title: [Experimental study on the retentive force of cobalt-chromium alloy, pure titanium and vitallium cast clasps in the simulated 3-year clinical use].
abstract: OBJECTIVE
  To investigate the changes of retentive force of cobalt-chromium alloy, pure titanium and vitallium cast clasps in the simulated 3-year clinical use.
  
  
  METHODS
  Fifteen metal abutment crowns made of No.QT800-2 nodular cast iron were used in the test. Five clasps from each of the following alloys: cobalt-chromium alloy, pure titanium and vitallium were fabricated. The undercut depth was 0.25 mm. A masticatory simulator was used to cycle the clasp on and off the metal abutment crown 5000 times, simulating 3-year clinical use. Retentive force was measured 11 times during this process. SPSS13.0 software package was used to analyze the results. Casting defects were observed using X-ray non destructive testing (X-ray NDT) before cyclic test. Surface characteristics were qualitatively evaluated using scanning electron microscope (SEM) before and after cyclic test.
  
  
  RESULTS
  The results indicated that there were significant differences (P=0.000) in the retentive force of the 3 groups before and after the cyclic test. The highest retentive force was recorded in the vitallium clasps, and the lowest retentive force was measured in the pure titanium clasps. The results of X-ray NDT depicted the typical casting defect seen at the end of the connector. SEM examination revealed that no evidence of pores and cracks in the inner surfaces of the 3 groups was found before cyclic test. Wear was evident in the inner surfaces of the 3 groups but none of the clasps exhibited any evidence of cracks after cyclic test through SEM examination.
  
  
  CONCLUSIONS
  In this in vitro test, vitallium clasps show the best retentive force in the 3 groups before and after 5000 cycles at 0.25 mm undercut depth. Cobalt-chromium alloy and vitallium clasps can maintain ideal retentive force at 0.25mm undercut depth in the long-term use. Wear may be one of the reasons for the loss of retentive force of clasps in the cyclic test.
authors.affiliation: Department of Prosthodontics, School of Stomatology, China Medical University. Shenyang 110002;Key Lab of Oral Disease,Liaoning Province. Shengyang 110002,China. E-mail:ydkqyhx@163.com.
authors.forename: Hai-xin
authors.initials: HX
authors.lastname: Yan
authors.affiliation: Department of Stomatology, People's Hospital of Liaoning Province. Shenyang 110016, Liaoning Province,China.
authors.forename: Yan-bo
authors.initials: YB
authors.lastname: Zhao
authors.affiliation: Department of Prosthodontics, School of Stomatology, China Medical University. Shenyang 110002;Key Lab of Oral Disease,Liaoning Province. Shengyang 110002,China.
authors.forename: Li-mei
authors.initials: LM
authors.lastname: Qin
authors.affiliation: Department of Prosthodontics, School of Stomatology, China Medical University. Shenyang 110002;Key Lab of Oral Disease,Liaoning Province. Shengyang 110002,China.
authors.forename: Hai-ting
authors.initials: HT
authors.lastname: Zhu
authors.affiliation: Department of Prosthodontics, School of Stomatology, China Medical University. Shenyang 110002;Key Lab of Oral Disease,Liaoning Province. Shengyang 110002,China.
authors.forename: Lin
authors.initials: L
authors.lastname: Wu
mesh_terms: D002858:Chromium Alloys; D016734:Dental Clasps; D003799:Dental Stress Analysis; D003781:Denture Retention; D006801:Humans; D014025:Titanium; D014800:Vitallium
chemical_list: D002858:Chromium Alloys; D014800:Vitallium; D014025:Titanium