+

06 Tooth Development and Eruption Tooth development Root development PDL and alveolar bone

development

Primary tooth eruption and shedding

Permanent tooth eruption

Q. Where and how tooth starts to form?

Primitive oral cavity

+Tooth development (Odontogenesis)Primary epithelial band

Tooth germPrimary epithelial band

Future Tongue

Future Maxilla

Future Mandible

Midsagittal section of embryo at 4 weeks

Future Tooth

Stomodeum

ectomesenchyme

epithelium

Future Tooth

+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 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

+Tooth development (Odontogenesis)

1. Initiation stage

2. Bud stage

3. Cap stage

4. Bell stage

5. Apposition stage

6. Maturation stage

+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

+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

+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

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)

+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

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

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

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

+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

+

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)

+

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

+

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

** 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)>

** Common dental developmental disturbances and involved stage 1. Initiation stage2. Bud stage3. Cap stage4. Apposition and maturation stages

<Microdontia/Macrodontia>

** Common dental developmental disturbances and involved stage 1. Initiation stage2. Bud stage3. Cap stage4. Apposition and maturation stages

<Dens in dente> <Gemination>

<Fusion> <Tubercle>

** Common dental developmental disturbances and involved stage 1. Initiation stage2. Bud stage3. Cap stage4. Apposition and maturation stages

<Enamel dysplasia>

<Concrescence> <Enamel pearl>

+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)

+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

+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)

+Root development

Pulp formation Central cells of the dental papilla

Periodontal ligament and alveolar bone development

Cementum and pulp formation

+ 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

+

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

+Primary tooth eruption and shedding

Root growth

Existence of a temporary ligament

Vascular pressure

Contractile collagen

Hormonal signals

+

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

+

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

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)

** Developmental disturbances during eruption1. Dentigerous cyst 2. Eruption cyst

Eruption cyst

Nasmyth’s membrane