PLASTICITY OF CRANIOMANDIBULAR MUSCLE FUNCTION - P-31 MAGNETIC-RESONANCE SPECTROSCOPY OF THE RABBIT MASSETER MUSCLE

The masseter muscle was studied during postnatal development of the ra bbit from the juvenile to adult stage in which the oral function was a ltered during maturation by modifying the diet to soft food. The muscl e was assessed using phosphate magnetic resonance (P-31 NMR) spectrosc opy with a single-turn copper surface coil to study potential changes in phosphate metabolism. The P-31 NMR spectra consisted of five peaks related to unbound forms of inorganic phosphate (Pi), creatine phospha te (PCr), and three peaks related to the adenosine triphosphate (ATP). The masseter was assessed in one group of five rabbits at 8 weeks pos tnatally (juvenile) and after 4 months of this experimental group mast icating on soft food. They were compared with a control group of five rabbits raised on a normal hard diet. The Pi/PCr ratio increased in th e adult masseter much higher during twitching, tetany, and periodic co ntraction than in the juvenile regardless as to whether the adult anim al had been raised from the juvenile period on soft or hard diet. Ther e were relatively few differences between the experimental adult anima ls raised on a soft diet and the normal adult animals despite the soft diet animals demonstrating a significantly lower weight and smaller m uscle mass. These findings suggest that chronic underuse of the masset er muscle by decreasing the masticatory loads has a minimal effect on the phosphate metabolism of the maturing masseter.