ObjectivePartial maxillectomy and postoperative radiotherapy are both risk factors associated with trismus. This retrospective study aimed to evaluate the incidence and severity of trismus in patients following partial maxillectomy with or without postoperative radiotherapy and to compare free flap reconstruction and prosthetic obturation. MethodsA retrospective review of 40 oral cancer patients who underwent partial maxillectomy with or without postoperative radiotherapy was performed. Maximum interincisal distance recorded at least 6 months after surgery was classified according to a revised subjective-objective management-analytical (SOMA) scale and compared between the free flap reconstruction group (n = 12) and the prosthetic obturation group (n = 28). ResultsTrismus was observed in 16/40 (40%) patients, and severe trismus was observed in 4/40 (10%) patients. Although no significant difference in trismus grade was observed between the free flap reconstruction and prosthetic obturation groups, both severe trismus and radiation-induced osteonecrosis were only seen in the prosthetic obturation group with postoperative radiotherapy. ConclusionFree flap reconstruction was preferable to prosthetic obturation to avoid severe trismus and radiation-induced osteonecrosis in patients who underwent both partial maxillectomy and postoperative radiotherapy.