The purpose of this study was to investigate fracture strength of different lithium disilicate occlusal veneers designs with different tooth preparations.

Material and method: Fifty-six extracted human mandibular molars were collected with relatively comparable size and standardization done by diamond saw and it will receive. 6mm lithium disilicate occlusal veneers. Specimens will be divided into two main groups, each of these groups contains 28 samples (group A&B), the first group represents occlusal veneers with 1.0 ml with radial shoulder finish line design includes axial surfaces for a2 ml length, while the second group represents occlusal veneers preparation without finish line. Each main group will be subdivided into 2 subtypes groups (A1, A2, B1, B2), each subtype group contains 14 samples, the first subtype group will receive a buccal groove, while the second subgroup will be without grooves. Each subgroup will be divided into 2 classes (7 samples) according to the type of test it will be subjected to: microleakage, bond strength.

Results: The fracture strength is (mean value+ standard deviation) in plain occlusal reduction without vs with buccal groove (890.36 [+ or -] 42.51N), (865.69 [+ or -] 36.79N). The fracture strength is (mean value [+ or -] standard deviation) in occlusal reduction with radial shoulder, without or with buccal groove (835.36 [+ or -] 42.51N), (820.69 [+ or -] 36.79N), with non-significant difference p value 0.05.

Conclusions: All tested occlusal veneer designs proved to withstand normal and parafunctional masticatory forces with non-significant statistical difference.