A calibrator for monitoring maxillary incisor position during orthognathic surgery

Abstract

I t is now well established that the orthognathic surgeon can successfully change maxillary or mandibular position in one or any combination of the three dimensions. The LeFort I maxillary downfracture osteotomy is arguably the most commonly used procedure for correction of midfacial dysplasias. A thorough clinical assessment, followed by records that include the patient’s photographs, cephalograms, and articulated study models, is required for the development of a comprehensive treatment plan. Despite careful model surgery and prediction tracings, the scope for significant error in the surgical positioning of the maxilla has been recognized.L-5 Attempts to accurately determine maxillary incisor position by additions to semiadjustable articulators have been described> 3 but these do not influence maxillary misplacements in the vertical dimension during surgery. The surgeon may elect to monitor the intraoperative change in the vertical dimension in one or more ways when impacting the maxilla. Measurement of the width of bone to be removed as a segment has been suggested6 (Fig. 1, A), so that, after osteotomy and apposition of the bone margins, the desired movement is assumed to have been achieved. Another method advocated involves the removal of a predetermined retangle of bone from the lateral pyriform rim.’ In this technique, the maxillomandibular complex is hinged intermittently with removal of interfacing bone until the impaction is completed (Fig. 1, B). Bennet and Wolfords drew attention to the change in vertical dimension that may occur when the maxilla is moved in an anteroposterior direction. The angle of the osteotomies can produce a “ramping” effect, and they recommended a stepped osteotomy cut to eliminate this vertical change by keeping the osteotomies parallel to the occlusal plane (Fig. 2, A). External methods of ensuring intraoperatively that maxillary incisor position has been altered as intended have included the Fig. 1. A, Osteotomy lines are marked out according to width of bone to be removed in a segment.6 B, Rectangle of bone at the pyriform aperture is removed as a record of the amount of anterior impaction desired.’