Changes in marginal gap size of provisional resin crowns after occlusal loading and thermal cycling

Statement of problem. Resin materials used for provisional crowns tend to d evelop enlarged marginal gaps overtime. With the advent of new interim resi n materials in dentistry that are used for longer clinical periods,, contro lled comparative analysis of the structural stability of these materials in the oral environment is required. Purpose. This study analyzed marginal gal, size changes resulting from occl usal loading and thermal cycling and related these results to material prop erties. Material and methods. Groups (n = 10) of provisional crowns were made using 4 resin materials (Jet-relined, Snap-relined, Snap-unrelined, Alike-unreli ned). Specimens n ere first fabricated on a metal master die and fitted wit h and relined on the master die to standardize pretreatment marginal gay si ze. Custom die stems were fabricated from a low-fusing alloy (Cerroblend) a nd cemented with Tempbond cement. The samples were treated with occlusal lo ading (50,000 cycles, 40 N, 4 Hz) and thermocycling (8,000 cycles, 5 degree s C to 60 degrees C). Measurements of marginal gaps were recorded before an d after treatment. Results. The mean changes in marginal gap sizes were Jet-unrelined, 152.1 m u m +/- 69.6; Snap-relined, 548.9 mu m +/- 168.3; Snap-unrelined, 446.6 mu m +/- 91.8; and Alike-unrelined 43.9 mu m +/- 48.7. Two-way ANOVA revealed a significant difference between groups (F = 51.758, df 3,1, P less than or equal to.0001). Tukey/Kramer (P less than or equal to.01 level) indicated a significantly larger gap increase for the Snap-relined and Snap unrelined groups. Conclusion. There were significant differences between different brands of resin materials used fur provisional crowns. Each must be evaluated individ ually for stability in the oral environment.