Combined implant-residual tooth supported prosthesis after tooth hemisection: A finite element analysis.

Tooth hemisection preserves partial tooth structure and reduces the resorption of alveolar bone. The aim of this study was to analyze the feasibility of preserving a molar after hemisection and inserting a dental implant with different prosthetic superstructures by means of finite element analysis. First, the distance between the root of the mandibular second premolar and the distal root of the first molar were measured in 80 cone beam computed tomography (CBCT) data sets. Based on these data, the lower right posterior jaw segment was reconstructed and the geometries of the appropriate implant were imported. Four models were created: (1) Hemi-1: An implant (3.7×9mm) replaced the mesial root of the molar, and a single crown was placed on the implant and residual tooth. (2) Hemi-2: Two separate crowns were generated for the implant and the residual tooth. (3) Single: An implant (5.5×9mm) with crown replaced the whole molar. (4) FPD: A 3-unit fixed partial denture combined the distal residual part of the molar and premolar. The results indicated that stresses in the cortical bone and strains in the majority region of the spongious bone were below the physiological upper limits. There were higher stresses in implant with the Hemi-1 and Single models, which had the same maximum values of 45.0MPa. The FPD models represented the higher values of stresses in the teeth and strains in PDL compared to other models. From a biomechanical point of view, it can be concluded that a combination of an implant and residual molar after tooth hemisection is an acceptable treatment option.