the complete process of development of teeth.pptx

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1. GOOD MORNING

2. Development of teeth

3. Content Introduction Dental and vestibular lamina Dental sac Stages of tooth development Root development Developmental disturbances

4. Introduction The primitive oral cavity, or stomodeum, is lined by stratified squamous epithelium called the oral ectoderm .

5. The oral ectoderm contacts the endoderm of the foregut to form the BUCCOPHARYNGEAL MEMBRANE. Membrane ruptures at about 27th day of gestation and the primitive oral cavity establishes a connection with the foregut. Most of the connective tissue cells underlying the oral ectoderm are of NEURAL CREST OR ECTOMESENCHYME in origin . These cells instruct the overlying ectoderm to start the tooth development, which begins in the anterior portion of the future maxilla and mandible and proceeds posteriorly.

6. Dental lamina 2-3 weeks after the rupture of buccopharyngeal membrane, certain areas of basal cells of oral ectoderm proliferate rapidly, leading to the formation of primary epithelial band The band invades the underlying ectomesenchyme along each of the horseshoe shaped future dental arches.

7. At about 7 th week, the primary epithelial band divides into an inner (lingual) process called Dental Lamina & an outer ( buccal) process called Vestibular lamina. The dental lamina serves as the primordium for the ectoderm portion of the deciduous teeth.

8. Later during the development of jaws , permanent molars arise directly from the distal extension of the dental lamina . The lingual extension of the dental lamina is named the successional lamina & develops from the 5 th month in utero ( permanent central incisor) to the 10 th month of age (second premolar)

9. Fate of dental lamina It is evident that total activity of dental lamina exceeds over a period of atleast 5years. As the teeth continue to develop, they loose their connection with the dental lamina. Remnants of dental lamina persists, as epithelial pearls or islands within the jaw as well as in the gingiva , called as cell rests of serres . However the dental lamina may still be active in the third molar region after has disappeared elsewhere, except for occasional epithelial remnants.

10. Vestibular lamina Labial and buccal to the dental lamina in each dental arch, another epithelial thickening develops independently. It is Vestibular Lamina also termed as lip furrow band. It Subsequently hollows and form the oral vestibule between the alveolar portion of the jaws and the lips and cheeks.

11. Tooth development At certain points along the dental lamina, each representing the location of one of the 10 mandibular & 10 maxillary teeth, ectodermal cells multiply rapidly & little knobs that grow into the underlying mesenchyme . Each of these little down growths from the dental lamina represents the beginning of the enamel organ of the tooth bud of a deciduous tooth. First to appear are those of anterior mandibular region. As the cell proliferation occurs each enamel organ changes to a shape that resembles a bud, cap and bell.

12. The tooth germ consists of ectodermal component- the enamel organ, the ectomesenchymal components- the dental papilla & the dental follicle. The enamel is formed from the enamel organ, the dentin and the pulp from the dental papilla and the supporting tissues namely the cementum, periodontal ligament & the alveolar bone from the dental follicle.

13. Stages of tooth development

14. MORPHOLOGICAL Dental lamina Bud stage Cap stage Early bell stage Advanced bell stage Formation of enamel and dentin matrix PHYSIOLOGICAL Initiation Proliferation Histodifferentiation Morphodifferentiation Apposition

15. Bud stage/ proliferation This is the initial stage of tooth formation where enamel organ resembles a small bud . During the bud stage, the enamel organ consists of peripherally located low columnar cells & centrally located polygonal cells. The surrounding mesenchymal cells proliferate, which results in their condensation in two areas. The area of condensation immediately below the enamel organ is the dental papilla . The ectomesenchymal condensation that surrounds the tooth bud and the dental papilla is the tooth sac .

16. Cap stage / proliferation As the tooth bud continues to proliferate, it does not expand uniformly into large sphere. Instead unequal growth in different parts of the tooth bud leads to the cap stage which is characterized by a shallow invagination on the deep surface of the bud.

17. Outer and inner epithelium The peripheral cells of the cap stage are cuboidal, cover the convexity of the cap & are called the outer enamel epithelium The cells in the concavity of the cap become tall columnar cells & represent the inner enamel epithelium

18. The outer enamel epithelium is separated from the dental sac and the inner enamel epithelium from the dental papilla, by a delicate basement membrane.

19. Stellate reticulum Polygonal cells located between the outer and the inner enamel epithelium, begin to separate due to water being drawn into the enamel organ from the surrounding dental papilla. As a result the polygonal cells become star shaped but maintain contact with each other by their cytoplasmic process. As the star shaped cells form a cellular network, they are called the stellate reticulum.

20. The cells in the center of the enamel organ are densely packed and form the enamel knot. This knot projects toward the underlying dental papilla. At the same time a vertical extension of the enamel knot , called the enamel cord.

21. The function of enamel knot & cord may act as a reservoir of the dividing cells for the growing enamel organ. The enamel knot act as a signaling centers as many important growth factors are expressed & thus play an important role in determining the shape of the tooth Dental papilla and Dental sac The ectomesenchymal condensation i.e the dental papilla & the dental sac are pronounced during this stage of dental development.

22. Bell stage / histodifferentiation Due to continued uneven growth of the enamel organ it acquires a bell shape. In bell stage crown shape is determined. It was thought that the shape of the crown is due to pressure exerted by the growing dental papilla cells on the inner enamel epithelium. This pressure however was shown to be opposed equally by the pressure exerted by fluid present in the stellate reticulum. The folding of enamel organ to cause different crown shapes is shown to be due to different rates of mitosis and difference in cell differentiation time.

23. Inner enamel epitheliun The inner enamel epithelium consists of a single layer of cells that differentiate prior to amelogenesis into tall columnar cells called ameloblasts . These elongated cells are attached to one another by junctional complexes laterally & to cells in the stratum intermedium by desmosomes . The cells of the inner enamel epithelium exert a strong influence on the underlying mesenchymal cells of the dental papilla, which later differentiate into odontoblasts .

24. Stratum intermedium A few layers of squamous cells form the stratum intermedium , between the inner enamel epithelium & the stellate reticulum. These cells are closely attached by desmosomes and gap junctions. This layer seems to be essential to enamel formation.

25. Stellate reticulum The stellate reticulum expands further due to continued accumulation of intra-cellular fluid These star shaped cells, having a large processes anastomose with those of adjacent cells As the enamel formation starts, the Stellate reticulum collapses to a narrow zone thereby reducing the distance between the outer & inner enamel epithelium

26. Outer enamel epithelium The cells of the outer enamel epithelium flatten to form low cuboidal cell.s The outer enamel epithelium is thrown into folds which are rich in capillary network, this provides a source of nutrition for the enamel organ. Before the inner enamel epithelium begins to produce enamel, Peripheral cells of the dental papilla differentiate into odontoblasts . These cuboidal cells later assumes a columnar form & produce dentin

27. Advanced bell stage / morphodifferentiation Characterized by the commencement of mineralization & root formation. The boundary between the inner enamel epithelium & odontoblasts outline the future dentino -enamel junction. Formation of dentin occurs first as a layer along the future dentino -enamel junction in the region of future cusps & proceeds pulpally & apically.

28. After the first layer of dentin is formed , the ameloblasts lay down enamel over the dentin in the future incisal and cuspal area. The enamel formation then proceeds coronally & cervically in all the regions from the dentino -enamel junction toward the surface The cervical portion of enamel organ gives rise to Hertwig Epithelial Root Sheath (HERS) This HERS outlines the future root and thus responsible for the size, shape, length and number of roots.

29. Formation of enamel and dentin matrix/ apposition Apposition is the deposition of the matrix of the hard enamel structures Appositional growth of the enamel & dentin is a layer like deposition of an extracellular matrix. This type of growth is therefore additive Appositional growth is characterised by regular & rhythmic deposition of the extracellular matrix , which is of itself incapable of further growth.

30. Root formation The development of roots begin after enamel & dentin formation has reached the future cementoenamel junction. The enamel organ plays an important role in root development by forming HERS, which models the shape of the root. Its remnants persists as an epithelial network of strands or clumps near the external surface of the root. These epithelial remnants are found in the periodontal ligament of erupted teeth and are called as rests of mallasez . Prior to the beginning of root formation, the root sheath forms the epithelial diaphragm.

31. MECHANISM OF ROOT FORMATION

32. Developmental disturbances in size of teeth Microdontia Macrodontia

33. Microdontia This term is used to describe teeth which are smaller than normal

34. Macrodontia Teeth are larger than normal

35. Developmental Disturbances In Shape of Teeth Gemination Fusion Concrescence Dilaceration Talons cusp Dens invaginatus Dens evaginatus Taurodontism Enamel pearls Supernumerary root

36. Gemination • Geminated teeth are anomalies which arise from an attempt at division of single tooth germ by an invagination , with resultant incomplete formation of two teeth.

37. Fusion • Fused teeth arise through union of two normally separated tooth germ.

38. CLINICAL FEATURES Talon cusp projects lingually from the cingulum areas of maxillary or mandibular permanent incisor. The cusp blends smoothly with the tooth. Except that deep developmental groove is present where the cusp blends with the sloping lingual tooth surface. Composed of normal enamel, dentin and contains a horn of pulp tissue. Most commonly seen in association with Rubinstein- Taybi syndrome.

39. Clinical significance Talon cusp on maxillary teeth interfere with occlusion and should be removed. The developmental groove may be prone to caries. Removal without loss of vitality may be accomplished through periodic grinding of the cusp resulting tertiary dentine deposition and pulpal recession.

40. Dens Invaginatus • Dens Invaginatus is a deep surface invagination of the crown or root that is lined by enamel. • TYPES Coronal Radicular

41. Radicular Dens invaginatus arises secondary to proliferation of hertwig’s root sheath with the formation of strip of enamel that extends along the surface of the root. Three types of invagination is seen:

42. CLINICAL FEATURES Most commonly affected teeth are permanent lateral incisors. Invagination may be large and resemble a tooth with in a tooth and hence the term ‘Dens In Dente’

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