Fundamental And Applied Research On The Fatigue Resistance Of Titanium And Titanium Alloy Cast Denture Clasp

When the denture is token off and worn, in masticatory process the clasp is loaded with a low-frequency circle loading which will lead the clasp to the fatigue fracture. Therefore, the design and manufacture of a denture should consider the phenomenon of the clasp, but there have been not enough studies on the fatigue of casting clasp compared with its application. The present study simulated the behavior of clasp in oral cavity and the action bending clasp arm to increase retention of denture, and employed constant-deflection fatigue test to study the fatigue behavior of three types of titanium & titanium alloy and the factors affecting their fatigue resistance. It will provide a solid basis for the clinical application of these materials.1. The research on the deflection fatigue resistance of titanium & titanium alloy cast clasp.The fatigue resistances of different domestic commercial types of metals including pure titanium, two titanium alloy(Ti-6Al-4V, Ti75), cobalt-chromium alloy were measured in the present study. The results showed that the resistance of fatigue cobalt-chromiumalloy was the highest, while that of TA2 was the lowest. The fatigue resistance of Ti75 was greater than Ti~6Al-4V. Fatigue resistance increased of Ti75 and cobalt-chromium alloy clasps that are bended to reinforce retentions, while that of the TA2 and Ti~6Al-4V clasps decreased. Ti75, a new type titanium alloy, doesn' t include Vanadium, which is safer for human being. When Ti75 was first used to manufacture cast clasp, it possessed good fatigue resistance, and thus it was a suitable alloy to manufacture casting denture clasp.2. The reshearch of the effect of two kinds of cooing-downmethods on the fatigue resistance of cast denture clasps.This study investigated the different effects of cooing-down methods on fatigue resistance of clasps made from two kinds of metals (TA2, Co-Cr). The result suggested that significant difference existed in the fatigue resistance of cast denture clasps. From the metallograph, the grain size of the room-temperature water-cooling clasps was known to be smaller than that of the air-cooling clasps. The yield strength of the room-temperature water-cooling clasps is higher, but their residual tension stress is higher than that of the air-cooling clasps, thus the fatigue resistance of the room-temperature water-cooling clasps is not as high as that of the air-cooling clasps.3. The effect of three kinds of the heat-treatment on the deflect fatigue of pure titanium.Three kinds of heat-treatment (relief annealing, full annealing and vacuum annealing) were applied into pure titanium clasps to improve the fatigue resistance of the clasps. The results showed that significant difference existed in the fatigue resistance of the three kinds of heat treatment. All the three treatments could increase the FFCLN significantly, but FFCLN was always under 106. In addition, only the fatigue crack appeared on the surface of thetitanium clasp, and no fatigue fracture occurred. Vacuum annealingwas the best treatment to improve fatigue resistance of TA2 claspThe decrease of the hydrogen content in the pure titanium canresist the harm the titanium hydride does to the fatigue resistance of the pure titanium clasps and can improve the adjustment of the clasps. Relief annealing and full annealing need finish the clasps for the second time, which can influence the accuracy of the denture. Therefore, compared with them, the vacuum annealing is more suitable to improve the fatigue resistance.