Objectively documenting functional deficits is important because most orthognathic surgery patients perceive limitations in their masticatory function, but perceptions can be influenced by psychological factors that surgery might not address. It is well established that masticatory performance and maximum voluntary bite forces are both significantly lower than normal in orthognathic surgery patients. Patients may also use lower than normal occlusal forces during mastication. However, the reasons for these deficits are not well understood. Although orthognathic surgery patients have some degree of mandibular hypomobility, the deficit is small and its relationship to reduced performance is not clear. There may be differences in jaw muscle size, jaw muscle strength, and mechanical advantage among patient groups, but none of these anatomical and physiological differences correlate well with the observed reduction in occlusal forces. Better clinical assessment of functional deficits would probably benefit patients and lead to treatments designed to improve both esthetics and function.
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