The mandible is the 2nd bone (next to clavicle) to ossify in the body. It develops as intramembranous bone lateral to Meckel's cartilage.

 A single ossification centre for each half of mandible arises in the area of future mental foramen, lateral to the Meckel's cartilage where the inferior alveolar nerve bifurcates into mental and incisive branches

 (Note: - Maxilla has three ossification centres, one primary ossification centre is for maxilla proper and the remaining two centres are for premaxilla).


1) In infants and children below 5 years of age, the mental foramen is near the lower border and opens below the sockets for deciduous molars. This is so because; the bone is made up of only alveolar part.

The mandibular canal runs about 0.5 cm below the occlusal plane due to underdeveloped ramus of mandible. So, the needle is inserted below the occlusal plane during inferior alveolar technique.

The angle of mandible is obtuse (140 or more).

2) In children of about the age group of 6 years, the foramen is at the level of the occlusal plane. So, the needle is inserted at the level of occlusal plane.

3) In adults, the mental foramen opens midway between upper and lower border, because the upper alveolar and sub-alveolar parts are equally developed. The needle should be placed above the occlusal plane as foramen is above the level of occlusion.

The angle reduces to 110 or 120 degrees.

4) In old age, both the mental foramen and the mandibular canal are close to the alveolar border.

The angle again becomes obtuse (140) because the ramus is oblique.