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Development of teeth


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Development of teeth

  1. 1. DEVELOPMENT OF TEETH09/24/12
  2. 2. DEVELOPMENT OF TEETH INTRODUCTION The morphogenesis of teeth and development of dentition involve a number of closely related processes. It begins with local changes and there is growth of corresponding parts of jaw. Appearance of teeth in the mouth at appropriate time can have very profound effect on the feeding behavior and mastication skills.09/24/12
  3. 3. HOW TOOTH DEVELOPMENT INITIATES * During development of embryo, there is formation of 3 germ layers a) Ectoderm b) Endoderm c) Mesoderm * The primitive oral cavity or stomodeum is lined by stratified squamous epithelium called ORAL ECTODERM. * Ectoderm contacts with endoderm of foregut to form the bucco pharyngeal membrane. * At about 27th day of gestation the membrane ruptures and primitive oral cavity establishes a connection with foregut. * Connective tissue cells underlying the oral ectoderm induce overlying ectoderm to start tooth development. These ectomesenchymal cells consist of few spindle shaped cells separated by gelatinous ground substance.09/24/12
  4. 4. PRIMARY EPITHELIAL BAND •It is a continuous band of thickened epithelium formed in both upper & lower jaw. •Formed by fusion of separate plates of thickened epithelium after 37 days of development. •It is a horseshoe shaped structure, which corresponds in position to the future dental arches. •It results due to change in orientation of the plane of cleavage of dividing cells. * It gives rise to 2 subdivisions. a) Vestibular Lamina b) Dental Lamina09/24/12
  5. 5. DENTAL LAMINA Dental lamina is a band of epithelium that has been invaded by underlying mesenchyme and dental arches. Formed when certain areas of the basal cell proliferate at more rapid rate than the cells of adjacent areas. FUNCTIONS : 1) First Phase- Act as primordium for the ectodermal portion of deciduous teeth - 8th week. 2) Second Phase-Initiation of successor of deciduous teeth by successional dental lamina. 3) Third Phase- Initiation of permanent molar.09/24/12
  6. 6. FATE OF DENTAL LAMINA * Total activity of dental lamina extends over a period of min of 5 years. * As dentine and enamel start to develop dental lamina begins to degenerate separating into clumps but whose thickness of lamina is not perforated. * Give whorled appearance over developing deciduous teeth. * Persist as epithelial rests but sometimes they proliferate to form cystu cavities known as eruption cyst recognized as blush swelling over erupting teeth and they delay eruption. * Breaking upon of dental lamina determine crown pattern. * Degeneration of lamina separates developing tooth from oral epithelium as a result of degeneration tooth continues its development within tissues of jaw. * Penetration of lingual epithelium by tooth is unique example of natural break in the epithelium of the body.09/24/12
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  8. 8. VESTIBULAR LAMINA •Also called up furrow band or vestibular band. •Horseshoe shaped in growth of epithelium, which develops buccal to dental lamina. •Vestibular band grows deeply into mesenchyme of premature jaws separating lips and cheeks from tooth forming region. It subsequently thickens & clears at vestibular growth form oral vestibular lamina. TOOTH DEVELOPMENT Development history is divided into several morphologic stages. They do not properly describe the functional changes that occur during development. Different stages are named according to shape of epithelial part of tooth germ.09/24/12
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  10. 10. TIME SCALE OF HUMAN TOOTH DEVELOPMENT AGE Development characteristics 42-48 days Dental lamina formation 55-56 days Bud stage, deciduous incisor canine & molar. 14 weeks Bell stage for deciduous teeth, bud stage for permanent teeth 18 weeks Dentin and functional ameloblastes in deciduous teeth. 32 weeks Dentine & functional ameloblast in permanent teeth.09/24/12
  11. 11. STAGES BUD STAGE • Differentiation of dental lamina leads to formation of round, ovoid swelling at 10 different points corresponding to future position of deciduous teeth. These are the primordia of enamel organ. • Enamel organ consists of peripherally located low columnar cells and centrally located polygonal cells. • Dental papilla : It is the area of ectomesenchymal condensation subjacent to enamel organ. Cells of dental papilla will form tooth pulp & dentine. * Dental sac: It is area of ectomesenchymal condensation surrounding the tooth bud & dental papilla. Cells of dental sac will form cementum & periodontal ligament.09/24/12
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  13. 13. CAP STAGE : * Characterized by a shallow invagination of deep surface of a bud. * Outer & inner enamel epithelium. * Cuboidal cells cover the convexity of the cap. •Columnar cells cover the concavity of the cap. * Stellate Reticulum: Polygonal cells begin to separate as more intercellular fluid is produced and forms cellular network called stellate reticulum. •Enamel Knot: Cells in center of the enamel organ are densly packed. This knot projects towards underlying dental papilla. Vertical extension of enamel knot forms enamel cord. Both the structures disappear before enamel formation begins. *Dental papilla & dental sac : Dental papilla is for mature organ of dentine & shows active budding of capillaries & mitotic figures. • Dental sac are important for formations of cementum & periodontal ligament.09/24/12
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  15. 15. BELL STAGE :  Stage of Histodifferentiation and Morph differentiation.  During histodifferentiation some cells of dental organ diffentiates into specific form and shape. This is seen in early Bell stage.  During morph differentiation Dental organ assumes characteristic shape of the tooth. This is seen in late Bell stage.  The invagination of the epithelium deepens and its margins continue to grow and enamel organ assumes a bell shape.  During histodifferentiation cells acquire their functional assignment. Odontoblasts are differentiated from mesenchymal cells with formation of dentin the cells of inner dental epithelium transform into ameloblasts and enamel matrix is lead down opposite the dentin. Presence of dentin is absolutely essential for laying down of enamel.  Differentiation of epithelial cells are essential for differentiation of epithelial Odontoblasts and initiation of dentin formation. Future dentino enamel junction is outlined and the form of crown is established.  Tooth germ shows the following structures:09/24/12
  16. 16. I. Dental organ : a) Outer dental epithelium: A single rows of cuboidal cells is thrown into folds and contain blood vessels at late bell stage. b) Stellate reticulum: There is increase in intercellular fluid and layer expands. The cells assume star shape with long processes that anastomose with adjacent cells. c) Stratum intermedium: Several layers of squamsus cells appear between stellate reticulum and inner dental epithelium and are called stratum intermedium. This layer is essential for enamel formation. It helps in calcification of enamel and is a reserve source for new ameloblasts. d) Inner dental epithelium: This consists of single layer of cells that differentiates into tall columnar cells, the ameloblasts. They have a hexagonal shape on cross section and are 4u in diameter and 40u in height. These cells influence the underlying mesenchymal cells, which differentiates into Odontoblasts.09/24/12
  17. 17. II. Dental Papilla : It is the mesenchyme enclosed portion of the Dental organ. The peripheral cells under the influence of inner dental epithelium assume an cuboidal shape first & columnar later and are called Odon oblast, which produce dentin. The basement membrane separating the epithelial dental organ and dental papilla is called membrana performativa which forms future dentino enamel junction. III. Dental sac: Before formation of dental tissues begins, the dental sac shows a circular arrangement of its fibres and resembles a capsular structure. With the development of the root the fibers of dental sac differentiates into the periodontal fibres that become embedded in the developing cementum and alveolar bone.09/24/12
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  19. 19. Apposition The tooth germ forms calcified tissues of the tooth, the enamel, the dentin and the cementum. There is a layer like deposition of an extra cellular matrix resulting in additive growth. There is regular and rhythmic deposition, which is incapable of further growth.09/24/12
  20. 20. FORMATION OF ROOT Root start forming after dentin formation has reached future cementoenamel junction. Both dental organ and dental papilla play part in formation of root. Hertwigs epithelial root sheath : * The outer and inner dental epithelium meets one another at future cervical area and is called cervical loop. * This cervical loop forms epithelial sheath of Hertwig, which moulds the shape of the root and initiates dentin formation.09/24/12
  21. 21.  The root sheath consists of only outer and inner dental epithelium.  The inner layer of cells remains short and do not produce enamel. These cells induce the differentiation of cell of dental papilla into Odontoblasts, which lay a layer of dentin. At the same time the continuity of Hertwigs sheath is destroyed due to infiltration of connective tissue and the root sheath breaks up into small strands of epithelium called epithelial rests of Molassez.  While the coronal part of the sheath degenerates, the apical part continues to grow in length and aid in lengthening of root.  The cells of dental sac differentiate into cementoblasts, which lay cementum over the outer surface of the dentin in root portion. At the same time precollagenous fibers appear between cementoblasts and become continuous with outer surface of dentin. They become collagenous and are transformed into cementoid tissue, which calcifies to form cementum.09/24/12
  22. 22.  The sheath is folded first at future cemento enamel junction into a horizontal plane. This is called epithelial diaphragm.  Differential growth of the epithelial diaphragm in multirooted teeth causes the division of the root trunk into two or three roots. During the general growth of the enamel organ the expansion of its cervical opening occurs in such a way that long tongue like extensions of the horizontal diaphragm develop.  Before division of the root trunk occurs the free ends of these horizontal epithelial flaps grow toward each other and fuse. The single cervical opening of the coronal enamel organ is then divided into two or three openings. Enamel pearls: If the cells of epithelial root sheath remain adherent to the dentin surface, they may differentiates into fully functioning ameloblasts and produce enamel. Such droplets of enamel called enamel pearls.09/24/12
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  24. 24. The tooth buds of all primary teeth are present and in various stages ofdevelopment at the time of birth.About 7 to 8 months after birth, all the teeth except the 7’s & 8’s are present insome stage of development.By the 1st year, a normal & desirable dentition will usually exhibit spacing09/24/12
  25. 25. The 1st primary tooth to erupt is the lower central incisor between 6&8 months of age, followed by the U.Centrals, U.Laterals & L.Laterals. The 1st primary molar erupts by about the 14th month. The primary cuspids & 2nd primary molars erupt by about 2 & 1/2 yrs of age.  09/24/12
  26. 26.   This is the period between the completion of eruption of Primary dentition & the emergence of the Permanent teeth. According to Baume(1950) Primate Space(Type I Spacing) Spacing invariably is seen mesial to the max canine &distal to the mand canines these physiological space are called primate spaces or simian spaces or anthropoid spaces as they are seen commonly in primates These spaces help in placement of canine cusps of the opposing arch 09/24/12
  27. 27.   The tooth buds of the 4’s & 5’s begin to form. 09/24/12
  28. 28.  Eruption of the 1st permanent molars: The Terminal plane is very important in determining the interocclusal relationship of the 1st permanent molars. Vertical plane Mesial step Distal step09/24/12
  29. 29. When deciduous 2nd molar in flush terminal plane , the 1st molar eruptsinto a cusp to cusp relationship,Which later transform into a class 1 molar relation using primate space andleeway spaceIf deciduous molar in distal step, the permanent molar erupt into a class 11relation, this molar configuration is not self correctingIf primary 2nd molar in mesial step relationship, leads to class 1 molarrelation in mixed dentition this may remain or progress to a half or full cuspclass 111 with continued mandibular growth 09/24/12
  30. 30.  Exchange of incisors : The primary incisors begin to exchange with the permanent incisors before & after the eruption of the 6’s. The total sum of the M-D width of the 4 permanent incisors is > that of the primary incisors by about 7mm in the maxilla & 5mm in the mandible. Incisor liability (Mayne 1968 ) -Interdental spacing in primary incisors should exist. -Intercanine arch width growth should occur. - Intercanine archlength should increase through anterior positioning of the permanent incisors. Favourable size ratio between the primary & permanent teeth.  09/24/12
  31. 31.  This period is referred to as the “Mixed Dentition period”/ “Ugly Duckling stage” ( Broadbent 1937 ) Around the age of 8 yrs a midline diatema is commonly seen in the upper arch Which is usually misinterpreted by the parent as malocclusion09/24/12
  32. 32. Crown of the canine impinge on developing lateral incisor roots, thus driving the roots medially and causing the crown to flare laterally The roots of central incisor are also forced together thus causing midline diastemaThis period from the eruption of lateral incisor to canine is termed as the ugly duckling stageWith the eruption of canine, the impingement from the root shifts incisally thus driving theincisor crown medially, resulting in closure of the diastema 09/24/12
  33. 33.    The “GABLE EFFECT” : The mand. cuspids & bicuspids are in the shape of a ‘V’, in sequence, in relation to the occlusal plane.  The sequence of eruption being 3,4,5 in the mandible, 3 makes its way much ahead of 4 & 5.  09/24/12
  34. 34.  Here, exchange of teeth occurs between c,d,e & 3,4, 5. Emergence of 7’s takes place by virtue of increase in arch-circumference, after the Dental arch upto 6, is established .(mixed to permanent ) During the exchange & emergence, smooth utilization of “Leeway space” . The sequence of eruption of the teeth in: Maxilla - 4, 3, 5 ( 3,4,5 /4,5,3 are exceptions ). Mandible - 3,4, 5.   09/24/12
  35. 35. The Leeway Spaces , the sum of the mesiodistal width of the primary canineand the primary first and second molars is larger than the sum of theirsuccedaneous teeth, namely, the permanent canine and first and secondpremolars. This differenceis called the leeway space and is present in both the maxillaryand mandibular arches .Themost favorable dental arch pattern is when leeway space is excessiveThe leeway space is larger in the mandibular arch than in the maxillary arch. 09/24/12
  36. 36. On the average, the 1.8 mm in the lower arch In the upper arch, the leewayspace averages only 0.9 mm per side. combined sizes of the unerupted teethare larger than the space available.This condition is called a leeway space deficiency, and dental arch crowdingoften results. The leeway space differential between the two arches allows the firstpermanent molars to move mesially relatively more in the mandibular archthan in the maxillary arch. 09/24/12
  37. 37.  The permanent dentition stage of dental development starts after the shedding of the last primary tooth and the eruption of all the permanent teeth excluding third molars.  This is considered to be between 18 & 25 yrs Nose & chin become more prominent to enhance profile. Increase in jaw growth continues ( mandible ) to accommodate the 8’s.  09/24/12
  38. 38. Clinical Considerations : 1. Ectodermal dysplasia : Tooth bud may be absent. 2. Anodontia: Complete absence of teeth. 3. Accessory teeth: There may be extra or supernumerary teeth buds resulting in accessory teeth. 4. Predeciduous or neonatal tooth: Teeth are seen to erupt immediately after birth. 5. Gemination: 2 teeth may be fused to each other. 6. Malocclusion: The alignment of upper and lower teeth maybe incorrect.09/24/12
  39. 39. 7. Teeth may form in abnormal situations e.g. in the ovary or in the hypo physis cerebrae.8. In vitamin A deficiency ameloblasts fail to differentiate properly. Consequently, their organizing influence on the adjacent mesenchymal cells is disturbed and a typical dentin known as osteodentin is formed.9. Endocrine disturbances affect the size or form of the crown of teeth clinical examinations shows that retarded eruption that occurs in persons with hypo pituitarism and hypothyroidism results in a small clinical crown that is often mistaken for a small anatomic crown.10. The upper central incisors may become notched at the edge or screwdriver shaped in individuals born with congenital syphilis. This condition is known as Hutchinsons incisor.11. Genetic and environmental factors may disturb the normal synthesis and secretion of the organic matrix of enamel leading to a condition called enamel hypoplasia.12. If organic matrix is normal but its mineralization is defective then enamel or dentin is said to be hypo calcified or hypo mineralized.09/24/12