Anatomy of the Mandible

The mandible, also called the mandible, is the largest and strongest bone in the face. Responsible for holding the lower row of teeth in place, this bone has a symmetrical horseshoe shape. The mandible is not directly connected to the other bones of the skull, it is the only bone in the skull that moves, and is connected to the major muscle groups for mastication (chewing) and the ligaments that make up the temporomandibular joint that allows movement.

Health problems with this bone are often associated with fractures or dislocations caused by trauma. Additionally, corrective surgery on the mandible may be performed to correct misalignment due to underdevelopment of the jaw.

anatomy

The largest facial bone, the mandible is roughly horseshoe-shaped and defines the lower edge and sides of the face. Anatomically, it is divided into two main parts: the body and the ramus.

structure

The mandibular body is the almost rectangular front part of the bone (anterior part), which is grafted to the lateral branches (wing parts). In adults, its outer surface has a slight ridge at its midline, called the mandibular symphysis, which, as it moves down, separates and encloses a depression called the chin process. The edge of this part rises to form the mental tubercle.

On one side of it, below the incisors (front teeth), is a depression called the incisor socket, with an opening called the mental foramen on each side adjacent to the premolars. The upper border, also called the alveolar border, contains the hollow space of the tooth.

Representing the “wings” of the mandible, branches appear on each side of the body, terminating in two ridges separated by the mandibular notch: one toward the front called the coronoid process, and the other toward the back of the head called the condyle. These Constrains the temporomandibular joint, allowing the bone to move.

The lower surface of the ramus defines the mandibular line and connects laterally to the masseter muscle (used for chewing). The inner surface contains several openings (fossa) that allow important nerves and arteries to enter the oral area.

Place

The relationship of the mandible to surrounding structures helps determine its function. Notably, the inferior alveolar nerve is a branch of the mandibular nerve that enters the mandibular foramen and extends forward to provide sensation to the lower row of teeth. At the mental foramen, the branches are the incisor and mental nerves; the latter debilitates the lower lip, while the former handles sensation in the mandibular premolars, canines, and lateral and central incisors.

READ ALSO:  iliac muscle anatomy

Given that this bone is involved in mouth movement, many important muscle groups are also in contact with the mandible. Many muscles grow from this bone.

  • From the sharp fossa, the mentalis (allows the lower lip to pout) and the orbicularis oris (muscles around the lips) emerge.
  • The oblique line of the mandible is where the depressor labialis and depressor anguliformis appear. These are related to frowning.
  • The alveolar process of the mandible is the origin of the buccal muscle; this muscle aids in chewing.
  • Extending from the mandibular line is the mandibular muscle, which is the main muscle on the floor of the mouth. In addition, this segment is connected to the superior pharyngeal constrictor, which plays a major role in swallowing.
  • The mental spine produces two important muscles: the geniohyoid (connecting the mandigohyoid to the jaw) and the geniohyoid (the fan-shaped muscle that forms the main part of the tongue).

In addition, other muscles are attached to the mandible, including:

  • The platysma originates from the clavicle and progresses below the mandible.
  • Inserted into the lateral surface is the superficial masseter muscle, which is the main muscle for chewing and mouth movement.
  • The deep masseter muscle also inserts into the mandible on the outer surface of the mandibular ramus and participates in chewing movements.
  • The mandibular angle (the outer angle of the mandible) and the medial angle of the ramus are where the medial pterygoid muscle inserts. This thick, roughly rectangular muscle is also involved in chewing.
  • At the condyle, the inferior head of the lateral pterygoid muscle, which moves the mandible down and side to side, is another important masticatory structure.
  • The temporalis muscle, a broad fan-shaped structure that runs along the sides of the head and also aids in chewing, enters the coronoid process of the mandible.
READ ALSO:  Anatomy of the common hepatic artery

Anatomical variation

Typically, men have more mandibular angles than women because they have a larger mental process and a smaller mandibular angle.

However, in rare cases, the alveolar canal may be duplicated or even tripled. This is often seen on X-rays and can complicate the practice of anesthesia in oral or facial surgery because of the risk of accidentally puncturing and damaging the nerves in these ducts.

Additionally, some people may suffer from “micrognathia,” which is an abnormally small jawbone; others have the opposite — “prognathia” — resulting in an underbite.

Finally, a mandibular cleft may occur during embryonic development, which is basically an incomplete connection of the mandible. In these cases, there is a Y-shaped dimple in the middle of the chin.

Function

Along with the upper jaw or maxilla, the mandible has important structural and protective functions. Not only do important nerves and muscles pass through and emerge from this bone, but it’s also where the lower teeth are located.

The mandible is closely related to chewing function and most mouth movements.

Related conditions

The most common problems with the mandible are fractures or dislocations due to accidents or falls. These breaks are most commonly found in the condylar part of the bone, although they may also occur in other parts, such as the body, mandibular angle, and other parts of the ramus.

Misalignment can also occur, the most common of which is due to the mandible being pushed back. These can result in patients being unable to close their mouths or structurally dislocated.

There can also be other problems with this part of the body, not necessarily related to the trauma. A misaligned jaw — whether due to trauma or naturally — can severely damage teeth and affect other parts of the head and neck.

Additionally, the positioning of the mandible may be associated with sleep apnea (excessive snoring), cleft palate, and temporomandibular joint disease (pain at the maxillary and mandibular junction).

READ ALSO:  Anatomy of the parotid gland

A rare but equally important disease is osteomyelitis, a bone infection.This causes the bone inside the mandible to disintegrate, which is irreversible. In addition, sac-like structures—sac-like structures—form in the molars, and if left untreated, the jawbone itself can be damaged.

recovery

Treatment for a mandibular fracture depends on the location and extent of the problem. After a computed tomography (CT) scan, X-ray, or magnetic resonance imaging (MRI) to evaluate the fracture, doctors usually have two options: reduction or immobilization.

The reduction involves an approximate stump and the lower jaw is set to that position, usually with a wire wrapped around the teeth. Fixation is similar in nature to reduction, but involves the use of additional bow rods to secure the upper and lower teeth to each other for proper positioning. Depending on the injury, soft tissue may also need to be pierced and used as additional support.

Orthognathic surgery treats problems caused by a misplaced jaw, sleep apnea, cleft palate, and temporomandibular joint disorders.Basically, it’s an osteotomy, where a portion of the bone is cut and shaped to manipulate the fit. Those with micrognathia may need this type of surgery to correct the alignment.

After surgery, extensive rehabilitation is required, focusing on ensuring the correct positioning of the mandible relative to the rest of the skull.

Frequently Asked Questions

  • What is the mandible?

    The mandible is the bone that makes up the lower half of the lower jaw, containing the set of teeth at the bottom. The mandible is the only facial bone that moves.

  • What is a jawbone?

    The lower jaw consists of two bones – the lower jaw and the upper jaw. The lower teeth are fixed in the mandible and the upper teeth are in the maxilla. The word jawbone when used as a noun refers to the mandible. As a verb, jawbone means to say a lot, usually to convince someone to cooperate.

  • What bone is the jaw?

    The mandible is the bone that makes up the jaw and jaw line. The bone is covered with a layer of fat that helps shape the jaw.