The RMS in the temporalis and masseter muscles increased with time ( right masseter P = 0.001 , left masseter P = .004 , right temporalis P = .22 , left temporalis P = .006 ) , whereas the MPF decreased ( right masseter P = .0001 , left masseter P < .0001 , right temporalis P = .51 , left temporalis P = .0005 ) .