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)