title: [Circulating test and analysis of clasp retention].
abstract: OBJECTIVE
  To show the trend of the retention change during the circulation of the clasp dislodging and inserting, and to discuss the proper depth of the undercut for a specific clasp. It is also a basic study for the best designing of RPD.
  
  
  METHODS
  The Chatillon force measuring instrument was used to record the variation of the retention of Co-Cr alloy casting Akers clasp when they were dislodging from undercuts of different depths (0.25 mm, 0.50 mm, 0.75 mm) on bicuspid and molar.
  
  
  RESULTS
  The data was analysed of Correlation and Regression by SPSS 10.0 statistic software. The variations of the retention in the circulation are obvious from the different teeth and different undercut depths. It shows an attenuation trend in circulation (P < 0.01). After 400 times dislodging, in bicuspid group, the retention of the clasp used in 0.50 mm undercut became less than the one used in 0.25 mm undercut. While the retention of the clasp used in 0.75 mm decreases most obviously, it values 0.7670 kg. In molar group, the attenuations of the retention at different depths of undercut are similar, the retentions of the clasp still rank as, from great to less, 0.75 mm, 0.50 mm and 0.25 mm, in the depth of undercut.
  
  
  CONCLUSIONS
  the proper depth of the undercut for bicuspid is 0.25 mm, and 0.50 mm for molar.
authors.affiliation: Department of Prosthodontics, School of Stomatology, Shanghai Second Medical University, Shanghai 200011, China.
authors.forename: Qi-min
authors.initials: QM
authors.lastname: Ge
authors.forename: Fu-qiang
authors.initials: FQ
authors.lastname: Zhang
mesh_terms: D016734:Dental Clasps; D017268:Dental Prosthesis Retention; D006801:Humans