Jaw reflexes in healthy old people

to investigate variations in the masseteric myotatic reflex (jaw-jerk) and the silent period from the 5th to the 9th decades of life.

electromyographic data were recorded from the masseter muscle of the preferred chewing side by surface electrodes, using a computerized recording and analysis system. Chin taps were applied with a neurologist's hammer during mandibular rest and at 40% intercuspal clenching in 30 healthy people aged from 49 to 87 years. The influence of age, gender and silent period type were analysed by multiple regression analysis (P < or = 0.05).

even in the very old subjects all reflexes were elicited, at least once. However, with increasing age the overall occurrence of the jaw-jerk reflex at rest (%) and its amplitude, at rest and at clench, were reduced, while its latency at rest was significantly increased (P < or = 0.05). No age effects were recorded in most parameters of the jaw-jerk reflex at clench and in the silent period. Women showed a tendency for reduced latencies of the jaw-jerk and the early silent period and increased silent period duration (P < or = 0.05). They also had a steeper decline in myotatic reflex activity, particularly at rest.

simple masseteric reflex activity is maintained until very old age, particularly when elicited during contraction of the jaw elevators.