IMPRESSION TECHNIQUES IN REMIVABLE PARTIAL DENTURE

A partial denture impression is defined as “A negative likeness of a part or all of a partially edentulous arch”. The critical need for finely detailed and meticulously accurate impressions in the practice of partial denture prosthodontics does not need elaboration. Unless the cast upon which the prosthesis is to be fabricated is an exact replica of the mouth, the prosthesis cannot be expected to fit properly, and, of course, an accurate cast can only be obtained from an accurate impression. The impression for a removable partial denture differs from one for a complete denture in important respects

1. Impression techniques in RPD . DR SYLVANA AM PROFESSOR DEPARTMENT OF PROSTHODONTICS SREE ANJANEYA INTITUTE OF DENTAL SCIENCES

2. INTRODUCTION TERMINOLOGIES ANATOMIC FORM AND FUNCTIONAL FORM CONCEPT FOR FUNCTIONAL IMPRESSION DIFFERENT IMPRESSION TECHNIQUES CONCLUSION BIBLIOGRAPHY

3. INTRODUCTION

4. `

5. 1. McLean physiologic impression Realized the need of recording the tissues of the residual ridge that would eventually support a distal extension denture base in the functional or supporting form and then relating this functional impression to the remainder of the arch by means of a second impression Mclean so introduced the first dual impression technique

6. Custom tray for distal extension areas without relief

7. A functional impression is completed Impression is removed from the oral cavity and examined. If acceptable, the functional impression is repositioned in the mouth

8. An alginate over impression made while applying pressure to the previously completed functional impression. The resultant two-piece impression relates the functional form of the posterior ridges to the anatomic form of the remaining teeth

9. After the denture base has been processed, the metal spacer is removed.

10. Heated modelling plastic is carefully applied to the intaglio of the denture base

11. The completed modeling plastic impression

12. Modeling plastic is removed from the ridge crest before the final impression the final impression is made from flowing zinc oxide eugenol paste or a light bodied polysulfide a rubber base

13. Selective pressure impression method The selective pressure impression attempted to direct more force to those portions of the ridge able to absorb the stress without adverse response and to protect the areas of the ridge least able to absorb force. To do this, the tissue surface of the tray is selectively relieved.

14. For the mandibular posterior ridge, the crest of the ridge is not considered to be a pressure-bearing area, so the undersurface of the tray is relieved down to the metal retention struts. The amount of relief obtained will depend on the amount of relief the laboratory provided as the master cast was blocked out, relieved, and duplicated in producing the refractory cast. This will usually be at least 1mm.

15. The buccal shelf is the primary stress-bearing area, so only slight relief is provided, again with the acrylic bur. Any excess of modeling plastic that flowed onto the tissue or inner surface of the tray should be removed. The tissue contact area of the border molding should be scraped lightly with a knife

16. In some patients the soft tissue covering the ridge will be softer and easily displaced. To obtain more relief and prevent excessive tissue displacement, holes may be made through the impression tray to permit the impression material to flow through and dissipate pressure that might otherwise occur

17. Techniques for pouring corrected cast impressions Boxing with a plaster/pumice mix and wax, Beading and boxing with wax, Beading with wax and the two-stage pour, North Carolina technique

18. 4. North carolina technique Large Carborundum wheel is used to trim the ridge area of master cast . No area of functional impression touches cast when framework is seated on cast. Framework and functional impression are placed on master cast and inspected to determine if contact exists between cast and impression.

19. Leading edge of impression is sealed to cast (arrow) to prevent stone from flowing onto teeth during pouring of new ridge area

20. Strip of wax is adapted to box buccal side of impression. Its purpose is to confine stone in area between buccal wax beading and base of cast

21. Correctly proportioned and mixed improved dental stone is poured into boxed impression.

22. Beading and boxing wax as well as sticky wax used for luting framework to cast are removed

23. Framework and impression are removed from cast

24. But; On a practical point of view the impression techniques presented have shortcomings that limit their use in normal clinical conditions. Physiologic impression procedures have a theoretical significance only now as they Use stock trays Unreliable amount of forces to residual ridges Place residual ridges under constant compression May cause premature contacts. Functional relining is time consuming Difficulties in maintaining the occlusal contacts.

25. Altered cast procedure Time consuming Technique sensitive Lingual frenum area is not border molded And need a cast metal framework. fluid wax technique Patient has to open mouth for a long time during the procedure Extremely time consuming Needs more equipments Technique sensitive

26. CONCLUSION

27. Achieving successful function of an RPD depends on equilibrating the resiliency differential between the relatively non-resilient periodontal ligament and the more resilient mucosa covering the residual ridge in such a way that, in function, the RPD will generate and dissipate forces equitably between these two media. If this effort is successful, the goal of the RPD service will be enhanced where finely detailed and meticulously accurate impressions have an indispensable role.

28. REFERENCES: Text book of Dental lab procedures-RPD; Rudd & Morrow, 3rd edi Text book of Mc- crackens - RPD ;11 th edi Text book of Stewart Clinical RPD 3 rd edi Text book of Essentials of RPD Prosthesis; Oliver C Applegate Influence of Impression procedures and occlusal loading on Partial Denture movement--John B. Holmes --J Prosthet Dent. 15:474-481 Load Distribution in extension Saddle Partial Dentures--George W Hindels J Prosthet . Dent 2:1952;92-100 The Partial Denture Base -- O.C.Applegate,J Prosthet Dent. 5:1955;636-648