Modified Versus Clear Twin Block for Skeletal Class II Malocclusion

Evaluation of the Efficacy of Functional Therapy Using Modified Twin Block Versus Clear Twin Block in Class II Skeletal Patients: A Randomized Controlled Clinical Trial

This study aims to evaluate the effectiveness of a modified Twin Block appliance compared to a conventional clear Twin Block appliance in the treatment of skeletal Class II malocclusion caused by mandibular retrusion in growing patients.

This is a two-arm randomized controlled clinical trial including patients aged 10-13 years diagnosed with skeletal Class II malocclusion. Participants will be randomly allocated into two equal groups.

Skeletal, dental, and soft tissue changes will be assessed using lateral cephalometric analysis and cone-beam computed tomography (CBCT). Additionally, temporomandibular joint (TMJ) health, pain perception, and functional tolerance will be evaluated using standardized clinical indices and patient-reported outcome measures.

The study aims to compare the modified appliance with the conventional design in terms of skeletal improvement, TMJ safety, and patient acceptance.

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.