Microhardness of dentin underneath fluoride-releasing adhesive systems subjected to cariogenic challenge and fluoride therapy

ObjectivesThe aim of this study was to evaluate the microhardness of dentin subjacent to the bonding interface of composite restorations using fluoride-releasing adhesive systems submitted to pH-cycling regimen associated or not to fluoride therapies.MethodsThirty human third molars were prepared with class V cavities with dentin cervical margins. The adhesive systems One-Up Bond F Plus (OU), Prime&Bond NT (NT), Clearfil Protect Bond (CF), Optibond Solo Plus (OP) and also the controls [−] Single Bond 2 (SB) and [+] Ketac Molar (KM) were used previously to composite resin restorations. The restorations were sectioned into four slabs and submitted to different storage media for 15 days: distilled water, pH-cycling, pH-cycling associated to NaF 0.05% and associated to NaF 1.23%. The Knoop microhardness test was performed in dentin at 50, 100, 150 and 300 μm from the adhesive interface. Data was analyzed by three-way ANOVA and Tukey HSD test (p < 0.05).ResultsKM resulted in significantly higher microhardness when compared to all the adhesive systems at 50 μm, with the exception of OU, that was similar to KM when submitted to pH-cycling alone or associated to 1.23% NaF. Microhardness of dentin was significantly higher with all the tested materials, when pH-cycling was associated to NaF 0.05%, at 50 μm and 100 μm depths. OU resulted in similar dentin hardness at all depths and storage media.ConclusionsThe incorporation of NaF 0.05% fluoride therapy to the cariogenic challenge was capable to recover the original microhardness of dentin at 50 and 100 μm with all the tested materials.