## 4 Discussion  
Photobiomodulation therapy was significantly more effective than the placebo for the major aphtha treatment. Statistically, significant efficacy was shown in the primary end point; the aphtha healed faster, about 8 days, compared to the placebo group, which needed about 31 days. Moreover, the secondary end point, such as pain, was also significantly reached in the photobiomodulation group. Figure 5: Effect of photobiomodulation (**A**,**A**) and placebo (**B**,**B**’) treatment on aphtha’s healing-(**A**–**B**), the aphtha before treatments. (**A**–**B**’), recovery at 8 days after treatments. Photobiomodulation therapy induced complete healing at 8 days from the photobiomodulation treatment (**A**), while, in the meantime, the patient treated with the placebo kept an evident and inflamed aphtha (**B**’). Figure 6: Effect of photobiomodulation and placebo treatment on pain. Photobiomodulation therapy induced a statistically significant reduction of the pain 24 and 48 h after photobiomodulation treatment. * \(p<0.05\) = before treatment vs. 24 h after treatment; # \(p<0.05\) = 24 h after treatment vs. 48 h after treatment. VAS = Visual Analogue Scale. These clinical results support and are supported by our previous in vitro and preclinical evidence [32; 33; 34; 35; 36; 37; 38]. The photobiomodulation therapy through flat-top irradiation of 808-nm, and 1 W, 1 W/cm\({}^{2}\), 60 J/cm\({}^{2}\), CW induced an increment of oxygen consumption and ATP production in extracted mitochondria [32], in eukaryotic unicellular organisms [33; 34], and in human endothelial cells [36]. Additionally, the effect on the homeostasis of calcium and the production of nitric oxide from a calcium-calmodulin dependent nitric oxide synthase enzyme was evidenced [42]. Studies on stem cells show that the therapy was significantly able to induce cell differentiation through a reduction in inflammation [38] and stimulation of biochemical/differentiating pathways involving key activators that regulate _de novo_ actin polymerization and cytoskeletal rearrangement [37]. Preclinical evidence suggested that the therapy affected muscular and blood vessel contraction, decremented bacteria load, and tissue degeneration [35; 43]. Reduction of inflammation markers and stimulated telomerase activity allowed us to speculate that a cell energized by photobiomodulation improves its proliferative potential thanks to the equilibrated recovery of homeostasis through the mitigating effect on both inflammation and tissue degeneration and a supportive effect on the energetic cellular metabolism. This evidence can therefore explain the effect of photobiomodulation on our patients compared to the placebo. Concerning the literature, our screening of papers did not show works focused on photobiomodulation and major aphtha management. However, a comparison with the effect of photobiomodulation on common aphtha healing ranks our clinical results in the supportive evidence. Indeed, in the selected papers [20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31], the pain had mainly disappeared in an average time of 4.9 days. However, [PERSON] et al. [25] found a 71% pain reduction at 7 days, and [PERSON] et al. [27] showed a pain decrement from 81% to 16% in the same given period and in accordance with the photobiomodulation therapy employed. Additionally, the same papers showed that the healing process was completed in an average time of 6.3 days after photobiomodulation [20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31]. In the research by [PERSON] et al. [28], the healing was 97% by 7 days, and [PERSON] et al. [25] showed in the meantime an aphtha reduction of only 60%. Additionally, photobiomodulation therapy seems to be helpful compared to drugs. Authors [23] completely recovered the pain over two days through 1064 nm irradiation or three days with 830 nm laser light, while the Solcoseryl adhesive paste (polidocanol anesthetic and antipurritic component) showed the same effect in 6 days; no synergic effect was found.