mandible development

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Slide 1: 

DEVELOPMENT OF THE MANDIBLE

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Is the largest and strongest bone of the face, serves for the reception of the lower teeth. 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. The Mandible

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ANATOMY OF THE MANDIBLE

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I’ll ask u a question..

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Do you remember the 1st. Branchial arch?

Slide 8: 

DEVELOPMENT OF THE MANDIBLE

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THE BODY OF THE MANDIBLE

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The mandible is ossified in the fibrous membrane covering the outer surfaces of Meckel's cartilages. These cartilages form the cartilaginous bar of the mandibular arch and are two in number, a right and a left.

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Their proximal or cranial ends are connected with the ear capsules, and their distal extremities are joined to one another at the symphysis by mesodermal tissue.

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Meckel’s cartilage has a close, relationship to the mandibular nerve, at the junction between posterior and middle thirds, where the mandibular nerve divides into the lingual and inferior dental nerve.

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The lingual nerve passes forward, on the medial side of the cartilage, while the inferior dental lies lateral to its upper margins & runs forward parallel to it and terminates by dividing into the mental and incisive branches.

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From the proximal end of each cartilage the and , two of the bones of the middle ear, are developed; the next succeeding portion, as far as the lingula, is replaced by fibrous tissue, which persists to form the sphenomandibular ligament & the perichondrium of the cartilage persist as sphenomallular ligament. malleus incus

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Between the lingula and the canine tooth the cartilage disappears, while the portion of it below and behind the incisor teeth becomes ossified and incorporated with this part of the mandible.

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The mandible first appears as a band of dense fibrocellular tissue which lies on the lateral side of the inferior dental and incisive nerves. For each half of the mandible,

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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.

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NOW….. What is the remnants of the Meckel’s cartilage?

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Ossification grows medially below the incisive nerve and then spread upwards between this nerve and Meckel’s cartilage and so the incisive nerve is contained in a trough or a groove of bone formed by the lateral and medial plates which are united beneath the nerve.

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At the same stage the notch containing the incisive nerve extends ventrally around the mental nerve to form the mental foramen. Also the bony trough grow rapidly forwards towards the middle line where it comes into close relationship with the similar bone of the opposite side, but from which it is separated by connective tissue.

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A similar spread of ossification in the backward direction produces at first a trough of bone in which lies the inferior dental nerve and much later the mandibular canal is formed. The ossification stops at the site of future lingula. By these processes of growth the original primary center ossification produces the body of the mandible.

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THE RAMI OF THE MANDIBLE

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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.

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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.

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The condylar cartilage: Carrot shaped cartilage appears in the region of the condyle and occupies most of the developing ramus. It is rapidly converted to bone by endochondral ossification (14th. WIU) it gives rise to: Condyle head and neck of the mandible. The posterior half of the ramus to the level of inferior dental foramen

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

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These accessory nuclei possess no separate ossific centers, but are invaded by the surrounding membrane bone and undergo absorption.

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The alveolar process

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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.

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Later on, septa of bone between the adjacent tooth germs develop, keeping each tooth separate in its bony crept. 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.

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GROWTH OF THE MANDIBLE

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II. Development of the alveolar process: Due to the increase in the space between the upper and lower jaws ( why ) a space created between the opposing teeth to erupt. At the same time bone apposition occurs at the crest of the alveolar prpcess and the fundus of the alveolus. The deposited bone at the fundus of the alveolus counts later to the body of the mandible.this process also responsible for the distance between the mandibular canal and the apices of the premolars and first two molars. This means that bone deposition contributes to the growth of the body of the mandible in height.

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III. Subperiosteal bone apposition and bone resorption:

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Age changes in the mandible

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At birth 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 is of large size, and runs near the lower border of the bone; the mental foramen opens beneath the socket of the first deciduous molar tooth. The angle is obtuse (175°), and the condyloid portion is nearly in line with the body. The coronoid process is of comparatively large size, and projects above the level of the condyle.

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childhood 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; 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; 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°.

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adulthood 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°.

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Old age The bone becomes greatly reduced in size, for with the loss of the teeth the alveolar process is absorbed, and, consequently, the chief part of the bone is below the oblique line. The mandibular canal, with the mental foramen opening from it, is close 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.

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DEVELOPMENT OF THE MAXILLA

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The maxillæ are the largest bones of the face, excepting the mandible, and form, by their union, the whole of the upper jaw. Each assists in forming the boundaries of three cavities, the roof of the mouth, the floor and lateral wall of the nose and the floor of the orbit; it also enters into the formation of two fossæ, the infratemporal and pterygopalatine, and two fissures, the inferior orbital and pterygomaxillary. Each bone consists of a body and four processes—zygomatic, frontal, alveolar, and palatine. The Maxilla

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ANATOMY OF THE MAXILLA

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I’ll ask u a question..

Slide 48: 

Do you remember the 1st. Branchial arch?

Slide 49: 

DEVELOPMENT OF THE MAXILLA

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Do u remember the development of the body of the mandible?

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MAXILLA PROPER

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It develops in the mesenchyme of the maxillary process of the mandibular arch as intramembranous ossification. It has one center of ossification which appears in a band of fibrocellular tissue immediately lateral to and slightly below the infra orbital where it gives off its anterior superior dental branch. The ossification center lies above that part of the dental lamina from which develop the enamel organ of the canine.

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The ossified tissue appears as a thin strip of bone. It spread in different directions as: Backward: Below the orbit toward the developing zygomatic bone.

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The ossified tissue appears as a thin strip of bone. It spread in different directions as: Forward: Toward the future incisor region

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The ossified tissue appears as a thin strip of bone. It spread in different directions as: Upward: To form the frontal process of the maxilla.

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As a result of this pattren of bone deposition, a bony trough is formed (infraorbital groove) where the infraorbital nerves lies. The inner and outer edges of this groove grow up, meet and fuse forming a canal that encloses the nerve & open anteriorly at the infraorbital foramen

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The ossified tissue appears as a thin strip of bone. It spread in different directions as: downward: To form the outer alveolar plate for the maxillary tooth germs

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The ossified tissue appears as a thin strip of bone. It spread in different directions as: Toward the medline: Ossification spreads with the development of the palatal process in the substance of the united palatal folds to form the hard palate. At the union between the palatal process and the main part of the developing maxilla, a large mass of bone produced. From this region & on the inner side of the dental lamina & tooth germs, the inner alveolar plate of deciduous canines and molars develops.

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Development of the maxillary sinus: At 4 MIU as a small depression of the mucosa of the lateral wall of the nasal cavity. In its gradual extension the sinus comes into relation with the maxilla above the level of the palatal process & a hallows out the interior of the bone, so separating its upper or orbital surface from its lower or dental region.

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PREMAXILLA

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Two centers of ossification for the premaxilla: A) The palato-ficial center: Appear at the end of 6 WIU. It starts close to the external surface of the nasal capsule, in front of the anterior superior dental nerve and above the germ of the lateral deciduous incisor. From this center bone formation spreads: Above the teeth germ of the incisors. Then downward behind them. To form the inner wall of their alveoli & palatal part of the premaxilla. B) The prevomerine center ( paraseptal center ): It begins at about 8-9 WIU along the outer alveolar wall. It is situated beneath the anterior part of the vomer bone and it forms that part of the bone lies mesial to the nasal paraseptal cartilage.

Slide 63: 

Two centers of ossification for the premaxilla: A) The palato-ficial center: Appear at the end of 6 WIU. It starts close to the external surface of the nasal capsule, in front of the anterior superior dental nerve and above the germ of the lateral deciduous incisor. From this center bone formation spreads: Above the teeth germ of the incisors. Then downward behind them. To form the inner wall of their alveoli & palatal part of the premaxilla. B) The prevomerine center ( paraseptal center ): It begins at about 8-9 WIU along the outer alveolar wall. It is situated beneath the anterior part of the vomer bone and it forms that part of the bone lies mesial to the nasal paraseptal cartilage.

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At 8 WIU union occurs between the maxilla and premaxilla

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ACCESSORY CARTILAGES

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Unlike the mandible the development and growth are little affected by the appearance of secondry cartilages.

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What was the accessory cartilages we mentioned in the development of the mandible

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Accessory cartilagenous center appears in the region of the future zygomatic or molar process and this undergoes rapid ossification & adds considerable thickness to the bulk of this part. Also small areas of secondry cartilagenous center appears along the growing margin of the alveolar plate. In the middle line of the developing hard palate between the two palatine processes.

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Accessory cartilagenous center appears in the region of the future zygomatic or molar process and this undergoes rapid ossification & adds considerable thickness to the bulk of this part. Also small areas of secondry cartilagenous center appears along the growing margin of the alveolar plate. In the middle line of the developing hard palate between the two palatine processes.

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GROWTH OF THE MAXILLA

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1. Sutural Growth It continues till 10 years of age then becomes less significant. The maxilla articulates with the other bones of the skull by 4 main sutures: Frontomaxillary suture. Zygomaticomaxillary suture. Zygomaticotemporal suture. Pterygopalatine suture.

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All these sutures are parallel to each other and directed from upward anteriorly to downward posteriorly. So growth at these sutures will shift the maxilla forward and downward.

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2. Alveolar process development It will add to the height of the maxilla. Eruption of teeth specially the permenant set that serves much in this direction, while eruption of the upper permenant molars adds to the lengt of the arch.

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3. Subperiosteal bone formation Occures throughout life serves as a main factor for the growth of the maxilla

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4. Enlargement of the maxillary sinus It plays an important role in the growth of the body of the maxilla. The sinus, which occupies most of the body of the maxilla, expands by bone resorption on the sinus side and bone deposition on the facial surface of the maxillary process. A process known as pneumotization

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5. Bone resorption & bone deposition Occurs also in other sites than the sinus. Bone resorbtion at the floor of the nasal cavity compensated by bone deposition on the oral surface of the palate will aid in the enlargement of the nasal cavity and consequently increase the height of the maxilla

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5. Bone resorption & bone deposition Occurs also in other sites than the sinus. Bone resorbtion at the floor of the nasal cavity compensated by bone deposition on the oral surface of the palate will aid in the enlargement of the nasal cavity and consequently increase the height of the maxilla

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AGE CHANGES OF THE MAXILLA

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At birth The transverse and antero-posterior diameters of the bone are each greater than the vertical. The frontal process is well-marked and the body of the bone consists of little more than the alveolar process. the teeth sockets reaching almost to the floor of the orbit. The maxillary sinus presents the appearance of a furrow on the lateral wall of the nose

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Adulthood In the adult the vertical diameter is the greatest, ( why )?

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Old age In old age the bone reverts in some measure to the infantile condition as: its height is diminished. after the loss of the teeth the alveolar process is resorbed, and the lower part of the bone contracted and reduced in thickness.

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Questions???

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Your exit ticket