الفهرس 
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Abstract
Aim of the study: The purpose of this in vitro study was to evaluate the effect of using different material type and different incisal preparation designs on fracture resistance of ceramic laminate veneer restorations on mandibular incisors. Materials and methods: Ninety-six freshly extracted mandibular lateral incisors were randomly allocated into four main groups (n=24) according to the design of the incisal preparation (horizontal bevel, incisal overlap, facial bevel, lingual bevel). Each group was subdivided into three subgroups(n=8) according to restorative material type used(zirconia, Lithium disilicate, polymer-infiltrated). Laminate veneer restorations were constructed and then cemented to their corresponding. The specimens were subjected to 10,000 cycles in temperature between 5˚ C and 55˚ C to simulate one year in oral cavity. Also, were subjected to 240,000 repeated load cycles to simulate one year in the oral cavity. Fracture resistance test was done using universal testing machine with load vertically on incisal edge along with the long axis. The load needed for fracture of each specimen was recorded automatically in Newtons (N) using a special software. Then, the data were statistically analyzed. Three-dimensional finite element analysis models were modeled. Conclusions: Incisal preparation design and material type influenced the fracture resistance of mandibular incisors restored with laminate veneers. Based on the fracture load, all tested laminate veneers with horizontal bevel, incisal overlap, facial bevel and lingual bevel can withstand the normal bite force in mandibular incisor area. The lingual bevel and incisal overlap designs can increase the fracture load of monolithic zirconia laminate veneers. All incisal preparation designs performed equally with lithium disilicate laminate veneers with increased fracture load with horizontal and facial bevel designs. Only the incisal overlap design performed better than any other design in polymer-infiltrated laminate veneers.