The oral preparatory phase is a part of the swallowing process and brings a bite of food to a state ready for swallowing. This phase is followed by the oral transport phase, during which the swallowing reflex is triggered. Disorders of oral preparation are present, for example, in abnormal saliva production.
What is the oral preparation phase?
The oral preparatory phase is a part of the swallowing process and brings a bite of food to a state ready for swallowing. The act of swallowing is a human reflex triggered by touch stimuli at the base of the tongue. Overall, the swallowing process, as narrowly defined, consists of three phases of transport. The triggering of the swallowing reflex is at the end of the first, the so-called oral transport phase. However, in order for the oral transport phase to begin, the food must first be chewed into a pulp and interspersed with saliva. This process takes place during the oral preparation phase. In the broader definition, the oral preparation phase is included in the act of swallowing. In the narrower definition, the phase is considered separate from the swallowing act. Overall, processes that make the swallowing act possible take place in the oral preparatory phase. The product of the preparatory phase is a bolus of food that holds between five and 20 milliliters and is mixed with saliva. In addition to the salivary glands, the masticatory muscles, periodontium, teeth, lips, temporomandibular joint, and tongue are involved in the oral preparatory phase.
Function and task
The oral preparatory phase immediately follows or overlaps with food intake. Food is absorbed into the mouth, primarily involving the lips. It is crushed by the teeth as the masticatory muscles contract. The chewing movement corresponds to a rotational movement, which is made possible by an ideal coordination of jaw, tongue, cheek and hyoid bone movements. During chewing, the tongue performs a rotational movement in the direction of the preferred chewing side. During chewing, the soft palate also straightens forward to close off the oral cavity backward, thus keeping food in the mouth. If the pharynx were not closed backward by the soft palate, the food bolus would trigger the swallowing reflex much sooner. During chewing, the cheek muscles also perform important tasks. The muscles remove food debris from the cheek pouches and assist in transporting food to the tongue. Meanwhile, the salivary glands produce saliva, which is mixed with the food during chewing and gives the bite lubricity. The ready-to-swallow bolus of food is placed on the tongue. At this point, the oral preparation phase overlaps with the oral transport phase, which is now initiated. On the middle third of the tongue, the texture, taste, temperature and volume of the food are determined. This process is made possible by sensory cells of the cutaneous sense and the gustatory sense, which bind to molecules of temperature and taste, and the tongue estimates the consistency and shape of the food by touch. At the end of the phase, the tongue forms a ready-to-swallow morsel of food and stabilizes the bolus by means of the tongue bowl at about the mid-palate. With these steps, the oral preparation phase plays a role primarily for solid foods. Liquids are passed on by the tongue directly in the direction of the pharynx. Unlike the subsequent phases of the swallowing process, the oral preparation phase can be controlled voluntarily. This means, for example, that each person determines how long he or she chews. Only the saliva production of the salivary glands escapes voluntary control.
Diseases and complaints
The oral preparatory phase can be disturbed by pathological processes. One example is hyposalivation. In this condition, saliva production by the salivary glands is reduced by more than 50 percent in some cases. Extreme hyposalivation promotes dry mouth and leads to dysphagia because the food bolus does not receive sufficient lubrication during the oral preparation phase. Hyposalivation is to some extent an age-physiological phenomenon, as less and less saliva is produced in older age. Medications such as cytostatics also promote the phenomenon. In addition, reduced saliva production can be the symptom of a superordinate disease, such as AIDS or sepsis.In addition, radiation treatment patients also suffer from reduced saliva production. The opposite of this is hypersalivation, in which excessive amounts of saliva are produced. Hypersalivation can be related to excessive consumption of chewing gum, for example. Parkinson’s disease, infections, inflammation or poisoning also frequently occur in conjunction with saliva overproduction. This phenomenon also disturbs the oral preparation phase, so especially when saliva flows uncontrollably towards the throat and patients choke on it. Not only abnormal activity of salivary glands, but also injury of muscle groups involved in the preparatory phase, soft palate, teeth or lips complicate the preparatory process of the swallowing act. For example, disorders occur in congenital malformations such as cleft lip and palate. If the soft palate is affected by dysplasia (malformation), this sometimes has the most serious consequences. The pharynx may then no longer be closed by the anatomical structure when chewing. The swallowing reflex is triggered earlier. However, since the food is not yet ready to swallow, patients often swallow. Apart from the difficulties described above, neurogenic disorders can also disrupt the coordination of individual movements during chewing. The cause of such a phenomenon is either a centrally or peripherally located lesion of nervous tissue. In the central nervous system, the cause of such lesions is often multiple sclerosis. In the peripheral nervous system, polyneuropathy may be to blame, for example. All swallowing disorders are grouped under the term dysphagia.
