Influence of Anatomical Parameters on the Accuracy of Electronic Apex Locators in C-shaped Canals: A Novel Micro-CT Analysis Incorporating Feret Diameter

INTRODUCTION: This study aimed to evaluate the influence of anatomical parameters on the accuracy of 2 electronic apex locators (Raypex 6 and Root ZX II) in C-shaped canal mandibular molars using a novel micro-computed tomography (micro-CT) analysis incorporating Feret diameter. METHODS: The actual root canal length was measured using the visual method. The electronic canal length, which determined the apical foramen (AF), and the electronic working length, which determined the apical constriction (AC), were obtained using Raypex 6 and Root ZX II. The root working length, calculated by subtracting the AC-AF distance from the root canal length, served as a reference to evaluate the accuracy of the electronic working length. Anatomical parameters were derived from micro-CT scans and included Feret diameters of AC and AF, AC-AF distance, presence/absence of accessory canal, C-shaped type, AF position and AC morphology. Statistical analysis involved Fisher's exact test and multinomial logistic regression. RESULTS: The study included 42 C-shaped molar teeth and 119 canals. Raypex 6 and Root ZX II determined AF within ±0.5 mm in 97.5% and 96.4% of canals, respectively. A statistically significant difference was found in accuracy between detecting AF and AC (P < .05). After multinomial logistic regression, multiple AC morphology was the only factor negatively affecting AC accuracy in both electronic apex locators. CONCLUSIONS: Raypex 6 and Root ZX II accurately detected AF but were less reliable for AC in C-shaped canal mandibular molars. Reduced AC accuracy was associated with multiple AC morphology, indicating that electronic apex locators may detect the first narrow part of the canal apically rather than the narrowest part.