Evaluation of the accuracy and reliability of two electronic apex locators using micro-computed tomography

BACKGROUND: This study evaluated the accuracy and reliability of two electronic apex locators (EALs), DentaPort ZX (DTP) and EQ-Pex (EQP), at the 0.0 (APEX) and 0.5 display marks using micro-computed tomography (micro-CT), referencing the 0.0 mark to the apical foramen (AF) and the 0.5 mark to the apical constriction (AC). METHODS: Sixty extracted single-rooted mandibular premolars with fully formed apices were included. Preoperative micro-CT was used to identify the AF and AC and measure the AC-AF distance. Working length measurements were obtained in randomized order using a standardized mounting model. The file was fixed at the 0.0 position and scanned with micro-CT; positions corresponding to the 0.5 readings were calculated from micrometer displacement. Distances from the file tip to the AF and AC were compared using the Wilcoxon signed-rank test. Accuracy within ± 0.1, ± 0.25, and ± 0.5 mm was compared using McNemar's test. Reliability was evaluated using Bland-Altman-style plots and Levene's test. RESULTS: Two specimens were excluded (n = 58). The AC was located 0.33 ± 0.12 mm coronal to the AF. At the 0.0 mark, mean distances from the AF were - 0.17 ± 0.18 mm (DTP) and - 0.14 ± 0.20 mm (EQP), with EQP closer to the AF (p = 0.045). At the 0.5 mark, mean distances from the AC were - 0.25 ± 0.27 mm (DTP) and - 0.21 ± 0.24 mm (EQP), with EQP closer to the AC (p = 0.004). Accuracy at the AF did not differ between devices. At the AC, accuracy within ± 0.5 mm was higher for DTP than EQP (89.7% vs. 77.6%, p = 0.039). Agreement was acceptable; however, variability was greater at the AC, with no significant variance differences. CONCLUSIONS: Both EALs demonstrated acceptable accuracy and comparable reliability within ± 0.5 mm. Although a statistically significant difference in accuracy was observed at the 0.5 mark, the magnitude of the difference may have limited clinical relevance. Clinicians should interpret display marks cautiously when determining working length.