Finite element analysis of maxillary first molar with mesial-occlusal-distal-palatal defect restored with different post-and-core strategies

Purpose: To explore which restoration strategy generates the most favorable stress distribution in an endodontically-treated maxillary first molar with mesial-occlusal-distal-palatal defect.Methods: Models with one post in palatal canal (PP), each post in palatal and distobuccal canals (PDP), each post in palatal and mesiobuccal canals (PMP), and each post in all canals (PDMP) were established for an endodontically-treated maxillary first molar with mesial-occlusal-distalpalatal defect either with fiber-reinforced composite (FRC) post or gold alloy cast (GAC) post. A 400-N vertical force and a 225-N lateral force were respectively applied. The Mohr-Coulomb stress ratio (aMC ratio) in the residual tooth structure (RTS), the resin cement, and the crowns, the tensile stress (at) and compressive stress (ac) in the FRC posts, the von-Mises stress ratio (avM ratio) in the GAC post-and-cores, and the at and shear stress (as) at the adhesive interfaces were calculated using finite element analysis.Results: FRC posts generated lower aMC ratio than GAC posts in the RTS (0.3274-0.3643 vs. 0.3399-0.4118). Among the FRC post groups, the PDMP group got the lowest as at the dentin-post interface (14.92 MPa) and the abutment-crown interface (8.242 MPa) under vertical loading, as well as the lowest aMC ratio in the RTS (0.3381) and the lowest as at the dentin-post interface (38.00 MPa) under lateral loading.Conclusions: From the point of stress distribution, placing FRC posts in the palatal, distobuccal, and mesiobuccal canals is the optimal strategy in restoring a severely damaged maxillary first molar, provided that lateral occlusal force is reduced.