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The effects of Twin Blocks: a prospective controlled study
1Department of Orthodontics, Chesterfield Royal Hospital, Derbyshire, U.K.
Summary
The Twin Block appliance effectively reduces overjet by advancing the mandible and altering incisor positions, with minimal impact on maxillary growth. This orthodontic treatment aids in correcting Class II malocclusions.
Area of Science:
- Orthodontics
- Craniofacial Growth
- Dental Biomechanics
Background:
- Functional appliances are widely used in orthodontics to manage skeletal discrepancies.
- The Twin Block appliance is a popular choice for correcting Class II malocclusions.
- Understanding the net effects of functional appliances, accounting for normal growth, is crucial for treatment evaluation.
Purpose of the Study:
- To investigate the net effects of the Twin Block functional appliance on craniofacial skeletal relationships.
- To differentiate the effects of Twin Block treatment from the effects of normal growth in an untreated control group.
- To quantify changes in skeletal and dental parameters, including overjet and incisor positions.
Main Methods:
- Prospective controlled study comparing a Twin Block treatment group (36 subjects) with an untreated control group (27 subjects).
- Lateral cephalograms were analyzed pre- and post-treatment for the intervention group and over a similar time interval for the control group.
- Data were annualized and analyzed using multiple regression to determine net treatment effects.
Main Results:
- Twin Block treatment significantly reduced the ANB angle by 2.0 degrees, primarily due to an increase in the SNB angle (1.9 degrees).
- A net increase of 2.4 mm in the Ar-Pog dimension was observed, indicating mandibular advancement beyond normal growth.
- Overjet reduction was achieved through maxillary incisor retroclination (10.8 degrees), mandibular incisor proclination (7.9 degrees), and mandibular forward movement.
Conclusions:
- The Twin Block appliance effectively promotes mandibular growth and corrects skeletal Class II malocclusions.
- The observed skeletal changes are primarily due to mandibular advancement and dental compensation, with no significant maxillary growth restraint.
- The appliance demonstrates efficacy in reducing overjet and improving sagittal relationships, contributing to improved buccal segment relationships.