The accuracy of electronic working length determination

Aim To determine in vivo the accuracy of two impedance quotient apex locators under clinical conditions. Methodology Electronic working length determination was carried out before extraction in 79 human teeth with 93 root canals. In 51 root canals, the determination was performed using the apex locator Justy II(R) (Hager & Werken, Duisburg, Germany); in 42 canals, the apex locator Endy 5000(R) (Loser, Leverkusen, Germany) was used. A root canal instrument was fixed at working length with composite material prior to extraction followed by the exposure of a radiograph. After histological preparation of the apical region, the teeth were examined under a light microscope. The distance of the file tips to the target intervals 'minor foramen - major foramen' and 'apical canal constriction' was determined. These values were compared with the calculated working lengths, determined by radiographic assessment. The data were statistically analysed by a paired t-test. Results For both apex locators and both target intervals, no significant differences between the electronic and radiographical assessments were recorded. The probability of determining the area between minor and major foramen was 82.4% for Justy II and 81% for Endy 5000. However, accurate determination of the apical constriction was only successful in 51% (Justy II) and 64.3% (Endy 5000) of canals. Variation of the inaccurate measurements was higher for Endy 5000 than for Justy II. Conclusions Under clinical conditions, it is possible to determine the region between the minor and major apical foramen with electronic length measuring devices (ELD). However, use of these devices does not result in precise determination of the apical constriction.