TThe Effect of Head Position on Crown/Root Ratio Assessed from Panoramic Radiographs

Assessment of crown/root ratio is important in many clinical situations. In orthodontics, practitioners commonly use panoramic radiographs to assess external orthodontically induced apical root resorption. Unfortunately, using panoramic radiographs for this purpose may not lead to reliable and accurate conclusions due to multiple drawbacks of the technique. This research focuses on assessment of crown/root ratio measurements of teeth from dried skulls and the possible effect of patient positioning in the panoramic machine on the measurements. We also evaluated the accuracy of the crown/root ratio of incisors and canines measured on panoramic radiographs at ideal head position compared to the same measurements performed on cone beam computer tomographs (CBCT). The sample consisted of 24 dried skulls. Panoramic and CBCT radiographs were taken. Panoramic radiographs were taken under 7 different head positions. Baseline head position (0 ) was established when the horizontal laser orientation line passed through Porion-Orbitale. The skull was then tilted +5o, +10o, +15o upward and -5o, -10, -15o downward. Crown/root ratios of all teeth were measured on panoramic radiographs. Only incisors and canines were measured on the CBCT. We found upward/downward head tilt to significantly affect crown/root ratio measurements of all groups of teeth except lower incisors. Maxillary teeth were more sensitive to upward head tilt, while downward head tilt was more forgiving, affecting only molars. There were no differences in crown/root ratio measurements of lower incisors and canines between panoramic radiographs at ideal head position and CBCT scans. However, there were differences in crown/root ratio measurements of upper incisors and canines between panoramic radiographs at ideal head position and CBCT scans.