Development of face and oral Cavity Development of the mandible

The mandible is the largest and strongest bone of the face It consists of a curved, horizontal portion, the body, and two perpendicular portions, the rami, which unite with the ends of the body nearly at right angles. For better description development of the mandible will be divided into: 1. Body of the mandible. 2. The rami 3. The alveolar process

Devel. of the mandibular body The basic growth pattern of the mandibular body and condyle appeared in week 7 of fertilization. Histologically, the embryonic mandible originated in the lower part of the first branchial arch from primary intramembranous ossification in the fibrous mesenchymal tissue around the Meckel's cartilage.

Devel. of the mandibular body

Meckel’s cartilage has a close, relationship to the mandibular nerve, at the junction between poximal and middle thirds, where the mandibular nerve divides into the lingual and inferior alveolar nerve. The lingual nerve passes forward, on the medial side of the cartilage, while the inferior alverolar lies lateral to its upper margins. Before the begin of ossification the mandibular nerve and its branches are developed and they ensure the formation of canals around them.

Devel. of the mandibular body

Development of the mandible The Ossification takes place in the membrane covering the outer surface of Meckel's cartilage and each half of the bone is formed from a single center which appears, in the region of the bifurcation of the mental and incisive branches, about the sixth week of fetal life. From this initial ossification, the ramifying trabecular bones developed forward, backward and upward, to form the symphysis and the mandibular body respectively, following the path way of the incisive and the inferior alveolar nerve.

Devel. of the mandibular body From the proximal end of each cartilage the Malleus and Incus, two of the bones of the middle ear, are developed.

Devel. of the mandibular body

Development of the rami The ramus of the mandible develops by a rapid spread of ossification backwards into the mesenchyme of the first branchial arch diverging away from Meckel’s cartilage. This point of divergence is marked by the mandibular foramen. Somewhat later, accessory nuclei of cartilage make their appearance: A wedge-shaped nucleus in the condyloid process and extending downward through the ramus. A small strip along the anterior border of the coronoid process.

Development of the rami The accessory cartilages: 1.Symphysal cartilage 2.Condylar cartilage: 3.Coronoid cartilage Coronoid

Development of the rami Condylar cartilage: Carrot shaped cartilage appears in the region of the condyle and occupies most of the developing rami. It is the largest and most important one. It appears in the 12 th WIU and is rapidly converted to bone by endochondral ossification (14 th WIU).

Development of the rami It gives rise to: Condyle head and neck of the mandible. The posterior half of the ramus to the level of inferior alveolar foramen. A thin layer of cartilage remains in the condylar head and persists until the 20 years of life providing a mechanism of mandibular growth.

Development of the rami The coronoid cartilage: It is relatively transient growth cartilage center ( 4th to 6 th MIU). it gives rise to: Coronoid process. The anterior half of the ramus to the level of inferior alveolar foramen.

Development of the alveolar process It starts when the deciduous tooth germs reach the early bell stage. The bone of the mandible begins to grow on each side of the tooth germ. By this growth the tooth germs come to be in a trough or groove of bone, which also includes the alveolar nerves and blood vessels. Later on, septa of bone between the adjacent tooth germs develop, keeping each tooth separate in its bony crept.

Development of the alveolar process The mandibular canal is separated from the bony crypts by a horizontal plate of bone. The alveolar processes grow at a rapid rate during the periods of tooth eruption.

Growth of the mandible The shape and size of the mandible undergo considerable transformation from embryonic to adult mandible. The process of transformation occurs in three steps: Growth by accessory Cartilage Growth with the alveolar process Subperiosteal bone apposition and bone resorption.

Growth of the mandible

The mandible grows in all directions: Anterio-posterior by bone deposition along the posterior border of the ramus. Vertical by growth of the condyle, along the upper border of the ramus and the formation of the alveolar process. Transverse by bone deposition on the external surface and bone resorption at the inner surface.

Growth of the mandible