Fracture Strength of Two Types of Hybrid Ceramic Posterior Occlusal Veneers with Different Thicknesses

Objective: the purpose of this study was to investigate fracture strength of two types of hybrid ceramic posterior occlusal veneers with different thicknesses. Materials and methods: Eighty natural maxillary molars of comparable size and morphology will be selected. Standardization of the teeth preparations will be accomplished using a diamond saw; teeth will be sectioned horizontally, removing all coronal tooth structure 4 mm occlusal to the CEJs leaving exposed dentin centrally and peripheral enamel. Samples will be randomly divided into two groups (n=40) based on restorative materials that will be used: computer-milled hybrid ceramic (ENAMIC) and Resin Nano Ceramic (LAVA ULTIMATE). Each group will be divided into two subgroups (20 samples each) according to the type of preparation (conventional and experimental). The experimental preparation will have an additional preparation feature. Within each subgroup, specimens were subdivided into two classes (consisting of 10 specimens each n=10) based on restoration thickness (0.3, 0.6 mm). Each class will be divided into 2 subclasses (n=5) for testing the fracture resistance and the microleakage. Specimens will be stored in distilled water 37oC for 7 days. Restorations will be adhesively bonded to their respective teeth for measuring fracture. Result: The fracture strengths (mean standard deviation) were 2416 676, and 1777 697, N for Lava Ultimate, and Vita Enamic, respectively. Lava Ultimate had significantly higher fracture strength than the Vita Enamic (p less than 0.05) ;. 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. Conclusions: The 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.