Corpus: Mastication

Mastication or mastication is a mechanical action of the masticatory apparatus that serves to grind solid food and mix it with saliva in such a way that a slippery, swallowable chyme (bolus) is formed. In addition, the enzymes present in the saliva during chewing achieve an initial digestion of some food components.

See also: Swallowing

The upper and lower jaw with the teeth, the two jaw joints and the masticatory muscles are primarily involved in the chewing process. In addition, the tongue, cheeks, palate, lips and floor of the mouth serve to contain and place food in the oral cavity.

Chewing immediately follows biting off. The chewing movement is not a simple hinge movement, but a complex, rhythmic movement that is guided three-dimensionally via the temporomandibular joint and the occlusal tooth surfaces. An up-and-down movement is combined with a lateral movement.

The grinding process is essentially influenced by the shape and number of teeth, the guidance of the lower jaw in the temporomandibular joint, the muscle force exerted and the structure of the food.

...from a mechanical point of view[Bearbeiten]

The rhythmic process of chewing is known as the masticatory cycle. It is divided into three phases with regard to the mechanics of jaw movement:

• Opening phase: the lower jaw slides forwards and downwards.
• Rapid closing phase: The incisal point moves laterally. The condyle of the working side moves backwards and upwards in the mandibular fossa. The condyle of the balance side moves forwards, downwards and inwards. The incisal point then moves back into the median plane.
• Slow closing phase: This is the actual phase of force application in which the food is penetrated by the teeth. The slow closing phase includes a short occlusal holding phase before the next opening.

Several of these chewing cycles result in a chewing sequence. It extends from the first chewing to the act of swallowing.

...from a functional point of view[Bearbeiten]

From a functional point of view, the act of chewing can be roughly divided into the following sub-activities:

• Positioning the food between the rows of teeth
• Crushing and grinding of the food by alternating jaw opening and jaw closing
• Grinding the food by performing grinding movements

Physiological chewing forces of around 30 Newtons are achieved during the chewing act. Theoretically, much higher chewing forces can be achieved, but excessive jaw closure fails due to the sensation of pain when the rows of teeth are pressed together too strongly.

Positioning the food[Bearbeiten]

The muscles of the lips, cheeks and tongue are used to position and hold ingested morsels of food between the rows of teeth.

Crushing and grinding[Bearbeiten]

By repeatedly opening and closing the jaw, chewing pressure is generated and the food is effectively crushed.

The jaw is opened by contracting the muscles of the floor of the mouth and the lateral pterygoid muscle. The opening of the jaw is facilitated by gravity. If the floor of the mouth is paralysed, the lateral pterygoid muscle can also open the jaw on its own. When the jaw opens strongly, the head is tilted dorsally by contraction of the neck muscles.

The jaw is closed by the temporalis, masseter and medial pterygoid muscles working together. The temporalis muscle is the strongest jaw closer. Its strength is only surpassed by the muscle loop formed by the masseter and pterygoid medialis muscles.

Grinding[Bearbeiten]

To grind food effectively, the lower jaw must be alternately pushed forwards and backwards. This causes the rows of teeth to act like a millstone on the food.

The lower head of the lateral pterygoid muscle pushes the mandible forward, while the horizontal muscle fibres of the temporalis muscle are mainly responsible for pushing it back.

The chewing act serves to break up solid food, to form a bite that can be swallowed and to mix the resulting chyme with saliva. Chewing is an important step in the preparation and onset of digestion.

By grinding the food, a larger surface area is created for salivary enzymes (e.g. amylase, tongue lipase) to attack. By softening and grinding the food, it can pass safely through the gullet and oesophagus.

Chewing can be made difficult or even impossible by tooth loss, jaw fractures, diseases of the temporomandibular joint and other pathologies. These restrictions can result in weight loss.

Pain that occurs when chewing is known as masseteric claudication.

The chewing of abrasive foods leads to a gradual loss of tooth structure, known as demastication.

Pathological chewing of the fingernails is called onychophagia.

With targeted training, circus performers regularly manage to hold on to many times their body weight by closing their jaws.