THE EFFECT OF LOW-LEVEL LASER THERAPY IN SURFACE ELECTROMYOGRAPHY OF MASSETER MUSCLE

Pereira S.C.¹, Chagas E.B.², Renno A.C.M.³, Pedroni C.R.⁴

¹Sao Paulo State University (UNESP), Physical Therapy Department, Marilia, Brazil, ²Marilia University (UNIMAR), Marilia, Brazil, ³Federal University of São Paulo - UNIFESP, Santos, Brazil, ⁴Sao Paulo State University, Physical Therapy Department, Marilia, Brazil

Background: Temporomandibular disorder (TMD) involves changes in the temporomandibular joint (TMJ), masticatory muscles and associated structures and often include hyperactivity of the stomatognathic muscles. Low-level laser therapy (LLLT) is a technology used to treat conditions that require stimulation of healing, relief of pain and inflammation, and restoration of function. LLLT acts on the mitochondria to increase adenosine triphosphate (ATP) production, accelerate the collagen production and the local microcirculation.

Purpose: The aim of this study was to evaluate the effects of LLLT therapy on electromyographic activity of the masseter muscle.

Methods: 15 health subjects of both genders aged between 18 and 25 years participated in this study. The SEMG signal was recorded of the right and left masseter muscle, but only one site was irradiated by a random selection and the oposite side received a placebo treatment. Briefly, simple active differential surface electrodes were used, composed of two parallel bars of pure silver, 1mm thick and 10mm long, with a distance of 10mm between electrodes, gain of 20 times, an input impedance of 1015 Ohms and a common-mode rejection ratio (CMRR) of 92dB (Datahominis Tecnologia Ltda). The electrodes were connected to a MyosystemBr1_P84 (portable model) signal acquisition module. The SEMG signals were amplified 100-fold at a frequency of 2 kHz and band-pass filtered (20-1000Hz - Butterworth). Three 5-second recordings of SEMG signals were collected with the mandible at rest, and three 15-second recordings were collected at maximum intercuspation (isometry), while clenching “Parafilm M” between the premolars and molars to ensure the reliability and effectiveness of the recording. Data acquisition was controlled by a specific software program with 16-bit resolution, the Myosystem-Br1 software application, based on the Root Means Square (RMS) and the median frequency (MF) The data were subjected to an analysis of variance (ANOVA), followed by Tukey’s post hoc test. The calculations were performed using the SAS system (SAS Institute Inc, release 9.2 – TS Level 2M0. SAS Institute Inc., Cary, NC, 2008) and the level of significance was set at 5%. To complement the analysis of variance and test the effect of windows and covariables on the median frequencies, the Greenhouse-Geisser test was applied, maintaining the 5% level of significance.

Results: There was a tendency for a decrease in the median frequency of the irradiated muscles (p=0.063) when the first and tenth values were analyzed. Significant values could be found if this there were more subjects or if they were myogenic TMD patients with a previous fatigue condition of masticatory muscle. Further studies are needed to verify the LLLT efficacy in this condition.

Conclusion(s): There was no difference between irradiated and placebo masseter when they were treated with LLLT, but there was a tendency for a decrease in the median frequency of the irradiated muscles

Implications: We believe that TMD patients could have a better response to LLLT than health subjects and this could be an helpfull technology for treatment.

Funding acknowledgements: Thank you to the Research Commitee of Sao Paulo State University for supporting this study.

Topic: Human movement analysis

Ethics approval: This study was approved by the Ethics Committee on Research of Sao Paulo State University, Brazil, under protocol number 0750/2013.

All authors, affiliations and abstracts have been published as submitted.