In Vitro Study On The Impact Wear Behavior Of Human Teeth And Dental Materials

As an important masticatory organ, human teeth perform the continuous cycle of mastication under the control of central nervous system, powered by chewing muscles. Impact wear probably occurs during the process of mastication when the mandibular teeth are closed onto the opposing maxillary teeth so as to cut, tear and grind food particles under the action of biting force. Usually, the wear on the occlusal surface of teeth is the combined results of impact contact and sliding friction of teeth. Therefore, to study the impact wear of teeth could not only fully reveal the wear mechanism of human teeth but also provide important theoretical basis to both the clinical prophylaxis and treatment of excessive tooth wear and the development of new dental materials.In this paper, the impact wear behavior and mechanism of human teeth were investigated in vitro using a specially designed impact test. The influence of water content within the enamel on its impact wear behavior was also explored. The surface morphologies, mechanical and tribological properties of samples were examined using microhardness tester, laser confocal scanning microscopy (LCSM), scanning electron microscopy (SEM) and profilometer. Moreover, the impact wear behaviors of human teeth, titanium alloy and synthetic hydroxyapatite ceramic were comparatively studied. The main research conclusions were drawn as follows:(1) The wear volume of tooth samples increased nonlinearly with the number of impact cycles. The wear on the surface of tooth sample was mainly characterized with slight plastic deformation at the early stage of impact wear. And then delamination occurred on the worn surface. As the wear proceeded further, tooth surface was gradually covered with a layer of wear particles, and the wear rate decreased. No cracks were observed on the cross section of wear scars. The water content of human tooth enamel had an obvious influence on the impact wear behavior of human teeth. The longer drying time was, the lower the fracture toughness of enamel surface was. With the drying time increasing, the delamination was more easily to occur on the surface of teeth, and the formation time of debris layer decreased. Hence, cracks appeared on the cross section of wear scars for the dried tooth samples, and their wear rate was observed to be a little lower at the late stage of impact wear than that of the tooth samples without drying treatment.(2) The wear volume of both titanium alloy and synthetic hydroxyapatite were increased nonlinearly with the number of impact cycles. For the titanium alloy, no cracks were observed on the cross section of wear scars during the process of impact. But some microcracks appear on the cross section of wear scars for the synthetic hydroxyapatite, and no surface hardening occurred.(3) In terms of the morphology and the mechanical properties of wear surface, the impact wear behavior of human teeth was more similar to that of the ductile material of titanium alloy than that of the brittle material of hydroxyapatite ceramic.