Do repeated changes of abutments have any influence on the stability of peri-implant tissues? One-year post-loading results from a multicentre randomised controlled trial

PURPOSE: To evaluate the influence of at least three abutment changes in conventionally loaded implants against placement of a definitive abutment in immediately non-occlusal loaded implants on hard and soft tissue changes. MATERIALS AND METHODS: Eighty patients requiring one single crown or one fixed partial prosthesis supported by a maximum of three implants were randomised, after implants were placed with more than 35 Ncm, according to a parallel group design to receive definitive abutments which were loaded immediately (definitive abutment or immediate loading group) or transmucosal abutments. These were delayed loaded after 3 months and were removed at least three times: 1) at impression taking (3 months after implant placement); 2) when checking the zirconium core on titanium abutments at single crowns or the fitting the metal structure at prostheses supported by multiple implants; 3) at delivery of the definitive prostheses (repeated disconnection or conventional loading group). Patients were treated in four centres and each patient contributed to the study with only one prosthesis followed for 1 year after initial loading. Outcome measures were: prosthesis failures, implant failures, complications, pink esthetic score (PES), buccal recessions, patient satisfaction, peri-implant marginal bone level changes and height of the keratinised mucosa. RESULTS: Forty patients were randomly allocated to each group according to a parallel group design. Two patients dropped out from the definitive abutment group but no implant failed. Four provisional and one definitive single crowns had to be remade (due of misfitting) and one definitive crown (due to ceramic fracture) in the repeated disconnection group versus one provisional prosthesis of the immediate loading group due to frequent debondings (difference = 12%; CI95%: 0%, 25%; P = 0.109). Eight patients were affected by complications: four patients from each group (difference = 1%; CI95%: -13%, 14%; P = 1). PES scores assessed at 1 year post-loading were 11.4 (1.5) mm for the definitive abutment group and 11.0 (2.0) mm for the repeated abutment changes group (difference = 0.4; CI95%: -0.4, 1.2; P = 0.289). Buccal recessions at 1 year post-loading amounted to 0.07 (0.35) mm for the definitive abutment group and 0.12 (0.65) mm for the repeated abutment changes group (actually it was a soft tissue gain; difference = 0.05 CI 95%: -0.19, 0.29; P = 0.659). All patients declared to be very satisfied or satisfied with the function and aesthetics of the prostheses and would undergo the same procedure again. Mean peri-implant marginal bone loss at 1 year after loading was 0.06 (0.12) mm for the definitive abutment group and 0.23 (0.49) mm for the repeated abutment changes group (difference = -0.16; CI95%: -0.33,-0.00; P = 0.046). The height of the keratinised mucosa at 1 year post-loading was 2.8 (1.5) mm for the definitive abutment group and 2.8 (1.7) mm for the repeated abutment changes group (difference = -0.0; CI 95%: -0.8, 0.7); P = 0.966. Up to 1 year after initial loading, there were no statistically significant differences between the two procedures, with the exception of 0.16 mm more marginal bone loss at implants subjected to three abutment removals. CONCLUSIONS: One-year post-loading data showed that repeated abutment changes significantly increased bone loss of 0.16, but this difference cannot be considered clinically relevant, therefore clinicians can use the procedure they find more convenient for their specific patient. In addition, immediately non-occlusally loaded dental implants are a viable alternative to conventional loading. Conflict-of-interest statement: This trial was partially funded by Dentsply Sirona Implants, the manufacturer of the implants and other products evaluated in this investigation. However, data belonged to the authors and by no means did the manufacturer interfere with the conduct of the trial or the publication of the results with exception of rejecting the proposal of changing the protocol, after the trial was started, allowing the use of indexed abutments.