Endocrown fixed partial denture: Is it possible?

Whether the replacement of a missing tooth with a fixed partial denture supported by an endodontically treated abutment could be improved with endocrowns is unclear. The purpose of the study was to evaluate the mechanical behavior of a fixed partial denture (FPD) according to the preparation of the abutment teeth (endocrown or complete crown) in terms of stress magnitude in the prosthesis, cement layer, and tooth. A posterior model with 2 abutment teeth (first molar and first premolar) was modeled with a computer-aided design (CAD) software program for conducting a 3-dimensional finite element analysis (FEA). To replace the missing second premolar, the model was replicated in different possible FPDs according to the abutment preparation design (complete crown [Conventional], 2 endocrowns [EC]) or an endocrown on one of the abutment teeth (first molar [ECM] and first premolar [ECP]) for a total of 4 designs. All FPDs were in lithium disilicate. The solids were imported to an analysis software program (ANSYS 19.2) in the standard for the exchange of product data (STEP) format. The mechanical properties were considered isotropic and the materials to show linear elastic and homogeneous behavior. An axial load (300 N) was applied at the occlusal surface of the pontic. The results were evaluated by colorimetric stress maps of von Mises and maximum principal stress in the prosthesis, maximum principal stress and shear stresses on the cement layer, and maximum principal stress in the abutment teeth. The von Mises stresses revealed that all FPD designs behaved similarly and that, considering the maximum principal stress criteria, the pontic was the most stressed region. For the cement layer, the combined designs presented an intermediate behavior, with the ECM more suitable to reducing the stress peak. The conventional preparation allowed less stress concentration in both teeth, and higher stress concentration in the premolar was observed with an endocrown. The endocrown decreased the risk of fracture failure. Considering the risk of debonding failure for the prosthesis, the endocrown preparation was only able to decrease the failure risk when the EC design was used and when only the shear stress was considered. Performing endocrown preparations to retain a 3-unit lithium disilicate FPD is an alternative to conventional complete crown preparations.

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