Dynamic wear characteristics and fracture strength of high-translucent monolithic zirconia crowns

The dental ceramic restorations inevitably undergo a wear damage. The dynamic wear behavior and fracture strength after wear fatigue of the high-translucent zirconia crowns have rarely been studied. In the present study, the zirconia crowns were fabricated using a high-translucent zirconia material and subsequently cemented to the PMMA abutments with a resin cement. The specimens were fixed in a chewing simulator and dynamically loaded for 3.6 million fatigue cycles (a maximal load of 350 N, 1.7 Hz). The wear volume and wear rate at the designated checkpoints between 0-36 x 10(5) cycles with an interval of 3 x 10(5) cycles were measured. The fracture strength of the zirconia specimens before wear fatigue as well as after 9, 24 and 36 x 10(5) cycles was analyzed. The morphology of the wear surface was observed by SEM. The results showed that the wear volume increased with the wear cycles. In the initial stage (0-9 x 10(5) cycles), the wear rate remained at a significantly high level (about 0.289-0.349 mm(3)/10(5) cycles). Subsequently, it decreased rapidly and stabilized at a relatively low level (about 0.052-0.081 mm(3)/10(5) cycles). As the number of fatigue cycles was increased, the fractured strength decreased significantly, except after 9 x 10(5)cycles. The worn surface after wear were flattened, and only a small number of scattered cracks and small punctate defects were observed. The high-translucent zirconia crowns exhibited dynamic wear characteristics, and the fracture strength decreased significantly.