title: Effect of cement washout on loosening of abutment screws and vice versa in screw- and cement- retained implant-supported dental prosthesis.
abstract: OBJECTIVE
  The purpose of this study was to examine the abutment screw stability of screw- and cement-retained implant-supported dental prosthesis (SCP) after simulated cement washout as well as the stability of SCP cements after complete loosening of abutment screws.
  
  
  METHODS
  Thirty-six titanium CAD/CAM-made implant prostheses were fabricated on two implants placed in the resin models. Each prosthesis is a two-unit SCP: one screw-retained and the other cemented. After evaluating the passive fit of each prosthesis, all implant prostheses were randomly divided into 3 groups: screwed and cemented SCP (Control), screwed and noncemented SCP (Group 1), unscrewed and cemented SCP (Group 2). Each prosthesis in Control and Group 1 was screwed and/or cemented, and the preloading reverse torque value (RTV) was evaluated. SCP in Group 2 was screwed and cemented, and then unscrewed (RTV=0) after the cement was set. After cyclic loading was applied, the postloading RTV was measured. RTV loss and decementation ratios were calculated for statistical analysis.
  
  
  RESULTS
  There was no significant difference in RTV loss ratio between Control and Group 1 (P=.16). No decemented prosthesis was found among Control and Group 2.
  
  
  CONCLUSIONS
  Within the limits of this in vitro study, the stabilities of SCP abutment screws and cement were not significantly changed after simulated cement washout or screw loosening.
authors.affiliation: Department of Prosthodontics, Samsung Medical Center, College of Medicine, Sungkyunkwan University, Seoul, Republic of Korea.
authors.forename: Seok-Gyu
authors.initials: SG
authors.lastname: Kim
authors.affiliation: Department of Prosthodontics, College of Dentistry, Chosun University, Gwangju, Republic of Korea.
authors.forename: Chae-Heon
authors.initials: CH
authors.lastname: Chung
authors.affiliation: Department of Prosthodontics, College of Dentistry, Chosun University, Gwangju, Republic of Korea.
authors.forename: Mee-Kyoung
authors.initials: MK
authors.lastname: Son
keywords: Dental cement; Implant-supported dental prosthesis; Torque