An excitatory response preceding the silent period in masseter electromyographs

A masseteric excitatory reflex response preceding the silent period which appears following tapping movement of the jaw, was investigated in order to evaluate its origin. In the pre-anaesthetic state, the latency of response did not change with the intensity of tapping. However, its amplitude increased depending on the intensity of tapping. The response did not disappear even after the anaesthesia. After the anaesthesia the lighter the intensity of tapping was, the longer the latency of the response, coming up to that of the jaw-jerk reflex. The pre-anaesthetic response had an intricate wave form comparing with the post-anaesthetic one. From the above findings it was concluded that the response must be a complex one in nature originating in the muscle spindle of jaw closing muscles and in a certain receptor of the structures surrounding the tooth.