tooth development - i man-kyo chung, dmd, phd ([email protected]) assistant professor department...

Tooth Development - I

Man-Kyo Chung, DMD, PhD([email protected])

Assistant ProfessorDepartment of Neural and Pain Sciences

University of Maryland Dental School

Developmental histology of tooth

Whole organism > organ > tissue > cell > cellular organelle

Ex) human heart muscle myocyte nucleus

Gross anatomy microscopic anatomy (histology)

zygote(a cell from fertilization)

Methods) naked eyelight microscopy

electron microscopy

development

Two types of cells give rise to teeth

Proliferation(increase in

number) Migration

(change in location)

Differentiation(specialization)

Ameloblasts forming enamelOdontoblasts forming dentinCementoblasts forming cementum

epithelial cells

ectomesenchymal cells

Enamel

Dentin

Cementum

Pulp

zygote

Early embryonic development

Mesoderm (connective tissues / heart, muscle, blood cells, bone, dermis etc)

Ectoderm (tissues covering outside the body / epidermis, hair etc)

Endoderm (tissues lining inside the body / lung, stomach, intestine, liver etc)

<trilaminar germ disc>

Oral Histology and Embryology by Leslie P. Gartner, 1988

bilaminar germ disc

<1 wk ~2 wks

~3 wks

Tissues originated from ectoderm besides epidermis

3. connective tissues of head and neck (bone, cartilage, muscles, tooth etc)

epithelium

(Ectomesenchymal origin)

embryonic connective tissue

ectodermal origin

ectoderm

neural tube

neural crest

1. brain (neuroectodermal origin)

2. sensory ganglia

Location of tooth formation

6 weeks old embryo

Maxillary process

Mandibular process


auricle

eye

Coronal section

Oral epithelium of maxillary and mandibular processes

tongue

nasal septum

Stages of tooth development

1. Bud stage

2. Cap stage

3. Bell stage

4. Appositional stage (mineralization)

5. Root formation

6. Eruption

(epithelial ingrowth into ectomesenchyme)

(further epithelial growth)

(histo- and morpho-differentiation)

(formation of enamel and dentin of crown)

(formation of dentin and cementum of root)


Bud stage

Mx

Mn

dental lamina

tooth bud

developing maxillalry bone

tongue

palate

http://www.iob.uio.no/studier/undervisning/histologi/index.php

• Dental lamina - outgrowth of horse shoe-shaped epithelial band from oral epithelium- one dental lamina per arch- 10 tooth buds per lamina

developing mandibular bone

Mx

Mn

vestibular lamina


vestibule

Bud stage

ectomesenchymal cells


Bud stage

condensation of ectomesenchymal cellsaround tooth bud


Bud stage

Cap stage

1. Enamel organ (=dental organ)(proliferation of epithelial cells)

2. Dental papilla(condensation of ectomesenchymal cells)

3. Dental sac (=dental follicle)(capsule like condensation of ectomesenchymal cells)

1

2

3


Future tooth products

1. Enamel organ

2. Dental papilla

3. Dental sac1

2

3

enamel

dentin pulp

cementumperiodontal ligamentalveolar boneconnective tissues of gingiva


Tooth germ means

1. Enamel organ

2. Dental papilla

3. Dental follicle1

2

3


+

+

Differentiation of enamel organTransformation of a cell mass into morphologically and functionally distinct components

Secreting proteoglycan (absorbing water increase extracellular space)

1) Outer enamel epithelium

2) Stellate reticulum

3) Inner enamel epithelium

desmosome

Flattened (squamous or cuboidal)

Star shaped

Elongated and polarized (columnar)

Enamel organ

Enamel organ of cap stage

21

3

1) Inner enamel ep

2) Outer enamel ep

3) Cervical loop


5) Enamel knot

6) Enamel cord

7) Enamel navel

4

5

6

7

transient structure during cap stage


(inner+outer enamel ep.)

21

3

1) Inner enamel ep

2) Outer enamel ep

3) Cervical loop


5) Enamel knot

6) Enamel cord

7) Enamel navel

4

5

6

7

transient structure during cap stage

root formation

generate enamel

location of cusp?


Enamel organ of cap stage

(protect inner enamel ep.)

Tooth germ of late cap stage


(tooth bud of permanent tooth)

Bell stage

1. Tooth shape is identifiable.

2. Further differentiation of enamel organ

1) outer enamel ep.2) inner enamel ep.3) stellate reticulum4) stratum intermedium

3

2

14


stratum intermedium

inner enamel ep

basement membrane

dental papilla



Bell stage

Differentiation of inner enamel ep.

Cusptip

root

differentiated to ameloblast without proliferation

Keep proliferatingand migrate downward

oldertallerpolarized

younger shorter unpolarized


cap stage

bellstage

appositionalstage

Appositional stage

1. oral ep.2. outer enamel ep.3. stellate reticulum4. inner enamel ep.5. dental papilla6. cervical loop

3

2

1

5

4

6

blood vessels


Stage of mineralization

Epithelial and mesenchymal cells interact throughout

tooth formationoral epithelium

dental lamina

mesenchymal cellsb

ud

Cap

min

era

lizati

on

bell

1

signal

proliferation

1

epithelium

mesenchyme

Epithelial mesenchyaml

interactionoral epithelium

dental lamina

inner enamel epithelium

preameloblast

mesenchymal cells

preodontoblast

1

2

2

epitheliummesenchyme

1

2

3

4

5

6

7

8

9

1

2

3

4

5

6

7

8

9

10

11

12

13

a

b

c

d

e

f

g

h

i

a

b

c

d

e

f

g

h

i

j

k

l

m

PreameloblastsPreodontoblasts

bu

dC

ap

min

era

lizati

on

bell

oral epithelium

dental lamina

inner enamel epithelium

preameloblast

ameloblast

mesenchymal cells

preodontoblast

odontoblast

Predentin

enamel matrix

enamel

dentin

bu

dC

ap

min

era

lizati

on

bell

1

2

3

odontoblasts preameloblasts

ameloblasts

Predentin (dentin matrix)

dentinenamel matrix

3

a. predentinb. dentinc. enamel

1. ameloblasts 2. preameloblasts3. odontoblasts4. preodontoblasts5. dental papilla6. stratum intermedium

4

2

6

a

3

1b

c

5


Appositional stage

stratum intermedium

ameloblasts

enameldentin

predentin

odontoblasts


Developmental lobes

Initiation of mineralizationat 5 points

continued mineralizationtoward cervical direction Coalescence of 5 segments

Developmental lobes

tooth germ of mandibular molar

groove (junction of 2 lobes)

Pit (junction of >3 lobes)cusp

Biomineralization

Concrete = metal framework + cement

• Dentin = collagen + hydroxyapatite crystals• Enamel = amelogenin + hydroxyapatite crystals

resorbable

allows further packing of crystals

inorganic component, hardnessenamel >>> dentin

Essential components of calcification

Ca2+ + PO43-

Ca10(PO4)6(OH)2

Alkaline phosphatase (supply phosphate)

Pyrophosphatase (hydrolyze pyrophosphate)

pyrophosphate

ATP

AMP

3

21

Matrix vesiclesContain essential componentsContain seed of crystalReleased from odontoblasts to collagen matrix

Acid can reverse calcification

Ca2+ + PO43-

Ca10(PO4)6(OH)2

acid acidogenic bacteria

• Dental caries decalcification of inorganic tooth substances by acid produced by bacteria

• Only very limited remineralization can occur in tooth.(cf: bone maintains a balance between mineralization and demineralization )

Appositional stage

(alkaline phosphatase )


dentino-enameljunction

(collagen fibers of mantle dentin)

Aprismatic

Mantle

odontoblasts

(predentin)

Reduced stellate reticulum

tooth development - i man-kyo chung, dmd, phd ([email protected]) assistant professor department...

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