What is force?
Force is an action exerted by a body (wire, coil, elastic, etc.) over another body (teeth or bone), It expresses itself as mass times acceleration (mass x acceleration) and is a vector that presents;
- Intensity (measured in g).
- Sense/Direction (straight or angular). The latter is included between the straight line and an axis of reference.
- Modulus (sense or direction of the force).
A force is also defined as a vector with magnitude and direction. The correct unit tor force expression is the Newton (N). But in orthodontics forces are expressed normally in g.
This vector is graphically defined by an arrow, indicating the direction of the force (bucco-lingual, mesh-distal, etc.) and the line of action, (where the force is going). The force direction (from buccal to lingual, From mesial to distal, etc.) is defined by the point of the arrow. The vector also shows us the force magnitude that is proportional to the length of the body of the arrow; the point of force application is indicated by the origin or tail of the arrow.
The units employed in orthodontics are force and distance. Force is defined, as previously mentioned, as the action of a body (wire) over another body (tooth) that changes or tends to change the way the second body moves, due to a push or traction. Sometimes we do not work in orthodontics with a single force, frequently two or more elements add up.
In these cases we can use the Parallelogram law, which determines the resultant of two forces applied over the same point.