Modified Versus Clear Twin Block for Skeletal Class II Malocclusion

Skeletal and dentofacial anomalies, particularly Class II malocclusion due to mandibular retrusion, represent one of the most prevalent orthodontic problems during growth. Functional appliances, especially the Twin Block appliance, are widely used to enhance mandibular development and correct jaw discrepancies. However, variations in treatment protocols, particularly regarding advancement mechanics and appliance modifications, may influence both skeletal outcomes and temporomandibular joint (TMJ) response.

This study aims to investigate the effects of a modified Twin Block appliance, incorporating progressive mandibular advancement and additional design modifications such as lower lip pads intended to influence muscular activity, compared to a conventional clear Twin Block appliance.

A two-arm randomized controlled trial will be conducted on growing patients aged 10-13 years diagnosed with skeletal Class II malocclusion due to mandibular retrusion. Participants will be randomly allocated into two equal groups using a computer-generated randomization sequence with allocation concealment.

Skeletal and dental changes will be evaluated using lateral cephalometric radiographs and cone-beam computed tomography (CBCT), with particular attention to condylar morphology, joint space dimensions, and craniofacial skeletal relationships. TMJ health will be assessed using the Helkimo Index. Patient comfort, pain perception, and functional adaptation will be evaluated using validated questionnaires administered at multiple time points throughout the treatment period.

Radiographic and clinical assessments will be performed at baseline (T0) and after 7 months of functional appliance therapy (T1). Repeated patient-reported outcome measures will be collected at predefined intervals during treatment.

The objective of this study is to determine whether the modified Twin Block appliance provides superior skeletal and functional outcomes while maintaining temporomandibular joint safety and improving patient tolerance compared to the conventional appliance.

Inclusion criteria

• Systemically healthy patients.
• Patients willing to accept removable functional appliance therapy.
• Skeletal Class II malocclusion (Angle Class II Division 1).
• Skeletal Class II due to mandibular retrusion (ANB ≥ 5°, 6 mm ≤ OJ ≤ 13 mm , SNB ≤ 78°, with normal maxillary position).
• Growth stage corresponding to MP3 stage or pre-pubertal peak according to hand-wrist radiograph (Björk and Helm, 1967).
• No severe dental crowding in the dental arches and no significant maxillary dental protrusion.
• Absence of congenital anomalies, trauma, burns, or surgical scars affecting the temporomandibular joint or craniofacial structures.
• Absence of systemic or rheumatologic diseases affecting the temporomandibular joint.

Exclusion criteria

• Presence of clinical signs or symptoms of temporomandibular joint disorders.
• Functional mandibular deviation.
• Previous orthodontic treatment.