Implants (3.3 mm Diameter) for the Rehabilitation of Edentulous Posterior Regions: A Retrospective Clinical Study with Up to 11 Years of Follow-Up

Background: There is limited evidence for the use of narrow-diameter implants for rehabilitation of the posterior regions of the jaws using different surgical techniques. Purpose: The purpose of this study was to report the clinical results of implant-supported prosthetic rehabilitations in the posterior regions of both jaws, using narrow-diameter implants. Materials and Methods: The study included 147 patients (115 males and 32 females), with an age range of 26 to 77 years (mean = 47.5 years), with a total of 247 implants inserted and followed between 1 and 11 years, with a median follow-up time of 5 years. The patients were in need of fixed prosthetic implant-supported rehabilitations in the posterior region of the jaw, presenting a reduced interradicular bone or a thin alveolar crest. The implant survival estimate was computed using the Kaplan-Meier product limit estimator. Results: The survival rate for narrow diameter implants was 95.1% at 11 years (Kaplan-Meier), with a distribution of 91.4% at 11 years, 95.9% at 10 years, and 95.5% at 9 years for the two-stage, one-stage, and immediate function techniques, respectively. The mean marginal bone resorption recorded at 1, 5, and 10 years were 1.16, 1.53, and 1.74 mm, respectively. Backward conditional logistic regression identified type of implant as a strong protective factor against implant failure (MkIII and NobelSpeedy implants compared to the MkII implant; OR = 0.14), and type of rehabilitation as a strong risk factor for implant failure (partial rehabilitations compared to single teeth rehabilitations; OR = 4.75). Conclusions: The results indicate that within the limitations of this study, the use of narrow-diameter implants for the prosthetic rehabilitation of posterior regions of the jaws is viable, with good outcomes in the long-term, irrespective of the surgical technique implemented.