The most important aspect in the exploration of mastication is the possibility that the patient can easily move the mandible to both sides. The chewing capacity must be the same on both sides. Although this laterality movement is not functional in itself, it is nevertheless the one that best imitates the masticatory functional situation. The key element of the study of mastication is the examination of the functional masticatory angles of Planas (FMAPs). We compared the results of this examination in 15 patients with the results of electromyographic recording of the activity of the masseter and anterior temporal muscles during food chewing in order to assess the reliability of FMAPs in the exploration of chewing function. We found that the electromyographic activity of the above-named muscles is higher on the side of the smallest FMAP or on the side usually used by the patient for chewing, thus confirming the reliability of Planas FMAPs.