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Dental Histology - Erupt/Exfol
Exam 4
13
Medical
Professional
11/29/2008

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Term
Tooth Eruption
Definition
-Teeth must undergo movement from their place of development to thei place of function
The movements are:
1. Pre-Eruptive - occurs in jaw before eruption (space out a bit)
2. Eruptive - movement from bone to place of function
3. Post-Eruptive -compensatory movement to maintain function dispite tooth attrition
Term
Pre-Eruptive Movement
Definition
-Tooth occupies a place within bone, therefore movement requires bone remodeling
-Most movement occurs from early crowding of tooth germs in fetal head
-Jaw lengthens, crowding alleviated and tooth germs shift to "normal" position
-Rotational movement occurs in molars
Maxilla: Occlusal surfaces face distally
Mandible: Occlusal surfaces face mesially
 
Term
Eruptive Movement
Definition
-Begins after root formation has take place (which also leads to development of PDL)
-Contrast to primary, secondary teeth are almost completely encased in bony crypt
-Follicle surround tooth communicates with lamina propria through Gubernacular Canal
-The Gubernacular Cord (remnant of Dental Lamina) passes through canal, recruits osteoclasts to open space and tooth passes through
Term
Proposed Mechanisms for Eruptive Movement
Definition
1. Root Formation
2. Bone Remodeling
3. Dental Follicle
4. PDL
Term
Eruptive - Root Formation
Definition
"The crown of the tooth is propelled upward by force of the developing root"
 
-NO! A force is produced but needs a static object to puch against (which there is none)
-Also rootless teeth can erupt as well as eruption after root is completed
Term
Eruptive - Bone Remodeling
Definition
"Tooth is forced upward through bone resorption around the Gubernacular Canal and apposition at the crypt base"
Term
Eruptive - Dental Follicle (NOT THE SAME ONE)
Definition
This dental follicle is the name for the CT that is adjacent to the crown

"Cells of the REE secrete proteases to degrade collagen and CSF-1 that stimulates the differentiation of osteoclasts"
Term
Eruptive - PDL
Definition
"Tooth is pulled into position due to contraction of PDL fibroblasts"
 
-But, rootless teeth can erupt and teeth with a fully formed PDL necome impacted
Term
Eruptive - CONCLUSION
Definition
-Eruption mainly driven by Developing PDL
-But, root formation, dental follicle activity and bone remodeling do help
-Root formation has a larger role in producing a force after tooth clears the gingiva
Term
Post-Eruptive Movement
Definition
-Occurs after teeth reach level of occlusion
Reasons include:
1. Accomodate continued growth of jaws (via bone apposition)
2. Compensate occlusal wear (attrition)
3. Compensate interproximal wear (mesial drift)
Term

Mesial Drift Mechanisms

(Teeth tend to move towards midline)

Definition
1. Anterior Component of Occlusal Force - occlusla table has slight tilt, small forward force
2. Soft Tissue Pressure (cheekls, lips, tongue) - Almost nothing
3. Contraction of Transseptal Ligament - main mechanism, pulling cementum to cementum
Term
Exfoliation
Definition
-Cementum and dentin of primary teeth are resobed via Odontoclasts (identical to osteoclasts)
-Pulp and PDL cells undergo apoptosis
-Pressure on primary tooth by erupting secondary decreases its PDL support
-After root resorption occurs, the epithelium of DGJ migrates across underside of tooth
-Chewing eventually causes tooth to exfoliate
Term
Exfoliation Summary
Definition
1. Loss of Root Substance - from odontoclast resorption
2. Loss of Bone - through remodeling
3. Increased Force On Primary Tooth - support decreases and tissues must support comparatively increased masticatory forces
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