EFFECT OF MASTICATORY MUSCLE FATIGUE ON CRANIO-VERTICAL HEAD POSTURE AND REST POSITION OF THE MANDIBLE

The aim of this study was to investigate whether induced fatigue of th e masticatory muscles had any influence on the head posture, and wheth er this influence is related to the rest position and the movement cha racteristics of the mandible. The sample consisted of 13 female indivi duals, aged 23-34 yr. For the evaluation of possible changes in the na tural cranio-vertical head posture, standardized facial profile photog raphs were used, Photographs were also used for the study of the facia l characteristics. The freeway space and the opening and closing veloc ity of the mandibular displacement, as well as the duration of the mas ticatory cycles, were monitored with an optoelectronic method. A contr olled dynamic fatigue was induced by a specially constructed spring-lo aded device placed in the premolar region, No significant changes in t he mean cranio-vertical postural position of the head were found durin g the various recording stages, while the freeway space was found to i ncrease significantly after the fatigue test. No significant differenc es were observed concerning the average values of the mandibular movem ent characteristics. The analysis of the associations between the indi vidual changes showed an increase in the freeway space after the fatig ue test in the subjects which exhibited an increase in the duration of the masticatory cycle in that period. No significant associations cou ld be found between the changes in the head posture and the mandibular movement characteristics. Also, no significant correlation could be f ound between the facial type of the subjects and the variables studied .