RESUMO
UNLABELLED: The dentistry literature shows consensus to use the Garvie and Nicholson equation modified by Toraya to quantify the Y-TZP phase transformation. However, this method does not include the possibility of cubic phase transformation and crystallographic texture after artificial ageing, and in this case, it is possible to observe errors of quantification. OBJECTIVES: The aim of this study was to evaluate a dental Y-TZP ageing kinetic of phase transformation under pressure and hydrothermal conditions (130°C, 2bar) and to compare the methods of quantification by the equation of Garvie and Nicholson modified by Toraya and the Rietveld refinement method. METHODS: Discs of Y-TZP (12mm Ø×1.2mm in height) were divided into groups (n=4) according to the ageing times (in the range of 6 and 138h). The superficial characterisation was made using SEM and the XDR for crystallographic analysis. RESULTS: An aggressive superficial degradation process at the beginning of phase transformation in 6-10h of ageing was observed by SEM. The phase transformation quantification showed differences between the methods. It was observed the increase and stabilisation of monoclinic phase until 80% at 40h of ageing by the Garvie and Nicholson modified by Toraya equation, compared to 60% of monoclinic phase and approximately 30% of cubic phase observed by the Rietveld method. CONCLUSION: The Toraya equation showed an overestimated result of monoclinic quantification compared to the Rietveld method. CLINICAL SIGNIFICANCE: The overestimated result of monoclinic phase could lead to different interpretation about the dental Y-TZP ageing process.
