Mastication in Man

Abstract

In this chapter the timing mechanism of the “central pattern generator” creating rhythmicity in the masticatory movements, as well as the voluntary control of the masticatory muscles are discussed thoroughly. In the voluntary control of the masticatory muscles the output of the motor cortex bypasses the central pattern generator to reach directly the trigeminal motor neurons. Then the masticatory movements and forces can be generated without invoking rhythmicity.

A prevailing problem in motor coordination is how the motor systems are organized and related. In this context, there are two antithetical mechanisms to adjust the muscle force required during chewing. The “closed loop” theory of motor control proposes that sensory feedback from muscle spindles and joint receptors is necessary for movement regulation. According to this theory feedback augmentation (increase in sensory input) will lead to an increase in accuracy of motor performance. Conversely the “open loop” theory suggests that the motor command of the motor cortex is all that is necessary for regulation of movement. The peripheral feedback is unnecessary for movement regulation. There is a substantial amount of evidence for both theories of motor control. For example, in the early mixed dentition there is augmentation of occlusal feedback which supports the closed loop theory and the early treatment of certain malocclusions of the teeth. The augmented occlusal feedback in the early dentition suggests that slow learning occurs through multisensory experiences, lasting until completion of the permanent dentition through the gradual maturation of the cerebral cortex.