Jacoby H
Am J Orthod. 1983 Aug;84(2):125-32. doi: 10.1016/0002-9416(83)90176-8.
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.
牙齿阻生的病因长期以来一直与牙弓长度不足有关。这对大多数阻生情况是成立的，但对上颌尖牙的腭侧阻生则不适用。本研究表明，85%的腭侧阻生尖牙有足够的萌出空间。上颌尖牙的牙胚楔入鼻腔、眼眶和上颌窦前壁之间。侧切牙和第一前磨牙的牙胚位于尖牙腭面的后方。牙弓长度不足会使上颌尖牙无法“越过”牙胚、鼻腔或鼻窦而重新出现在腭部。如果上颌骨有额外的空间，尖牙就可能发生腭侧阻生。这个空间可以由以下情况提供：(1)上颌骨基部过度生长；(2)侧切牙先天缺失或呈钉状侧切牙所产生的空间；(3)侧切牙或第一前磨牙的萌出受到刺激。在这些情况下，尖牙可以在骨内自由“潜入”并发生腭侧阻生。上颌-前上颌缝的发育异常也会改变上颌尖牙的萌出方向。
