| Objective:The purpose of this study is to evaluate the effects of sintering temperature,sintering times and heating rate on the mechanical properties and microstructure of chairside CAD/CAM machinable IPS e.max CAD lithium disilicate glass-ceramics.Maternal and methods:According to the requirements,15 specimens(diameter 12.0mm,thickness 2.0mm)were made from the commercial IPS e.max CAD lithium disilicate glass-ceramic blocks.The specimens were randomly divided into three groups,5specimens in each group;75 strips(15.0mm in length,4.0mm in width and 1.2mm in thickness)were randomly divided into three groups,25 specimens in each group.Cylindrical specimens were used for the Vickers hardness testing,and strip specimens were used for the flexural strength testing.The two kinds of specimens were put into the sintering temperature group,sintering times group and heating rate group respectively.The specimens in the sintering temperature group were sintered at 700 ℃、750 ℃、800 ℃、850 ℃ and 900 ℃ respectively;the specimens in the sintering times group were sintered for 1、2、3、4 and 5 times respectively;the specimens in the heating rate group were treated with heating rate of 30 ℃/min、60 ℃/min、90℃/min、120℃/min and 140℃/min;and sintering according to the set sintering parameters.According to the standard of GB/T16534-2009,the Vickers hardness of three groups of cylindrical specimens was tested by micro-Vickers hardness tester.According to the ISO 6872 standard,the flexural strength of each strip specimen was tested by the three-point bending method on a universal testing machine.The microstructure of the specimens was observed by field emission scanning electron microscopy(SEM).The data obtained from this experiment was based on SPSS Statistical 20.0 statistical software,and suspicious data were discarded,the data of each group were analyzed by one-way ANOVA,and LSDmethod was used to make a post-test comparative analysis,test level α=0.05,P<0.05 was found to be statistically significant.Results:There was a significantly difference in the Vickers hardness values and flexural strength values of the specimens sintered at different sintering temperatures(P<0.05).There was no significant difference in the Vickers hardness values and flexural strength values of the specimens sintered at at different sintering times(P>0.05).There was a significant difference on the Vickers hardness values of the specimens sintered at different heating rate(P<0.05),but no significant difference in flexural strength values(P>0.05).Scanning electron microscopy(SEM)showed that the microstructure of the specimens treated with different sintering temperature,sintering times and heating rate was different.Conclusion:Sintering temperature had an effect on the Vickers hardness and flexural strength values of chairside CAD/CAM machinable IPS e.max CAD lithium disilicate glass-ceramics.Sintering times had little effect on the Vickers hardness and flexural strength values of IPS e.max CAD.Heating rate had an effect on the Vickers hardness values of IPS e.max CAD,but had little effect on the flexural strength values.The microstructure of IPS e.max CAD could be changed by different sintering temperature,sintering times and heating rate. |
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