STANDARDIZED ELECTROMYOGRAPHIC INDEXES ALLOW A RELIABLE MEASUREMENT OF MASTICATORY MUSCLES FUNCTION
Figure 5 . First test clenching wearing the jig Figure 6 . Final test wearing the ( modified ) jig
Figure 7 . Final sEMG test clenching with cemented overlay
Figure 8 . Final reconstructions
3 . the activity index ( ATTIV , unit %), was obtained as the percentage ratio of the difference between the mean Masseter and Temporalis Anterior muscles standardized potentials and the sum of the same standardized potentials , to individuate the most prevalent pair of masticatory muscles . The index is positive ( up to 100 %) if the Masseter muscles standardized potentials are larger than those of the Temporalis Anterior muscles , negative ( up to 100 %) if the Temporalis Anterior muscle potentials are larger 26 .
4 . the standardized activity index ( IMPACT , unit %* s ) was calculated to quantify the total muscular activity performed during MVC relative to the standardization clenching on cotton rolls ; IMPACT was estimated computing the mean ( Masseter and Temporalis Anterior ) total muscle activities as the integrated areas of the sEMG potentials over time 26 . 3.4 . Statistical evaluation To quantify the acquisition session effect on the sEMG standardized indexes , the values obtained from T1 and T2 were compared . Normality data distribution was assessed using Shapiro-Wilk test . Paired Student ’ s T test ( p < 0.05 ) was used to evaluate the systematic error between the two muscular measurements . Table 1 shows the mean values and standard deviation of the standardized indexes obtained in the two data acquisition sessions , together with
the mean difference in individual values . Paired Student ’ s T tests found no statistically significant differences .
4 . Discussion The surface electromyogram comprises the sum of the electrical contributions produced by the active motor units as detected by cutaneous electrodes . Several parameters could be analysed in the captured electrical signal . The discharge rates , signal amplitude , spectral analysis could be investigated to estimate the neural control strategies involved in the muscles management . 27 These instrumental assessments should be performed applying the correct protocols ; in fact , the myoelectric activity signal may vary due to many factors such as change in the electrode location , change in the tissue properties , tissue temperature , muscle resting length , velocity of contraction and fiber type 27-30 . In the last 30 years the effect of electrodes position on conduction velocity estimation ( CV ), amplitude and spectral variables of the surface EMG has been addressed in a number of methodological and clinical publications taking into account muscles ( or groups of muscles ) ranging from the masticatory muscles to the muscles of the shoulder , of the arm and leg too 31 . Changing the electrode location through innervation zones to tendons affect the detected activity : signal spectrum shifts towards higher frequencies , the amplitude
238 STOMA . EDUJ ( 2016 ) 3 ( 2 )