Root Formation

Question 1

Explain the interactions to form the crown:

Root:

Answer 1

Crown:

• epithelium - ameloblasts - enamel
• dental papilla - odontoblasts - dentine
• requires reciprocal induction: i.e. epithelial signal required for initiation of dentine formation and vice versa

Root:

• dental papilla - odontoblasts - dentine
• dental follicle - cementoblasts - cementum
• both ectomesenchymal - need an epithelial initiating signal

Question 2

When does the root form?

What is root development driven by?

Answer 2

As the tooth erupts the root s formed

Root development is driven by Hertwig’s Epithelial Root Sheath (HERS)

Question 3

Where is the dental follicle?

What does it give rise to?

Name its 3 layers:

Answer 3

Dental follicle:

• between enamel organ and bone

Gives rise to cells of tooth support:

• cementoblasts - form cementum
• fibroblasts - forms PDL collagen fibres
• osteoblasts - forms alveolar bone
• no involvement in gingival tissues

3 layers:

• inner investing layer - vascular, become cementoblasts
• loose connective tissue layer
• outer layer - lines alveolus with bone

Question 4

What are enamel matrix proteins?

Answer 4

Enamel proteins: bind to dentine and pre-dentine to form hyaline layer of Hopewell Smith

Question 5

Explain the stages of root development?

Answer 5

1. HERS induces odontoblast formation - growth factors BMP4, TGF-beta family, Shh
2. Pre-dentine then dentine form, HERS basal lamina breaks down when dentine starts to form
3. HERS cells secrete enamel matrix proteins (amelogenins_ on to predentine surface
4. Enamel matrix proteins mineralise to form the hyaline layer of Hopewell Smith
5. HERS disintegrates and move away from hyaline layer
6. Induction of follicle cells to migrate to root surface and form cementoblasts
7. Cementoblasts secrete cementum matrix and retreat outwards
8. Cementum matrix mineralises, entrapping PDL fibres
9. Remnants of HERS cells form cell rests of Malassez in PDL - cystic potential

Question 6

What is the hyaline layer of Hopewell-Smith?

Answer 6

Hyaline Layer of Hopewell Smith:

• between dentine and cementum
• highly mineralised
• 10 microns thick
• origin - matrix from: epithelial cells - enamel matrix proteins, ectomesenchymal cells as well
• role: induces cementoblast formation
• cements cementum to tooth

Question 7

What is cementogenesis?

Where is it derived?

What are gubernacular canals?

Answer 7

Cementogenesis: formation of cementum, the calcified connective tissue that covers the roots of the teeth, from the root sheath

• two types: acellular (primary) and cellular (secondary)

Cementoblasts - derived from dental follicle

Gubernacular canals: area between apex of deciduous and permanent tooth germ - connective tilssue through the alveolus bone

Question 8

Answer 8

Question 9

Answer 9