Tooth movement and tissue reaction
- Introduction :
The movement of a tooth on its arch or of the arches on their bony bases is the goal of all orthodontic therapy, which also means provoking tissue chain reactions which will occur within the framework of a real periodontal remodeling which affects the desmodont, alveolar bone and sometimes the cementum and the root dentine.
- Basic tissue reactions:
2-1- Histological modifications at the level of a compressed or pressure zone:
Any force applied to a tooth will produce a mechanical effect on the tooth which will cause it to move and a biological response which will allow the movement to be maintained by tissue reorganization.
2-1-1- At the level of the periodontal ligament (desmodont):
The desmodont is composed of two elements: the periodontal hydraulic system (vessels, cellular and sub-fundamental elements), and desmodontal fibers.
- Mechanical effects:
As soon as a force is applied and this pressure exceeds the vascular pressure, it will cause vascular compression with collapse, the desmodontal thickness decreases and the tooth will move slightly.
If the force remains applied, the pressure will therefore remain increased, interstitial fluids which will in turn be driven out of the peridontium.
This results in real dehydration of the ligaments.
If the force is heavy and prolonged, the cells will in turn be ejected from the periodontal space. The space is very reduced and the displacement is carried out. Flexion of the cribriform plate of the alveolar bone.
- The biological response:
On the pressure side, the desmodontal fibers are compressed along the cribriform plate, which explains the sensation of pain after activation.
This ligament shortening aims to maintain their normal attachment to the tooth and in the long term a molecular reorganization occurs.
2-1-2- At the level of the alveolar bone:
- Mechanical effect:
The mechanical effect observed is alveolar flexion which is a secondary deformation of the alveolar bone following desmodontal compression.
- The biological response:
Osteoclasts are essential for bone resorption.
- Direct absorption:
If a light and well-distributed force is applied over the entire root surface, the ligament undergoes only slight compression and blood circulation is not impeded and osteoclasts appear in the ligament and in the lacunae of the underlying bone.
Resorption thus occurs directly at the level of the internal cortex of the alveolar bone or the lamina dura. It begins a few hours after the application of force.
If the mechanical conditions remain the same, it will continue regularly and the tooth will move in the same way.
- Indirect absorption:
When the force increases, the periodontal ligament is compressed; in the extreme case, the tooth can even come into contact with the internal cortex of the alveolar bone.
This results in the formation of a Hyalic zone, in this zone only compacted collagen fifes with a vitrified or hyaline appearance will persist, this is what is called the hyalinization phase, we will note at the level of this hyalinization zone that cellular life is temporarily suspended and that there is no formation of osteoclasts in the internal part of the alveolus, therefore no bone resorption.
This hyalinization phase begins around 36 hours and can last from 10 days to a few weeks. –
Indirect resorption occurs within the cancellous bone.
Tooth movement is stopped until resorption reaches the ligament in 2 to 3 weeks.
2-2- Histological modifications at the level of a tension zone:
This area is located on the side opposite the points of application of the force.
2-2-1- At the ligament level:
- Mechanical effects:
Immediately it will be summarized as a desmodontal widening quantitatively equal to the narrowings on the opposite side, stretching of the desmodontal fibers which takes an elongated and rectilinear shape.
- The biological response:
At the end of the 2nd and 3rd day after the application of the forces we will witness a differentiation of the mesenchymal cells into fibroblasts which will be at the origin of the fibrillar synthesis.
2-2-2- At the level of the alveolar bone:
Under the effect of traction, new bone is deposited on the internal surface of the alveolus along the stretched periodontal fibers, this opposition tends to constantly maintain the desmodontal space.
Bone opposition always begins with the formation of transitional tissue, osteoid tissue, which will subsequently mineralize to form mature bone.
Osteoid is an immature bone that is invisible on X-rays and is non-resorbable.
So this osteoid tissue will oppose any dental movement in its direction. The osteoid will begin to calcify after 10 to 15 days and will not become resorbable (therefore mature bone) until 3 to 4 weeks later.
Pressure zone Tension zone
Desmodontal space 
Desmodontal space
Compressed desmodontal fiber Stretched desmodontal fiber
Alveolar resorption alveolar apposition
Osteoclast number Osteoclast number
Metabolism metabolism
Hyalinization
- Reaction of the tooth itself (cementum and dentin):
3-1 root resorption:
According to Dougherty, root resorption is observed whenever the force applied is very high, attempting to move the tooth towards the osteoid wall.
The tooth is in a situation where its cementum comes into contact with the bone, hyalinization is therefore intense, the tooth will flee trauma by root resorption, the latter are generally observed in certain types of displacement which cause significant pressures such as intrusion, and rotation to avoid or limit its resorption it is always necessary to intrude rather than extrude and apply light forces each time an aspect of resorption is radiologically visible.
It is necessary to remove the force and stop moving for 4 weeks at a time.
3-2 hypercementosis:
Are generally observed on teeth without antagonism or teeth subjected to significant traction and can lead to dental ankylosis.
3-3- Root bends:
They are observed whenever orthodontic treatment is applied to teeth whose root formation and calcifications are not complete, this results in a displacement of the crown and the calcified root zone while the non-calcified root zone undergoes a deflection, the zone calcifies in a second stage following this bend.
- Factors influencing movement:
- 1/ Intrinsic biological factors:
1- General factors:
- Age: The adaptive capacity is greater during the period of active growth, there are more fibroblasts and the alveolar wall is lined by osteoblasts.
In addition to the much more intense cell turnover in children.
The alveolar bone contains more marrow spaces in young people.
On the other hand, senescence (aging) with consequent degenerative changes reduces the resistance of the periodontium to tooth movement.
- Nutritional factors: Orthodontic treatments should be avoided in people with poor health.
- Endocrine factors: Were also cited.
- Pregnancy
2- Local factors:
a- The tooth:
- Morphological characteristics: A multi-rooted tooth or a canine with a very long root are more difficult to move, which influences the choice of force intensity and the determination of the anchorage value.
- Pulp removal: A pulpless tooth moves as well as a healthy tooth, if the canal is properly treated and there are no apical lesions.
In any case, it is the periodontium that is affected.
b- The alveolar bone:
Its density varies depending on the individual and the site.
c- The site of the move:
Due to different bone density and better vascularization, it will be easier to move teeth in the maxilla than in the mandible, easier also to vestibulate upper incisors than lower incisors (because of the thickness of the cortex and proximity of the cribriform plate), it is more difficult to move lower molars than upper molars because the lower bone table is very thick.
d- Osteoid tissue:
It appears that this tissue is not initially resorbable in a compressed area, so it can block or delay movement when the direction of the force is reversed.
– if we try to do this, there may be a cementum lesion.
e- Gingival condition:
If the patient has gingivitis before treatment, it is essential to treat it because gingival inflammation worsens with movement.
- 2/ Extrinsic factors:
1- the primary factor is represented by the intensity of the force applied, in the light of the biological notions previously described, it appears that light and continuous forces approaching physiological forces are optimal, that is to say producing the maximum displacement in a minimum of time and without damage to the tooth and its supporting tissues.
2- Patient motivation and collaboration.
- Recidivism and restraint:
All orthodontic dental movements require a period of retention to allow mineralization of the newly formed bone and neo-organization of the stretched desmodontal fibers.
If this containment phase is neglected or eliminated, relapse is inevitable.
If we come to undo this relapse it is the periodontal tissue reaction observed just after the removal of the force.
That is to say, at the end of the desired movement, this reaction causes a retrograde movement of the tooth or return movement of the previously stretched fibers, hence the role of the retention which opposes the relapse.
Tooth movement and tissue reaction
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