The mechanism of synergistic effect between wear and microbe corrosion in the degradation process of dental materials

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The purpose of this investigation is to develop testing methods to evaluate dental materials that are exposed in mouth to the combined attack of microbe corrosion and mechanical forces that are caused through the collision of teeth.1. The determination of dynamic wear condition : Stresses which are originated on teeth while chewing soft or hard foods were determined by use of a load sensor (Tekscan) to obtain the extent of the maximum load, loading speed and the contact duration, which were ranged from 4-13 kgf, 0.03-0.07 kgf/ms, 420-500 ms respectively.2. The degradation process of dental materials and the index of degradation : The delinquent in teeth meeting due the decrease in teeth height was taken up so that the decrease in the teeth height was chosen as the index of degradation.3. Development of testing method : As to metallic materials, the teeth meeting were simulated through the combination of a flat plate (specimen) and a sphere (Al_2O_3). Repeated load was applied through t … More he sphere to the specimen to produce an indentation on the surface of which diameter is proportional to the depth of indentation, that is, the decrease in teeth height.It increased with the test duration as an exponential function of loading frequency, which revealed some relation with the delayed movement of dislocation. Those test results obtained in a 3 % NaCl solution were proved to represent well the characteristic behavior of metallic materials that are exposed to the combined attack of wear and corrosion.As to dental resin materials, a whole piece of false tooth was used as test specimen because it is a composite that consists of three different types of resin. Repeated collision test revealed firstly that the decrease in teeth height is caused not through wear but through the deformation of whole tooth piece, secondly that the deformation behavior changes its manner at the collision frequency of about 50000 times, and thirdly that the repeated collision test with low load reveals a characteristic behavior of material different from that of a single time loading test with a much higher load.4. Basing on the test results, a new test method for the dental materials in mouth environment were proposed. Less