Influence of apico-coronal positioning of tissue-level implants on marginal bone stability during supracrestal tissue height establishment: A multi-center prospective study

Introduction Supracrestal tissue height establishment is a crucial factor influencing peri-implant marginal bone modifications prior to prosthesis delivery. If mucosal thickness is insufficient, peri-implant marginal bone resorption occurs to allow appropriate supracrestal tissue height formation. This study evaluates if marginal bone resorption occurring around tissue-level implants before prosthetic loading could be compensated by adapting apico-coronal positioning to mucosal thickness. Methods Patients requiring placement of one single implant in the posterior mandible were treated with tissue-level implants with a 3-mm high transmucosal machined component and moderately rough implant body. Based upon vertical mucosal thickness measured after buccal flap reflection, implants were placed with the treated part: (group 1) 2 mm below crestal level in presence of thin mucosa (<2.5 mm); (group 2) 1 mm below the crestal level in presence of medium mucosa (2.5-3.5 mm); (group 3) at equicrestal level in presence of thick mucosa (>3.5 mm). Results Forty-nine implants, placed in 49 patients were included in final analysis (group 1: 18 implants; group 2: 16 implants; group 3: 15 implants). Mean marginal bone resorption after 5 months of healing was 0.66 +/- 0.49 mm, 0.32 +/- 0.41 mm, and 0.22 +/- 0.52 mm in groups 1, 2, and 3, respectively. Inter-group analysis highlighted significant differences between the three groups after ANOVA test (p = 0.025). However, adaptation of apico-coronal implant positioning in relation to mucosal thickness, allowed to avoid early exposure of the treated surface in 100%, 93.7%, and 53.3% of the implants in groups 1, 2, and 3, respectively. Conclusion During supracrestal tissue height formation, tissue-level implants inserted adapting apico-coronal positioning in relation to mucosal thickness exhibited greater marginal bone resorption at sites with thin mucosa than at sites with medium or thick mucosa. However, anticipating supracrestal tissue height establishment by adapting apico-coronal implant positioning in relation to mucosal thickness may effectively prevent unwanted exposure of treated implant surface.