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Orthodontic forces exerted by activators with varying construction bite heights
1Department of Orthodontics, Osaka University Faculty of Dentistry, Japan.
Summary
This study reveals that passive tension from soft tissues, not muscle activity, drives orthopedic changes during activator therapy for malocclusion. Higher activator settings increase force magnitude and alter direction, impacting jaw alignment.
Area of Science:
- Orthodontics
- Biomedical Engineering
- Physiology
Background:
- Orthodontic treatment for Class II and Class III malocclusions often utilizes activators.
- Understanding the forces generated during activator use is crucial for treatment efficacy.
- Previous research has focused less on the role of passive tissue tension versus muscle activity.
Purpose of the Study:
- To investigate the forces induced by activators during sleep.
- To measure strains, electromyogram (EMG), and electroencephalogram (EEG) during activator use.
- To differentiate the contribution of passive tissue tension versus muscle contraction in activator therapy.
Main Methods:
- Fifteen adolescent patients with Class II and III malocclusions (30 subjects) participated.
- Four activator types with varying construction bite heights (2-8 mm) were used.
- Strains, EMG, and EEG were recorded during a 2-hour sleep period.
Main Results:
- Passive tissue tension significantly increased with higher construction bites (p < 0.01).
- Force direction shifted with increased bite heights in both Class II and III groups.
- Passive tension duration exceeded active muscle contraction duration, regardless of bite height.
Conclusions:
- Passive tension from soft tissue viscoelasticity is a primary driver in activator therapy.
- Phasic stretch reflex is influenced more by passive tension than active muscle contraction.
- Optimizing construction bite height is key for effective orthopedic changes with activators.