The Zygoma Anchorage System.

clusions often requires intrusion and retraction of the anterior segment, which, in turn, usually necessitate mechanical reinforcement of posterior anchorage.1 Intraoral devices such as transpalatal bars or Nance appliances2 can reduce the need to wear Class II elastics, but can cause mesial movement of the lower first molars and protrusion of the incisors. Additional extraoral anchorage in the form of headgear3,4 is often rejected by adult patients for social and professional reasons. Even when headgear is worn 14 hours a day, some anchorage loss and mesial movement of the upper molars are usually observed. Osseointegrated titanium implants have recently been used to enhance orthodontic anchorage without the need for special patient compliance.5 After orthodontic treatment, these implants can be used to replace one or more missing teeth.6 Removable implants have also been placed distal to the molars to close first molar extraction spaces7 and prevent tipping of the second and third molars. These implants are unpredictable, however, because their relationship to the adjacent teeth and the occlusion changes considerably during treatment. The thickness of the anterior midpalatal bone allows a more stable implant to be placed there,8,9 and a rigid appliance can be connected from the central implant to the first premolars or molars.10 Because the transpalatal arch must be as rigid as possible, however, the amount of anchorage cannot be adjusted during treatment. The reaction forces generated during intrusion of the anterior teeth are first applied to the upper molars and then transmitted to the implant by the transpalatal arch, making the implant system an indirect anchorage unit. Because of osseointegration and the large diameter of the implant, a hollow explantation drill must be used to remove the implant at the end of treatment, leaving a bone cavity with a diameter of about 5mm. Some authors advise leaving the subgingival part of the implant in the bone permanently. Miniscrews are small enough to be placed between the roots of the teeth in the alveolar bone.11-14 By connecting two or more miniscrews, the orthodontic reaction forces can be neutralized. The surgical procedure is uncomplicated because the screws are placed directly through the gingiva, without a mucoperiosteal flap, and can be loaded immediately after insertion. Miniscrews can be used in the anterior or posterior region and attached with elastics or coil springs to the fixed appliance for direct anchorage. Anchorage can be adapted to changing treatment needs in different parts of the dental arches.