Development Of Teeth

Question 1

How are neural crest cells formed

Answer 1

Gastrulation once blastocyst is implanted. Bilayered embryonic disc made up of epiblast and hypoblast. Primitive streak forms within hypoblast forming endoderm. Cells in epiblast differentiate to form endoderm. Second wave of invagination forms mesoderm. Above the notochord, ectoderm cells differentiate to form neural plate. Neural plate folds, neural groove pinches off to form neural tube and neural crest cells. Neural crest cells migrate into mesoderm to form ecto mesenchyme

Question 2

How does vestibular lamina and dental lamina form

Answer 2

At 5-6 weeks, oral epithelium cells above ectomesenchyme proliferate faster than surrounding cells, forming horse shoe shaped primary epithelial band that separates into the two lamina

Question 3

What happens at the bud stage

Answer 3

Dental placode signal regulates dental placode epithelium to give rise to tooth bud. Buds of epithelial cells on dental lamina correspond to dveloping enamel organs of deciduous dentition. Lingual extensions form permanent teeth

Question 4

Key process at cap stage

Answer 4

Differential mitosis (unequal growth). Shallow invagination of dental lamina on deep surface of enamel organ. Start of histodifferentiation and morphodifferentiation

Question 5

What does enamel organ form

Answer 5

Enamel

Question 6

What does dental papilla form

Answer 6

Dentine and pulp

Question 7

What does dental follicle form

Answer 7

Cementum and PDL

Question 8

Key idea in bell stage

Answer 8

Differential mitosis along internal enamel epithelium, creating occlusal pattern of crown of teeth. Results in 4 distinct layers of enamel organ: inner enamel epithelium, stratum intermedium, stellate reticulum, outer enamel epithelium

Iesisroe

Question 9

What happens at late bell stage

Answer 9

1. Inner dental epithelium cells differentiate to pre-ameloblasts
2. Outer cells form odontoblasts (secrete dentin) via differentiation at region of cusps. This is initiated by formation of pre ameloblasts
3. Iee cells differentiate to form ameloblasts, initiated by odontoblasts
4. Formation of ameloblasts signal odontoblasts to lay down predentin. Cells move into into dental papilla and older layers start to mineralise
5. Deposition of predentin induces emloblasts to lay down enamel matrix. Cells move into enamel organ and older layers start to mineralise
6. Once enamel is formed, dental lamina starts to disintegrate. Epithelial cell clusters are resorbed

Question 10

Describe process of root formation

Answer 10

Iee and oee fuse together at cervical loop to form bilayered Herwig’s epithelial root sheath.

HERS grows horizontally into dental papilla to form epithelial diaphragm that separates dental follicle and papilla.

HERS induce peripheral dental papilla cells to differentiate to odontoblasts. Odontoblasts deposite radicular dentin. HERS secrete hyaline layer of hopewell smith.

When tooth is erupting, hers proliferates and elongates. Radicular dentin is deposited, leading to HERS disintegration.

Dental follicle cells attach to hyaline layer, inducing differentiation to cementoblasts which lay down cementum and differentiation to periodontal fibroblasts that lay down collagen fibres to form periodontal ligament

Question 11

What can defects in tooth bud stage cause

Answer 11

Hypodontia (lateral incisor, third molar, second premolar), anodontia (all teeth absent), supernumerary teeth, neonatal teeth, post permanent dentition

Question 12

What can defects in cap stage cause

Answer 12

Crown shape!! Accessory cusps. Dens invaginatus.

Question 13

What can defects in bell stage cause

Answer 13

Matrix maturation and formation problem. Amelogenesis imperfecta. Dentinogenesis imperfecta. Enamel hypoplasia. Dentin dysplasia

Question 14

Defects in root formation

Answer 14

Supernumerary roots. Dwarfed roots. Hypercementosis