Fracture Strength, and Marginalfit of a new, Shrinkage-free ZrSiO4 Ceramic

OBJECTIVES: The aim of this in-vitro study was to evaulate the survival rate, fracture strength and the marginal accuracy of crowns of a new, shrinkage-free ZrSiO4 ceramic. METHODS: Thirty-two teeth were randomly divided into two groups of 16 samples each. All teeth were prepared and restored with new, shrinkage-free ZrSiO4 ceramic crowns, produced by a CAD/CAM (KaVo, Everest®) System. Measurements of the marginal accuracy before and after cementation were made using an epoxy replica. To record the measurements a computer system consisting of a stereomicroscope, a 3CCD camera and a personal computer with a special software were used. The value of marginal discrepancy was calculated for each speciment, and this value was used to determine the mean marginal discrepancy for each group before and after cementation of the ceramic crowns. All specimens, were loaded in a computer-controlled dual-axis chewing simulator to 1.2 million cycles of thermo-mechanical fatigue. Surviving specimens were subsequently loaded until fracture in a static testing device. A significance level of P<0.05 was used for all comparisons. RESULTS: The median fracture loads (± standard deviations) were as follows: Group A, 1665 N (±433); group B, 1718 N (±806). Wilcoxon rank tests showed no significant differences between the two groups, respectively (P<0.05). The median marginal gap values before cementation were (± standard deviations): Group A, 32,79 µm (±6,82); group B, 33,72 µm (±6,69). The median marginal gap values after cementation were (± standard deviations): Group A, 42,99 µm (±6,67); group B, 47,75 µm (±7,68). The Paired T-test of the marginal accuracy showed significant differences between, before and after cementation for both groups. CONCLUSION: All test groups demonstrated fracture strength values above the range of suggested load of clinical acceptability. Before and after cementation the marginal accuracy of the crowns consist of the tested ceramic was more than satisfactory.