Marginal Bone Loss and Peri-Implant Health Around One-Piece and Two-Piece Tissue-Level Zirconia Implants: A Multicenter Retrospective Cohort Study With 5 to 11 Years of Follow-Up

Abstract Purpose To compare marginal bone loss (MBL) and peri-implant health between one-piece and two-piece tissue-level zirconia implants in routine practice under different placement and loading protocols. Methods This retrospective multicenter cohort included 470 implants in 137 patients, placed between 2014 and 2020 in three private practices. MBL was measured at mesial and distal sites on serial radiographs and analyzed with linear mixed-effects models using a piecewise time structure, random effects at implant and patient level, and covariate adjustment. Peri-implant parameters were assessed cross-sectionally at the last follow-up. Results Mean radiographic follow-up was 6.3 ± 1.6 years. MBL occurred mainly during the first year (− 0.88 mm, 95% CI -0.955 to -0.801; P = < 0.001) and was near-stable thereafter (− 0.018 mm/year; 95% CI − 0.044 to 0.007; P = 0.152). Mean MBL at the last radiograph was − 1.01 ± 1.02 mm, and 22.9% of implants showed bone loss exceeding 2 mm. Bone level trajectories did not differ between designs; the 95% CI of the interaction after the first year limited the plausible divergence to − 0.13 to 0.18 mm over five years. Immediate placement was associated with greater first-year loss in an exploratory analysis (P = 0.039) but not with overall MBL (P = 0.282). Peri-implantitis affected 1.5% of implants and 5.1% of patients. Bleeding on probing was more frequent at two-piece implants (adjusted OR 1.75; 95% CI 0.97 to 3.13). Five-year complication-free survival exceeded 98% in both designs. Conclusions One-piece and two-piece tissue-level zirconia implants of this system showed comparable marginal bone maintenance, with most bone remodeling occurring during the first year.