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

Background: 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, orofacial resting postures, and patient adherence. These factors often limit direct comparison of different appliance systems. Monozygotic twin studies provide a unique biological model by minimizing genetic and environmental variability, allowing more accurate evaluation of appliance-specific effects. Methods: This case report presents a comparative evaluation of a clear functional jaw corrector and a conventional twin block appliance in two 11-year-old female monozygotic twins at cervical vertebral maturation index stage 3. Both patients exhibited similar skeletal Class II patterns, vertical growth tendencies, proclined maxillary incisors, and convex soft tissue profiles. Twin A was treated with a removable clear functional jaw corrector fabricated using mandibular advancement blocks incorporated into a 1.5-mm Essix retainer sheet, while Twin B received a conventional twin block appliance. Treatment objectives, wear protocol, and duration were identical. Neither patient received orofacial myofunctional therapy. Results: Post-treatment clinical and cephalometric evaluation demonstrated improvement in sagittal jaw relationships, facial profile, and occlusal relationships in both patients. However, differences were observed in the magnitude of skeletal correction, dentoalveolar effects, vertical control, and the extent of molar and canine relationship correction. Conclusions: Both appliance designs were effective in improving sagittal relationships under similar biological conditions, with minor differences favoring the clear functional jaw corrector. However, the findings also highlight that orthodontic appliance therapy alone does not address underlying orofacial myofunctional factors, emphasizing the importance of incorporating functional assessment and adjunctive myofunctional therapy for optimal and stable outcomes.