Jaw reflexes in healthy old people.

OBJECTIVE to investigate variations in the masseteric myotatic reflex (jaw-jerk) and the silent period from the 5th to the 9th decades of life. SUBJECTS AND METHODS 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). RESULTS 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. CONCLUSION simple masseteric reflex activity is maintained until very old age, particularly when elicited during contraction of the jaw elevators.