Aim: The study assesses the effect of different restorative materials and preparation designs on the marginal adaptation of occlusal veneers measured using different methods. Materials and Methods: 60 teeth were prepared to receive occlusal veneers made with three materials (milled and pressed PEEK and lithium disilicate) (20 samples each) and two preparation designs (anatomical and beveled) (10 samples each). After adhesion, samples were mechanically aged, and marginal gaps were evaluated visually using a stereomicroscope and digitally using reverse engineering software. The effect of their different variables on measured outcomes was analyzed using two-way ANOVA, and method agreement was analyzed using paired t-test, intra-class correlation coefficient, and Bland-Altman plot. Results: There was a strong agreement between both methods of evaluation. There was also a significant difference between different materials, with milled PEEK having the best adaptation, followed by lithium disilicate, and pressed PEEK having the highest gaps. The effect of preparation designs was not statistically significant. Conclusions: Milled PEEK had a superior marginal adaptation than Lithium disilicate. PEEK pressing procedure had a negative impact on marginal adaptation. Occlusal veneer preparation design does not affect marginal adaptation that affected the rate of alignment.