Anatomy of the Face - Flipbook - Page 35
Mandible Bone (Mandibula)
The mandible is the largest bone and strongest in the human skull. It holds the lower teeth in place, it assists in mastication and
forms the lower jawline. The mandible is the only bone in the entire skull that doesn’t articulate with its adjacent skull bones via
sutures. When the skull is observed purely as a bony structure, there is nothing anatomically holding the rest of the skull and the
mandible together.
This bone is also known as the lower jaw and it articulates dentally with the upper jaw or the maxilla in the viscerocranium via the
teeth when the mouth is closed. It also articulates to the neurocranium via the temporal bone, forming the temporomandibular
joint (TMJ).
The mandible is composed of the body and two rami and is located inferior to the maxilla. The body is a horizontally curved
portion that creates the lower jawline. The rami are two vertical processes located on either side of the body; they join the body
at the angle of the mandible. At the superior aspect of each ramus, the coronoid and condylar processes articulate with the
temporal bone to create the temporomandibular joint which permits mobility. Other than the ossicles of the ear, the mandible is
the only skull bone that is mobile, allowing the bone to contribute to mastication.
At birth, the mandible is 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 mandible constantly changes throughout an individual's life. At birth, the gonial
angle is approximately 160 degrees. By age four, teeth have formed, causing the jaw to elongate and widen; these changes in
the mandible's dimensions cause the gonial angle to decrease to approximately 140 degrees. By adulthood, the gonial angle is
decreased to approximately 120 degrees. Because the mandible progressively changes over an individual’s life, it is routinely used
to determine the age of the deceased in the forensic evidence.
Blood supply to the mandible is via small periosteal and endosteal vessels. Lymphatic drainage of the mandible and mandibular
teeth are primarily via the submandibular lymph nodes; however, the mandibular symphysis region drains into the submental
lymph node, which subsequently drains into the submandibular nodes.
It’s interesting to point that males generally have squarer, more prominent mandibles than females. This is due to the larger size of
the mental protuberance in males and the decreased gonial angle. The gonial angle is 90 degrees in males, compared to 110 in
females.
MUSCLES ORIGINATING FROM THE MANDIBLE
Mentalis - originates from the incisive fossa
Orbicularis oris - originates from the incisive fossa
Depressor labii inferioris - originates from the oblique line
Depressor anguli oris - originates from the oblique line
Buccinator - originates from the alveolar process
Digastric anterior belly - originates from the digastric fossa
Mylohyoid - originates from the mylohyoid line
Geniohyoid - originates from the inferior portion of the mental spine
Genioglossus - originates from the superior portion of the mental spine
Superior pharyngeal constrictor - originates partially from the pterygomandibular raphe, which originates from the mylohyoid line
MUSCLES INSERTING ON THE MANDIBLE
Platysma - inserts on the inferior border of the mandible
Superficial masseter - inserts on the lateral surface of the ramus and angle of the mandible
Deep masseter - inserts on the lateral surface of the ramus and angle of the mandible
Medial pterygoid - inserts on the medial surface of the mandibular angle and ramus of the mandible
Inferior head of the lateral pterygoid - inserts on the condyloid process
Temporalis - inserts on the coronoid process
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