Determination of impedance changes at varying frequencies in relation to root canal file position and irrigant.

This study was conducted on 10 anterior and premolar teeth that were scheduled for endodontic treatment. After length of tooth determination, a series of test K-file handles were locked at lengths varying from 3 mm short to 0.5 mm long of the foramen. Samples of impedance were taken at each length with a digital signal processor at six different frequencies and for each of seven different irrigants or canal conditions. A total of five different root canal irrigants were used in each tooth (RC Prep, 70% isopropyl alcohol, 14.45% EDTA sodium solution, normal saline, and 5.25% NaOCl), along with two variations of a dry canal. The greatest impedance changes occurred +/- 0.25 mm from the foramen. No significant difference was noted in prediction error at different frequencies (p > 0.05); however, prediction error was significant with respect to different irrigants (p < 0.02). Conductive irrigants demonstrated less change of electrical characteristics with length than nonconductive irrigants, thus allowing a greater prediction of file position in relation to the foramen using electrically nonconductive irrigants.