Introduction:
It is mandatory for everyone to chew and eat food. Mastication is a physiologic act in human beings and is a complex coordination of jaw movements. The act of chewing yields the experience of taste and initiates digestion. It also aids in the circulation of vital dietary nutrients. Mastication includes various phases to convert the food into a bolus for digestion. This article will discuss the significance, the phases, the role of the tongue, and the neuromuscular control and various studies about human mastication.
What Is the Significance of Chewing Food?
The process of mastication involves neuromuscular activities. They involve a sequel of events running consistently while chewing food by elevation and depression of the mandible (lower jaw).
-
The food can be converted into a digestible bolus by the masticatory stress applied to it. This prepares the food for swallowing process inside the oral cavity. Also, there are the integrated movements of the tongue, the muscles controlling the perioral areas, the pharynx (throat), and the larynx (voice box).
-
The mandible is extremely crucial to support the process of mastication through its controlled forces and movements. In fact, these movements are equally important for speech and sound production.
-
However, control of masticatory forces is not bilaterally reciprocating but is bilaterally organized.
-
The food also is efficiently mixed up with the saliva in the oral cavity in order to prepare it for the first stage of digestion.
What Are the Phases of Human Mastication?
Most primates including human beings have a non-specialized yet adaptive mandibular movement in order to accommodate high-stress masticatory forces to chew any type of food material. A single chewing cycle is divided into four phases.
-
The first phase of mastication consists of minimal opening of the jaw to chew food wherein there is a slow yet downward progression of the mandible.
-
The second phase is a faster opening phase involving the bilateral masticatory muscles such as the left and right masseter, temporalis, and medial and lateral pterygoid muscles with the possible involvement of the suprahyoid muscle. The involvement of suprahyoid muscles is observed from research by the muscle EMG (electromyography).
-
The third phase is fast-paced, it involves upwardly directed closing movement.
-
The fourth phase of chewing is comparatively slower, as the food is chewed and crushed in between the teeth and slow closing of the jaw occurs.
What Is the Role of the Tongue in Mastication?
During the course of these masticatory phases, the tongue also plays an equally important role in controlling food movements as well as in the formation of the bolus.
-
In order for the food to break down, it is essential that it is positioned by the tongue in accordance with the buccinator cheek muscle and also in between the occlusal tooth surfaces of the posterior teeth such as premolars and molars.
-
Both solid and liquid forms of foods are transported in equal force by the tongue within the oral cavity.
-
The tongue plays a pivotal role in the process of the slow phase of mouth opening which involves the forward movement of the tongue and its expansion beneath the food.
-
The hyoid bone (U-shaped bone in the neck) and the main body of the tongue move in conjunction and retract during the fast opening and closing phases of the masticatory cycle. This helps in forming a passage to move the food to the posterior side of the oral cavity in between the occlusal tooth surfaces.
-
After reaching the posterior surface, the food is further moved backward by the action of the soft palate through the squeezing mechanism or force exerted by the tongue.
-
Whereas when very large chunks of food are consumed, the tongue will return the food back to the occlusal table of the teeth for further grinding and reduction.
What Is the Physiology and Neuromuscular Coordination of Chewing?
Various research and studies are still needed to explore the actions of the tongue during the masticatory cycle. When food is encountered in between the tooth, it undergoes complex interdigitation between the upper and the lower teeth increasing the forces over the food along with the orofacial masticatory muscles. Food tends to be more concentrated towards the working side of the jaw and experiences more pressure while chewing as opposed to the less active or contralateral side of the jaw.
-
Neurophysiologic research suggests that the rhythmical synchronous activity produced by the jaws while chewing food is by the activity of brain stem motor nuclei.
-
These nuclei form a pattern generator in the central nervous system (CNS) to facilitate the sensory oral inputs received during mastication.
-
As per the neuro research, this pattern generator is also responsible for modifying chewing movements.
-
It can be deduced that the patterns of mastication occur as a result of both sensory oral feedback and of these inputs that are coordinated in the brain.
Conclusion:
Human mastication or the act of chewing involves complex neuromuscular coordination of dental as well as mandibular movement to facilitate facial functions and aid in the digestion of food by bolus formation. In patients with severe dental prosthetic issues, TMJ (temporomandibular joint) disorders, orofacial syndromes, chronic trismus (restriction in the mouth opening), and mandibular deficiencies, dental surgeons always aim to reinstate the suitable mandibular positions in order to restore masticatory efficiency in these patients. They focus on the occlusal form of the teeth to ensure tooth contact that integrates with jaw patterns. They also make sure that the patients can chew food and grind it efficiently.
