The Effect Of Different Backgrounds And Resin Cements On The Color Of Machined Composite Materials

Objective:To analyze the effect of shades and thickness of resin cements on the color of machined composite materials under the different resin backgrounds,this study compared the translucency parameters（TP）and the color parameters of different thickness of machined composite materials and resin cements,in order to be guiding for the clinical selection of composite materials and cements.Materials and methods:The machined composite material Vita ENAMIC（2M2-HT）was selected and cut into disk-shaped specimens with thickness of 2.1mm,1.6mm and 1.1mm respectively by using low-speed diamond cutter and full-sintered diamond saw blades（n=10）.Polishing with silicon carbide paper and water,the thickness of the specimens was controlled at2.0±0.02mm,1.5±0.02mm and 1.0±0.02mm respectively.The Crystaleye Spectrophotometer was used to measure the color parameters of specimens in the dark box individually which were placed on the black and white ceramic tiles and different resin backgrounds（A2,A4,B3,C4 shades）.Variolink^?Esthetic DC was applied onto the surface of specimens.Polishing with silicon carbide paper and water,the thickness of resin cement was 0.2mm.After the color measurement was completed,continue to polish,the thickness of cement was reduced to 0.1mm.After measuring the color parameters again,polish and remove all the resin cement,change another shade of cement on the surface,and repeat the above steps to measure the specimens.The middle color parameters of each group were measured to calculate the TP value and the color differencesΔE₁(ΔE_A2,ΔE_A4,ΔE_B3,ΔE_C4)before and after cementation,and the color differencesΔE₂(ΔE_A4-A2,ΔE_B3-A2,ΔE_C4-A2)between the resin backgrounds of A4,B3,C4shades and A2 shade after cementation.Results:Tree-way ANOVA showed that the thickness of specimens,the shades and thickness of cements were statistically significant on the TP value of translucency parameters（p<0.001）.The thickness of specimens and the shades of cements and backgrounds significantly influenced on the color parameter L^*a^*b^*value,the color differenceΔE₁before and after cementation,and the color differenceΔE₂between the resin backgrounds of the specimens with cement（p<0.001）.TP value ranged from 20.37 to 38.34.The thickness of specimens decreased,and the TP values of the specimens increased.The TP values of the specimens decreased significantly with the 0.2mm cement of light+（p<0.001）.When three shades of cements were used for specimens of the same thickness,L^*values increased,and a^*and b^*values decreased in the cement of light+group.In the cement of warm+group,L^*values decreased,a^*and b^*values increased.The L^*,a^*,and b^*values changed little in the cement of neutral group.The comparison between groups Tukey’s HSD indicated that the L^*,a^*and b^*values of each group with different thickness of cements were statistically significant（P<0.05）.The range of color difference before and after cementation was 0.41-5.35 on the different shades of resin backgrounds.The color difference of specimens with three shades of cementsΔE_A2 less than 3.0 on the A2 shade background.At the same time,the color difference of specimens with cements of warm+and neutral on the A4,B3 and C4backgroundsΔE₁ less than 3.0.It could be observed that the color difference was clinically significant（ΔE₁>3.0）in some specimens with 1.0mm cement of light+group.The color differenceΔE₂ of machined composite material with three kinds of thickness between different shades of resin backgrounds and A2 shade background of control group ranged from 2.16 to 11.71.The color differenceΔE_B3-A2 value of 2.0mm specimen and 1.5mm specimen with 0.2mm cements of light+and warm+were less than3.0,which were the clinically acceptable color differences between B3 shade background and control group.While the color of specimens with cements was affected by the resin backgrounds（△E₂>3.0）.Conclusions:The optical properties of restoration were closely related to the thickness of the machined composite material,and also affected by the shades of the cements.The cement of Light+could significantly change the masking ability of the machined composite restoration,while the transparent shade cement of neutral had the least effect on the restoration.The thickness of composite material,the shades and thickness of cements,and the shades of resin backgrounds had a significant effect on the final color of restoration.When the thickness of composite material was 2.0mm,yellow background（B3 shade）had the least influence on the restoration color;but brown yellow（A4 shade）and dark gray（C4shade）had significant clinical color difference on the restoration.