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The purpose of this study was to predict the fracture resistance of an endodontically treated first maxillary molar with diverse access cavities using the extended finite element model (XFEM).Based on micro–computed tomographic data of first maxillary molars, the model of a natural tooth and 3 endodontically treated teeth with conservative endodontic cavity, modified endodontic cavity, and traditional endodontic cavity were generated. Four static loads (800 N in total) were applied vertically to the contact points. The distributions of von Mises stress and maximum principal stress were calculated. XFEM was performed to simulate crack initiation and propagation in enamel and dentin.In the cervical region, larger stress concentration areas were found in the modified endodontics cavity and the traditional endodontic cavity compared with the natural tooth and the conservative endodontic cavity. Von Mises stress was concentrated around the palatal root, and tensile stress was concentrated on the mesiobuccal root. The XFEM results showed that the cracks in the enamel were initiated from the mesial groove, propagated to the central fossa, and finally initiated the damage in the dentin.The fracture resistance of an endodontically treated tooth was increased by preparing the conservative endodontic cavity. The fracture of the maxillary first molar originated from the mesial groove of the enamel, propagated through the groove, and finally induced the damage in the dentin.