الفهرس 
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Abstract
Numerous studies from throughout the world show that most people are unhappy with the color of their teeth. Currently, it is feasible to make an effort to improve the shade of teeth by utilizing a variety of techniques, including expert scaling and prophylaxis carried out in a dental office, tooth augmentation the usage of laminate veneers, crowns, and tooth whitening.
One of most used method for bleaching is Toothpastes contain bleaching active agents and abrasives. The most abrasive recently used in whitening toothpaste is CaCO3, it was used as abrasive as a combination with perlite material and now it used alone. One of the other types of whitening toothpaste which depends on film of covarine with blue color attached to tooth surface. That film reflects the light and change color to white according to CIE lab.
this study aimed to know the effect of two active agents which used in over the counter whitening toothpastes (calcium carbonate and covarine) was evaluated on enamel surface and subsurface of extracted human teeth.
• Materials and methods:
- Teeth grouping:
The collected premolars were brushed gently to get rid of any residual debris and were equally divided into three groups as follows:
a- group I :
16 premolars were preserved in distilled water. b- group II :
16 premolars were brushed by CaCO3 gel day and night at an interval of 12 hours. During the interval time the teeth were placed in distilled water till the end of experimental period.
c- group III :
16 premolars were brushed by covarine gel day and night at an interval of 12 hours. During the interval time the teeth were placed in distilled water till the end of experimental period
Each group were further subdivided equally into 2 subgroups (n=8) as follows:
- Subgroup A in which premolars were examined after 3 weeks.
- Subgroup B in which premolars were examined after 7 weeks.
Teeth were brushed using electrical tooth brush on standard speed for one minute to save stable brushing system and power. Active agent gel was applied on buccal surface as a solution of distilled water and active agent gel with ratio 3:1 (distilled water: active agent gel).
After the end of experiment the enamel of all teeth in each group was assessed by:
a- Light microscope to study the internal histological changes in ground teeth sections.
b- Scanning electron microscope (SEM) to detect surface morphological changes.
c- Energy dispersive x-ray analyzer (EDXA) to assess Ca, P and C concentration values in the collecting samples.
d- Microhardness tester to detect the hardness of enamel.
• Results:
- Light Microscope:
In light microscope detection there was no significant change between the three groups.
- Scanning electron microscope:
In scanning electron microscope there was obvious precipitation of calcium particles on enamel surface in calcium carbonate group.
Covarine blue group show nearly no difference between it and control group except for only some cracks.
- EDXA:
The weight of C and P in enamel after 3 weeks brushing, showed significance difference between calcium carbonate and covarine blue group. The highest of carbon was recorded in calcium carbonate group while P weight was higher in covarine blue. On other hand there was no difference in Ca weight in both groups.
After 7 weeks brushing there were no significance difference between all groups in C and Ca weight but there was difference in phosphorus percentage. P recorded the highest weight in calcium carbonate group.
- Microhardness:
After 3 weeks there was significance difference between calcium carbonate and other groups as it was the lowest group, but after seven weeks there was no significant difference between all groups. So, the only group which increased in microhardness is calcium carbonate group.