Measurement accuracy of dental cone-beam computed tomography for assessing submillimeter distances between implant and mandibular canal: a phantom study

Accurate assessment of the distance between dental implants and the mandibular canal is essential for preventing nerve injury. Although cone-beam computed tomography (CBCT) is widely used for implant planning, its accuracy in resolving submillimeter distances remains uncertain. This study evaluated the measurement accuracy of CBCT for assessing distances below 1.0 mm.

A custom phantom enabling 0.0–1.0 mm implant–canal distances in 0.1-mm increments was developed. CBCT images were acquired at varying distances, positional shifts (X, Y, Z), and tube voltages. Five dentists involved in implant treatment measured the implant–canal distances using medical-grade and general-purpose monitors. Measurement error and contributing imaging factors were statistically analyzed.

CBCT did not reliably distinguish distances ≤ 0.4 mm, with the greatest instability observed at 0.3 mm (interquartile range = 0.121). Although a linear trend was observed from 0.1 to 0.4 mm, variability exceeded clinically acceptable limits. For distances ≥ 0.5 mm, reproducibility was high, but CBCT consistently underestimated the true gap by 0.2–0.3 mm. The central field of view produced the most stable measurements, whereas accuracy decreased with off-center positioning. Tube voltage and monitor type had minimal influence on measurement accuracy.

CBCT cannot accurately identify implant–canal distances ≤ 0.4 mm, which may directly affect clinical risk assessment. Even for distances ≥ 0.5 mm, CBCT underestimates the true distance by 0.2–0.3 mm. These findings provide practical guidance for setting safe margins in implant planning and postoperative evaluation.