Impact of implant-abutment connection design on biological and mechanical outcomes in posterior single-tooth restorations: A randomized clinical trial

Abstract

Statement of problem: The implant-abutment interface has been identified as a key factor in preserving peri-implant marginal bone levels. However, current evidence remains insufficient to identify the most suitable connection design since most published studies fail to control critical variables such as the implant surface or design. Purpose: The purpose of this randomized clinical trial was to assess vertical marginal bone loss after 1 year of function of implants with identical macroscopic and microscopic designs and 3 different implant-abutment connections (external hexagon, internal hexagon, and conical) placed in the molar or premolar area. The secondary aims were to assess the mechanical and biological complications after 1 year of function. Material and methods: An open-label, randomized controlled trial with 3 treatment arms was carried out. Participants were assessed at implant placement, prosthesis installation, and after 1 year of loading. The main outcome variable was the distance from the implant shoulder to the marginal bone at the mesial and distal aspect of each implant. Probing depth, plaque index, and bleeding on probing, as well as mechanical or biological complications, were also assessed. A descriptive, bivariate and multivariate analysis (linear models and binary logistic models) of the data was performed. Results: Seventy-five participants with 105 implants were consecutively enrolled and randomized to the external hexagon, internal hexagon, and conical connection groups (35 implants each). The 3 groups had similar baseline features. The distance from the implant shoulder to the marginal bone varied significantly over time (P<.001) but was similar for all groups (P=.152) and followed the same evolution pattern over time (P=.995). Seven failures in 7 participants were registered during the study (3 in external hexagon, 1 in internal hexagon, and 3 in conical connection (P=.356). Conclusions: The implant-abutment connection design did not significantly affect the changes in interproximal bone levels of posterior single-unit implant-supported crowns after 12 months of loading. Furthermore, the risk of developing biological or mechanical complications was similar for all the tested connection designs.