The mandible is the largest bone of the fascial skeleton (viscerocranium). Besides the bones of the middle ear, the mandible is the only mobile bone in the skull. Unlike other bones of the skull, the mandible doesn’t articulate with the surrounding bones via sutures, but rather via a synovial joint called the temporomandibular joint. This joint allows the mandible to be attached to the skull while at the same time being capable of producing various translatory and rotatory movements. These movements allow complex actions like chewing and speaking.
The mandible consists of two main parts: a body and two rami. These parts feature various anatomical landmarks participate in important functions of the mandible, for example housing the teeth and providing the passage for neurovascular structures.
This article will discuss the anatomy of the mandible.
|Definition||A horseshoe-shaped mobile bone of the viscerocranium that forms the lower jaw and houses the mandibular teeth|
|Main parts||Body of mandible, ramus of mandible|
|Bony landmarks of the body||Mental protuberance, mental tubercle, mental foramen, oblique line of mandible, sublingual fossa, mylohyoid line, submandibular fossa, mental spines, digastric fossa, alveolar part, interalveolar septa|
|Bony landmarks of the ramus||Coronoid process, mandibular notch, condylar process, head of mandible, neck of mandible, pterygoid fovea, pterygoid tuberosity, masseteric tuberosity, angle of mandible, mandibular foramen, lingula, mylohyoid groove|
The mandible is a horseshoe shaped bone of the viscerocranium. It consists of the body and two rami, connected at the angle of mandible.
The body of mandible is its horizontal portion. It consists of two parts:
- The alveolar part
- The base of mandible
The alveolar part is the upper portion of the body. It consists of two bony lamellae: a thick buccal lamella, and a thin lingual lamella. They are parallel to each other, forming a shallow trench on the upper surface of the alveolar part. The lamellae are connected by interalveolar septa, which cut the trench into sockets which house the mandibular teeth.
The base is the inferior part of the body that features several anatomical landmarks. On its external surface, we can identify:
- The mandibular symphysis: Fibrous tissue in the midline of the mandibular body, which ossifies by the first year of life. It unites the left and right halves of the mandible in order to form a single, symmetrical bone.
- The mental protuberance: A bony prominence at the midline of the body.
- The mental tubercle: A paired bony prominence on each side of the mental protuberance.
- The oblique line: A crest extending from the ramus to the body of mandible. It provides the insertion point for the depressor anguli oris muscle.
The mental foramen: An opening located inferior to the second mandibular premolar tooth which provides the passage for the mental nerve and vessels.
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The internal surface of the base of mandible features the following landmarks:
- The digastric fossa: A paired depression on the lower margin of the mandibular body, located on each side of the midline.
- The superior and inferior mental spines: Paired bony eminences on the midline of the internal surface of the body. They provide the attaching point for the genioglossus and geniohyoid muscles.
- The submandibular fossa: A paired depression on each side of the mental spines which houses the submandibular gland.
- The sublingual fossa: A depression located superior to the mental spines which hosts the sublingual gland.
- The mylohyoid line: A paired oblique crest on the sides of the body to which the mylohyoid muscle attaches.
The ramus is the vertical part of the mandible. The point at which it unites with the body is called the angle of mandible (i.e. gonial angle). The angle can range from 110° to 130° and can vary depending on the age, sex and etnicity. Usually, the angulation is larger in men.
The superior part of the ramus consists of two processes: the coronoid process (anterior process) and the condylar process (posterior process). The incisure between them is called the mandibular notch and it is crossed by the masseteric nerve and vessels.
The coronoid process features the temporal crest, which serves as an attachment point for the temporalis muscle. The condylar process has an articular surface (the condyle), via which the mandible articulates with the articular tubercle of the temporal bone to form the temporomandibular joint.
On the posterolateral aspect of the ramus there is a single landmark called the masseteric tuberosity, a rough surface that serves for the insertion of the masseter muscle.
The medial surface of the rami harbours following landmarks:
- The pterygoid tuberosity: A rough area for the insertion of the medial pterygoid muscle.
- The mandibular foramen: The starting point of the mandibular canal which is traversed by the inferior alveolar nerve and its branches.
- The mylohyoid sulcus: A small sulcus which contains the mylohyoid artery and nerve.
Muscles that attach to the mandible
Besides the sphenomandibular and stylomandibular ligaments, and the pterygomandibular raphe, there are numerous muscles that attach to the mandible.
They are presented in the tables below:
|Buccinator muscle||Buccinator ridge of mandible|
|Mentalis muscle||Incisive fossa of mandible|
|Depressor labii inferioris muscle||Oblique line of mandible|
|Depressor anguli oris muscle||Mental tubercle and oblique line of mandible|
|Anterior belly of digastric muscle||Digastric fossa|
|Genioglossus muscle||Superior mental spine|
|Geniohyoid muscle||Inferior mental spine|
|Mylohyoid muscle||Mylohyoid line|
|Lateral pterygoid muscle||Pterygoid fossa|
|Temporalis muscle||Apex and medial surface of coronoid process of mandible|
|Medial pterygoid muscle||Medial surface of ramus (pterygoid tuberosity) and angle of mandible|
|Masseter muscle||Lateral surface of ramus and angle of mandible|
|Platysma||Lateral surface of ramus and angle of mandible|
Clinically, there are many types of pathological conditions within the mandible. Here, the most common bony disturbances have been noted:
- Alveolar bone resorption occurs when the teeth are lost; there is a lack of structures to support the bone and there is increased pressure upon the bone due to chronic denture wearing.
- Intra- and extracapsular condylar fractures are the most frequent mandibular fractures and usually result due to car accidents or indirect force due to violence. Other mandibular fracture areas include the body, the angle, the symphysis, the ramus, the alveolus and the coronoid process (in decreasing order of frequency).
- Tooth aplasia is not uncommon in the third molars, the premolars and especially the lateral incisors. This can lead to gaps in the teeth and an uneven alveolar ridge.
- Osteoradionecrosis is a disorder that occurs due to cancer treatment and the bone disintegrates because of radiation.
- Osteomyelitis is an infection that can cause chronic sequestrations and bone disintegration within the mandible. It is irreversible and the mandible often needs resecting.
- Cyst formation most often happens in the mandible where the molars sit. There are many types of cyst but the common symptom is large bone resorption and bone weakening if the cyst is left untreated.
Mandible: want to learn more about it?
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