Distortion of tooth axes on panoramic radiographs taken at various head positions / 대한치과교정학회지

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.

A comparative study on reliability of the root parallelism of the posterior teeth projected on the orthopantomogram with the 45 degrees oblique cephalogram / 대한치과교정학회지

At present, many orthodontists regard the root parallelism of the posterior teeth important not only in diagnosis and treatment planning but also for predicting posttreatment stability. To evaluate it, they usually refer to the orthopantomogram. At this study, 97 samples were collected from students of Yonsei University, who have well-proportioned face, Angles's class I canine & molar relationships and no crown axis deviation of the posterior teeth including canines. Reliability of the root parallelism observed from orthopantomogram was evaluated by comparison with 45degrees oblique cephalogram. The results were as follows : 1. In comparing the differences between anglular measurements in 45degrees oblique cephalogram & orthopantomogram with 5degrees, those to mandibular plane were significantly less than to occlusal plane in number of items which showed less differences than 5degrees. 2. Compared the root parallelisms in the orthopantomogram with those in 45degrees oblique cephalogram with 1% significance level, parallelism between upper canine & 1st premolar, lower canine & Ist premolar, lower 1st premolar & 2nd premolar, and lower right 2nd molar & 3rd molar showed statistically significant differences. 3. When the significance between the differences of the root parallelism between above two kinds of film and 5degrees was verified by two sided paired t-test, more or less large difference was shown between lower right 2nd molar & 3rd molar, a little larger than 5degrees between lower canine & 1st premolar, smaller at the rest of them. 4. In 45degrees oblique cephalogram, lower canine & 1st premolar showed convergent root arrangements each other, while in orthopantomogram they were divergent each other. All the others except them showed convergency on the upper, divergency on the lower in both films.