Anatomical guidelines for miniscrew insertion: palatal sites.

A previous Overview described suitable sites for vestibular miniscrew insertion.1 Although these locations are commonly used in orthodontic applications because of their ease of access, the interradicular spaces are limited by the proximity of neighboring roots (Fig. 1), presenting the following problems: • Risk of damaging the roots or the periodontium. • Possibility of miniscrew-root contact resulting in early screw failure. • Risk of screw fracture during placement, due to the narrower miniscrew dimensions needed for interradicular positions. • A loss rate as high as 25%.2 These risk factors can be avoided by using “rootless areas” such as the hard palate, the maxillary tuberosity, or the portions of the zygomatic arches adjacent to the maxilla. The tuberosity cannot be regarded as entirely safe, since unerupted third molars or thick layers of gingiva may prevent successful insertion3 (Fig. 2). Insertion into the inferior portion of the zygomatic arch carries the risk of perforating the maxillary sinus.4 Therefore, the only safe alternatives to buccal miniscrew placement are in the palate. In the mandible, where lingual screw insertion is associated with higher loss rates,5 the mentalis region is better suited for miniscrews and miniplates.6 In the maxilla, the hard palate appears to be an ideal insertion site. While the anterior palate definitely offers sufficient bone, consensus has yet to be reached regarding the minimal amount of bone required to avoid penetration into neighboring anatomical structures. Liou and colleagues suggested 2mm,7 Poggio and colleagues