The effect of posture and anesthesia on the occlusal relationship in orthognathic surgery

Purpose: This study investigated the differences in centric occlusion (intercuspal-CO) and centric relation contact position (CR) in patients in an upright and supine posture when conscious and when supine under general anesthesia to rationalize planning for complex bimaxillary osteotomies. Patients and Methods: Twenty-four men and 37 women, with a mean age of 24.7 +/- 4.5 years were included in this study. Occlusal records on each patient included 1 in CO and 3 in CR in each of the following postures: conscious upright, conscious supine, and anesthetized supine. Casts were mounted in the Denar Mark II articulator and transferred to the Denar Vericheck (Denar Corp, Anaheim, CA) recording tool for measurements. The centric relation displacement vectors (CO-CR) were projected in various axes by 3D graphics. Results: The upright conscious CO-CR (mm) vectors were significantly different from both the supine conscious and anesthetized positions in the anteroposterior plane. The difference in the vertical plane was only significant in Class II division 1 patients. Conclusion: The posterior change in centric relation explains the apparent occlusal discrepancies created by rigid fixation of the mandible applied in the supine anesthetized position. By taking the CR records in the supine conscious position, the "loss" of maxillary advancement call be avoided.