Influence of the implant-abutment connection on the ratio between height and thickness of tissues at the buccal zenith: a randomized controlled trial on 188 implants placed in 104 patients

Background To compare tissue response to two implant systems, featuring internal hexed connections with different designs. Methods Patients enrolled in this randomized controlled trial were assigned to two groups. In Group 1, patients were treated with implants with a 5 degrees conical internal hexed connection (Anyridge (R), MegaGen, South Korea). In Group 2, patients were treated with implants with an internal hexed connection (Core (R), Kristal, Italy). After implant placement and a provisionalisation period of 12 months, impressions were taken, stone casts were poured and digitised with a desktop scanner (D700 (R), 3Shape, Copenhagen, Denmark). In a digital environment, for each fixture, two values were collected at the buccal zenith: the height of the peri-implant mucosa (mucosal height; MH), calculated from the vestibular shoulder of the implant analogue to the upper gingival margin of the supra-implant tissue; and the width of the peri-implant mucosa (mucosal thickness; MT), calculated from the vestibular shoulder of the analogue to the external mucosa point perpendicular to the implant major axis. The mean and standard deviation for MH and MT, as well as their ratios, were calculated for each group; the sectors in which the implants were placed were also considered. Finally, correlation between MH, MT, connection type and sector was assessed by Pearson's correlation coefficient, with significance level set at 0.05, and a confidence interval (CI) set at 95%. Results Data deriving from 188 implants placed in 104 patients were evaluated. The mean MH values were 3.32 (+/- 0.12) and 2.70 (+/- 0.16) mm for Groups 1 and 2, respectively. The mean MT values were 4.37 (+/- 0.16) and 3.93 (+/- 0.18) mm for Groups 1 and 2, respectively. Group 1 showed higher MH and MT values and a better ratio (1.50 +/- 0.88) than Group 2 (1.81 +/- 1.20). The MH, MT and MH/MT ratio were significantly influenced both by sector (p = 0.015) and group (p = 0.047). Conclusions Within the limits of this study, the 5 degrees connection implants supported a more extended tissue height and thickness at the buccal zenith, and a better ratio between them.