Correlation between early perforation of cover screws and marginal bone loss: a retrospective study

Aim: This retrospective study aimed to determine the consequence of early cover screw exposure on peri-implant marginal bone level. Material and Methods: Sixty Astra Tech((R)) MicroThread implants installed in partially edentulous jaws were compared: 20 implants were placed following a two-stage procedure and were unintentionally exposed to the oral cavity (two-stage exposed), 20 implants were placed following a two-stage procedure and were surgically exposed after a subgingival healing time of 3-6 months (two-stage submerged), and 20 implants were placed following a one-stage surgical protocol (one-stage). Digital radiographs were taken at implant placement for all implants, and after abutment surgery for the two-stage exposed and two-stage submerged groups or after 3 months for the one-stage group. Bone loss mesially and distally was measured with an on-screen cursor after calibration. Results: Mean bone re-modelling was 1.96 mm (range: 0.2-3.2 mm) around the two-stage exposed implants, 0.01 mm (range: 0.0-0.3 mm) around the two-stage submerged implants and 0.14 mm (range: 0.0-1.2 mm) around the one-stage implants. Conclusion: The unintentional perforation of two-stage implants resulted in significant bone destruction, probably because the biological width was not considered.