spl imp tech.pptx

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1. SPECIAL IMPRESSION TECHNIQUES FOR DISTAL EXTENSION RPD/CPD BY DR PUTTARAJ.T.K. Prof.& H.O.D. Dept of Prosthodontics & D.M.

2. INTRODUCTION DEFINITIONS RPD IMPRESSION Vs C D IMPRESSION PRIMARY IMPRESSION  FINAL IMPRESSION METHODS  Mc LEAN’S TECHNIQUE HINDEL’S TECHNIQUE SELECTIVE PRESSURE TECHNIQUE FUNCTIONAL RELINING TECHNIQUE FLUID WAX TECHNIQUE ALTERED CAST TECHNIQUE MODIFICATION CONCLUSION REFERENCES

3. INTRODUCTION The construction of a removable partial denture in distal extension cases is a delicate procedure since the prosthesis is supported by two different tissues, namely teeth and mucosa. The different resiliency of these supporting tissues may lead to the instability of the prosthesis. The viscoelastic reaction of ridge mucosa and abutment teeth, by virtue of their periodontal ligaments are not the same.

4. The possible modalities are (1) removable partial dentures with flexible denture bases ( stressbreakers ), (2) use of a floating denture base impression technique , (3) use of a mucofunctional impression technique to relate the denture base to the framework, and (4) use of an end osseous implant. An evaluation of each modality is utmost important INTRODUCTION

5. Definitions of Impression  A negative likeness or copy in reverse of the surface of an object ; imprint of teeth and adjacent structures for use in dentistry. GPT – 8 Partial denture impression . A negative likeness of a part or all of a partially edentulous arch - GPT – 8

6. IMPRESSION TRAYS A receptacle into which suitable impression material is placed to make negative likeness OR A device that is used to carry, confine and control impression material while making an impression.

7. Impression trays can be classified broadly in to stock trays and custom trays Stock trays for partially edentulous patients may be perforated to retain the impression material or they may be constructed with a rimlock for this purpose. Rim lock TRAY-- Another type of stock tray designed for the reversible type of hydrocolloid is water cooled trays. It contains tubes through which water can be circulated for purpose of cooling the tray.

8. Disadvantages: STOCK TRAY A. The peripheral borders cannot be accurately recorded. b. Considerably more bulkier than a custom tray. 

9. Custom impression trays: A. Peripheral borders can be precisely recorded in the impression B. Thickness of impression material can be controlled.

10. Well fitted tray will better support the impression in the palate, then avoiding even present danger of material slumping in vital areas. Custom trays are sometimes needed for mouths that are abnormally or of unusual configuration

11. Classification of impression materials

12. RPD IMPRESSION V/s COMPLETE DENTURE IMPRESSION Partial denture impression records relative soft yielding tissues (the oral mucosa) as well as a hard unyielding substance (the remaining teeth). The complete denture impression records the edentulous mucosa with underlying bone only

13. Removable partial denture impression need to record the teeth that are irregular in contour as well as varying in their vertical relations to occlusal plane. The chosen impression material must be capable of recording the tissue contours as accurately as possible without distortion, which occurs as impression is withdrawn.

14. PRIMARY IMPRESSION Objective: To obtain an impression of all the standing teeth and denture - supporting tissues of each jaw from which study casts may be prepared. 

15. study casts The purpose of the study casts are: To enable special trays and occlusion rims to be constructed if necessary. To examine the occlusion in detail on an articulator . By use of a surveyor, to plan the path of insertion of the proposed denture, arrive at a tentative design and plan any mouth preparation .

16. RATIONALE FOR DEB

17. Factors Influencing Support of Distal Extension Base  Contour and Quality of Soft tissue covering edentulous ridge  Type of bone making up denture-bearing area  Design of partial denture  Amount of tissue coverage of denture base  Amount of occlusal forces  Denture bearing area  Fit of the denture base

18. 1.Contour & Quality of Soft tissue covering edentulous ridge

19. 2. Amount of tissue coverage of denture base

20. 3.Type & accuracy of the impression making

21. 4. Amount of occlusal forces/load

22. 5. Design of partial denture

23. 6.Accuracy &Fit of the denture base

24. 7. Type of bone making up denture-bearing area

25. Impression Methods There are basically two dual impression techniques. 1. The physiologic impression techniques are as follows: A. McLean’s and B. Hindel’s methods, 2.The functional relining method, and 3.The fluid wax method . 4. Selected pressure impression  

26. Indications

27. Physiologic impression techniques The need for physiologic impressions was first recognized by McLean For this dual impression a custom impression tray was constructed over a preliminary cast of the arch  A functional impression of the distal extension ridge was made, and then hydrocolloid impression was made with the first impression held in its functional position with finger pressure  Its an over impression or pick up impression

28. The greatest weakness of the technique was that finger pressure could not produce the same functional displacement of the tissue that biting force produced. Many variations of this technique have been developed and advocated, but all require some form of finger loading pressure as the second impression is made. Physiologic impression techniques

29. Hindels and other developed irreversible hydrocolloid trays for the second impression that were provided with holes so that finger pressure could be applied through the tray as the hydrocolloid impression was made. Physiologic impression techniques

30. The main change that Hindels introduced to McLean ‘s original technique was that The impression of the edentulous ridge was not made under pressure but was an anatomic impression of the ridge at rest made with a free flowing zinc oxide eugenol paste. 

31. As the hydrocolloid second impression was being made, finger pressure was applied through the holes in the tray to the anatomic impression. The pressure had to be maintained until the alginate was completely set By Hindels

32. the main purpose of these techniques was to relate an impression of the edentulous ridge to the teeth under a form of functional loading.

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34. ii. FUNCTIONAL RELINE TECHNIQUE. Most methods of obtaining a physiologic impression for support of a distal extension denture base accomplish the impression procedure before completion of the denture, usually following the construction of the framework. It is possible, however, to obtain the same results after the partial denture has been completed. The technique is referred to as a functional reline. It consists of adding a new surface to the inner, or tissue, side of the denture base. 

35. the procedure may be accomplished before the insertion of the partial denture, or it may be done at a later date because of bone resorption , the denture base no longer fits the ridge adequately. Although the functional reline has many advantages, and for correcting the fit of denture base that has been worn for a period of time is essential, it does present many difficulties.  FUNCTIONAL RELINE TECHNIQUE.

36. To allow room for the impression material between the denture base and the ridge, space must be provided. One of the most accurate methods of ensuring uniform space for the impression is to adapt a soft metal spacer over the ridge on the cast before processing the denture base. After processing, the metal is removed leaving an even space between the base and the edentulous ridge. FUNCTIONAL RELINE TECHNIQUE.

37. The patient must maintain the mouth in a partially open position while the border molding and impression are being accomplished because: 1.The border tissues, cheek, and tongue are thus best controlled and 2.The relationship between the partial denture frame work and the teeth must be observed. FUNCTIONAL RELINE TECHNIQUE.

38. The functional reline method has the advantage that the amount of soft tissue displacement can be controlled by the amount of relief given to the modeling plastic before the final impression is made. The greater the relief the less will be the tissue displacement.  FUNCTIONAL RELINE TECHNIQUE.

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40. OBJECTIVES To obtain maximum extension of the peripheral borders of the denture base while not interfering with the function of movable border tissues. To record the stress bearing areas of the ridges in their functional form. To record non pressure bearing areas in their anatomic form

41. Fluid wax technique The term fluid wax is used to denote waxes that are firm at room temperature and have the ability to flow at mouth temperature. 

42. The key to the use of fluid wax lies in two areas: SPACE AND TIME . Space refers to the amount of relief provided between the impression tray and the edentulous ridge--1 to 2 mm is desired. Each time the tray is introduced into the mouth, it must remain in place 5 to 7 minutes to allow the wax to flow and to prevent build-up of pressure under the tray with resulting distortion or displacement of the tissue. Fluid wax technique

43. The water bath maintained at 51° to 54° C into which a container of the wax is placed. At this temperature the wax becomes fluid. The wax is painted on the tissue side of the impression tray with a brush.  Fluid wax technique

44. The tray is seated in the mouth. The patients must remain with the mouth approximately half open for about 5 minutes. The tray is removed, and the wax examined for evidence of tissue contact, Where tissue contact is present the wax surface will be dull.  Fluid wax technique

45.  If needed additional wax is painted on those areas not in contact with the tissue. For the buccal and distobuccal extension in a mandibular impression the patient must move to a wide- open-mouth position. This will activate the buccinator muscle and pterygomandibular raphe and produce the desired border anatomy.  Fluid wax technique

46. For the proper lingual extension for a mandibular impression the patient must thrust the tongue into the cheek opposite the side of the arch being border molded . The distolingual extension is obtained by having the patient press the tongue forward against the lingual surface of the anterior teeth. Fluid wax technique

47. These movements must be repeated a number of times after the impression has been in the mouth long enough for the wax to have softened sufficiently to flow.  Fluid wax technique

48. When the impression evidences complete tissue contact and when the anatomy of the limiting border structure is evident, the impression should be replaced in the mouth for 12 minutes. This final time to be certain that the wax has completely flowed and released any pressure that may be present.  Fluid wax technique

49. T he fluid wax impression technique can produce an accurate impression if the technique is properly executed The procedure is time consuming , but if the time periods are not followed accurately, an impression with excessive tissue displacement will result.  Fluid wax technique Limitations

50. Selective Pressure technique Impression materials Zinc-oxide Eugenol paste Rubber base materials 

51. Impression technique Border molding Making impression with the ZOE or Rubber base materials The critical point is to determine visually that all rest and indirect retainers are completely seated 

52. Technique

53. Selective pressure technique

54. Altered cast technique

55. Altered cast technique

56. conclusion Partially edentulous mouths with distal-extension ridges present the challenge of correctly registering two tissues as dissimilar as teeth and edentulous ridges . In removable partial denture, impression need to consider into the harmony between uncompressible hard tissue and delicate structures with variable compressibility's.

57. Thank you-stay SAFE