Tooth development

Dr. Gábor Varga

Department of Oral Biology

February, 2016

Jawbone in cross section

CP cortical plates

(compact lamellar bone)

AB alveolar bone

(spongy/bundle bone)

BB basal bone

ABP alveolar bone proper

PDL periodontal ligament

MS medullary spaces

E enamel

D dentin

Tooth development (introduction)

• Bone formation (brief overview)

• Tooth development

• Common vs. different

• Stem cells (potential in dentistry)

Macromorphological structure of bone

Macromorphological structure of bone

Havers lamella

Periosteum

Osteocyte

Osteon

Compact bone Trabeculae (spongy bone)

Bone formation 1 - intramembranous ossification

Intramembranous ossification involves the replacement of sheet-like connective tissue membranes with bony tissue.

Bones formed in this manner are called intramembranous bones. They include certain flat bones of the skull and some of the irregular bones.

The future bones are first formed as connective tissue membranes.

Then osteoblasts migrate to the membranes and deposit bony matrix around themselves.

When the osteoblasts are surrounded by matrix they are called osteocytes.

Intramembranous ossification in mandible – calcification occurs in a separate site from Merckel’s cartilage

Bone formation 2 - Endochondral

ossification The process of bone formation occurs in three stages, orchestrated by specialized bone cells that secrete and absorb materials as needed.

First, a soft cartilage-based foundation is laid, upon which mature bone will solidify.

Then, minerals containing calcium and phosphate are deposited throughout the foundation, creating a framework for the bone.

Finally, this raw material is sculpted and hardened into bone.

Missteps in this process can result in developmental defects and bone diseases

Endochondral ossification: the epiphysis of a long bone.

First is cartilage formation, then replaced by bone

Major cell types of bone

- the basis to achieve continuous renewal!!!)

Molar

longitudinal

section

the enamel

covers the dentin

Pulp Horn

LAMINA BUD STAGE CAP STAGE BELL STAGE ERUPTION

Tooth development

Tooth development – details 1

Tooth development – details 2

Section of tooth – enamel and dentin formation

Histologic slide showing a tooth bud

A: enamel organ

B: dental papilla

C: dental follicle

Tooth bud

formation

Histologic slide of tooth in cap stage

Histologic slide of tooth in early bell stage. Note cell organization

Histologic slide of tooth in late bell stage.

Note disintegration of dental lamina at top

Histologic slide of developing hard tissues. Ameloblasts form enamel,

while odontoblasts form dentin.

Histologic slide of tooth erupting into the

mouth.

A: tooth

B: gingiva

C: bone

D: periodontal ligaments

Histologic slide of tooth. Note the tubular appearance of dentin.

A: enamel

B: dentin

Cross-section of tooth at root. Note clear, acellular appearance of cementum.

A: dentin

B: cementum

Sections of tooth undergoing development.

Tucker, A., and Sharpe, P.

The cutting-edge of mammalian development; how the embryo makes teeth.

Nature reviews 5, 499, 2004.

Neuronal development:

a link to tooth development

Enamel organ and dental papilla

– Their interaction is crucial for tooth developments

Control of tooth shape – ectomesemchymal dominance

OBSERVE THAT TOOTH FORM IS DETERMINED BY THE

DENTAL PAPILLA (ie the ectomesenchymal side)

Barx1 gene expression is strongly related to molar formation

a) its suppression leads to incisor formation in molar area)

b) its ectopic expression in incisor area leads to molar formation)

Control of tissue differentiation –

inductive action of mesenchyme

OBSERVE THAT TISSUE TYPE FORMATION IS

DETERMINED BY THE MESENCHYMAL SIDE

Morphogenesis of tooth

Tooth development is driven by

communication between cells using signal

molecules activating specific receptors

Molecular components of control

A model of the molecular regulation of

tooth development from initiation to

crown morphogenesis Epithelium

Mesenchyme

The Runx2 gene is necessary for tooth

development - In Runx2 knockout mice tooth developments stops at

very early stage

Oligodontia in a human patient with

hypohydrotic ectodermal dysplasia (HED) -

The ectodysplasin gene is crucial for tooth development

Ectodysplasin stimulates tooth formation

Normal

Ectodysplasin

KO -/-

Ectodysplasin

overexpression

Effect of knock-out

(KO) and

overexpression of

ectodysplasin gene in

mouse

Decreased number of

molars

Increased number of

molars

Tooth development (summary)

• Bone formation (brief overview)

• Tooth development

• Common vs. Different

• Stem cells (potential in dentistry)