4 - Tooth germ - Physiological stages in teeth development

Question 1

Origin of teeth

Answer 1

• Teeth have a dual origin - ectodermal + mesodermal
• Ectomesenchyme is also involved
• In tooth development - interaction occurs between oral ectoderm + ectomesenchyme to initiate process
• Cellular interactions between epithelium + ectomesenchyme = formation of dentin, cementum, enamel + a crown

Question 2

Morphogenesis

Answer 2

• Stimulated by molecular signals that control ⇢ cell growth, migration + differentiation
• Also known as morpho differentation
• The development of form + specific tissues as a result from ⇢ migration of embryonic cells + their interactions

Question 3

Induction

Answer 3

• First process to occur during embryogenesis of interaction between developing embryonic cells

Question 4

Patterning

Answer 4

• Specification of embryo through segmentation
• Is both a spatial + temporal event ⇢ regional development of teeth that occurs at different times
• Involves processes of ⇢ induction, competence + differentiation

Question 5

Differentiation

Answer 5

• Process of specialisation of embryonic cells
• Interstitial growth = growth deep within a tissue/organ
• Appositional growth = growth at periphery through addition of additional cell layers

Question 6

Physiological stages

Answer 6

1. Initiation
2. Proliferation
3. Histodifferentiation
4. Morphodifferentiation
5. Apposition
6. Maturation
7. Eruption

Question 7

Initiation - Primary epithelial band stage

Answer 7

Stage 1 - Primary epithelilal band

• A thickening in epithelium around the mouth in upper + lower jaw
• Band is horse shoe shape + correspond w/position of future dental arches of jaw
• Gives rise to 2 subdivisions

1. Vestibular lamina ⇢ cells rapidly enlarge + then degenerate to form a cleft that forms vestibule between cheek + tooth bearing area
2. Dental Lamina ⇢ proliferative activity leads to formation of epithelial outgrowths into ectomesenchyme at sites of positions of future primary teeth (tooth bud formation)

Question 8

Stage 2 - Proliferation

Answer 8

• Multiplication of cells + increase in amount of tooth bud
• Observed in epithelium + ectomesenchyme
• Cells of basal layer begin to proliferate at rapid rate + contain the entire growth potential of teeth

Question 9

Stage 3 - Histodifferentiation

Answer 9

• Histological appearance of different cells w/different forms, sizes + functions
• Next step ⇢ formation of different cell layers in the epithelium + ectomesenchyme

Question 10

Stage 4 - Morphodifferentiation

Answer 10

• Differentiated cells are arranged under different layers
• Each layer has its own function + takes part in creating structures of tooth + determining shape + size
• At this stage elements of tooth germ are formed:

1. Enamel Organ - ectodermal ⇢ forms enamel
2. Dental Papilla - mesenchymal + ectomesenchymal ⇢ Form dentin + pulp
3. Dental Follicle - mesenchymal + ectomesenchymal ⇢ All around tooth

Question 11

Rest of the stages

Answer 11

Stage 5 - Apposition

Stage 6 - Maturation

Stage 7 - Eruption