mechanisms of tooth eruption#

Question 1

what are the three stages of eruption tooth movement?

Answer 1

1. PRE-ERUPTIVE TOOTH MOVEMENT
   * Made by deciduous and permanent tooth germs within the tissues of the jaw prior to eruption
2. ERUPTIVE TOOTH MOVEMENT
   * Made by a tooth moving from within the bone of the jaw to functional position within the occlusion (along with root formation)
3. POST-ERUPTIVE TOOTH MOVEMENT

• Maintains position of erupted teeth in occlusion.
• Compensates for occlusal / proximal tooth wear
• Starts when teeth attend occlusion
• Continues as long as tooth is in oral cavity

Question 2

what occurs during pre-eruptive tooth movement?

Answer 2

• teeth are best positioned in the jaw for eruptive tooth movement
• bony remodelling of crypt wall
• signalling events between dental follicle and stellate reticulum

Question 3

what occurs during the eruptive tooth movement stage

what stages are there

Answer 3

Two stages

• Intraosseous stage
• Extraosseous stage

Question 4

what occurs in intraosseous stage?

Answer 4

Movement within bony crypt,

Eruption speed - 1mM/day

• Slow
• High resistant forces from the bone

Question 5

what occurs in the extraosseous stage?

Answer 5

• Movement out of bony crypt,
• Eruption speed - 75mM/day
• Less resistance from soft tissues

Question 6

during eruptive tooth movement, what occurs in the overlying soft tissues?

Answer 6

• Proliferated epithelium produces enzymes to degrade connective tissue
• Tissue degradation could also be due to lack of blood supply
• cells of oral epithelium and reduced enamel epithelium unite
• Forming Junctional Epithelium

Question 7

what happens to the gubernacular canal during eruption?

Answer 7

osteoclasts widen the canal

Question 8

what occurs during post-eruptive tooth movement ?

Answer 8

• Accommodates growing jaws (remodels socket)
  
  • Age 14-19, jaw growth stops
  • Readjustment of the position of tooth socket by bone remodelling
• Compensates for occlusal wear (axial movement)
  
  • Occlusal force makes tooth movement
    
    • By continued cementum formation at root apical site
• Accommodates interproximal (mesial drift)
  
  • Occlusal force
  • ligament contraction
  • pressures of cheeks/tongue

Question 9

what signalling events occur for osteoclasts to form?

Answer 9

Question 10

how do osteoclasts resorb bone?

Answer 10

• TRAP+ and H+ Secretion
• Proteolytic enzyme secretion
• Produces acid and enzymes
• Ruffled edge (Action site)
  
  • To resorb the bone

Question 11

what are the possible mechanisms of tooth eruption?

Answer 11

• Root Formation
  
  • Growing root accommodated by occlusal movement
• Bone Remodelling
  
  • Deposition / resorption of bone around teeth
    
    • Formation of gubernucular canals
• Periodontal Ligament (PDL) remodelling
  
  • Functions of PDL cells / fibres in controlling eruption
• Dental follicles:
  
  • Periodontal fibroblast contraction
    
    • Vascular/Tissue Hydrostatic Pressure
  • Local increases in tissue fluid push teeth occlusally

Question 12

evidence supporting root formation as the mechanism for eruption?

Answer 12

• Root formation associates with tooth eruption
• Extending the length of root may serves eruption force

Question 13

evidence against root formation as the mechanism for eruption?

Answer 13

• Tooth eruption continued without further root formation
• Surgical removed HERS did not stop tooth eruption
• Resection and pinned remaining root of rodent incisor to bone resulted in bone resorbed and eruption continued
• Some teeth erupted greater distance than their root extension

Question 14

is root formation the main force of tooth eruption?

Answer 14

• A consequence, not a cause, of the eruption process
• Not required for tooth eruption
• But may accelerate tooth eruption
• Root Formation is not the main source of eruptive force

Question 15

evidence supporting bone remodelling as the mechanism of tooth eruption

Answer 15

• Mandible and Maxilla move teeth in eruptional position by bone remodelling
• Gubernacular canal widen by osteoclast
• Bone deposition on crypt floor may result tooth eruption
  
  • May create force to push tooth

Question 16

evidence against bone remodelling as the mechanism of tooth eruption

Answer 16

• Base of crypt continues resorbed during tooth eruption
• Without follicular tissue, bone deposition on crypt floor can not result in tooth eruption
  
  • Dental follicle is involved in tooth eruption

Question 17

evidence supporting PDL remodelling as the mechanism for tooth eruption

Answer 17

• Tooth eruption continues after root resection or transection of the rodent incisor
  
  • Shows PDL contribution

Question 18

evidence against PDL remodelling as the mechanism for tooth eruption

Answer 18

• Surgical removed premolar and replaced by metal or silicon replica, the replica can erupt without PDL attached on
• Laythyrogen selectively disrupts collagen crosslinking, but it did not slow tooth eruption.
• Teeth can be erupted in absent of well developed PDL

Question 19

what are the hypotheses for dental follicles playing a part in the mechanism of tooth eruption?

Answer 19

• The Periodontal Fibroblast Contraction Hypothesis
  
  • Fibroblast cells in dental follicles produce contraction force for tooth eruption
• Vascular/Tissue Hydrostatic Pressure Hypothesis
  
  • An eruption force might be generated via the periodontal vasculature
    
    • Directly through blood pressure
    • Indirectly by influencing periodontal tissue (hydrostatic) pressures

Question 20

evidence supporting periodontal fibroblast contraction as a mechanism for tooth eruption

Answer 20

• Migration along with eruption
• Myofibroblast like in vitro culture
  
  • generated tension and contraction in collagen gel
• Cyclophosphamide suppressed tooth eruption
• Colchicine resulted in retarded the tooth eruption and also suppressed contraction in vitro

Question 21

evidence against periodontal fibroblast contraction as a mechanism for tooth eruption

Answer 21

• Periodontal fibroblast in vivo showed higher ER contains
• Fibroblasts in dental follicle do not show migratory or contractility morphology in vivo
• no evidence support they can produce force
• The cell/cell contacts in desmosome, but not fibronexus in vivo
  
  • Fibroblasts do not show contact in fibronexus
• No microfilament bundle

Question 22

evidence supporting vascular / tissue hydrostatic pressure being the mechanism for tooth eruption

Answer 22

• Tooth moves (0.4mM) in synchrony with the artery pulse
• Blood pressure influence the tooth eruption
• Hypotensive drug increased capillary and periodontal tissue hydrostatic pressures, result in tooth eruption
• Osmotic pressure generated by increasing concentration of proteoglycan associated with eruption
• Number of fenestrated capillaries increased 3 times in eruption phase than non-eruption phase
• Decreasing eruption by stimulation of the cervical sympathetics via decreased capillary and periodontal tissue pressures
  
  • Decreases eruption speed
• Non of above evidences is incontrovertible
• But more studies are needed