الفهرس 
Effect of Remineralization Using Hydroxyapatite Prior to In-office or Combined In-office/At-home Bleaching on Surface Microhardness and Color change of Bleached Enamel: In vitro study
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Abstract
: This research was conducted to evaluate the effect of performing remineralization before bleaching on enamel surface microhardness and its impact on bleaching efficacy using nano-hydroxyapatite as a remineralizing agent with fluoride-containing and fluoride-free bleaching agents to test the added benefit of using both remineralization methods versus using one of them only.
A total of thirty-two bovine incisors were selected and divided into two main groups of sixteen teeth each according to bleaching protocol (B); where (B1) is the in-office bleaching protocol and (B2) is the combined protocol (in-office/at-home bleaching). Each group was further subdivided into two subgroups of eight specimens each according to presence of remineralizing agent in the bleaching material (M); (M1) fluoride-containing bleaching material and (M2) fluoride-free bleaching material. Each tooth was sectioned buccolingually into two halves according to the application of hydroxyapatite remineralizing agent before bleaching (R); one half was used for (R0): no remineralization (Control) and the other half was the intervention (R1): remineralization using hydroxyapatite. Thus, 64 specimens were tested.
All specimens were inspected carefully for defects, thoroughly cleaned and polished to prepare samples for bleaching. Each tooth half was embedded in an acrylic mold where the labial surface was facing upward and fully exposed for the purpose of testing. Remineralization was first performed according to the manufacturer’s instruction on the exposure groups and then samples were stored in artificial saliva for 24 hours to allow for remineralization process to initiate, at the same time, the control groups were stored in artificial saliva. In-office bleaching was then performed to all specimens
according to manufacturer’s instructions using either fluoride-free or fluoride-containing bleaching agents then samples were stored in artificial saliva for the next day. At-home bleaching was then performed in the combined bleaching groups according to the manufacturer’s instructions using either fluoride-free or fluoride-containing bleaching agents for seven days. Specimens were stored in artificial saliva between applications till the end of the bleaching process.
Microhardness testing was done using Vicker’s Microhardness tester at baseline, after remineralization and immediately after bleaching in the incisal third of the labial surface. Afterwards, the mean surface microhardness recovery percentage was
calculated (SMHR %).
Color was measured before intervention, after remineralization and forty-eight hours after bleaching using a spectrophotometer (Vita EasyShade). Color change was then calculated according to (Commission Internationale de l’ Eclaraige system) CIE L* a* b* system.
Results were statistically analyzed and tabulated revealing that different bleaching protocols showed a statistically insignificant difference on surface microhardness percentage change in all groups except in bleaching groups not using either of the remineralization methods. It was also found that prior remineralization showed a statistically significant difference on surface microhardness percentage change in all groups except the in-office bleaching groups using fluoride-containing bleaching materials. Besides, the incorporation of remineralizing agent into the bleaching materials showed a statistically significant difference on surface microhardness percentage change in all groups except the in-office bleaching groups with prior remineralization.