06 Tooth Development and Eruption

Transcription

1 + 06 Tooth Development and Eruption Tooth development Root development PDL and alveolar bone development Primary tooth eruption and shedding Permanent tooth eruption

2 Q. Where and how tooth starts to form? Primitive oral cavity

3 + Tooth development (Odontogenesis) Primary epithelial band Primary epithelial band Tooth germ

4 Midsagittal section of embryo at 4 weeks Future Maxilla ectomesenchyme Future Tooth epithelium Stomodeum Future Tongue Future Mandible Future Tooth

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6 + Tooth development (Odontogenesis) A continuous process Be divided into 4 stages based on the appearance of the developing structures Initiation, bud, cap, bell, apposition, and maturation stage Physiological processes: induction, proliferation, differentiation, morphogenesis, and maturation Not all the teeth begin to develop at the same time. Teeth have the longest developmental period.

7 Table 6-1 Stages of Tooth Development Initiation stage/sixth to seventh week Bud stage/eighth week Induction Proliferation Ectoderm lining stomodeum gives rise to oral epithelium and then to dental lamina; adjacent to deeper ectomesenchyme, which is influenced by the neural crest cells. Both tissue types are separated by a basement membrane Growth of dental lamina into bud shape that penetrates growing ectomesenchyme Cap stage/ninth to tenth week Proliferation, differentiation, morphogenesis Formation of tooth germ as enamel organ forms into cap shape that surrounds inside mass of dental papilla, with an outside mass of dental sac, both from the ectomesenchyme. Bell stage/eleventh to twelfth week Proliferation, differentiation, morphogenesis Differentiation of enamel organ into bell shape with four cell types and dental papilla into two cell types Apposition stage/varies per tooth Induction, proliferation Dental tissue types secreted in successive layers as matrix Maturation stage/varies per tooth Maturation Dental tissue types fully mineralize to mature form

8 + Tooth development (Odontogenesis) 1. Initiation stage 2. Bud stage 5. Apposition stage 6. Maturation stage 3. Cap stage 4. Bell stage

9 + Tooth development (Odontogenesis) Initiation stage Begins between 6 th to 7 th weeks, FIRST stage Induction :the mesenchymal tissue must influence the ectodermal tissue to initiate odotogenesis Ectoderm lining stomodeum gives rise to oral epithelium and dental lamina

10 + Tooth development (Odontogenesis) Bud stage 8 th weeks Growth of dental lamina into bud that penetrates growing ectomesenchyme Condensation of the ectomesenchyme Epithelial bud Ectomesenchyme Basement membrane ** Tooth germ : epithelial bud + ectomesenchyme

11 + Tooth development (Odontogenesis) Cap stage 9 th to 10 th weeks Proliferation Differentiation : cytodifferentiation histodifferentiation morphodifferentiation Unequal growth in different parts of the tooth bud, leads to concave surface forming cap-like structure. Morphogenesis

12 Tooth germ 1. dental organ Formation of tooth bud in a cap shape with deep central depression Derived from ectoderm Enamel 2. dental papilla Condensed mass within the concavity of the enamel organ Derived form ectomesenchyme Dentin and pulp 3. dental follicle or dental sac Condensed mass of ectomesenchyme surrounding outside of the enamel organ Cementum, periodontal ligament, alveolar bone Basement membrane dentinoenamel junction (DEJ) Tooth germ enamel organ dental papilla dental follicle

13 + Tooth development (Odontogenesis) Bell stage 11 th to 12 th weeks Proliferation, differentiation*, morphogenesis Enamel organ with four cell layers Dental papilla with two cell types Tooth germ enamel organ dental papilla dental follicle

14 ** Cell Layers of the Tooth during the Bell stage Enamel Organ 1 inner enamel epithelium, IEE Innermost tall, columnar cells Will differentiate into ameloblasts 2 stratum intermedium, SI More inner compressed layer of flat to cuboidal cells 3 stellate reticulum, SR More outer star-shaped cells in many layers, forming a network within the enamel organ 4 outer enamel epithelium, OEE Outer cuboidal cells

15 ** Cell Layers of the Tooth during the Bell stage Dental papilla 1 Outer cells of dental papilla peripheral layer of cells of the dental papilla nearest the inner enamel epithelium of the enamel organ will differentiate into odontoblast 2 Central cells of dental papilla inner cell mass of the dental papilla will differentiate into pulp tissue

16 ** Cell Layers of the Tooth during the Bell stage Dental follicle Increasing amount of collagen fibers forming around the enamel organ will differentiate into cementum, periodontal ligament, and alveolar bone

17 + Tooth development (Odontogenesis) Stages of apposition and maturation The final stage of tooth development Apposition stage (or secretory stage) Enamel, dentin, cementum are secreted in successive layers. Maturation stage Matrices of the hard dental tissue types subsequently fully mineralize Ameloblasts Odontoblasts Amelogenesis & Dentiogenesis Formation of preameloblasts Formation of odontoblasts and dentin matrix Formation of ameloblasts, dentinoenamel junction, and enamel matrix Enamel Predentin Dentin

18 + Formation of preameloblasts IEE cells grow even more columnar or elongate preameloblasts Repolarization : the nucleus in preameloblasts moves away from the center of the cell to the position farthest away from the basement membrane Preameloblasts will first induce dental papilla cells to differentiate into dentin-forming cells (odontoblasts) Preameloblasts will differentiate into enamel-forming cells (ameloblasts)

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20 + Formation of odontoblasts and dentin matrix outer cells of the dental papilla are differentiated into odontoblasts. Repolarization Dentinogenesis : apposition of predentin (dentin matrix) by odontoblasts

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22 + Formation of ameloblasts, dentinoenamel junction, and enamel matrix Disintegration of basement membrane between preameloblasts and odontobalsts Predentin induces the preameloblasts to differentiate into ameloblasts. Amelogenesis : Apposition of enamel matrix by ameloblasts Dentinoenamel junction (DEJ) formation : With enamel matrix in contact with predentin, mineralization of disintegrating basement membrane occurs. Odontoblasts will leave attached cellular extensions in the length of the predentin. : odontoblast process dentinal tubule Tomes process

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25 ** Common dental developmental disturbances and involved stage 1. Initiation stage 2. Bud stage 3. Cap stage 4. Apposition and maturation stages <Anodontia> complete partial <Supernumerary teeth (Hyperdontia)>

26 ** Common dental developmental disturbances and involved stage 1. Initiation stage 2. Bud stage 3. Cap stage 4. Apposition and maturation stages <Microdontia/Macrodontia>

27 ** Common dental developmental disturbances and involved stage 1. Initiation stage 2. Bud stage 3. Cap stage 4. Apposition and maturation stages <Dens in dente> <Gemination> <Fusion> <Tubercle>

28 ** Common dental developmental disturbances and involved stage 1. Initiation stage 2. Bud stage 3. Cap stage 4. Apposition and maturation stages <Enamel dysplasia> <Concrescence> <Enamel pearl>

29 + Root development Cervical loop most cervical portion of enamel organ Grows deeper into the dental sac to become Hertwig s epithelial root sheath (HERS) Hertwig s epithelial root sheath (HERS) Bilayer rim consisting of ONLY inner and outer enamel epithelium Function of HERS is to shape the root(s). Also induces dentin formation in root area so that it is continuous with coronal dentin, as well as cementum on roots overlying the newly formed dentin. Epithelial rests of Malassez (ERM)

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31 + Root development Root dentin formation Cervical loop IEE cells of HERS Outer cells of the dental papilla odontoblasts Begin to secrete predentin Root dentin formation Disintegration of basement membrane Disintegration of HERS Epithelial rest of Malassez

32 + Root development Cementum and pulp formation Cementogenesis Disintegration of HERS Dental follicle cells contact with root dentin Dental follicle cells cementoblasts Cementoid (cementum matrix) setretion Early : leave no cellular bodies in their secreted products Later: become entrapped by their products (cementocyte) mineralization or maturation cementum *** DCJ (dentinocemental junction)

33 + Root development Cementum and pulp formation Pulp formation Central cells of the dental papilla Periodontal ligament and alveolar bone development

34 + Periodontal ligament and alveolar bone development Periodontal ligament (PDL) formation After cementum formation The ectomesenchyme (from the dental sac) begins to form the PDL Collagen fiber formation These fibers insert into the cementum and alveolar bone Alveolar bone formation The ectomesenchyme from the dental follicle

35 + Development of multirooted teeth Root trunk A single root on the base of the crown Differential growth of HERS divides the root trunk into the correct number of root Cervical loop of multirooted teeth Long, tongue like horizontal epithelial extensions Extensions can be present on multirooted teeth, depending on the similar number of roots on the mature tooth.

36 + Primary tooth eruption and shedding Root growth Existence of a temporary ligament Vascular pressure Contractile collagen Hormonal signals

37 + Primary tooth eruption and shedding After enamel apposition ameloblasts place an acellular dental cuticle on new enamel surface the enamel organ is compressed, forming reduced enamel epithelium (REE) The REE fuses with oral epithelium lining the oral cavity Disintegration of the central part in the fused tissues epithelial tunnel Cervical part of the fused tissues attachs to the neck of the tooth Junctional epithelium

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39 + Primary tooth shedding Is lost, exfoliated, or shed, as the succedaneous permanent tooth develops lingual to it Resorption of tooth Osteoclast: alveolar bone Odontoclast: primary s root dentin, cementum, small parts of enamel

40 + Permanent tooth eruption Erupts into the oral cavity in a position lingual to the roots of the shedding primary tooth Additional teeth Successional dental lamina of permanent teeth primordia Oral epithelium (cut to show tooth buds) Tooth germ of nonsuccedaneous permanent molars Developing mandibular dental arch Developing primary teeth Tongue Developing mandible

41 ** Developmental disturbances during eruption 1. Dentigerous cyst 2. Eruption cyst Nasmyth s membrane Eruption cyst