The Investigation Of The Color Differences Among Three Discoloration Models In Vitro Before And After Bleaching

Objective To establish the intrinsic, extrinsic or mixed discoloration models in vitro and to measure the chroma parameters of them before and after bleaching operations with the spectrophotometric tooth colorimeter (Olympus Crystaleye); To obtain the chroma alteration data after bleaching and to compare the data of the three models and three areas of teeth, neck, central, and incisal margin parts; To provide the evidence for making the individual bleaching plans.Materials and MethodsEighty premolar teeth extracted according to orthodontics needs were collected and randomly allocated into4groups, including intrinsic discoloration group (IDG), extrinsic discoloration group (EDG), mixed discoloration group (MDG) and control group. There were20teeth for each of the experimental groups and8teeth for the control group. Twelve teeth were used to measure the optimistic concentration of black tea for staining. After the samples of three models and control group were prepared, they were bleached with BEYOND whitening method. The spectrophotometric tooth colorimeter was used to measure the chroma parameters (⊿E,⊿L*,⊿a*,⊿b*) of the neck, central, and incisal margin areas of the samples before bleaching and different time points (0d,1d,3d,5d,7d,14d) after bleaching. The comparisons of the chroma alteration data among three different groups and three different areas of teeth were made. The extent and speed of color recurrence were observed and the comparisons among three groups were made.Results1. The optimistic concentration of black tea for staining the in vitro models were4g/100ml.2. The moment after bleaching, fantastic whitening effect was obtained in all the three in vitro models. The value of L*of all the samples became higher. However, the values of a*and b*of most of the samples became lower.3. During the first5days after bleaching, rapid color recurrence happened in all the three groups and most rapid speed was in IDG. The extent of color recurrence differed among three groups (p<0.05). The extent of that in IDG was much more than that in EDG (p<0.05).4. In IDG, the values of⊿E and⊿L*of the incisal margin area were more than that of the central area (p<0.05), which was more than that of neck area (p<0.05) after bleaching. In MDG, the values of⊿E of the incisal margin area were more than that of the neck area (p<0.05). However, in EDG, the differences among the three areas were not significant.5. The value of⊿E of the neck, central, and incisal margin areas differed significantly among IDG, EDG and MDG (p<0.01). The values of⊿E of the neck and central areas in EDG were more than those in MDG, which were more than those in IDG. The values of⊿E of the incisal margin area in EDG were more than those in MDG and IDG.The value of⊿L*of the neck, central, and incisal margin areas differed significantly among IDG, EDG and MDG (p<0.05). The values of⊿L*of the neck, central and incisal margin areas in EDG were more than those in MDG and IDG.The value of⊿a*of the neck, central, and incisal margin areas differed significantly among IDG, EDG and MDG (p<0.05). The values of⊿a*of the neck, central and incisal margin areas in EDG were more than those in MDG and IDG. The value of⊿a*of the neck area in MDG were more than that in IDG (p<0.05).The value of⊿b*of the neck, central, and incisal margin areas differed significantly among IDG, EDG and MDG (p<0.05). The values of⊿a*of the neck, central and incisal margin areas in EDG were more than those in MDG and IDG. The value of⊿b*of the neck area in MDG were more than that in IDG (p<0.05).Conclusion1. Black tea could be used to establish the intrinsic, extrinsic or mixed discoloration models in vitro;2. Beyond Whitening Technique could be used to bleach all the three modles and fantastic whitening effect was obtained; 3. The speed and degree of color recurrence differed in three models. The values of them in intrinsic model were higher than those in other two models. The bleaching effect of EDG was more significant than the other two. The regional differences among incisal, central and neck areas were not significant in EDG, but were significant in IDG and MDG. The chroma alteration was most significant in incisal region and least significant in neck region in these two models;4. The values of chroma alteration differed among three models in vitro and three regions of one teeth. It suggested that individual bleaching plan should be made according to the different situation of individual teeth before the treating.