Load-bearing capacities of occlusal veneers made of all-ceramic and resin composite: do the substrate and material type affect mechanical durability?

Abstract Background The aim of this study was to evaluate the load-bearing capacity of zirconia, lithium disilicate, and resin-matrix composite occlusal veneers bonded to different substrates: dentin surrounded by enamel (DE), dentin (D), and resin composite (C), simulating eroded teeth. Methods Occlusal veneers (1.0 mm thick) were milled from zirconia (IPS e.max ZirCAD), lithium disilicate (IPS e.max CAD; Initial LiSi Block), and resin-matrix composite (Lava Ultimate), and bonded to the different substrates ( n = 10 per group). Specimens were cemented, subjected to thermo-mechanical aging (1,200,000 cycles; 5–50 °C), and tested under monotonic load-to-fracture. Maximum fracture load (Fmax) data were analyzed using the Shapiro–Wilk and Levene tests for normality and homoscedasticity, followed by two-way ANOVA and Tukey’s post hoc test (α = 0.05). Weibull analysis was performed to assess structural reliability, and Pearson’s correlation analysis was used to evaluate the relationship between bonded surface area and Fmax. Results The results indicated that both restorative material and substrate type significantly affected Fmax. Lithium disilicate veneers exhibited substrate-dependent behavior, with higher fracture loads when bonded to resin composite, intermediate values when bonded to DE, and the lowest values when bonded to D. The resin-matrix composite showed a more homogeneous response across substrates, although Fmax decreased from resin composite to dentin. Zirconia restorations demonstrated consistently high fracture loads across all substrates, without a substrate-dependent trend. Failure modes were predominantly adhesive or mixed for lithium disilicate, whereas cohesive veneer failures predominated for zirconia. Conclusions Both restorative material and substrate condition significantly affected the strength and reliability of ultra-thin occlusal veneers. Zirconia showed the most robust performance and the lowest sensitivity to substrate variations, whereas bonding to resin composite substrates improved reliability compared with dentin. These findings highlight the importance of substrate management and adhesive optimization when restoring eroded teeth.