| The wear of human teeth is an inevitable physiological process. Clinical problems due to tooth wear have being increased, because people are keeping their own teeth for more years. Understanding of the tribological property of teeth would help the clinical treatment for excessive wear of teeth and develop new dental restorative materials.Normal human teeth (primary teeth and permanent teeth), pathological teeth (tetracycline stained teeth) and plastic teeth (three types of plastic teeth) have been tested under ball-on-flat contact using a reciprocating apparatus. Various analyses by using microhardness tester, profilometer, laser confocal scanning microscopy (LCSM), scanning electron microscopy (SEM), energy dispersive spectroscope (EDX), X-ray photoelectron spectroscope (XPS), X-ray diffraction (XRD) and Fouriee transform infrared spectrometer (FT-IR), have been performed. Main conclusions are drawn as follows:1. Microhardness and tribological properties differ remarkably between layers in permanent tooth. Higher microhardness, lower friction coefficient and better wear-resistance are observed in the enamel zone than in the dentin, which appears both on the occlusal section and on the axial section. Furthermore, friction and wear behaviors of tooth depend strongly on microstructure orientations. A tooth shows better wear-resistance along the occlusal section than along the axial section due to the orientation of the enamel rods and the dentinal tubule.2. Friction and wear test results show that the wear of human tooth enamel changes gradually from two-body wear into three-body wear with plastic delamination occurring on the enamel surface during wear process. With the number of cycles increasing, wear rate decreases and finally the wear of enamel stays in a stable stage. In conclusion, the wear of human tooth enamel is controlled by mechanical removal process. It is also found that increasing normal load is associated with a progressive increase in the wear volume of enamel. In addition, because of the lubrication and the stress decentralization of food slurry on the contact, enamelshows better wear-resistance in food slurry medium than in artificial saliva medium. Therefore, both low friction coefficient and small wear depth can be observed in food slurry medium.3. Tribological behavior of human tooth depends strongly upon its age. The friction and wear behaviors of permanent teeth at the young age are similar to those of permanent teeth at the middle age, and the worn surfaces are characterized mainly by slight plough and delamination traces, which have better wear-resistance. However, significant plough and massive delamination are dominant for the primary teeth and permanent teeth at the old age, accompanying with strong fluctuation in the evolution of friction coefficient.4. Tribological properties of tetracycline stained teeth are found to be correlative with its color. Friction and wear behaviors of lightly tetracycline stained teeth are similar to those of normal permanent teeth. For heavily tetracycline stained teeth, strong fluctuation and rather high stable value are found in the evolution of friction coefficient, and significant plough and delamination are dominant on the wear scar, whose tribological properties are inferior to normal permanent teeth. It is suggested that the resistance against wear of human teeth decreases with the increase of tetracycline stained extent.5. Plastic teeth are found to have good friction and wear properties sliding against titanium ball in artificial saliva medium. They are characterized by mild abrasive wear at relatively small normal loads and by severe adhesive wear at high normal loads. The immersion of plastic teeth samples in the artificial saliva or carbon beverage has little effect on the tribological properties. However, the thermally cycling of plastic teeth samples within 0-60 leads to a significant decrease in the wear-resistance. Furthermore, plastic teeth are more readily worn away by food particles. In this case, plough and... |
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