The effect of tooth position on the image of unerupted canines on panoramic radiographs

The purpose of this study was to evaluate whether panoramic tomograms, whic h are routinely used in orthodontic practice, can provide adequate informat ion to localize an impacted canine. The effect of changes in position and i nclination of an impacted canine on orthopantomograms was investigated in a n experimental set-up. An upper canine was removed from a human skull and r eplaced in a positioning system, enabling simulated positional variations i n impactions. In comparison with the image of a contralateral well-aligned canine, the le ngth of the impacted tooth always decreased or remained unchanged, whereas the tooth width increased or remained unchanged. The angulation of the imag e was unaffected by varying the position of the impacted canine, but altere d when the inclination of the tooth in a sagittal or frontal direction was changed. If there was any transversal shift of the impacted canine on the o rthopantomogram, it was always towards the mid-sagitta I plane. The curvatu re of the tooth increased after dorsal inclination and decreased after vent ral inclination (in comparison with the contralateral well-aligned canine).