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TOOTH MOVEMENT AND ERUPTION. Tooth eruption. eruption takes place in chronological order involves active eruption – vertical movement of the tooth as opposed to passive eruption – receding of the gingiva how it occurs is not understood

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tooth eruption
Tooth eruption
  • eruption takes place in chronological order
  • involves active eruption – vertical movement of the tooth
  • as opposed to passive eruption – receding 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-eruptive – initiation of tooth development
    • 2. tooth eruption – prefunctional phase
      • begins as the roots begin to form
    • 3. development and maintenance of occlusion – functional phase
      • after the teeth have emerged into the oral cavity
tooth eruption3
Tooth eruption
  • defined as the axial movement of tooth from its developmental position in the alveolar socket into its functional position within the oral cavity
  • no evidence to suggest that eruption entirely ceases once the tooth meets ints antagonist
    • outward axial movements experienced during the functional phase may also be a type of eruptive movement
    • also seen after tooth extraction
  • eruptive forces also experience in adolescents – “growth spurts”
  • preeruptive forces and those generated during the prefunctional and functional stages may be different mechanisms – not proven
  • accompanying eruptive forces are resistive forces which prevent eruption – soft tissues and alveolar bone, PDL and occlusal forces
directions and rates of tooth eruption
Directions and rates of tooth eruption
  • main direction is axial (i.e. long axis of the tooth)
  • also movement in other planes – resulting in tilting and drifting
  • eruption rates are greatest during times of crown emergence
  • rates will differ based on tooth type – balance between eruptive forces and resistive forces
    • permanent maxillary incisors – 1mm/month
    • mandibular second molars – 4.5 mm in 14 weeks
    • permanent third molars – 1 mm in 3 months
    • eruption rates can slow to 1 mm/6 months in crowded dentitions
primary tooth eruption
Primary tooth eruption
  • several stages
    • after apposition of the enamel into the crown area of the tooth stops, the ABs create an acellular dental cuticle on the new enamel’s surface
      • cuticle – protection of emerging enamel
        • two thin layers
        • degraded with mastication
    • as the tooth erupts it is still covered with a layer of amelobasts and the remaining layers of the enamel organ
    • these layers become compressed as the tooth moves – forming a reduced enamel epithelium (REE) or reduced dental epithelium
      • 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 fused tissue – results in an epithelial tunnel through which the tooth erupts
      • collagenases and acid hydrolases
    • this disintegration results in an inflammatory response – interpreted as the teething response
slide6

-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 junctional epithelium (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

permanent tooth eruption
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 as they erupt
  • loss of primary teeth should occur first
    • involves the differentiation of osteoclasts which absorb the alveolar bone between the primary and permanent teeth
    • development of odontoclasts which resorb portions of the primary tooth’s root dentin and cementum
  • eruption process is the same for the primary teeth – formation of an epithelium lined tunnel for eruption
  • the process is also similar for the nonsuccedaneous teeth except no primary tooth is shed
mechanisms of tooth eruption current research
Mechanisms of tooth eruption: current research
  • not well understood
  • bone deposition at the base of the underlying root may initiate eruption and move the tooth axially
  • role for growth factors
    • initiation of eruption – role 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 enhances the production of monocyte chemotactic protein/MCP1 and colony stimulating 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 osteoclasts – resorb the overlying alveolar bone