Impression anoop/prosthodontic courses

THEORIES OF IMPRESSION MAKINGAND IMPRESSION PROCEDURE FOR

COMPLETE DENTURE

INDIAN DENTAL ACADEMYLeader in continuing Dental Education

www.indiandentalacademy.com

ContentsIntroductionHistoryReview of literatureBasic requirements of impression makingPrinciples of impression makingClassification of impression techniquesVarious impression techniquesSteps in impression makingPrimary impression makingBorder molding and secondary impression makingImpression techniques in compromised situationsSummary and conclusionReferences


Introduction Complete denture impression procedures are perhaps one phase on which much has been spoken about. The literature on the subject shows a persistent disagreement ever since 1850.Much of this confusion results from the fact that many impression procedures have been developed on empirical basis. Many have used the available knowledge of functional and histological anatomy for the development of their procedures, but the variation in these techniques indicate a wide difference in interpretation of the foundation of dentures. Whatever the method used it is generally agreed that good impressions are basic for the construction of a good denture.


“Ideal impression must be in the mind of the dentist before it is in his hand. He must literally make the impression rather

than take it”

- M.M. Devan


History1711 Matthian G. Purman introduced the use of wax. 1728 Pierre Fauchard1844 Plaster of paris was first used as an impression material. 1845-1899 concepts of atmospheric pressure, maximum extension of denture bearing area, equal distribution of pressure and close adaptation of the denture bearing tissues were stressed. 1886 Richardson 1896 Green brothers introduced mucocompressive theory. 1900-1920 Concepts like Rebase impressions, border molding and techniques for flabby tissues were introduced.


1920-1946 1944 Addison1946 Page introduced mucostatic concept1948-1964 more emphasis on biologic factor of impression making was given. 1950 selective pressure theory by boucher. 1965-1980 new techniques to manage compromised situations were introduced. New techniques are periodically been formulated to overcome the drawbacks faced.

“We have come a long way from the use of wooden blocks to the use of modern elastomeric materials to make impressions and from the use of pressure

technique to selective pressure technique”.


Review of Literature


Fischer in 1951 laid down six fundamental rules for making an impression

Radiographs ,visual and digital examinationSurgicalRequired extension outlineRequired retention outline Required adaptation Location and position of variable tissue displaceability


A critical analysis of Mid-century impression techniques for full dentures

Boucher in 1951 – he classified impression techniques

1. Based on the use of actual anatomy of the individual patient or on arbitrary landmarksAnatomic or Arbitrary

2. Based upon the mouth position while the impression is made.Open mouth or closed mouth

3. Based upon the relative amount of pressure exerted on the tissues by the impression material at the time of set. Pressure, non pressure or selective pressure


Impression by the use of subatmospheric pressure – Milo V. Kubalek, Bert C. Buffington (1966)

The objective of this technique is to reduce the stress on any given tissue by increasing the load bearing area. To realize the ideal the form of tissues must be recorded both vertically and laterally so that all surfaces can bear an equal load and vacustatic technique is an attempt to achieve this. When a controlled partial vacuum is established, an impression tray specially built for the patient is maintained in the mouth without direct mechanical support of any kind. The difference between subatmospheric pressure within the tray and atmospheric pressure outside is all that retained the impression in a static position. It denotes the equilibrium of forces which results when a controlled vacuum is established.



Fabrication of a custom made impression tray for making preliminary impressions of edentulous mandible- A.M. Sofou, Mordohai, Pissiotis (1998)

The purpose of this article was to demonstrate a technique in which custom tray is fabricated to achieve suitable coverage of the edentulous areas in patients with extreme ridge resorption and thus to obtain proper preliminary impressions.


The management of abused oral tissues in complete denture construction – Robert B. Lytle (1957)

The purpose of this article is to emphasize the need for permitting abused tissues to recover and to suggest measures for accomplishing their recovery. In order to eliminate pressure areas that might destroy the supporting structures abused soft tissues must be allowed to recover and return to a more normal form before impressions are made for new dentures. We must be concerned with the health of soft tissues if the ridges are to be preserved and dentures to function properly.


Diurnal variation in palatal tissue thickness – Stephens, Cox, Sharry (1966)

In this study the variation in palatal thickness at different time of the day is measured. A small micrometer was attached to an acrylic resin hood which straddled the upper arch and fitted the occlusal surface of the molar and premolar teeth was used to measure the diurnal changes in palatal tissue. The results indicated that the palatal tissues were thickest when the subjects were lying in bed after a full night sleep and it starts to shrink in the morning and continues in the afternoon. Slight increase in tissue thickness is seen again in the evening.


Impressions for complete denture using new silicone impression materials – Iwao Hayakawa, Ikki Watanabe (2003)

This article describes a convenient technique for making impressions of complete dentures using two newly developed silicone materials. One of these materials, heavy-bodied silicone materials, is used for simultaneous molding of all borders. This material is designed to have a low elasticity after setting.The other newly developed material, a light-bodied silicone material, possesses better flow than the usual light-bodied silicones.In addition, since viscosity is controlled an adequate flow is maintained during seating in the mouth, mucosal detail was found to be superior.


Basic Requirements for Impression Making

Knowledge of Basic anatomyKnowledge of basic reliable techniqueKnowledge and understanding of impression materials SkillPatient management


Definition: A complete denture impression is a negative registration of the entire denture bearing, stabilizing and border seal areas present in the edentulous mouth

PRINCIPLES OF IMPRESSION MAKINGPreservation of Alveolar RidgesSupportRetentionStabilityEsthetics


M.M.DEVAN DICTUM

PRESERVATION OF WHAT REMAINS RATHER THAN METICULOUS REPLACEMENT OF WHAT IS MISSING

PRESERVATION OF ALVEOLAR RIDGES

Resistance to vertical forces of mastication and to occlusal or other forces applied in direction toward the basal seat

SUPPORT


FACTORS FOR RETENTIONADHESIONCOHESIONINTERFACIAL SURFACE TENSIONATMOSPHERIC PRESSUREORAL AND FACIAL MASCULATUREMECHANICAL INTERLOCKING INTO UNDERCUTS

RETENTION


Ability to remain in place when it is subjected to horizontal forces.Factors :-1. Retention2. Non interfering occlusion. 3. Proper form & contour of the polished surfaces 4. Proper orientation of occlusal plane5. Good control and coordination of patients musculature. 6. Proper tooth arrangement.

ESTHETICSRefers to development of labial and buccal borders so that they are not only retentive but also support the lips and cheeks properly

STABILITY


Impression techniques may be classified depending on:

a) Amount of pressure used1. Pressure technique2. Minimal pressure technique3. Selective pressure technique

b) Based on the position of the mouth while making impression

1. Open mouth 2. Close mouth

c) Based on the method of manipulation for border molding. 1. Hand manipulation2. Functional movements


Pressure theory or mucocompressive theory:

This theory was proposed on the assumption that tissues recorded under functional pressure provided better support and retention for the denture.

Green in 1896 gave this concept Technique by Green as described by Liberthal


Greene all compound technique described by Liberthal

Primary impression made with impression compoundSpecial tray made Impression made with compoundBite rim made with compoundRelief of mid palatine raphae Peripheral muscle trimmingBorders are molded by asking the patient to perform functional movements.


Demerits of the theory

1. Excess pressure could lead to increase alveolar bone resorption.

2. Excess pressure was often applied to the peripheral tissues and the palate.

3. Dentures which fit well during mastication tend to rebound when the tissue resume their normal resting state.

4. Pressure on sharp bony ridges results in pain.


Applied aspects:

The technique tells that border tissues are recorded in their functional positions and denture cannot be dislodged during functional movements of jaws. The pressure applied is more and directed towards the palate and peripheral tissues. So the retention will be for short time and will be lost as soon as the bone undergoes resorption. Usually this technique is used for preliminary impression making as it gives a positive peripheral seal and tissues are recorded in function. Amount of pressure applied is for short duration and the areas can be relieved during the final impression.


Minimal pressure or mucostatic theory – The main advantage of this technique is its high regard for tissue health & preservation.

1886 Richardson made impressions of tissues at rest. 1944 Addison emphasized on interfacial surface tension.1946 Page gave the concept of mucostatic based on Pascal’s law. 1956 Tilton G.E.stated that minimum pressure is just the amount that will hold movable tissue for enough away so that the required coverage may be secured and in substance it is little more than the weight of a free-flowing material.


Technique

A compound impression is made.

A baseplate wax space is adapted.

A special tray is made.

Spacer is removed and an impression is made with a free flowing material with little pressure.

Escape holes are made for relief.


Demerits

Application of Pascals law is partially correctRetention obtained only by interfacial surface tension is not correctThe lack of border molding reduces effective peripheral seal.The short flanges may reduce support for the face. The shorter flanges prevent the wider distribution of masticatory stresses. Least importance to polished surface and muscle relation


Applied aspect:

The technique holds good in the sense it helps in preservation of tissue health. In practice which short flanges the oral musculature is non supported and stresses are not widely distributed. Food can slip beneath the denture and tongue can readily access the denture borders. This technique is useful in impressions of flabby and sharp or thin ridges.


Selective pressure theoryAdvocated by Boucher in 1950 it combines the principles of both pressure and minimal pressure technique. In this technique idea of tissue preservation is combined with mechanical factor of achieving retention, through minimum pressure which is within physiologic limits of tissue tolerance. This theory is based on a thorough understanding of the anatomy and physiology of basal seat and surrounding areas.Boucher also advocated maximum extension within the comfort and functional limits of the surrounding muscle and tissues.


Demerits

It is impossible to record areas with varying pressure. Some areas still recorded under functional load, the dentures still faces the potential danger of rebounding and loosing retention.


Applied aspect:

Inspite of some of its apparent drawbacks all the impression techniques based on the selective pressure technique are still popular. Final impressions using this technique are made where relief areas are provided and pressure is distributed on the stress bearing areas. “Yesterday’s controversies will become today’s reality & today’s reality will become tomorrow’s

controversy”


Open mouth technique

Made with tray held by dentist and mouth openMuscle movements may be emphasized and can be seen by the operator


Closed mouth technique

The rational behind this technique is that the supporting tissues are recorded in a functional relationship.Requires occlusal rims to be made Border molding done and final impressions madeJaw relations either tentative or final made


Disadvantages-Fatiguing to patient and dentistTendency for over extensionRelease of pressure of occlusion may permit a rebound of denture Pressure applied cannot be controlled


Hand manipulation

Dentist uses hand manipulation for movements of lips and cheeks

Functional movements

Patient makes functional movements such as sucking, swallowing, licking or grinning


STEPS IN MAKING AN IMPRESSION

Preliminary examination of the patientSeating the patientSelection of the tray Selection of the materialMaking impression-primary border molding secondary


Preliminary examination of the patient

A complete case history and thorough clinical examination is done. Factors that can complicate impression making are identified. Patient education.


Seating of the patientPosition of the operator for

maxillary impression

Position of the operator for mandibular impression


Selection of tray:“The journey of thousand miles begins with one step”

The beginning of good impression starts with the selection of the correct stock tray.Tray is a device that is used to carry, confine and control impression material while making an impression.The space available in the mouth for upper impression is studied carefully by observation of the width and height of the vestibular spaces with mouth partly open. And in the lower the general form and size of basal seat is studied.





Primary impression making

With alginate (Maxillary)


(Mandibular impression with alginate)


Preliminary impressions using impression compound (Maxillary)


(Mandibular)


Making of special tray


Border molding


Secondary impression


Mandibular border molding


Mandibular secondary impression


Impression techniques in compromised situations

Techniques are modified in compromised situations to achieve as much retention and stability as possible within limits. 1. Hyper active gag reflex2. Restricted mouth opening3. Severely resorbed mandibular ridge4. Hypermobile / hyperplastic ridges


Hyperactive gag reflexPatients problems should be identified before impression is made.a) Prosthodontic management- Avoid thick or over extended trays.- Avoid excess loading of material- Use a fast setting material- Singer’s marble technique can be followedb) Distraction maneuvers- Engage the patient in conversation of some special interest.- Kovats and Krol suggested method can be followedc) Pharmacologic measures- Local anaesthetics - Antihistamines, Sedatives, CNS depressants d) Psychological intervention - Hypnosis helpful in certain cases


Restricted mouth opening

Patient’s may exhibit limited opening of the mouth following radical surgery or a sequel facial burns, or due to other pathological conditions.Impressions with the use of sectional trays are made.


Severely resorbed mandibular ridge

Lack of ideal amount of supporting structures decreases support and encroachment of the surrounding mobile tissues onto the denture border reduces both stability and retention. The main is to gain maximum area of coverage.

Flange technique by Lott & Levin involves making impressions of the soft structures of the mouth adjacent to the buccal, lingual and palatal surfaces and incorporating the resulting extension or flange into the denture.

Tryde used the dynamic impression method.

Krammeck used modelling compound to record the extensions.


Hypermobile or hyperplastic ridges

These ridges should be recorded without distortion. Zafrulla Khan technique. Hobkirk technique and Filler technique




SUMMARY & CONCLUSION

The main objective of impression making is to construct dentures, having maximum retention and stability, without causing any damage to the supporting structures. Dentists should be able to modify his technique to cope with the conditions of the basal tissues as presented by each patient.Thus, it is the responsibility of the dentist, to select the best possible procedures, based on sound knowledge, for achieving the best possible results for the patient.


REFERENCESBernard Levin – Impression for complete dentures. Boucher’s – Prosthodontic treatment for edentulous patients – 11th Edition. Charles M. Heartwell – Syllabus of complete dentures – 4th Edition. Sheldon Winkler – Essentials of complete denture prosthodontics – 2nd Edition. John Joy Manappallil – Complete denture prosthodontics – 1st Edition. Boucher C.O. – A critical analysis of mid-century impression technique for complete denture. JPD 1951; Vol-1. Lee Singer – The marble technique:A method for treating the hopeless gagger for complete dentures.JPD 1973;VOL-29Behruz J Abadi,Gatlazzi –Impression tray for making complete denture impressions.Quintessance Int 1986;vol-10


M.M. Devan – Basic principles of impression making. JPD 1952, Vol-2. Chastain and Porter – “Mucostatics” – Panacea or Propoganda – JPD, 1953; Vol-3. George A. Buckley – Diagnostic factors in the choice of impression material and methods. JPD, 1955 Vol-5.Henry A. Collett – Complete denture impressions. JPD 1965; Vol-15. Iwao Hayakawa, Ikki Watanabe - Impressions for complete denture using new silicone impression materials Quintessence Int. 2003;34.A.M Sofou,Mordohai,Pissoti – Fabrication of a custom made impression tray for making preliminary impression of edentulous mandible. Quintessence Int.1998;VOL-29Tryde,Kaisa olsson,A.A Jensen – Dynamic impression methods.JPD 1965;VOL-16


THANK YOU

“Good Impressions Last Forever”


Date post:	26-Jan-2017
Category:	Education
Upload:	indian-dental-academy
View:	172 times
Download:	1 times