الفهرس 
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Abstract
This in vitro study was conducted to evaluate the effect of WTPs and brush bristles using a custom-made tooth brushing simulator on: color of enamel, surface roughness and micro -hardness of enamel.
A total of 240 sound bovine incisors were included in this study. The coronal portion of each tooth were sectioned, mounted into acrylic resin blocks, making the labial surface 2- 3 mm above and parallel to the base. The samples were labeled and randomly divided into8 groups (30 each) based on the commercial type of whitening TPs as the following: (water (control), (Depurdent), (Closeup- white now), (Closeup – diamond attraction), (Signal – whitening), (Signal complete -8 (charcoal white & detox)), (Sensodyne (multi care +whitening)), (Colgate (optic white)) from group I-VIII respectively. Furthermore, each group was divided into three subgroups (n=10) based on the type of tooth brush bristles (soft (S), medium(M) or hard (H)).
The labial surfaces of samples were ground to be flat using an Aluminum oxide fine grit grinding wheel then finished and polished using 800, 1000 grit Aluminum oxide abrasive papers a slurry of fine talc respectively. For staining, each sample was immersed into 50ml a concentrated black tea solution (16g of tea in 500ml water) for 18h followed by 6h of drying up to 4 complete cycles of staining. After that the samples were rinsed with water and stored for 7 days in saline.
Each sample was submitted to 5500 double strokes of brushing regarding the type of TPs and brushes. By using a speed of 60 cycle/min, loaded with 200 ± 20g (2N) using accustom made brushing simulator and a slurry of 1:1 toothpaste to water.
For color measurement, reflecting spectrophotometer was used to measure L*, a* and b* before staining and brushing (T0), after staining and before brushing (T1) and after brushing (T2). For surface roughness in (nm) and micro-hardness in (VHN) measurement a contact profilometer surface roughness tester and Vickers micro-hardness tester were used respectively. The collected data from all tests were statistically calculated and analyzed.
For color measurement, all parameters at T0, T1and T2 of all groups and subgroups showed a statistically significant difference compared to each other except group I in comparing T2 to T1. Regarding ΔE1, all whitening TPs had a significant effect on color. group II and III showed the highest significant whitening effect. While group I showed the least one. Moreover, all brushes subgroups showed a non-significant effect on ΔE1.
For roughness, FR for all groups and subgroups showed a statistically significant increase in roughness compared to IR. The roughness percent change of both tooth brushes and TPs types had a significant effect on increasing roughness. group I showed the least significant increase in roughness while group V showed the highest statistically significant increase in roughness followed by group VII and VIII. Moreover, H subgroups showed the highest significant increase in Ra compared to S subgroups.
For micro-hardness, FH for all groups and subgroups showed a statistically significant decrease in means compared to IH. group I showed the least significant decrease in micro-hardness while group VII showed the highest significant decrease in micro-hardness followed by group VIII. Moreover, all brushes subgroups showed a nonsignificant effect on micro-hardness.