الفهرس 
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Abstract
Aim: investigate the effect of 980 nm diode laser surface treatment before or after gamma irradiation with or without fluoride on surface microhardness and microstructure of human enamel. Methodology: Seventy enamel specimens were allocated into seven groups according to the applied treatments (n=10); C, G, L, GL, LG, GFL & FLG. Each specimen was evaluated twice before and after artificial caries induction. Results: Before artificial caries, results showed a marked decrease in microhardness values due to gamma and a marked increase in them after laser. Significant differences were detected between group C and either LG and FLG groups. Highly significant differences were detected comparing microhardness results of group G with all other groups. The same results were reported after artificial caries like lesions however fluoride significantly enhanced the protective effect of laser when performed after gamma irradiation. Conclusions: Gamma has a drastic effect on microhardness and ultrastructure of enamel. Laser with or without fluoride, could counteract this drastic effect either done before or after gamma radiation. Demineralization resistance of enamel could be improved by laser or by laser preceded with fluoride, done either before or after gamma irradiation. Fluoride deepens the protective effect of laser on gamma irradiated enamel regarding its resistance to demineralization. Recommendations: 980 nm diode laser could be implemented as one of the oral care protocols recommended in radiotherapeutic patients preferably before gamma irradiation. Fluoride could be useful as an adjunctive to laser in the resistance of gamma irradiated human enamel against caries attack.