Abstract:

Abstract:Objective To study the changes of retentive force during the circulation of the acetal resin clasp dislodging and inserting and discuss the proper depth of the abutment undercut and cross-section diameter of the acetal resin clasp. Methods The instron force measuring instrument was used to record the variation of the retentive force of acetal resin and Co-Cr alloy casting akers clasp when they were dislodging 2 880 times from abutment undercuts of different depths (0.50,0.75,and 1.00 mm) and different diameters of the acetal resin clasp (1.20 and 2.00 mm) on bicuspid. Results The variations of the retention in the measurement were aceording to  different undercut depths and different diameters. The value of acetal resin clasp’s retentive force became largerwith the increasing of the diameter of cross-section of the clasp and the  depth of abutment undercut（P<0.05）.  Conclusion The  acetal resin clasp of 2.00 mm diameter and the abutment undercut with 0.75 mm are suitable for bicuspid.

Key words: thermoplastic homoplymer polyoxymethylene;retentive force;undercut