The effect of different CAD/CAM materials and thickness on the immediate load-bearing capacity of occlusal veneers

Minimally invasive occlusal veneers fabricated from ceramic and resin-based materials have gained increasing popularity in recent years. The aim of this study was to evaluate the effect of different CAD/CAM materials and restoration thicknesses on the immediate load-bearing capacity of occlusal veneers.

A total of 100 human mandibular molars were prepared for occlusal veneers with a 1-mm circumferential rounded chamfer finish line. A preparation height of 1.5 mm extending from the preparation margin to the occlusal plane was created. The teeth were divided into 10 groups (n = 10), and occlusal veneers were fabricated in two different thicknesses (0.6 and 1.5 mm) using four CAD/CAM block materials: lithium disilicate glass ceramic (IPS e.max), nanoceramic composite (Lava Ultimate and Cerasmart 270), hybrid ceramic (Enamic), and an experimental short fiber-reinforced composite (SFRC CAD). The tested thickness of 0.6 mm is below the minimum thickness recommended by all manufacturers. Restorations were designed using Cerec software. After adhesive cementation, all specimens were stored in water at 37 °C for 2 days, followed by quasi-static loading testing. Data were analyzed using 2-way ANOVA (´restorative material´ and ´restoration thickness`) and Tukey's post hoc test (α <0.05).

The two-way ANOVA demonstrated significant main effects of both restorative material and restoration thickness on fracture load (p < 0.001), whereas the material-thickness interaction was not significant (p = 0.200). SFRC CAD exhibited the highest fracture load (SFRC 0.6 mm = 2560.2 ± 424.5N and SFRC 1.5 mm = 2799.0 ± 655.9N) while IPS e.max (IPS e.max 0.6 mm = 1224.2 ± 363.4N and IPS e.max 1.5 mm = 1799.9 ± 436.8N) showed the lowest. Increasing restoration thickness from 0.6 mm to 1.5 mm significantly resulted in higher fracture load regardless of the restorative material.

Both restorative material and restoration thickness play important roles in the mechanical performance of occlusal veneers. Among the evaluated CAD/CAM materials, the experimental short fiber-reinforced composite demonstrated the highest load-bearing capacity, whereas ceramic and resin-based CAD/CAM materials showed lower values. However, the higher incidence of catastrophic failures involving both restoration and tooth structure in the SFRC CAD groups indicates that fracture load alone should not be considered the only factor for material selection. These findings suggest that ultrathin occlusal veneers may have potential for minimally invasive restorative applications; however, their long-term clinical performance and failure behavior should be further investigated before clinical recommendations can be established.

Occlusal veneers with a thickness of 0.6 mm, minimum thickness recommended by manufacturers, exhibited promising immediate load-bearing capacity, supporting their potential use in minimally invasive restorative. Furthermore, the experimental short fiber-reinforced composite CAD/CAM material demonstrated superior load-bearing capacity compared with the other CAD/CAM materials evaluated in this study.