First-order couples and their anchorage

Couples are an interesting topic in technical mechanics because they have the ability to rotate a rigid body about its center of gravity. In orthodontics, this can be used to rotate a tooth in place around its center of resistance. However, this only appears to make clinical sense in the context of first-order considerations. The following article addresses the relevant principles, resulting side effects, and anchorage situations. Keywords: anchorage, couple, center of resistance, rotation, loss of space, collinear forces, cantilever, transpalatal arch, space opening, R-spring