Orthodontic forces exerted by activators with varying construction bite heights.
The present study was conducted to investigate the nature of forces induced with activators by measuring strains, electromyogram (EMG) and electroencephalogram (EEG) during a 2-hour sleep period. Fifteen adolescent patients with Class II and Class III malocclusions, (30 subjects) were used. Four types of activators were made for each patient with construction bites taken at incisal edge clearances of 2, 4, 6, and 8 mm vertically. The magnitude of forces generated by passive tension of soft tissues increased significantly (p < 0.01) from approximately 80 to 160 gf in the Class II group and from approximately 130 to 200 gf in the Class III group with varying construction bite heights from 2 to 8 mm. Higher construction bites also significantly changed (p < 0.01) the direction of forces by passive tension from vertical to posterior and from vertical to anterior in relation to the reference plane in the Class II and Class III groups, respectively. Duration of forces generated by passive tension was most significantly longer than that of active contraction of the jaw closing muscles, irrespective of the construction bite heights. It is concluded that passive tension, derived from viscoelasticity of soft tissues, plays a more important role in inducing changes that phasic stretch reflex during jaw orthopedic therapy with activators.
Noro
T
T
Department of Orthodontics, Osaka University Faculty of Dentistry, Japan.
Tanne
K
K
Sakuda
M
M
D000202:Activator Appliances; D000293:Adolescent; D002648:Child; D003799:Dental Stress Analysis; D004548:Elasticity; D004576:Electromyography; D006801:Humans; D016014:Linear Models; D008310:Malocclusion / Q000628:therapy; D008410:Masticatory Muscles / Q000502:physiology*; D010513:Periodontal Ligament / Q000502:physiology; D012026:Reflex, Stretch; D015203:Reproducibility of Results; D012894:Sleep Stages; D014716:Vertical Dimension