Defenition:
The movement of teeth from the development position to the functional position in the jaw is called eruption.
Average rate of eruption is - 1 - 10 Um/ days - intraosseous
75 um / days - extraosseous.
The process of eruption is explained under the following hypothesis:
Root formation theory.
Bone remodeling theory.
Vascular pressure theory.
Ligament traction theory.
1. Root formation theory :
It suggests that tooth movement in the occlusal direction is mainly because of the formation of roots. This theory suggests that root formation is a prerequisite for the eruption of a tooth.
Points contradicting the theory:
if root formation were to cause pushing force then the root has to be in a fixed place.
They suggested Cushing - hammock ligament play this role.
It is not acceptable because the Cushing hammock ligament - a soft tissue.
In certain developmental defects, teeth are rootless but still erupts,
No direct relationship between the length of root and distance traveled during the eruption.
The tooth still erupts even after competition of root formation.
2. Bone remodeling theory
This theory suggests that resorption of bone at the site of pressure and deposition of bone at the site of resorption cause eruption.
Pressure excerpted by the tooth germ causes remodeling of bone
supporting points;
replacement of dental follicle with silica replica showed no eruptive pathway.
This shows dental follicle plays a vital role in remodeling.
Dental follicles regulate osteoclast which is responsible for bone resorption.
3. Vascular pressure theory
the vascular pressure theory suggests that the change in the arterial pressure of the surrounding vessel could be responsible for the eruption of the tooth
supporting points:
experiments in dogs show that differential pressure in ground substances influenced tooth eruption.
hypotensive drugs cause vasodilation, vasodilation increases hydrostatic pressure Experimentally increased hydrostatic pressure caused an increase in the rate of tooth eruption.
vasoconstriction by stimulation of sympathetic nerve caused decreased hydrostatic pressure. Decreased hydrostatic pressure caused a decrease in the rate of tooth eruption.
Though vascular pressure plays a role in the tooth-eruption, the pressure is too small to be the sole reason for tooth eruption to take place.
4. Ligament traction theory
This theory suggests that the dental follicle periodontal ligament complex pulls the tooth into the oral cavity through traction.
The ligament traction theory is the most accepted theory so far.
Supporting points:
when a silica replica was placed instead of the tooth germ eruption took place. This proved that the dental follicle played a major role in the tooth eruption.
Drugs that interfere with collagen formation interrupted the tooth eruption.
Lack of development of periodontal ligament resulted in lack of tooth eruption.
These eviences make ligament traction theory is the most accepted theory.
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