## 4 Discussion  
In our study we analyzed the effects of repeated LLLT on pain management in patients with orthodontic treatment. We evaluated the intensity of the pain consecutive to mechanical forces and compared the values for each patient in the laser half-arch (HL) and the control half-arch (HC). Analyzing the VAS score values reported after applying the orthodontic device, we noticed that the pain increased in the first few hours, it was the highest 24 h after, and it decreased towards the 7 th day. The highest value of the VAS score at T00, in HC was 7, reported by three patients, whilst in HL it was reported by one patient. For T01 (24 h after) severe pain was reported, in HC, the VAS score value was nine in four patients and eight in three patients. At the same time in HL, the VAS score value was nine in one patient and eight in one patient. On the 7 th day, in HC most patients reported mild pain, four patients moderate pain, and six patients had no more pain, whereas in HL most patients had mild pain, and 11 had no more pain. None of the patients reported a VAS score value of 10, which represents the worst pain imaginable. One month after applying the orthodontic device, when the first activation was performed, the pain reported by the patients had similar characteristics to the one reported at the beginning of the treatment, the values reported 24 h after being higher than those registered 3 h after the procedure, then decreasing towards the 7 th day. Figure 3: (**a**) VAS score value after applying the orthodontic device; (**b**) VAS score value after the first activation. Figure 2: VAS score value reported by the subjects 24 h after the first activation. Analyzing VAS score values for the two half-arches, the pain reported by most patients was significantly reduced in HL compared to HC, both at the beginning of the treatment, when the orthodontic device was placed and one month after, when the first activation was performed. However, four patients reported same VAS score values for HL and HC, probably due to an increased sensitivity to pain, given the high VAS score values registered by these patients. For the activations performed 2 months and 3 months after beginning the treatment, the characteristics of the pain reported by the patients were not significantly different compared to the pain reported in the beginning and one month after applying the orthodontic device at the first activation. Significant decreases in pain reported by patients treated with LLLT after applying orthodontics wires were demonstrated by a double-blind study [21]. Similar conclusions were reported by other studies that showed immediate lowering of pain values after using LLLT [22]. Similar to our study, another research showed maximum values of pain 24 h after activating the orthodontic device, both for the patients treated with LLLT and for the placebo group. Afterwards, the pain decreased gradually and disappeared after the 7 th day [23]. These results are in accordance with other studies that also illustrate a maximum value of pain 24 h after applying orthodontic forces [24]. Furthermore, there are numerous studies that report pain lasting for less time in patients who received laser therapy [25; 26; 27; 28]. The exact mechanisms that lead to the analgesic effects of LLLT are unclear. Certain studies assume that the LLLT has antinociceptive properties as a result of biologic mechanisms that stimulate cellular differentiation and proliferation [29; 30; 31]. A study on experimental animals showed that the anti-inflammatory effects of LLLT can be similar to those of NSAIDs (nonsteroidal anti-inflammatory drugs) [32]. The literature shows that the inflammatory infiltrate located in the lamina propria is the critical morphological trait for controlling the healing process. Laser therapy can help diminish the number of lymphocytes and macrophages, which will implicitly determine a lower production of chemical mediators interfering with the sequence of the healing process.