RESUMO
OBJECTIVE: The purpose of this study was to evaluate the effect of head position changes on the root parallelism between adjacent teeth on panoramic radiographs. METHODS: A model with normal occlusion was constructed in the SolidWorks program, then RP (rapid protyping) model was fabricated. The model was repeatedly imaged and repositioned five times at each of the following nine positions: ideal head position, 5degrees C up, 10degrees C up, 5degrees C down, 10degrees C down, 5degrees C right, 10degrees C right up, and 5degrees C right rotation, 10degrees C right rotation. Panoramic radiographs were taken by Planmeca ProMax and the angle between the long axes of adjacent teeth was directly measured in the monitor. RESULTS: Axes of adjacent teeth tended to converge toward the occlusal plane when the head tilted up and converged in the opposite direction to the occlusal plane when the head tilted down. Anterior teeth showed the most notable differences. When one side of the head tilted up 5degrees C and 10degrees C along the anteroposterior axis (Y axis), tooth axes of the same side tended to converge toward the occlusal plane and tooth axes of the opposite side tended to converge in the opposite direction to the occlusal plane. When the head rotated to one side along the vertical axis (Z axis), the canine and lateral incisor of the same side converged in the opposite direction to the occlusal plane and the canine and lateral incisor of the other side converged toward the occlusal plane. CONCLUSIONS: When assessing the root parallelism on panoramic radiographs, the occlusal plane cant (anteroposterior or lateral) or asymmetry of the dental arch should be considered because these can cause distortion of tooth axes on panoramic radiographs.