Jaw muscles are versatile entities that are able to adapt their anatomical characteristics, such as size, cross-sectional
area, and fibre properties, to altered functional demands. The dynamic nature of muscle fibres allows them to change their
phenotype to optimize the required contractile function while minimizing energy use. Changes in these anatomical parameters
are associated with changes in neuromuscular activity as the pattern of muscle activation by the central nervous system plays
an important role in the modulation of muscle properties.
This review summarizes the adaptive response of jaw muscles
to various stimuli or perturbations in the orofacial system and addresses general changes in muscles as they adapt, specific
adaptive changes in jaw muscles under various physiologic and pathologic conditions, and their adaptive response to non-surgical
and surgical therapeutic interventions.
Although the jaw muscles are used concertedly in the masticatory system,
their adaptive changes are not always uniform and vary with the nature, intensity, and duration of the stimulus. In general,
stretch, increases neuromuscular activity, and resistance training result in hypertrophy, elicits increases in mitochondrial
content and cross-sectional area of the fibres, and may change the fibre-type composition of the muscle towards a larger percentage
of slow-type fibres. In contrast, changes in the opposite direction occur when neuromuscular activity is reduced, the muscle
is immobilized in a shortened position, or paralysed. The broad range of stimuli that affect the properties of jaw muscles
might help explain the large variability in the anatomical and physiological characteristics found among individuals, muscles,
and muscle portions.