Root Development

Question 1

When does root development occur?

Answer 1

After the formation of the crown of the tooth, at the same time as the axial phase of tooth eruption

Question 2

Name the three components of root development.

Answer 2

• Dental papilla
• Hertwig’s Epithelial Root Sheath (HERS)
• Dental follicle/sac

Question 3

What is Hertwig’s Epithelial Root Sheath?

Answer 3

A double layer of epithelium formed from the internal enamel epithelium and external enamel epithelium at the cervical loop. (Forms after crown formation)

Question 4

Describe the following 4 steps of root formation after the formation of HERS.

Answer 4

1. The root sheath grows apically
2. The primary apical foramen may subdivide by the ingrowth of shelves
   (tooth erupts when 2/3 is formed)
3. The root sheath moves in at an angle of 45 degrees, forming the epithelial diaphragm
4. Cells of the internal enamel epithelium in the root sheath induce the mesenchymal cells in the papilla to differenciate into odontoblasts, producing root dentin matrix.

Question 5

What are the epithelial cell rests of Malassez?

Answer 5

The HERS cells which have pulls away from root dentin when dentogenesis has begun. These are thought to repair and regenerate the PDL.

Question 6

What happens the cells of the dental follicle after root dentogenesis has begun?

Answer 6

The dental follicle cells differenciate into cementoblasts, which begin to form dentin, and fibroblasts, which secrete collagen as part of the PDL