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Mandible: Definition, Anatomy and Muscle movements.

Mandible Definition

The mandible supports the lower teeth and is the biggest bone in the human skull. It is the skull’s only moveable bone and is required for chewing, swallowing, and speaking. The mandible bone is where several muscles originate or insert. This bone is made up of a body and two rami, which vary somewhat in form and angle between males and females.

Where is the mandible located?

The lower jaw is formed by the mandible, which is located at the bottom of the face. It articulates with the left and right temporal bones to allow for a wide range of motion, including down and up, forward and backward, and side-to-side movement.

Mandible Anatomy

The mobility, structure, and function of the mandible should all be considered. Nonetheless, the mandible bone may be divided into two parts: the body and the left and right rami.

Anatomy of the Mandibular Body

The mandibular body, also known as the mandible bone’s body, is formed like a horseshoe or a U. Follow the bony ridge from your chin to the corner of your lower jaw to get a sense of its shape (called the mandibular angle, or angle of the mandible).

An indentation may be felt if you push the bone right behind your chin. Both sides of the mandible body have merged at this point (mandibular symphysis). The bone is slightly elevated on each side of the symphysis to generate two mental tubercles.

The two projecting tubercles migrate diagonally toward the upper teeth, eventually merging higher on the mandibular symphysis to form a triangle.

The mental protuberance, also known as the mental trigone, is the triangle that gives the chin its form.

The mental foramina—openings to the left and right of the mandibular body—are located on each side of the mental tubercles. Blood vessels and nerve branches may flow through them. Both holes are around two millimetres below the corners of the lips.

The lingula of the mandible or the Spix spine on the inside surface of the jaw defines each foramen. The jaw-supporting sphenomandibular ligaments connect to lingulae, which are bony outcrops.

The lower teeth are supported by the mandibular body in a region of bone termed the alveolar process of the jaw. There are two forms of alveolar bone: normal and supporting bone.

Normal alveolar bone is a firm, cortical bone that creates the sockets of the teeth (alveoli).

Cancellous or spongy bone makes up the majority of the supporting alveolar bone.

There are many ridges and grooves on the rear of the mandibular body (the inner surface). The paired mylohyoid muscle, which extends from the mandible to the tongue bone, attaches to them (the hyoid bone). The act of swallowing necessitates the use of this muscle.

A depression directly before the mandibular angle is known as the submandibular fossa (corner of the jaw). It makes room for the submandibular glands on the left and right sides (see below). The sublingual glands are partially surrounded by indentations closer to the teeth.

The digastric fossa is formed by two side-by-side indentations under the chin. The anterior portion of the digastric muscle aids in mouth opening.

If you press beneath the centre of your chin and swallow, you may feel the deep-lying anterior belly of the digastric muscle contract as it pushes the tongue bone up.

The Ramus of the Mandible

The mandibular body comes to an end at the lower jaw’s mandibular angle (also known as the gonial angle). The ramus is the continuation of the mandible. We have two rami and one mandibular body.

Two processes in the rami offer articulation points: the coronoid and condyloid (or condylar) processes. More on them will be discussed later.

The mandible’s ramus has two surfaces: lateral and medial. With a lengthy hump at the bottom, the lateral (external) surface is flat and smooth. The masseter muscle attaches to this ridge, which is vital for chewing or mastication.

The ramus features a groove for the mylohyoid blood vessels and nerves, as well as an attachment site for the pterygoideus internus muscle on its medial (internal) surface, much like the body. A description of mandibular muscles is provided in a subsequent section.

There are four boundaries on each ramus. The ramus has the thickest lower border, which follows the angle of the jaw.

The anterior (front) border almost reaches the coronoid process, whereas the posterior (back) border, which is covered by the parotid gland, comes close to the condyloid process.

The top border is where the two mandibular processes come together. This bone is rather frail. The mandibular notch is a dip that separates the two processes.

Processes of the Mandible

The coronoid process (processus coronoideus) of the mandible is a thin, flat section of bone. The temporalis and masseter muscles, as well as fibres from the buccinator muscle, are inserted here. Chewing, swallowing, and speaking all need the use of these muscles.

This procedure does not result in the formation of a joint with another bone. A coronoid process crack is seen in the computer-generated picture below.

The mandible’s condylar process (processus condyloideus) is thicker and divided into two sections than the coronoid process. The condyle is at the top, and it is supported by the neck, the second component. The condyle articulates inside the temporal bone’s mandibular fossa, which is an indentation.

The mandibular fossa is located directly behind the temporal bone’s zygomatic process. The temporomandibular joint, or TMJ for short, is the site of articulation.

A bi-arthrodial hinge, The synovial joint is the temporomandibular joint. A sliding joint that allows the lower jaw to move forward and backward is referred to as a hinged joint. You’re making excellent use of your TMJ if you jut out your chin.

The TMJ consists of the convex head of the condyle and the concave depression of the temporal bone’s mandibular fossa. The articular disc that separates the two bones is surrounded by a capsule or membrane; each bone has its own synovial membrane.

While chewing, temporomandibular joint syndrome produces discomfort and a clicking or popping sound when the lower jaw moves. Muscle stiffness and a limited range of motion are other frequent complaints.

Sensory and motor nerve signalling, nutrients, and oxygen are all provided via vascular and innervated tissue beyond the articular disc. TMJ syndrome is frequently caused by inflammation of this tissue. Dislocated discs or arthritis are two more possible reasons.

Mandible and Maxilla

The jaw is formed by the mandible and maxilla bones, which do not articulate with one another. Muscles and ligaments, on the other hand, link them. When the mouth is closed, only the lower and upper jaw teeth touch. Therefore, articulations between the mandible and maxilla bone are dental.

The unpleasant trend of mandible piercing has resulted in a slew of infections and long-term damage to the salivary glands and facial nerve branches. Despite the fact that piercings do not penetrate through the mandible bone, their proximity to the mouth increases the risk of infection.

People performing mandible piercing procedures often damage important structures by passing the curved needle up through the skin of the underside of the chin and into the oral cavity without a good understanding of anatomy and because nerve pathways and anatomical landmarks differ from person to person. 

Mandibular necrosis may result from an untreated infection that spreads to the mandible bone.

Mandible Muscle Attachments

The rami and the mandibular body are both attachment points for the face and cranial muscles. Masticatory muscles make up the majority of them.

The following muscles are located on the mandibular body’s outside (lateral) surface:

  • Buccinator (pushes food into the teeth by holding the cheek to the teeth.
  • Mentalis (the “pouting” muscle) is the major muscle of the lower lip.
  • Platysma: A thick, thin layer that extends from the lower jaw to just below the collar bone is known as a platysma. The platysma pushes the lower jaw down when you open your mouth in surprise or shock.
  • Depressor anguli oris-pulls the mouth corners down.
  • The depressor labii inferior pushes the lower lip down.

The mandibular body’s inner (medial) surface has attachment sites for the following:

  • When we swallow, the mylohyoid elevates the tongue bone while simultaneously depressing (lowering) the mandible.
  • The digastric (anterior belly) muscle, like the mylohyoid, raises the hyoid bone.
  • The genioglossus is an extrinsic tongue muscle that enables you to push your tongue out and move it from side to side. When swallowing, it also pulls the centre of the tongue down.
  • The geniohyoid is responsible for swallowing, as well as raising the hyoid and lowering the jaw.

The temporalis muscle connects to the coronoid process, and the lateral pterygoid muscle inserts directly below the condyle of the condyloid process at the rami. The lateral pterygoid is responsible for pushing the mandible to the side, down, and forward. The temporomandibular joint is controlled by the paired temporalis muscles.

The masseter muscle goes all the way around the rami’s smooth outer surface. One of the most essential mastication and communication muscles. It causes the jaw to shut.

The medial pterygoid muscle has an attachment site on the inner surfaces of the rami, near the angle of the jaw. This also closes the mouth by lifting the jaw.

Lower jaw rotation and protrusion are two more activities of the medial pterygoid muscle (underbite).

References

  • Breeland G, Aktar A, Patel BC. (Updated 2020). Anatomy, Head, and Neck: Mandible. Treasure Island (FL): StatPearls Publishing. Retrieved from: https://www.ncbi.nlm.nih.gov/books/NBK532292/
  • Brennan PA, Mahadevan V, Evans BT (Eds.). (2016). Clinical Head and Neck Anatomy for Surgeons. Florida, CRC Press, Taylor & Francis Group.
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