This title seems a bit odd for an orthodontic article, but this analogy illustrates well what does not happen by moving the teeth in the jaw bone during orthodontic movements! However, this is what many believe is happening, that is to say that a tooth behaves like a nail that can be sunk into, pulled out or moved into a piece of wood as if it were hit with a hammer!
Orthodontic movements and dental displacements
|The main movements we perform to move teeth orthodontically can be categorized as follows:
Intrusion or ingression of teeth
It is often necessary to move a tooth in the vertical dimension. This may be necessary in the presence of an excessive overbite of the anterior teeth or when a posterior tooth got “longer” because it is no longer in contact with a tooth in the opposite arch.
Examples of dental intrusion to reduce an excessive overbite.
In the following two cases, the upper and lower incisors have been “intruded” into the direction of the arrows; the upper ones were thus “brought upward” and the lower ones were “brought downward”. Despite several millimeters of vertical movement, the length of the teeth did not decrease because the teeth have not been moved into the bone. Instead, the gums and bone surrounding the teeth followed them in their vertical movement.
➡ To see more examples of vertical adjustment of the level of teeth that allows the optimization of the smile esthetics, the gingival contour and incisal edges of the teeth.
Extrusion or egression of teeth
This movement aims at bringing teeth of opposing arches (top and bottom) that do not touch closer to one another in order to create overbite to the anterior teeth or to enable posterior teeth to touch.
The typical example is the closure of anterior or posterior open bites.
The first exception to this “rule” would be during the process of normal tooth eruption. When a tooth breaks through the gum, it gets longer and comes out of the bone and gum until it reaches its final position, which can take several years. The tooth that erupts thus becomes gradually more visible as it comes out. The following example illustrates well this eruption phenomenon.
|Two phenomena are illustrated with this case. (A) The lower teeth grow upward by extrusion and maintain their crown length, dragging the gingiva and bone with them. The upper teeth erupt by piercing the gum and bone and the crown becomes more apparent and longer as the tooth comes out (normal eruption). (B) Some time after wearing a device to prevent the posterior teeth to touch (articulated plane), we see the result of the eruption at the top and extrusion at the bottom (a small portion of eruption has also occurred).|
|(A) In this example, an 8-year-old little boy has a significant open bite (teeth that do not touch in front). (B) The use of a tongue crib blocks the tongue and allows the upper incisors to “go down”, dragging the gingiva and bone with them. Both central incisors are lower, but of the same length because the bone and the gingiva followed. These changes have occurred in only 4 months. This vertical movement will be later supplemented by the natural eruption of teeth which will then allow the teeth to come out slightly of the gingiva and look longer. This may take several years to complete.|
Another situation where the vertical movement of a tooth would not be accompanied by an equivalent movement of the gingiva and the supporting bone surrounding the tooth is in the presence of periodontal diseases around a tooth to move. This state of inflammation around the tooth can destroy the tissues and prevent the bone and gingiva from remaining attached during movement of the tooth. This is why it is important to have a healthy periodontium during an orthodontic treatment to prevent the loss of tissues that support the teeth (bone and gum).
(A) The periodontal disease having caused loss of tissues (bone and gum), the affected teeth appear longer (arrows). (B) A posterior tooth got longer and lost bone. Therefore, it seems longer. (C) X-rays show the severity of bone loss, which is why the teeth appear longer. If we attempt to extrude more such a tooth affected by an active periodontal disease, it will come out more from the bone and will become longer. It is essential to control periodontal diseases before an orthodontic treatment to avoid additional loss of tissues.
Multiple simultaneous movements
The different types of movements described in this page do not occur individually and it is common to see that different teeth require different movements to move them toward their ultimate goal, contributing to obtain a normal or ideal occlusion.
Horizontal movements (translation)
(A) During the horizontal movement of a tooth (translation), you would think that the tooth is gradually moving (A, B and C) while staying straight in the bone, but it is not the case. (B) Because the bone resists to movement, the crown of the tooth (the part that is out of the bone) tilts forward or backward in the direction of movement. (C) The tooth must then be uprighted so the crown and the root become straight again, but in a new, more advanced position. This phenomenon is one of the reasons why the closing of large spaces by translational movement may take a relatively long time.
Reality: a combination of simultaneous movements
- In fact, orthodontic movements are a combination of all these movements that can occur simultaneously: intrusion, extrusion, translation/uprighting.
- However, if the situation justifies it, a movement can be specifically performed on a tooth without moving others. The orthodontist will then adjust its “mechanics” (corrective appliances/braces) accordingly.
- A buccolingual movement is performed when it is required to move teeth either forward (buccal) or toward the tongue (lingual) to align the teeth in the dental arch.
- This movement, no matter how small it is, is required in almost all cases of orthodontic corrections.
|➡ For more Information on dental movement in orthodontics.|
Different types of orthodontic movements
Depending on where an orthodontic force will be applied (arrows) with respect to the centre of rotation of the tooth (red dot), a different movement can be generated.