Introduction: The present study was undertaken to determine the accuracy of working length using cone-beam computed tomography and Ingle's method and to compare it with actual working length using visual method. Materials and Methods: A total number of 52 single-rooted human teeth mounted on blocks of dental stone were subjected to cone-beam computed tomography (CBCT) by tracing a line between the apical foramen and the corresponding cusp tip from the scans taken before instrumentation. The measurement was taken in two planes in preoperative periapical radiographs. Working length was calculated using Ingle's method from periapical radiographs. The actual working length was measured using visual method under magnification (×2.5). All the measurement procedures were performed by an endodontist and a radiologist. Data were analyzed using SPSS software version 15. Results: One sample t-test was applied to compare between the actual working length determined by the visual method and the working length determined by CBCT, and Ingle's method showed that there was no statistically significant difference (P > 0.05) between the groups. Inter-examiner reliability test using Cronbach's alpha showed a good agreement between the radiologist and the endodontist for both periapical radiography and CBCT. Conclusion: The preoperative CBCT is better than Ingle's method in determining working length within a narrow range of ±0.5 mm. If preoperative CBCT scans are available, the dentist should make the use of the scan for determining the working length instead of exposing them for repetitive radiographs.
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