Abstract
Titanium and its alloys are gathering much attention as dental alloys because of their good corrosion resistance and biocompatibility.However, their applications are limited as compared to other conventional dental alloys.Especially, studies for clinical application are insufficient.The mechanical properties of dental alloys are estimated as an ultimate tensile strength, proof strength and hardness by the tensile test, the bending test and the hardness measurement.Although, these static data of the materials are useful to determine the properties of the macroscopic materials, considering the actual environment for the alloys, the dynamic properties must be determined by the fatigue test.For development of the application of titanium in the dental field, it is important to clarify its basic fatugue data.In this study, the fatigue test for cast titanium specimens was carried out.The findings ware compared with those of cobalt-chromium alloy.In the fatigue test the specimens ruptured under a small stress below the ultimate tensile strength.The number of stress cycles to rupture was decreased with the in crease of repeated stress.In the case of relatively small stress, the strain of the specimens was small by the work hardening during the test.In the case of large stress, fatigue cracks were initiated in the early stage of the test and a fast propagation was observed.There were different kinds of mechanisms on the crack initiation and propagation between titanium and cobalt-chromium alloy.Many small cracks were initiated on the surface of titanium instead of a few large cracks on the cobalt-chromium alloy propagating to the internal of the specimens.In conclusion from the view point of fatigue strength, the design of cast materials having a stress of 1/5 of the ultimate tensile strength is necessary to be good for ten years for an adult person.This is also the case for the cobalt-chromium alloy.This stress level was below the elastic limit.
