An Investigation of Jaw Stiffness in Children

D Finan, A Smith


Stiffness of a muscle-joint complex refers to resistance to applied displacement.  Joint stiffness consists of intrinsic and reflex components, both of which appear to change through development.  In adults, the short latency and powerful excitatory response of the jaw stretch reflex appears to contribute to functional stability of the mandible to external perturbation.  Properties of the jaw stretch reflex in children are similar to that of adults in terms of resultant force magnitude, but children have shorter reflex onset latencies.  Differences in reflex and intrinsic (mechanical) components of mandibular stiffness in children likely influence the magnitude and variability of jaw stiffness.  It was hypothesized that the properties of jaw stiffness would show a developmental progression that mirrored these reflex and intrinsic changes.  Sinusoidal displacements of the mandible at frequencies ranging from 3-12 Hz were applied to children (ages 5-10) and adults in order to calculate the magnitude and variability of mandibular stiffness.  Results indicated an increase in the magnitude of jaw stiffness with age as well as an increase in stiffness variability.  Data will be discussed in light of studies demonstrating decreases in speech motor variability with age.