الفهرس 
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Abstract
Background: Acidulated phosphate fluoride (APF) application is used for dental caries prevention. Combination of APF with different laser wavelengths increases acid resistance in enamel. Aim: To assess the effects of Er-Yag (2.94 μm) laser and Diode (940 nm) laser after the application of APF on the morphology, mineral content, and micro-hardness of the enamel surface of human teeth in-vitro. Materials and Methods: 40 freshly extracted 3rd molars crowns were collected then splitted longitudinally into 80 halves.(20 halves/ group; 10 halves/assessment). The four groups were divided as follows; group 1(Control group), group 2 (Application of 1.23% APF gel only), group 3 (diode laser; 1W for 60 sec, contact mode after APF gel) and group 4 (Er-YAG; 80 mJ, 0.8 W, 10 Hz; pulsed mode for 10 sec after APF gel). Specimens were morphologically examined by Scanning electron microscope (SEM and microhardness by Vickers Microhardness (VMH) test. Collected data were statistically analyzed by ANOVA test. Results: Applying diode laser after APF showed superior VMHand obliterated ERE in SEM while Er-YAG laser application after APF revealed the least microhardnesswith obliterated EREs and more cracks over other groups. Conclusion: Diode laser (940 nm) after APF application showed superior SEM with less cracks and VMH results over application of APF alone then control group. However, the poorest SEM with more cracks and least VMH was obtained upon Er-YAG laser application after APF.