Abstract
Due to growing demand for metal-free dental restorations, dental ceramics, especially dental zirconia, represent an increasing share of the dental implants market. They may offer mechanical performances of the same range as titanium ones. However, their use is still restricted by a lack of confidence in their durability and, in particular, in their ability to resist hydrothermal ageing. In the present study, the ageing kinetics of commercial zirconia dental implants are characterized by X-ray diffraction after accelerated ageing in an autoclave at different temperatures, enabling their extrapolation to body temperature. Measurements of the fracture loads show no effect of hydrothermal ageing even after ageing treatments simulated a 90-year implantation.
Highlights
Zirconia ceramics used in dental implants are mostly 3Y-TZPs, standing for tetragonal zirconia polycrystal, stabilized in the tetragonal phase by 3 mol.% Y2 O3
The potentially lesser stability may explain the good mechanical properties obtained on zirconia PURE ceramic implants
Ageing has no measurable effect on the mechanical properties so far: fracture loads are not affected by ageing, and, in the first approximation, scratch tests yield similar results for aged and non-aged samples
Summary
Zirconia ceramics used in dental implants are mostly 3Y-TZPs, standing for tetragonal zirconia polycrystal, stabilized in the tetragonal phase by 3 mol.% Y2 O3. This ceramic can exist at room temperature in two main phases: the stable monoclinic phase and the metastable tetragonal phase. The tetragonal phase is prone to a tetragonal-to-monoclinic transformation in the presence of water. The martensitic tetragonal-to-monoclinic (t–m) phase transformation results in a 5–7% volume increase in the transformed grains [1]. In the presence of water, the t–m transformation proceeds from the surface to the bulk, accompanied by roughening and microcracking, and is called hydrothermal ageing or low temperature degradation (LTD)
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