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Objectives: Clear guidelines on when to remove an implant are missing. This study aimed to evaluate the amount of peri-implant bone loss at explantation by specialists.
Material and Methods: Implantology specialists were asked to provide implants explanted due to peri-implantitis with related clinical information. Questionnaires inquired age, sex, smoking habit, implant location, usage of bone substitutes, and implant brand. Early failures (survival time <12 months) were analysed separately. Explants were measured and bone loss and type of bone loss were assessed using radiographs. Bivariate analysis was used for the type of bone loss, and covariate-adjusted mixed-effects models were evaluated for the amount of bone loss and survival time.
Results: Twelve dental offices provided 192 explants from 161 patients with 99 related radiographs. Most implants were affected by vertical bone loss (51.1%), followed by combined horizontal and vertical bone loss (22.3%), peri-implant gap (11.7%), horizontal bone loss (10.6%), and only a few by apical inflammation (4.3%). Thirty-three (17.2%) explants were early failures. Type of bone loss was significantly associated with survival time and implant brand. Implant brand also showed a significant correlation with early/late implant failure. Excluding early failures, combined horizontal and vertical bone loss was additionally significantly associated with smoking, and the location when grouped to incisor, canine, premolar, and molar showed a significant association with the type of bone loss. Further, the average survival time was 9.5 ± 5.8 years with absolute and relative bone loss of 7.0 ± 2.7 mm and 66.2 ± 23.7%, respectively. Late failures were removed at a mean bone loss of 50.0% with 5.44 mm residual alveolar bone in the posterior maxilla and 73.8% with 2.89 mm residual alveolar bone in other locations. In fully adjusted mixed-effects models, only the age at implantation (B=-0.19; 95% CI: -0.27 to -0.10) remained a significant factor for survival time. Implants exhibited significantly more relative bone loss if they were positioned in the mandible (B=17.3; 95% CI: 3.91 to 30.72) or if they were shorter (B=-2.79; 95% CI: -5.50 to -0.08).
Conclusions: Though the mean bone loss (66.2%) at which implants were explanted was in accordance with the literature, its wide variation and differentiation between the posterior maxilla and other locations showed that the profession has no universally accepted threshold beyond which an implant cannot be preserved.