RESTORATION OF CARIOUS EXPOSED ABUTMENT TEETH

teeth are also exposed. An impression is made with the impression material of choice and is poured with die stone. The cast, the patient’s fixed partial denture, and the matrix are sent to the laboratory. The post and core is made to fit the prepared tooth and the fixed partial denture. During the period of time for constructing the cast post and core, the abutment teeth must be protected by a temporary restoration.

CONCLUSION An abutment tooth that has sustained extensive root

caries can be successfully preserved and a preexisting

fixed partial denture can be salvaged and reused with the techniques described. This technique will reduce the time and cost to the patient.

REFERENCE

1. Taleghani M, Carter G. Rebuilding abutment teeth to permit use of an existing bridge. Gen Dent 1985;33:54-6.

Reprint requests to: DR. DOMINIC P. Lu NORTHWESTERN MEDICAL CENTER NEW TRIPOLI, PA 18066

Considerations for adhesion of impression materials to impression trays

T. J. Bomberg, D.D.S.,* M. H. Goldfogel, D.D.S.,** W. Hoffman, Jr., D.D.S.,*** and S. E. Bomberg, D.D.S.**** University of Colorado, School of Dentistry, Denver, Colo.

A n impression made with an elastic impression material must be securely attached to the tray to assure an accurate impression. If the material pulls away from the tray during removal from the mouth, the completed impression may fail to return to its original shape and dimension, resulting in a distorted die, wax pattern, and casting.

Several methods for adhesion that involve liquid paint-on cement and mechanical means may be used. These include (1) bonding with an adhesive material, (2) the use of perforations or other devices to retain the material, or (3) a combination of these two methods.

The conventional or liquid paint-on adhesive method is the most commonly used. Each class of elastomeric impression materials has its own specific adhesive for application on impression trays. Failure to adequately apply adhesive material to the tray could compromise retention of the impression material.’

Some of the newer impression materials (polyethers and the addition silicones or polysiloxanes) set up harder than the materials used earlier (polysulfides and conden- sation silicones). This lower flexibility creates more

This study was supported by BRSG Grant 5SO7 RR05890 and G-C International Corp., Scottsdale, Ark.

*Professor, Department of Applied Dentistry. **Associate Professor and Chair, Division of Fixed Prosthodontics. ***Associate Professor, Division of Removable Prosthodontics. ****Lieutenant (Dental Corps), U. S. Navy; Dental Department,

U.S.S. Samuel Gompers, FPO San Francisco, Calif.

THE JOURNAL OF PROSTHETIC DENTISTRY

resistance when the impression and tray are removed from the mouth over undercuts. The polysulfide and polyether adhesives provide the highest bond strengths of the materials to the impression trays. The silicone base impression materials, including the condensation reac- tion and most of the addition reaction materials, have lower bonding values to the adhesive materials.le4

The adhesive must be applied thoroughly to assure retention of the impression material to the impression tray, and a variety of techniques have been described.5-1i All are consistent in emphasizing the completeness of application of the adhesive and the importance of complete drying of the adhesive before starting an impression. Nevertheless, it is common to observe impression trays that either lack or have only a partial application of adhesive.

The most common mechanical method of providing or increasing retention is through the use of perforations in a variety of forms in the impression tray.

This study determined the effect of some of the adhesion factors of various combinations of trays and adhesive usage. These included the use or lack of use of liquid adhesive cement bonding in perforated and non- perforated custom acrylic resin and stock impression trays.

METHOD

A master posterior quadrant model was made by using extracted teeth mounted in a dental stone base. One tooth was prepared for a full veneer cast gold

681

BOMBERG ET AL

Fig. 1. Master model and casting.

Fig. 2. Casting seated on master model and stabilized for measuring.

crown. A casting was made on this preparation by using a direct waxing technique (Fig. 1). The casting was seated on the master model, stabilized with an elastic band, and the marginal opening was measured at two points, one at the midpoint on the facial surface and one at the midpoint on the lingual surface, for later reference (Fig. 2). Measurements to 0.001 mm were made on a traveling microscope (Gaertner Scientific Corporation, Chicago, Ill.)

A series of 60 impressions of the master model were made with one brand of impression material (Exaflex, Regular Body, Lot No. 051584, and Putty, Lot No. 081886, G-C International, Scottsdale, Ariz.) in 12 test cells of five impressions each. Perforated and nonperfo- rated custom acrylic resin trays (COE Tray Plastic, Coe Laboratories, Chicago, Ill.), perforated (Disposable Impression Tray [Perforated], D.L. Saslow, Inc., Mount Prospect, Ill.), and nonperforated (Getz Sanitray, Tele- dyne Getz, Elk Grove Village, Ill.) stock trays were used (Fig. 3). The custom trays of autopolymerizing acrylic resin were made on the master model by following the manufacturer’s instructions (Fig. 4). A double thickness

Fig. 3. Perforated and nonperforated quadrant stock impression trays.

of baseplate wax was adapted over the teeth for a spacer. Aluminum foil was used as a separation medium over the wax spacer.2 Autopolymerizing custom acrylic trays should not be used for a period of time until they become dimensionally stable. ‘z-l5 No newly made custom trays were used within 24 hours for impressions for this study. The perforations in the custom trays were drilled with a No. 8 round bur at approximately 1 cm spacing.

Two impression techniques were used. The first was a single-mix technique. This technique used one mix of the regular viscosity material, part of which was applied directly to and around the prepared and adjacent teeth with the large end of a No. 7 wax spatula. A cold-air syringe was used to direct a light stream of air against the impression material to spread it over the appropriate teeth. Extra material was added if needed. The remain- der of the material was placed in the tray to be seated on the master modelI The second technique used a putty/ wash system. The putty-wash impressions used in this study were made by using the laminated single-mix technique. Regular viscosity material was mixed; some was applied around the prepared and adjacent teeth and the remainder was placed over newly mixed unset putty material in the impression tray and seated on the master model.”

Single-mix impressions were made by using conven- tional adhesive application techniques with either full or no application of the impression material adhesive recommended by the manufacturer. The laminated put- ty/wash impressions were made in trays with either full application or no application of the appropriate impres- sion material adhesive.

Stone dies (Die-Keen, Columbus Dental, St. Louis, MO.) were poured in the impressions under standardized conditions. The casting was seated on each die, the stabilizing elastic band placed, and the marginal opening measured at the same two points as the reference measurements (Fig. 5). Data were analyzed by using a

682 DECEMBER 1988 VOLUME 60 NUMBER 6

CONSIDERATIONS FOR ADHESION

Table I. Effect of adhesive application

Marginal opening in microns

Fig. 4. Custom acrylic resin impression tray on master model.

Fig. 5. Casting seated on die and stabilized for measur- ing.

multiple regression approach. The predictive value of the independent variables was evaluated in terms of the relative contribution of each variable in explaining the variation in marginal opening.

RESULTS

The casting fit on the master model was used as a reference. The reference measurements were compared with the measurements of the marginal opening of the dies made from the various tray, technique, and adhesive combinations and are summarized in Table I. The most replicative impression and resultant die were found in the single-mix technique with full adhesive application to the custom acrylic resin, stock nonperforated and perforated impression trays, a.nd with mechanical reten- tion in perforated custom acrylic resin and stock impres- sion trays. The putty-wash impression technique with full adhesive application yielded poorer but similar results in stock perforated and nonperforated trays, closely followed by the stock perforated tray with no adhesive application.

Impression tray

Full application

Mean SD

None

Mean SD

Custom (acrylic resin) Perforated

Single mix 99.90 Custom (acrylic resin)

Nonperforated Single mix 70.40

Stock Perforated

Single mix 75.70 Putty/wash 85.70

Stock Nonperforated

Single mix 72.40 Putty/wash 88.90

27.88 71.00 13.74

6.54 131.90 63.23

21.80 79.70 34.17 14.96 93.30 20.66

8.92 181.30 114.99 23.65 113.50 45.85

Table II. Regression of marginal opening distance on adhesive use, tray type, perforations, impression technique

Variable B SEB B

Tray selection -8.92500 10.92951 -.08134 Tray perforation -25.10000 8.92391 -.24262= Adhesive -29.20000 8.92391 -.28226* Impression technique 7.55000 10.92951 -.06881

Constant 121.82500 9.7723 Adjusted R* .I1452

B = Unstandardized regression coefficients; SE,, = standard error of’ regression coefficients; (3 = standardized regression coefficient. *p < .Ol.

The casting fit on the dies from single-mix impres- sions made in custom trays and nonperforated stock impression trays with no adhesive applied were signifi- cantly different. The marginal opening was 1.87 to 2.5 times greater and a standard deviation of 10 to 12.9 times greater than the previously described more accurate tray and adhesive combinations used for the replicative impressions and resultant dies.

When the four independent variables (application or nonapplication of adhesive, stock or custom tray, single mix or putty/wash technique, and perforated or nonper- forated trays) were entered in a regression equation using a stepwise approach, only two of the variables showed a significant predictive value. Use of full appli- cation of adhesive and the use of perforated trays were associated with the minimization of marginal opening. The use of stock or custom trays, and the use of the putty/wash or single-mix technique had no significant

THE JOURNAL OF PROSTHETIC DENTISTRY 683

effects on the observed marginal opening. These findings are presented in Table II.

7.

PRACTICAL SIGNIFICANCE 8.

Adequate retention of impression material in the tray is necessary for consistent results. Complete application of impression material adhesive is a critical step in the impression process to assure accurate and consistent results. The results are enhanced, both in accuracy and consistency, when the adhesive is used in a perforated tray. The perforated stock trays used in this study may have had a higher retentive value than other stock perforated trays available on the market because of the size and location of the perforations. Furthermore, the position (parallel or perpendicular to the tensile axis) of retentive perforations affects mechanical retention values and should be a design consideration in stock trays or perforation placement in custom acrylic resin trays.‘* Further examination of current and improved mechani- cal retention factors should be made.

9.

10.

11.

12.

13.

14.

15.

REFERENCES 16.

17.

18.

1.

2.

3.

4.

5.

6.

Davis GB, Moser JB, Brinsden GI. The bonding properties of elastomer tray adhesives. J PROSTHET DENT 1976;36:278-85. Farah JW, Powers JM. On making good impressions. The Dental Advisor 1984;1:1-8. Nicholson J, Porter I, Dolan T. Comparing addition silicone adhesive bond strengths to other elastomeric adhesives [Abstract]. J Dent Res 1983;62:299. Pines M, Penugonda B, Vaidyanathan TK, Schulman A. Adhe- sive bond strength of PVS impression material adhesives [Ab- stract]. J Dent Res 1986;65:259. Shillingburg HT Jr, Hobo S, Whitsett LD. Fundamentals of fixed prosthodontics. 2nd ed. Chicago: Quintessence Publishing Co, 1981;230. Baum L, Phillips RW, Lund MR. Textbook of operative dentistry. Philadelphia: WB Saunders Co, 1981;430.

BOMBERG ET AL

Khera SC. Impression materials and techniques. In: Thayer KE, ed. Fixed prosthodontics. Chicago: Year Book Medical Publish- ers, Inc, 1984;102-3. McCoy RB. Impression techniques utilizing elastomeric materials. In: Baum L, McCoy RB, eds. Advanced restorative dentistry. Philadelphia: WB Saunders Co, 1984;204-5. Dykema RW, Goodacre CJ, Phillips RW. Johnston’s modern practice in fixed prosthodontics. Philadelphia: WB Saunders Co, 1986:115. Gilmore HW, Lund MR, Bales DJ, Vernetti JP. Operative Dentistry. 4th ed. St Louis: CV Mosby Co, 1982;277-8. Sturdevant JR, Sturdevant CM. Gold inlay and gold onlay preparations for class II cavity preparations. In: Sturdevant CM, Barton RE, Sockwell CE, Strickland WD, eds. The art and science of operative dentistry. 2nd ed. St Louis: CV Mosby Co, 1985;458. Eames WB, Sieweke JC. Seven acrylic resins for custom trays and five putty-wash systems compared. J Oper Dent 1980;5: 162-7. Craig RG, ed. Restorative dental materials. 7th ed. St Louis: CV Mosby Co, 1985;508-9. Goldfogel MH, Harvey WL, Winter D. Dimensional change of acrylic resin materials. J PR~STHET DENT 1985;54:284-6. Fehling AW, Hesby RA, Pelleu GB Jr. Dimensional stability of autopolymerizing acrylic resin impression trays. J PR~~THET

DENT 1986;55:592-7. Brokaw WC. A modified technique for rubber-base impressions. Gen Dent 1985;33:230-1. Fusayama T. Laminated single impression technique with silicone. Quintessence Int 1977;8: 15-25. Pines M, Penugonda B, Vaidyanathan TK, Schulman A. Tray perforation effects on the retention of PVS impression material [Abstract]. J Dent Res 1987;66:133.

Reprint requests to: DR. THOMAS J. BOMBERG

UNIVERSITY OF COLORADO HEALTH SCIENCES CENTER SCHOLL OF DENTISTRY DENVER, CO 80262

Contributing author B. Flower, D.D.S., Denver, Colo.

Temperature gradients at two locations within the tooth during cavity preparation in vitro

.

Harold E. Goodis, D.D.S.,” Benjamin Schein, D.D.S., M.Sc.D.,* and Paul Stauffer, M.Sc., E.E.** University of California at San Francisco, Schools of Dentistry and Medicine, San Francisco, Calif.

T his study sought to establish a methodology for measuring temperatures at the dentinoenamel and pul- podentin junctions (DEJ and PD J) during a tooth

reduction procedure. Although temperature itself may not be harmful to the pulp, it is a good guide to other modalities of harm to the pulp, such as intrapulpal pressure.‘,’ Most studies of this kind have been carried

*Assistant Professor, Department of Restorative Dentistry. out by placing a temperature probe through the lingual **Assistant Adjunct Professor, Department of Radiation Oncology. surface of the test tooth until it is in contact with the

684 DECEMBER 1988 VOLUME 60 NUMBER 6