Finite element analysis of Onlay restorations: Influence of Design and Onlay Material on Stress Distribution in Mandibular Molars

Abstract

Background & Objective: Onalys are considered as conservative restorations for posterior teeth. The aim of this study was to evaluate the influence of the preparation design and the material of onlays on stress distribution in mandibular molars, using finite element analysis. Materials & Methods: A 3D model of a mandibular molar was obtained from a CBCT image. Using reverse engineering programs, modification was performed to isolate the dental structures and create their 3D objects. Then, mesio-occluso-distal (MOD) cavities were represented with two widths of the occlusal cavity: one third and two thirds of the intercuspal distance. Therefore, two designs of preparation were performed, conservative and extensive designs. Onlays from three restorative materials were represented; lithium disilicate ceramic, polymer-infiltrated ceramic network (PICN) and nanofill composite resin. Vertical and oblique loads of 600N were applied. Then, stress distribution was studied according to von Mises theory. Results: Color maps showed that stress highly concentrated in tooth structures in the conservative models than in the extensive models. Lithium disilicate ceramic onlays absorbed most of the stress with the least stress concentration in the adjacent structures. On the Contrary, composite resin onlays transmitted most of the stress to the neighboring structures. Furthermore, PICN onlays associated with more stress concentration in dental tissues than lithium disilicate ceramic onlays. The oblique load caused higher stresses in all models than vertical load. Conclusion: Within the limitations of this study, lithium disilicate ceramic onlay was seen to be a suitable choice to restore mandibular molars with large cavities. Moreover, resin composite onlay might be an unfavorable restoration in terms of stress redistribution in restored dental structures.