Methods:12 healthy volunteers(11 men,1 women,mean age 25.3 years)participated in two sessions in which the application to lower right incisor periodontal ligament of the carbocain or capsaicin was randomized.Transcranial magnetic stimulation (TMS) was applied to the primary motor cortex in each session and motor evoked potentials (MEPs) were recorded in the left tongue muscle,left masseter muscle and the left first dorsal interosseous (FDI) muscle (as control).For MEP recording of left masseter muscle, auto-trigger was used by clenching at 10% level of maximum voluntary contraction(MVC).
Results:As reflected in TMS – MEP stimulus-response curves and motor maps of three muscles, there are no significant differences between two sessions.(ANOVAs: P>0.50)
Conclusions:Changes in periodontal afferent input does not have a detectable effect on the corticomotor pathways.Nonetheless,the present findings did not support the so-called ‘vicious cycle'between pain-central hyperexcitability-muscle hyperactivity.