Accuracy of three types of electronic apex locators using histological sections as gold standard

One of the most important steps in root canal treatment is to determine the exact working length as an effective factor in the success of treatment. Various tools and methods have been introduced to determine the working length, including electronic apex locators. This study was undertaken to compare the accuracy of three electronic apex locators, Root ZX, Woodpecker and Coxo in determining the actual working length. In this in vitro study, 30 maxillary central incisors meeting the inclusion criteria were selected and the working length of each tooth was determined by three electronic apex locators: Root ZX, Woodpecker and Coxo. After irrigating the root canals with 6% hypochlorite and 0.9% normal saline solutions, electronic measurements were performed using a #15 K-file in the range of 1±0.5 mm at the apical constriction according to the manufacturer's instructions. After abrading 4 mm of the root end, the actual working length was calculated under a microscope from the distance between the coronal reference point and the apical constriction. Data were analyzed with chi-squared test and Fisher’s exact test, using SPSS 16 (α = 0.05). The accuracy rates of Root ZX, Woodpecker and Coxo apex locators were 76.7% and 100%, 90% and 100%, and 93.3% and 100% in the range of 1 ± 0.5 mm, respectively. No significant differences were found between the working lengths measured by three apex locators and the actual working lengths. According to the results of this study, none of the three apex locators exhibited accuracy of 100% exactly at the apical constriction. There were no statistically significant differences between the working lengths obtained by three apex locators and the actual working lengths.