The Orofacial System
The masticatory system, or orofacial system (system of mouth + face system; in Latin, os = mouth, facies = face; facial = relating to the face), includes all the different types of tissue that are involved in the chewing process.The stomatognathic system, as the masticatory system is also called, is not described as an organ unit according to the biologic descriptive model but as a unit with functionally coordinated tissue structures.
The orofacial system comprises the following functional components: teeth and their supporting tissues, jaws and their alveolar sections, the temporomandibular (jaw) joints (TMJs), muscles responsible for facial expression, nerve and vessel pathways, mucous membranes, salivary glands, mucous glands, cheeks, lips, and the tongue.
The system forms a functional cycle in which each part has a specific role to play that contributes to the operation of the whole system. Within such a controlled cycle, the functionality of each component is important because the operation of the whole cycle is disrupted if just one component fails.
A functional cycle will work successfully only if all the parts of the system involved are present and functioning in a normal physiologic manner. This is because the individual components mutually influence each other. Because the individual parts of the system have a unique function, they have evolved and developed so that they can meet these requirements. Any changes due to disease in any of the components of the system will influence the entire functional cycle. Furthermore, a defect in one area of the system will not only lead to alterations in the functioning of the whole system but also affect the other components of the system.
The biologic functional cycle is controlled by the central nervous system and regulates the actions of the system. For example, in the regulation of the degree of force needed to crush food, the jaw muscles first receive a stimulus that activates the teeth to crush the food.The nerves around the teeth and in the jawbone, in addition to the TMJ itself, act as sensors to measure and record the actual force applied so that an optimal pressure can be achieved.
In the orofacial system, a normal occlusion describes a regular, well-formed, and perfectly functioning masticatory system. It is the didactic descriptive model of an ideal occlusion based on statistical mean measurements. In terms of the form and function of a masticatory system, the normal occlusion is the standard to which all dental technicians work, since the purpose of their work is to produce a well-formed and, most importantly, a properly functioning (artificial) occlusion.
In exceptional cases where a dental prosthesis that differs from the normal occlusion has to be used because the individual conditions do not permit any other solution, the aim is always to provide the best possible compromise between what is available and the ideal occlusion. If there is anything in dentistry to which the term "skillful" can best be applied, it is the ability to produce an individual denture that is close to the ideal normal occlusion.
To achieve an appropriate understanding of the functions of the masticatory system and teeth, they should be regarded as a single system (an integrated whole). Detailed observation of the individual components in isolation is only appropriate where a precise description of form is required. Because form has an effect on the functions of a component, any description of the overall system should include form, function, and the interdependence of the components of the system (Figs 1-6 and 1-7).
Functions of the orofacial system include:
- Mechanical preparation of food, biting, and chewing
- Salivation and preparation of food for swallowing
- Identification of tastes
- Preventing the ingestion of harmful substances that may be present in food by identifying them and separating them out
- Formation of speech using the closed rows of teeth and the resonance chamber of the oral cavity
- Providing static support for the facial skeleton
- Giving shape to the face, the esthetics of which will have psychologic effects
- Self-cleaning during chewing through the activity of the tongue
The individual components of the orofacial system are examined in the following sections, starting with the surface topography of the face and head and including the oral cavity with the teeth, jawbone, muscles, nerves, TMJs, and the movement of the mandible.