Abstract: PURPOSE: The purpose of the present investigation was to locate the instantaneous rotation center of the mandible during maxillary surgical impaction, and explore the relationship between automatic rotation center of the mandible and maxillary elevation amount, the length of the mandible and mandibular plane angle. METHODS: Twenty-five patients who underwent maxillary Le Fort I impaction without concomitant major mandibular ramus split osteotomies were included. The preoperative and postoperative lateral cephalograms were used to evaluate the surgical changes and locate the mandibular autorotation center with Reuleaux method. The automatic rotation center of the mandible was compared to the maxillary elevation amount, the length of the mandible and mandibular plane angle with Pearson correlation and linear regression analysis. The data was analyzed by SPSS 13.0 software package. RESULTS: The mandibular automatic rotation center was located in average 15.64 mm below and 0.82 mm behind the center of the condylar head in these 25 patients. The correlation analysis demonstrated a positive correlation between maxillary elevation amount, the length of the mandible and the position of the rotation center of the mandible. Similar positive correlation was presented between the mandibular plane angle and the vertical position of the rotation center of the mandible. CONCLUSIONS: The rotation center in 25 cases were located outside the condylar head. The maxillary elevation amount, the length of the mandible and the mandibular plane angle was positively correlated to the position of the rotation center of the mandible.

Key words: Vertical maxillary excess, Le Fort I osteotomy, Impaction of maxilla, Mandibular autorotation, Rotation center