Influence of instrument size and varying electrical resistance of root canal instruments on accuracy of three electronic root canal length measurement devices.

Abstract

To evaluate the influence of instrument size and the effect of the electrical resistance of endodontic instruments on the accuracy of three electronic root canal length measurement devices (ERCLMDs). Thirty single-rooted extracted human teeth were divided into three groups (n=10) on the basis of the ERCLMD used: Root ZX II (J. Morita, Kyoto, Japan); ProPex (Dentsply Maillefer, Ballaigues, Switzerland); and iPex II (NSK, Tochigi, Japan). The electronic working length measurements (EWL) were made with K-files in the sequence sizes 08, 10, 15, 20, 25 and 30. The actual working length (AWL) was calculated by fixing a size 30K-file in the canal and exposing the apical 5mm of the root. The minor foramen was identified under an optical microscope, and its distance from the file tip was calculated. The accuracy of the ERCLMDs was evaluated in terms of percentages of accurate measurements (0.0mm tolerance) and measurements with tolerance limits of ±0.5mm and ±1.0mm. The findings were analysed with the McNemar test, Pearson's chi-square tests and two-way analysis of variance. The multiple comparison procedures were carried out using Holm-Sidak method. The maximum electrical resistance tolerated by ERCLMDs was evaluated by connecting commercially available resistors between the file clip and the root canal instrument. The resistance was gradually increased until it started to affect the ERCLMD readings. The ERCLMDs were able to actually locate the minor foramen in 7% of samples. File size did not affect the accuracy of ERCLMDs (P>0.05). Overall, the ERCLMDs gave 65% readings within a tolerance limit of ±0.5mm and 90% within a tolerance of ±1.0mm. The electrical resistance of endodontic files was less than the maximum electrical resistance tolerated by ERCLMDs (0.6-1Ω vs. 2500-4000Ω). The size of the root canal instrument did not affect the accuracy of ERCLMDs in this laboratory study.