The jaw is made up of two structures near the entrance to the mouth that support the teeth: the upper jaw and the mandible. The latter is a mobile bone which ensures chewing. The musculature and innervation of the jaw guarantee power, precision and sensitivity.

The jaw is the set of two bony structures on the lower level of the face, with teeth located in the mouth. These two structures are called respectively: the mandible and the upper maxilla.

The mandible is a horseshoe-shaped bone surmounted by lower teeth allowing the jaw to perform its main functions:

• food grasping;
• chewing;
• breathing;
• articulate language.

This bone has the particularity of being the only mobile bone in the skull, articulating with the temporal bone by the temporomandibular joint (TMJ).

The upper jawbone bears the upper teeth. The top of the upper jaw forms the floor of the eye sockets (bony cavity in which the eye is located). This bone is hollowed out on each side by an air-filled cavity, open to the nasal cavity, and called the maxillary sinus.

The masticatory muscles (masseter muscle, temporalis muscle and medial and lateral pterygoid muscle) ensure mobility and power of the jaw.

The lower part of the jaw

The mandible

The term mandible designates them impair (that is, present in a single copy in the entire human skeleton) which forms the lower jaw. In reality, the mandible results from the fusion of two bones (carried out during fetal life) forming the symphyse mentonnière. The mandible bears the lower teeth and consists of a body and two branches.

The mandibular body

The mandibular body is made up basal bone on which the alveolar bone that surrounds the teeth rests. The basal bone is dense and hard while the alveolar process is spongy.

The alveolar bone is susceptible to atrophy in the event of periodontal disease, tooth loss, osteoporosis, infection, dental granuloma or trauma, etc. The cause of this bone loss must be treated at the risk of leading to aesthetic, morphological and functional changes.

The mandibular bone is hollowed out of a channel allowing the passage of the nerves and the lower alveolar arteries. Finally, the mandibular body presents a hole called mental foramen: the latter allows the mental nerve to pass.

The mandibular branches (or ramus)

The mandibular branches articulate with the temporomandibular joint (or TMJ) and the temporal bone. They provide mobility to the mandible. They carry at their upper extremities the condyles and a coronoid process which allow the insertion of the temporalis muscle. The external face of the branches gives access to the masseter muscle, a very powerful muscle. The internal faces of the branches allow the introduction of the medial pterygoid muscle and the lateral pterygoid muscle, which ensure the mandibular elevation and propulsion.

The musculature of the mandible

The adductor muscles of the mandible are used to open and close the jaw. The three main ones are:

• the masseter muscle attached to the zygomatic arch and the side of the mandible. It is this muscle that you feel harden when you grit your teeth;
• the temporalis muscle attached to the bone of the temple and to the top of the mandible (at the level of the coronoid process);
• the pterygoid muscle attached to the internal face of the mandible and to the base of the skull.

The masseter muscle and the pterygoid muscle allow complex movements thanks to their subdivision into several bundles. In humans (and all mammals), most of the power of the jaw is provided by the contraction of the temporal muscle and masseter.

The innervation of the mandible

The mandible is innervated by the mandibular nerve which is the third branch of the trigeminal nerve. The other two branches of the latter are respectively the maxillary nerve and the ophthalmic nerve. The mandibular nerve allows the sensory innervation of the teeth and the adjacent gum tissue. It is divided into a multitude of smaller nerves: the nerve of the mylohyoid muscle, the nerve of the tensor muscle of the soft palate, etc.

The vascularization of the mandible

The arteries located at the level of the mandible are branches of the primitive carotid artery (lingual artery, facial artery, chin artery, inferior and superior coronary artery, etc.).

The veins located in the mandible are part of a network drained by the jugular veins located in the neck (labial vein, retro-mandibular vein, etc.).

The upper part of the jaw

The jawbone is an even bone: it is present in two symmetrical copies belonging to the facial mass.

The two maxillary bones are immobile and articulate with the other bones of the superior facial mass (zygomatic bone, lacrimal bone, palatine bone, inferior nasal turbinate, etc.) and the bones of the skull (frontal bone and ethmoid bone).

They consist of a hollow body, a maxillary sinus and a frontal process. Like the mandible, part of the maxillary bones surround the teeth: the alveolar bone. Many muscles allow movement in this region (masseter muscle, buccinator, levator of the upper lip, etc.). The upper part of the jaw is innervated by the maxillary nerve and its various branches. The arteries located in the maxillary area are branches of the primary carotid artery: maxillary artery, superior coronary artery, etc. The veins located in the mandible are part of a network joining the jugular veins located in the neck.

The jaws are primarily intended for obtaining, carrying to the mouth and chewing food. The lower jaw is mobile, it articulates in the posterior process with the temporal bones. The upper jaw, or maxilla, is more or less attached to the skeleton. It consists of two bones fused together in the midline by a suture. The jawbones form the roof of the mouth, the floor and sides of the nasal cavity, and the floor of the eye sockets.

Symptoms in the jaw can suggest different pathologies:

• an algo-dysfunctional syndrome of the manducator apparatus (called SADAM or Costen’s syndrome) which manifests itself by pain in the jaw and difficulty opening the mouth;
• bruxism (daytime or nighttime) which results in stress-related clenching of teeth or chattering / grinding of teeth during sleep;
• osteoarthritis of the temporomandibular joint (TMJ) which manifests itself by pain but also by a blockage in the opening and closing movements of the mouth;
• cancer of the jaw which may be secondary to cancer of the mouth and which spreads to the bones of the jaw (this represents the majority of cases of cancer of the jaw) or primary cancer of the bones of the jaw (lower jaw or upper mandible) or cartilaginous parts of the jaw. The symptoms are not specific: pain in the jaw, dental problems, bleeding in the mouth, deterioration of the general condition, etc.

In the event of jaw pathologies, different treatments can be offered:

• analgesics and anti-inflammatory drugs may be prescribed for jaw pain. In the event of significant pain associated with SADAM, infiltrations (corticosteroid injections) can be performed;
• hyaluronic acid injections: these can be administered in cases of osteoarthritis by the rheumatologist. The latter may also have recourse to injections of hyaluronate in the temporomandicular joint (TMJ);
• surgery is the first-line treatment for cancer of the jaw, when the latter is of oral, cartilage or bone origin. It consists of removing the tumor and then rebuilding the jaw bone by means of a bone graft;
• chemotherapy is the first-line treatment for lymphoma or myeloma that affects the jaw and does not require surgery. On the other hand, it intervenes only in second intention for cancers of oral, cartilaginous and bone origin. Radiation therapy is rarely used for cancer of the jaw;
• occlusal splints prevent the sequelae of bruxism.

Other non-drug methods can help relieve jaw pain:

• stress therapy (relaxation, psychotherapy, meditation, hypnotherapy, etc.);
• osteopathic manipulations at the TMJ, etc.

In case of jaw pain, it is recommended to go to your general practitioner. The latter can refer you to another health professional or specialist: dentist, ENT, rheumatologist, osteopath, etc.

• An algo-dysfunctional syndrome of the manducator apparatus (called SADAM or Costen’s syndrome) is diagnosed by a clinical examination as well as additional examinations: dental panoramic, or even MRI of TMJ.
• Bruxism is diagnosed by physical examination. In the event of bruxism, the doctor may observe tooth wear, an increase in the volume of the jaw muscle, oral pain, evidence of grinding or chattering of teeth by the patient or a third party … Some cases require an evaluation in sleep medicine.
• Osteoarthritis is diagnosed by physical examination. An x-ray (volume cone-beam computed tomography (CFVT) or magnetic resonance imaging (MRI)) can confirm the diagnosis.
• Jaw cancer is diagnosed by a clinical examination as well as additional examinations: generally an endoscopy makes it possible to visualize the tumor and a biopsy of the oral cavity can be performed in order to know the nature of the tumor. An extension assessment is necessary in order to look for other locations of cancer cells in the body.