The etiology of maxillary canine impactions.

The etiology of tooth impactions has long been related to an arch-length deficiency. This is valid for most impactions, but not for palatal impaction of the maxillary canine. This study shows that 85 percent of the palatally impacted canines have sufficient space for eruption. The bud of the maxillary canine is wedged between the nasal cavity, the orbit, and the anterior wall of the maxillary sinus. The buds of the lateral incisor and the first premolar are located behind the canine's palatal surface. An arch-length deficiency will not allow the maxillary canine to "jump" the buds, the nasal cavity, or the sinus in order to reappear in the palate. A canine can be palatally impacted if an extra space is available in the maxillary bone. This space can be provided by (1) excessive growth in the base of the maxillary bone, (2) space created by agenesis or peg-shaped lateral incisors, or (3) stimulated eruption of the lateral incisor or the first premolar. In those conditions the canine is free to "dive" in the bone and to become palatally impacted. A dysplasia in the maxillary-premaxillary suture can also modify the direction of the maxillary canine's eruption.