title: Implant survival and crestal bone loss around extra-short implants supporting a fixed denture: the effect of crown height space, crown-to-implant ratio, and offset placement of the prosthesis.
abstract: OBJECTIVE
  To determine the effect of crown height space, crown-to-implant ratio, and offset placement of a prosthesis on implant survival, crestal bone loss, and prosthetic complications; and to determine whether detrimental values for crown height space and crown-to-implant ratio exist for implant-supported restorations.
  
  
  METHODS
  Extra-short implants (length ≤6.5 mm) supporting a fixed denture in the posterior mandible and followed for at least 12 months were analyzed. Radiographic and clinical examinations were conducted to retrieve data about patients' dental and medical history, prosthetic complications, antagonist type, crown height space, crown-to-implant ratio, offset placement of the prosthesis, crestal bone loss, and implant failure.
  
  
  RESULTS
  Thirty-four patients (mean age, 60 ± 10 years) with 45 extra-short implants participated in this study. Patients were followed for up to 4 years (mean, 2 years) and no implants were lost. The mean crown-to-implant ratio was 2.4 (range, 1.5 to 3.69). Mean crown height space was 17.05 ± 3.05 mm, and 65.4% of the implants had a crown height space in the range of 15 to 20 mm. About 90% of the implants had a distal or mesial offset placement greater than 1 mm. The type of antagonist significantly affected marginal bone loss around extra-short implants: bone loss was greatest for implants opposing a partial denture (mean, 1.28 ± 1.09 mm) and was lower for implants opposing a natural dentition (mean, 0.73 ± 0.60 mm) or a complete denture (mean, 0.89 ± 0.60 mm). Analysis of marginal bone loss and the factors crown-to-implant ratio, crown height space, and offset placement according to antagonist dentition indicated a significant positive correlation only between bone loss and crown height space.
  
  
  CONCLUSIONS
  When an increased crown-to-implant ratio is present, crown height space may influence crestal bone loss more significantly.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Anitua
authors.forename: Mohammad Hamdan
authors.initials: MH
authors.lastname: Alkhraist
authors.forename: Laura
authors.initials: L
authors.lastname: Piñas
authors.forename: Leire
authors.initials: L
authors.lastname: Begoña
authors.forename: Gorka
authors.initials: G
authors.lastname: Orive
mesh_terms: D016301:Alveolar Bone Loss / Q000000981:diagnostic imaging / Q000209:etiology*; D003442:Crowns; D015921:Dental Implants; D017267:Dental Prosthesis Design / Q000009:adverse effects*; D019094:Dental Prosthesis, Implant-Supported / Q000009:adverse effects*; D019232:Dental Restoration Failure; D003830:Denture, Partial, Fixed / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008297:Male; D008334:Mandible / Q000000981:diagnostic imaging; D008875:Middle Aged; D011859:Radiography
chemical_list: D015921:Dental Implants