engleski

Jaw reflexes of dentate individuals in open-close-clench cycles at different mandibular positions

Purpose: Functional meaning and underlying mechanisms of jaw elevator silent period (SP) have still not been completely understood. Fully dentate individuals (DI) with healthy occlusion without interferences always have only one SP of short latency and duration and complete inhibition of motoneuron activity during open-close-clench cycles (OCC) in maximal intercuspal position (MIP). The aims were to broaden the knowledge about the jaw reflexes and to try to elicit SPs and jaw jerk reflexes (JJ) during OCC cycles in tete a tete (incisal) position (IP) and retruded contact position (RCP). Methods and materials: Thirty DIs (skeletal/occlusal Class I) participated. Surface EMG signals were registered using the EMGA-1 apparatus from the left and the right anterior temporalis (ATM) and masseter muscles (MM). Ten registrations of an OCC cycle were obtained from each individual in MIP, IP and RCP. Results: During OCC cycles in MIP only one short latency (11.3-11, 7 ms) and short duration (21.5-23.4 ms) SP appeared. The JJ was not registered. During OCC cycles in IP, SP did not apper in 39% of registrations in ATM and in 15% in MM. The most frequent was the irregular prolonged SP (single prolonged, double, SP with 3 inhibitory pauses, periods of depressed muscle activity following the inhibitory pause, SPs of relative inhibition). During OCC cycles in RCP short (normal) SP was registered in 64% in ATM and in 40-50% in MM. The SP was missing in 2-5% in ATM and in 10-12% in MM. The latency in IP and RCP was the same as in MIP (p>0.05). The frequency of JJ eliciting during OCC cycles in IP was significantly higher in MM (50%) than in ATM (35%) (p<0.05) ; contrary, in RCP the frequency of JJ was significantly higher in ATM (45-65%) than in MM (35%). Conclusion: Occlusal instability during OCC cycles in IP and RCP probably elicited JJ reflexes in muscle fibers parallel with the direction of mandibular movement. It seems that the the type and the duration of the SP depends on occlusal factors: the force direction regarding the periodontal liggament or the vibration elicited by teeth contact.

jaw reflexes; jaw position

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