[Biomechanical aspects of the spring-active-appliance during the night sleep]

1. During the night the mandibular activities caused by the spring-active-appliance are increased. Seven times more mandibular movements occur compared to the activator according to Andresen-Häupl. 2. A distinct increased mandibular activity during the time the patient fall asleep or in the wake up time can be registered, especially in the adaptation phase or after reactivating the springs. 3. Powerful activities of the m. masseter did not lead to an inversion of the mandibular movement. 4. A regular movement of the mandible is the most frequent movement whilst mandibular activities. 5. During the night asymmetrical activities of the mm. masseters very often occur. 6. An inversion of the mandibular movement, that means a counter-clockwise-rotation of the m. mandible, occurs if the force direction of the m. temporalis is directed more distally or if the ratio between masseter- and temporalis activities are for the benefit of the temporalis-activities. 7. During the night the springs in the spring-active-appliance cause a counter-clock wise-rotation of the mandible without mandibular activities around a transverse axis in the region of the molars. This leads to an approach of the anterior teeth whilst the distance between the molars remains constant. 8. Contrary movements and rotations around a transverse axis in the region of the molars lead to a distraction of the condyle of about one millimeter.