14.5.3 Radiographic assessment
Where the canine is not palpable it should be assessed radiographically. A periapical
radiograph shows whether the primary canine root is resorbing normally and whether
the canine follicle is enlarged. If the apex of the primary canine is not resorbing, with
either no root resorption or only lateral resorption, the path of eruption of the
permanent canine may be abnormal. However, a single radiograph cannot fully
determine the unerupted canine's position relative to the other teeth⎯two views are
needed for this, either at right angles to each other or for the parallax technique.
Parallax technique
This method, also known as the tube-shift method, compares two views of the area
taken with the X-ray tube in two different positions. 942HFigure 14.18 (a) shows a palatal
canine on a periapical film being taken with the tube positioned forward or mesially.
A second film taken with the tube positioned further distally gives an image which
apparently shows the canine crown in a different position relative to the adjacent roots
(943HFig. 14.18 (b)). In this case the image of the canine appears to have shifted distally
when compared with the first film, that is in the same direction that the tube was
moved, which indicates that the canine is palatal to the other teeth. An apparent shift
in the opposite direction to the tube shift would indicate that the tooth is lying
buccally to the other teeth.
The parallax technique works best using two periapical views, but with care it can
also be applied to a panoramic tomogram with a standard occlusal view, using vertical
shift (944HFig. 14.19 (a) and (b)). The tube position is low down for the panoramic
tomogram and much higher for the occlusal view, and so in this example the palatal
canine appears to be nearer the incisor apices in the occlusal view, i.e. its apparent
movement is upwards with the tube. The size of the image of a displaced tooth on a
panoramic radiograph is another indicator, being enlarged if it is palatal and reduced
if it is labial or buccal. However, a periapical view is still necessary to check for
associated pathology, and this can be used with the occlusal view to make another
parallax pair. The combination of panoramic, standard occlusal, and periapical views,
such as that in 945HFig. 14.19, allows comprehensive assessment of a maxillary canine.
Two films at right angles
This method is more applicable to the specialist as it involves a taking lateral skull
view and a posteroanterior (p-a) view: possibly a p-a skull, but more commonly using
a panoramic radiograph for the same purpose (946HFig. 14.20 (a) and (b)). The lateral skull
view shows whether the canine crown is buccal or palatal to the incisor roots, and the
p-a or panoramic view shows how close it is to the mid-line. The angulation of the
tooth and its vertical position are assessed using both views. An intraoral view must
also be taken to check for any associated pathology.
The position of the impacted canine's crown should be determined as being buccal,
palatal, or in the line of the arch. The degree of displacement should be assessed
horizontally, that is how close it is to the mid-line, in terms of how far it overlaps the
roots of the incisors. The canine crown's vertical position is assessed relative to the