Fracture strength of ultrathin occlusal veneer restorations made from CAD/CAM composite or hybrid ceramic materials

PurposeThis study compared the fracture strengths and failure modes of ultrathin (0.3-mm) occlusal composite or hybrid ceramic veneers.MethodsSixty extracted maxillary molars were sectioned to remove the entire coronal structure 4 mm occlusal to the cementoenamel junction (CEJ), leaving a flat area of exposed dentin and peripheral enamel. Standardized occlusal veneers with a central fossa thickness of 0.3 mm were milled from a computer-aided design (CAD)/computer-aided manufacturing (CAM) composite (Paradigm MZ100), a resin nanoceramic (Lava Ultimate), and a hybrid ceramic (Vita Enamic) (N = 20). Each occlusal veneer was cemented with a self-adhesive resin cement (RelyX Unicem) on the prepared teeth. The restored teeth were loaded vertically to determine the fracture strength. Strength values were statistically analyzed using one-way analysis of variance (ANOVA) and Scheffe's post hoc test (significance level 0.05). The mode of failure of each specimen was classified and the correlation between fracture strength and failure mode was analyzed using Spearman's rank-order test.ResultsThe fracture strengths (mean ± standard deviation) were 2416 ± 640, 1752 ± 676, and 1777 ± 697 N for Lava Ultimate, Paradigm MZ100, and Vita Enamic, respectively. Lava Ultimate had significantly higher fracture strength than the other two materials (p < 0.05); the fracture strengths of Paradigm MZ100 and Vita Enamic were not significantly different. No correlation between fracture strengths and failure modes was found within each material. Most specimens (48 out of 60) fractured in the restoration without involving tooth structures.ConclusionsThe fracture strength of ultrathin occlusal veneers made from the novel ceramic hybrid matched the strength of CAD/CAM composite. The highest strength was found with the resin nanoceramic material.