Influence of implant cover screw loosening on early peri-implant marginal bone loss: a retrospective evaluation of risk factors

Background: This study aimed to evaluate the risk factors of cover screw loosening (CSL) and its influence on peri-implant marginal bone during early bone healing process.Methods: A total of 91 implants in 90 patients (75 normal patients and 15 patients with CSL) were included in this study. Panoramic radiographs were taken for the measurement of peri-implant marginal bone loss (MBL). A piece of soft tissue above the cover screw during the second-stage surgery was taken for pathological examination. The differences between the two groups were evaluated and the possible risk factors associated with CSL were analyzed.Results: Increased frequency of CSL showed significant association with maxillary region (p=0.038). The mean MBL at implants with CSL was 0.82 ± 0.56 mm, and it was 0.22 ± 0.20 mm at normal implants (p<0.001). The inflammatory granulation tissue around the loose cover screws showed infiltration of a large number of inflammatory cells.Conclusions: CSL during healing process is associated with early peri-implant MBL. The location of the maxilla is considered as a significant risk factor for CSL.