The blocking effect of iontophoretic administration of lidocaine on neurogenic vascular reactions in rat dental pulp

The blocking effect of lidocaine on nerve-induced vascular reactions was investigated in lower incisor teeth of anaesthetized rats. Pulpal blood flow was measured with laser Doppler flowmetry. Monopolar electrical stimulation of the rat incisor evoked a biphasic vascular response: an initial vasoconstriction was followed by a long-lasting vasodilation. Iontophoresis of lidocaine on a superficially exposed dentin surface with 60 μA of anodal direct current for 20 min blocked almost completely the stimulus-induced blood flow increase for about 25 min without any systemic effects. Iontophoresis of lidocaine with 40 μA for 20 min was almost without effect. Topical application of a mixture of lidocaine and prilocaine (25+25 mg/ml) in deep dentinal cavities was also without effect on the neurogenic reactions. Intravenous administration of lidocaine at 5 and 10 mg/kg in rats pretreated with phenoxybenzamine reduced the stimulus-induced increase in blood flow by an average of 29% and 54%, respectively, whereas the remaining α-adrenoceptor resistant vasoconstriction was not influenced. The present results show that iontophoresis of lidocaine on exposed dentin blocks nerve-induced vascular responses without causing systemic effects.