ABSTRACT
Objective Few studies are reported on the aging of veneering ceramics. This study was to investigate the effects of aging on surface roughness, composition and hardness of veneering ceramics for zirconia frameworks.Methods Twenty specimens were fabricated with each of the five types of veneering ceramics for zirconia frameworks － Vintage ZR (ZR), Cerabien ZR (CZR), VitaVM9 (VM9), Cercon ceram KISS (KISS) and IPS e.max ceram (e.max). The specimens were randomly divided into an aging and a control group of equal number, the former subjected to accelerated aging at 200 ℃ and 2 atm for 5 hours while the latter left untreated. The surface roughness and Vickers hardness of the specimens were measured using laser profilometry and Vicker's indentation test machine and their surface topography and chemical composition examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).Results Compared with the control group, the aged specimens fabricated with ZR showed significantly increased surface roughness parameters Ra (\[0.157±0.009\] vs \[0.197±0.008\] μm, P=0.000), Rp (\[0.356±0.031\] vs \[0.446±0.036\] μm, P=0.000) and Rv (\[0.411±0.034\] vs \[0.498±0.036\] μm, P=0.000), and so did those fabricated with CZR, VM9 and KISS (P=0.000). The Ra, Rp and Rv parameter values of the aged specimens with CZR were remarkably higher than those with VM9, KISS and e.max (P < 0.001), but those of the aged specimens with e.max markedly lower than those with ZR, CZR, VM9 and KISS (P<0.01). The RSm value was significantly higher in all the aged specimens than in the control (P<0.001), and so was the oxygen content (P<0.05), but the levels of sodium and potassium were lower in the former than in the latter group (P<0.05). Compared with the control group, the silicon content was significantly decreased in the aged specimens with ZR, KISS and e.max (P<0.01), and so was that of calcium in those with ZR and VM9 (P<0.05). The Vickers hardness of the aged specimens with ZR was remarkably lower than that of the control (\[5.01±0.28\] vs \[6.91±0.51\] GPa, P=0.000), and so was that of the other aged specemens (P=0.000).Conclusion Accelerated aging can significantly alter the surface properties, enhance the stability and prolong the working life of veneering ceramics for zirconia frameworks.