Growth and Development of Maxilla and Mandible PDF

Growth and development of Maxilla and Mandible Dr. Sandeep Gupta Learning objectives At the end o the lecture one should be able to know: Embryological development of both the jaws Process of growth of maxilla and mandible Age changes in mandible Growth and Developmen...

Growth and development of Maxilla and Mandible Dr. Sandeep Gupta Learning objectives At the end o the lecture one should be able to know: Embryological development of both the jaws Process of growth of maxilla and mandible Age changes in mandible Growth and Development of Jaw Both the jaws develop from the tissues of first branchial arch Mandible forming within mandibular process Maxilla forming within maxillary process  Development of the maxilla It includes development of: 1. Maxilla proper 2. Premaxilla 3. Accessory cartilages 1. Maxilla proper 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 fibrous tissue immediately lateral to and slightly below the eye bulges  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. Forward: Toward the future incisor region Upward: To form the frontal process of the maxilla. downward: To form the outer alveolar plate for the maxillary tooth germs  Toward the midline: Ossification spreads with the development of the palatal process towards midline. This pattern of bone deposition forms a bony trough that carries infraorbital nerve From this trough a downward extension forms the lateral alveolar process 2. Premaxilla Two centers of ossification for the premaxilla Palato-facial center The prevomerine center ( paraseptal center )  The palato-facial center: Appear at the end of 6 week intrauterine It starts close to the external surface of the nasal capsule 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.  The prevomerine center ( paraseptal center ): It begins at about 8-9 weeks of intrauterine life along the outer alveolar wall. It is situated beneath the anterior part of the vomer bone it forms that part of the bone which lies mesial to the nasal paraseptal cartilage. At 8 week of Intrauterine life union occurs between the maxilla and premaxilla  ACCESSORY CARTILAGES Accessory cartilaginous center appears in the region of the future zygomatic process and this undergoes rapid ossification Also small areas of secondary cartilaginous center appears along the growing margin of the alveolar plate. In the midline of the developing hard palate between the two palatine processes. GROWTH OF THE MAXILLA Sutural growth Alveolar process development Subperiosteal bone formation Enlargement of maxillary sinus Bone resorption and bone deposition  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: a) Fronto-maxillary suture. b) Zygomatico-maxillary suture. c) Zygomaticotemporal suture. d) Pterygopalatine suture  All these sutures are parallel to each other They are directed from upward anteriorly to downward posteriorly. So growth at these sutures will shift the maxilla forward and downward.  Alveolar process development It will add to the height of the maxilla. Eruption of teeth specially the permanent set that serves much in this direction Eruption of the upper permanent molars adds to the length of the arch.  Subperiosteal bone formation Occurs throughout life serves as a main factor for the growth of the maxilla  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 pneumatization.  Bone resorption and bone deposition Occurs also in other sites than the sinus. Bone resorbtion at the floor of the nasal cavity Bone deposition on the oral surface of the palate Aids in the enlargement of the nasal cavity and increase the height of the maxilla  DEVELOPMENT OF THE MANDIBLE The Mandible 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, Unite with the ends of the body nearly at right angles.  Development of the mandible will be divided into: Body of the mandible. The rami The alveolar process  THE BODY OF THE MANDIBLE 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.  Meckel’s cartilage has a close relationship to the mandibular nerve at the junction between proximal and middle third Here the mandibular nerve divides into the lingual and inferior alveolar nerve. The lingual nerve passes forward, on the medial side of the cartilage, The inferior dental nerve lies lateral to its upper margins Then runs forward parallel to it and terminates by dividing into the mental and incisive branches.  From the proximal end of each cartilage the Malleus and Incus, two of the bones of the middle ear, are developed The Ossification takes place in the membrane covering the outer surface of Meckel's cartilage at 6th week Each half of the bone is formed from a single center that appears in the region of the bifurcation of the mental and incisive branches From this initial ossification, the ramifying bones developed forward, backward and upward, to form the symphysis and the mandibular body respectively  At the same stage the notch containing the incisive nerve extends ventrally around the mental nerve to form the mental foramen. A similar spread of ossification in the backward direction produces a trough of bone in which lies the inferior dental nerve and much later the mandibular canal is formed.  THE RAMUS OF THE MANDIBLE 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 as 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. Condylar cartilage (appears in the 12th ): Carrot shaped cartilage appears in the region of the condyle and occupies most of the developing rami. Forms condyle head and neck of the mandible. Forms posterior half of the ramus to the level of inferior dental foramen  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  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 to keep 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. GROWTH OF THE MANDIBLE This process occurs with: Growth by secondary Cartilage. Growth with the alveolar process Subperiosteal bone apposition and bone resorption  Growth by secondary Cartilage It occurs mainly by secondary cartilages (mainly condylar cartilage), this helps in: Increase in height of the mandibular ramus Increase in the overall length of the mandible Increase of the inter condylar distance Age changes in the mandible At birth Childhood Adulthood Old age  At birth The body of the bone is a simple shell contains the sockets of the two incisor, the canine, and the two deciduous molar teeth, 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. Mandible At birth (175 degrees)  At Childhood The two segments of the bone become joined at the symphysis, from below upward, in the first year The body becomes elongated in its whole length, 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  thickening of the sub-dental portion to withstand the powerful action of the masticatory muscles; The mandibular canal, after the permanent dentition, is situated just above the level of the mylohyoid line The mental foramen occupies the position usual to it in the adult The angle becomes less obtuse about the fourth year it is 140°. At Childhood 140 degrees  Adulthood The alveolar and sub-dental 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°. At adulthood – 110-120 degrees  Old age The bone becomes greatly reduced in size With the loss of the teeth the alveolar process is absorbed, 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. At Old age