For free bodies like extracted teeth, which point is used?

The appropriate point used for free bodies such as extracted teeth is the center of mass. The center of mass is the point in a body or system where the mass is evenly distributed, and it plays a critical role in understanding the dynamics and behavior of that body when forces are applied.

When considering forces acting on an extracted tooth, the center of mass is essential for predicting how the tooth will move in response to those forces. It serves as an average location of mass that helps in analyzing movement and stability. In orthodontic applications, understanding the center of mass can be vital for effectively applying forces that will lead to desired tooth movement and overall treatment success.

Other points like the center of resistance and center of rotation refer to specific mechanics in the context of teeth still supported by their periodontal ligament, and they are less relevant for free bodies such as extracted teeth, where force interactions can be simplified to just considering mass distribution. The center of pivot is more associated with rotational dynamics, which is not applicable to the free body situation of an extracted tooth.