Objective: Purpose of this retrospective clinical study was to determine differences in bone level changes by using butt and conical implant abutment junctions. The comparison of CAMLOG and CONELOG implants should allow comparable conditions concerning outer implant geometry. Material and Methods: Inclusion criteria: All patients were treated by the same surgeon, the same prosthodontist, the same dental technician, and with single crown restorations. Mesial and distal distances from the crestal bone level to the implant shoulder were measured radiographically after surgery as well as after prosthetic rehabilitation. Bone level changes were determined. Results: Thirty CAMLOG (without platform switch) and 30 CONELOG implants were investigated. Mean follow-up time after surgery was 25 months in the CAMLOG group and 18 months within the CONELOG group. The mean marginal bone level change for CAMLOG was significant from surgery to follow-up (p0.002; p0.008). CONELOG showed no significant difference (p0.992; p0.999). The comparison of CAMLOG and CONELOG revealed a significant difference between the groups (p0.001). Bone loss was noted for 67 % of the CAMLOG implants. Bone gain was noted for 47 % and no bone loss for further 30 % of the CONELOG implants. Conclusions: Within the limits of this study conical connections may prevent peri-implant bone loss and have a positive effect on marginal bone in comparison to butt connections. Keywords: Dental Implant, Camlog, Conelog, Conical Joints, Crestal Bone Level Changes