Abstract
This case report discusses the genetic influence and treatment of class III malocclusion in identical twin sisters, in their early 20s, who presented with mandibular prognathism. Both exhibited concave profiles with hypodivergent growth patterns, but Sister A had a more pronounced concavity. Diagnosis revealed skeletal class III malocclusion with mandibular prognathism and negative overjet (9 mm in Sister A, 6 mm in Sister B). Treatment involved pre-surgical orthodontics, bilateral sagittal split osteotomy (BSSO) with mandibular setbacks (7 mm for Sister A, 5 mm for Sister B), followed by post-surgical orthodontics and retention. Both sisters achieved improved facial aesthetics, class I occlusion and functional stability. However, Sister B experienced transient paraesthesia and a bad split, leading to temporary splinting of the second molar. The case highlights the genetic basis of mandibular prognathism, the effectiveness of BSSO and the importance of meticulous surgical planning and interdisciplinary management for optimal long-term results.