Orthodontic treatment of Class II malocclusion in a patient with hypophosphatasia

Hypophosphatasia (HPP) is an inherited skeletal dysplasia characterized by low serum alkaline phosphatase (ALP) activity, essential for bone mineralization. Its main manifestations include defective bone mineralization and premature loss of primary teeth. This case report describes a patient with HPP who underwent orthodontic treatment using edgewise appliances. Despite the condition, no premature tooth loss or alveolar bone loss was observed. The patient presented with a skeletal Class II, Angle Class II molar relationship, and dental crowding. Orthodontic treatment began with the successful distalization of maxillary molars to confirm the possibility of normal tooth movement before starting ALP replacement therapy. After initiating ALP therapy, the maxillary and mandibular first premolars were extracted, and full-arch treatment started when the patient was 16 years, 9 months. Abnormal tooth movement and gingival recession were not observed. The treatment goals of achieving a favorable facial profile and acceptable occlusion were successfully met. Contrary to expectations of relapse in HPP patients, stable occlusion was maintained after 2 years of retention. This is because the patient had normal bone mineral density and used not only removable retainers but also canine-to-canine bonded flexible spiral-wire lingual retainers in the maxillary and mandibular arches. Long-term follow-up is crucial because of the high relapse risk associated with HPP. Further research on orthodontic treatment in patients with HPP is necessary to establish comprehensive guidelines and improve clinical outcomes.