The mandible is the bone for the lower jaw, both in humans and animals. When remains of humans are found, the mandible is one of the common findings, sometimes the only bone found. Skilled experts can estimate the age of the human upon death because the mandible changes over a person's life, as described in this article.

At birth [Fig. 1] the body of the bone is a mere shell, containing the sockets of the two incisor, the canine, and the two deciduous molar teeth, imperfectly partitioned off from one another. The mandibular canal

Mandibular canal

The mandibular canal is a canal within the mandible that contains the inferior alveolar nerve, inferior alveolar artery, and inferior alveolar vein...

 is of large size, and runs near the lower border of the bone; the mental foramen

Mental foramen

The mental foramen is one of two holes located on the anterior surface of the mandible. It permits passage of the mental nerve and vessels. The mental foramen descends slightly in edentulous individuals.- Variations :...

 opens beneath the socket of the first deciduous molar tooth

Molar (tooth)

Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....

. The angle is obtuse (175°), and the condyloid portion is nearly in line with the body. The coronoid process

Coronoid process

The Coronoid process can refer to:* The coronoid process of the mandible, part of the ramus mandibulae of the mandible...

 is of comparatively large size, and projects above the level of the condyle.

After birth [Fig. 2] the two segments of the bone become joined at the symphysis, from below upward, in the first year; but a trace of separation may be visible in the beginning of the second year, near the alveolar margin. The body becomes elongated in its whole length, but more especially behind the mental foramen, to provide space for the three additional teeth developed in this part. The depth of the body increases owing to increased growth of the alveolar part, to afford room for the roots of the teeth, and by thickening of the subdental portion which enables the jaw to withstand the powerful action of the masticatory muscles

Mastication

Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...

; but the alveolar portion is the deeper of the two, and, consequently, the chief part of the body lies above the oblique line. The mandibular canal, after the second dentition, is situated just above the level of the mylohyoid line

Mylohyoid line

Extending upward and backward on either side from the lower part of the symphysis of the mandible is the mylohyoid line, which is the origin of the mylohyoid muscle; the posterior part of this line, near the alveolar margin, gives attachment to a small part of the Constrictor pharyngis superior,...

; and the mental foramen occupies the position usual to it in the adult. The angle becomes less obtuse, owing to the separation of the jaws by the teeth; about the fourth year it is 140°.

In the adult [Fig. 3] the alveolar and subdental portions of the body are usually of equal depth. The mental foramen opens midway between the upper and lower borders of the bone, and the mandibular canal runs nearly parallel with the mylohyoid line. The ramus is almost vertical in direction, the angle measuring from 110° to 120°, also the adult condyle is higher than the coronoid process and the sigmoid notch becomes deeper.

In old age [Fig. 4] the bone becomes greatly reduced in volume due to the loss of teeth and consequent resorption of the alveolar processes and interalveolar septa. Consequently, the chief part of the bone is below the oblique line. The mandibular canal, with the mental foramen opening from it, is closer to the alveolar border. The ramus is oblique in direction, the angle measures about 140°, and the neck of the condyle is more or less bent backward.