Ceramic inlays can be used on premolars requiring a class II restoration instead posterior composite resins, amalgam or gold inlays and offer a durable and aesthetic alternative. MOD inlays may increase the susceptibility to fracture. The aim of the study was to investigate the effect of preparation design on stress distribution in premolars with different class II and MOD cavity preparations restored with ceramic inlays. The study was performed on an upper first premolar, using a finite element analysis. Enlarged plaster teeth (scale 2:1) were scanned using a manufactured device. Twenty-two 3D models of maxillary first premolars, with the following designs of class II and MOD ceramic restorations were generated: eleven class II inlays with butt joint margins, eleven MOD inlays with butt joint margins, both with different tapers (between 0 and 10 degree). Computational simulation of an occlusal load of 200 N was conducted, and stresses occurring in the ceramic restorations, and teeth structures were calculated using Ansys finite element analysis software. Occlusal load on inlays restored teeth produces stress surrounding the contact areas. In the teeth restored with ceramic class II inlays, the von Mises equivalent stress values were similar to those the intact tooth. In the teeth restored with ceramic MOD inlays, the von Mises equivalent stress values were higher than in the intact tooth. Within the limitations of the study, it was demonstrated that ceramic inlays on premolars prevent failure and produce a low stress values, even if MOD restorations are used. A taper between 0 and 10 degree of the preparation is not decisive for the stress values. Acknowledgements: This study was supported by the Grant ID_1264 from the Ministry of Education and Research, Romania. Keywords: ceramic inlays, class II restoration, preparation design, finite element analysis