Objective: Marginal bone loss (MBL), a prognostic parameter for implant success, is associated with implant- and patient-related variables. The purpose of this study was to analyze the effects of the crown-to-implant ratio and independent factors of implant diameter, implant length, implant type, location, and platform switching on distal and mesial MBLs at the 6-, 12-, 24-, and 36-month recall sessions of single crown implant-supported restorations. Method and materials: Radiographic and clinical data of patients treated with single crown implants were collected. MBL was measured at the baseline and recall sessions on panoramic radiographs. The crown-to-implant ratio was calculated by dividing the length of the crown by that of the dental implant. Results: The crown-to-implant ratio had a moderately positive correlation with distal MBL at the 6-month recall session (P .05, r = 0.469) and a weakly positive correlation at the 12- (P .05, r = 0.220), 24- (P .05, r = 0.214), and 36- (P .05, r = 0.250) month recall sessions. Distal and mesial MBL did not significantly differ among the four implant types at any recall session (P > .05). The crown-to-implant ratio had no significant correlation with mesial MBL at the 12-, 24-, or 36-month recall session (P > .05), and a moderately positive correlation at the 6-month recall session (P .001, r = 0.434). Conclusions: MBL was similar among different implant types in the short and medium terms. There was a positive correlation between distal MBL and the crown-to-implant ratio. Keywords: alveolar bone loss, bone resorption, dental implants, implant-supported dental prosthesis, single-tooth dental implants