title: Evaluation of stability of interface between CCM (Co-Cr-Mo) UCLA abutment and external hex implant.
abstract: OBJECTIVE
  The purpose of this study is to evaluate the stability of interface between Co-Cr-Mo (CCM) UCLA abutment and external hex implant.
  
  
  METHODS
  Sixteen external hex implant fixtures were assigned to two groups (CCM and Gold group) and were embedded in molds using clear acrylic resin. Screw-retained prostheses were constructed using CCM UCLA abutment and Gold UCLA abutment. The external implant fixture and screw-retained prostheses were connected using abutment screws. After the abutments were tightened to 30 Ncm torque, 5 kg thermocyclic functional loading was applied by chewing simulator. A target of 1.0 × 106cycles was applied. After cyclic loading, removal torque values were recorded using a driving torque tester, and the interface between implant fixture and abutment was evaluated by scanning electronic microscope (SEM). The means and standard deviations (SD) between the CCM and Gold groups were analyzed with independent t-test at the significance level of 0.05.
  
  
  RESULTS
  Fractures of crowns, abutments, abutment screws, and fixtures and loosening of abutment screws were not observed after thermocyclic loading. There were no statistically significant differences at the recorded removal torque values between CCM and Gold groups (P>.05). SEM analysis revealed that remarkable wear patterns were observed at the abutment interface only for Gold UCLA abutments. Those patterns were not observed for other specimens.
  
  
  CONCLUSIONS
  Within the limit of this study, CCM UCLA abutment has no statistically significant difference in the stability of interface with external hex implant, compared with Gold UCLA abutment.
authors.affiliation: Department of Prosthodontics, Oral Science Research Center, Yonsei University College of Dentistry, Seoul, Republic of Korea.
authors.forename: Ki-Joon
authors.initials: KJ
authors.lastname: Yoon
authors.affiliation: Department of Prosthodontics, Oral Science Research Center, Yonsei University College of Dentistry, Seoul, Republic of Korea.; BK21 PLUS Project, Yonsei University College of Dentistry, Seoul, Republic of Korea.
authors.forename: Young-Bum
authors.initials: YB
authors.lastname: Park
authors.affiliation: Department of Prosthodontics, Oral Science Research Center, Yonsei University College of Dentistry, Seoul, Republic of Korea.
authors.forename: Hyunmin
authors.initials: H
authors.lastname: Choi
authors.affiliation: Department of Prosthodontics, Oral Science Research Center, Yonsei University College of Dentistry, Seoul, Republic of Korea.
authors.forename: Youngsung
authors.initials: Y
authors.lastname: Cho
authors.affiliation: Department of Prosthodontics, Oral Science Research Center, Yonsei University College of Dentistry, Seoul, Republic of Korea.
authors.forename: Jae-Hoon
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Department of Prosthodontics, Oral Science Research Center, Yonsei University College of Dentistry, Seoul, Republic of Korea.
authors.forename: Keun-Woo
authors.identifier: 0000-0002-3153-190X
authors.initials: KW
authors.lastname: Lee
keywords: CCM UCLA abutment; Chewing simulator; External hex implant; Removal torque value