title: Influence of the crown-to-implant length ratio on the clinical performance of implants supporting single crown restorations: a cross-sectional retrospective 5-year investigation.
abstract: OBJECTIVE
  The aim of this study was to investigate the influence of the crown-to-implant length ratio (c/i ratio) on the implant survival, changes of the marginal bone level (MBL) and the occurrence of biological and technical complications.
  
  
  METHODS
  This cross-sectional retrospective study included all patients with implants in the posterior segments supporting single crown restorations with a minimum follow-up of 5 years. All patients were questioned and examined clinically and radiographically. The technical and biological c/i ratio and the MBL were measured on digitized periapical radiographs. The following outcome parameters in relation to the c/i ratio and the co-factors were statistically analyzed: implant survival rate, MBL, occurrence of technical and biological complications. For statistical analysis, regression, correlation and survival analyses were applied (P<0.05).
  
  
  RESULTS
  Seventy patients (mean age of 50.7 years [range 19.8-76.6 years]) with a total of 100 implants (24 Straumann type, 76 Brånemark type) were included in this study. The mean follow-up period was 6.2 years (range 4.73-11.7 years). Six implants failed during the follow-up period, yielding a cumulative survival rate of 95.8% at 5 years in function. The mean technical c/i ratio was 1.04 (±0.26, range 0.59-2.01). The mean biological c/i ratio was 1.48 (±0.42, range 0.82-3.24). No statistically significant influence of the technical and biological c/i ratio was found on the implant survival, MBL and occurrence of technical and biological complications. When adjusted for the biological c/i ratio, smoking was the only co-factor significantly associated with implant failure and biological complications.
  
  
  CONCLUSIONS
  In the present study, the c/i ratio did not influence the clinical performance of implants supporting single crown restorations in the posterior segments of the jaw within the range tested.
authors.affiliation: Center for Dental and Oral Medicine and Cranio-Maxillofacial Surgery, Clinic of Fixed and Removable Prosthodontics and Dental Material Science, University of Zurich, Zurich, SwitzerlandCenter for Dental and Oral Medicine and Cranio-Maxillofacial Surgery, University of Zurich, Zurich, Switzerland.
authors.forename: David
authors.initials: D
authors.lastname: Schneider
authors.affiliation: Center for Dental and Oral Medicine and Cranio-Maxillofacial Surgery, Clinic of Fixed and Removable Prosthodontics and Dental Material Science, University of Zurich, Zurich, SwitzerlandCenter for Dental and Oral Medicine and Cranio-Maxillofacial Surgery, University of Zurich, Zurich, Switzerland.
authors.forename: Lukas
authors.initials: L
authors.lastname: Witt
authors.affiliation: Center for Dental and Oral Medicine and Cranio-Maxillofacial Surgery, Clinic of Fixed and Removable Prosthodontics and Dental Material Science, University of Zurich, Zurich, SwitzerlandCenter for Dental and Oral Medicine and Cranio-Maxillofacial Surgery, University of Zurich, Zurich, Switzerland.
authors.forename: Christoph H F
authors.initials: CHF
authors.lastname: Hämmerle
mesh_terms: D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D003442:Crowns; D003758:Dental Implantation, Endosseous / Q000379:methods*; D019250:Dental Implants, Single-Tooth; D017267:Dental Prosthesis Design; D019094:Dental Prosthesis, Implant-Supported; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007576:Jaw, Edentulous, Partially / Q000534:rehabilitation; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D016896:Treatment Outcome