Transformation characteristics of dental 3Y-TZP by accelerated low temperature degradation

Abstract

Purpose: The purpose of present study is (1) to evaluate difference of t-m transformation between veneered zirconia and unveneered exposed zirconia by accelerated LTD(Low Temperature Degradation) test and (2) to evaluate mechanical change following accelerated LTD test.Materials and Methods: 60 fully sintered 3Y-TZP discs were made. Machined surface was veneered by ZirPress glass ceramic, and the opposite side was highly polished without veneering. By accelerated LTD time, 60 bilayered specimens were divided into three groups. Group A was control, group B and C were undergone accelerated LTD at 134 ℃ for 5 and 10 hours in distilled water, respectively. Maximum fracture load of bilayered specimens was measured by Piston-on-three-ball test. X-ray diffraction analysis was done to calculate monoclinic fraction(Xm) on veneered and exposed zirconia surfaces following fracture load test. SEM was taken to survey monoclinic zone in fractured area. To measure Yttrium weight %, energy dispersive X-ray spectroscopy analysis was used on both surfaces. Raman spectroscopy was taken to identify monoclinic peak at both surfaces and 6 ㎛ below each surfaces in fractured area. Results: There was significant increase of monoclinic fraction at exposed surface compared to veneered surface in group B and C(p<0.05), but maximum fracture load among three groups was not significantly different(p>0.05). We could not find clearly identified monoclinic layer by SEM. Yittrium weight % was statistically lower at exposed surface in group C(p<0.05). Raman spectrum showed monoclinic peak only 6 ㎛ below exposed surface in group C. Conclusions: T-m transformation occurred much more on exposed zirconia, but there was no change on veneered surface following accelerated LTD. And those change did not influence maximum fracture load of veneered zirconia.