Reliability and Stress Distribution of Hybrid materials Occlusal Veneers

Objectives: Thinner occlusal veneers have been proposed once they are less invasive when compared to full crowns. This study evaluated the reliability and stress distribution of occlusal veneers produced in two different hybrid materials and thicknesses.
Methods: Eighty-four occlusal veneers were milled using a CAD/CAM system and divided into four groups according to materials and thicknesses (n=21/group). The materials used were resin nanoceramic (RNC) or polymer-infiltrated ceramic (PIC) in two thicknesses (0.5 and 1.0mm). After, they were cemented on dentin-like epoxy resin replicas. Step-stress accelerated life testing was performed with the load applied at the distobuccal cusp tip until fracture or wear. The use level probability Weibull curves and reliability were calculated and plotted. For the finite element analysis (FEA) an axial load of 250N was applied on the distobuccal cusp tip of the fist molar occlusal veneers models. The stress distribution was evaluated according to the criteria of maximum principal stress (σ_max) on the restoration and maximum shear stress (τ_max) on the cement layer.
Results: The beta (β) values were less than 1 for all groups. PIC 0.5 mm group exhibited a significant reduction in the probability of survival at 200N compared to the PIC 1.0mm group (91% and 99% respectively). A significant reduction in the reliability was observed at 400 N compared to 200 N for the groups PIC 1.0mm (88% and 99%) and RNC 0.5mm (83% and 99%). The σ_max values increased from PIC 1.0mm group to PIC 0.5mm (14 MPa and 20 MPa respectively), while σ_max for RNC 0.5mm and RNC 1.0mm groups remained the same (13MPa).
Conclusions: Reliability seems to decrease as the load increases from 200N to 400N, except for PIC 0.5mm and RNC 1.0mm groups. The decrease in occlusal veneer thickness seems to affect the reliability and stress distribution of PIC.