Histological healing outcomes at the bone-titanium interface of loaded and unloaded dental implants placed in humans: A systematic review of controlled clinical trials

Purpose: The purpose of this systematic review was to assess the histological healing outcomes at the bone-titanium interface of loaded and unloaded dental implants placed in humans. Materials and methods: An electronic search was conducted using the PubMed, Embase and Cochrane Central Register of Controlled Trials (Central) databases up to and including April 2020 to identify clinical trials reporting human histological data of bone healing around titanium dental implants placed in healed alveolar ridges. The search was conducted by two independent reviewers with no language restrictions. The risk of bias of each included study was assessed using the Cochrane Collaboration's domain-based, two-part tool. Results: Of the 4564 potentially eligible articles, only 25 were included in this systematic review (13 randomised and 12 controlled clinical trials), with a total of 548 micro/transitional implants evaluated. The marked heterogeneity between studies did not allow the data to be combined for meta-analyses. In general, based on mean values of bone-to-implant contact (range 9% to 73%), bone density outside the threaded area (range 14.9% to 31.6%), bone density in the threaded area (range 17.9% to 56.9%) and osteocyte index (range 19.79 to 37.88 cells/mm²), all implant surface modifications demonstrated osseointegration potential. Furthermore, immediate loading was related to higher bone-to-implant contact, bone density outside the threaded area and osteocyte index; longer healing periods to higher bone-to-implant contact; and smoking to lower bone-to-implant contact, bone density in the threaded area and bone density outside the threaded area. Conclusions: Despite the fact that several modifications were made to the implant surface, when considering the values for bone-to-implant contact, bone density in the threaded area, bone density outside the threaded area and osteocyte index, machined surfaces showed the worst healing outcomes. Nevertheless, osseointegration was improved by both immediate loading and longer healing periods and worsened by smoking.