| Tooth wear is defined as the loss of the tooth substance which is not caused by dental plague, caries and injuries. In recent years, much attention was paid to the aetiology of tooth wear, however, most of researches focused on the epidemiologic investigation and some external causing factors (such as erosion by acidic substance, abrasion by solid granules, and the effect of some systematic diseases or drugs, and etc). As we know, teeth exist and function in a complex oral biomechanical system. However, whether the degree of tooth wear has something to do with tooth microstructure, how specific occlusal factors affect the development of tooth wear, and what kind of relationship exists between tooth wear and bruxism or TMD, all these are not clear yet.In the present study, 104 patients with severe tooth wear were collected from TMD clinics of Qingdu stomatological hospital. The TMJ X-ray images were taken and the degree of tooth wear on each tooth was measured and used as assessing indexes. Combined with clinical information of each patient, the clinical features of severe tooth wear, and the relationship between tooth wear and oral biomechanical system were investigated. Furthermore, by measuring 30 mandibular first molars, the effect of tooth wear on the shape of the tooth was analyzed; hi the process of the study, the traditional method of making tooth groundsection was modified. Finally, the alignment rules of enamel prisms and the relationship between tooth microstructure and tooth wear were investigated by scanning electron microscope (SEM).The results showed as follow:1. In this study, most of patients were middle-aged (30-59 years old). The incidence of TMD raised with age, while bruxism was mainly in younger patients. No significant relationship was found between the degree of tooth wear and the age. It is suggested that though the volume of tooth wear increased with age, the speed of wear was different in individuals.2. In this study, male patients were more than female in all the patients and patients with bruxism, while the female with TMD was more than male.3. Patients with TMD suffered from bruxism less than those without it, while patients with bruxism suffered from TMD less than those without it,suggested that a negative correlationship existed between bruxism and TMD.4. No significant difference among four groups was found in the changes of TMJ structure in X-ray images. However the incidence of condyle displacement was negatively related to that of TMJ osseous change, suggested that patients suffering from condyle displacement might have lower risk of osseous change.5. Anterior teeth of male patients were worn more severely than those of female patients, while molars of female patients were worn more severely than those of male patients.6. As to the degree of tooth wear in whole dentition, the teeth of patients with only tooth wear were worn more severely than those of other groups, especially in anterior teeth and premolars. Patients with bruxism showed severer tooth wear on premolars and lighter tooth wear on molars than those of patients with only TMD.7. The teeth in mandible showed severer wear than in maxilla; Molars and canines were worn more severely than incisors and premolars.8. In the patients with severe tooth wear, there were 43.33% having normal occlusion, which was significantly lower than the malocclusion incidence in normal people. The whole dentition and molars wear was severer in patients with edge-to-edge bite of anterior teeth than in patients with normal occlusion; The whole dentition and anterior teeth wear was lighter in patients with edge-to-edge bite of posterior teeth or deep over-jet of anterior teeth or cross-bite of anterior teeth than in patients with normal occlusion; The premolars wear was lighter in patients with edge-to-edge bite of posterior teeth or deep over-jet of anterior teeth than normal; Anterior teeth wear was lighter in patients with cross-bite of anterior teeth than in patients with normal occlusion; There was no sig...
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