Effects Of Different Aging Treatments On The Mechanical Properties Of A CAD/CAM Resin Composite Containing Nanozirconia Fillers

ObjectivesRecently a CAD/CAM resin composite containing nano-zirconia fillers has been widely used as a chair-side material.This study was aimed to investigate the effects of hydrothermal aging,thermal cycling,and water storage on the mechanical properties of this material.MethodsA CAD/CAM resin composite containing nano-zirconia fillers(Lava Ultimate,LU)and a resin-based composite with a similar resin matrix-to-filler ratio but without zirconia fillers(Tetric N-Ceram,TNC)were prepared into bars with the same dimension of 14 mm×4 mm×1.4 mm.To verify the effectiveness of the subsequent hydrothermal aging,a 3Y-TZP ceramic(Ceramill Zolid,CZ)was prepared into the bar with the same dimension.Specimens of LU and TNC were assigned into four groups separately based on the type of aging treatment(hydrothermal aging,thermal cycling,water storage,or no aging).The phase transformation of the zirconia fillers in LU after aging were evaluated by X-ray diffraction(XRD)in the first part of this paper.In the second part of this paper,specimens of each group underwent three-point flexural test with a universal testing machine,and the flexural strength,flexural modulus and Weibull modulus were calculated and analyzed,then the surface Vickers hardness of each group were investigated.The fracture surface morphologies of this two resin composites before and after aging were observed by a scanning electron microscopy(SEM).ResultsNo matter before or after aging,only tetragonal zirconia(t-Zr O₂)was detected in the LU samples.Both before and after hydrothermal aging or thermal cycling aging,the flexural strength,flexural modulus,and Vickers hardness values of LU were significantly higher than those of TNC(p<0.05),while the flexural modulus of LU showed no difference with that of TNC after water storage(p=0.68).Hydrothermal aging,thermal cycling,and water storage had no significant effects on the surface Vickers hardnesses of the two resin composites(p>0.05).Hydrothermal aging significantly improved the flexural strength of LU(p=0.00).Thermal cycling(p=0.00)and water storage(p=0.00)significantly decreased the flexural strength of LU.The flexural strength of TNC was not decreased by hydrothermal aging(p=0.82)or water storage(p=0.36),while it was decreased by thermal cycling(p=0.00).The hydrothermal aging group of LU exhibited the highest Weibull modulus.Conclusions1.LTD treatment does not trigger the t?m phase transformation of zirconia particles in LU.2.LU presents good aging resistance to hydrothermal aging but not to thermal cycling and water storage.3.LU provides better flexural strength,flexural modulus,and Vickers hardness than TNC,while it does not provide better aging resistance.