Role of enamel and dentin on color changes after internal bleaching associated or not with external bleaching

Abstract Objective To evaluate the effect of the association between external and internal tooth bleaching on color changes in dentin and enamel, individually or recombined, previously stained with triple antibiotic paste (TAP). Methodology Forty enamel-dentin specimens from bovine incisors were separated into ten blocks according to similarity in their whiteness index (WID). Three specimens within each block were stained by dentin exposure to TAP, and the remaining specimen was used as control to estimate color changes. Specimens were sectioned to separate tissues, and dentin and enamel colors were measured individually and after being recombined. Alterations in color (CIEDE2000 - ΔE00) and translucency parameter (TP) resulting from staining were estimated by color difference between stained and control specimens. The contribution of each tissue to the color change (CTCC) was also calculated. Non-sectioned stained specimens were bleached by applying sodium perborate on dentin, associated or not with 35% hydrogen peroxide on enamel. Color changes caused by bleaching procedures were estimated and data were analyzed using the paired t-test or Two-way repeated measures ANOVA. Results TAP caused more pronounced changes in dentin, but enamel color was also affected. Both protocols presented a similar ΔE00, and dentin showed the greater color change. After exposure to TAP, we observed a reduction in WID; WID values were the same for bleached and control specimens regardless of protocol. We found no significant effect of substrate and bleaching technique on TP. Enamel played a more critical role in color changes caused by either staining or bleaching procedures. Conclusion Enamel color played a greater role on tooth color changes than dentin. External and internal bleaching association did not improve bleaching effect on specimens stained with TAP.

摘要
目的：评估外源性与内源性牙齿漂白联合或单独使用时，对经三联抗生素糊剂（triple antibiotic paste, TAP）染色后的牙本质与牙釉质颜色变化的影响。
方法：选取40颗牛切牙制备的牙釉质-牙本质复合标本，依据白度指数（whiteness index, WID）的相似性分为10个组块。每个组块内的3份标本通过使牙本质接触三联抗生素糊剂进行染色，剩余1份标本作为对照，用于评估颜色变化。将标本切片以分离两种组织，分别测量牙本质、牙釉质的颜色，并在重组为复合标本后再次测量颜色。通过染色标本与对照标本间的色差，评估染色所致的颜色变化（采用CIEDE2000色差公式，记为ΔE00）与半透明度参数（translucency parameter, TP），同时计算各组织对颜色变化的贡献度（CTCC）。对未切片的染色标本，采用在牙本质处施加过硼酸钠、或联合在牙釉质处施加35%过氧化氢的方案进行漂白。评估漂白操作所致的颜色变化，采用配对t检验或双向重复测量方差分析对数据进行统计学分析。
结果：三联抗生素糊剂对牙本质的颜色改变更为显著，但牙釉质的颜色亦受影响。两种漂白方案的ΔE00值相近，且牙本质的颜色变化幅度更大。经三联抗生素糊剂染色后，标本的WID值降低；无论采用何种漂白方案，漂白后标本与对照标本的WID值均无显著差异。未发现基底组织类型与漂白技术对半透明度参数存在显著影响。无论是染色操作还是漂白操作，牙釉质在颜色变化中均发挥更为关键的作用。
结论：相较于牙本质，牙釉质颜色对牙齿整体颜色变化的影响更大。外源性与内源性漂白联合使用，并未增强对经三联抗生素糊剂染色标本的漂白效果。