This project has three specific aims: 1) Extending the study on determining the effects of altered proprioceptive feedback on the neuromuscular system and craniofacial morphology in response to tactile stimulation of the tongue; 2) Determine what characteristics of programmed sensory stimulation may modify craniofacial muscles and cranioskeleton; 3) Determine the direct effect of chronic motor nerve stimulation on the cranioskeleton. Rhesus monkeys will be used as the experimental animal and electrodes will be chronically implanted within the mesencephalic trigeminal nucleus to synaptically recruit motor neurons of the trigeminal motor system, and directly within the motor nucleus. The stimulus will be applied at two different frequencies (i.e. 5/sec continuously and 30/sec for 10 sec of every minute) for the same total number of pulses to unilaterally recuit mandibular elevator muscles and the digastric muscle. The stimulation will be applied by a free running constant current pulse generator. Muscles will be analyzed by electromyography, histochemistry and computer tomography to ascertain long-term changes in the neuromuscular system to specific stimulation parameters. The cranioskeleton will be analyzed by standard radiographs and computer tomography to ascertain for the long-term changes which are expected to occur within 12 months. The long-term objectives of the proposal are to determine what characteristics of active muscle recruitment in terms of frequency of discharge, level of discharge and total duration, will modify bone density or reshape the bone. The project is based on the concept that muscle has specific properties that modify bone and that these specific properties reside in the active recruitment of motor units at a certain frequency and intensity. The project emphasizes that craniofacial muscles are one key factor in reshaping some aspects of the mandible. The interaction between form and function is important in the field of orthodontic treatment, growth and development of the craniofacial region, and orthopedics, and this project focuses on those aspects of muscle which might relate to bone reshaping.
