Knoop hardness of enamel and shear bond strength of brackets bonded with composite resin with and without fluoride

objective: the aim of this study was to evaluate the knoop hardness of enamel, shear bond strength and failure pattern (adhesive, bracket/resin interface or mixed) after bonding and debonding brackets, using resin composite with fluoride (ortho lite cure, ortho source？) and without fluoride (orthobond, morelli？). methods: fragments (6 mm x 6 mm) of 40 bovine incisor crowns were embedded in acrylic self-polymerizing resin. the knoop hardness measurements were performed before and after bonding metal brackets. the specimens were divided into two groups, according to composite resin: with fluoride (ortho lite cure, ortho source？) and without fluoride (orthobond, morelli？). after bonding, the specimens were submitted to demineralization and remineralization cycling for 14 days. shear bond strength testing was performed in a universal test machine (emic), at 5 mm/min crosshead speed. results: there was no significant difference in shear bond strength between groups i and ii. after demineralization and remineralization procedures (de/re), the specimens bonded with ortho lite cure showed higher knoop hardness than orthobond. for both groups there was predominance of failure at bracket/resin interface. conclusion: specimens bonded with fluoride resin composite showed higher microhardness after de/re cycling than those bonded with resin composite without fluoride, although no difference in shear bond strength was found.