الفهرس 
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Abstract
The present investigation was designed to study the effect of different occlusal veneers design on the microleakage, fracture resistance and mode of failure of bonded posterior occlusal veneers.
Fifty six natural mandibular molars of comparable size and morphology were selected. Teeth were mounted in self cure acrylic resin using a cylindrical Teflon mold at a level of 3 mm apical to their respective CEJs with the aid of a parallelometer for placement standardization.
Standardization of the teeth preparations was accomplished using a diamond saw; teeth were sectioned horizontally, removing all coronal tooth structure 4 mm occlusal to the CEJs leaving exposed dentin centrally and peripheral enamel. Intra-enamel indexing notches were created on the mesial and distal aspects and index was made for all the teeth.
Samples were randomly divided into two groups (n=28) based on preparation design restricted only to occlusal surface or with radial shoulder1ml (axial preparation): computer-milled hybrid ceramic (lithium disilicate).
Each group was divided into two subgroups (14 samples each) according to the type of preparation either with buccal groove or without buccal groove. Each class was divided into 2 subclasses (n=7) for testing the microleakage, fracture resistance and mode of failure. Specimens were stored in distilled water 37oC for 7 days.
A CAD/CAM system (CEREC software version 4.3.1) was used for the fabrication of all samples in this study. Before any intervention, all teeth were scanned, as the “biogeneric copy” mode was used for the construction of the occlusal veneers.
After tooth preparation, each prepared tooth was scanned using the Omnicam. With the aid of both Cerec software and the biogeneric copy option, the scanned unprepared tooth was correlated to the preparation in order to construct a virtual occlusal veneer identical to the tooth form before preparation. The occlusal veneers were cemented over their respective teeth with RelyX™ Ultimate Clicker ™ (Dual cure adhesive Resin Cement).