Fracture Resistance and Failure Mode of Occlusal Veneer Restorations: Effect of Material Type and Bonded Substrate

Purpose: To assess the effect of material type and bonded substrate on fracture resistance and failure mode of occlusal veneer restorations.
Materials and Methods: 90 natural mandibular first molars received occlusal veneer restorations of 1.0 mm thickness, divided into three main groups (n=30) according to the CAD/CAM material type: lithium disilicate ceramic (L), monolithic zirconia (Z) and hybrid ceramic (H). Each main group was further divided into 3 subgroups (n=10) depending on the bonded substrate: dentin (D), dentin with intracoronal cavity (C) and dentin / composite filling (F). Lithium disilicate and hybrid ceramics restorations were etched with 9.5% HF acid and silanated. Monolithic zirconia restorations were sandblasted with 50 μm aluminum oxide particles, then zirconia primer was applied. All restorations were adhesively luted using a dual cure adhesive resin cement. After thermocycling process (5000 cycles; 5-55^o C), specimens were subjected to dynamic loading in a chewing simulator (120.000 cycle; 98N/1.6 Hz). All specimens loaded until fracture using a universal testing machine.
Results: ANOVA and post hoc tukey tests revealed that no statistical significant difference in fracture resistance (P> 0.05). A significant difference was found regarding the restorations bonded to dentin (D) and dentin / composite filling (F) (P<0.05).
Conclusion: Materials type and bonded substrates showed no effect on the fracture resistance of occlusal veneer restorations after aging while, they affect the failure mode of occlusal veneers.