Accuracy of linear and angular measurements on panoramic radiographs taken at various positions in vitro.

The accuracy of measurement of tooth length and angulation on dental panoramic tomograms (DPTs) is thought to be highly dependent on head positioning technique. A model representing the dentition and the functional occlusal plane was designed using an acrylic framework and stainless steel wires. The aim was to investigate whether varying the position of the model affects the linear and angular measurements on DPTs. Four different positions were investigated: initial position representing natural head posture (NHP) (T1); lateral right cant of the occlusal plane (T2); lateral left cant of the occlusal plane (T3); and tilting the occlusal plane up anteriorly (T4). On each DPT, four sets of measurements were recorded: (1) Vertical linear measurements of the stainless steel pins and ratio calculations of the 'crown' and 'root' segments (represented by the wire above and below the occlusal plane, respectively); (2) angular measurements of the pins relative to the occlusal plane; (3) angular measurements of the pins relative to a constructed reference line; and (4) angular measurements of pins relative to each other in the same segment. The results showed a significant error (P < 0.05) in all measurements when the occlusal plane was tilted up anteriorly by 8 degrees. A lateral cant of the occlusal plane by less than 10 degrees without an upward anterior rotation showed no significant effect on the measurements. This would suggest that there is some tolerance of variation in head position.