Effect of flavonoid-based experimental primer solutions on dentin bond strength and dentin-adhesive bonding interface morphology

The degradation of collagen fibrils is one of the causes of adhesion failures. Somo compounds have been suggested to be applied before adhesives or incorporated into them. The objective of this in vitro study was to evaluate the effect of four experimental primer solutions on dentin bond strength (µTBS), after 24 hours and one year of storage in artificial saliva, and the dentin-resin bonding interface morphology. Two different flavonoids were diluted in absolute alcohol: Kaempferol (Ka) e Naringin (Na) at different concentrations (10 mM and 20 mM), obtaining four primer solutions. Primers were applied for 30 or 60 seconds in dentin previously conditioned with 35% phosphoric acid, followed by the application of a two-steps etch-and-rinse adhesive system (Optibond S, Kerr). The Negative Control (NC) consisted of no primer application prior to adhesive, while the Positive Control (PC) comprised 0.2% Chlorhexidine Digluconate solution used for 30 seconds or 60 seconds. Eighty-eight third human molars were randomly assigned into eleven groups (n=8), according to the type, concentration and time of application of the primer for the µTBS test. The teeth were restored according to each group and were cut into lingual-buccal and mesial-distal directions sections, obtaining stick-shaped specimens. Half of the specimens were submitted to the µTBS test after 24 hours, while the other half was stored at 37ºC in an artificial saliva solution for one year and tested. For the analysis of the morphology of the bonding interface morphology, forty-four teeth (n=4) were restored following the same methodology of the µTBS methodology. However, the Rhodamine B dye was added to the adhesive at 0.1% weight concentration. After 24 hours, the teeth were sectioned into 1 mm thick slices. The slices were polished and analyzed in Confocal Laser Scanning Microscopy (CLSM). All methodological analyses were evaluated for distribution and homoscedasticity, followed by appropriate statistical analyses (?=0.05). Regarding µTBS, no statistical difference was found among the experimental groups and NC at 24 hours. However, experimental primers containing 20 mM Na, 10 and 20 mM Ka applied for 60 s presented higher means than that obtained for NC and PC at one year. Hybrid layer formation and adhesive penetration into dentinal tubules were observed in all groups. The application of all flavonoid-based experimental primers for 60 s was able to produce higher µTBS than those obtained with NC after one-year of artificial aging (AU)