ToothEruption

7/29/2019 ToothEruption

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TOOTH MOVEMENT AND ERUPTION


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Tooth eruption

eruption takes place in chronological order involves active eruptionvertical movement of the tooth

as opposed to passive eruptionreceding of the gingiva

how it occurs is not understood root growth, hormonal action, contractile collagen, vascular pressure??

no requirement for the root

three distinct phases to the development of the dentition

1. pre-eruptiveinitiation of tooth development 2. tooth eruptionprefunctional phase

begins as the roots begin to form

3. development and maintenance of occlusionfunctional phase after the teeth have emerged into the oral cavity


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Tooth eruption defined as the axial movement of tooth from its

developmental position in the alveolar socket into itsfunctional position within the oral cavity

no evidence to suggest that eruption entirely ceases oncethe tooth meets ints antagonist

outward axial movements experienced during the functional phasemay also be a type of eruptive movement

also seen after tooth extraction

eruptive forces also experience in adolescentsgrowthspurts

preeruptive forces and those generated during the

prefunctional and functional stages may be differentmechanismsnot proven

accompanying eruptive forces are resistive forces whichprevent eruptionsoft tissues and alveolar bone, PDL andocclusal forces


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Directions and rates of tooth

eruption main direction is axial (i.e. long axis of the tooth)

also movement in other planesresulting in tilting anddrifting

eruption rates are greatest during times of crownemergence

rates will differ based on tooth typebalance betweeneruptive forces and resistive forces

permanent maxillary incisors1mm/month mandibular second molars4.5 mm in 14 weeks

permanent third molars1 mm in 3 months

eruption rates can slow to 1 mm/6 months in crowdeddentitions


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several stages after apposition of the enamel into the crown

area of the tooth stops, the ABs create an

acellular dental cuticleon the new enamelssurface cuticleprotection of emerging enamel

two thin layers

degraded with mastication

as the tooth erupts it is still covered with alayer of amelobasts and the remaining layers

of the enamel organ these layers become compressed as the tooth

movesforming a reduced enamelepithelium (REE) or reduced dentalepithelium

the REE is required for eruption

the REE fuses with the oral epithelium lining

the oral cavity (see figure 6-28) the REE produces enzymes which

disintegrates the central portion of this fusedtissueresults in an epithelial tunnel throughwhich the tooth erupts

collagenases and acid hydrolases

this disintegration results in an inflammatoryresponseinterpreted as the teethingres onse

Primary tooth eruption


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-as the tooth erupts, the portion of the epithelium

covering the crown pulls back and exposes the

crown

-the cervical portion of the epithelium is still attached

to the neck of the tooth (figure 6-28)

-this fused tissue serves as the initial junctionalepithelium (thin dotted line) and creates a seal

between the tooth and the surrounding tissue

-i.e. as the tooth pierces the oral epithelium, the

cells of the reduced dental epithelium and the

oral epithelium form the initial junctional

epithelium (thin dotted line)-the REE portion of this junctional epithelium becomes

replaced by oral epithelium

-later replaced by the definitive dentogingival junction


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Permanent tooth eruption as the succedaneous permanent teeth develop below the primary teeth,

the primary tooth is exfoliated

eruption is lingual to the roots of the primary teeth

exception is the maxillary incisors which move to a more facial position asthey erupt

loss of primary teeth should occur first

involves the differentiation of osteoclasts which absorb the alveolar bonebetween the primary and permanent teeth

development of odontoclasts which resorb portions of the primary toothsroot dentin and cementum

eruption process is the same for the primary teethformation of anepithelium lined tunnel for eruption

the process is also similar for the nonsuccedaneous teeth except noprimary tooth is shed


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Mechanisms of tooth eruption:

current research

not well understood

bone deposition at the base of the underlying root may initiateeruption and move the tooth axially

role for growth factors initiation of eruptionrole for EGF and TGF alpha also can be induced by macrophage colony-stimulating factor (MCSF)

production of TGF beta1, interleukin 1a by the stellate reticulum enhancesthe production of monocyte chemotactic protein/MCP1 and colonystimulating factor/CSF1 by dental follicle

CSF1 induces the dental follicle to make MCSF MCSF and MCP induce the recruitment of monocytes into the dental follicle

monocytes transform into osteoclastsresorb the overlying alveolar bone

ToothEruption

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