Evaluation of stress distribution generated by endocrown restorations fabricated using CAD/CAM materials on teeth with different crown length and margin designs, using 3-dimensional finite element analysis

Purpose: The aim of this research was to evaluate the influence of endocrown restorations fabricated using different CAD/CAM (computer aided design / manufacturing) materials on stress distributions of mandibular molar teeth with different crown length and margin design under axial and oblique loading conditions, using 3 dimensional (3D) finite element analysis (FEA). Materials and Methods: First, a mandibular molar tooth with root canal treatment based on Wheeler's dental anatomy, and also mandibular spongious and cortical bone models were formed using a 3D modeling software. Next, prepared tooth models were formed with the remaining tooth length of 1.5 and 3 mm, and 2 different margin designs (shoulder and butt margin). A total of 12 models were obtained by applying endocrown restorations fabricated using 3 different CAD/CAM materials (lithium disilicate glass ceramic [IPS e.max CAD; EC], zirconia reinforced lithium silicate glass ceramic [Vita Suprinity; VS] and hybrid ceramic [Vita Enamic; VE]). A total of 300 N force was applied from 4 different areas on occlusal surfaces in both axial or oblique directions. Stress distributions of each model were analyzed by the 3D-FEA method. Von-Mises stresses (VMS) and maximum principal stresses (Pmax) of endocrown, dentin, enamel and resin cement were evaluated using colored images. Results: In both axial and oblique loading conditions stress was concentrated at the loading areas. Among the CAD/CAM materials used, the highest Pmax value was observed in EC material, whereas the lowest value was found in VE material. In general, for resin cement and enamel maximum principal stress values were higher in VE groups compared to VS and VC. For each models, the highest stress values of dentin were found at furcation areas. Regardless of the margin design and force direction, the groups with shorter crown length showed lower Pmax values. Under the oblique loading condition, stresses were observed in wider areas compared to that of axial loading. Conclusion: Within the limitations of this research it can be concluded that CAD/CAM materials, margin design and remaining tooth length are important factors for the magnitude and distribution of generated stress in endocrowns and tooth structures. Further investigations are needed to support the results obtained from this research.