title: Influence of instrument size and varying electrical resistance of root canal instruments on accuracy of three electronic root canal length measurement devices.
abstract: OBJECTIVE
  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).
  
  
  METHODS
  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 30 K-file in the canal and exposing the apical 5 mm 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 (0.0 mm tolerance) and measurements with tolerance limits of ±0.5 mm and ±1.0 mm. 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.
  
  
  RESULTS
  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 ±0.5 mm and 90% within a tolerance of ±1.0 mm. The electrical resistance of endodontic files was less than the maximum electrical resistance tolerated by ERCLMDs (0.6-1 Ω vs. 2500-4000 Ω).
  
  
  CONCLUSIONS
  The size of the root canal instrument did not affect the accuracy of ERCLMDs in this laboratory study.
authors.affiliation: Department of Conservative Dentistry & Endodontics, Faculty of Dentistry, Jamia Millia Islamia, New Delhi, India.
authors.forename: V
authors.initials: V
authors.lastname: Aggarwal
authors.affiliation: Department of Conservative Dentistry & Endodontics, SGT Dental College, Gurgaon, India.
authors.forename: M
authors.initials: M
authors.lastname: Singla
authors.affiliation: Faculty of Dentistry, Jamia Millia Islamia, New Delhi, India.
authors.forename: S S
authors.initials: SS
authors.lastname: Bhasin
mesh_terms: D003762:Dental Instruments; D017097:Electric Impedance; D004867:Equipment Design; D006801:Humans; D009811:Odontometry / Q000295:instrumentation; D018915:Root Canal Preparation / Q000295:instrumentation*; D012390:Root Canal Therapy / Q000295:instrumentation*
keywords: electrical resistance; electronic root canal length measurement devices; root canal length; working length