effects of fl uoride release from orthodontic bonding materials on nanomechanical properties of the enamel around orthodontic brackets

background: the aim of the present study is to evaluate the effects of a fl uoride-releasing composite resin bonding material on reducing enamel demineralization underneath and around orthodontic brackets and compare that with a conventional adhesive system. materials and methods: buccal surfaces of 10 intact extracted premolar teeth were divided into two parts with nail varnish and stainless steel brackets were randomly bonded by two resin composite systems: (transbond xt) and (transbond xt plus color change) (3m, unitek, monrovia, ca, usa) on two sides of the teeth and then samples were placed in a demineralization solution. it is claimed that the second system has the ability of fl uoride release. elastic modulus and hardness of enamel were measured with nanoindentation test in 6 depths in 1-36 μm from the enamel surface and in 7 regions: control (intact enamel surface), underneath the brackets and also 50 and 100 μm from the brackets edge. these nanomechanical features were evaluated in different regions and depths using analysis of variance and paired t -test ( p < 0.05). results: considerable difference can be seen in different depths and regions in terms of hardness and elastic modulus. the region under the bracket with fl uoridated adhesive shows similar results with intact enamel, whereas these parameters in fl uoride less side show a signifi cant reduction ( p < 0.05). conclusion: results show that use of resin composite bonding system with the ability of fl uoride release for bracket bonding, may reduce demineralization of enamel around brackets during orthodontic treatment. key words: elastic modulus, enamel demineralization, fl uoride releasing adhesive, hardness nanoindentation