The lower jaw (Latin mandible) is a part of the human facial skull. Together with the upper jaw, it forms the masticatory apparatus. The upper jaw represents the immovable and the lower jaw the movable part in the chewing process.
What is the lower jaw?
The lower jaw of humans is also called the maxillary jaw. It is one of the bones of the facial skull. Its Latin name, mandible, is derived from the Latin word “mandere” meaning “to chew.” This is due to its crucial function in the chewing process. In contrast to the upper jaw, which is firmly fused with the other bones of the skull, the human lower jaw is movable. It is connected to the upper jaw by the temporomandibular joint. Therefore, it can be opened, closed and also moved laterally in both directions by the masticatory muscles. During embryonic development, the mandible arises from the first gill arch. The mandibular nerve supplying it develops analogously from the first gill arch nerve.
Anatomy and structure
The actual mandibular body corpus mandibulae resembles a horseshoe in its curved shape. The center of the arch supports the chin. On each side, the mandible has an ascending mandibular branch (ramus mandibulae). On each mandibular branch is a muscular process (processus coronoideus) leading to the insertion of the temporalis muscle. The mandibular branches each open into the articular process Processus condylaris. Between the muscular process and the articular process there is an indentation (incisura mandibulae). The articular process together with the mandibular condyle caput mandibulae form the temporomandibular joint articulatio temporomandibularis. Between the temporomandibular joint head and the socket on the skull lies a movable, buffering cartilage disc (discus). The masseter muscles also attach to the mandibular branches. These are four paired muscles: The masseter muscle, the temporalis muscle, the medial pterygoid wing muscle, and the lateral pterygoid wing muscle. A bone tongue (lingula mandibulae) is located on the inner side of each mandibular branch. It covers the mandibular hole foramen mandibulae. Through the mandibular holes, the nerve of the mandibular tooth compartments (nervus alveolaris inferior) enters the mandibular canal (canalis mandibulae). This nerve is an extension of the mandibular nerve
The inferior alveolar nerve passes under the root tips of the posterior teeth. Its terminal branch is the chin nerve mentalis. It exits the mandibular body through the chin hole foramen mentale in the region of the root tips of the premolars. Other nerves localized in the mandible include the masseteric nerve, the profundal temporal nerve, and the medial and lateral pterygoid nerves. The mandibular hole also acts as a passageway for the inferior alveolar artery and the associated inferior alveolar vein.
Function and Tasks
In general, the mandible has the tasks of closing off the oral cavity and performing chewing movements. This is only possible because it is movable in all directions due to the temporomandibular joint. In addition, it is also necessary for the production of specific sounds, such as human speech. The four pairs of muscles of the lower jaw each have specific, complementary functions. The masseter muscle serves to close the jaw, as does the temporalis muscle. The latter is also needed to retract the lower jaw. The inner wing muscle (M. pterygoideus medialis) also plays a role in jaw closure. The outer wing muscle (M. pterygoideus lateralis) causes the opening and the advancement of the lower jaw. In addition, it realizes the grinding sliding movements to the left and right side. The nerves of the mandible are also assigned to precise functional areas: The inferior alveolar nerve denervates the teeth and dental compartments of the mandible. The chin nerve serves to supply the skin of the chin and lower lip. The masseteric nerve conducts information to and from the masseter muscle. The profundal temporal nerves supply the temporal muscles. The medial and lateral pterygoid nerves provide motor innervation to the internal and external wing muscles, respectively. The inferior dental artery (A. alveolaris inferior) and the respective vein (V. alveolaris inferior) serve to supply blood to the mandible.
Diseases
Complaints of the lower jaw almost always occur in combination with disorders of the entire masticatory apparatus. In Germany, the diagnosis for complaints in the masticatory apparatus is therefore often craniomandibular dysfunction (CMD). This is a combination of functional, structural, psychological and biochemical disorders. It manifests itself in dysregulation of the joint and muscle functions of the temporomandibular joints. Due to its broad and often combined causes, CMD manifests itself in numerous symptoms: the temporomandibular joints may rub or crack when opening and closing. In some cases, the ability to open the jaw wide is severely limited. This can also lead to problems with biting off, laughing and speaking. Pain originating from the jaw can radiate to the teeth, the entire oral cavity, the face, the head, the neck and shoulder area and the spine. Sometimes the fit of the teeth to each other is suddenly no longer correct. Earache, tinnitus and dizziness can also be caused by (lower) jaw problems. So can eye problems and swallowing difficulties. In general, (mandibular) jaw problems are thought to have either ascending or descending symptomatology. In ascending symptomatology, displacements of the spine affect the cervical spine and from there the temporomandibular joints. In descending symptomatology, imbalances in the jaw area lead to complaints in the neck, shoulders and spine. The causes of disorders in the (lower) jaw area are manifold. They can lie in bacterial and viral inflammations of the jaw bones and jaw joints. Another frequent cause is nocturnal teeth grinding (bruxism) due to psychological tension and/or malocclusion of the teeth. Since the temporomandibular joint is the most frequently used joint in the body, signs of wear can also occur with increasing age (temporomandibular joint arthrosis). Pain and signs of wear can also result from a displacement of the cartilage disc of the temporomandibular joint. The dentist is the first point of contact for all the disorders summarized in CMD. This person will then request further services, for example (maxillofacial) orthopedic services, if necessary.
