An Assessment of Interrelationship between Surgical Superior Repositioning of the Maxilla and Lower Incisors Inclination Change after Mandibular Autorotation

Abstract

Background and Objective: Correction of vertical maxillary excess (VME) via superior surgical repositioning of the maxilla can lead to counterclockwise rotation of the mandible along with alteration of jaw relationship and dental occlusion. The aim of this study was to determine the interrelationship between surgical superior repositioning of the maxilla and lower incisors inclination change after mandibular autorotation. Methods: In this correlational study, 13 patients with Class II malocclusion, mandibular plane angle greater than 27 degrees, and fully-erupted lower second molars were examined. Superior maxillary repositioning of 4mm was simulated on lateral cephalometric radiographs and maxillary dental models. Degree of mandibular autorotation was then predicted on lateral cephalograms, considering radiographic center of the condyle as the center of rotation, and on semi-adjustable articulator, measuring the articulator’s upper arm inclination change in degrees by digital inclinometer. As lower incisors rotate on the same arc of rotation as the mandible, measuring mandibular autorotation also indicates the amount of change in lower incisors’ inclination. Findings: Mean (standard deviation) values of mandibular autorotation and lower incisors’ inclination change after 4mm superior repositioning of the maxilla were 3.38±0.93 and 2.63±0.83 degrees based on Prediction Planning and Model Planning techniques, respectively. The difference between two methods was statistically significant (p<0.05). Conclusion: After superior repositioning of the maxilla, the counterclockwise rotation of the mandible causes the retroclination of the lower incisors, which should be considered in the cephalometric prediction before surgery.

Keywords

• vertical maxillary excess
• anterior openbite
• lefort i osteotomy
• molar intrusion
• mandibular autorotation.