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Abstract
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, 5° up, 10° up, 5° down, 10° down, 5° right, 10° right up, and 5° right rotation, 10° 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 5° and 10° 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.
Figures and Tables
Fig 1
3D model and axes of rotation that were used in this study. X, transverse axis; Y, anteroposterior axis; Z, vertical axis. The model was constructed using SolidWorks program. Arrows show the model being tilted anteroposteriorly along the transverse axis (X axis), tilted laterally along the anteroposterior axis (Y axis), and rotated laterally along the vertical axis (Z axis).
Fig 2
Model positioning in the panoramic radiograph machine. A, Frontal view; B, lateral view; midsagittal positioning beam (a) was aligned to model's midline and focal layer positioning beam (b) was aligned between the upper lateral incisor and upper canine.
Fig 3
Angular measurement of panoramic radiographs using the measurement tool (Cobb's angle) of the π-ViewStar program. a, Angle between long axes of adjacent teeth was measured on the occlusal side when long axes of adjacent teeth was converged toward the occlusal plane; b, angle between long axes of adjacent teeth was measured on the apical side when long axes of adjacent teeth were converged in the opposite direction to the occlusal plane. This was assigned a negative value (??.
Fig 4
Angle between long axes of adjacent teeth at ideal head position and head positions tilted anteroposteriorly along the transverse axis (5° up, 10° up, 5° down, and 10° down). Values with (?? indicate that the long axes of adjacent teeth were converged in the opposite direction to the occlusal plane.
Fig 5
Angle between long axes of adjacent teeth at ideal head position and head positions tilted laterally along the anteroposterior axis (5° right up and 10° right up). Values with (-) indicate that the long axes of adjacent teeth were converged in the opposite direction to the occlusal plane.
Fig 6
Angle between long axes of adjacent teeth at ideal head position and head positions rotated laterally along the vertical axis (5° right rotation and 10° right rotation). Values with (-) indicate that the long axes of adjacent teeth were converged in the opposite direction to the occlusal plane.
Table 2
Paired t-test comparisons of root parallelism between ideal head position and head positions tilted anteroposteriorly along the transverse axis (X axis)
Numbers in the measurement row indicate tooth number (FDI system); ∠, root parallelism between adjacent teeth; mean difference (°), amount of change in measured angulation between ideal position and various head position; values with (-) indicate that the measured long axes of adjacent teeth were converged in the opposite direction to the occlusal plane; Sig, significance; NS, no significance; *p < 0.05; †p < 0.01; ‡p < 0.001.
Table 3
Paired t-test comparisons of root parallelism between ideal head position and head positions tilted laterally along the anteroposterior axis (Y axis)
Numbers in the measurement row indicate tooth number (FDI system); ∠, root parallelism between adjacent teeth; mean difference (°), amount of changes in measured angulation between ideal position and various head positions; values with (-) indicate that the measured long axes of adjacent teeth were converged in the opposite direction to the occlusal plane; NS, no significance; *p < 0.01; †p < 0.001.
Table 4
Paired t-test comparisons of root parallelism between ideal head position and head positions rotated laterally along the vertical axis (Z axis)
Numbers in the measurement row indicate tooth number (FDI system); ∠, root parallelism between adjacent teeth; mean difference (°), amount of changes in measured angulation between ideal position and various head positions; values with (-) indicate that the measured long axes of adjacent teeth were converged toward opposite of the occlusal plane; NS, no significance; *p < 0.01; †p < 0.001.
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