DENTAL, TECHNOLOGY SECTION EDITOR

DANIEL H. GEH:L

Impression technique for maxillary removable partial dentures

Clyde D. Leaih, D.D.S.,* and T. E. Donovan, D.D.S.** University of Southern California, Los Angeles, Calif.

T he preferred design for major connectors of maxil- lary removable partial dentures is a broad palatal plate or anterior and posterior palatal bars.‘” Regardless of which design is selected, intimate contact between the major connector and the palatal mucosa is essential to obtain maximum stability and prevent food entrapment under the major connector.

The cast recovered from the master impression must be an accurate duplication of both the teeth and the palatal tissues. Irreversible hydrocolloid has been rec- ommended as an acceptable material to use in making impressions for metal framework fabrication.‘* ‘, 5 A recent study has demonstrated that properly manipu- lated irreversible hydrocolloid will provide adequate accuracy in the region of the teeth. However, a clinically significant amount of distortion would be expected in the hard palate.6 The amount of distortion that occurs in this region is of sufficient magnitude to prevent contact of the major connector with the palatal mucosa.

Techniques tal compensate for this inaccuracy of the impression have been suggested. One alternative is to use a slightly thicker mix of alginate (irreversible hydrocolloid) in an attempt to minimize the amount of distortion attributed to “slumping” of the impression material.’ Alter:ing the water/powder ratio of the irreversible hydrocolloid from that recommended by the manufacturer can impair certain characteristics of the gel and weaken the final set material.’ Another suggestion has been to place a mound of utility wax in the palatal part of the tray to support the impression material and prevent slumping or distortion5 A poten- tial problem witb this technique is uneven application of the wax, resulting in impression material that is either too thick or too thin in the palatal area. The potential for adhesive failure between the wax and the irreversible hydrocolloid exists and would result in a lack of accurate (duplication. Further, distortion of the

*Assistant Professor and Chairman, Operative Section. **Assistant Professor and Chairman, Biomaterials Science.

THE JOURNAL OF ‘PROSTHETIC DENTISTRY

underlying wax could occur during removal of the impression from the mouth and during manipulations involved in pouring the cast.

One solution is to arbitrarily scrape or relieve the master cast to ensure positive contact between the major connector and palatal mucosa. Because this relief is arbitrary, exact compensation is impossible and may result in either lack of contact in some parts or hypercontact, which would require extensive chairside adjustment. Either of these sequelae is undesirable.

A similar distortion phenomenon has been reported with reversible hydrocolloid impression material. The double duplicating technique developed by Morrison” was designed to compensate for this inaccuracy. This method is successful but has not achieved widespread popularity. Another solution is use of elastomeric impression material in a custom-fabricated acrylic resin tray. This technique yields excellent results; however, the additional step of tray fabrication has been a hindrance to routine use.

This article presents a simplified alternative tech- nique that has given satisfactory results for several years. The master cast recovered from this impression procedure will accurately reproduce the palatal tissues and will require no arbitrary alteration.

TECHNIQUE

1. Make a preliminary impression in a stock tray with irreversible hydrocolloid impression material. Pour the impression in dental stone and recover the diagnostic cast.

2. Outline the palatal tissues to be included in the final impression on the diagnostic cast (Fig. 1). Include all the palatal tissues to within 4 mm of the remaining teeth, along the crest of the ridges and distal to the anticipated posterior extension of the partial denture framework.

3. With autopolymerizing acrylic resin fabricate a custom tray that will cover the outlined area. With a No. 2 round bur, make multiple perforations in the tray (Fig. 2). The tray should be approximately 2 mm thick with no handle.

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Figs. 1 to 8. For legend, see opposite page.

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IMPRESSION TECHNIQUE

4. Try the may in the patient’s mouth and adjust discrepancies that interfere with seating or cause patient discomfort.

5. Mix equal lengths of zinc oxide-eugenol paste (Multiform Impression Paste, Lactona-Surgident, Columbus Mfg. Co., Columbus, Ohio) to a creamy consistency and place on the tissue surface of the tray. Carry the tray to the mouth and make an impression of the palatal tissues.

6. Remove the impression from the mouth and carefully trim excess impression material from the edge of the tray (Fig. 3).

7. Place a ball of utility wax on the ventral surface of the acrylic resin tray (Fig. 4). The wax must be of sufficient thickness to contact the stock tray that will be used to make the overimpression.

8. Position the zinc oxide impression carefully, but firmly, back into the patient’s mouth. The factors of adhesion and interfacial surface tension will retain the tray in a stable Iposition.

9. Try the selected stock tray in the patient’s mouth to verify adequate posterior length and ensure that contact is made with the utility wax. This will main- tain positive pressure on the acrylic resin tray on the palatal mucosa during the impression procedure.

10. Make the overimpression with either reversible or irreversible hydrocolloid impression material. If the former material is used, syringe material is injected around the borders of the resin tray into the rest preparations and around the remaining teeth (Fig. 5). The tempered tray material is then carefully positioned in the mouth, us:ing positive initial pressure so that the resin tray is seated firmly by the impression tray through the wax stop. The washed acrylic resin tray and impression should remain in the overimpression on removal from the patient’s mouth (Figs. 6 to 8).

If irreversible hydrocolloid material is used for the

overimpression, a disposable plastic syringe (Monoject Disposable Dental Syringe, Sherwood Medical Indus- tries, Deland, Fla.) with the tip cut off to allow the material to flow more easily is used to inject the alginate around the resin tray. The stock tray is subsequently filled with irreversible hydrocolloid and the overimpression procedure completed. Alginate- silicone (Ultrafine Impression Material, Buffalo Den- tal Mfg. Co., Inc., Brooklyn, N.Y.) material could also be used for the overimpression.

11. Pour the impression with an improved die stone and recover the master cast in a conventional manner.

DISCUSSION

The technique described will produce an extremely accurate master cast both in the region of the abutment teeth and the palatal mucosa. A precise metal frame- work fabricated on this cast will have intimate, positive contact with the palatal tissues.

The technique is relatively simple and eliminates possible palatal distortions inherent with use of revers- ible or irreversible hydrocolloid materials in stock trays. The technique is time efficient and while it requires fabrication of a custom tray, the design of the tray simplifies the construction when compared to conventional custom trays.

REFERENCES

1. Henderson, D., and Steffel, V. L.: McCracken’s Removable Partial Prostbodontics, ed 5. St. Louis, 1977, The C. V. Mosby co., p 26.

2. Krol, A. J.: Removable Partial Denture Design Outline Syllabus, ed 3. San Francisco, 1981, University of the Pacific Bookstore, p 34.

3. Henderson, D.: Major connectors-united it stands. Dent Clin North Am 17~661, 1973.

4. Kratochvil, F. J., and Vig, R. G.: Principles of Removable

Fig;. 1. Diagnostic cast is outlined for autopolymerizing acrylic resin tray. Fig. 2. Acrylic resin tray is completed, perforated, and ready for try-in. Fig. 3. Impression of palatal tissue is completed with a zinc oxide-eugenol wash. Fig. 4. Impression of palatal tissue is trimmed and a wax stop is placed in preparation for overimpression. Fig. 5. Syringe impression material is carefully injected around palatal impression, teeth, and rest seats. Fig. 6. Final overimpression with palatal impression in place. Fig. 7. Crosscut section of fir& overimpression taken in reversible hydrocolloid illustrates overall impression technique. Fig. 8. Each layer of material is identified in diagrammatic view. 2 = Cast representing patient’s maxillary anatomy; 2 = zinc oxide-eugenol paste; 3 = acrylic resin tray with perforations; 4 = syringe impression material; 5 = wax stop; 6 = overimpression body material; and 7 = reversible hydrocolloid water-cooled tray.

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Partial Dentures. Los Angeles, 1979, University of California, p 57.

5. Applegate, 0. C.: Essentials of Removable Partial Denture Prostheses, ed 2. Philadelphia, 1960, W. B. Saunders Co., p 52.

6. Kaiser, D. A., and Nicholls, J. I.: A study of distortion and surface hardness of improved artificial stone casts. J PRWXHET DENT 36~373, 1976.

7. Phillips, R. W.: Skinner’s Science of Dental Materials, ed 8. Philadelphia, 1982, W. B. Saunders Co., p 131.

8. Morrison, M. L.: Internal precision attachment retainers for partial dentures. J Am Dent Assoc 64:209, 1962.

Reprint requests to: DR. CLYDE D. LEACH

DENTISTRY, UNIVERSITY PARK MC 0641, UNIVEJLWY OF SOUTHERN CALIFORNIA Los ANGELES, CA 90089-0641

AADR PROSTHODONTIC ABSTRACT

Mandibular dysfunction symptoms in a random population C. S. Greene, C. Turner, and D. M. La&in University of Illinois, TMJ and Facial Pain Research Center, Chicago, Ill.

The validity of the diagnosis of mandibular dysfunc- tion (MD) in recent epidemiologic studies has been criticized because of the inclusion of insignificant or inappropriate symptoms such as headache, tenderness, and deviation. The current study was designed to determine the incidence of significant MD symptoms in a random group of 103 patients presenting for admission to a school dental clinic (38 males and 65 females; racial distribution: 52 black, 24 white, 17 Hispanic, 10 other; age range: 11 to 83 years). In the interview phase, patients were asked if they previously or currently had jaw pain on opening, chewing, or yawning; limited jaw movement; sticking or catching during opening or clos-

Supported by USPHS Grant No. DE-5679. Reprinted from the Journal of Dental Research 162 (Special Issue), 1983 (Abst No. 1218)] with permission of the author and the editor.

ing; and clicking or grating noises in the TMJ. In the clinical phase, the TM J and masticator-y muscles were examined for tenderness, jaw opening was measured, and TMJ sounds were noted. A total of 33 patients responded positively to one or more of the interview questions; 18 reported clicking only, while five reported clicking plus occasional catching or sticking. The remaining 10 patients had had various combinations of painful symptoms at some time, which could be regarded as significant. During examination 36 patients were found to have joint sounds, nine had minor tenderness in one or more masticatory muscles, and two were tender over the TMJ area. Interincisal opening ranged from 35 to 57 mm. When painless TMJ sounds and occasional sticking or catching were excluded, only 10% of the patients had previous or current symptoms compatible with the clinical disorders of MD. This figure is much lower than those reported in recent epidemiologic surveys of these disorders.

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