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Statement of the problem: Thin, posterior occlusal veneers establish a conservative approach to conventional complete coverage restorations. Information about the proper material and its effect upon fracture resistance, which may affect the durability of the restoration, is still unknown.Objective: This in-vitro study was carried out to assess the effect of variable materials and preparation designs on marginal fit and fracture resistance of CAD/CAM fabricated occlusal veneers.Materials and Methods: A total number of sixty freshly extracted maxillary first premolars were collected. The selected teeth were inspected for being intact, non-restored and free from caries, cracks and severe occlusal erosive lesions. The teeth were chosen to be of comparable bucco-lingual and mesio-distal dimensions. All teeth were mounted along their long axis in epoxy resin templates. A standardized occlusal preparation (simulating advanced occlusal erosion) including enamel removal, dentin exposure and immediate dentin sealing were made. Teeth were randomly assigned equally to three test groups (n=20) according to the material of the CAD/CAM blocks used for fabrication of the occlusal veneers, group (I): Lithium di-silicate glass ceramics (IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein), group (II): Hybrid all-ceramic material (VITA ENAMIC, VITA Zahnfabrik, Germa­ny) and group (III): Nano ceramic reinforced resin composite (BRILLIANT Crios, Coltene/Whaledent AG, Switzerland). Each group was then sub-divided into two equal sub groups (n=10) according the preparation design used for occlusal veneer, where subgroup (1): represented the minimally invasive occlusal veneer preparation resembling occlusal erosion. Subgroup (2): represented occlusal veneer preparation with marginal chamfer. Teeth were restored with 1.0 mm thickness occlusal veneers. Vertical marginal gap distance for all occlusal veneers was measured using stereomicroscope. Following Vertical marginal gap distance measurements, the samples were subjected to cyclic fatigue loading for 60000 cycles which is equivalent to six months clinical service. Then vertical marginal gap distance for all samples was recalculated after fatigue loading testing. Fracture resistance test was done using universal testing machine. The load to fracture for all samples was recorded in Newton. Data were collected, tabulated and statistically analyzed. Results: Two ways ANOVA test results showed that CAD/CAM restorative materials used in this study, regardless of preparation design had a statistically significant effect on mean fracture resistance, whereas, preparation design regardless of type of material used had no statistically significant effect on mean fracture resistance. With Nano ceramic reinforced resin composite, hybrid ceramic and Lithium Di-silicate glass ceramics before or after cyclic fatigue loading; there was no statistically significant difference between marginal gap distances for the two preparation designs. Conclusions: All the tested CAD/CAM materials showed fracture loads above the recommended minimum fracture strength for posterior restorations. CAD/CAM composite resin posterior occlusal veneers were superior to ceramic ones in terms of fracture resistance. All tested materials in both preparation designs whether before or after fatigue loading, exhibited marginal gap distance not exceeding that described in the literature as acceptable range.

Influence of Different Materials and Preparation Designs on Marginal Adaptation and Fracture Resistance of CAD/CAM Fabricated Occlusal Veneers