Stress evaluation of different cad-on material combinations in crown design over conventional hand-layered zirconia - an in vitro 3d finite element analysis.

Objective: Zirconia-based restorations are widely used for fixed partial dentures but are prone to veneering porcelain chipping. The CAD-on technique, combining a zirconia or polymer coping with a lithium disilicate veneer, may enhance biomechanical performance. This study evaluated stress distribution and deformation of different CAD-on combinations versus conventional hand-layered zirconia crowns using finite element analysis (FEA). Materials and Methods: Mandibular molar crowns were modelled in four groups: Group 1 - conventional hand-layered zirconia; Group 2 - zirconia coping with lithium disilicate veneer; Group 3 - BioHPP (polyethyleetherketone) coping with lithium disilicate veneer; Group 4 - PEKK (polyethyleketoneketone) coping with lithium disilicate veneer. A 280 N static occlusal load was applied at five points of occlusal surface. Stress and deformation were analyzed with ANSYS; results were compared statistically (ANOVA, post hoc Tukey, p < 0.05). Results: Group 1 showed the highest occlusal von mises stress (1.341 ± 0.086) and deformation (0.099 - 0.100 mm). CAD-on crowns significantly reduced stress and deformation, with BioHPP and PEKK groups showing the most favorable outcomes. Conclusion: CAD-on crowns, especially with polymer copings, provided superior biomechanical performance compared to conventional hand-layered zirconia crowns. Clinical implementation: CAD-on crowns, particularly those with BioHPP and PEKK copings, demonstrated lower stress concentration and deformation, indicating their suitability for patients with high occlusal loads or parafunctional habits. Incorporating these polymer-based copings may improve long-term success rates compared to conventional hand-layered zirconia crowns.