The aim of this study was to investigate the loss of teeth in positions mesially adjacent to implant-supported fixed dentures (IFDs) after insertion of IFDs in unilateral free-end edentulous spaces in the mandible at dental clinics. There were a total of 157 adjacent teeth. Nine adjacent teeth (5.73%, 9 of 157), 9 opposing teeth (2.59%, 9 of 348), 38 posterior teeth (1.93%, 38 of 1,964), and 3 anterior teeth (0.22%, 3 of 1,380) were lost during the observation period. The percentage of lost adjacent teeth was higher than that of posterior teeth (P = .002). Teeth in positions adjacent to the IFDs require more attention than other remaining teeth.