title: Impact of implant-abutment connection and positioning of the machined collar/microgap on crestal bone level changes: a systematic review.
abstract: OBJECTIVE
  To address the following focused question: What is the impact of implant-abutment configuration and the positioning of the machined collar/microgap on crestal bone level changes?
  
  
  METHODS
  Electronic databases of the PubMed and the Web of Knowledge were searched for animal and human studies reporting on histological/radiological crestal bone level changes (CBL) at nonsubmerged one-/two-piece implants (placed in healed ridges) exhibiting different abutment configurations, positioning of the machined collar/microgap (between 1992 and November 2012: n = 318 titles). Quality assessment of selected full-text articles was performed according to the ARRIVE and CONSORT statement guidelines.
  
  
  RESULTS
  A total of 13 publications (risk of bias: high) were eligible for the review. The weighted mean difference (WMD) (95% CI) between machined collars placed either above or below the bone crest amounted to 0.835 mm favoring an epicrestal positioning of the rough/smooth border (P < 0.001) (P-value for heterogeneity: 0.885, I2: 0.000% = no heterogeneity). WMD (95% CI) between microgaps placed either at or below the bone crest amounted to -0.479 mm favoring a subcrestal position of the implant neck (P < 0.001) (P-value for heterogeneity: 0.333, I2: 12.404% = low heterogeneity). Only two studies compared different implant-abutment configurations. Due to a high heterogeneity, a meta-analysis was not feasible.
  
  
  CONCLUSIONS
  While the positioning of the machined neck and microgap may limit crestal bone level changes at nonsubmerged implants, the impact of the implant-abutment connection lacks documentation.
authors.affiliation: Department of Oral Surgery, Heinrich Heine University, Düsseldorf, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Schwarz
authors.forename: Andrea
authors.initials: A
authors.lastname: Hegewald
authors.forename: Jürgen
authors.initials: J
authors.lastname: Becker
mesh_terms: D016301:Alveolar Bone Loss / Q000209:etiology*; D000539:Alveolar Process / Q000601:surgery*; D000818:Animals; D016723:Bone Remodeling; D000044:Dental Abutments; D003758:Dental Implantation, Endosseous; D015921:Dental Implants; D017267:Dental Prosthesis Design; D006801:Humans; D013499:Surface Properties
chemical_list: D015921:Dental Implants
keywords: animal studies; clinical studies; crestal bone level changes; systematic review