الفهرس 
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Abstract
Objective : To evaluate stress distribution within and around lithium disilicate, zirconia and hybrid ceramic occlusal veneers bonded to dentin, dentin with prepared cavity and dentin with composite filling. Materials and Methods: Nine freshly extracted human mandibular first molars were distributed into three equal groups (n=3) according to the substrate; group I lithium disilicate (L): LD, LC and LF subgroups, group II zirconia (Z): ZD, ZC and ZF subgroups, group III hybrid ceramic (H): HD, HC and HF subgroups. A dual cure, adhesive resin cement was used to bond all occlusal veneers to corresponding prepared teeth. Finite element analysis was carried out to evaluate the distribution of stresses. Results: Different occlusal veneers preparation designs showed minor differences appeared by changing restoration materials in each model. Under vertical loading zirconia occlusal veneer showed the lowest deformation followed by lithium disilicate occlusal veneer and hybrid ceramics occlusal veneer showed the highest deformations. LF, ZF and HF subgroups and LD, ZD and HD subgroups occlusal veneer can be conservative and safe to use as a restoration to worn posterior teeth. Cement under zirconia restoration showed the lowest deformation followed by lithium disilicate and hybrid ceramics showed the highest deformations. The dentin for the model of LF, ZF and HF subgroup showed the lowest stresses then the model of LD, ZD and HD subgroup and the highest values appeared on model of LC, ZC and HC subgroup Conclusions: All the occlusal veneers preparation designs showed stress values within the safety factor when subjecting the models to the average biting force.