Abstract: Objective　To investigate the effect of in vitro low temperature aging treatment on the crystalline phase, structure and flexural property of a CAD/CAM composite resin block containing zirconia fillers. Methods Sixteen Lava Ultimate (LU) bars with the same size were prepared. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to evaluate the crystalline phase and structure stability of LU before and after low temperature aging (in an autoclave at 134℃ and 0.2 MPa for 20 hours). Meanwhile, the flexural property of specimens was tested by the universal testing machine, and then the statistical analysis of flexural strength and flexural modulus was performed using the SPSS 22.0 statistical software package to evaluate the flexural stability of LU after low temperature aging. Results　The flexural strengths of LU were (185.33±19.22）, (220.89±20.88） MPa and the flexural moduli were (14.16±0.92), (20.93±0.97） GPa before and after low temperature aging. They were significantly higher than those before aging (P＜0.05). XRD patterns showed that zirconia crystal phase of LU did not change after low temperature aging, and the results of SEM showed that the microstructure of LU after aging was more compact. Conclusion Lava Ultimate performs good crystalline phase, structure and flexural stability under low temperature aging treatment.

Key words: CAD/CAM composite resin block, low temperature aging, crystalline phase, flexural resistance, micro-structure