Influence of Preaging Temperature on the Indentation Strength of 3Y-TZP Aged in Ambient Atmosphere.

Ki-Won Jeong,Gi-Uk Yang,Dae-Joon Kim,Jung-Suk Han

doi:10.3390/ma14112767

Abstract

Yttria-stabilized zirconia (3Y-TZP) containing 0.25% Al2O3, which is resistant to low temperature degradation (LTD), was aged for 10 h at 130–220 °C in air. The aged specimens were subsequently indented at loads ranging from 9.8 to 490 N using a Vickers indenter. The influence of preaging temperature on the biaxial strength of the specimens was investigated to elucidate the relationship between the extent of LTD and the strength of zirconia restorations that underwent LTD. The indented strength of the specimens increased as the preaging temperature was increased higher than 160 °C, which was accompanied by extensive t-ZrO2 (t) to m-ZrO2 (m) and c-ZrO2 (c) to r-ZrO2 (r) phase transformations. The influence of preaging temperature on the indented strength was rationalized by the residual stresses raised by the t→m transformation and the reversal of tensile residual stress on the aged specimen surface due to the indentation. The results suggested that the longevity of restorations would not be deteriorated if the aged restorations retain compressive residual stress on the surface, which corresponds to the extent of t→m phase transformation less than 52% in ambient environment.

Highlights

Zirconia is currently one of the most commonly used ceramic materials in restorative dentistry
This suggests that the uneven microstructures were mainly due to the volume expansion accompanied by the t→m phase transformation and boosted because of thermal etching after polishing for SEM observations, which may ease the restriction that retained the pristine grains inside the grain boundaries
This study demonstrates that low temperature degradation (LTD) tolerant 3Y-TZP encounters t→m phase transformation in an ambient atmosphere, where no intentional water species are involved like autoclave treatments, as 3Y-TZP is stressed internally by the enlargement of grain size

Summary

Introduction

Zirconia is currently one of the most commonly used ceramic materials in restorative dentistry. The application of the first generation of 3 mol.% Y2 O3 -stabilized tetragonal zirconia polycrystal (3Y-TZP) was limited to frameworks for all-ceramic restorations, on which feldspathic porcelain was layered, owing to its insufficient translucency [1]. Veneering is a technique sensitive and time-consuming procedure, accompanied by significant tooth reduction and a high risk of chipping, which is a major cause of failure in zirconia veneering ceramics [2,3]. To alleviate such drawbacks, the monolithic zirconia restorations are adapted [4]. The extent of LTD is determined by the fraction of monoclinic phase of ZrO2 (m-ZrO2 ) transformed from tetragonal crystal structure of ZrO2

Methods

Results

Discussion

Conclusion