User:Globalorthodontist/Orthodontic tooth movement
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Orthodontic tooth movement is a general term that defines different ways a tooth can move.
Key Terms[edit]
- Center of Resistance - It is a point of an object as force applied through center of mass which leads to an object moving in linear fashion or translation without any rotational movement. A center of resistance of a tooth can depend on its size of the root and the associated bone support of that tooth. The center resistance of each tooth is an arbitrary point that has been a point of discussion throughout orthodontic literature. Over the years several different definitions have been circulated in the literature such as
- Center of Rotation - It is point of an object through which when a force is applied, leads to a rotational movement.
- Moment (force) - This moment is produced when a line of force does not go through a center of resistance of an object. The moment due to force causes a rotational effect that is either clockwise or counterclockwise. The MF = F (force) x D (distance) is measured in g/mm. It is important to understand that when a force is applied in orthodontics to move teeth, the force acts on a bracket which does not lie in the same plane as a center of resistance of that tooth. Therefore, MF is produced in most cases.
- Moment (couple) - A moment due to couple is created
- Counter-moment -
- Couple - A couple is a type of movement that is produced by two forces that are equal, opposite and parallel to each other.
- Torque -
- Tip -
M/F Ratios[edit]
The moment due to force ratios are determine the counterbalancing moment that is acting to oppose the net force being acted on a tooth. This counterbalacing moment always acts opposite to the moment due force.
| Movement | M/F Ratio | Mc/Mf Ratio | Center of Rotation |
|---|---|---|---|
| Uncontrolled Tipping | 5:1 | Apical to center of resistance | |
| Controlled Tipping | 7:1 | 0 <Mc/Mf> 1 | Root of a tooth |
| Translation | 10:1 | Mc/Mf = 0 | Infinity |
| Torque/Root Movement | 12:1 | Mc/Mf > 1 | Crown of a tooth |
Types of Orthodontic tooth movements[edit]
Orthodontic tooth movements can occur in 5 different ways as described below. In orthodontic literature, these movements are defined by the location of their center of rotation.
- Translation Movement -
- Rotational Movement - It is a pure rotation of a tooth as its center of rotation of is located at the center of resistance point.
- Controlled Tipping
- Uncontrolled Tipping
- Root Movement - It is defined by movement of the root of a tooth only, without the crown moving. Some have also defined it as the center of rotation at the crown due to which the root moves.