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 develop enlarged marginal gaps over time. With the advent of new interim resin materials in dentistry that are used for longer clinical periods, controlled comparative analysis of the structural stability of these materials in the oral environment is required. Purpose. This study analyzed marginal gap size changes resulting from occlusal loading and thermal cycling and related these results to material properties. Material and methods. Groups (n = 10) of provisional crowns were made using 4 resin materials (Jet-relined, Snap-relined, Snap-unrelined, Alike-unrelined). Specimens were first fabricated on a metal master die and fitted with and relined on the master die to standardize pretreatment marginal gap size. Custom die stems were fabricated from a low-fusing alloy (Cerroblend) and cemented with Tempbond cement. The samples were treated with occlusal loading (50,000 cycles, 40 N, 4 Hz) and thermocycling (8,000 cycles, 5°C to 60°C). Measurements of marginal gaps were recorded before and after treatment. Results. The mean changes in marginal gap sizes were Jet-relined, 152.1 μm ± 69.6; Snap-relined, 548.9 μm ± 168.3; Snap-unrelined, 446.6 μm ± 91.8; and Alike-unrelined, 43.9 μm ± 48.7. Two-way ANOVA revealed a significant difference between groups (F=51.758, df 3,1, P≤.0001). Tukey/ Kramer (P≤.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 for provisional crowns. Each must be evaluated individually for stability in the oral environment.