14 - Histogenesis of dental cementum

Question 1

Cementum

Answer 1

Hard avascular tissue that covers roots of teeth

Question 2

Cementogenesis

Answer 2

Formation of cementum by cementoblasts

• Occurs right after enamel formation
• Inner + outer enamel epithelium fuse together ⇢ epithelial root sheath of Hertwig

Question 3

Root sheath of Hertwig

Answer 3

Determines the root shape:

• Proliferation of cells of sheath ⇢ cause upward movement of developing tooth
• Sheath initiates dentin formation in root via ⇢ causing differentiation of odontoblasts from dental papilla
• Sheath disintegrates ⇢ residual peices = Epithelial cell rests of Malassez (ERM)
• Disintegration allows undifferentiated cells of dental sac to come into contact w/ newly formed root’s dentin
• This induces cells to become immature cementoblasts

During root development all of these processes occur in an APICAL direction

Question 4

Cementoblasts

Answer 4

Cells responsible for deposition + secretion of organic matrix of cementum ⇢ peptidoglycans + intrinsic collagen fibres

• Also responsible for mineralisation of organic matrix ⇢ Which is called cementoid

Question 5

Differentiated cells of dental follicle

Answer 5

There are 2 types of differentiated cells of dental follicle

Cementoblasts:

• Directly over dentin
• Involved in secretion + mineralisation of organic matrix of cementum

Sub-cementoblasts/Fibroblasts

• Found below cementoblasts
• Produce fibres that enter the matrix

Note! ⇢ Follicle cells/Cells of ERSoH ⇢ differentiate to form cementoblasts

Question 6

Mineralisation

Answer 6

Mineralisation occurs when:

• Thin layer of cementoid has formed
• Calcium + phosphate ions deposit collagen fibres in the form of hydroxyapatite crystals

As cementum ⇡ thickness ⇢ ⇡ follicular fibres become included in cementum

• Fibres are known as sharpey’s fibres
• Occurs after periodontal ligament is established

Question 7

Before tooth eruption

Answer 7

• Extrinsic/Folilcular fibres are incorporated in cementum + lie parallel to root structure

Question 8

After tooth eruption

Answer 8

• Fibres become oblique + become precursor of periodontal ligament fibres
• Cementum is formed first ⇢ Doesn’t contain any closed cells
• Cementoblasts are included in later cementum ⇢ Cementocytes found in lacunae

Question 9

Acellular cementum

Answer 9

This forms first

• Contains secreted matrix of proteins + fibres
• Fibres join periodontal ligaments when mineralisation takes place

Question 10

Cellular cementum

Answer 10

Develops after tooth formation is almost complete

• Forms around fibre bundles of periodontal ligament
• In molars + premolars ⇢ forms near root apex + interradicular areas