Fracture Resistance and Wear Behavior of Ultra-Thin Occlusal Veneers Made From Translucent Zirconia Ceramics Bonded to Different Tooth Substrates

Objective: Investigation of the mechanical properties of occlusal veneers made from zirconia with varying translucency, bonded to different tooth substrates.

Materials and methods: Sixty-four extracted molars were divided into two groups: preparation within enamel (E) or extending into dentin (D). Veneers were milled from four zirconia ceramics (n = 8): 5Y-TZP (HT), a multilayer of 5 and 3Y-TZP (GT), 3Y-TZP (LT), and 4Y-TZP (MT). After bonding, specimens underwent thermocycling (7500 cycles; 5°C-55°C) and chewing simulation (1,200,000 cycles; 10 kg), followed by investigation of the wear behavior using optical and laser scanning microscopy. Specimens were then loaded to examine fracture resistance.

Results: All specimens except one in the HT group survived artificial aging. Zirconia wear was below the resolution of the 3D scanner, with no significant difference in antagonist vertical loss across materials (p > 0.05). Fracture resistance was significantly higher in E-LT compared with E-HT (p = 0.003). No significant differences (p > 0.05) were observed in fracture resistance between materials bonded to dentin, or between the materials within different substrates.

Conclusions: Veneers made of 3 and 4Y-TZP zirconia showed promising in vitro performance and fracture resistance, regardless of the tooth substrate. All zirconia ceramics exhibited favorable wear behavior.

Clinical significance: As tooth wear rates increase, the use of minimally invasive occlusal veneers is becoming more important. The goal is to create restorations that are both esthetically pleasing and mechanically durable, while keeping them thin to minimize occlusal preparation and still ensure sufficient fracture resistance. Ultra-thin (0.3 mm in the fissures/0.6 mm at the cusps) occlusal veneers made of 4Y-TZP, multilayer and 3Y-TZP zirconia ceramics survived chewing simulation corresponding 5-years. All zirconia restorations showed wear-resistant behavior.