الفهرس 
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Abstract
Over the years, the world has known the significance of dental bleaching and become the most important and conservative treatment option. Ever since, the dental research showed a distinctive interest in reducing the adverse effects resulting from bleaching procedure like decrease in enamel microhardness and increase permeability and surface roughness which in turn influence re-staining susceptibility of bleached enamel. Based on that, usage of post bleaching remineralizing agent is now considered a mandatory step. Accordingly, deciding which remineralizing agent is used, mode of application and its effect on different enamel properties should be properly considered.
One type of mineralizing agents are the bioactive glasses. These materials are oxides of calcium, sodium, phosphorus and silica in ratios that impart bioactivity. These glasses are able to bond chemically to hard dental tissues and form a layer of hydroxyapatite on their surface.
The current study aimed to evaluate the effect of BAG application within the bleaching agent or after bleaching in the form of gel on the enamel microhardness and restaining of bleached enamel.
Enamel hardness was evaluated using Vicker micro-hardness tester while color stability after bleaching and applying restaining solution was measured using spectrophotometer (Vita Easy shade) device.
The specimens were divided into five groups according to mode of BAG application (Control, bleaching agent modified with BAG and post bleaching BAG gel application) and how long the BAG gel remained on the bleached enamel (BAG gel application for 6, 8 and 12 hours).
Regarding to the hardness results it was found that after bleaching the micro-hardness of all groups reduced when compared with the baseline including the group of bleaching agent modified by BAG powder but when BAG gel was applied as a separate step after bleaching, the enamel micro-hardness increased in 6, 8 and 12 hours of BAG gel groups with no significant difference found between them.
On the other hand, after bleaching the color coordinates (L*a*b*) showed increase in L* value (lightness) and decrease in b* mean value (more bluish) for Groups A, B and C while Groups D & E showed increase in b* mean value. However, the color stability of bleached enamel after applying restaining solution revealed that the lowest color changes were recorded for the control group followed by BAG within bleaching and post bleaching BAG gel applied for 6 hours’ groups with no statistical significant difference between them. While the highest color changes were found in Groups D &E where BAG gel applied for 8 and 12 hours with no significant difference between them.
Under limitation of this study, we can conclude that the application of bioactive glass as remineralizing agent after bleaching can increase deposition of inorganic ions which increase the microhardness of the enamel while application of BAG had adverse effect on the color stability of the bleached enamel.
from the current work, the following conclusions could be reached:
1. The bleaching procedure negatively affects the enamel microhardness.
2. Incorporation of BAG into the bleaching agent isn’t recommended as a method of increasing the surface microhardness of bleached enamel.
3. BAG gel application for 6 hours after bleaching is the optimal way to reduce the microhardness loss of enamel.
4. Application of BAG after bleaching can’t be considered as an effective method in increasing color stability after bleaching and exposure to coloring media.
5. Exposure to colored beverages after bleaching is strongly prohibited.