The effect of changes in tooth position of unerupted canines on cephalograms.

Although many radiographic procedures have been described to localize an impacted canine, they all submit the patient to extra radiation. The purpose of the entire study was to evaluate if the combined interpretation of cephalograms and dental panoramic tomograms (DPTs), which are used in orthodontic practice, can provide adequate information as to the position of impacted canines. In a previous study the radiographic image of impacted canines on DPTs was evaluated. In this investigation, the effect of changes in position and inclination of an impacted canine on cephalograms was studied in an experimental set-up. An upper canine was removed from a human skull and placed in a positioning device to imitate various positions of impaction. Starting from a buccally impacted position, three different displacements were simulated: 10 mm frontally, 10 mm sagittally, and 5 mm vertically. In each of these positions nine different changes in inclination (in the sagittal and the frontal plane) were registered, resulting in 36 different cephalographic exposures. Analysis revealed the following: the degree of vertical and sagittal displacement of the incisal point of the impacted canine, the angulation of the tooth as well as the tooth length, measured on a cephalogram, appeared to give an accurate representation of the experimental set-up. Combining these findings and those from the previous study, it became possible to define a series of points to enable an adequate three-dimensional (3D) estimation of the canine's position. A clinical case of an impacted canine is used as an illustration of this experimental set-up.

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, which are routinely used in orthodontic practice, can provide adequate information to localize an impacted canine. The effect of changes in position and inclination of an impacted canine on orthopantomograms was investigated in an experimental set-up. An upper canine was removed from a human skull and replaced in a positioning system, enabling simulated positional variations in impactions. In comparison with the image of a contralateral well-aligned canine, the length of the impacted tooth always decreased or remained unchanged, whereas the tooth width increased or remained unchanged. The angulation of the image was unaffected by varying the position of the impacted canine, but altered 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 orthopantomogram, it was always towards the mid-sagittal plane. The curvature of the tooth increased after dorsal inclination and decreased after ventral inclination (in comparison with the contralateral well-aligned canine).