Evaluation provisional Jack

of fracture restorations

H. Koumjian,

D.D.S.,

M.S.D.,*

resistance and Arthur

of resins Nimmo,

used for

D.D.S.**

University of California, Schoolof Dentistry, San Francisco,Calif.; and Temple University, School of Dentistry, Philadelphia, Pa. Fracture resistance of provisional restorations is an important concern for the restorative dentist. Fracture resistance of a material is directly related to the transverse strength. This study evaluated the transverse strengths of provisional resins under varied conditions. Uniform samples were made from seven resins and tested immediately after the set of the material, after 7 days of dry storage, and after 7 days of wet storage. The fractured samples from the 7-day wet storage group were repaired with the same provisional material the sample was made from and fractured again to determine transverse strength for repaired samples. Five of the resins tested demonstrated statistically similar strength in the 7-day wet group. Two were found to he significantly weaker. Absorption of water resulted in a slight, but insignificant decrease in strength. Transverse strengths varied widely in the repaired group, and all materials showed a statistically significant reduction compared with the 7-day wet storage group. (J PROSTHETDENT

1990;64:654-8.)

T

-

00th colored acrylic resin is the material of choice for provisional coverage of teeth that have been prepared for fixed prosthodontic restorations. Acrylic resin is convenient to use and provisional restorations can be made by use of a variety of techniques. l-5 However, some alternative resins have been used for provisional restorations. Two of these alternatives are visible light-cured microfilled composite resin6 and urethane dimethacrylate resin.7y* The ideal provisional restoration should cover and protect the prepared abutment teeth, maintain occlusal and proximal contacts to prevent supereruption or drifting of teeth, preserve marginal integrity, provide acceptable contour, and maintain esthetics. These objectives depend on important physical properties of resins, including polymerization shrinkage, wear resistance, color stability, and strength. In long-span provisional restorations, strength is a critical property. When masticatory forces are applied to a long-span provisional restoration, fracture of the restoration is more likely than with a short-span restoration (Fig. 1). This problem is compounded by the need to place proper embrasures for periodontal health. Fracture of a provisional restoration is annoying to the patient and the dentist. If the restoration is repaired, it may refracture in the future. Alternatively, remaking of the

Presentedat the American Associationfor Dental Researchmeeting, San Francisco,Calif. *Assistant Professor, Restorative Dentistry, University of California, School of Dentistry. **Associate Professor and Director, Division odontics, Department of Prosthodontics, School of Dentistry.

10/l/22009 654

of Removable ProsthTemple University,

provisional restoration can be time consuming. Previous studies of resins used for provisional restorations have evaluated the effect of polymerization in a pressure pot on transverse strength9 and resistance to crack propagation as related to fracture toughness.1° However, there is little in the dental literature concerning fracture resistance of repaired provisional resins. This study determined fracture resistance in vitro of seven resins commonly used for fixed provisional restorations. The effects of water absorption and repair were also evaluated.

MATERIAL

AND

METHODS

The seven resins tested were: Cold Pat (Molloid, Chicago, Ill.), Duralay (Duralay Corp., Worth, Ill.), Protemp (ESPE Premiere, Norristown, Pa.), Snap (Parkell, Farmingdale, N.Y.), Triad (Dentsply International, York, Pa.), Trim (H.J. Bosworth Co., Skokie, Ill.), and Tru Kit (H.J. Bosworth Co.). Test specimens of each material were made according to ADA specification No. 12.11Each material was mixed in accordance with the manufacturer’s specifications, poured into a mold, and allowed to set. The test specimens were 65 mm long, 10 mm wide, and 2.5 mm thick. A total of 210 specimens were prepared, 10 of each of the seven materials for three of our experimental groups. Specimens used in the third group were later repaired and retested as the fourth group. The first group was tested immediately after the set of the specimens. The second group was tested after 7 days of dry storage at room temperature (25’ C). The third group was tested after 7 days of storage in water at 37’ C. The fourth group consisted of the fractured samples from the third group, which were then repaired with the initial material. The unbroken ends

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1990

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NUMBER

6

FRACTURE

RESISTANCE

OF PROVISIONAL

RESINS

Fig. 2. Two halves of broken sample from group III were repositioned with broken edges to outside and unbroken edges to middle. A 45-degree bevel was created before repair.

Fig. 3. Positioning of resin sample on supports before fracture with Instron machine.

of the sample were positioned together with the broken edges to the outside (Fig. 2). A 22.5-degree bevel was placed on each of the two unbroken ends to produce a 45-degree notch, and the original resin material was used to repair the pieces. The repaired samples were tested again after storage for 24 hours. Each specimen was subjected to an increasing load

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applied at a go-degree angle to the center of the specimen with an Instron machine (Instron Corp., Canton, Mass.) with a crosshead speed of 0.05 inch/minute (Fig. 3). The specimens were supported by two stainless steel rods 8 mm in diameter and 50 mm apart. Load values at the time of fracture were recorded. Fracture resistance of resins is related to the transverse

655

KOUMJIAN

60

immediate

7

Day Dry

7

Day Wet

H

Triad

n q

Tru Kit Cold Pat

H

Duralay

0

Protemp

El H

snap Trim

AND

NIMMO

Repair

Testing Condition 4. Transverse strengths (MPa) of resins by testing conditions.

Fig.

Table

I.

Transverse strength of seven resins used for provisional restorations Immediate

Material Cold Pat Tru Kit Duralay Triad Protemp Snap Trim

Mean

?-day

MPa

SD 4.68 10.08 1.98 8.00 4.59 1.96 1.33

76.81 68.31 56.88 51.24 47.27 35.54 29.10

Mean

I

dry

?-day

MPa

72.28 t 73.09 69.06 80.06 66.27 50.57 37.03

SD

Mean

MPa

6.90 4.72 5.90

70.24 70.56 64.96

14.06 3.62 3.09 3.37

70.94 65.67 47.83 35.17

wet

Repaired SD 9.00 4.69 6.15 4.03 6.67 5.92 5.80

Mean

MPa

SD

24.22 I 47.23 40.73 C 35.35 [ 10.00 29.72 26.96

4.45 8.11 14.34 7.16 8.71 6.65 4.68

1

% Reduced 66 33 36 50 85 38 23

Ten samples of each of seven materiala were tested immediately after set, after ‘I-day dry storage, and after ‘I-day wet storage. Samples from wet storage testing were repaired with original material and tested again to test reduction of strength after repair (total of 30 samples of each material). Means of materials connected by vertical line indicates no statistically significant difference (p < 0.05).

strength. The transverse strength of each sample was calculated using the following formula12: 3PI S = 2bd2 where P = fracture load, b = width of the specimen,

I = distance between the supports, and d = thickness of the specimen.

RESULTS Mean values and standard deviations of transverse strength for the materials tested are listed in Table I and summarized in Fig. 4. A two-way analysis of variance (ANOVA) was performed, revealing significant differences (p < 0.05) among the materials and among the four test conditions. Subsequent Student Newman-Keuls tests were performed within paired groups with p < 0.05 indicating significance.

656

In the group tested immediately, Cold Pat resin showed the highest transverse strength, followed by Tru Kit, Duralay, Triad, and Protemp resins. No significant difference was found between Triad and Protemp resins. Snap and Trim resins demonstrated significantly lower strength. In the dry-storage group, Triad resin was the strongest, followed by Tru Kit, Cold Pat, Duralay, and Protemp resins, which did not differ statistically in strength. Snap and Trim resins demonstrated significantly lower strength. In the wet-storage group Triad, Tru Kit, Cold Pat, and Protemp resins were the strongest; the strengths of these materials did not differ significantly. Snap and Trim resins demonstrated lower strength. In the repaired group, Tru Kit and Duralay resins were the strongest. These were followed by Triad and Snap resins. Protemp resin was the weakest material in this group.

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1990

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FRACTURE

RESISTANCE

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DISCUSSION All materials tested showed a significant increase in transverse strength after 7 days of dry storage except Cold Pat resin, which showed a slight but insignificant decrease, and Tru Kit resin, which showed a slight but insignificant increase. Triad, Protemp, Snap, and Trim resins showed significant increases in transverse strength after 7 days of wet storage. The transverse strength values were higher after dry storage than after wet storage for all materials, except Triad, but the differences were not significant. Although a wide variation was noted in the immediate transverse strength, five of the seven materials tested provided statistically similar strength in the 7-day wet-and dry-storage groups. Two materials, Snap and Trim, were consistently weaker than the other materials tested in the immediate, dry-storage, and wet-storage groups. All materials demonstrated a significant weakening of the material after repair.

CLINICAL

IMPLICATIONS

The most important groups in terms of clinical relevance are III and IV. The wet storage group (III) simulates a clinical environment and five of seven resins showed superior fracture resistance, whereas two resins demonstrated markedly weaker resistance. The repair group (IV) demonstrated that a repaired specimen is significantly weaker than the original unfractured specimen. There was wide variation in the weaker fracture-resistance values. Two materials that ranked in the strongest materials in the dry and wet storage groups, Cold Pat and Protemp, showed 66 % and 85 % decreases in transverse strength after repair. When using these materials, it may be more advantageous to make a new provisional restoration than to repair the fractured restoration. The information presented in this study will aid the restorative dentist in selection of a provisional material. It should be kept in mind that these tests are in vitro and that other factors, such as marginal integrity, color stability, and ease of manipulation should also be considered.

SUMMARY

AND

tal conditions. Five of the seven resins demonstrated statistically similar strength and resistance to fracture. However, two resins were significantly weaker. Water absorption did not significantly affect transverse strength. All materials were significantly weaker after repair. The authors acknowledge the efforts of Ms. Hilary Pritchard, editor; Mr. Larry Watanabe, research technician; and Ms. Vickie Leow, graphic artist. Each is affiliated with the Department of Restorative Dentistry, University of California-San Francisco School of Dentistry.

REFERENCES 1. Sotera AJ. A direct technique for fabricating acrylic resin temporary crowns using the Omnivac. J PROSTHET DENT 1973;29:577-80. 2. Federick DR. The provisional fixed partial denture. J PROSTHET DENT 1975;34:520-6. 3. Preston JD. A systematic approach to the control of esthetic form. J PROSTHET DENT 1976;35:393-402. 4. Kaiser DA. Accurate acrylic resin temporary restorations. J PROSTHET DENT 1978;39:158-61. 5. Kaiser DA, Cavazos E. Temporization techniques in fixed prosthodontics. Dent Clin North Am 1985;29:403-12. 6. Wood M. Halpern BG, Lamb MF. Visible light-cured composite resins: an alternative for anterior provisional restorations. J PROSTHET DENT 1984;51:192-4. 7. Haddix JE. A technique for visible light-cured provisional restorations. J PROSTHET DENT 1988;59:512-4. 8. Dennis YB, Mullick SC, Johansen RE. Provisional fixed partial denture using the new visible light curing resin system. Clin Prev Dent 1988;10:10-3. 9. Donovan TE, Hurst RG, Campagni WV. Physical properties of acrylic resin polymerized by four different techniques. J PROSTHET DENT 1985;54:522-4. 10. Gegauff AG, Pryor HG. Fracture toughness of provisional resin for fixed prosthodontics. J PROSTHET DENT 1987;58:23-9. 11. Swaney AC, Paffenbarger GC, Caul HJ, Sweeney WT. American Dental Association Specification No. 12 for denture base resin: Second revision J Am Dent Assoc 1953;46:54-66. 12. Craig RG. Restorative dental materials. S: Louis: CV Mosby Co, 1980;83.

Reprint

requests

to:

DR. JACK H. KOUMJIAN UNIVERSITY OF CALIFORNIA, SAN FRANCISCO SCHOOL OF DENTISTRY D-3244, Box 0758 SAN FRANCISCO, CA 94143-0758

CONCLUSIONS

Seven resins commonly used for provisional restorations were tested for transverse strength under four experimen-

THE

JOURNAL

OF PROSTHETIC

DENTISTRY

657

Evaluation of fracture resistance of resins used for provisional restorations.

Fracture resistance of provisional restorations is an important concern for the restorative dentist. Fracture resistance of a material is directly rel...
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