Unit C module 2 Flashcards
What are the steps that occur in tooth eruption?
Pre-emergent:
1) Crown formation
2) Movement towards emergence
Post-emergent eruption:
3) Post-emergent spurt as tooth moves up the occlusal plane
4) Juvenile occlusal equilibrium
5) Pubertal eruption spurt
6) Adult occlusal equilibrium
What are the major phases of eruption?
Pre-emergent eruption
Post-emergent eruption
What happens during crown formation?
The layers of the tooth begin formation.
No movement towards eruption takes place until crown formation ends. This only occurs when the root is beginning to form.
What must happen for pre-emergent eruption to take place?
2 things need to happen:
Resorption of bone over the crown of the tooth.
Development of a force to move the tooth.
How do teeth move pre-emergently?
The overlying alveolar bone is resorbed to form a path for the eruption to take place.
Odontoclasts begin to remove bone over the crown of a tooth just at the point that root formatino begins.
How do odontoclasts “know” to start degrading the overlying alveolar bone to forma path for tooth eruption?
The inhibition of the osteoclasts over the crown that relates to amelogenesis ends and they are up-regulated and become active as cementogenesis begins.
What happens to bone resorption overlying teeth if the tooth is erupting in an altered path?
The path opens up in the wrong direction.
Does the formation of the root “push” the tooth into eruption?
No, in many experiments it has been noticed that when the tooth is sectioned above the apex the crown and whats left of the tooth continues to erupt.
What are the mechanisms of eruption proposed? (what are the 3 theories of eruption mechanism?)
1) Contraction of myofibroblasts in the periodontal ligament (Fibroblasts have too low a contractile ability which makes it difficult believe they could cause tooth eruption)
2) Fluid pressure from blood flow within PDL. Difficult to locate such shunts. Evidence indicates that the blood flow theory is likely to be correct but is poorly understood.
3) Shortening of collagen fibers as they mature. There is no doubt that this happens and is important for tooth eruption. However, they are so randomly arranged that they can’t be the source of force for eruptive movement
How does eruption take place after the bony covering of the tooth has been removed?
Fibroclastic activity takes place
Does loss of a primary tooth affect eruption rate of permanent tooth?
It depends on how much the primary tooth removed from the bone surrounding the permanent tooth.
If the primary tooth is lost at a point when the permanent tooth is nearly through the bone and inflammatory resorption or some pathologic process removes the rest of the bone over the crown, the permanent tooth erupts more quickly.
If the primary tooth is lost early, and a considerable amount of bone is still seen above the permanent tooth eruption is slowed down. This is because when primary tooth is gone there is a lower blood supply to the area so eruption path is cleared more slowly.
What condition commonly causes bone resorption above permanent tooth and early eruption?
Periapical abscesses
What are the implications of early extraction of primary teeth by a dentist?
When the dentist needs to remove primary canines or molars early to encourage permanent canine eruption timing the extraction becomes more important. If it is extracted too soon it would delay the eruption of permanent teeth.
What controls post-emergent eruption?
Once tooth is in occlusion it is exposed to chewing and other forces opposed to eruption.
PDL collagen fibers attach to the bone above their attachment to the root and shorten. The collagen fibers shorten to push the tooth up into occlusion. PDL collagen is constantly replaced.
A very small resistance of less than a gram stops a tooth from erupting.
How long should a load be applied to an erupting tooth to stop it from growing?
if a force large enough to stop eruption is applied 50% of the time it is similar to loading constantly.
25% is the threshold for any effect on eruption.
