Purpose: This « in-vitro » study had two specific aims: the first, to test using a universal testing machine whether sub-ablative Er:YAG laser irradiation prior to acid etching is effective in orthodontic bracket bonding and secondly using micro-hardness measurements and Scanning Electron Microscopy (SEM) observations to investigate the effectiveness of de-mineralization reduction in enamel treated with sub-ablative Er:YAG laser irradiation followed by fluoride varnish application. Materials and Methods: One hundred and eighty bovine permanent maxillary incisors were selected for shear bond strength testing and microhardness measurements. Sub-ablative Er:YAG laser irradiation was set at a power density of 2.5 J/cm 2 , a frequency of 7 Hz and air/water spray. Brackets were bonded with an auto-curing resin paste. The shear bond strength was measured comparing laser irradiated and non-irradiated enamel surface, followed by SEM observation of the bracket-resin-enamel interface. Microhardness measurements were made on enamel samples before treatment, after samples preparation, and after demineralization. Results: While the adhesion of orthodontic brackets to bovine enamel after sub-ablative Er:YAG laser irradiation and acid etching is comparable to that obtained after conventional acid etching, the effect of laser irradiation associated with topical application of fluoride varnish increases the microhardness of enamel. Conclusion: Sub-ablative Er:YAG laser irradiation before the acid etching doesn't reduce the shear bond whereas when associated with fluoride application it may play a role in caries prevention. Further studies will be necessary to establish the mechanism by which the protective laser activated fluoride effect is achieved.