Zhang Y, et al. - Using the extended finite element model (XFEM), researchers predicted the fracture resistance of an endodontically treated first maxillary molar with diverse access cavities. The model of a natural tooth and 3 endodontically treated teeth with conservative endodontic cavity, modified endodontic cavity and traditional endodontic cavity were generated based on micro–computed tomographic data of first maxillary molars. By preparing the conservative endodontic cavity, the fracture resistance of an endodontically treated tooth was increased. The first molar maxillary fracture originated from the enamel's mesial groove, spread through the groove and eventually caused dentin damage.