Statement of the problem Ultrathin veneers were introduced as a more conservative approach for restoration of lost occlusal tissue but limited data is present regarding its performance.

Objective: An in-vitro study done to assess the effect of occlusal veneer thickness variation of diverse CAD/CAM materials on the marginal adaptation of the indirect restoration.

Materials and Methods: Sixty freshly extracted premolars were gathered and prepared. CAD/CAM occlusal veneers were milled from 3 different materials: IPS e-max, Vita Enamic and Lava Ultimate
In two thickness 1 mm and 0.5mm thickness (n=10). Marginal gap was measured. Two way ANOVA test was used to examine the effect of different ceramic materials and different thicknesses on marginal adaptation of occlusal veneer.

Results: The results showed that with the 1mm thickness, no statistically significant differences in marginal gap mean values between different materials. On the other hand, with the 0.5mm thickness, IPS e.max CAD presented statistically significant higher mean marginal gap compared to the other groups.

Conclusion: 0.5 mm ultrathin CAD/CAM manufactured occlusal veneers showed non-Significantly higher mean marginal gap values compared to 1mm thickness occlusal veneers. IPS e.max ultrathin occlusal veneers showed less adaptation compared to hybrid CAD/CAM veneers used in the study.