title: Correlation between early perforation of cover screws and marginal bone loss: a retrospective study.
abstract: OBJECTIVE
  This retrospective study aimed to determine the consequence of early cover screw exposure on peri-implant marginal bone level.
  
  
  METHODS
  Sixty Astra Tech 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.
  
  
  CONCLUSIONS
  The unintentional perforation of two-stage implants resulted in significant bone destruction, probably because the biological width was not considered.
authors.affiliation: Department of periodontology, Catholic University Leuven, Leuven, Belgium. nele.vanassche@uz.kuleuven.ac.be
authors.forename: Nele
authors.initials: N
authors.lastname: Van Assche
authors.forename: Bruno
authors.initials: B
authors.lastname: Collaert
authors.forename: Wim
authors.initials: W
authors.lastname: Coucke
authors.forename: Marc
authors.initials: M
authors.lastname: Quirynen
mesh_terms: D016301:Alveolar Bone Loss / Q000209:etiology* / Q000601:surgery; D003758:Dental Implantation, Endosseous / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods; D015921:Dental Implants / Q000009:adverse effects*; D006801:Humans; D007576:Jaw, Edentulous, Partially / Q000601:surgery*; D016014:Linear Models; D008336:Mandibular Diseases / Q000209:etiology / Q000601:surgery; D008439:Maxillary Diseases / Q000209:etiology / Q000601:surgery; D012189:Retrospective Studies; D013997:Time Factors
chemical_list: D015921:Dental Implants