OE L16 Mechanisms of Tooth Eruption Flashcards
What are the stages of tooth eruption?
- Pre-eruptive tooth movement
- Eruptive tooth movement
- Post-eruptive tooth movement
Outline pre-eruptive tooth movement.
- 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
Outline eruptive tooth movement.
Movement of tooth from alveolar bone to functional position within the oral cavity.
What are the 2 stages of eruptive tooth movement?
- Intraosseus stage (in bony crypt)
- Extraosseus stage (out of bony crypt)
What happens to the epithelium during eruptive tooth movement?
- Cells of oral epithelium and reduced enamel epithelium fuse together, epithelium degenerates from centre as tip of tooth emerges, and junctional epithelium forms
What is an important feature of eruptive tooth movement?
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
Permanent tooth eruptions causes deciduous tooth what?
Deciduous tooth shedding (exfoliation)
- Involves root resoprtion and cementum resorption
- Pulp remains intact
Outline post-eruptive tooth movement.
- Remodelling of socket
- Axial movement
- Mesial drift
What are the effects of post-eruptive tooth movement?
- 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
Describe the role of CSF-1 in tooth eruption.
- Colony stimulating factor 1
- Involved in bone resorption
Describe the role of RANK in tooth eruption.
- Drives macrophages to become osteoclasts
Describe the role of OPG in tooth eruption.
- Osteoprotegerin
- Can bind to RANK ligand and therfore inhibit osteoclast differentation
What are the precursor cells of osteoclasts?
Monocytes and macrophages
How do macrophages become osteoclasts.
Macrophages produce macrophage colony stimulating factor (M-CSF) and RANK.
RANK ligand binds to RANK and induces macrophages to become osteoclasts.
How do osteoclasts resorb bone?
- Produce protons, creating an acidic environment
- Acidic environment dissolves minerlaised tissue
- Releases enzymes to degrade collagen fibres in bone matrix
What are the 4 forces behind eruptive tooth movement?
- Root formation: provides force in occlusal direction
- Bone remodelling: deposition of bone in space of bony crypt
- PDL remodelling: PDL contraction forces pulls toothupwards
- Dental follicles: either periodontal fibroblast contraction or hydrostatic pressure theory
Describe root formation as a force behind eruptive tooth movement.
- 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
Describe bone remodelling as a force behind eruptive tooth movement.
- 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
Describe PDL remodelling as a force behind eruptive tooth movement.
- 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
Describe how dental follicles act as a force behind eruptive tooth movement.
2 hypothoses:
- Periodontal fibroblast contraction hypothesis
- Hydrostatic pressure hypothesis
What is the periodontal fibroblast contraction hypothesis?
- 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
What is the hydrostatic pressure hypothesis?
- 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.
