Craniofacial Histology - Tooth Movement

Front 1

Name the different types of tooth movements

Back 1

Preeruptive Tooth Movement – Made by the deciduous and permanent teeth within tissues of the jaw before they begin to erupt.
Eruptive Tooth Movement – Made by a tooth to move from its position within the bone of the jaw to its functional position in occlusion. This phase is sometimes subdivided into intraosseous and extraosseous components.
Posteruptive Tooth Movement – Maintaining the position of the erupted tooth in occlusion while the jaws continue to grow and compensate for occlusal and proximal tooth wear.

Front 2

Preeruptive tooth movement

Back 2

The preeruptive movements of deciduous and permanent teeth position them within the jaw for eruptive movement.
Preeruptive movements of teeth are a combination of two factors:
1) Total movement of the tooth (bodily movement).
2) Growth of one part of the tooth while the rest of the tooth remains fixed.

Preeruptive movements occur within the remodeling jaw bones.

Preeruptive Movements are intraosseous (occur within bone) and remodel the bone. For example, bodily movement in a mesial direction (mesial is the surface of a tooth that faces toward the midline) causes bone resorption on the mesial surface of the crypt wall, and bone deposition fills in behind the tooth on the distal crypt wall.
Eccentric growth causes only bone resorption to accommodate the change in shape of the tooth.

Front 3

Gubernacular Canals

Back 3

holes in the jaws on the lingual aspects of the deciduous teeth which once contained the gubernacular cords. As the successional tooth erupts, its gubernacular canal is widened rapidly by local osteoclastic activity, delineating the eruptive pathway for the tooth. The rate of eruption depends on the phase of movement. During intraosseous phase, the rate averages 1 to 10 microns per day and it increases to about 75 microns per day once the tooth escapes from its body cell.

Front 4

Mechanism for eruptive tooth movement

Back 4

The mechanism for eruption of deciduous and permanent teeth are similar in that they result in axial and/or occlusal movement of the tooth from its developmental position within the jaw to its final functional position in the occlusal plane.
The periodontal ligament must also remodel to accommodate eruptive tooth movements. Fibroblasts simultaneously synthesize and degrade collagen fibrils as required along the entire ligament.
Proposed mechanisms of eruptive tooth movement include:
- root formation
- alveolar bone remodeling
- dental follicle
- PDL formation

Front 5

Relation of root formation and eruptive tooth movement?

Back 5

Observation: The root elongates as a tooth erupts.
Question: Does root elongation cause tooth eruption?


Experimental evidence: If a continuously erupting tooth (rodent incisor) is prevented from erupting by pinning it to the bone, the root continues to grow and it is accommodated by some resorption of bone at the base of the socket.
Conclusion: Although the root elongates as a tooth erupts, it does not appear to be required for eruption because the alveolar bone can not withstand the force exerted by the elongating root. Also, in some cases, rootless teeth still erupt and some teeth erupt a greater distance than the total length of their roots. Therefore, root formation is accommodated during tooth eruption and is not a cause of eruption. Although root formation is not required for eruption, root formation may accelerate tooth eruption.

Front 6

Relationship of bone remodeling and eruptive tooth movement

Back 6

Observation: During eruption, bone is reabsorbed over teeth and deposited under teeth.
Question: Does bone remodeling
cause tooth movement?


Experimental evidence: If a developing tooth is replaced by a metal or silicone replica without disturbing the dental follicle, the replica will erupt. If a developing tooth is wired to the underlying bone, an eruptive pathway still forms within the bone overlying the tooth. If a tooth is removed, or pinned to the underlying bone, or replaced with a replica without disturbing the dental follicle, an eruptive pathway still forms within the bone overlying the tooth.
Conclusion: The dental follicle is involved in some programmed bone remodeling. However, this alone would not cause eruption. The follicle causes bone resorption over the tooth, but the follicle does not induce bone deposition in the base of the alveolus that would raise the tooth.

Front 7

Relationship of dental follicle and eruptive tooth movement

Back 7

Observation: The follicle is associated with tooth eruption and appears to facilitate connective tissue degradation and bone resorption. Tooth eruption does not occur in animal models that lack a colony stimulating factor (CSF-1), a factor that stimulates osteoclasts. Local administration of CSF-1 permits differentiation of osteoclasts and eruption occurs. The enamel epithelium secretes proteases that break down connective tissues along the path of tooth eruption.
Question: Does the dental follicle cause tooth movement?
Conclusion: The stellate reticulum may serve as a biological clock that regulates timing of tooth eruption. The enamel epithelium of the dental follicle initiates intercellular signals that attract osteoclasts to the follicle. Osteoclasts are necessary for the bone remodeling that occurs with tooth movement. Cell signaling and apoptosis could explain the consistency of tooth eruption times.

Front 8

Relationship of periodontal ligament formation and eruptive tooth movement.

Back 8

Observation: The PDL changes and grows significantly during tooth eruption.
Question: Does the PDL cause tooth eruption?
Experimental evidence: PDL fibroblasts exhibit significant traction power. The fibroblast of the PDL have a cytoskeleton that enables it to contract. This contractility is a characteristic of all fibroblasts, but it is especially well developed in PDL fibroblasts. PDL fibroblasts have many (20-30 per cell) adherent junctions with other cells and also exhibit a close relationship to PDL collagen fiber bundles.
However, there are cases in which a PDL is present and the tooth does not erupt, and cases in which rootless teeth erupt.

Front 9

Posteruptive tooth movement

Back 9

Posteruptive tooth movements are those made by the tooth after it has reached its functional position in the occlusal plane.
Accommodation for Growth – tooth socket remodeling between ages of 14-18 forms new bone at the alveolar crest and on the socket floor to keep up with the increasing height of the jaws.
Compensation for Continued Occlusal Wear – axial movement to compensate for wear is probably achieved by the same mechanism as eruptive tooth movement.
Accommodation for Interproximal Wear – mesial or approximal drift compensates for wear on the points of contact between teeth. Mechanisms include contraction of the transseptal ligament between the teeth, soft tissue pressure, and the anterior component of occlusal force.

Front 10

Shedding of teeth

Back 10

Permanent incisors, canines and premolars normally develop lingually to the deciduous teeth. Resorption of deciduous teeth roots occurs on the lingual surface.
Permanent premolars develop between the divergent roots of deciduous molars and erupt in an occlusal direction. Resorption of interraducular dentin takes place with some resorption of the pulp chamber, dentin and sometimes enamel.

Front 11

Pressure and its affect on tooth movement and development

Back 11

Pressure from the erupting successional tooth appears to initiate resorption, although it is not necessary for shedding the deciduous tooth. If there is no successional tooth, the deciduous tooth is eventually shed anyway.
Growth of the face, jaws and muscles of mastication increase the forces applied to the deciduous teeth. These increased forces can damage the PDL of the deciduous tooth which also initiates tooth resorption.
Cementum is resorbed in local pockets (short arrows) and the oblique PDL fibers (arrowhead) are progressively lost.
Resorption of dentin and pulp is also occurring at the apex of the tooth (long arrow).

Front 12

How is resorption of dental hard tissue achieved?

Back 12

The resorption of dental hard tissue is achieved by cells histologically identical to osteoclasts, but because they remove dental tissue (i.e. dentin) they are called odontoclasts. Odontoclasts are derived from circulating monocytes that migrate to the resorption site where they fuse to form the characteristic multinucleated cells with an active ruffled border.

Front 13

What happens to the roots of exfoliated deciduous teeth?

Back 13

Roots of the deciduous molar are completely resorbed. Dentin and pulp of the deciduous molar are in contact with the premolar enamel.

Remains of an exfoliated deciduous molar. The roots have been lost completely, and part of the enamel of the crown has eroded.

Front 14

Orthodontic Tooth Movement

Back 14

Plasticity of the PDL and alveolar bone makes orthodontic tooth movement possible. Ideally, light force similar to natural physiologic forces would minimize tissue damage.
Osteoclasts differentiate and resorb alveolar bone on the pressure (compression) side of the socket. The PDL undergoes hyalinization (loss of cells from an area of the ligament due to trauma). Loss of cells slows or stops tooth movement until new cells repopulate the hyalinized part of the ligament. Then, osteoclasts can remove bone and the tooth can move. Heavier forces cause larger areas of hyalinization that require a longer period of repair and result in slower tooth movement.
Osteoblasts and fibroblasts remodel bone and PDL on the tension side of the socket.
No changes should occur in tooth structure. Cementum should not be affected because cementum resists resorption more than bone. More than 30 days of heavy force is usually required to damage cementum. However, rapid movement can damage root canal vessels resulting in pulp necrosis.