Ageing kinetics and strength of airborne-particle abraded 3Y-TZP ceramics

- A 10 μm thick altered zone is present under the airborne-particle abraded 3Y-TZP surface.
- Ageing penetrates through the altered zone and decreases the surface strengthening.
- When the altered zone is annihilated, strength returns to values measured in intact 3Y-TZP.
- Ageing of airborne-particle abraded 3Y-TZP follows a two-step linear kinetics.
- Airborne-particle abrasion is not harmful to the 3Y-TZP ceramics' stability.

ObjectiveThe combined effects of alumina airborne-particle abrasion and prolonged in vitro ageing on the flexural strength of 3Y-TZP ceramic have been studied. The aim was to identify the different effects on the surface and subsurface regions that govern the performance of this popular bioceramic known for its susceptibility to low-temperature degradation (LTD).MethodsAs-sintered or airborne-particle abraded 3Y-TZP discs were subjected to ageing at 134 °C for up to 480 h. Biaxial flexural strength was measured and the relative amount of monoclinic phase determined using X-ray diffraction. The transformed zone depth (TZD) was observed on cross-sections with scanning electron microscopy coupled with a focused ion beam. Segmented linear regression was used to analyze the flexural strength and TZD as functions of the ageing time.ResultsA two-step linear ageing kinetics was detected in airborne-particle abraded specimens, reflecting the different microstructures through which the LTD proceeds into the bulk. A 10 μm thick altered zone under the abraded surface was involved in both the surface strengthening and the increased ageing resistance. When the zone was annihilated by the LTD, the strength of the ceramic specimens and the speed of LTD returned to the values measured before abrasion. Even at prolonged ageing times, the strength of abraded groups was not lower than that of as-sintered groups.SignificanceBoth the ageing kinetics and the flexural strength were prominently affected by airborne-particle abrasion, which altered the subsurface microstructure and phase composition. Airborne-particle abrasion was not harmful to the 3Y-TZP ceramics' stability.

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