Electric versus magnetic transcranial stimulation of the trigeminal system in healthy subjects. Clinical applications in gnathology.

This investigation is focused on the analysis of the masseter responses evoked by means of magnetic and electric stimulation of the cortex and root of the trigeminal system of 20 healthy subjects. Moreover, in order to determine jaw elevation in centric occlusion, the analysis also focused on the motor response of the trigeminal bilateral roots evoked simultaneously using two stimulators. The masseter responses show a high level of symmetry in both latency and amplitude. The difference between the hinge axis in natural centric occlusion (CO) and in centric relation (CR) as determined by electric and magnetic transcranial stimulation is lesser than 2.5 mm. This is due to two main factors: (i) the response is evoked from the trigeminal motor neural pool involving all the masticatory muscles and hence simulating the natural 'muscular coactivation'; (ii) there is no manual manipulation to guide the jaw into the centric relation (CR). This method could be of some help for diagnosis in patients suffering from TMJ dysfunction who have lost stereognostic control over the jaw and display obvious signs of deviation during closure of the mandible.