Impact of implant–abutment connection and positioning of the machined collar/microgap on crestal bone level changes: a systematic review

<jats:title>Abstract</jats:title><jats:sec><jats:title>Objectives</jats:title><jats:p>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?</jats:p></jats:sec><jats:sec><jats:title>Material and methods</jats:title><jats:p>Electronic databases of the <jats:italic><jats:styled-content style="fixed-case">P</jats:styled-content>ubMed</jats:italic> and the <jats:italic><jats:styled-content style="fixed-case">W</jats:styled-content>eb of Knowledge</jats:italic> were searched for animal and human studies reporting on histological/radiological crestal bone level changes (<jats:styled-content style="fixed-case">CBL</jats:styled-content>) 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: <jats:italic>n </jats:italic>= 318 titles). Quality assessment of selected full‐text articles was performed according to the <jats:styled-content style="fixed-case">ARRIVE</jats:styled-content> and <jats:styled-content style="fixed-case">CONSORT</jats:styled-content> statement guidelines.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>A total of 13 publications (risk of bias: high) were eligible for the review. The weighted mean difference (<jats:styled-content style="fixed-case">WMD</jats:styled-content>) (95% <jats:styled-content style="fixed-case">CI</jats:styled-content>) 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 (<jats:italic>P </jats:italic><<jats:italic> </jats:italic>0.001) (<jats:italic>P</jats:italic>‐value for heterogeneity: 0.885, I2: 0.000% = no heterogeneity). <jats:styled-content style="fixed-case">WMD</jats:styled-content> (95% <jats:styled-content style="fixed-case">CI</jats:styled-content>) between microgaps placed either at or below the bone crest amounted to −0.479 mm favoring a subcrestal position of the implant neck (<jats:italic>P </jats:italic><<jats:italic> </jats:italic>0.001) (<jats:italic>P</jats:italic>‐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.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>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.</jats:p></jats:sec>