Cementogenesis

Question 1

What is cementum?

Answer 1

• mineralised tissue
• ectomesenchymal - from dental follicle
• covers tooth roots
• tooth support

Cervical 2/3rds: acellular

Apical 1/3: cellular - thicker as you go apically

• 65% mineral
• 23% matrix
• 12% water

Question 2

What drives root development?

What is the root sheath?

Answer 2

Root development: driven by Hertwigs Epithelial Root Sheath (HERS)

• forms a belt of cells around the developing root, breaking down and disintegrating cervically and the root sheath moves apically

Root sheath: governs number and shape of roots of each tooth

As development progresses, root sheath proliferates inwards, forming the pattern of roots

Question 3

What is Hertwig’s epithelial root sheath?

Answer 3

• apical development of the inner and outer enamel epithelium at the cervical loop
• defines root morphology
• inductive influence: root dentinogenesis, cementogenesis (indirectly)
• proliferates (cell division) spically
• disintegrates cervically

Some HERS cells may form cementoblasts - MES

Question 4

Explain how the root is formed:

Answer 4

1. HERS induces odontoblast formation - root sheath cells send signal to dental papilla to differentiate into odontoblasts
2. Pre-dentine then dentine formed, HERS basal lamina breaks down when mineralised dentine formed
3. HERS secrete enamel matrix proteins (amelogenins) onto dentine surface
4. Enamel matrix proteins mineralise to form hyaline layer of Hopewell Smith
5. HERS disintegrate once hyaline layer been laid down
6. Induction of follicle cells: migrate to root surface and form cementoblasts
7. Cementoblasts secrete cementum matrix and retreat outwards
8. Cementum matrix mineralises, entrapping PDL fibres (sharpey fibres)
9. Remnants of HERS form cell rests of Malassez in PDL - cystic potential

Question 5

What is the hyaline layer of Hopewell Smith?

Answer 5

Hyaline layer of Hopewell Smith:

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

Question 6

Give an overview of cementogenesis:

How do cementoblasts form?

Answer 6

• cementoblasts migrate outwards
• deposit matrix (pre-cementum): collagen, extracellular matrix
• mineralisation, no matrix vesicles
• PDL collagen fibres become trapped in cementum and mineralise - sharpeys fibres

Enamel matrix proteins - induces cementoblast differentiation from follicle - cementogenesis - acellular cementum - attachment