The aim of this study was to evaluate the deflection and stress distribution in endodontically treated molars restored by endocrowns from different materials available for the computer-aided design/computer-aided manufacturing (CAD/CAM) technique using three-dimensional finite element analysis. The models represented extensively damaged molars restored by endocrowns from the following materials: translucent zirconia; zirconia-reinforced glass ceramic; lithium disilicate glass ceramic; polymer-infiltrated ceramic network (PICN) and resin nanoceramic. Axial and oblique loadings were applied and the resulting stress distribution and deflection were analyzed. The Mohr–Coulomb (MC) ratio was also calculated in all models. The translucent zirconia endocrown showed the highest stress concentration within it and the least stress in dental structures. The resin nanoceramic model was associated with the greatest stress concentration in dental tissues, followed by the PICN model. Stress was also concentrated in the distal region of the cement layer. The MC ratio in the cement was higher than 1 in the resin nanoceramic model. Oblique loading caused higher stresses in all components and greater displacement than axial loading, whatever the material of the endocrown was. The translucent zirconia model recorded deflections of enamel and dentin (38.4 µm and 35.7 µm, respectively), while resin nanoceramic showed the highest stress concentration and displacement in the tooth–endocrown complex.

Objectives The aim of this study was to evaluate the influence of inlays/onlays with or without pulp extension from different materials on stress distribution in endodontically treated molars by three-dimensional finite element analysis (3D FEA). Materials and Methods We used 3D mandibular molar models in this study. The models represented mesio-occluso-distal (MOD) cavities restored by inlays, onlays that covered buccal cusps, and onlays that covered all cusps with pulp extension (modified inlay/onlay) or without pulp extension (conventional inlay/onlay). Three materials (L: lithium disilicate glass-ceramic, P: polymer-infiltrated ceramic network [PICN], and C: nanofilled composite resin) were utilized. A force of 600 N was applied vertically and obliquely. Stress distribution in FEA models was analyzed using the von Mises theory. Results The results revealed that an oblique load generated higher stresses than vertical load. Composite resin restorations transmitted almost all the stress to the neighboring tooth structures, while lithium disilicate ceramic restorations absorbed most of the stresses. Moreover, modified inlays and onlays with pulp extension proved better than conventional inlays/onlays in terms of stress redistribution in dental structures. Onlays showed a better pattern of stress distribution than inlays within the restoration and the restored tooth. Conclusions According to stress distribution in dental structures, modified lithium disilicate ceramic onlays with pulp extension have been found to be the best choice to restore endodontically treated molars among the studied restorations.

Background: This study aimed to evaluate the influence of inlays/onlays and their material on stress distribution in mandibular molars with large cavities, using finite element analysis (FEA). Methods: 3D models of the first mandibular molar were created. Then, a mesio-occluso-distal cavity was created, and cusps were reduced (1.5 mm for buccal cusps and 1 mm for lingual cusps). The restorations were: inlay, onlay that covered buccal cusps (B models), and onlay that covered all cusps (LB models). Inlays and onlays were represented by two materials: nanofill composite resin and polymer-infiltrated ceramic network (PICN). Vertical load of 600 N was applied and von Mises stresses were calculated. Results: Inlay models showed higher stress concentration in tooth structures than onlay models. Composite resin inlays and onlays transmitted most of the stress to adjacent structures. On the other hand, PICN inlays/onlays absorbed most of stress and transmitted less stress to dental structures than composite resin restorations. Moreover, stress concentrations in PICN onlay models (B-buccal cusps and LB-all cusps) were similar, while composite resin LB onlay showed higher stress concentration in dental structures than composite resin B onlay. Conclusions: Onlays showed better stress distribution than inlays. PICN might be a suitable choice as a restorative material of inlay/onlay for large cavities in molars, while the composite resin is unfavorable material for such restorations in terms of stress redistribution in dental structures.

Introduction: Onlays are conservative restorations for posterior teeth that cover one cusp or more. Objectives: The aim of this study was to evaluate fatigue behavior and stress distribution in mandibular molars with different onlays and preparation designs under static and cyclic conditions, using finite element analysis. Material and methods: A model of a mandibular molar was obtained from a CBCT image. Mesio-occluso-distal cavities were presented with conservative and extensive buccolingual widths of the occlusal cavity. Buccal and lingual cusps were reduced. Therefore, onlays that covered buccal cusps and onlays that covered all cusps designs were obtained. All onlays were produced from three materials: lithium disilicate ceramic (LDS), polymer-infiltrated ceramic network (PICN), and zirconia ceramic. Safety factor was calculated and stress distribution was analyzed according to von Mises and maximum principal stress theories under static and cyclic conditions. Results: Cyclic loading caused higher stresses than static loading. The safety factor of zirconia and LDS onlays was higher than 1, except for conservative preparation with all-cusp coverage. PICN showed the lowest values of safety factors and the highest stress concentration in the dental tissues, which was associated with the least stresses in onlays. LDS and zirconia ceramic onlays showed lower stress concentration in dental structures than PICN. Conclusions: Loading conditions affected the results of stress in all models. Zirconia ceramic could be a suitable choice to restore mandibular molars, while PICN onlay might be an inappropriate restoration in terms of safety factors and stress distribution in restored dental structures.