Marginal bone changes around platform-switched conical connection implants placed 1 or 2 mm subcrestally: A multicenter crossover randomized controlled trial

Introduction: This study analyzes early marginal bone modifications occurring around platform-switched implants with conical connection placed 1 or 2 mm subcrestally. Methods: This crossover randomized controlled trial enrolled partially edentulous patients needing two implants in either the posterior maxilla or mandible. Each patient received two platform-switched implants with conical connection inserted 2 mm (Test) and 1 mm (Control) subcrestally. Definitive abutments were immediately connected and, after 4 months of unsubmerged healing, screwed metal-ceramic crowns were delivered. Radiographs were taken at implant placement (T0), prosthesis delivery (T1), and after 1 year of prosthetic loading (T2). Results: Fifty-one patients (25 males and 26 females; mean age 61.2 ± 12.1 years) totaling 102 implants were included in the final analysis. Mean peri-implant bone level (PBL) reduction from T0 to T2 was not significantly different around Test (0.49 ± 0.32 mm) and Control implants (0.46 ± 0.35 mm; p = 0.66). Multivariate linear regression models highlighted a significant positive correlation between history of periodontitis and PBL reduction. At T2, no Test group implant and 6 Control group implants exhibited PBL below the implant platform (11.8% of Control group implants). Conclusion: No significant differences in peri-implant marginal bone changes were demonstrated after 1 year of prosthetic loading between platform-switched implants with conical connection inserted either 1 or 2 mm subcrestally. However, 2 mm subcrestal placement resulted in deeper implant positioning at T2, with no exposure of treated implant surface and potential preventive effect against subsequent peri-implant pathology.