[Different orthodontic anchorage systems. A critical examination].

Every orthodontic measure requires a detailed analysis of the individual anchorage situation in order to absorb (stationary anchorage) or control (reciprocal anchorage) the reactive forces and moments. Basically, an anchorage is oriented to the quality of the biological anchorage of the teeth. This is influenced by a number of factors: size of root surface, attachment level, density and structure of alveolar bone, periodontal reactivity, muscular activity, occlusal forces, craniofacial morphology and the nature of the tooth movement resulting from the planned correction. The quality of the biological anchorage may be enhanced by selective modification of the position of the anchor teeth: cortical anchorage of the first molar (Ricketts), distal inclination of the molars (Tweed, Begg) and differential torque control (Burstone). In this context, undesired anchorage effects also need to be discussed, for example interaction between the teeth being corrected and compact bone structures (symphysis menti, floor of the maxillary sinus) or the loss of anchorage by periodontal hyalinization or excessive friction within the bracket slot. In addition, the anchorage situation of ankylosed teeth and endosseous implants, as well as the advantages and disadvantages of additional mechanical anchorage aids (head-gear, Nance holding arch, lingual arch) are discussed. On the basis of the complexity of the individual biological and biomechanical aspects, guidelines are derived with which to establish anchorage control matched to the specific situation.