Objectives: To explore the relationship between the electrical impedance of a tooth and the number of unfilled canals during root canal treatment. Methods: Ten extracted human molar teeth and ten premolar teeth with mature roots were selected. An alternating electrical current with a frequency of 1 kHz was applied simultaneously to the saline in the glass container and to the pulp chamber. The impedance of the saline and the tooth were measured. Root canal treatment was conducted starting with the largest root canal. After the root canal was filled, a second impedance measurement procedure was conducted. This procedure was repeated until all root canals were filled. The association between the number of unfilled root canals and the logarithm of the impedance of the tooth during root canal treatment was expressed in Pearson correlation coefficients. The influence of tooth type (lower, upper), the number of canals (3 or 4), and the number of open canals (0 to 3 or 4) on the logarithm of the impedance of the tooth were assessed by an analysis of variance. Results: The mean values of the logarithm of the impedance of the tooth increased with a decrease in the number of unfilled root canals (r=-0.87). The impedance of the tooth was significantly influenced by the number of unfilled canals (P=0.00), not by tooth type nor by the number of root canals (P>0.05). Conclusion: The results of this study indicate that a strong inverse association exists between the electrical impedance of molar teeth when exposed to a 1 kHz electrical current and the number of unfilled root canals. The mean values of log(impedance) from teeth with four canals were largely, yet not significantly lower than those of teeth with three canals. Given the promising results from this pilot study, a more comprehensive study is envisaged.

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