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ORTHO TRIBUNE | APRIl 2010 Trends 9 A positive side effect of this is that the oxide layer formed results in firmer anchorage of the implant in the bone.34 Screw head Some suppliers have a special head variant for each potential applica- tion in their range, such as: • hook tops; • ball-shaped heads; • eyelets; • simple slots; • cross-shaped slots; and • universal heads (Figs. 8a–8d). The screw head should be very small and compact, to ensure that the patient experiences minimal discomfort. However, it must be large enough for the coupling ele- ments to be securely fastened to it (Figs. 9a, 9b). Transgingival portion The transgingival portion, also known as the gingival neck, is the most vulnerable part of an implant or a miniscrew. Perfo- ration of the gingiva provides a potential access point for micro- organisms, posing the risk of peri- mucositis or peri-implantitis. This is one of the main causes of the pre- mature loss of miniscrews.35–36 During the immediate post-oper- ative phase, the mucosa should be as close as possible to the screw, to seal the area.37 The most advanta- geous shape transgingival collum is that of a cone, as this shape natu- rally results in safe sealing with- out a pressure zone. This makes it more difficult for micro-organisms to penetrate, thus preventing infec- tions. The cone shape also seals the perforation wound, as a cork would seal a bottle, thus reducing bleeding. Conclusion The correct method of anchorage with regard to shape and quality is crucial for successful treatment. Maximum anchorage is not neces- sary in all cases, and thus, neither is the use of a miniscrew necessarily essential. From an historical point of view, the cortical anchorage system is, in common with other jaw orthodontic techniques, not new at all. The idea was conceived more than 75 years ago. Of all forms of skeletal anchor- age, the mini-implant is the most universally used and is the most suitable for routine use. However, before practitioners can select the most appropriate miniscrew for use in their practice from the large range on offer, they will need to review the literature thoroughly. OT Editorial note: A complete list of references is available from the pub- lisher. This article first appeared in Dental Tribune Asia Pacific, Nos. 1 & 2, 2009. The next edition of Ortho Tribune will feature “Part II — Basic information on the insertion of mini- screws.” All photos were provided by the authors. AD Figs. 8a–8d: For practical reasons, it is advisable to use systems that offer only one universally applicable head vari- ant. This single head should allow for the attachment of all types of coupling elements (threads, elastic chains, round wires and square wires). Figs. 9a, 9b (above and right): Height difference of the screw head in two clinical situations. Dr. Björn Ludwig can be reached at bludwig@kieferorthopaedie-mosel.de. ContactOT 8c. 8d. 8a. 8b.