A total of 48 implants were eventually accompanied by a peri-implant infection: the cumulative incidence of peri-implantitis was 9.5, 15.3, 21.0, and 27.9% at 5, 10, 15, and 25 years after the prosthesis delivery, respectively (Fig. 3). After stepwise backward selection, the gender, implant type, and width of keratinized mucosa showed the significant difference in the cumulative survival rate (Table 6, Fig. 4a, b, and e). The difference in implant position and additional soft tissue management did not result in significant differences with respect to the cumulative incidence of peri-implantitis (Fig. 4c, d).

A total of 106 prostheses were applied to 92 patients. Nine prostheses were single crowns, 17 prostheses were implant-supported overdentures, and the other 80 prostheses were multiunit fixed partial dentures. Thirty-seven of the multiunit fixed partial dentures were splinted with natural teeth as an abutment (i.e., tooth implant-supported fixed prostheses). With respect to the materials of the occlusal surface, 21 of the fixed prostheses were veneered with porcelain, and the other 68 were made from dental alloys (Au-Pt or Au-Ag-Pd alloys).

The Kaplan-Meier cumulative survival rate of mechanical complication-free prostheses was 74.9, 68.8, and 56.4% at 10, 15, and 25 years (Fig. 5). The gender difference did not result in a significant difference with respect to the rate of mechanical complication-free prosthesis, but the difference in the type of prosthesis did (Table 7, Fig. 6a, b). For 11 of the 37 tooth implant-supported prostheses, the abutment teeth were extracted due to caries, periodontitis, or root fracture during the observation period. Regarding the implant-supported overdentures, the following mechanical complications were observed: the total number of relinings was 22 times; that of artificial tooth replacement was 17; attachment replacements were performed 15 times; bar fractures were observed in three cases, and screw loosening occurred twice.