Study On Elastic Deformation Limit And Cyclic Fatigue Test Of Cobalt-chromium Alloy Cast Clasps

Objective The aim of this study was to investigate the elastic deformation limit and the fatigue resistance of cobalt- chromium alloy cast clasps, and to probe into the rules of this variation.Methods Thirty cast straight clasps made of three types of cobalt-chromium alloys were subjected to compression-deformation test in the universal material test mechine, the elastic deformation limit and relevant enclasp forces were got after the datas produced from the mechine were analyzed by a serial of softwares. Then another 30 clasps casted by the three types of cobalt-chromium alloys were made to engage one of 2 retentive undercut depths (0.25mm or 0.50mm). The force(N) required to remove the clasps was measured using the universal testing machine with the crosshead speed of 20mm/min. After measuring the retentive force, the clasps were cycled on and off the metal abutment tooth for 360 times, simulating the insertion and removal of a removable partial denture clasp for 3 months. The cycling sequence was repeated 20 times, and the retention force was measured after each sequence, simulating the clinical usage for 5 years in total. Data were subuected to one-way analysis of variance and Kruskal-Wallis test, followed by repeated measures analysis of variance. Results⑴The elastic deformation limit of the three types of cobalt-chromium alloys and relevant enclasp forces were not all the same, the result Shanghai group was significance smaller than other 2 groups. No significance were found in enclasp forces amound 3 groups when the clasp deformation was 0.25mm, and the Vera PDSTM showed the greatest forces when the deformation reached 0.50mm.⑵All of the 3 groups experienced a significance decrease in retentive force measruements before and after the cyclic fatigue test. The greatest decrease was found in RegalloyTM 0.25mm group with the figue of 4.954N , and the smallest was found in Vera PDSTM 0.25mm group, the figue was 1.832N. The Vera PDSTM maintained the greatest retentive forces until the final cycling sequence in both undercuts. Conclusions⑴The cobalt-chromium alloy cast clasps should be designed with the best undercut of 0.25mm.⑵The retention force of cobalt-chromium alloy cast clasps experienced a gradual decrease along the cycling sequence, they assumes the logarithm changing pattern.⑶Vera PDSTM showed the best resistance to cyclic fatigue amoung the 3 types of cobalt-chromium alloys, which could maintained retention over a simulated 5-year period in both undercups.