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 and 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.