Methods: For mechanical fatigue testing, thirty intact maxillary-central-incisors were randomly divided into three groups (n=10) according to tooth-preparation and laminate-veneer design. Group (C): Control conventional wingless laminate-veneers, group (1W): One-proximal-wing laminate-veneers, and group (2W): Two-proximal-wing laminate-veneers. Ceramic-laminate-veneers were milled from IPS-Empress-CAD blocks (Ivoclar,Vivadent) using CAD/CAM technology and bonded onto their corresponding teeth by adhesive-resin-cement (RelyX unicem, 3M ESPE).Teeth were subjected to fatigue loading and failure loads were statistically analyzed using ANOVA and Newman Keuls post-hoc tests (P≤ 0.05).For the 3D-FEA, representative restored tooth from each tested group was scanned (Micro-CT-scanner, Extlore Locus SP,GE) and 3D-FE models were constructed. Distributed load of 100N was applied on the palatal surface of model and stresses within laminate-veneers as well as within remaining tooth structure were analyzed for each model.
Results: Group(C) recorded highest mean failure load at 274.9N followed by Group (1W) at 231.7N, while lowest failure load was recorded for Group (2W) at 196.6N. FEA validated fatigue results by revealing that stresses maximized within the remaining tooth structure for all tested groups in palatal dentin with highest stresses recorded for group (2W) FE-model. Similarly, stress patterns concentrated at middle half of the laminate-veneers for all tested groups with highest stresses recorded within the laminate-veneer of group (2W) FE-model.
Conclusions: Within the limitations of this study, it was demonstrated that both tooth-preparation and Laminate-veneer designs had a significant effect on fatigue failure and stress distribution within CAD/CAM ceramic-laminate-veneers.