ORTHODONTIC FORCES EXERTED BY ACTIVATORS WITH VARYING CONSTRUCTION BITE HEIGHTS

The present study was conducted to investigate the nature of forces in duced with activators by measuring strains, electromyogram (EMG) and e lectroencephalogram (EEG) during a 2-hour sleep period. Fifteen adoles cent patients with Class II and Class III malocclusions, (30 subjects) were used. Four types of activators were made for each patient with c onstruction bites taken at incisal edge clearances of 2, 4, 6, and 8 m m 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 11 group and from approximately 130 to 200 gf i n 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 t he Class II and Class III groups, respectively. Duration of forces gen erated by passive tension was most significantly longer than that of a ctive contraction of the jaw closing muscles, irrespective of the cons truction bite heights. It is concluded that passive tension, derived f rom viscoelasticity of soft tissues, plays a more important role in in ducing changes than phasic stretch reflex during jaw orthopedic therap y with activators.