Methods: Electrical impedance of different concentrations of LH was measured using a bipolar platinum electrode. The relation between concentration and conductance of the solution was examined. Two chambers were used; one was filled with ultrapure water and the other with different concentrations of LH. Six premolars were extracted for orthodontic treatment and were sectioned at the cementoenamel junction. Tooth crowns were held between two chambers with a double O-ring. The enamel side chamber was filled with LH, the pulp side one with ultrapure water. A simulated interstitial pulp pressure was applied to the pulp side chamber. Change in the concentrations of LH was measured every 2 minutes with a platinum recording electrode positioned at the center of the pulp side chamber. Two platinum plates were set at the both ends of the chambers to pass alternating current. Passive diffusion without the iontophoresis was used as control. After the measurements, the enamel surfaces of sample teeth were examined by scanning electron microscopy.
Results: One sample that had enamel cracks was excluded from the study. Electrical conductance (G, mho) correlated closely to the concentration (x, mmol/L) of LH (G=2.16x2+0.0289x+0.000376, r2=0.999). LH that passed through enamel/dentin against dentinal fluid flow increased with time.
Conclusions: Conductometry showed LH diffusion through enamel/dentin was increased in quantity by AC iontophoresis. Anion delivery through human enamel/dentin may be affected by ζ-potential.