The management of horizontal root fracture still presents a challenge to clinicians. The case of a 10-year-old boy with a horizontal root fracture in the left maxillary central incisor (tooth number 21) is described here. The fracture was present at the junction of the apical and the middle thirds. We report both the emergency care and the 5-year follow-up. At the same time, an orthodontic treatment was planned for a retained maxillary cuspid (tooth number 23), first composed of a high-pull headgear and then by a fixed multi-bracket appliance. Today, the tooth number 21 remains vital and symptomless. This report highlights the successful management of a horizontally fractured tooth requiring orthodontic treatment. Our work also underlines the advantages of 3D images [cone-beam computed tomography (CBCT)] in positive and differential diagnosis especially in the event of a suspicion of post-traumatic complication.