title: Retrospective cohort study of 4591 Straumann implants in private practice setting, with up to 10-year follow-up. Part 1: multivariate survival analysis.
abstract: OBJECTIVE
  The purpose of this retrospective, noninterventional, open cohort study is to report on the long-term survival of dental implants, in private practice representing the daily realities of implant treatment. The data are analyzed to discern statistical relationships between explanatory variables and implant failure.
  
  
  METHODS
  A total of 4591 Straumann implants were placed in 2060 patients between 1999 and 2012. Patients were evaluated after 2-3 months, 1, 3, 5, and 7 years and, in some cases, up to 10 years. The cumulative survival rate (CSR) was calculated according to the life table method and illustrated with Kaplan-Meier survival curves. Univariate analysis was performed to investigate the association between study variables and time to implant-failure. Variables with P -value < 0.15 were further selected for a multivariate analysis. Statistical methods which take into account the fact that some patients have more than one implant (therefore, dependency between implants within mouth) had been applied.
  
  
  RESULTS
  At the implant level, the cumulative survival rates at 3, 5, and 7 years were 99.3%, 99.0%, and 98.4%, respectively, and at the patient level, they were 98.6%, 97.7%, and 95.9%, respectively. After adjustment to possible confounders, the multivariate analysis identified a relationship between the following risk indicators for implant failure: implant location, length and design, timing of implantation, bone grafting procedures and gender. Tissue-Level implants (n = 3863) had a very high survival rate of 99% at 3 years, which was maintained over the entire study period. Bone-Level implants (n = 600) were as predictable with a survival rate of 99% up to 3 years, while Tapered Effect implants (n = 128) demonstrated a lower survival rate of 95% at 5 years. Short 6-mm implants in the mandibular posterior sites had a high survival rate of 100%, while in maxillary posterior positions a survival rate of only 87% was achieved. Patient factors such as smoking, autoimmune disease, and penicillin allergy were tending to associate with higher failure rates.
  
  
  CONCLUSIONS
  High long-term survival rates were observed for a large cohort of Straumann implants. Tissue- and Bone-Level implants had higher survival rates than Tapered Effect implants, and although short implants faired well in the mandibular posterior sites, they faired less well in the maxillary posterior sites. The study represents private practice insight into large-scale, long-term implant results.
authors.affiliation: Faculty of Dentistry, Division of Periodontics, University of British Columbia, Vancouver, BC, Canada.|Private Practice, Calgary, AB, Canada.
authors.forename: David
authors.initials: D
authors.lastname: French
authors.affiliation: Faculty of Dentistry, Division of Periodontics, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Hannu
authors.initials: H
authors.lastname: Larjava
authors.affiliation: Department of Statistics and Operations Research, Tel-Aviv University & Private Dental Practice, Tel-Aviv, Israel.
authors.forename: Ronen
authors.initials: R
authors.lastname: Ofec
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D016723:Bone Remodeling; D015331:Cohort Studies; D003758:Dental Implantation, Endosseous / Q000706:statistics & numerical data*; D015921:Dental Implants / Q000706:statistics & numerical data*; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D011331:Private Practice / Q000706:statistics & numerical data*; D011379:Prognosis; D012189:Retrospective Studies; D016896:Treatment Outcome
chemical_list: D015921:Dental Implants
keywords: Intraclass correlation; bone implant interactions; bone regeneration; clinical research; cohort study; patient centered outcomes; sinus floor elevation; smoking; survival analysis; time to implant failure