OB P8 - tooth eruption Flashcards
what is tooth eruption?
movement of a tooth:
– from developmental position in the jaw
– to its functional position in occlusion in the mouth
what do “eruptive” movement continue and give examples.
“eruptive” movements continue adjusting tooth e.g.:
– over-eruption in response to opposing extraction
– compensation for wear
why is over eruption a problem?
the teeth are aligned in the occlusal plan which is a gentle curve and not flat and so over eruption disturbs the occlusal plane and forms a step in the occlusion which can alter jaw movement (chewing movements)
what is compensation for wear?
gradual over eruption- wear out teeth away so it will compensate by over erupting
what is active eruption?
Bodily movement of the tooth
what is passive eruption?
uncovering of the tooth by apical gingival migration
what is the deciduous eruptive movement called?
Bloodless eruption
what is the permanent eruptive movement?
deciduous exfoliation
where does the permanent successor start?
at the palatal or lingual side and migrates it way underneath the deciduous
What happens in pre-eruptive movement?
- during tooth development
- teeth move as jaw grows
- successional teeth move from a lingual/palatal position:
( e.g. lower premolars: start lingually and move between the roots of the deciduous molars) - bone remodelling
what is the eruption movement?
into the mouth and into occlusion
what direction is eruption?
mainly axial movement
what are the eruptive forces?
5-10g force
what are the variable speeds of eruption?
– 1mm in month – upper 1’s
– 4.5mm in 14 months – lower 5’s
– 1mm in 3 months – 8’s
what is the balance between in eruption?
- Eruptive forces
- Resistive forces – overlying tissues
Name the 4 push eruption theories.
- Root formation
- Pulp proliferation
- Bone formation
- Fluid pressure
Name the 3 pull eruption theories.
– collagen contraction
– fibroblast contraction
– fibroblast migration
what are the reason for push: root formation?
Roots normally form during eruption
what are the reasons against push : root formation?
- Some teeth have eruption paths»_space; root length
- Impacted teeth with fully formed teeth can erupt of impaction released
- Experimental evidence…
what happens in the rat experiment (root formation)?
- Rat incisor: •continuously erupts •remains sharp - Incisal tip removed: Proliferating root end removed - Tooth continues to erupt then exfoliates as root formation stopped and no bone form
what does this rat experiment suggest?
As any push from papilla/pulp or root growth is eliminated, yet eruption continues.
Therefore likely force is a pull from the PDL.
what are the reasons for push: bone formation?
Bone forms under an erupting tooth
what are the reasons against push : bone formation?
- Root resected teeth erupt
- Bone fills in as tooth moves away
what are the reasons for push : hydrostatic pressure?
> Periodontal vasculature > Cervical Sympathetic stimulation: – vasoconstriction – cessation of eruption – Reversible on cessation > Sympathectomy – Vasodilation – increased tissue pressure – Increase eruption rate
what are the against push : hydrostatic pressure?
– Root resected rodent incisor erupt normally
where is the evidence for pull : role of the PDL fibres?
Evidence from root resection experiments
what do PDL fibres do ?
> Disrupt collagen formation:
– no Vitamin C - essential for collagen synthesis
– lathyrogens - prevent cross-linking
what is the result of PDL fibres disrupting collagen formation?
- slower eruption rate or no change in eruption rate
- root formation continues
- ? collagen synthesis affects eruption rate
- but does the collagen generate the force?
when do teeth erupt?
when PDL fibres are not well developed
what are the reasons for pull: collagen contraction?
Collagen can contract in vitro
what are the reasons against pull: collagen contraction?
No proof that collagen contracts in vivo
what is the theory of pull: fibroblast migration/contraction?
- Forces transmitted along principle oblique fibres
- like scar tissue contraction
what are the reasons for pull: fibroblast migration/ contraction?
- Fibroblasts show motility when cultured
- Fibroblasts move cervically on eruption
- Colchicine: - reduces cell motility -> retards
eruption
what are the reasons against pull: fibroblast migration/ contraction?
- PDL fibroblasts don’t have organelles for motility
- No evidence that they can exert eruptive force
what is the summary of eruption theories?
multifactorial likely not due: – to bone formation • more likely a result rather than a cause – root formation Probably due to: – Pull - by PDL fibroblasts – Push - hydrostatic pressure
what are the steps of bloodless eruption?
- Oral mucosa
- collagen degrades (REE proliferation)
- Fusion of oral epithelium and REE
- Epithelial cell death
- Epithelial pathway
- REE forms JE
Describe deciduous exfoliation.
- Deciduous tooth must be resorbed to facilitate successional eruption.
- Pressure of tooth on bone -> resorption
- Deciduous teeth resorbed by Odontoclasts :
> multinucleated osteoclast like cells
> derived from monocytes
Describe post-eruptive movements.
- accommodate for growth
- compensate for occlusal wear
- accommodate approxinal wear
- following extraction of opposing teeth
