| Objective: By determining the color values of polymer-ceramic restorations of different resin layer thickness and the color parameter under repeated light curing,analyzing its influence of the thickness and light frequency on the color, and exploring the mixed color of polymer-ceramic materials and the rule of change color, we tend to provide the experimental basis for the manufacture and clinical application of polymer-ceramic restorationsMethods:1 Specimens preparation1.1 The making of the body resin of different thickness:Making use of the mold making and the A2 shade body resin of Ceramage polymer-ceramic, we make the specimens of the diameter of 10mm and the thickness of body resin of respectively 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm .The testing sufaces of all the specimens are burnished in turn by water sand paper of 400#, 600#, 800#,1000#, 1200# and 1,500# .The other sides are to be burnished in turn to 800 #.By using the mould , Ceramage color agent is spread on them. The thickness of opaque layer of 0.2 mm can be obtained in the same way.According to different body resin layer thickness ,all the specimens of opaque-body layered resin are to be divided into the groups of 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm . Each group has 5 specimens, and the total number is 30.In addition, by the use of the mold ,we make 5 specimens of body resin without opaque layer. And they are bunished to 1500 # by water sand paper as control groups.All thickness errors of specimens are controlled in±0.01 mm.1.2 The manufacture of the incisal resin of different thickness: Based on the thickness of 0.2 mm of opaque layer and the thickness of 1.2 mm of the body resin layer, the incisal resin of the thicknesss of paste-on-paste of respectively 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, are made into the specimens of opaque- body- incisal layer. According to the thickness of the incisal layer,all the specimens are to be divided into 5 groups. Each group has 5 specimens, and the total number is 25.The thickness error are controlled in±0.01 mm.2 The measurement of surface roughness:The measuring apparatus of surface roughness measures the roughness(Ra) of the testing surfaces.3 The color measurement: By the use of the spectrophotometer of Vita Easyshade, we measure the specimens of the body resin layer and incisal resin layer of different thickness, and the specimens of body resin without opaque layer of 10mm thickness.We also calculate the color difference value between the body resin layer and the control group of 10mm thickness, and between the arbitrary two groups of body resin thickness groups,and between the arbitrary two groups of the thickness groups of incisal resin .4 Repeat the determination of color value after light curings:The Specimens determined of 1.4mm thickness group and the pieces of 0.8mm thickness group of incisal resin( a total of 10 ) are put in the the Solidilite Light-curing unit and they are be shined by the first light and respectively by the light of the second, fourth, sixth, eighth, 3 minutes each time.By the use of the spectrophotometer of Vita Easyshade, we measure the color value of specimens under different light curing cycle ,and calculate the color difference value between the first light curing and each light curing.5 The statistics analysis of data measurement: By the use of SPSS 13.0 of statistical analysis software, we take the statistical analysis of roughness and color value of the surfaces of each specimen, and analyze single factor of variance. The SNK inspection between groups comparison concludes that the inspection standards is that alpha equals 0.05.Results:1 By single factor analysis of variance(One-Way ANOVA), the roughness value results of specimens surface(Table1), P > 0.05, shows that by each specimen there is no statistical significance between the surface roughness difference of the testing sides.2 The chromaticity value and color difference results of the specimens of different thickness groups of the body resin(Table2,3) : With the increase of the thickness of body layer, the L ~* value, a ~* value and b ~* value of the specimens gradually decrease.After single factor analysis of variance (P < 0.05), we believe there is statistical significance of the overall mean differences of L ~* a ~* b ~* value of each thickness group. The SNK inspection between groups comparison concludes that except the differences of L ~* value of the 1.4mm group,the 1.6mm group and the control group,the differences of a~* value of the1.2mm,1.4mm and 1.6mm groups; the differences of b~* value of the 1.4mm and 1.6mm ,1.2mm and the control group have no statistically significance, the differences of L ~* a~* b~*values between the other arbitrary two groups are statistically significant.In the comparison of color, the color difference values of 1.4 mm thickness group and the control group, 1.6 mm thickness group and the control group are respectively 1.45 NBS and 1.49 NBS, and the chromatic aberrations between other thickness groups and control group is greater than 1.5NBS;the color values between thickness groups of the adjacent body resin are less than 1.5NBS, and the color values among the other arbitrary thickness groups of body resin are greater than 1.5NBS .3 The chromaticity value and color difference results of the specimens of different thickness groups of the incisal resin:With the increase of the thickness of incisal resin, the L~* value, a~* value and b~* value of the specimens are gradually reduced. After single factor analysis of variance (P < 0.05), we believe there is statistical significance of the overall mean differences of L~* a~* b~* value of each thickness group. The SNK inspection between groups comparison concludes that except the differences of L~* value of the 0.8mm and 1.0mm groups have no statistically significance, the differences of L~* value between the other arbitrary two groups are statistically significant. The differences of a~* value and b~*value between arbitrary two groups are statistically significant. The color difference values among arbitrary thickness groups of incisal resin are greater than 1.5NBS .4 The chromaticity value and color difference results of the first light curing and respectively the light of second, fouth, sixth, eighth time: After the second time of light curing, the L ~* value of each group of specimens drops, and the a ~* value of the groups of 1.4 mm and 1.6mm of the body layer decreases too. They both have statistical significance;the differences of L ~* a ~* b ~* value of each group in the other situation have no statistically significance.The color differences between being shined for the first time and being shined in the other situation are less than 1.5NBS.Conclusion:1 Within the clinical suitable application, the thickness changes of the body resin have influence on the color of the restoration of polymer-ceramic . Under the opaque layer background of the same thickness, with the increase of the thickness of body resin, the color of the restoration of polymer-ceramic has a low brightness,the chroma decrease,the hue is towards blue and green.2 When opaque layer is 0.2mm ,the thickness of body resin is between 1.4 ~1.6 mm, the own color of the polymer-ceramic materials of A2 shade can be reappeared better.3 Within the clinical suitable application, the thickness changes of the incisal resin have influence on the color of the restoration of polymer-ceramic . Under the mixed background of the opaque layer of same thickness and the body layer resin, with the increase of the thickness of incisal resin, the color of the restoration of polymer-ceramic has a low brightness,the chroma decrease,the hue is towards blue and green.4 Repeated light curing have little influence on the color of the restoration of polymer-ceramic.The color changes after being shined for different times are imperceptible by eyes, which is within the clinical acceptable application.
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