Teeth move based on the mechanical principle from the science called Statics. In order to fully understand the forces involved in creating orthodontic tooth movement, some basic terms must be defined.

Force (F): A load applied to an object which tends to move the object

Couple: Two parallel forces equal in magnitude and opposite in direction. Couples always produce pure rotation around the center of resistance. Coules also create moment.

Center of Resistance (CR): The point of concentrated resistance to movement

Moment (M): The rotation caused by a force acting at a distnace from the center of resistance.
A moment (M) = Force (F) X Distance (mm)

Tipping: The type of motion created by a force acting at a distance from the center of resistance (CR). Tipping has two (2) components - translation and rotation.

Uncontrolled Tipping (UT): The motion created by a single force acting at a distance for the center of resistance (CR).

Controlled Tipping (CT): The motion of an object that has a force applied at a distance from CR and a counterbalancing couple (CBC) to regulate the rotation of the object.

Counterbalancing Couple (CBC): A couple that creates a moment that is opposite in direction to the moment created by the force responsible for UT.

Review of Concepts