الفهرس 
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Abstract
BACKGROUND: White spot lesions (WSLs) are one of the most common problems which occur on tooth enamel surface around bonded brackets after prolonged orthodontic treatment. AIM: Evaluate the effect of Er,Cr:YSGG (λ = 2780 nm) laser and 45S5 bioactive glass (BAG) paste either alone or in combination with each other in re-mineralization of enamel WSLs. MATERIAL AND METHODS: Fifty enamel surface samples were prepared to acquire WSLs. There are 5 groups (n=10). group 1, control samples; group 2, 45S5 BAG paste treatment alone; group 3, Er,Cr:YSGG laser irradiated (0.5 W, 20 Hz, 10 s) alone, group 4, 45S5 BAG paste treatment applied before irradiation with same laser parameters in group 3 and group 5, 45S5 BAG paste treatment applied after laser irradiation similar to group 3 and 4. The morphological changes of enamel texture, Methylene blue (M.B) dye penetration depth length and area were assessed by Stereomicroscope. Calcium (Ca), Phosphorous (P), Ca/P ratio and Carbon (C) mass٪, were assessed by Energy Dispersive X-ray Analysis (EDXA), the results were statistically analyzed by ANOVA test using IBM SPSS software package version 20.0. (Armonk, NY: IBM Corp). RESULTS: EDXA revealed the highest Ca & Ca/P ratio mass٪ in group 4, highest P and least C mass% in group 5. There was no statistical significance between both group 4 & 5 in Ca, P, Ca/P ratio & C mass ٪ results. Both groups 4 & 5 showed a significant difference increase in Ca, & P mass ٪ and non-significant increase in Ca/P ratio mass ٪ upon comparing them with other groups. A significant increase in C mass٪ was noticed in group 3 when compared to group 4 & 5, nonsignificant increase when compared to group 2 and significant decrease when compared to group 1. Stereomicroscopic results of outer enamel surface revealed that WSLs was reduced in group 2 and completely disappeared in group 3, 4 & 5. where group 3 showed some cracks, group 4 showed less homogenous enamel surfaces and group 5 showed homogenous & translucent remineralized enamel surface. Stereomicroscopic enamel subsurface results revealed the least M.B dye penetration depth in group 3 followed by 5 then 4 respectively with no statistical significance in terms of area (mm2 ) and with statistical significance decrease in terms of length (mm). Moreover, there was a statistical significance increase in M.B dye penetration depth in terms of length & area in group 2 followed by group 1 when compared to groups 4, 5 & 3 correspondingly. CONCLUSIONS: 45S5 BAG paste treatment after Er,Cr:YSGG laser (0.5 W, 20 Hz, 10 s) showed the best esthetic, homogenous, translucent, re-mineralized enamel surface with complete absence of WSLs than applying 45S5 BAG paste before laser irradiation. Whereas, using laser alone with the same parameters removed WSLs, but induced cracks & enamel melting with increased C٪. Moreover, 45S5 BAG paste application alone didn’t completely remove WSLs with increased C٪ as well.