Tooth development
…from initiation until eruption
26. 5. 2021
Neural crest migration (towards the oral epithelium)
Dental lamina formation (epithelial thickening)
Bud stage
Cap stage
Bell stage
Aposition (hard tissues formation)
Root formation
Eruption
Dental development initiation
Oral epithelium
Direction of cell
division change
(Ecto)mesenchyme
Epithelial
thickening
Dental vs. Vestibular lamina
Ectodermal – to – (ecto)mesenchymal interactions
Ectodermal – to – (ecto)mesenchymal interactions
Complicated interaction
system (reciprocal)
• Inner enamel epithelium induces differentiation of odontoblasts from
ectomezenchyme
• Ectomezenchyme transplantation under oral ectoderm induces its conversion into
enamel protein producing cells
• Transplantation of ectomezenchyme of incisor under molar ectoderm – incisor
• Transplantation of molar ectomezenchyme under cutter ectoderm – molar
Odontogenesis (dental development)
Primary dentition as well as permanent dentition develop from both ectoderm and
ectomezenchyme
• Ectodermal origin – enamel (ameloblasts), ERM
• Ectomesenchymal origin – dental pulp, dentin, cementum, periodontium, alveolus
• Similar morphogenesis
• Proliferation, migration, embryonal induction, apoptosis
Primary information for tooth development (number, size) originates from ectomezenchyme
(damage to cranial neural crest or its removal causes anodontia)
Ectomezenchyme induces proliferation and differentiation of oral ectoderm into odontogenic
epithelium and primary dental lamina
The interaction of ectomezenchyme and oral ectoderm ultimately leads to the formation of a
complete organ
Evolutionary conserved pathways
Do birds have teeth?
Do birds have teeth?
• Ptáci ztratili zuby asi před 70-80 miliony let
• Recent birds lost the ability to form teeth around 70–80 million years ago
• Still, birds retain the evolutionary conserved tooth-forming pathways in both oral
epithelium and ectomesenchyme
• In vitro co-culture and in vivo transplantation experiments
Mouse ektomezenchyme Chicken oral epithelium
Developmental stages of tooth - overview
Primary dentition development
Kondenzace ektomezenchymu pod ektodermem dásňového valu na budoucí horní a dolní
čelisti (po založení předsíně - vestibulum oris) - ve druhé polovině 6. týdne
nitroděložního života
Ectomezenchymal condensation under the oral ectoderm in the upper and lower jaw in
the second half of the 6th week of intrauterine life
Ektomezenchyme stimulates the basal layer cells of the oral ectoderm to cell division
which leads to primary dental lamina formation
Bud stage
After setting up the maxillary and mandibular dental lamina, 10 dental buds (primordia) are
formed on both: maxilla and mandible
The buds proliferate on the side neighboring with ectomesenchyme and increase in size
Primordia formation:
end of the 7th to the beginning of 8th week
(mandibular - firstly)
Cap stage
9. - 10. week of development
Enamel knot formation in the middle of the bud leads to the epithelial overgrowth on sides
and formation of the „Cap“
Ectomesenchyme is entrapped and forms dental papilla
Histological differentiation of cells: cells on the surface of the dental follicle become cubic to low
cylindrical, while the inner cells become polymorphic (the origin of future stellate reticulum)
Similar process in dental papilla
Basal membrane - lamina basalis ameloblastica
lamina basalis ameloblastica
Youtube channel
Youtube channel
Bell stage
10. - 12. week
Enamel organ in contact with dental papilla
Enamel organ have 4 layers
Inner enamel epithelium – On the border with
ectomezenchyme on dental papilla surface. Tall
columnal cells (up to 50 µm) about 4 µm thick.
Cells annealed to l. basalis ameloblastica.
Stratum intermedium – contains 3-5 layers of
flattened cells divided by intercellular space
and connected with desmosomes
Stellate reticulum – epithelial cell reticulum,
star-shaped cells
Outer enamel epithelium – have its own basal
lamina, in the beginning cubical and later
flattened cells
Enamel knot
6 - 7. week
8. week
9. - 10. week
11. - 12. week
Developmental stages (timing)
Beginning of
4. m. intra-utero
post partum
Developmental stages (timing)
• Period of hard tooth tissue formation
• Begings during the second half of 4th month of foetal
development
Crown – formed firstly (dentin, enamel)
Enamel and dentin aposition begins in the place of signaling
center and spread apically
Enamel formation = amelogenesis
Dentin formation = dentinogenesis
Root – emegres later (dentin and cementum)
Cementum formation = cementogenesis
Mineralization
starting poing
Aposition
(Krivanek, Adameyko, Fried, Front Physiol. 2017)
Cell types in tooth and their origin
https://www.youtube.com/watch?v=QLNBjHgUHSU
Chronology of primary and secondary dentition formation
Crown development
• Polarity change of cells in inner enamel epithelium (IEE)
• Preameloblasts differentiate as a first ones (epithelium differentiate faster then ectomesenchyme)
• Preodontoblasts differentiate based on mutual interactions with preameloblasts
• Lamina basalis ameloblastica degradation
• Maturation of preodontoblasts into odontoblasts = dentin synthesis initiation
• Followed by maturation of preameloblasts into ameloblasts = enamel synthesis initiation
Repolarization of inner enamel epithelium
→ preameloblasty
Repolarization of dental papilla cells
→ preodontoblasty
Lamina basalis ameloblastica degradation –
by maturation of preameloblasts into
ameloblasts
Amelogenesis
Apexes of differentiated ameloblasts after repolarization are directing towards the deposited
dentin matrix and odontoblasts. Base (with nuclei) is located next to the stratum intermedium
Thin and long cells (50 µm), apical part of cells contain Golgi aparatus and rER (secretory grain
formation)
Ecrine secretion of granules above the junction complexes
Granules contains proteins essential for enamel backbone formation:
a) Amelogenins (90 %)
- Main product of ameloblasts secretory stage
- Spherical polymers, regulation of enamel prisms growth
b) Non-amelogenins
- Enamelin – Nucleation and direction of growth regulation of crystals
- Ameloblastin – Adhesive molecule
- Kalikrein 4 – Protease secreted by ameloblasts in the final sectretory stage
- Tuftelin – Stabilizes connection to dentin
c) Proteins with enzymatic activity
- Metaloproteases (MMP20) – amelogenin degradation
- Alkalic phosphatase, phosphomonoesterase and serinprotease 1
Amelogenesis
All ameloblasts are gradually engaged in enamel secretion and each creates single prism.
Prisms grow from the apical ends of the ameloblasts.
Prisms doesn‘t grow continuously, but periodically (with regular alternation of the
maximum secretory activity phase and the resting phase)
During one cycle the prism is prolonged by about 15-30 micrometers with the manifestation
on the dental cuts – the Retzius lines – (ending by perikymata)
Period lenght: about 4 days
Prisms formation - 3 phases:
- Organic backbone formation – proteins, glykopolysacharides, lipids
- Mineralization - crystallization centers are formed in the matrix. Hydroxylapatite is
deposited here in the form of submicroscopic crystals
- Maturation - crystal growth associated with organic matrix loss
Amelogenesis
Incremental enamel lines
Result of periodical ameloblasts activity
a) Day lines
- Cause prisms cross-striation, very thin (2,5 - 6 μm)
- Circardial rhytms
b) Stripes of Retzius (enamel striae)
- Can be observed under optical microscope on ground sections
- From DEJ to enamel surface
- Forms perikymata
c) Neonatal line
- Belongs to Striae of Retzius
- Due to abrupt change in nutrition
Retziusovy linie
Retzius striae
Perikymata
Neonatal line
Nutrition of ameloblasts
Develops before the formation of
prisms - focal death of cells from
the outer enamel epithelium
(apoptosis)
Through these openings in the
outer enamel epithelium, blood
vessels penetrate into the stellate
reticulum - providing ameloblast
nutrition
Reduction of epithelial reticulum
and intracellular mucoid substance
Finally stays only:
Stratum intermedium +
Ameloblasts
https://pocketdentistry.com/7-enamel-composition-formation-and-structure/
Schematic representation of the various functional
stages in the life cycle of ameloblasts as would occur
in a human tooth
1) Morphogenetic stage
2) Histodifferentiation stage
3) Initial secretory stage (no Tomes’ process)
4) Secretory stage (Tomes’ process)
5) Ruffle-ended ameloblast of the maturative stage
6) Smooth-ended ameloblast of the maturative stage
7) Protective stage
https://pocketdentistry.com/7-enamel-composition-formation-and-structure/
Before the end of secretory activity, the ameloblasts form a thin layer of organic substance
on the enamel surface - cuticula dentis
After the end of the secretion, the ameloblasts shorten and blend into the stratum
intermedium cells, resulting in the so-called reduced enamel epithelium - protects
the crown during its pruning.
Zodpovědné procesy:
1. Primary patterning of tooth shape – enamel knots
2. The number of growth centers in the dental cup - the sites where cells start secretory
aktivity. They are defined during the differentiation of ameloblasts by the mechanisms of
embryonic induction by odontoblast signalling molecules
3. Ameloblasts nutrition during enamel production (Häkkinen et al., 2019 BioRxiv)
Crown shape
Dentinogenesis
Dentinogenesis
The dentine matrix is secreted by the odontoblasts that originate from the surface layer of
the ectomezenchyme of the dental papilla
Odontoblasts located on the growth center (top of the dental papilla) initiates secretory
activity
Dentine matrix precursors are collected in odontoblasts‘
apexes located opposite to ameloblasts‘ apexes
Firstly formed matrix is non-calcified composed of
Collagens (I + III) and proteoglycans (versican,
keratansulphate, decorin, chondroitisulphate)
Odontoblasts and ameloblasts are moving away
from each other during matrix formation
In addition to the odontoblasts on the growth center, also odontoblasts of other
dental papilla compartments are gradually involved into matrix production
All odontoblasts forms together a dentine base of the crown (and later root)
In the first layers of matrix are only reticular fibres
Radial bundles – Korff‘s bundles - can be visualized by silver salts (in mantle dentine)
Only after depositing the Korff‘s bundles, odontoblasts will begin
to deposit collagen fibers that run longitudinally - perpendicular
to the dentinal tubules
Calcification of the dentin matrix is a complex process of
participation of the alkaline phosphatase enzyme. Its aktivity
had beed demonstrated both in the bodies and the processes
of odontoblast.
4 day increments calcify together
(subcrystalline crystallization centers → calcispheres and
interglobular regions → calcisphere merging)
Dentine matrix in the closest proximity of odontoblasts never
calcify
= predentin
Periodical matrix formation
4-8 um/day
(Ebner‘s lines on decalcified slides)
4 day increments calcify together
(Owen's line on dental
cuts)
As the dentine matrix growths, the apical parts of the odontoblasts are pulled out into
thinner and thinner processes, and after calcification of the matrix, they are
permanently embedded as Tomes' fibers in the dentin channels
Odontoblastsdevelopment
Odontoblasts development
Root development
Root development
• The root dentine begins to develop only after the crown dentine is deposited
• Development is under the supervision of the enamel organ
• Cells from the cervical loop proliferate towards the apex of the future root
• Proliferating and extending part of the dental cup, consisting only of IEE and OEE = Hertwig's
epithelial root sheath (HERS)
Cervical loop
(Paul T Sharpe, Development 2016)
• Maintaining of Stem cell niche
• Extensive signalization both inside
and outside the epithelium
• Model system for the study of tissue
regeneration and repair
Dentinogenesis (root)
The inductive effect of the Hertwig's epithelial root sheath (HERS) provide differentiation
signals to ectomezenchyme to differentiate into odontoblasts that initiate the deposition of
the dentin matrix of the root
Once the dentine of the root is formed, HERS disintegrate and cells of ectomesenchymalorigin
from dental sac migrate near the root to form cementum and periodontium
Remnants of the Hertwig sheath in periodontium exist as Epithelial Rests of Malassez (ERM)
Shape of root depends on the shape of apical opening
Apical opening of HERS can be:
- circular - one root
- divided by horizontal discs - called diaphragms on several secondary apical holes
The number of diaphragms determines the number of roots (branches) of the tooth
(in multi-root tooth diaphragm divides papilla into sections)
Apical part of HERS
Cementogenesis
• Hard, bone-like tissue covering
the root of the tooth
• Yellowish color
• Avascular tissue
• Does NOT rebuild (as opposed to
bone tissue)
• Can be resorbed by
cementoclasts - during the tooth
replacement
• During life, is being replaced by
the apposition of new layers of
vital tissue
Composed of:
• Cellular part
• ECM
Dental cementum
Microscopic anatomy
Cementocytes, Cementoblasts, Cementoclasts
Extracellular matris (ECM) = Cementum
Cementoblasts
Actively involved in ECM
formation
Cementocytes
Cells surrounded by cementous
tissue, bodies placed in cavities,
processed in small tubules (similar
to Osteocytes in Bone)
Cementoclasts
Involved in cementum
resorbation in temporary
teeth
Acelular (primary)
Celular (secondary)Cells
Cementum matrix
Collagen fibres and calcified amorphous mass
Collagen fibres run in bundles (orientation is
determined by the forces on teeth)
Cementum is divided by origin into:
Primary (acellular)
Does not contain cementocytes
In the range of the entire tooth root
Directly connected to the dentine
Thickness: 10 to 200 µm
Secondary (cellular)
Contains cementocytes
Especially on dental apexes
Grows up to 500 µm thick
Cementogenesis
Begins after the disintegration of the Hertwig's epithelial sheath
Its place will be taken by ectomezenchymal cells that form a cementogenic mantle around
the root of the dentine base
By differetniation of ectomesenchymal
mantle – cementoblasts are formed
In the beginning, the cementum is
deposited very slow, so cementoblasts
have time to relocate into superficial
layers
- acellular (primary) cementum
In the period just before eruption,
cementoblasts forms the matrix much
faster which prevents cells to migrate
on the surface and they will remain
permanently entrapped inside
- Cellular (secondary) cementum
Chronology of primary and secondary dentition formation