Anchorage consideration forms an integral part of orthodontic treatment planning and specific measures and precautions have been indicated to ensure adequate anchorage control so that reactionary forces produce minimal reciprocal tooth movement i.e. anchorage loss. Traditionally a variety of extra oral and intra-oral devices have been used to conserve anchorage but the cumbersome designs and demand for patient cooperation are limitations that have been difficult to overcome. Of late, the incorporation of dental implants and temporary anchorage devices (TAD) into orthodontic treatment make possible infinite or absolute anchorage which has been defined in terms of implants as showing no movement (zero anchorage loss) as a consequence of reactionary forces. A Temporary anchorage device (TAD) is a device that is temporarily fixed to bone for the purpose of enhancing orthodontic anchorage either by supporting the teeth of the reactive unit or by obviating the need for the reactive unit altogether, and which is subsequently removed after use. They can be located transosteally, subperiosteally or endosteally; and they can be fixed to the bone either mechanically (cortically stabilized) or biochemically (osseointegrated). As presently defined, all TAD’s are invasive devices and are best reserved for problems that cannot be effectively managed with conventional mechanics. Most common TAD’s include the Miniscrews, Microscrews, Miniature Implants (Mini-Implants), Palatal Implants, Modified Bone Plates and Retromolar Implants. In addition, a TAD may be a temporary prosthetic component that is removed after treatment. Therefore temporary anchorage devices can range from non integrated miniscrews to implant supported prosthesis with temporary orthodontic attachments. Most current miniscrews are stainless steel, titanium or titanium alloys and are manufactured with a smooth machined surface that is not designed to osseointegrate. By definition, TAD’s are temporary devices; no long term esthetic goal is planned. Thus most TAD’s are removed after orthodontic treatment. However some osseointegrated TAD’s may be covered with soft tissue or retained for sustained prosthetic function
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