Anchorage maybe defined as resistance to the unwanted three dimensional forces generated in reaction to the active components of an appliance. The reactive forces are equal and opposite to the active forces according to Newton’s third law of motion (every action produces an equal and opposite reaction). Poor anchorage management can result in a non-ideal occlusion, over-retraction or under-retraction of the incisors, and poor facial aesthetics.
Anchorage requirements should be assessed by space analysis during treatment planning (Chapter 18). If 75–100% of extraction space is required for the correction of malocclusion, anchorage requirements can be considered to be high.
Classification of anchorage devices
Anchorage devices can be classified according to the tissue(s) providing resistance to unwanted tooth movement.
Intra-orally the teeth, skeletal structures and soft tissues can provide anchorage. When the teeth are used, the anchor unit should incorporate as many teeth as possible, so that the force threshold needed to initiate tooth movement is not exceeded. Teeth from the opposing dental arch can also be used to provide inter-arch anchorage with Class II or III intermaxillary elastics (Figure 37.1A). The bone covering the palate can be a useful source of anchorage because of its large surface area. Removable appliances and the Nance palatal arch (Figure 37.1Bi) commonly use the palate as a source of anchorage. More recently, skeletal anchorage has become increasingly popular with the introduction of implants and mini-screws (Figure 37.1Bii). These devices provide maximum anchorage, unlike previously mentioned methods, which means that space loss is />