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Abstract The purpose of this study is to evaluate effect of frequent bleaching regimens (at home bleaching and in office bleaching) on the color stability of bovine teeth enamel. Thirty sound bovine incisor teeth were used in this study representing three main groups. They were inspected under atomic force microscope (AFM) to exclude those with stains, cracks, fractures, dental fluorosis, or enamel defects as attrition, abrasion or erosion. The teeth were cleaned from all debris and calculus using tap water and manual scalars, disinfected and stored from one week to one month maximum in 0.1% thymol solution until using. The roots were sectioned using a water-cooled diamond saw and the pulp tissue was removed using endodontic broach from pulp chamber. Crowns of all the specimens, with the labial surface faced upward, were individually embeded in chemically cured acrylic resin, then were polished with polishing brush and washed. The specimens were stored throughout the experiment in artificial saliva that were renewed daily. Specimens of the first group (control group) weren’t subjected to any bleaching procedure. group II (At home bleaching regimen) was bleached with 15% (CP) gel; Opalescence PF for 14 days and 4h/day according to manufacture instructions. group III (In-office bleaching regimen) chemical-activated bleaching gel (Opalescence® Boost PF 40%) was applied as done in group II. Two applications (of 20-minutes each). Another application was performed after 3 days and the teeth were immersed in artificial saliva (renewed every day) between the two sessions. After the bleaching procedure, and washing with water, the specimens were dried and re-immersed in artificial daily renewed saliva. All the groups were subdivided into two subgroups A and B according to the storage solution. Subgroup A was not subjected to any staining cycles but just stored in artificial saliva. Subgroups B was subjected to a staining cycle containing three staining solutions (Coffee, Tea, and Hibiscus). Specimens were immersed for two hours period in each staining solution per day for 30 consecutive days. The solutions were cooled to room temperature before being used, freshly prepared and changed daily. The specimens were stored in artificial saliva for two months which was daily renewed. This enables enamel remineralization. All the bleaching procedures and the staining cycles were repeated twice with two-month interval. All the procedures were carried out at room temperature (23±1° C). The shade was repeatedly determined for all specimens at base line before any treatment, 2hrs. after bleaching (first and second bleaching procedure) and after immersion in storage solution (30 days) (first and second staining cycles) using a spectrophotometer (Vita Easy Shade V). Data were collected, tabulated, and statistically analyzed by software SPSS version 23; description statistics were shown as Means ± SD. One-way ANOVA test, Standard student t- test at a level of significance (P ≤ 0.05) were used to compare the recorded total color change values of both tested materials either after bleaching or staining. |