Ankylosis is generally discovered following resistance to orthodontic displacement of an impacted canine. This retrospective study, drawing on direct perioperative observation of impacted teeth and of their sites, is intended, among other things, to analyze the causes of resistance to orthodontic movement and to report on the therapeutic interest of the surgical tooth displacement technique in this type of clinical situation. We demonstrate that primary coronal ankylosis can be detected by the orthodontic practitioner using radiographic records, that cervical ankylosis consequent to operative trauma during release is necessarily unpredictable and that it should be suspected when the tooth resists traction for more than 3months in the absence of any other obvious cause of resistance. Hence, the risk of ankylosis linked to the level of surgical difficulty increases with the depth of coronal submergence within the bone. Moreover, the immediate placement of traction following release reduces the risk of ankylosis. In addition, temporarily suspending traction is a risk factor for secondary apical ankylosis. Finally, surgical positioning should be borne in mind as the final effective option when faced with any form of dental retention.