06 tooth development and eruption -...
TRANSCRIPT
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06 Tooth Development and Eruption Tooth development Root development PDL and alveolar bone
development
Primary tooth eruption and shedding
Permanent tooth eruption
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Q. Where and how tooth starts to form?
Primitive oral cavity
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+Tooth development (Odontogenesis)Primary epithelial band
Tooth germPrimary epithelial band
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Future Tongue
Future Maxilla
Future Mandible
Midsagittal section of embryo at 4 weeks
Future Tooth
Stomodeum
ectomesenchyme
epithelium
Future Tooth
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+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.
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Table 6-1 Stages of Tooth Development
Initiation stage/sixth to seventh week
Induction 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
Bud stage/eighth week
Proliferation 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 theectomesenchyme.
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
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+Tooth development (Odontogenesis)
1. Initiation stage
2. Bud stage
3. Cap stage
4. Bell stage
5. Apposition stage
6. Maturation stage
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+Tooth development (Odontogenesis)
Begins between 6th to 7th 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
Initiation stage
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+Tooth development (Odontogenesis)
8th weeks
Growth of dental lamina into bud that penetrates growing ectomesenchyme
Condensation of the ectomesenchyme
Basement membrane
Bud stage
Epithelial bud
Ectomesenchyme
** Tooth germ : epithelial bud + ectomesenchyme
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+Tooth development (Odontogenesis)
9th to 10th weeks
Proliferation
Differentiation : cytodifferentiation histodifferentiation morphodifferentiation
Unequal growth in different parts of the tooth bud, leads to concave surface forming cap-like structure.
Morphogenesis
Cap stage
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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
enamel organ
dental papilla
dental follicle
Tooth germ
Basement membrane dentinoenamel junction (DEJ)
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+Tooth development (Odontogenesis)
11th to 12th weeks
Proliferation, differentiation*, morphogenesis
Enamel organ with four cell layers
Dental papilla with two cell types
Bell stage
enamel organ
dental papilla
dental follicle
Tooth germ
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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
** Cell Layers of the Tooth during the Bell stage
Enamel Organ
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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
** Cell Layers of the Tooth during the Bell stage
Dental papilla
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Increasing amount of collagen fibers forming
around the enamel organ
will differentiate into cementum, periodontal
ligament, and alveolar bone
** Cell Layers of the Tooth during the Bell stage
Dental follicle
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+Tooth development (Odontogenesis)
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
Amelogenesis & Dentiogenesis Formation of preameloblasts Formation of odontoblasts and dentin matrix Formation of ameloblasts, dentinoenamel
junction, and enamel matrix
Stages of apposition and maturation
DentinPredentin
Enamel
OdontoblastsAmeloblasts
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Formation of preameloblasts① IEE cells grow even more columnar or elongate preameloblasts② Repolarization
: the nucleus in preameloblasts moves away from the center of the cell to the position farthest away from the basement membrane
③ Preameloblasts will first induce dental papilla cells to differentiate into dentin-forming cells (odontoblasts)
④ Preameloblasts will differentiate into enamel-forming cells (ameloblasts)
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Formation of odontoblasts and dentin matrix① outer cells of the dental papilla are differentiated into odontoblasts.② Repolarization③ Dentinogenesis
: apposition of predentin (dentin matrix) by odontoblasts
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Formation of ameloblasts, dentinoenamel junction, and enamel matrix① Disintegration of basement membrane between preameloblasts and
odontobalsts② Predentin induces the preameloblasts to differentiate into
ameloblasts.③ Amelogenesis
: Apposition of enamel matrix by ameloblasts
④ Dentinoenamel junction (DEJ) formation: With enamel matrix in contact with predentin, mineralization of disintegrating basement membrane occurs.
⑤ Odontoblasts will leave attached cellular extensions in the length of the predentin. : odontoblast process
dentinal tubule Tomes’ process
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** Common dental developmental disturbances and involved stage 1. Initiation stage2. Bud stage3. Cap stage4. Apposition and maturation stages
** Common dental developmental disturbances and involved stage 1. Initiation stage2. Bud stage3. Cap stage4. Apposition and maturation stages
<Anodontia>
complete partial
<Supernumerary teeth (Hyperdontia)>
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** Common dental developmental disturbances and involved stage 1. Initiation stage2. Bud stage3. Cap stage4. Apposition and maturation stages
<Microdontia/Macrodontia>
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** Common dental developmental disturbances and involved stage 1. Initiation stage2. Bud stage3. Cap stage4. Apposition and maturation stages
<Dens in dente> <Gemination>
<Fusion> <Tubercle>
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** Common dental developmental disturbances and involved stage 1. Initiation stage2. Bud stage3. Cap stage4. Apposition and maturation stages
<Enamel dysplasia>
<Concrescence> <Enamel pearl>
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+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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+Root developmentRoot dentin formation
IEE cells of HERS
Cervical loop
Epithelial rest of Malassez
Disintegration of HERS
Disintegration of basement membrane
Root dentin formation
Begin to secrete predentin
odontoblasts
Outer cells of the dental papilla
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+Root development
Cementogenesis
Cementum and pulp formation
cementum
mineralization or maturation
Early : leave no cellular bodies in their secreted productsLater: become entrapped by their products (cementocyte)
Cementoid (cementum matrix) setretion
Dental follicle cells cementoblasts
Dental follicle cells contact with root dentin
Disintegration of HERS
*** DCJ(dentinocemental junction)
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+Root development
Pulp formation Central cells of the dental papilla
Periodontal ligament and alveolar bone development
Cementum and pulp formation
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+ Periodontal ligament and alveolar bone development
The ectomesenchyme from the dental follicle
Periodontal ligament (PDL) formation
These fibers insert into the cementum and alveolar bone
Collagen fiber formation
The ectomesenchyme (from the dental sac) begins to form the PDL
After cementum formation
Alveolar bone formation
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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.
Development of multirooted teeth
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+Primary tooth eruption and shedding
Root growth
Existence of a temporary ligament
Vascular pressure
Contractile collagen
Hormonal signals
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Junctional epithelium
Cervical part of the fused tissues attachs to the neck of the tooth
Disintegration of the central part in the fused tissues epithelial tunnel
The REE fuses with oral epithelium lining the oral cavity
the enamel organ is compressed, forming reduced enamel epithelium (REE)
ameloblasts place an acellular dental cuticle on new enamel surface
After enamel apposition
Primary tooth eruption and shedding
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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
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+Permanent tooth eruption
Erupts into the oral cavity in a position lingual to the roots of the shedding primary tooth
Additional teeth
Tongue
Tooth germ of nonsuccedaneouspermanent molars
Successional dental lamina of permanent teeth primordia
Developing mandibular dental arch
Developing primary teeth
Developing mandible
Oral epithelium (cut to show tooth buds)
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** Developmental disturbances during eruption1. Dentigerous cyst 2. Eruption cyst
Eruption cyst
Nasmyth’s membrane