Soft tissue changes and crestal bone loss around platform-switched implants placed at crestal and subcrestal levels: 36-month results from a prospective split-mouth clinical trial

Objective: The aim of the present 36-month prospective split-mouth clinical trial was to investigate the peri-implant soft tissue changes and crestal bone loss (CBL) around delayed loaded platform-switched implants placed at crestal and subcrestal levels. Material and methods: Twenty-three individuals with bilaterally missing either mandibular first or second molars were included. The test and control sites were defined as follows: (i) test sites: implants placed 2 mm below the alveolar crest (subcrestal); (ii) control sites: implants placed at bone level (crestal). Forty-six implants (23 implants in test sites and 23 in control sites) were placed in the center of the healed alveolar ridge in the posterior mandible. Peri-implant bleeding on probing (BOP), probing depth (PD >= 4 mm), and CBL was compared at 6, 18, and 36 months of follow-up. P < 0.05 was considered statistically significant. Results: Sixteen males and seven females with a mean age of 43.5 years (29-50) were included. In the control group (n = 23), the highest mean percentage of sites that showed BOP and PD >= 4 mm were at 6 months (7.4% and 1.4%, respectively). In the test group (n = 23), the highest mean percentage of sites that showed BOP and PD >= 4 mm were at 6 months (2.4% and 1.2%, respectively). The total amount of CBL around crestal and subcrestal implants after 36 months of loading was 0.45 +/- 0.2 and 0.3 +/- 0.2 mm, respectively. At all follow-up intervals, all intragroup and intergroup comparisons showed no significant differences in BOP, PD >= 4 mm, and CBL around implants placed at crestal and subcrestal levels. Conclusion: Up to 36 months of follow-up, soft tissue parameters and crestal bone levels can remain equally stable around dental implants placed at crestal and subcrestal levels. The need for long-term follow-up clinical trials is also emphasized.