No posterior mandibular displacement in Angle Class II, division 2 malocclusion as revealed with electromyography and sirognathography

The activity of the anterior and posterior temporal, and of the masseter muscles was studied by electromyography and the position of the mandible by sirognathography. The recordings were made in 22 children, aged 8–13 years, with Angle Class II, division 2 malocclusion before and during treatment of their malocclusion. The treatment comprised two phases: proclination of the upper incisors and bite raising with a removable plate, and the subsequent correction of the distal occlusion with an activator. The aim of the study was to reveal signs of anterior mandibular positioning during the treatment.
The electromyographic recordings were made in the rest position of the mandible, and during maximal biting, chewing, and swallowing. The sirognathographic recordings comprised the positions of the mandible at rest, at intercuspation, and during tooth contact during chewing and maximal mandibular movements.
The muscle activity at rest was unchanged during the period of observation. The activity during maximal biting, chewing, and swallowing decreased during the phase of proclination, which was interpreted as a result of occlusal instability. The positions of the mandible at rest, at intercuspation, and during chewing were stable during the treatment. Neither the electromyographic recordings nor the recordings of mandibular positions revealed any signs of anterior mandibular positioning during the treatment of the Class II, division 2 malocclusion.