Facilitatory effect of AC-iontophoresis of lidocaine hydrochloride on the permeability of human enamel and dentine in extracted teeth

Objectives: The objectives of the present study were to quantitatively evaluate chemical permeability through human enamel/dentine using conductometry and to clarify if alternating current (AC) iontophoresis facilitates such permeability. Materials and methods: Electrical impedance of different concentrations of lidocaine hydrochloride was measured using a bipolar platinum impedance probe. A quadratic curve closely fitted to the response functions between conductance and lidocaine hydrochloride. For analysis of the passage of lidocaine hydrochloride through human enamel/dentine, eight premolars that were extracted for orthodontic treatment were sectioned at the cemento-enamel junction. The tooth crowns were held between two chambers with a double O-ring. The enamel-side chamber was filled with lidocaine hydrochloride, and the pulp-side chamber was filled with extrapure water. Two platinum plate electrodes were set at the end of each chamber to pass alternating current. A simulated interstitial pulp pressure was applied to the pulp-side chamber. The change in the concentration of lidocaine hydrochloride in the pulp-side chamber was measured every 2 mm using a platinum recording probe positioned at the centre of the pulp-side chamber. Passive entry without iontophoresis was used as a control. Results: The level of lidocaine hydrochloride that passed through enamel/dentine against the dentinal fluid flow increased with time. Electrical conductance (G, mho) correlated closely to the concentration (x, mmol/L) of lidocaine hydrochloride (G = 2.16x(2) + 0.0289x + 0.000376, r(2)=0.999). Conclusions: Lidocaine hydrochloride can pass through enamel/dentine. Conductometry showed that the level of lidocaine hydrochloride that passed through enamel/dentine was increased by AC iontophoresis. (C) 2012 Elsevier Ltd. All rights reserved.