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06 Tooth Development and Eruption . Tooth development . Primary tooth eruption and . Root development shedding . PDL and alveolar bone . Permanent tooth eruption development Q. Where and how tooth starts to form?
Primitive oral cavity + Tooth development (Odontogenesis) Primary epithelial band
Primary epithelial band Tooth germ Midsagittal section of embryo at 4 weeks
Future Maxilla
Future Tooth ectomesenchyme
epithelium Stomodeum
Future Future Future Tooth Tongue Mandible
+ 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. Table 6-1 Stages of Tooth Development
Initiation Induction Ectoderm lining stomodeum gives rise to oral epithelium stage/sixth to and then to dental lamina; adjacent to deeper seventh week ectomesenchyme, which is influenced by the neural crest cells. Both tissue types are separated by a basement membrane Bud stage/eighth Proliferation Growth of dental lamina into bud shape that penetrates week growing ectomesenchyme
Cap stage/ninth to Proliferation, Formation of tooth germ as enamel organ forms into cap tenth week differentiation, shape that surrounds inside mass of dental papilla, with an morphogenesis outside mass of dental sac, both from the ectomesenchyme.
Bell stage/eleventh Proliferation, Differentiation of enamel organ into bell shape with four to twelfth week differentiation, cell types and dental papilla into two cell types morphogenesis
Apposition Induction, Dental tissue types secreted in successive layers as matrix stage/varies per proliferation tooth
Maturation Maturation Dental tissue types fully mineralize to mature form stage/varies per tooth + Tooth development (Odontogenesis)
1. Initiation stage 5. Apposition stage
2. Bud stage 6. Maturation stage
3. Cap stage
4. Bell stage + Tooth development (Odontogenesis) Initiation stage
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 + Tooth development (Odontogenesis) Bud stage
8th weeks
Growth of dental lamina into bud that penetrates growing ectomesenchyme Epithelial bud
Condensation of the Ectomesenchyme ectomesenchyme
Basement membrane
** Tooth germ : epithelial bud + ectomesenchyme + Tooth development (Odontogenesis) Cap stage
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 Tooth germ
1. dental organ . Formation of tooth bud in a cap shape with deep central depression . Derived from ectoderm Tooth germ enamel organ . Enamel
2. dental papilla dental papilla . Condensed mass within the concavity of the enamel organ dental follicle . 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 Basement membrane bone . dentinoenamel junction (DEJ) + Tooth development (Odontogenesis) Bell stage
11th to 12th weeks
Proliferation, differentiation*, Tooth germ morphogenesis enamel organ
Enamel organ with four cell layers dental papilla
Dental papilla with two cell types dental follicle ** 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 ** 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 ** 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 + 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 Ameloblasts Odontoblasts subsequently fully mineralize
Amelogenesis & Dentiogenesis Formation of preameloblasts Predentin Formation of odontoblasts and dentin matrix Dentin Enamel Formation of ameloblasts, dentinoenamel junction, and enamel matrix +
Formation of preameloblasts ① IEE cells grow even more columnar or elongate preameloblasts ② 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 matrix ① outer cells of the dental papilla are differentiated into odontoblasts. ② Repolarization ③ Dentinogenesis : apposition of predentin (dentin matrix) by odontoblasts
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Formation of ameloblasts, dentinoenamel junction, and enamel matrix ① Disintegration of basement membrane between preameloblasts and odontobalsts ② 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
** Common dental developmental disturbances and involved stage 1. Initiation stage 2. Bud stage 3. Cap stage 4. Apposition and maturation stages
complete partial
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)
+ Root development Root dentin formation
Cervical loop Outer cells of the dental papilla
IEE cells of HERS odontoblasts
Begin to secrete predentin
Root dentin formation
Disintegration of basement membrane
Disintegration of HERS
Epithelial rest of Malassez + 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 *** DCJ cementum (dentinocemental junction) + Root development Cementum and pulp formation
Pulp formation Central cells of the dental papilla
Periodontal ligament and alveolar bone development 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 +
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. + Primary tooth eruption and shedding
Root growth
Existence of a temporary ligament
Vascular pressure
Contractile collagen
Hormonal signals + 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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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 + Permanent tooth eruption
Erupts into the oral cavity in a position lingual to the roots of the shedding primary tooth
Additional teeth Oral epithelium Successional dental lamina of (cut to show tooth buds) permanent teeth primordia Tooth germ of nonsuccedaneous permanent molars
Developing mandibular dental arch
Developing primary teeth Tongue
Developing mandible ** Developmental disturbances during eruption 1. Dentigerous cyst 2. Eruption cyst
Nasmyth’s membrane
Eruption cyst