الفهرس 
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Abstract
Statement of problem : Laminate veneer restorations represent an esthetic conservative treatment in diastema closure. However, the ceramic materials are poor in tensile strength which may affect the success of porcelain laminate veneer, especially when used in diastema closure, due to increased stress in free extensions of ceramic into the interproximal area. Aim of the study: To evaluate the effect of using three different ceramic materials and two light cured resin cements on the fracture resistance and stress distribution of the laminate veneer used for diastema closure. Materials and methods : A typodont maxillary central incisor was prepared with a butt-joint design. Sixty prepared resin abutments were milled from PMMA resin disk (Yamahachi) and used in this study. The resin abutments were divided into three groups according to ceramic materials (n=20). Sixty laminate veneers were milled from IPS e.max CAD, Celtra Duo, and Katana UTML. Each group was divided into two subgroups according to cement type (n=10). Half of the laminate veneers of each group were cemented with Variolink Esthetic resin cement and the other half were cemented with RelyX Veneer resin cement. The specimens were subjected to thermocycling (10 000 cycles) and cyclic loading (150 000 cycles). The specimens were subjected to a fracture resistance test with angle 135 ˚ at the lingual surface of the incisal edge. Then, the data were statistically analyzed. Three-dimensional finite element models were modeled and the maximum principal stresses were evaluated. Results : There was a significant difference between ceramic materials and resin cements in fracture resistance of laminate veneer with the highest fracture resistance in IPS e.max CAD (272.57±8.44 N), followed by Katana UMTL (249.77±18.43 N). The least fracture resistance was in Celtra Duo (195.34±38.22 N). Variolink Esthetic cement showed higher fracture resistance than RelyX Veneer cement. The highest maximum modified von Mises was recorded in Celtra Duo and the lowest in IPS e.max CAD. Conclusions : Both restoration type and resin cement type affect the fracture resistance and stress distribution of laminate veneer. Variolink Esthetic cement enhanced the fracture resistance of the laminate veneer.