Effect of fluoride iontophoresis on the microtensile bond strength between dentin and two adhesive systems

To evaluate the effect of fluoride iontophoresis on the microtensile bond strength (MTBS) between coronal dentin and two resin-based adhesive systems, and to measure quantitatively dentinal tubule occlusion.

Twelve freshly extracted intact human mandibular third molars were divided randomly into four groups. The superficial occlusal dentin of each tooth was exposed and treated. Group A1: One-Step Plus total-etch adhesive system; group A2: One-Step Plus total-etch adhesive system after fluoride iontophoresis; group B1: ACE BOND SE self-etching adhesive system; group B2: ACE BOND SE self-etching adhesive system after fluoride iontophoresis. A resin composite buildup was made for each tooth, which was then sectioned along its long axis to produce 10 beams (1.0 mm x 1.0 mm) for the microtensile bond strength (MTBS) test. Five dentin disks were cut in half and their occlusal surfaces etched with 6% citric acid. The test halves were treated with fluoride iontophoresis. Four SEM photomicrographs were taken from corresponding sites on each test and each non-treated control half-disk. Image-Pro Plus 4 software quantified the percentage of tubule occlusion. Data were analyzed using one-way ANOVA, chi(2)- and t-tests, with the probability level set at alpha=0.05.

The mean MTBS (MPa) for each group was, A1: 30.86 (S.D. 6.84); A2: 25.04 (8.49); B1: 19.22 (6.88); B2: 19.40 (6.92). There were significant differences among all groups (P < or = 0.02), except between groups B1 and B2 (P=0.92). Fluoride iontophoresis resulted in significantly increased dentinal tubule occlusion (P<0.001).

Fluoride iontophoresis treatment reduced significantly the dentin bond strength of One-Step Plus total-etch adhesive, but not that of ACE BOND SE self-etching adhesive. However, the bond strength of the former remained significantly higher than that of the latter adhesive system.