Objectives: Evaluating the fracture resistance and failure mode of human maxillary premolars restored with two ceramic onlay materials prepared with two preparation designs.
Materials and methods: A total of 40 extracted, human maxillary premolars were selected and divided into two groups according to preparation design; Group A: MOD cavity with anatomical reduction of functional cusp and Group F: MOD cavity with flat reduction of the functional cusp. Each group was divided into two subgroups according to the material of construction; Subgroup S: restored using zirconia-reinforced glass-ceramic and Subgroup E: restored using hybrid ceramic. The finished onlay restorations were luted to prepared teeth using self-adhesive resin cement. Specimens were exposed to thermocycling for 5000 cycles. Fracture resistance was assessed using a Universal testing machine. Failure mode was evaluated using a stereomicroscope. Two-way ANOVA was used to assess the effect of different tested variables and their interaction. Intergroup comparison was done using one-way ANOVA followed by Tukey's post hoc test. The significance level was set at p≤0.05 within all tests.
Results: Two-Way ANOVA showed that ceramic material had no significant effect on the fracture resistance of restored teeth. While the preparation design had a statistically significant effect. The interactions between the independent variables, ceramic materials, and preparation designs had a significant effect on the fracture resistance of teeth.
Conclusion: Both preparation designs and materials showed clinically acceptable fracture resistance of onlay restorations. All subgroups showed high fracture resistance and favorable failure modes except VITA SUPRINITY with anatomical reduction of the functional cusp.