This article reviews about the definition of ectopia and impaction;the development of maxillary canine;etiology ,occurrence, assessment and treatment of impacted canine.

• 本篇报告回顾上颚未萌出异位及阻生犬齿的定义、生长发育、阻生及未萌出的原因、发生率、评估方法及临床治疗等之相关文献。