Nocturnal Autonomic Nervous System and Jaw Muscle Activities and Ramus Height in Children.

Objective: Mandibular growth is influenced by function. This study tested for correlation amongst nocturnal autonomic nervous system (ANS) and jaw muscle activities and mandibular ramus height.

Materials and methods: According to Institutional Review Board oversight, children with skeletal Class II malocclusions were enrolled in this observational study. Subjects had cone-beam computed tomography images, participated in protocols to quantify jaw muscle activity per bite-force, and were trained to use portable recorders to collect jaw muscle and heart rate variability (HRV) data over four nights at home. Night-time ultradian cycling of ANS activity was characterised by fitting a polynomial to the HRV measures of sympathovagal tone (low/high frequency spectral powers, LF/HF). Twenty-minute windows around each inflection point of this polynomial were identified, within which HRV measures and jaw muscle activities (Duty Factor, DF) were quantified. DF versus HRV measures (DF/HRV) were plotted for each subject, and regression slopes calculated. Non-linear regression analysis was used to test for correlation between DF/HRV slopes, age (years), and ramus height (mm).

Results: Thirteen (eight males, five females) of 15 children enrolled completed protocols. DF versus LF/HF had average R² values of 0.66 ± 0.22 for masseter muscles (left and right), and 0.57 ± 0.19 and 0.55 ± 0.17 for left and right temporalis muscles, respectively. Regression analysis demonstrated that approximately 42% of the variance in mandibular ramus height could be explained by the combined effects of age and masseter muscle DF versus LF/HF.

Conclusions: Mandibular ramus height may reflect the influence of sympathovagal tone on nocturnal jaw muscle activity in children.