 EL-ARAMANY, GEORGE, AND SCOTT November-DEIE. %i

AT/ AT/

AT/

ATf

AT/

4MM 8MM

‘12MM

16MM

20MM

Fig. 12.-A diagram representing the records on the nonsmoked tracing paper after the completion of one experiment. A, The mark made at centric occlusal contact. B, The reference point made through the hole in the plastic disc attached to the upper part of the tracer. AT, The 5 holes made at the apexes of the 5 needle point tracings made at 5 .different degrees of jaw separation.

RESULTS

Since each subject was given five trials at each degree of jaw separation before being tested on the next degree of jaw separation, it was necessary to analyze the data treating the trials as a factor nested within the degrees of jaw separation. Neither the trials within degrees of jaw separation nor their interaction with sub- jects was significant. Therefore, variation due to these sources was combined with the residual to form the pooled error term. This error term was used in testing the significance between subjects’ variation and the degrees of jaw separation by subjects’ interaction. Since the degrees of jaw separation constitute a fixed variable, the separations by subjects’ interaction were used to test its significance as well as the significance of the trends. The results of this analysis of variance are shown in Table I.4s

There was a statistically significant change in the anteroposterior position of the centric relation as a function of changes in the degree of jaw separation. As the degree of jaw separation was increased, the apex moved away from point “A.” Both the linear and quadratic components of the trend analysis were significant. Of the variation attributable to the differences between degrees of jaw separation 99.8 per cent can be predicted from a linear regression equation. (Fig. 13).

The differences between subjects in anteroposterior centric relation were also statistically significant. The separations X subjects interaction was significant at less than .OOl level (Figs. 14 and 15).

Volume 1.5 Number 6 NEEDLE POINT TRACING FOR DETERMINING CENTRIC RELATION lo!51

TABLE I. ANALYSIS OF VARIANCE

= SOURCE OF VARIATION 1 &t::s ~ df 1 ;:::FZ 1 F ( I’

-

Between degrees of jaw separation 350.328 4 74.793 286.563 < ,001 Linear component 346.611 1 346.611 1328.01 < ,001 Quadratic component 3.557 1 3.557 13.63 <.OOl Cubic component 0.131 : 0.131 <l.O N.S. Quartic component 0.028 0.028 <l.O N.S.

Between subjects 26.960 9 2.996 39.95 < ,001

Separations X subjects 9.408 36 0.261 3.48 < ,001 (Error term for degrees of jaw separation)

Pooled error 15.044 200 0.075

Total 401.740 249 -

5.0

4.0

DISTAMCE fROM

POINT A ‘” Ma 3.0

4 I 12 10 20

JAW SEPARATION IN MM.

Fig. 13.-The mean distance from point A to the apexes of tracings made at various dis- tances of jaw separation (10 subjects).

Lateral deviations from the midline ranged from 0 to 2.4 mm. with the amount of deviation increasing in proportion to the increase in vertical separation of the jaw. Only one subject showed consistent deviations from the midline at the 4 mm. opening. One subject showed only negligible deviations at any of the degrees of opening. Three of the subjects deviated consistently to the right of the midline, three consistently to the left of the midline, and the remaining three showed mixed deviations from the midline.

1052 EL-ARAMANY, GEORGE, AND SCOTT November-Dkt ?;:i

DISTANCE FROM

POINT A IN MM.

5.0

4.0

3.0

2.0

10

0

0 I2 16 30

JAW SEPARATION IN MM’.

Fig. 14.-The distances from point A to the apexes of tracings made at various distances of jaw separation (subjects l-5).

DISCUSSION AND CONCLUSIONS

The problem of maxillomandibular relation is one of the most important prob- lems confronting dentists in the field of restorative dentistry. It is important to note that there is little agreement among the experts as to terminology, definition, and methods of procedure. This study was conducted to learn what differences would occur at various jaw openings on dentulous subjects when the appliances were held firmly in position by interdental wire loops. Since these tracers were wired firmly in position, it is not possible to compare these results with studies con- ducted on edentulous patients where the recording bases were supported by soft tissues. The distance between the arms of the tracer was checked frequently between and during trials to assure accurate measurements.

An analysis of the data showed no significant difference between trials within degrees of jaw separation. This indicates that the needle point tracing method yields reliable results, i.e., the needle point tracing can be accurately reproduced in an individual within the same sitting.

As the degree of jaw separation is increased, the apex of the needle point tracing moves posteriorly away from point “A” in a consistent manner. The amount of change in the distance between the apex and point “A” is linearly related to the degree of jaw separation. This is interpreted as indicating that the jaw functions as a hinge rotating from a central point.

SUM MARY

1. Needle point tracings were obtained from ten subjects at five different degrees of jaw separation.

Volume 15 Number 6

NEEDLE POINT TRACING FOR DETERMINING CENTRIC RELATION 10.53

4.0

DISTANCE FROM

POINT A IN MM. 1.0

I 12 16 20

JAW SEPARATION IN MM.

Fig. 15.-The distances from A to the apexes of tracings made at various distances of jaw separation (subjects 6-10).

2. All subjects showed anteroposterior change of the centric relation position as a factor of increases in the vertical dimension between the jaws. The mandibular centric relation position moved posteriorly when the vertical dimension between the jaws was increased.

3. Two subjects showed only negligible lateral deviations at any degree of opening while one subject showed consistent deviations from the midline when the vertical dimension between the jaws was increased.

4. The needle point tracings at a given vertical dimension of jaw separation under the same controlled conditions, on the same individual, at the same sitting, were not significantly different. On the basis of this study, the needle point tracing procedure is reliable.

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Department of Prosthodontics University of Pittsburgh Cairo University School of Dentistry School of Dentistry Cairo, Egypt Pittsburgh, Pa. 15213