In order to investigate the current path between the enamel surface and the pulp chamber, the electric potential was measured at the vertical surfaces of the teeth sectioned labiolingually when the potential with a frequency of 400 sine waves per second was maintained at 400 mV
p-p on the enamel surfaces, and the enamel and the dentin stained with methylene-blue solution introduced by electrophoresis were observed by grinding away one side of the teeth, using freshly extracted lower incisors of bovine.
The results obtained were as follows:
1) Owing to the isoelectric point, it was assumed that the electric current was radiated in the enamel, spread widely at the dentino-enamel junction and flowed towards the pulp in parallel with the dentinal tubules on the whole.
Electrophoresis with methylene-blue solution, however, revealed that the path of direct current was restricted in the enamel, showed a spread at the dentino-enamel junction and flowed along the dentinal tubules concentrically.
2) At the pulpal wall of the dentin, current density produced by sine waves was lower than that produced by direct current in electrophoresis.
3) As the quantity of electricity was increased in electrophoresis, the stained area with methylene-blue solution was observed widely.
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