RESUMEN
Orthodontic treatment is thoroughly planned considering the patient's facial and dental characteristics, the main complaint, treatment time and the orthodontist's experience. Transposition is a form of ectopia, in which two adjacent teeth exchange positions in the dental arch. Transposition can be partial or complete. This article reports the treatment of a female patient with two kinds of tooth transposition managed in the mixed and permanent dentitions. A girl, aged eight years and three months, came to routine paediatric consultation with an ectopic permanent mandibular left lateral incisor in the mixed dentition. Radiographic analysis indicated partial transposition of the permanent mandibular left lateral incisor and canine (Md.L2.C), and development of a complete tooth transposition between the permanent maxillary right first pre-molar and canine (Mx.C.P1). The patient was treated in two phases. The first, in the mixed dentition, and the second, in the permanent dentition with a three-year follow-up between them. These challenging treatment approaches are described in detail, including the mechanics used. The key points of this treatment were early diagnosis of the ectopic mandibular lateral incisor, use of light forces and interphase patient follow-up. These determined the best time to start the second treatment phase, enabling achievement of aesthetic and functional outcomes, and the results remained stable one year after the end of orthodontic treatment.