Finite element analysis of maxillary first molar with a 4-wall defect and 1.5-mm-high ferrule restored with fiber-reinforced composite resin posts and resin core: The number and placement of the posts

Statement of problem Whether fiber-reinforced composite (FRC) posts should be inserted in root canals to restore teeth with multiple roots remains unclear. Purpose The purpose of this finite element analysis (FEA) study was to determine the optimal use of FRC posts in an endodontically treated maxillary first molar with a 4-wall defect and 1.5-mm-high ferrule. Material and methods Eight different models of a maxillary first molar were established: no post (NP), post in palatal root (P), post in distobuccal root (DB), post in mesiobuccal root (MB), posts in palatal root and distobuccal root (P+DB), posts in palatal root and mesiobuccal root (P+MB), posts in 2 buccal roots (DB+MB), and posts in all roots (P+DB+MB). Two types of loading were applied: a force of 800 N parallel to the long axis of the tooth to simulate the vertical masticatory force and another force of 225 N at 45 degrees to the long axis of the tooth to simulate the lateral masticatory force. The equivalent stresses on the external surfaces of the tooth tissue, the internal surfaces of the root canals and in the posts, as well as the maximal shear stresses on the post-core interface and the core-dentin interface, were calculated with FEA. Results All the models showed similar maximal equivalent stress values on the external surfaces of the tooth tissue, and stress concentrations were found at the cervical and furcation area. On the internal surfaces of root canals, an increase of equivalent stress at the middle third of the canals with posts and a decrease at the cervical third were observed. Under vertical loading, the P+DB+MB group showed the largest equivalent stress in the post (76.45 MPa in the palatal post), the DB+MB group showed the largest shear stress on the post-core interface (19.02 MPa), and the MB group showed the largest shear stress on the core-dentin interface (12.07 MPa). Under lateral loading, the P+DB+MB group showed the largest equivalent stress in the post (60.11 MPa in the mesiobuccal post) and the largest shear stress on the post-core interface (13.48 MPa) and the DB group showed the largest shear stress on the core-dentin interface (21.03 MPa). Conclusions One post in the palatal canal was found to be appropriate for the FRC post and resin core restoration of a maxillary first molar with a 4-wall defect and 1.5-mm-high ferrule. An additional post in the mesiobuccal canal could help disperse lateral occlusal force and improve retention of the restoration.