The influence of mechanical surface treatment on fracture toughness of y-tzp dental ceramic

Introducton: The high strength of Y-TZP ceramics is derived from a stress-induced transformation from the metastable tetragonal form to the stable monoclinic form (t → m). This transformation is associated with an increase in volume of the grain, thereby closing the crack tip and preventing further crack propagation. It has been reported that grinding increases the strength of ceramics containing metastable tetragonal zirconia compared with fine polishing. This is due to the t→ m transformation and the associated development of surface compressive strains from the grain’s volume change. Fine polishing eliminates some of the transformed monoclinic phase without further inducing the formation of tetragonal phase, thereby reducing the surface strains. Aims: To evaluate the effects of surface mechanical treatments of all-Y-TZP restorations, surface roughness (Rs), fractal dimension (Df), fracture toughness (Ft),Vickers hardness (Hv), crack length (Cl) and opening (Co) were determined. Y-TZP specimens (n = 30) as received by milling center (M), after coarse polishing (CP) and after fine polishing (FP) were investigated. Findings: Rs was 97.4 ± 4.2 μm for FP, 112.5 ± 8.8 μm for CP and 118.3 ± 9.4 μm for M. Df was 1.339 ± 0.15 for Fp, 1.662 ± 0.11 for Cp and 1.59 ± 0.15 for M. Hv was 1681 ±166 for M, 1649 ±273 for FP and 1440 ±182 for CP. Ft was 7.2 ± 0.2 for M, 5.8 ± 0.7 for FP and 7.6 ± 0.3 for CP. The Cl was 93.2 ± 5.5 (μm) for M, 147.9 ±32.2 (μm) for FP and 83.2 ±8.3(μm) for CP. The Co 1.1 ±0.3 (μm) for M, 1.3 ±0.3(μm) for FP and finally 0.8 ±0.1(μm) for CP. The FP group showed a significant decrease for Rs, Ft and Df with a significant increase for Cl and Co. The Hv was not different. Conclusions: The fine polishing procedure in all-YTZP restorations produces a surface embrittlement.