Purpose: To evaluate how the crown-to-implant (C/I) ratio affects the loss of crestal bone at single-crown implants and bridges in patients with periodontal disease. Materials and Methods: A total of 39 patients treated for periodontitis were rehabilitated with 108 implant-supported single crowns and bridges. Each patient was examined over a 5- to 20-year period on a 3- to 6-month recall schedule. At each session, we recorded periodontal clinical parameters. In addition, intraoral radiographs were taken after superstructure insertion (baseline) and then at 1, 3, 5, 10, 15, and 20 years. The study population was divided by anatomical C/I ratio (Group 1: C/I ≤ 1, Group 2: C/I > 1). Results: Implants had a 96.2% 5-year survival rate and 92.6% 20-year survival rate. The overall prevalence was 10.1% for mucositis and 1.1% for peri-implantitis. The survival rate (P = .68), incidence of mucositis (P = .325), and incidence of peri-implantitis (P = .077) did not significantly differ in the group comparison. The mean annual peri-implant bone loss was 0.09 ± 0.41 mm and was not significantly different between the groups. Mean bone loss was not significantly different until the 10th year of observation, during which Group 2 presented significantly less bone loss. The correlation of annual bone loss and clinical C/I ratio showed a small but significant negative effect throughout the entire study period (R = –0.217; P < .01). Conclusions: Increased crestal bone loss was not observed with implants with higher C/I ratios, both anatomical and clinical, and they even showed signs of less crestal bone loss.