An In Vitro Study Of Masking Effect Of IPS E.max CAD Veneer

Objective:To study the effect of the substrate color and thickness and transparency of material on the color of the IPS e.max CAD lithium disilicate glass ceramic veneers.Materials and methods:The original shades of the VITAPAN classic shade guides served as the substrate color.The IPS e.max CAD A₂ shade lithium disilicate glass ceramics were fabricated into veneers through the computer aided design and computer aided manufacturing（CAD/CAM）technology with CEREC^?system.According to the transparency（low transparent（LT）and high transparent（HT））and the thickness（0.5mm and 1.0 mm）of the central 1/3 of the veneers were divided into:L 0.5,H 0.5,L 1.0and H 1.0,each group sample size（n=3）.ShadeEye NCC colorimeter（Shofu,Japan）was used to measure the L^*a^*b^*under uniform conditions.1.Set the substrate color of A₂ as control group（n=3）,and other substrate color as 15 experimental groups（n=3）.Calculated its color difference asΔE_S^*.Putted the substrate color in ascending order byΔE_S^*.2.Set the veneers coverd substrate color of A₂ as control group（n=3）,and the same veneers coverd other substrate color as experimental groups（n=3）.Calculated its color difference asΔE^*_V/S.Explored the linear relationship betweenΔE^*_V/S andΔE_S^*for four kinds of veneers.Compared the masking limit of the veneer.The masking limit was theΔE^*_S.l whenΔE^*_V/S was 2.0（acceptability thresholds（AT））.3.Set the substrate color as control group（n=1）,and four kinds of veneers with different thickness and transparency coverd the same substrate color as experimental groups（n=3）.Calculated its color difference asΔE_V^*.Compared the interaction effects of thickness and transparency onΔE_V^*of 16 substrate color.SPSS 19.0 statistical software was used for analysis and the test level wasα=0.05.Results:1.The overall difference ofΔE_S^*was statistically significant（P>0.05）.There was no significant difference in the comparison between substrate color of B₃ and A₃,D₃ and C₁,D₄ and A_3.5,D₂ and C₃（P>0.05）.The difference between the other groups was statistically significant（P>0.05）.2.The linear regression equations of four kinds of veneers were statistically significant.There was a linear relationship between the independent variable（ΔE_S^*）and the dependent variable(ΔE^*_V/S)（P>0.05）.With the exception of the lower R² value（0.634）in the H 1.0 group,the R² values in the other three groups were>0.7.The overall difference ofΔE^*_S.l was statistically significant（P>0.05）.The minimum was H 0.5 group（6.3±0.4）,followed by L 0.5 group（8.3±0.3）,then H 1.0 group（12.0±1.5）,and the largest was L 1.0 group（12.7±1.0）.There was no significant difference in the comparison betweenΔE^*_S.l of L1.0 group and H 1.0 group（P>0.05）.The difference between the other groups was statistically significant（P>0.05）.3.On the substrate color measured in this experiment.Thickness had a significant effect onΔE_V^*（P>0.05）.Transparency had a significant effect onΔE_V^*in general（P>0.05）,except the substrate color of B₁,C₂,C₃ and C₄.The overall interaction effect between thickness and transparency was significant（P>0.05）,except the substrate color of B₂,B₃ and C₂.Conclusion:1.The color difference between the VITAPAN classical shade guides and the substrate color of A₂ is arranged in an orderly manner and can be used to describe changes of the substrate color.2.The substrate color affects the color of the IPS e.max CAD veneer,and the relationship between the two is linear.As the color difference of the substrate color increases,the color difference of the veneer also increases,and the masking effect deteriorates.The masking limit of four kinds of veneers with different thickness and transparency are different in general.As the thickness of the veneers increase,the masking limit becomes larger.When the thickness of the veneer is 0.5 mm,the masking limit of the LT veneer is larger than the HT veneer.When the thickness of the veneer is 1.0 mm,the masking limit has no difference between the LT veneer and the HT veneer.3.Different thicknesses（0.5 mm and 1.0 mm）and transparency（LT and HT）have interactive effects on the masking effect of IPS e.max CAD veneers in general.Clinically,the thickness and transparency of the veneer should be selected based on the substrate color.