A multilevel analysis of platform-switching flapless implants placed at tissue level: 4-year prospective cohort study

Purpose: To evaluate the factors affecting peri-implant marginal bone level of single platform-switched implants with a smooth neck placed at gingival level (tissue level) using a flapless technique. Materials and Methods: Consecutive healthy patients requiring dental implant rehabilitations were enrolled in this study. Titanium implants with a zirconium-oxide-blasted surface and a platform-switch neck tulip configuration were used. Loading was performed 3 months after insertion with a provisional resin crown and after approximately 15 days with a definitive ceramic crown. Peri-implant marginal bone level (MBL) was measured on periapical radiographs at 1, 3, 6, 12, 24, 36, and 48 months by a blinded assessor. The following parameters were evaluated: location (maxillary/mandibular), position (anterior/posterior), sex (male/female), smoke (yes/no), implant placement timing (immediate, early, delayed), gingival thickness (thin/thick), endodontically treated adjacent teeth (yes/no), and diameter (3.8/4.25/5.0 mm). Multilevel analyses exploring factors associated with MBL at 36 and 48 months were performed. Results: A total of 76 patients (42 women, 34 men; mean age: 55.6 ± 10.7 years) received 128 implant rehabilitations. The survival rate was 98.4%. MBL displayed an initial increase during the first months from insertion (preload period). Cumulative mean MBL at T48 was 0.99 ± 0.68, which was not statistically significant from the values at T24 to T36 (P >.05). Mandibular location, delayed implants, and presence of adjacent endodontically treated teeth showed higher bone loss at 36 months (P <.05). Interestingly, at 48 months, only implant placement timing showed statistically significant differences. Delayed implants showed increased bone loss compared with both early and immediate groups (P <.05). Multilevel analysis confirmed the statistical significance of implant location (P =.031; 95% CI: 0.031 to 0.659), endodontically treated adjacent teeth (P =.001; 95% CI:-1.228 to 0.859), and implant placement (P =.045; 95% CI: 0.003 to 0.337) as factors affecting MBL at 36 months. All the investigated parameters, with the only exception being the implant placement group (P =.020; 95% CI: 0.334 to 1.432), were not statistically significant at 48 months (P >.05). Conclusion: Platform-switched implants placed nonsubmerged with a flapless approach showed a reduced bone loss progression in the first 4 years, as MBL remained stable at longer times (36 and 48 months). Implants placed with early and immediate timing showed reduced bone loss compared with delayed implants.