# Photobiomodulation as a Therapeutic Strategy in Burning Mouth Syndrome: A Scoping Review
## 4 Discussion
Since 2015, we have been talking about photobiomodulation (PBM) to describe the scientific basis of the use of non-ionizing electromagnetic energy to trigger photochemical changes within cellular structures and tissues [68]. PBM has analgesic and anti-inflammatory therapeutic effects, can stimulate biological tissues, and has documented antimicrobial effects [68]. Therefore, the correct use of the PBM can relieve painful symptoms, significantly reduce an inflammatory process, and accelerate and improve the healing of damaged tissues [69]. The mechanism of action of PBM is not yet fully understood. The most popular theory is that light is absorbed by mitochondrial cytochrome C oxidase (CoOx), causing an increase in adenosine triphosphate (Adenosine TriPhosphate ATP) [69; 70]. PBM, on the other hand, can induce a brief rise in reactive oxygen species (ROS) before decreasing oxidative stress. Nitric oxide (NO) competes with oxygen and binds to CoOx in cells with varying degrees of hypoxia, limiting oxygen use and thus mitochondrial cell respiration. PBM may restore this inhibition by dissociating NO from its binding location on CoOx, allowing mitochondria to enhance ATP synthesis and cellular energy [69; 70]. Another possible mechanism of PBM could be an increase in the concentrations of Ca\({}^{2+}\) ions, important for cellular metabolism and homeostasis, and cellular signal transmissions. Furthermore, the cellular temperature changes after a PBM must be considered [67; 68; 69; 70; 71; 72; 73]. PBM is not considered a heat treatment; however, selective absorption by CoOx can lead to intracellular thermal micro-changes that can positively influence the behavior of cells and tissues [73; 74]. The analgesic properties of PBM have been repeatedly recognized. It has been seen to reduce chronic low back pain, chronic neck pain, and other types of chronic pain such as BMS [74; 75; 76; 77; 78; 49]. Furthermore, at the oral level, it has proved to be useful in preventing and treating oral mucositis in cancer patients, in reducing pain and swelling after third molar extraction,in suffering from the temporomandibular joints, in orthodontic pain, and in reducing inflammation of the oral lichen [49; 80; 81; 82; 83; 84; 85; 86; 87; 88]. Primary BMS is to be considered a chronic oral pain pathology where PBM could perform a part of the new local therapeutic strategies. Indeed, in recent years, with the diagnostic and cognitive advances of the disease, PBM has emerged as a potential non-invasive treatment with no apparent side effects. Many therapeutic experiences have provided encouraging results in the reduction of oral burning symptoms. However, further therapeutic experiences will be needed to confirm and better protocol PBM treatments and correctly relate them to the clinical and symptomatic data of patients with BMS [57; 58; 59; 60]. In the analysis of the results in the literature, there are some studies where an improvement in pain symptoms in patients with BMS has been found. Sleep values were compared and measured with the VAS and the improvement rates ranged from 4 to 15% [58; 59; 62]. The study conducted by [PERSON] et al. highlights the improvement in microcirculatory patterns after photobiomodulation was applied in patients with BMS, analyzed by videocapillarose. The improvement of the pattern has been noticed lasting for a long time after the therapy [56]. As regards the parameters used by the authors of the articles analyzed, the wavelengths used are variable, from a minimum of 685 nm [55] to a maximum of 1064 nm [38] with a preference; however, for the wavelength of 810-830 nm [52; 53; 54; 56; 57; 59; 62]. All the studies confirm the improvement of the symptoms. For the evaluation of the symptoms, the OHIP-14 questionnaires and the VAS scale were mainly used [52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62]. In fact, all the studies report an improvement in VAS scale values and OHIP values, especially after almost three applications of photobiomodulation.