Effectiveness of low-level laser therapy on pain intensity, pressure pain threshold, and SF-MPQ indexes of women with myofascial pain

Abstract

Women with temporomandibular disorders (TMD) frequently report pain areas in body regions. This process is associated with central sensitization phenomena, present in chronic pain. The low-level laser therapy (LLLT) has been reported as a therapeutic option for the painful TMD treatment. The aim of this study was to analyze the effect of LLLT on pain intensity (visual analogue scale, VAS), pain sensitivity in orofacial and corporal points (pressure pain threshold, PPT), and on Short Form-McGill Pain Questionnaire (SF-MPQ) indexes of women with myofascial pain (subtype of muscle TMD). Ninety-one women (18-60 years) were included in the study, among which 61 were diagnosed with myofascial pain (Research Diagnostic Criteria for Temporomandibular Disorder-Ia and Ib) and were divided into laser (n = 31) and placebo group (n = 30), and 30 were controls. The LLLT was applied at pre-established points, twice a week, eight sessions (780 nm; masseter and anterior temporal = 5 J/cm, 20 mW, 10 s; TMJ area = 7.5 J/cm, 30 mW, 10 s). Pain intensity, pain sensitivity, and the SF-MPQ indexes were measured at the baseline, during laser sessions, and 30 days after treatment. For intra-group comparisons, the Friedman test was performed, and for inter-group, the Mann-Whitney test. Increased pain sensitivity was found in women with myofascial pain when compared to controls (p < 0.05). There was a reduction in pain intensity for both groups after LLLT. The LLLT did not change the PPT for any group (p > 0.05). Active laser and placebo reduced the indexes of sensory, total pain, and VAS, maintaining the results after 30 days; there was a reduction in the affective pain rating index for both groups, with no maintenance after 30 days for placebo, and the present pain intensity decreased in the laser group and did not change in the placebo after LLLT. In conclusion, the LLLT active or placebo are effective in reducing the overall subjective perception of myofascial pain (VAS and SF-MPQ indexes); however, they have no effectiveness in reducing the pain sensitivity in orofacial and corporal points (PPT increase).

Placebo and nocebo response magnitude on temporomandibular disorder‐related pain: A systematic review and meta‐analysis

“…The differences in meaning and interpretation of pain experience and, consequently, in placebo response could be influenced by culture, which may affect the verbal description of pain experience and responses to both active and placebo interventions through biologic predispositions and behaviour interacting with developmental history . This could explain the higher rates of placebo response obtained in studies done in Brazil when compared with other countries …”

“…Risk of bias was very heterogeneous among studies. Using Cochrane Collaboration's tool, nine studies were classified as low risk of bias, 13 as unclear and 20 as high risk of bias . The higher risk of bias was reporting bias.…”

“…Out of the 42 RCTs, sample size ranged from 13 20 to 99 21 with a total of 1657 patients, mostly women, that is from 47 22 up to 100% 23-31 of the sample. Studies were conducted in Brazil, 23,26,28,30,[32][33][34][35][36][37][38][39] Canada, 24,40 China, 41 Croatia, 20 Denmark, [42][43][44] India, 45 Iran, 29,46 Italy, 21 Korea, 22 Poland, 47 Spain, 48 Sweden, [49][50][51] Thailand, 52 the Netherlands, 53 Turkey, [54][55][56] United Kingdom 57 and United States of America (USA). 25,27,31,[58][59][60][61] All studies were published in the English language.…”

“…11 This could explain the higher rates of placebo response obtained in studies done in Brazil when compared with other countries. 23,28,30 Nocebo effect is a negative expectation of pain. The neurobiological mechanisms of the nocebo effect have been less investigated.…”

“…, 23,26,33,36,39,41,50,53,56 13 as unclear 20,27,30,37,38,[48][49][50][51]54,55,59,61 and 20 as high risk of bias. 21,24,25,28,29,31,32,34,40,[42][43][44][45][46][47]52,57,58,60,62 The higher risk of bias was reporting bias. Some studies provide unclear information about blinding outcome evaluators to knowledge of group allocation against detection bias, and many of them did not provide descriptions about all measurements in terms of means and standard deviation.…”