Clinical Outcomes of Bone-Level and Tissue-Level Short Implants Placed in Posterior Maxilla: A Case–Control Study

Introduction: Short implants are today a reliable, minimally invasive option for the rehabilitation of the posterior maxilla. However, maintaining marginal bone stability remains a crucial factor for long-term success, particularly in the case of short implants. The present multicenter prospective case-control study aimed to compare the clinical outcomes of bone-level and tissue-level short implants in the posterior maxilla, focusing on implant survival and peri-implant marginal bone stability over 1 year of function. Methods: Fifty-nine patients who met specific inclusion criteria were enrolled and treated by three clinical centers with a total of 74 short implants, either bone-level (7 mm in length, placed 1 mm sub-crestally) or tissue-level (5 or 6.5 mm in length). The primary outcome was physiological bone remodeling (PBR) measured via radiographs at baseline (T0), prosthesis delivery (T1), and 12 months post-loading (T2). Statistical analysis was performed to evaluate differences in PBR between groups, with multivariate analysis assessing the influence of various patient and site-specific factors. Results: The final analysis included 58 patients who were treated with a total of 71 short implants, comprising 36 tissue-level and 35 bone-level implants (one patient dropped out as he did not attend follow-up visits on time). All implants were rehabilitated with fixed, screwed prosthetics after 5 months, with no recorded complications up to 1 year of loading. Stability was similar between the two implant types at T0 and T1, with no significant differences in insertion torque and implant stability quotient (ISQ). Multivariate analysis revealed a significant positive correlation between insertion torque and ISQ at T0, as well as with bicortical engagement of the implant apex with the sinus floor. Tissue-level implants demonstrated significantly lower peri-implant bone remodeling (PBR) compared to bone-level implants at both T1 (0.11 +/- 0.27 mm vs. 0.34 +/- 0.35 mm, p = 0.004) and T2 (0.30 +/- 0.23 mm vs. 0.55 +/- 0.42 mm, p = 0.003). Multivariate analysis showed a significant positive correlation between PBR (T0-T1) and thin vertical mucosal thickness (<= 2 mm) at T0 in both tissue-level and bone-level implants. Additionally, PBR (T1-T2) in both groups significantly correlated with the use of short prosthetic abutments (<= 2 mm) and, only in bone-level implants, with crown emergence angles > 30 degrees. Conclusion: Both tissue-level and bone-level short implants are effective options for implant-supported rehabilitation in the posterior maxilla. Tissue-level short implants offer superior marginal bone stability compared to bone-level implants placed subcrestally, suggesting their favorable use in clinical practice.