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The Influence of the Masticatory Forces on the Isometric Activity of the Elevators of the Mandible in the Complete Upper Denture Wearers
Melita Valentić-Peruzović
; Zavod za mobilnu protetiku Stomatološkog fakulteta Sveučilišta u Zagrebu, Zagreb, Hrvatska
Andrej Meniga
; Z avod za dječju i preventivnu stom atologiju, Stomatološki fakultet Sveučilišta u Zagrebu, Zagreb, Hrvatska
Asja Čelebić
; Zavod za mobilnu protetiku Stomatološkog fakulteta Sveučilišta u Zagrebu, Zagreb, Hrvatska
Sažetak
A n EM G muscle activity from the main elevators o f the mandible - temporal and masseter muscles - was recorded during isometric contraction in maximal intercuspal position and during maximal
voluntary biting onto the cottonrolles positioned in the first phase of the experiment in the frontal (VF) and then in the left (VL) or right (VR) chewing centre, and in the last phase in all three positions together (VF-VD-VL), thus simulating the second phase o f the chewing cycle (crushing and diminishing o f the bolus) producing
strong masticatory force. The investigation was performed on the group o f 31 denture wearers with a complete upper denture and partial lower denture or natural teeth opposed. The aim o f this study was to examine the activity o f the masticatory muscles during biting o f the hard bolus. The action potentials were registered by the method o f surface electromyography on the four-channel polygraph with digital integration used for quantitative evaluation o f the obtained sums o f action potentials registered from each o f the examined muscles. For the statistical analysis the t-test for small dependent samples was used. The greatest isometric activity o f temporal and masseter muscles was recorded during the maximal voluntary clenching in the maximal intercuspal position, and the statistically significant difference (p < 0.05) is calculated for all registered biting positions, except for the left temporal muscle during biting onto the cottonroll positioned in left chewing centre (p >0.05) and for the right masseter during the simultaneous bite with the cottonrolles in all three positions (VF-VD-VL) (p > 0.05). In comparison between the muscles on the working and balancing side, it is obvious that there is statistically significant difference (p < 0.05) for the temporal muscles while bitting onto the cottonrolle positioned in the right (VD) or left (VL) chewing centre, with the higher temporal muscle activity on the working side, while the masseter muscles do not display such significance (p > 0.05). These results confirm the different feature o f the activity o f temporal and masseter muscles in the second phase o f the masticatory cycle; although they both belong primarily to the elevator group, each takes particular role in the process o f mastication o f hard food. While temporal muscles are mainly active during the displacement and motion, masseter muscles perform powerful contraction disregarding the position o f the bolus, participate in penetration and in cutting o f the bolus into small parts.
Activity o f the temporal and masseter muscles depends also on the position o f the bolus. I f bolus is placed in the chewing centre, temporal muscle displays higher activity and if bolus is placed
more anteriorly, masseter muscle is more active. Complex neuromuscular mechanisms are involved in the process of mastication o f the hard bolus, participating in the protection o f the teeth and joints from the noxious stimulus, and in controlling the direction and strength o f functional forces.
Ključne riječi
EMG isometric activity; masticatory load; complete upper denture wearers
Hrčak ID:
100699
URI
Datum izdavanja:
15.9.1992.
Posjeta: 1.059 *