title: Effects of crown retrieval on implants and the surrounding bone: a finite element analysis.
abstract: OBJECTIVE
  The aim of this study was to observe stress concentration in the implant, the surrounding bone, and other components under the pull-out force during the crown removal.
  
  
  METHODS
  Two 3-dimensional models of implant-supported conventional metal ceramic crowns were digitally constructed. One model was designed as a vertically placed implant (3.7 mm × 10 mm) with a straight abutment, and the other model was designed as a 30-degree inclined implant (3.7 mm × 10 mm) with an angled abutment. A pull-out force of 40 N was applied to the crown. The stress values were calculated within the dental implant, the abutment, the abutment screw, and the surrounding bone.
  
  
  RESULTS
  The highest stress concentration was observed at the coronal portion of the straight implant (9.29 MPa). The stress concentrations at the cortical bone were lower than at the implants, and maximum stress concentration in bone structure was 1.73 MPa. At the abutment screws, the stress concentration levels were similiar (3.09 MPa and 3.44 MPa), but the localizations were different. The stress at the angled abutment was higher than the stress at the straight abutment.
  
  
  CONCLUSIONS
  The pull-out force, applied during a crown removal, did not show an evident effect in bone structure. The higher stress concentrations were mostly observed at the implant and the abutment collar. In addition, the abutment screw, which is the weakest part of an implant system, also showed stress concentrations. Implant angulation affected the stress concentration levels and localizations.
  
  
  CONCLUSIONS
  These results will help clinicians understand the mechanical behavior of cement-retained implant-supported crowns during crown retrieval.
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Afyon Kocatepe University, Afyonkarahisar, Turkey.
authors.forename: Serhat Emre
authors.identifier: 0000-0001-5952-240X
authors.initials: SE
authors.lastname: Ozkir
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Afyon Kocatepe University, Afyonkarahisar, Turkey.
authors.forename: Server Mutluay
authors.initials: SM
authors.lastname: Unal
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Afyon Kocatepe University, Afyonkarahisar, Turkey.
authors.forename: Emel
authors.initials: E
authors.lastname: Yurekli
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Dicle University, Diyarbakir, Turkey.
authors.forename: Sedat
authors.initials: S
authors.lastname: Güven
keywords: Crown; FEA; Implant; Retrievability