title: Long-term results of implant-supported over-dentures retained by double crowns: a practice-based retrospective study after minimally 10 years follow-up.
abstract: BACKGROUND
  Different concepts regarding the number of implants and attachment systems for the preparation of implant-supported over-dentures (IODs) have been discussed. Nonetheless, long-term results for double-crown-retained IODs with an observational period of more than 10 years are still rare in the literature.
  
  
  OBJECTIVE
  The aim of this practice-based study was to retrospectively evaluate the long-term clinical outcome (success/survival rates, technical/biological complications) of IODs retained by double crowns.
  
  
  METHODS
  In a private practice, 36 non-smoking edentulous patients were restored between 1991 and 2002 with double-crown-retained IODs supported by 2-6 implants. For the retrospective evaluation of implant and prosthetic survival (in-situ criterion) and success (event-free observational period), only those patients were included who regularly (at least once a year) participated in a professional maintenance programme and who had a functional period for the restoration of more than 10 years.
  
  
  RESULTS
  Twenty-two patients (12 Women/10 men, mean age 60.1 ± 9.8 years) with 89 implants supporting nine maxillary and 13 mandibulary dentures (mean number of implants/prosthesis = 4) met the inclusion criteria. The mean follow-up period was 14.1 ± 2.8 years. One implant failed after 4.9 years (cumulative-survival rate: 98.9%). Seven implants in two patients showed peri-implantitis (prevalence: patient-based = 9.1%/implant-based = 8%). Five dentures were renewed (prosthetic-survival rate 77.3% Maintenance procedures (i.e. screw loosening or acrylic fractures) were required at a rate of 0.31/year and patient.
  
  
  CONCLUSIONS
  This study indicates that IODs retained with double crowns offer predictable long-term performance with a limited incidence of biological and technical complications.
authors.affiliation: Dental Practice, Hofgeismar, Germany.
authors.forename: Eberhard
authors.initials: E
authors.lastname: Frisch
authors.forename: Dirk
authors.initials: D
authors.lastname: Ziebolz
authors.forename: Sven
authors.initials: S
authors.lastname: Rinke
mesh_terms: D003442:Crowns; D017267:Dental Prosthesis Design; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D003781:Denture Retention; D003828:Denture, Overlay; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007575:Jaw, Edentulous / Q000000981:diagnostic imaging / Q000534:rehabilitation*; D008297:Male; D008437:Maxilla; D008875:Middle Aged; D052016:Mucositis / Q000000981:diagnostic imaging; D057873:Peri-Implantitis / Q000000981:diagnostic imaging; D011859:Radiography; D012189:Retrospective Studies; D016896:Treatment Outcome