Electroosmosis in human dentine in vitro

Objective: To determine the rate of fluid flow through human dentine due to electroosmosis during iontophoresis of either 2 % lignocaine with epinephrine, Ringer's solution, epinephrine, or distilled water. Design: Experiments were carried out on 24 intact extracted human premolars. Dentine was exposed at the tip of the buccal cusp. The cavity was filled with one of the test solutions and the pulp cavity, with Ringer's solution at a pressure of 11 mm Hg. Fluid flow through the dentine was measured using a capillary connected to the pulp cavity. Current was passed between a stainless-steel electrode in the cavity and one in the pulp cavity. The results were analysed using repeated measures, three-way ANOVA, with Bonfermni pairwise comparisons where this showed a significant effect. Results: The current passed produced a significant flow of fluid through the dentine but neither the composition of the test solution nor etching had a significant effect on the flow. During iontophoresis of 2 % lignocaine with epinephrine for example, currents of 0.2, 0.4, and 0.6 mA applied with the cavity electrode as anode produced inward flow rates of 2.25 +/- 0.87, 5.00 +/- 1.62, 8.60 +/- 1.97 (mean f s.d.) nL/s/mm(2) respectively, and applying the currents in the opposite direction caused outward flows of 0.76 +/- 0.72, 1.00 +/- 1.01, 1.12 +/- 1.18 nL/s/mm(2) respectively. Conclusions: It is concluded that electmosmosis can be produced in human dentine, it can enhance the effect of iontophoresis in transporting charged molecules through dentine, particularly large molecules, and it could also enable uncharged molecules to be carried through dentine into the pulp.