Comparison Of Fatigue Test On Casting Clasps Made Of Common Framework Alloy

Objectives:The aim of the study is to study the fatigue performance of different metal clasps by the way of comparing the fatigue life in different undercut depth of the two kinds of co-cr alloy and pure titanium cast clasps commonly used in clinic,and to provide theoretical evidence for choosing different material alloys according to different abutment tooth conditions.Methods:Two kinds of co-cr alloy (Vitallium2000,Vera PDS) and pure titanium were used to cast ten straight clasps respectively according to the recommanded investment system and corresponding casting method.Based on the different of deflection displacement,divided each clasp group into two groups 0.25mm/0.5mm. there were 6 groups,30 test pieces. The constant-deflection fatigue test was carried out with a pneumatic testing machine in this study.The alternating force was loaded on the clasp tip. Elastic deformation took place on the situation of 5 mm from the tip of the clasp arm. The load direction was from the flat side to curve side.The displacement of clasp tip was fixed. Two different displacements were set, according to undercut depth 0.25mm and 0.5mm.frenquency was 20Hz.The test was terminated when the force was reduced to less than 15% of the initial load.The initial load and number of loading cycles were recorded automatically.The fatigue-fracture surface of the clasps was examined with a scaning electron microscope.The data were subjected to analysis of variance and least significant difference to compare materials for the same undercunt.The Student t test was used to compare the same alloys with different undercut. Result:When the displacement of three kinds of alloy clasps was 0.25mm,the initial load of Vera PDS was more than Vitallium2000, Vital-lium2000 more than pure titanium.there is no significant difference between Vitallium2000 and pure titanium,but the number of loading cycles of Vera PDS was significant more than two others.When the displacement of three kinds of alloy clasps was 0.5mm, the initial load and number of loading cycles of pure titanium was less than Vitallium2000 and Vera PDS.There was no difference in Vitallium2000 and Vera PDS.The comparsion of the initial load and number of loading cycles of three kinds of material clasps respectively in two undercut depth show that to the same material,the initial load of 0.25mm clasp groups was significant less than 0.5mm clasp groups,but the number of loading cycles,formor was more than latter.Conclusion:the fatigue life of Vera PDS clasps were longer than that of Vitallium2000 clasps. The fatigue life of Vitallium2000 clasps were longer than that of pure titanium clasps.To the same clasps materials,with the growth of the abutment undercut,the fatigue life of clasps were shorter and shorter.