Comparative Evaluation of a Clear Functional Jaw Corrector and a Conventional Twin Block Appliance in Monozygotic Twins with Skeletal Class II Malocclusion: A Case Report

Functional appliance therapy is widely employed for the management of skeletal Class II malocclusion in growing patients. However, treatment outcomes are influenced by multiple biological and behavioural variables, including genetic background, craniofacial growth pattern, neuromuscular adaptability, and patient compliance. These factors often limit the ability to directly compare the effectiveness of different appliance systems in routine clinical studies. Monozygotic twin investigations provide a valuable biological model by minimizing genetic and environmental variability, thereby enabling a more accurate assessment of appliance related effects. This case report presents a comparative evaluation of a clear functional jaw corrector and a conventional twin block appliance in monozygotic twin patients presenting with similar skeletal and dental Class II malocclusion. Two 11-year-old female monozygotic twins at cervical vertebral maturation index stage 3 exhibited comparable skeletal Class II patterns, vertical growth tendencies, proclined maxillary incisors and convex soft tissue profiles. Twin A was treated using a removable clear functional jaw corrector fabricated by incorporating mandibular advancement blocks into a 1.5-mm Essix retainer sheet, whereas Twin B was treated using a conventional twin block appliance. Treatment objectives, appliance wear protocol, and treatment duration were identical for both patients. Post-treatment clinical and cephalometric evaluation demonstrated improvement in sagittal jaw relationships, facial profile, and occlusal relationships in both twins. However, differences were observed in the magnitude of skeletal correction, dentoalveolar changes, vertical control, and molar and canine relationship correction. The findings emphasize appliance specific effects under near identical biological conditions and support the scientific relevance of monozygotic twin comparisons in functional appliance research.