الفهرس 
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Abstract
In the current study photo-activated and chemically-activated in-office bleaching systems were used according to the manufacturer’s instructions with concentrations 32% and 40% (32% mixed) hydrogen peroxide respectively. An experimentally prepared 10% concentration of nano-hydroxyapatite (NHAP) and amorphous calcium phosphate (ACP) remineralizing agents were applied to the bleached enamel surfaces following bleaching procedures. Enamel specimens were stored in cola, artificial saliva and distilled water for 24 hours following bleaching and remineralizing agent treatments.
A total of 65 bovine teeth were used throughout the whole study. Specimens were divided into two main groups; control group (5 specimens) where the specimens were not subjected to any treatment (Baseline) and an experimental group (60 specimens). The experimental group was then divided into two subgroups consisting of 30 specimens each; representing the two different bleaching agents used in the study [White Smile photo-activated bleaching agent and White Smile chemically-activated bleaching agent]. Each subgroup was further divided into two divisions (15 specimens each) representing two different remineralizing agents applied in the study [Amorphous Calcium Phosphate and an experimentally prepared Nano-Hydroxyapatite remineralizing agents]. Then each division was further divided into three subdivisions (5 specimens each) according to the three different storage media [Cola, artificial saliva and distilled water] used in the study. Image analysis software was used to assess changes in the surface roughness in control and experimental groups. An environmental energy dispersive x-ray analysis (EDX) was used in conjunction with scanning electron microscope (SEM) to evaluate changes in Calcium and Phosphorus ions as well as morphological changes on the enamel surface. Assessments were performed following bleaching procedures, remineralizing agent’s applications and storage in the three different storage media (cola, artificial saliva and distilled water).
Results showed that both photo-activated and chemically-activated in-office bleaching systems slightly affected the chemistry and surface morphology but both had no significant effect on surface roughness of the enamel. Also it was shown that NHAP and ACP remineralizing agents had slight effect on the Calcium and Phosphorus levels of the bleached enamel surface. There was no significant difference between both remineralizing agent groups regarding surface roughness. However; NHAP showed slightly more roughness values compared to ACP application. Storage in cola, distilled water did not alter the chemistry and surface topography of the bleached enamel surface. On the other hand, artificial saliva showed slightly statistically significant effect on the chemistry and surface topography of the bleached enamel surface with photo-activated bleaching agent.
Under the conditions of the present study, the following was concluded:
1) Fourier transform infrared spectroscopy analysis (FTIR), X-ray diffraction analysis (XRD) and transmission electron microscope (TEM) seemed to be satisfactory for synthesis and characterization of an experimental hydroxyapatite-based remineralizing agent.
2) Experimental nano-hydroxyapatite did not show a significant effect on the chemistry and surface topography of bleached enamel.
3) Changes in the chemical formulations of the storage media; cola, artificial saliva and distilled water had no statistical effect on the chemistry and surface topography of bleached enamel.
4) Artificial saliva has the potential to significantly affect the chemistry and surface topography of bleached enamel.
5) Acquisition of Calcium and Phosphorus ions of bleached enamel substrate were increased following the application of nano-hydroxyapatite remineralizing agent compared with the other formula; ACP.
6) Surface roughness of values of the investigated levels were non-significant.
Recommendations:
1) Testing the effect of different NHAP concentrations on the chemistry and surface topography of sound and bleached enamel.
2) Further studies are required to assess the effect of increasing the storage time in different storage media on the chemistry and surface topography of sound and bleached enamel.
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