Long-term randomized clinical trial evaluating the effects of fixture surface acid-etching and machined collar design on bone healing

Objectives: An implant with an acid-etched fixture surface and internal-hex collar may achieve greater osseointegration. The goal of this research was to study the effects on long-term bone healing of fixture surface acid-etching and machined collar design. Method and Materials: Three two-part implant types were compared: standard Brånemark (with an external-hex 1.2 mm long machined flat collar), Swede-Vent (a copy of the Brånemark design, with an identical collar but a fixture surface acid-etched to 1 to 3 µm), and Screw-Vent (with a fixture surface acid-etched identically to that of Swede-Vent, but a longer internal-hex machined flat collar that did not require countersinking). Fifty-eight subjects each received the three types in alternate fashion at five sites between mental foramen, and a fixed full-arch prosthesis. Abutment-implant interface/microgap (MG) was placed at the crest, and first bone-to-implant contact point-to microgap (fBIC-MG) was measured at mesial and distal sides of each implant. Mean fBIC-MG values were compared after 15 to 20 years of function. Statistical analysis was based on the mixed linear model with the level of significance set at P .05 and Bonferroni correction for pairwise comparisons. Results: Brånemark had less mean marginal bone loss (−1.08 mm, standard error [SE] 0.20) compared with Swede-Vent (−1.28 mm, SE 0.20), but pairwise comparisons showed that the difference was not statistically significant (mean difference of 0.20 mm, P = .662). Screw-Vent had the greatest loss (−1.92 mm, SE 0.20), and pairwise comparisons showed that the difference was statistically significant compared with Brånemark and Swede-Vent (difference ≥ 0.64 mm, P .001). Conclusion: According to accepted standards for osseointegration, all three implant types achieved very acceptable long-term results. However, while Brånemark had the least bone loss, the implant with the acid-etched fixture surface and longer internal-hex collar design had the greatest loss. Within the confines of this study, shorter collar length of 1.2 mm may be more important to limit long-term bone loss with microgap placed at the crest. Keywords: acid-etched fixture, machined collar design, prospective study