OE L16 Mechanisms of Tooth Eruption

Question 1

What are the stages of tooth eruption?

Answer 1

1. Pre-eruptive tooth movement
2. Eruptive tooth movement
3. Post-eruptive tooth movement

Question 2

Outline pre-eruptive tooth movement.

Answer 2

• Means by which teeth are best positioned in the jaw for euptive tooth movement
• Complete movement of tooth germ
• Occurs through bony remodelling of crypt wall through a series of signalling events

Question 3

Outline eruptive tooth movement.

Answer 3

Movement of tooth from alveolar bone to functional position within the oral cavity.

Question 4

What are the 2 stages of eruptive tooth movement?

Answer 4

• Intraosseus stage (in bony crypt)

- Extraosseus stage (out of bony crypt)

Question 5

What happens to the epithelium during eruptive tooth movement?

Answer 5

• Cells of oral epithelium and reduced enamel epithelium fuse together, epithelium degenerates from centre as tip of tooth emerges, and junctional epithelium forms

Question 6

What is an important feature of eruptive tooth movement?

Answer 6

The gubernacular canal and cord:

• Canal positioned on lingual side of teeth
• Canal creates path for permanent tooth eruption, osteoclasts widen canal
• Canal contains cord made of remaining epithelial cells and fibres connecting to the permanent developing tooth

Question 7

Permanent tooth eruptions causes deciduous tooth what?

Answer 7

Deciduous tooth shedding (exfoliation)

• Involves root resoprtion and cementum resorption
• Pulp remains intact

Question 8

Outline post-eruptive tooth movement.

Answer 8

• Remodelling of socket
• Axial movement
• Mesial drift

Question 9

What are the effects of post-eruptive tooth movement?

Answer 9

• Readjustment of tooth socket accomodates for growing jaws
• Axial movement compensates for occlusal wear, continued cementum production at root apices
• Mesial drift accommodates interproximal movement

Question 10

Describe the role of CSF-1 in tooth eruption.

Answer 10

• Colony stimulating factor 1

- Involved in bone resorption

Question 11

Describe the role of RANK in tooth eruption.

Answer 11

• Drives macrophages to become osteoclasts

Question 12

Describe the role of OPG in tooth eruption.

Answer 12

• Osteoprotegerin

- Can bind to RANK ligand and therfore inhibit osteoclast differentation

Question 13

What are the precursor cells of osteoclasts?

Answer 13

Monocytes and macrophages

Question 14

How do macrophages become osteoclasts.

Answer 14

Macrophages produce macrophage colony stimulating factor (M-CSF) and RANK.
RANK ligand binds to RANK and induces macrophages to become osteoclasts.

Question 15

How do osteoclasts resorb bone?

Answer 15

• Produce protons, creating an acidic environment
• Acidic environment dissolves minerlaised tissue
• Releases enzymes to degrade collagen fibres in bone matrix

Question 16

What are the 4 forces behind eruptive tooth movement?

Answer 16

1. Root formation: provides force in occlusal direction
2. Bone remodelling: deposition of bone in space of bony crypt
3. PDL remodelling: PDL contraction forces pulls toothupwards
4. Dental follicles: either periodontal fibroblast contraction or hydrostatic pressure theory

Question 17

Describe root formation as a force behind eruptive tooth movement.

Answer 17

• Extending length of root may serve as eruption force
• Not required for tooth eruption but may accelerate tooth eruption

However:

• Tooth eruption continues once root formation is complete
• Removal of HERS arrests root formation but tooth can still erupt
• Some teeth erupt greater distance than their root extension

Question 18

Describe bone remodelling as a force behind eruptive tooth movement.

Answer 18

• Mandible and maxilla move teeth in eruptional position by bone remodelling
• Deposition on bony crypt floor drives tooth upwards
• Gubernacular canal widening

However:

• When tooth erupts, resorption of bony crypt sometimes continues, so during eruption resorption wasn’t present to act as a driving force yet the tooth still erupted
• Without follicular tissue, bone deposition on crypt floor cannot result in tooth eruption

Question 19

Describe PDL remodelling as a force behind eruptive tooth movement.

Answer 19

• When root is removed and PDL connection is maintained, tooth eruption can occur
  However:
• Replica tooth experiment, tooth erupted without PDL attachment
• Lathyrogen (blocks collagen crosslinkin) disrupts PDL but tooth eruption was not slowed

Question 20

Describe how dental follicles act as a force behind eruptive tooth movement.

Answer 20

2 hypothoses:

• Periodontal fibroblast contraction hypothesis
• Hydrostatic pressure hypothesis

Question 21

What is the periodontal fibroblast contraction hypothesis?

Answer 21

• Fibroblast cells in dental follicle contain collgen
• Collagen produces contractile forces for tooth eruption
• Studies showed that periodontal fibroblasts have contractile properties in collagen gel
• However, in vivo studies have not been able to show that fibroblasts have collagen fibre apparatus or have any contractile abilities

Question 22

What is the hydrostatic pressure hypothesis?

Answer 22

• Blood pressure drives eruption
• Tooth moves in synchrony with arterial pulse
• Hypotensive drug inreased capillary and perio tissue pressures, caused tooth eruption
• Number of fenestrated capillaries in eruption phase 3 times higher than non-eruption phase

Great deal of supportive evidence. No evidence against.