Effect of photobiomodulation therapy on painful temporomandibular disorders
Aisaiti, A., Zhou, Y., Wen, Y. et al. Effect of photobiomodulation therapy on painful temporomandibular disorders. Sci Rep11, 9049 (2021). https://rdcu.be/cDRcn
Temporomandibular disorders (TMD) cover a number of clinical conditions affecting the temporomandibular joint (TMJ), masticatory muscles and related structures1. Pain is one of the most common and limiting clinical manifestations of such disorders2. The pathophysiology of pain in TMD patients is still not fully understood, however, peripheral and central sensitization of the trigeminal nociceptive pathways in addition to impairment in endogenous pain modulatory mechanisms influenced by genetic and epigenetic factors, and a wide and multifaceted range of environmental conditions such as for example bruxism, psychosocial distress, mood, sleep patterns etc. are encapsulated in the bio-psycho-social model for chronic pain3,4. Recent classification schemes have taken the step to include TMD pain as a primary type of chronic pain meaning that pain in itself has become the disease without a clear and identifiable cause whereas the secondary types of (TMD) pain are viewed as painful conditions which are caused by a disease or disorder and therefore represent a symptom rather than a disease5,6. In this scenario, causal treatment is not an option and palliative and non-invasive treatment modalities should be preferred. Several non-invasive treatment modalities have been used to relieve painful TMD conditions including occlusal splints, ultrasonography, pharmacologic-based therapy7, manipulative therapy8, oral motor exercise9, transcutaneous electrical stimulation, and photobiomodulation therapy (PBMT)10. Studies in specific TMD pain populations are, however, needed before strong recommendations can made. PBMT has been widely used as an alternative or complementary treatment for TMD pain due to the non-invasive and safe features related to the low-intensity energy and wavelength characteristics11,12. The mechanism of photobiomodulation (PBM) is still debated but may be related to its potential influence on the synthesis, release, and metabolism of countless signaling substances involved in pain and analgesia13,14. Many prospective clinical trials have been performed to evaluate the efficacy of PBMT11,13,15,16,17, however, the results have been ambiguous due to the different laser parameters, lack of standardized operation procedures, lack of reliable methodology including placebo control, and small sample sizes. Therefore, more solid evidence is needed to evaluate the therapeutic effect of PBMT in TMD pain patients. A standardized quantitative sensory testing (QST) developed by the German Research Network on Neuropathic Pain (DFNS) has been shown to be reliable in the orofacial region and upper and lower limbs18,19,20. The QST technique has the advantage of more objective and accurate evaluation of patients’ somatosensory function. In addition, a mechanical sensitivity mapping technique which has recently been used in the field of headache disorders such as migraine21 and chronic tension-type headache22 has been confirmed to have excellent reliability to demonstrate changes in somatosensory function and mechanical sensitivity in the masseter muscle and TMJ regions23. Patients with TMJ pain often involve disorders of the articular surfaces, articular disk, bilaminar zone, joint capsule and ligaments, manifested as sound, limited mandibular movement and pain in these areas, while patients with muscle disorders often present with pain in the related muscle region, reduction of mandibular mobility and “pulling” sensations such as feeling of fatigue and bracing24. In addition to these differences in clinical manifestations, the mechanism of TMJ pain and myalgia may also be different24. Since there are different clinical manifestations and potentially different underlying pain mechanisms between TMD myalgia and TMJ arthralgia, studies may need to test the efficacy of interventions in both groups to obtain a better platform for evidenced-based recommendations for management. Therefore, the purpose of this study was to evaluate the effect of PBMT on myalgia and TMJ arthralgia patients by use of QST and pain sensitivity mapping techniques in a randomized, double-blinded, placebo-controlled manner.