Papers by Author: Cedomir Oblak

Abstract: This study was designed to evaluate the effects of dental grinding and sandblasting on the ageing and fatigue behavior of pressure less-sintered biomedical grade Y-TZP ceramic. It was found that upon dental grinding and sandblasting, the surface of the material was heavily damaged in part plastically deformed, but the amount of transformed monoclinic zirconia was low. The partitioned tetragonal zirconia grains and pre-existing monoclinic zirconia in the ground and sandblasted surfaces hindered the propagation of the diffusion-controlled transformation during subsequent ageing. Dental grinding at a high rotation speed lowered the mean strength under static loading and the survival rate under cyclic loading. Sandblasting, in contrast, resulted in surface strengthening and substantially higher survival rate under cyclic loading. For all tested groups, about 10-15 % lower survival strength values were obtained when tested in artificial saliva, compared to dry specimens, implying that stress-assisted corrosion plays an important role in the fatigue behavior of dental zirconia.

Abstract: The effects of dental grinding and sandblasting on ageing and fatigue behaviour of pressure less sintered biomedical grade Y-TZP ceramics were investigated. Disc-shaped specimens were sintered to high density for subsequent surface treatment and testing. Accelerated aging experiments by autoclaving in artificial saliva were performed under isothermal conditions at 1340C. The amount of monoclinic zirconia in the ground and sandblasted specimens was < 5% and about 15 %, respectively and the corresponding strength values were 920 MPa and 1290 MPa. After autoclaving for 24 hours, the amount of transformed monoclinic zirconia in as-sintered material was increased to 15 %, resulting in about 10% strength reduction. In contrast, no strength reduction was observed with the ground and sandblasted specimens subjected to prolonged ageing. At any ageing condition, the highest survival rate during mechanical fatigue testing was observed with the sandblasted samples and the lowest with the ground samples. The strength of the surviving specimens tested in air corresponded well to the mean flexural strength of the particular group before fatigue testing, whereas lower survival strength values and a larger variability in strength were obtained with specimens that were subjected to prolonged accelerated ageing prior to mechanical fatigue testing in artificial saliva.