Accuracy of working length measurement: electronic apex locator versus cone-beam computed tomography

To compare the accuracy of working length (WL) determination using the Raypex 6(®) electronic apex locator and cone-beam computed tomography (CBCT).

A total of 150 extracted human teeth were decoronated and randomly assigned to five groups (n = 30). WL was measured with the Raypex 6(®) at both the 'constriction' and the 'apex' marks under dry conditions (group 1) or with 2.5% NaOCl, distilled water or Ultracain(®) (groups 2-4). The radiological WL (group 5) was calculated from bucco-lingual and mesio-distal CBCT sections. Differences between electronic, CBCT measurements and actual length (AL) were calculated. Positive and negative values, respectively, indicate measurements falling short or long of AL. Two-way anova and the Bonferroni and Welch tests were used to compare mean differences amongst groups. The chi-squared and Fisher's exact tests were used to compare percentages of precise, ±0.5 and ±1.0 mm of the AL measurements amongst the experimental groups. Statistical analysis was performed at α = 0.05.

Mean differences with respect to AL ranged from 0.26 to -0.36 mm and from 0.05 to 0.18 mm, respectively, for the electronic measurements at the 'constriction' mark and 'apex' mark. CBCT measurements were an average of 0.59 mm shorter than AL. Percentages of electronic measurements falling within ±0.5 mm of the corresponding AL referred to the 'apex' mark were greater than at the 'constriction' mark, but the differences were only significant in group 4 (with Ultracain(®) ). Percentages of CBCT measurements falling within ±0.5 mm of AL (46.7%) were significantly lower than electronic measurements, regardless of the condition of the root canal. In 30-38.5% of the measurements taken at the 'apex' mark and in 3.4-13.3% of those at the 'constriction' mark, the file tip extended beyond the foramen.

Electronic measurements were more reliable than CBCT scans for WL determination. The Raypex 6(®) was more accurate in locating the major foramen than the apical constriction under the experimental set-up.