Development of maxilla1


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Development of maxilla1

  1. 1. Development of Maxilla Prenatal: It can be studied under following headings: - Maxilla proper. - Premaxilla. - Palatine bones. Maxilla proper: It develops from maxillary prominence out ending cranioventrally from much large mandibular prominence derived from first arch, maxillary process of mandibular arch. Like the mandible it first appears as a membranous ossification but unlike mandible, its further development and growth are little affected by appearance of secondary cartilage. First ossification center around of weeks IVL ossification in maxilla commences little later than in mandible. The center of ossification first appears in a bond of fibrocellular tissue which lies on the outer side of cartilage of nasal capsule immediately lateral 1
  2. 2. and slightly below infraorbital nerve where it gives of its anterior superior alveolar nerve. It lies above the part of dental lamina from which enamel organ of canine tooth gum areas. Ossification spreads backwards towards the developing zygomatic bone below the orbit and forward in front of anterior superior alveolar nerve below the terminal part of infra orbital nerve, towards developing premaxilla. At this stage bone takes the shape of curved strip vertically with convex side medially. From the anterior extraction, frontal process develops which with a corresponding process of premaxilla forms frontal process of adult bone. These processes of maxilla and premaxilla unite so rapidly that no suture appears between them from the beginning. The developing maxilla forms a bony trough for I.O. nerve. It forms outer alveolar plate by the downward growth in relation to canine-deciduous molar tooth germs. Maxilla continues to grow mainly upward and downward, backward and with the development palatal process also spreads in midline. 2
  3. 3. A secondary cartilage appears in the zygomatic process and its proliferation considerable adds to back of maxilla. During this period palatine process with grow backward and a large mass of bone of maxilla is formed. From this region lingual alveolar palate develops some what later than buccal plate. The trough of bone formed will be later divided by septa into alveoli small areas of secondary cartilage may be formed in midline of developing hard palate. Secondary ossification centers are: 1. Zygomatic. 2. Orbitonasal. 3. Nasopalatine. 4. Intermaxillary. The two intermaxillary ossification centers generate alveolar ridge and primary palate region which is demarcated by a fissure between LI and canine teeth. Comparison between maxillary and mandibular development 3
  4. 4. This bone disappear as a separate entity by fusion of the fissures during first post nasal. Both commence as centers of ossification in close life relations to a nerve at a place of bifurcation and close relation to elements of cartilaginous facial skeleton. Both have neural and alveolar elements. Both develop secondary cartilage in their backward extraction. However, condylar cartilage remains active for a long perio and zygomatic is limited to period of faetal life. Maxilla has no muscular process and mandible has no palatine process. Growth of maxilla is  surface deposition and sutural. Growth of mandible is  surface deposition and replacement by cartilage. Development of Premaxilla: By two ossification center (first 7 weeks and above incisive form, 2nd 10 weeks and ventral margin of nasal septum. Premaxilla is 4
  5. 5. formed by frontonasal process and limited with the junction of maxillary process. At seven weeks of age a separate center of ossification appears for premaxilla and it retains the identity for a very short period of time and during 8th week union takes place with maxillary ossification. Thus a single mass of bone called maxillary corpus is formed at the each side of face and later frontal process will arise which units with frontal process of maxilla. A heavy trabecularized network of bone appears on labial aspect of canine alveolar which spreads and fuses with underlying frontal process. The alveolar processes arise which surround the developing incisor tooth germ. On the facial aspect, union between maxilla and premaxilla disappears before birth but seen on palatal aspect after birth. Development of Palatine bone: It develops as a fibrocellular condensation on medial side of cartilaginous nasal capsule. Ossification starts at 7-8 weeks IUL in 5
  6. 6. the region of tuberosity in close relation to descending palatine nerve. Ossification extrudes upwards and horizontally. At first, the vertical plate of palatine bone is separated from maxilla by lateral wall of nasal capsule. Development of Maxilla Prenatal: By 8th week of IUL, ossification centers which become maxillary and mandibular skeleton become apparent in the lateral face. Bilateral frontal bones cover the forebrain above the eyes. Small nasal bones appear anterior to the nasal capsule. The premaxillary ossification centers may appear as separate or united sites on anterior surface of nasal capsule. The zygomatic bone and temporal bone appear posterior to maxillary bone. By 12 weeks, premaxillary and maxillary bones have increased in size. During 10th weeks, a ‘V’ shaped bone arises just below the nasal septum of ethamoid and is called Vomer and its two diverging parts grow up on either side of septum. The increase in height of 6
  7. 7. the face occurs with addition to the size of ethamoid and the vomer bone. The sphenoid is located just behind the ethmoid along the base of skull. During the faetal period, bone is deposted on the entire external surface of maxilla and resorption occurs in each alveolus surrounding the tooth buds and on the lingual surface of alveolar ridges. Maxillary arch length increases by both anterior and posterior growth. The orbit floor displaces throughout life (prenatal) inferiorly bone resorbs on the nasal side of the palate and forms on oral surface. In the anterior palate, premaxilla has lingual and plates of bone around incisor teeth. a suture septum the right and left sides. A posterior suture septal, the premaxillary form from the maxillary bones. At this stage the palate is relatively small compared with cranial skeletal. Later, the palate becomes much larger. By 8th month of IUL, the bony configuration of palate is well established and the sutures are still evident. Additional growth of 7
  8. 8. the palate occurs around periphery which assures that growth of the palate will keep pace with the growth of face. Post natal a) Sutures Growth of the maxilla depends upon the influence of several functional matrices that act upon different areas of bone. Thus theoretically can be divided into: The basal body develops beneath the infraorbital nerve, later surrounding it to form infraorbital canal. The orbital unit responds to growth of eye ball. Nasal unit responds to septal cartilage for its growth and the teeth provide functional matrix for the alveolar unit. The pneumatic unit reflects maxillary sinus expansion, which is more a responder than a determiner of the skeletal unit. The complexity of action of these function at forces on the facial bones results in different effects on different sutures. 8
  9. 9. Superozygomatic suture predominantly A-P direction. In order to keep pace with growth of brain and spheno-occipital synchondrosal cartilage. Nasomaxillary suture  A-P direction (predominantly) and creates elevation of bridge of nose. Frontomaxillary Fronto zygomatic Frontonasal Predominately vertically Fronto ethmoidal Ethmoido maxillary Facial width is relatively less on preparation to neurocranium in neonate than adult. The face of new born is twice as broad in comparison with its height than in adult. Growth at all these sutures is greatest until age of 4 years and completes by the end of first decade and of more spurt during puberty. Thereafter these sutures mainly act as sites of fibrous 9
  10. 10. union allowing for adjustments brought about by surface deposition and remodeling. Surface remodeling Remodelling takes place over all the surfaces of maxilla. Growth of alveolar process will add to the vertical height of face and depth of palate. Bone deposition on the posterior surface of maxillary tuberosity induces corresponding anterior displacement of entire maxilla. The growth pattern of dento-alveolar arch differs from other surfaces. It is related to the sequence of tooth eruption. Resorption along the anterior surface of body of maxilla creates supra-alveolar concavity (point A). The final form of maxillary complex is balanced by bone deposition and resorption. It differs between individuals and same individual at different periods. Deposition is most active at the alveolar process, undersurface of hard palate. Both resorption occurs in interior of the maxilla (increasing size of sinuses), upper surface of hard palate. The 10
  11. 11. overall effects is to increase the vertical component of facial growth and reduce the forward component giving a characteristic fracture of modern human face as compared with that of anthropoid apes and early human races. Surface deposition and resorption are more predominate during 2nd decade of life, predominately in vertical direction. Development of Palate: The palate develops from the elements: - Primary palate portion of the frontonasal process. - Two lateral maxillary processes. and palate is formed from one medial and two lateral palatine process. The term palate refers to the tissues that interposes between oral and nasal cavity. The median palatal process is also called as primary palate which begins at 6th week of IUL. It develops as a wedge shaped mass between the maxillary process of the 11
  12. 12. developing upper jaw. From this primary palate the developing four maxillary teeth are supported. At the end of 6th week, the lateral palatine process which form secondary palate develop from the medial edges of maxillary processes. The lateral palatine process grow medially first, then grow downward or vertically on either side of tongue. Shelf elevation: At about 8 ½ week of IUL, the lateral palatine shelves roll over the body of tongue. The process of elevation occurs when the shelves have developed sufficient strength to slide over tongue. It results from combined action of shelf and tongue movement. Palates shelf elevation begins in this posterior region and depresses the tongue downward and forward, which releases the out part of shelves. Thus the tongue utilizes lateral space occupied and broadens. Palatal shelf closure: After the shelves are in a horizontal position there is a final growth spurt, and shelf contact occurs in midline. 12
  13. 13. Closure fusion of LPP occurs first just posterior to median palatine process. It is a process of contact with loss of intervening epithelium and growth of connective tissue across the midline. After this initial contact, there is fusion of LPP with MPP anteriorly. Posteriorly, closure takes place gradually over the next several weeks and involves merging of the two LPP by cell proliferation at the depth of midline grade behind the initial fusion. Fusion of LPP also occurs with nasal septum except post where soft palate and ovula remain unattached . At about 12 week of IUL, palate is invaded anterior by bone from premaxillary, maxillary and palatal centers to form hard palate and post by muscle to form soft palate. Premaxillary ossification center ( primary) 8 week of IUL ( Secondary) Maxillary ossification center (single and appears at 6 week of IUL) 13
  14. 14. Palato maxillary suture Palatine ossification 8th week ossification starts. The fusion of three palatal components initially induced a flat, unarched roof of mouth. The line of fusion of lateral, palatal shelves is traced in adult the midpalatal suture. The mid palatal suture strength is first widest at 10 ½ weeks. In adults it becomes so interdigitated that mechanical interlocking and islets of bone are formed (after 30 years). In adulthood palatine bone elements of the palate remain separated from maxillary elements by transverse palato-maxillary sutures. The ossification does not occur in most posterior part of palate giving rise to region of soft palate. At birth, length and breadth of hard palate are almost equal. The postural increase in palatal length is due to appositional growth at tuberosity and to some extent at transverse maxillopalatine suture. Growth at midpalatine suture ceases between 1 and 2 years of age. 14
  15. 15. Lateral appositional growth continues till 7 years by which time palate achieves its ultimate anterior width. Posterior appositional growth continues after lateral growth has ceased so that palate becomes longer than wider during late childhood. The rougae which are most prominent in infant hold the nipple. The anterior palatal furrow is more marked during 1st year and life (active suckling period). This normally flattens by 3-4 years once the suckling is stopped. If complicated of thumb sucking, it may remain in childhood. Greater palatine foramen is situated between 2nd and 3rd maxillary molar about 1cm from the palatal gingival margin towards midline. In child with only primary dentition erupted, the injection should be made approximately 10mm posterior to the distal surface of the second primary molar. It is not necessary to outer greater palatine foramen. A few drops of solution can be injected slowly at the point where the nerve is emerging from the foramen. The distal line from the most posterior erupted teeth. 15
  16. 16. - Deficiencies of maxillary prominence and brachial arch ectomesenchyme may result in facial bones. - Deficient maxillary development may also be associated with clefts of upper lip and palate, downs syndrome. - Entrapment of epithelial rest cells in the live of fusion of the palatal shelves, may give rise to palatal rest cyst. The common forms are Eptin pearls along the medial raphe of hard palate and junction of hard and soft palate. Bohns modules are mucosal found retention cysts occurring on buccal and lingual aspect of alveolar ridges. - Torus palatinus is a common genetic commonly of palate with localized midpalatal over growth. It may enlarge in adulthood and interfere with appliances. - Delay in elevation of palatal shelves leads to clefting of the palate. - Inadequate use of the nasal cavity by mouth breathing has been associated with the narrow pinched fall and high- 16
  17. 17. vaulted palatal arch of adenoid facies. The erupt space of nasal cavity may influence facial growth and form the cause and effect relationship of this facial form with mouth breathing has not been substantiated. - Shapes of palate (u, v, high roofed). - Cleft palate is a result associated with habits of non-fusion. - R & L valves of embryonic palate. It may be of different degrees. In the least severe type, the defect is confined to soft palate and in severe cases it is continuous with cleft of lip. - Epigraphers is a teratome arising specifically from the palate. - Absence of neural crest ectomesenchyme in frontonasal prominence may result in cleft lips. - Hemifacial microsomin produces asymmetric face on affected side ear, zygomatic bone and mandible will be underdeveloped. - Supernumerary  the pattern of bone remodeling. 17
  18. 18. - It the palate thickness same all over? - It narrows posteriorly. 18
  19. 19. Development of Mandible Introduction: Human mandible does not have a single design for life. Rather it adapts and remodels through different stages of life. It is rather a exceptional bone in that it is largely derived from membrane bone, yet main site of growth is at cartilage. History: Hunter (1961) proposed that mandible grows by apposition in on its posterior border with resorption on anterior border. Humphry (1966) supported the Hunter’s theory. He tied the wire around the growing mandible of pig and found that wire was embedded in posterior portion of mandible after portion of mandible after growth. Alizarin study by Weinman in 1944 suggested that condyle was potential of growing in superior and posterior direction. Rickett’s in 1950 supported this. Prenatal: 19
  20. 20. At about 6 week of IUL, as the nasal capsule becomes the prominent cartilage in the upper face, Meekel’s cartilage bars become apparent in mandibular arches (1st pharyngeal arch). The posterior part of each of these bars enlarge to become the (dorsal) malleus, which articulates with a second small cartilage, the incus. These two cartilages become enclosed in otic capsule. They form a joint called primary TMJ articulation of these two cartilages occurs until they undergo endochondral bone formation during 18 week IUL. At this time secondary TMJ formed anterior to middle ear and begins functioning. The shift of primary to secondary occurs as Meekle’s cartilage is fused to mandible. The mandible is formed in the lower or deeper part of 1st arch. It is preceded by Mekels cartilage. Mekels cartilage attains its full form of 5mm by 6 weeks and then stretches downwards and forwards as an unbroken rod of cartilage. In midline the ventral line turns upward in contact with cartilage of opposite side. It is surrounded in its whole length by a thick investment of fibrocellular tissue. 20
  21. 21. Except for the dorsal part, the remaining part is associated with the development of mandible. The mandibular nerve: The main nerve issues from the skull medial and ventral to dorsal end of cartilage and comes into direct relation with it about the junction of its dorsal and midline 1/3rds. Here it gives lingual and inferior alveolar nerve. The lingual nerve passes medial to the cartilage and inferior A-N on lateral aspect. Running forward terminates by dividing into ----- and incisive branches. Body of the mandible: Figure The body of the mandible continues to develop as a rectangular membrane bone. The ossification center appears at 7 week of IUL I the angle by mental and incisive nerve. This is the area of future mental foramen. From this center, the formation of bone spreads rapidly backward below the mental nerve, which then lies in on notch in bone and on the lateral side of inferior alveolar nerve. The 21
  22. 22. bone in front of the region of the notch for mental nerve grows medially below the incisive nerve and spreads upwards between this nerve and Meckels cartilage, thus the incisive nerve contained in a trough of bone. The notch containing the mental nerve is converted into mental foramen. The bony trough grows rapidly forward towards the midline where it comes in close relationship with similar bone formation of opposite side but its separated from connective tissue union takes place before the end of first year postnatally. A similar spread of ossification (between 4-12months) takes place in backward direction. Thus by these process, original primary center of ossification produces the body proper of mandible form mandibular foramen to symphises. Fate of Meckels cartilage: With the exception of at midline, the anterior part of mandible, from in front of mental foramen included cartilage in its substance. This part of cartilage first surrounded by on extension of bone from the medial plate and then gradually resorbed and replaced by an extension of ossification from membrane bone around it. The rest 22
  23. 23. of Meckels cartilage disappears completely except for a part of its fibrous covering which persists as sphenomandibular and spheno- alveolar ligament. The ramus: The backward extension of mandible to form the ramus is produced by a spread of ossification from the body, behind and above mandibular foramen. As in body, here too the ramus and its processes are first mapped out by extension of this condensation. The formation of bone occurs rapidly so that the coronoid and condylar processes are ossified to a greater extent. The further growth of these processes is modified by secondary cartilages. Alveolar bone: As the enamel organ of deciduous tooth germs reach the early bell stage, the bone of the mandible begins to come into close relationship to them. This is brought about by the upward growth, on each side, of the lateral and medial plates of mandibular bone above the level where the roof of the canal for the incisive and 23
  24. 24. inferior alveolar nerve is formed. By this growth, the developing teeth come to lie in a trough of bone. This trough is later divided into small alveoli for the teeth by the formation of septa between two walls. Secondary cartilage: These occur at various sites in the region of membrane bone formation, also called as accessory cartilage. They have no connection with primary cartilage. The primary cartilage is hyaline. These cartilages have less intercellular matrix than hyaline. These cartilages increase in size by proliferation and transformation of the cells of thick layer of fibrous cellular tissue covering them. 24
  25. 25. Condylar cartilage: There are three sites of secondary cartilage formation appears between 10-14th weeks of IUL. The largest and first one is condylar cartilage. It appears on superior and lateral aspects of condylar process. The cartilage forms a cone-shaped mass which not only occupied the whole of condylar process but reaches forward and downward into ramus upto level of mandibular foramen. Cartilage in anterior part shows ossification and its continues till 5 month IUL where only cartilage is left unresorbed beneath the proliferating tissue of condylar articular surface. this persists until the end of second decade of life. During this period, thickeness of zone of cartilage disappears and the replacing bone forms whole of condyle. This cartilage is responsible for whole of normal growth period and increases length of mandible. Coronoid cartilage: Found along the anterior border and summit of coronoid process. All the traces of cartilage disappears long before birth. 25
  26. 26. Symphyseal cartilage: This is the 3rd cartilage occurring at the symphyseal end of each half of bony mandible. These enable the mandible to grow in with till they persist. Once the union of mandible occurs at birth, they do not take any further part in growth. At birth mandible has wide mandibular angle (135°), ramus is small compared to body and chin is poorly developed. Clinical importance: The shape and size of the fetal mandible undergoes transformation during its growth and development. The ascending ramus of neonatal mandible is low and wide and coronoid process is relatively large and projects well above the condyle. The mandibular canal runs low in the body. As the mandibular body is showing the direction of mental foramen during infancy and childhood changes. The mental neuromuscular bundle arises at right angles of slightly forward direction at birth. In adulthood it is characteristically directed backward. This change 26
  27. 27. may be due to forward growth in the body of mandible while neurovascular bundle drags along. This changing direction of foramen has clinical implication in administration of local anesthetic i.e. in infancy and childhood syringe needle may be applied at right angles where as in adult it has to be applied obliquely from behind. The location of the mental foramen also alters its vertical relationship within the body of mandible from infancy to old age. When teeth are present it located midway between upper and lower border of mandible and in edentulous mandible appears to be near the upper margin. The alveolar process develops as a protective trough in response to tooth buds and becomes superimposed upon basal bone of mandibular body. This bone fails to develop if teeth are absent and resorbs in response to tooth extraction. The orthodontic movement of teeth takes place in alveolar bone (bed) and does not involve basal bone. Torus mandibular is exostasis which usually develops bilaterally in the canine-premolar region. 27
  28. 28. During fetal life the relative sizes of the maxilla and mandible vary wide. Initially at 6 week IUL, mandible is considerably larger than maxilla. By about 8 week, greater development of maxilla. Subsequently relatively larger growth of mandible results at 11 week and lower and upper grows are of equal size between 13-20 week, mandibular growth lags behind due to change over from Meckels cartilage to condylar secondary cartilage. At birth mandible tends to be retrognathic though two jaws are of equal size. This is normally corrected by postnatal growth to develop Angle Class I relationship (maxillo-mandibular). Inadequate growth results in Class II and overgrowth into Class III relation. The mandible may be grossly deficient or absent. This condition is known as agnathia. Aplasia of mandible and hyoid bone is a rare and lethal condition called as 1st and 2nd arch syndrome. In this syndrome ischaemic necrosis of the mandible and hyoid bone occurs after formation of ear. Micrognathia is characteristic of several syndromes. 28
  29. 29. - Pierre robin syndrome. - Cat-cry syndrome. - Treacher Collin’s (mandibulofacial). - Down’s syndrome (trisomy 21). - Turners syndrome. There may be double condyle or bifid condyle that results from persistence of septa dividing fetal condylar cartilage. Unilateral condylar hyperplastic is also common. Prognathism is usually inherited condition hyperpituitarism may produce mandibular over growth. Angulation of angle of mandible is 135° at childhood and senilehood and at adult hood decreases to 160°. 29