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Trends ORTHO TRIBUNE | APRIl 20106 The extent of movement and countermovement does, however, depend on the anchorage strength of the individual teeth, i.e., on the number and length of the roots, the root surface, and the structure of the surrounding bone. Anchorage quality can be divided into three categories: 1. minimum anchorage; 2. medium anchorage; and 3. maximum anchorage. These three categories can be described using the example of a conventional canine retraction after removal of a first premolar (Fig. 1). In the case of minimal anchor- age, the support is provided by the individual teeth. Figure 1a shows that a single premolar is not suf- ficient as an abutment to distalise a canine. The premolar is clearly mesialised in reaction to the appli- cation of force. Figure 1b shows how two, equal- ly strong, anchorage segments are formed. Action and reaction are comparable in this case; the result is reciprocal tooth movement. In the case of maximum anchor- age (Fig. 1c), the posterior group of teeth is secured and held stationary by using a miniscrew. The canine can be retracted by the complete force vector, as the reactive force is completely absorbed by the anchor- age block formed. Apart from anchorage quality, the basis, i.e., the type of anchorage location, plays a role: Dental or desmodontal support: • use of additional intra-oral devic- es (nance, palatinal arch, lingual arch, lip bumper); • modification of fixed appliance (buccal root torque, blocking); and • incorporation of the teeth of the other jaw (Class II or III elastic bands). Extra-oral support: • headgear; and • face mask. Enossal support: • implants, miniscrews, etc. This article only deals with anchorage in bony structures. The terms skeletal or cortical anchorage are used interchangeably in this case. History and overview of skeletal anchorage Bony anchorage has its roots in Gainsforth’s unsuccessful attempt to insert screws into the jawbone as load anchors in 1945. Many later experiments were unsuccessful and the method had become obsolete by the late 1970s. From 1980 onward, various research groups (such as Creek- more, Roberts, and Turley2–7 ) took up the subject once more. Creekmore published the first, clin- ically successful patient treatment case. There are now numerous options for cortical anchorage (Fig. 2), including (artificial or pathologically) ankylosed teeth on the basis of miniplates normal- ly used in cranio-maxillo-facial surgery and the use of prosthetic implants. Wehrbein and Glatzmaier were the first to present an implant sys- tem specifically designed for jaw orthopaedics (Orthosystem, Strau- mann8–10 ). These orthopaedic jaw implants, which also included Mid- plant (HDC), are mainly inserted into the palate. This method has been found to be both safe and suc- cessful. In recent years, the requirements for cortical anchorage techniques have been defined in the literature. However, upon closer inspection, only orthopaedic mini-implants met these requirements favourably, in terms of: • biocompatibility; • small size; • simplicity of insertion and use; • primary stability; • immediate load capacity; • adequate resistance against orth- odontic forces; • usability with standard orthopae- dic appliances; • independence of patient coopera- tion; • clinically superior results in comparison with standard alternatives; • ease of removal; and • cost-effectiveness. AD Figs. 5a–5h: Eight examples of the more than 700 different forms of miniscrews currently available: a) Ortho easy (FORESTADENT), b) Aarhus Mini Implant (Medicon), c) AbsoAnchor (Dentos), d) Dual-Top (Jeil Medical), e) LOMAS (Mondeal), f) Osas (Dewimed), g) Spider Screw (HDC) and h) tomas-pin SD (DENTAURUM). Fig. 2: Overview of the range of cortical anchorage options. Figs. 4a, 4b: One-sided gap closure in the left lower jaw. Mini- screws prevented the expected reactive side effect of subsequent shifting of the middle line. Figs. 3a, 3b: Clinical example of two typical miniscrew treat- ment applications: gap closure (3a) and straightening of tooth No. 7. Figs. 1a–c: After removal of the first premolar, the canine is to be retracted; results for a) minimum, b) medium or reciprocal and c) maximum anchorage. f OT page 1 1a. 3a. 3b. 4b.4a. 5a. 5b. 5c. 5d. 5e 5f. 5g 5h. 1b. 1c. g OT page 8