The use of screw mechanics for achieving the effect

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The use of screw mechanics for achieving the effect of a Le Fort I impaction of the maxilla was proposed by Lin et al., 3 in which multiple screws are necessary: two miniscrews (diameter, 2 mm; length, 7 mm) are placed between the roots of the maxillary second premolars and first molars on both sides; two hook screws (diameter, 1.5 mm; length, 9 mm) are inserted into the buccal alveolus between the maxillary first and second molars on both sides; and two hook screws (diameter, 2 mm; length, 7 mm) are placed in the paramedian palatal area 2 mm from the midpalatal suture, near the imaginary midline between the maxillary first and second molars. In this case report, MAAS using the SMS screw implant accomplished the effect of a Le Fort I impaction of the maxilla with the aid of a modified lingual arch. The SMS screw withstood quite heavy orthodontic forces. An appropriately formed 0.032- × 0.032-inch stainless steel power arm was fixed to the head of the SMS screw and provided the force application points for the required absolute anchorage without using multiple screws. We propose that the MAAS used in this case is a minimally invasive alternative orthodontic approach that mimics Le Fort I maxillary impaction surgery. The center of resistance of the unit to be moved is the basic point around which the arrangement of a force system is established. By using the center of resistance for the maxillary dentition from second molar to se- cond molar, as defined by Billiet et al., 10 various force systems for maxillary postero-superior intrusion can be established and a number of different clinical situations Figure 11. Pretreatment and posttreatment cephalometric superimposition. A , Overall superimposition on the Sella- Nasion plane at Sella; B , regional superimpositions on the palatal plane at ANS and on the mandibular plane at Menton. Figure 12. Posttreatment cephalometric and panoramic radiographs.
Hong et al Orthodontic treatment of gummy smile by maxillary total intrusion 155 Figure 13. Facial and intraoral photographs 21 months into retention. Figure 14. Dental casts 21 months into retention.
Hong et al Orthodontic treatment of gummy smile by maxillary total intrusion 156 may arise. If the postero-superior intrusion force passes anterior to the center of resistance for the maxillary dentition, the anterior teeth will intrude more than the posterior teeth and an anterior open bite will occur. On the contrary, if the postero-superior intrusion force is applied posterior to the center of resistance for the maxillary dentition, more intrusion of the posterior than the anterior teeth is generated, resulting in a posterior open bite. The line of action of the postero-superior intrusive force through the center of resistance for the Figure 15. Posttreatment and 21-month retention cephalometric superimposition. A , Overall superimposition on the Sella-Nasion plane at Sella; B , regional superimpositions on the palatal plane at ANS and on the mandibular plane at Menton.

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