Lower incisor extraction is an effective option for treating lower anterior crowding in patients with a good facial profile, Class I molar occlusion, and narrow upper incisors. This report describes the successful treatment of an adolescent patient with lower anterior crowding and a transposed maxillary canine and premolar treated by extracting a lower incisor and keeping the transposed positions of the teeth. With the use of retainers, treatment results were stable up to the 2-year postretention visit. However, upon a 15-year postretention appointment, the fixed retainer had been removed and the removable retainer was no longer in use, which resulted in relapse of lower anterior alignment. Moreover, the transposed canine had extruded during this period, causing occlusal interference and gingival recession, as well as loss of tooth vitality, which indicates the importance of maintaining orthodontic retainers for long-term stable occlusion.
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