| The esthetic demands of patients increased considerably during recent years lead to substantial increase in the use of all-porcelain restoration which boom due to improved ceramic materials and porcelain bonding systems. All-porcelain crown possesses color-rendering properties and optical properties that simulate natural teeth. Furthermore based on the excellent biocompatibility, strength and surface texture of the material, it remains the material of choice for most clinicians.However, most research focused primarily on mechanical and materials science considerations, such as marginal integrity, fracture, bond strength and repair techniques, instead of esthetics.This relative dearth of research about esthetics may merely indicate that the esthetics of ceramics are taken for granted or may reflect the complexities inherent to quantifying color analyses and esthetics. A variety of all-ceramic crown systems are now commercially available.Therefore, varieties of substrate can have different influence on the color of all-ceramic restoration for its internal structure and manufactural process. The objective of this investigation was to determine the influence of material foctor, cement and post and core on the color of two kinds of all-ceramic restoration at the height of 1.5mm which innerstructure are quite different. The porcelains that we used in this study were In-Ceram and Cergogold. In-Ceram uses a high strength core material and Cergogold was heat-pressed porcelain that without any special core material being used.In the former system,low-translucency alumina is often used as the core material.This system has excellent strength but lower translucency.In contrast,leucite crystal used in the heat-pressed porcelain make the restoration has good translucency. Porcelain samples were prepared in thickness of 1.5±0.2mm which is similar to the thickness of the restoration at one third of middle labial of central incisor.On the other hand, it's believed that porcelain crown has good color stability, but current research reported that the accelerated aging may change the color of different kinds of porcelain. In this study, we use accelerated aging method to evaluate the color stability of these two all-porcelain material and it can simulate the oral environment to evaluate the UV-light, visible light, temperature and artificial saliva on the color stability of two porcelain and cement. In this study, spectrophotometer was used to test the optical parameter of specimen.The color classification system we used in this research was developed by the Commission Internaionale de I'Eclairage in 1978.Otherwise known as the CIE color system,it introduces three attributes to the perception of color named as L,a and b.L refers to the lightness variable and it is proportional to value in the Munsell Color System.a and b are chromaticity coordinates,wherein a corresponds to the red-green axis,while b refers to yellow-blue axis.Although they do not directly correlate to Hue and Chroma,the respective numerals serve to determine numeric correlates for these attributes. A spectrophotometer can measure color differences much smaller than that can be detected by human eyes, therefore, the clinical relevance of color changes recorded by the spectrophotometer must be evaluated.In this study,we suppose color changes withΔE value lower than 1.5 could not be detectable by human eyes.The results of the first part are listed below:1. The color of the core(0.5mm) of In-Ceram can be influenced by background and along with the increasing of the height of opaque dentin, the translucency of the core decrease, and L* value decease too. When the opaque detin was 0.2mm, the In-Ceram crown can well mask the ground when the height of the crown above 1.6mm, When the opaque detin was 0.4mm, the In-Ceram crown can well mask the ground when the height of the crown above 1.4mm.2. At the height of 1.5mm, the translucency of In-Ceram is not as good as that of Cergogold when both of these two porcelain have the same shade. As the shade increase from A1 to A4, both of the translucency and L* value of these two porcelain decrease. 3. When the shade is A3, and in the height of 1.5mm, both of the color of these two porcelain can be affected by ground (ΔE>1.5). Furthermore the ground has great influence on the Cergogold than on the In-Ceram. Different cements can have different influence on the porcelain and opaque cement increase the L* value of these two material, and decrease the C* value. The Panavia(brown) resin cement increase the L* value and decrease the C* value of both material. When use Choice A3 resin cement, the L* value of Cergogold increase and C* value has no noticeable change, but it has no influence on the In-Ceram. Glass ionomer and Panavia(white) can increase L* value of both these two porcelain but have no influence on the C* value4. According to Cergogold, gold alloy can make the L* value of tested group higher than that of controlled group. Titanium alloy can make the L* value of tested group lower than that of controlled group. The C* value of group of A4 is higher than other groups and in succession is group of gold alloy and titanium alloy. According to In-Ceram, gold alloy can make the L* value of tested group higher than that of controlled group and the lowest L* value was titanium alloy group which lower than controlled group.The group of A4 resin and resin core has no statistical difference with controlled group. The C* value of titanium alloy group is lower than controlled group.The results of the second and third parts are listed below:1. After immerged in artificial saliva, both of the two porcelain (A1, A3, B1) showed increasing color difference as time went on. But no group showed visible color change by human eye after immerged in artificial saliva for 2 month, 4 month and 6 month. Cergogold B1 group showed highest color difference after immerged in artificial saliva (△E=1.04). L* value and transmission ratio has the same change trend that is decrease as time went on, and the C* value has opposite change trend.2. After cemented with different luting agents, both of these two porcelain with three shade showed no color difference after immerged in artificial saliva for 2 month, 4 month and 6 month.The smallest color change appeared in In-Ceram A3 cemented with glass ionomer (△E=0.23). The biggest color change appeared in Cergogold B1 cemented with opaque resin cement (△E=0.84). The L* value of In-Ceram B1,Cergogold B1 cemented with opaque resin cement and Cergogold B1 cemented with translucent resin cement which immerged in artificial saliva for 4 month showed statistical difference(p<0.05),which showed decrease trend. The L* value of In-Ceram B1,Cergogold B1 cemented with opaque resin cement and Cergogold A1,Cergogold B1 cemented with translucent resin cement showed statistical difference after immerged in artificial saliva for 6 month(p<0.05). The C* value increased as time went on, the C* value of Cergogold B1 cemented with glass ionomer and opaque resin cement showed statisitical difference after immerged in artificial saliva for 6 month. The transmission ratio decreased as time went on.3. There were no visible color change after accelerated aging for both In-Ceram and Cergogold of three shades. But L* value and transmission ratio decreased and C* value increased.4. Only Cergogold B1 cemented with glass ionomer showed statistical color change after accelerated aging(△E=1.58).The L* values of both of these two porcelains (shade A1, A3, B1) decreased after accelerated aging, it showed stastical difference in group of In-Ceram B1 and Cergogold B1 cemented with translucent resin cement, and Cergogold A1, Cergogold B1 cemented with glass ionomer(p<0.05). The C* value of In-Ceram B1,Cergogold A1,Cergogold A3,Cergogold B1 cemented with glass ionomer, In-Ceram B1,Cergogold A1,Cergogold B1 cemented with opaque resin cement and Cergogold A1, Cergogold B1 cemented with translucent resin cement showed statistical difference(p<0.05).
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