The use of two-piece transmucosal implants designed with a convergent neck: a 6-year clinical prospective cohort study and impact on gingival and bone tissues.

PURPOSE: This prospective study evaluated the marginal bone level and periodontal parameters 6 years after placement of a convergent transmucosal neck implant.

MATERIALS AND METHODS: In total, 71 implants were placed in 60 patients. Of these, 52 implants were placed with a flapless technique and with the convergent neck exposed for 1.0 mm (early and delayed placement), while 19 implants were placed immediately after extraction (immediate placement). At least 3 months after insertion, customised abutments were applied and provisional resin crowns were cemented, while being careful to prevent any tissue compression. After 3 weeks, definitive metal-ceramic crowns were designed with the finishing line at the soft tissue level and free from any compression. The implant survival rate at 6 years, marginal bone level changes (MBL, mm), and Pink Esthetic Score (PES) were evaluated. Gingival phenotype was determined before the implant surgeries (thin/thick). A three-level hierarchical model was examined with a random intercept and random slope on follow-up time at the patient level, and a random intercept at the implant level.

RESULTS: In all, 57 patients with 67 implants reached the 6 year point; 3 (5.0%) dropped out. The implant survival rate was 100%. ΔMBL T0-T24 was 0.58 mm (95% CI 0.48, 0.68), while ΔMBL T24-T72 was 0.33 mm (95% CI 0.19, 0.47). PES improved steadily from 6 to 48 months (+0.96; 95% CI 0.71, 1.20), with overall stability at 72 months. No correlation between MBL and PES was observed. A significant association was found between the gingival phenotype and less MBL variation. Greater implant diameter offered more MBL stability after 3 years, but lower PES values.

CONCLUSION: The use of convergent transmucosal neck implants placed with a flapless transmucosal approach with the crown margin positioned at the gingival level preserved marginal bone and guided gingival morphology for up to 72 months. The gingival phenotype was the parameter that most affected the soft and hard tissues. In the long term, implant placement timing was not related to MBL.