Introduction[edit | edit source]
The mandible is the largest and strongest bone of the human skull. It is commonly known as the lower jaw and is located inferior to the maxilla. It is composed of a horseshoe-shaped body which lodges the teeth, and a pair of rami which projects upwards to form a temporomandibular joint.
Structure[edit | edit source]
The mandible is formed by a body and a pair of rami along with condyloid and coronoid processes.
Body[edit | edit source]
Body is the anterior portion of the mandible. Body has two surfaces: outer and inner and two borders: upper and lower border. The body ends and the rami begin on either side at the angle of the mandible, also known as the gonial angle. 
- Outer surface is also known as external surface and has following characteristics:
- Mandibular symphysis/ Symphysis menti at midline which joins left and right half of the bone, detected as a subtle ridge in the adult.
- The inferior portion of the ridge divides and encloses a midline depression called the mental protuberance, also known as chin. The edges of the mental protuberance are elevated, forming the mental tubercle.
- Laterally to the ridge and below the incisive teeth is a depression known as the incisive fossa.
- Below the second premolar is the mental foramen, in which the mental nerve and vessels exit.
- The oblique line courses posteriorly from the mental tubercle to the anterior border of the ramus.
- Inner surface is also known as internal surface and has following features:
- The mylohyoid line is a prominent ridge that runs obliquely downwards and forwards from below the third molar tooth to the median area below the genial tubercles.
- Below the mylohyoid line, the surface is slightly hollowed out to form the sub-mandibular fossa, which lodges the submandibular gland.
- Above the mylohyoid line, there is the sublingual fossa in which the sublingual gland lies.
- The posterior surface of the symphysis menti is marked by four small elevations called the superior and inferior genial tubercles.
- Upper border (Alveolar border)
- It consist of sockets for the teeth.
- Lower border (Inferior border)
- It is also known as base. There is a fossa present at the side of midline known as digastric fossa. 
Ramus[edit | edit source]
The ramus is lateral continuation of the body and is quadrilateral in shape. The coronoid process is the anterosuperior projection of the ramus which is triangular in shape. Whereas posterosuperior projection of ramus is known as condyloid process whose head is covered with fibrocartilage and form a temporomandibular joint. The constricted part below condyloid process is neck. Condyloid and coronoid process are separated by a mandibular notch. It has two surfaces: medial and lateral and four borders: superior, inferior, anterior and posterior.
Muscle Attachment[edit | edit source]
|Buccinator||Originates from Oblique line|
|Depressor labii inferioris and depressor anguli oris||Originates from Oblique line below mental foramen|
|Mentalis||Originates from Incisive fossa|
|Orbicularis oris||Originates from incisive fossa|
|Temporalis||Inserts on coronoid process|
|Masseter||Inserts on Outer surface of ramus and angle of the mandible|
|Medial Pterygoid||Inserts on medial surfaces of Angle of the mandible|
|Lateral Pterygoid||Inserts on the condyloid process|
|Platysma||Inserts on the Lower border of the body|
|Anterior belly of Digastric||Originates from Digastric fossa|
|Genioglossus||Originates from Upper tubercle|
|Geniohyoid||Originates from Lower tubercle|
|Mylohyoid||Originates from Mylohyoid line|
|Superior pharyngeal constrictor||Originates partially from the pterygomandibular raphe, which originates from the mylohyoid line|
Ossification[edit | edit source]
Mandible is the second bone to ossify after clavicle. Each half of the mandible ossifies from only one centre at the sixth week of intrauterine life in the mesenchymal sheath of Meckel's cartilage near the future mental foramen. The first pharyngeal arch, known as the mandibular arch, gives rise to the Meckel cartilage. A fibrous membrane covers the left and right Meckel cartilage at their ventral ends. These two halves eventually fuse via fibrocartilage at the mandibular symphysis. Thus, at birth, the mandible is still composed of two separate bones. Ossification and fusion of the mandibular symphysis occur during the first year of life, resulting in a single bone. The remnant of the mandibular symphysis is a subtle ridge at the midline of the mandible.
The mandible changes throughout the life. In infant and children, the angle of mandible is obtuse with 140 degrees or more making head in line with the body of the mandible. Whereas in adult the angle decreases to about 110-120 degree making ramus almost vertical.
Clinical Relevance[edit | edit source]
- Cleft chin: Cleft chin also known as chin dimple results from incomplete fusion of the two halves of the jaw during foetal development, forming a notch in an otherwise well-united mandibular symphysis. It can also be caused by a dehiscence or failure of the paired mentalis muscle over the chin to come together during development.
- Temporomandibular disorder
- Use of mandible in Forensics: As the mandible progressively changes over an individual’s life, it is routinely used to determine the age of the deceased.
- Mandibular fracture: Mandibular fractures are most commonly caused by trauma and typically occur in two places. The parasymphysis is especially prone to fracture due to the incisive fossa and mental foramen. Involvement of the inferior alveolar nerve in the callus may cause neuralgic pain, which may be referred to to the areas of the distribution of the buccal and articulotemporal nerves. Other common site for fractures are neck and angle of mandible. A direct blow to the mandible may cause a condylar neck fracture as the articular disk of the temporomandibular joint prevents it from moving posteriorly.
Resources[edit | edit source]
Also see these related pages:
- Facial Skeleton
- TMJ Anatomy
- TMJ Examination
- Bruxism and Temporomandibular Disorders
- Feeding and the Swallow Mechanism
References[edit | edit source]
- Breeland G, Aktar A, Patel BC. Anatomy, head and neck, mandible. StatPearls [Internet]. 2021 Jun 18.
- BD_Chaurasia’s_Human_Anatomy, Volume 3 - Head-Neck and Brain 6th Edition. Page number:32-36
- MANDIBLE - GENERAL FEATURES & ATTACHMENTS. Available from: https://www.youtube.com/watch?v=jp55Ohh1kDY lasted accessed: 2022-02-08
- Mokal N, Desai M. " Dimple"-matically correct-Revisiting the technique for the creation of a chin dimple. Indian Journal of Plastic Surgery. 2012;45(1):144.