RESUMO
<p><b>OBJECTIVE</b>To evaluate mechanical properties of zirconia toughened composite alumina (ZTCA) ceramic used for dental application, characterize the effect of different zirconia contents on mechanical properties of ZTCA.</p><p><b>METHODS</b>Dental alumina ceramic powder was prepared by sol-gel method, and four groups of ZTCA powders with different zirconia contents were prepared via surface-induced precipitation method. All five groups of powders were dry-pressed and then sintered to make standard specimens for mechanical tests. The flexural strength and fracture toughness of these specimens were evaluated, and the fractography was characterized by scanning electronic microscope (SEM). Phases of ZTCA were also determined using X-ray diffraction (XRD).</p><p><b>RESULTS</b>It was found that the flexural strength of ZTCA ceramics increases with ZrO2 content up to 30%, and decreases thereafter. ZTCA specimens containing 30% ZrO2 show the highest flexural strength, and the corresponding fracture toughness was 1.85 MPa x m(1/2). The XRD results of ZTCA ceramics showed the phase constituents of alpha-Al2O3, t-ZrO2 and a small amount of m-ZrO2.</p><p><b>CONCLUSION</b>The strengthening and toughening mechanisms of ZTCA depend on ZrO2 content. In the range of 15%-30% ZrO2, the stress-induced phase transformation toughening mechanism is dominant, while microcrack and deflection exist as the additional toughening mechanism when ZrO2 addition amount is above 30%.</p>
Assuntos
Óxido de Alumínio , Cerâmica , Porcelana Dentária , Teste de Materiais , ZircônioRESUMO
<p><b>OBJECTIVE</b>To investigate the relationship between wedge-shaped defects and occlusal interference.</p><p><b>METHODS</b>Following examination from 46 patients, a total of 157 teeth were identified to have the criteria set for wedge-shaped defects and regarded as the experiment group. Also, 157 adjacent teeth exhibiting no such noncarious cervical lesions were randomly selected from the same group of patients and regarded as the control group. The distribution of occlusal force and time were examined with T-Scan II system in 46 patients with wedge-shaped defects in intercuspal occlusion position, protrusive movement and lateral movement. Occlusal interference and premature contact were evaluated and compared between the two groups.</p><p><b>RESULTS</b>The proportion of the teeth with premature contact in experiment group was 6.37%, while the control group was 2.55%, there was no significant difference between the two groups (P > 0.05). The total proportion with occlusal interferences in experiment group was 23.57%, which was significantly higher than that of the control group (10.19%, P < 0.05), in experiment group the proportion with working side interferences was 15.92%, and in control group, the proportion was 3.82%, there was significant difference between the two groups (P < 0.01). At the same time, the teeth with occlusal interferences had more serious degree of the wedge-shape defects than those with no occlusal interference.</p><p><b>CONCLUSION</b>The increased occlusal force has relation to the formation as well as severity of wedge-shaped defects.</p>