Influence of Aging on Biaxial Flexural Strength and Hardness of Translucent 3Y-TZP.

Nawal M. Moqbel,Majed Al-Akhali,Matthias Kern,Sebastian Wille

doi:10.3390/ma13010027

Abstract

The purpose of this research was to evaluate the influence of aging and surface treatment on surface roughness, biaxial flexural strength (BFS), and Vickers hardness (VHN) of translucent dental zirconia. Half of 80 disc-shaped zirconia specimens (1.2 mm thickness and 12 mm diameter) were aged (group A) in an autoclave for 20 h (134 °C and 0.2 MPa) and the other half were not aged (group N). Specimens were subjected to: no surface treatment (SIN), particle air-abrasion with 50 µm alumina particles at 1 bar (0.1 MPa) and 2.5 bar (0.25 MPa), or polishing down to 1 µm (POL). Specimens were analyzed using X-ray diffraction, laser scanning microscope, BFS, and VHN tests. Three groups (N-SIN, N-POL, and A-POL) showed almost no monoclinic phase. While other groups showed monoclinic phase ratios ranging from 7.5 vol. % ± 2.4 vol. % (N-0.1 MPa) to 41.5 vol. % ± 0.3 vol. % (A-0.1 MPa). Aging and particle air-abrasion increased significantly the BFS, ranging from 720 ± 37 MPa (N-SIN) to 1153 ± 92 MPa (N-0.1 MPa). The hardness was not influenced significantly by aging. A certain amount of monoclinic phase at the surface strengthens the high translucent dental zirconia, while hardness and roughness are not influenced. The pressure of particle air-abrasion showed no influence on the evaluated properties.

Highlights

Y-TZP ceramics are the strongest alternative biomedical dental materials for all-ceramic dental restorations because of its esthetic, durability, and availability [1,2,3]
The mechanical behavior of Y-TZP zirconia might be deteriorated by a spontaneous transformation of the tetragonal phase to monoclinic phase (t→m) when triggered by external stresses such as grinding [7,8] particle air-abrasion [9,10] and hydrothermal aging [11,12] which is called hydrothermal degradation or low temperature degradation (LTD) [13]
LTD initially occurs at the superficial grains, where water is incorporated into zirconia grains by filling oxygen vacancies, and later spreads to the surface increasing its roughness [14,15]

Summary

Introduction

Y-TZP ceramics (yttria-stabilized tetragonal zirconia polycrystals) are the strongest alternative biomedical dental materials for all-ceramic dental restorations because of its esthetic, durability, and availability [1,2,3]. It is more biocompatible than other ceramics, titanium, and metal alloys, when it is in direct contact with the gingival tissues. The mechanical behavior of Y-TZP zirconia might be deteriorated by a spontaneous transformation of the tetragonal phase to monoclinic phase (t→m) when triggered by external stresses such as grinding [7,8] particle air-abrasion [9,10] and hydrothermal aging [11,12] which is called hydrothermal degradation or low temperature degradation (LTD) [13]. Afterwards, LTD proceeds into the bulk material [15] and affects negatively the density and mechanical properties of

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Conclusion