Er:YAG effects on dental enamel surface regarding the resistance to demineralization and the fluoride incorporation were evaluated. 80 samples were divided into 8 groups: G1) control - APF application; G2) conditioning with 37% phosphoric acid and APF application; G3) irradiation with 250 mJ/pulse, 7 Hz, 31,84 J/cm2 (contact) and APF application; G4) irradiation with 200 mJ/pulse, 7 Hz, 25,47 J/cm2 (contact) and APF application; G5) irradiation with 150 mJ/pulse, 7 Hz, 19,10 J/cm2 (contact) and APF application; G6) irradiation with 250 mJ/pulse, 7 Hz, 2,08 J/cm2 (non-contact) and APF application; G7) irradiation with 200 mJ/pulse, 7 Hz, 1,8 J/cm2 (non-contact) and APF application; G8) irradiation with 100 mJ/pulse, 7 Hz, 0,9 J/cm2 (noncontact) and APF application. All samples were immersed in 2,0 M acetic-acetate acid solution, pH 4,5 for 8 hours. The fluoride, calcium and phosphorous ions were analyzed, by atomic absorption spectrometry and spectrophotometry. Groups laser irradiated before topic APF application presented better results than the control. There was higher fluoride incorporation on G7 and G8. Calcium and phosphorous analysis reveled a decrease on the enamel demineralization on G2 and G3 groups. The Er:YAG laser on irradiation conditions of this work is a promissory alternative for the Preventive Dentistry.