الفهرس 
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Abstract
This study was designed to investigate the effect of light-assisted (CO2 laser, Er-YAG laser, Diode laser, and light emitting diode LED) bleaching methods on the surface micromorphology and roughness of enamel. Also it evaluated bonding strength of resin composite material to bleached enamel. Materials and Methods : One peroxide-based bleaching product (Opalescence Boost PF 40%) activated with the four different light sources was used in the study. Forty central and lateral incisor teeth were selected and randomly divided into four groups (n=10) following the activation modes. Surface roughness average (Ra) ones measured before and after bleaching of the teeth, using profilometer analysis technique. Twenty five central and lateral incisors teeth were selected and randomly divided into five groups (n=5), four groups were bleached by the four mentioned activation modes and one group was left without bleaching (control). After two weeks bleaching, microhybrid resin composite cores were built on the level surfaces using a two-step self-etch adhesive the bond strength was evaluated to enamel surface was bonded to microhybrid resin composite with two step self-etch bonds (strong acid primer 1.2pH). All the teeth were prepared for the microtensile bond strength test. The results then were compared using one-way analysis of variance (ANOVA) and Tukey HSD test. Results: Regarding to surface roughness, increase in Ra was observed after bleaching of the samples in all test groups the higher Ra value was obtained when CO2 was used for bleaching activation, to be followed by Er-YAG, diode laser and light emitting diode (LED) respectively. There were significant difference between groups activated by CO2 and LED. There was a decrease in the microtensile bond strength (TBs) of the four tested groups when compared with the control the highest bond strength was obtained with unbleached group, to be followed by CO2 activated bleached group, Er-YAG, diode and LED respectively. There were significant differences between unbleached and CO2 activated in comparison with LED activated group. Also, there was significant difference between the unbleached group and diode beached group. The SEM pictures of the tooth enamel confirmed the results of surface roughness when compared with the control group(x). Conclusion : The results of surface roughness, microtensile bond strength and SEM observation showed that the enamel surface affected by laser types following the effect proportional to the absorption coefficients of lasers wave lengths. There is a consensus between enamel surface roughness and bond strength.