Odontogenesis

Question 1

What is odontogenesis?

Define

• histogenesis:
• mineralised dental tissues:
• unmineralised dental tissues:
• dental lamina:
• vestibular lamina:

Answer 1

Odontogenesis - process of tooth development, stage based on shape of developing structure

• histogenesis: differentiation of undifferentiated cells to make new tissues
• mineralised dental tissues: enamel, dentine, cementum
• unmineralised dental tissues: dental pulp and periodontium
• dental lamina: contributes to development of teeth
• vestibular lamina: contributes to vestibule of mouth, delineating lips and cheeks from tooth formation of sulcus

Question 2

List the stages of odontogenesis and a brief explanation of each:

Answer 2

Initiation stage: first stage of tooth development

Bud stage: second stage, simple, spherical to ovoid, epithelial condensation of poorly morphodifferentiated and histodifferentiated into more complicated structure

Cap stage: 3rd stage of development, in which the tooth germ grows into cap shape

Bell stage: 4th stage, in which differentiation occurs to furthest extent and starts to resemble a bell

Crown stage: fully developed tooth e.g. hard tissue being formed

Question 3

Define:

• external enamel epithelium:
• stellate reticulum:
• stratum intermedium:
• inner enamel epithelium:
• ectomesenchyme:

Answer 3

• external enamel epithelium: outer layer of cuboidal cells that limits the enamel organ
• stellate reticulum: of epithelial origin but can behave like mesenchymal cells, can synthesis collagen I, II and III, but mainly epithelial
• stratum intermedium: two/three layers of cells sitting above IEE, express alkaline phosphatase like SR but not IEE
• inner enamel epithelium: columnar shaped cells rich in RNA, conencted by desmosomes to each other
• ectomesenchyme: interesting group of cells whose origin is controversial - neural crest or mesodermal somites

Question 4

When is preparation for tooth development carried out?

What happens?

What does the primary epithelial band give rise to?

What happens at week 7?

Answer 4

Preparing the area for tooth development is carried out around week 6:

• ectomesenchyme moving in to initiate the events
• condensation of ectomesenchyme
• formation of primary epithelial band

Primary epithelial band gives rise to:

• dental lamina
• vestibular lamina - undergoes programmed cell death to form vestibule between teeth and lips/cheeks

Week 7: differentiation between dental lamina and vestibular lamina

Question 5

Answer 5

Question 6

What happens during week 9?

Week 11?

Answer 6

Week 9: formation of tooth and cell death within vestibular lamina

Week 11: cell death continues in vestibular lamina

Question 7

What are the 3 overlapping phases of tooth development?

During these stages, there are interactions between:

Answer 7

• initiation, morphogenesis, histogenesis

Interactions between:

• epithelium (ectoderm): gives rise to enamel, hyaline layer of the root
• mesenchyme (ectomesenchyme): gives rise to dentine, pulp, cementum, periodontium (PDL and bone)

Question 8

When are the first signs of tooth development?

What occurs at this time?

Which tissue initiates tooth development?

Answer 8

First signs: 6 weeks IUL

• localised epithelial thickening in incisor and molar regions
• epithelium initially has odontogenic potential, then ectomesenchyme, then back and forth

Question 9

Name the stages of the tooth germ:

Answer 9

• bud stage - epithelial proliferation down into mesenchyme –> condense
• cap stage - migration and proliferation within mesenchyme by epithelium starting to surround condensed mesenchyme, layers of enamel organ
• bell stage - shape of tooth can be seen, differentiation, intense signals between two areas
• late bell stage - dental lamina is removed from external source
• crown stage - hard tissue formation

Question 10

What are the compnents of a tooth germ?

When does bud stage occur?

Cap stage?

Bell stage?

Answer 10

Tooth germ: enamel organ, dental papilla, dental follicle

Bud stage: 8 weeks

Cap stage: week 11

Bell stage: week 14

Question 11

What occurs at early bell stage?

Answer 11

• morpho and histodifferentiation
• enamel organ: IEE, SI, SR, OEE
• ectomesenchyme: differentiating into dental papilla (forms odontoblasts and pulp) and dental follicle (forms cementum, PDL and bone)

Question 12

What are the components of the enamel organ?

Answer 12

Inner enamel epithelium:

• basal lamina conforms to future ADJ
• columnar cells at cusp tips
• role: forms ameloblasts –> enamel

Stratum Intermedium:

• flattened cells
• role: synthesis and transport to and from IEE

Stellate Reticulum:

• star shaped
• fluid filled extracellular space
• osmotic gradient due to extracellular GAGs
• role: maintenance of shape and protection

Outer enamel epithelium:

• cuboidal cells
• role: maintenance of shape and exchange between ectomesenchyme and enamel organ

Question 13

When does the dental lamina begin to break down?

Which genes are activated during initiation?

Bud stage?

Morphogenesis?

Answer 13

Week 17: dental lamina breaks down, cell nests and cell rests form, tooth in final stages to begin laying down hard tissues of dentine and enamel

Initiation: epithelial signalling to dental mesenchyme - BMP2, EGF, Msx2, Shh

Bud stage: proliferation/condensation - Dlx1-3, Pax9, syndecan, tenacin

Morphogenesis: collagens, tuftelin