Xuejing Xu
| Xuejing Xu |
Xuejing Xu, Sonaj Vardhaman
Yu Zhang
Division of Restorative Dentistry, Preventive & Restorative Sciences, University of Pennsylvania, School of Dental Medicine
Introduction
Ceramic crowns fracture when flaws of various sizes are introduced by functional and para-functional forces. In addition, damage in ceramics also occurs during technician and clinician adjustments prior to or during placement in the mouth. These sharp defects can raise the stress concentration in the dental crowns. A damaged ceramic surface will behave differently since it is not as strong as its initial form. The goal of this study is to measure and analyze the effect of strength degradation of in-house fabricated, two-step sintered, high-strength 3Y-PSZ (3-Yttria-Partially Stabilized Zirconia) relative to its conventionally sintered counterparts through controlled flaws introduced via Vickers indentation.
Methods
Two-step sintered Zpex (3Y) samples (n = 60) were fabricated into thin discs (Ø13x1 mm) using Tosho powder and sintered at 1500°C for 1 minute followed by 1150°C for 10 hours. The conventionally sintered counterparts (n = 60) were produced following manufacturer’s instructions. All samples were polished with 15 µm diamond disc on both sides and with 6 µm, 3 µm, and 1 µm diamond discs on one surface. The samples were subjected to Vickers indentation (load P = 0.1 to 100 N) at the center of the polished surface. Strength of the samples was determined by the biaxial flexural test with the indented surface loaded in tension using a piston-on-three-ball testing jig. The samples were analyzed in an optical microscope before and after the flexural test to obtain the length of cracks. Data were plotted in the form of flexural strength vs. indentation load for strength degradation determination.
Results
All groups underwent strength degradation due to indentation flaw. The intrinsic flexural strength of the two-step sintered 3Y samples is higher than that of the conventionally sintered counterparts. The strength of the conventionally sintered 3Y dropped by 50% at a load of 10 N whereas the two-step sintered 3Y underwent a strength degradation at a significantly lower load of 3 N. It was shown by the optical images that low loads were sufficient to initiate cracks but did not degrade the strength of the samples.
Conclusion
The two-step sintering process improves the intrinsic strength of 3Y but made the material less resilient to contact damages when compared to the conventional sintering technique.