Comparison of the radiographic appearance of root canal size to its actual diameter

Clinically, the apparent radiographic diameter size does not always seem to correspond to the true canal size. The objective of this study was to compare canal size on periapical radiographs with the actual canal diameter as determined histologically. Periapical radiographs were exposed on 36 teeth on 5 human cadavers. Mesial-to-distal boundaries of canals were measured in the cervical, middle, and apical thirds. The teeth were extracted, the roots histologically processed, and cross-sections made in the cervical, middle, and apical thirds. Measured values of diameter from radiographs were compared with true canal widths as measured from the corresponding level of histological sections by using a correlated t test. All sections of all roots demonstrated a canal histologically, although some regions had no canal visible radiographically. In general, there was statistically no difference (p less than 0.001) between the histological and radiographic measurements even when pulpal calcifications were present. However, in some roots there were marked discrepancies between radiographs and histological sections as to canal diameter.