트윈블록 장치를 이용한 심한 골격성 Ⅱ급 및 치성Ⅰ급 부정교합 환자의 치료

Treatment of a Severe Skeletal Class II and Dental Class I Malocclusion Patient Using a Twin Block Appliance

This case report describes a 12-year and 4-month-old male patient who presented with a skeletal Class II malocclusion resulting from mandibular underdevelopment. Despite the skeletal discrepancy, the patient exhibited dental Class I canine and molar relationships—likely due to compensatory adjustments, such as mesial tipping of the mandibular molars and labial inclination of the mandibular incisors in response to the retruded mandible. In cases with severe lip protrusion, extracting the maxillary and mandibular premolars to address the issue can inadvertently lead to an excessive retraction of the maxillary dentition, compromising occlusal balance and yielding a blunted nasolabial angle along with an unesthetic facial profile. To avert these adverse outcomes, the treatment plan initially focused on advancing the retruded mandible using a Twin Block appliance. Although this approach temporarily produced Class III canine and molar relationships, it allowed for a functional improvement in skeletal harmony. Subsequently, extraction of the mandibular first premolars was performed, followed by retraction of the mandibular anterior teeth to reestablish a Class I canine relationship with appropriate overjet and overbite. This combined strategy of functional appliance therapy and fixed orthodontic treatment effectively addressed both skeletal and dental discrepancies, providing an instructive example of managing a growing patient with skeletal Class II malocclusion and dental Class I relationships.