Orthodontic treatment of acquired open bite accompanied with extreme mesially inclined mandibular molars

Acquired open bite mainly occurs after adolescence and is caused by a pathological or biological process. We herein report the case of an 18-year and 10-month-old Japanese woman. Her chief complaint was difficulty with mastication. Only distal cusps of first molars and second molars had contact. An angle class II molar relationship and extreme mesially inclined mandibular first molars were observed. The degree of overjet was +6.1mm and overbite was -2.0mm. There were no symptoms or abnormal findings in temporomandibular joints by radiography and magnetic resonance imaging. A skeletal class II jaw relationship was indicated. Therefore, the patient was diagnosed with a skeletal class II acquired open bite malocclusion accompanied with extreme mesial inclination of mandibular first molars. Orthodontic treatment with extraction of maxillary first premolars was performed. After stabilizing the maxillary dental arch, mandibular molars were uprighted and intruded by class III elastics. After treatment, overjet was +3.0mm and overbite was +2.3mm. Occlusal cusp-fossa relationships were established and canine relationships were class I. The lower occlusal plane and mandible were rotated counterclockwise, which helped to achieve proper overbite. After 2 years of retention, occlusion was well maintained.