## 2 Materials and Methods
### Procedures  
To improve the standardization and the repeatability of the photobiomodulation therapy, the 808-nm diode laser device (Doctor Smile, LAMBDA Spa, Vicenza, Italy) was used with a novel handpiece able to irradiate through a flat-top beam profile (AB 2799, Doctor Smile, LAMBDA Spa, Vicenza, Italy). Indeed, authors [39,41] explain that the divergence of the beam, the beam profile, and the diameter of the final emission device strongly influence the positive effect of the photobiomodulation. Firstly, the applied energy is distributed over an increasing area as the tip-to-tissue distance increases, greatly affecting the energy density at the cellular level [39]; in some cases, the energy density can be reduced by 95% with only 5 mm of target distance [41]. Secondly, if the use of a collimated beam with a predetermined diameter could resolve the problem, the laser energy emitted by an optical fiber or a therapeutic handpiece has a Gaussian profile; it is not uniformly distributed on its emission surface, and it therefore has a higher photon density at the center of the ray than at the edge [32,39,41].  
In accordance with our previous in vitro and preclinical studies [35, 36, 37, 38], photobiomodulation therapy was administered through the power of 1 W irradiated in continuous wave mode (CW) for an exposure time of 60 s and on a spot size of 1 cm\({}^{2}\), which allowed generating a power density of 1 W/cm\({}^{2}\) and a fluence of 60 J/cm\({}^{2}\) (energy administered = 60 J). Because the aphtha's area is wider than the laser spot size, irradiation on two points was necessary to cover the entire surface. The placebo therapy was processed under identical conditions, except the laser device was kept off at all times (0 W).  
The precision of the laser therapy parameter was secured by the Pronto-250 power meter (Gentec Electro-Optics, Inc., Quebec, QC, Canada).  
Adverse events due to a possible undesirable thermal effect were avoided by monitoring the irradiation with a thermal camera FLIR ONE Pro-iOS (FLIR Systems, Inc., designs, Portland, OR, USA) (dynamic range: \(-20\)\({}^{\circ}\)C/\(+400\)\({}^{\circ}\)C; resolution 0.1\({}^{\circ}\)C).  
All randomized patients, including those assigned to the placebo, underwent an evaluation of the aphtha area, pain, and discomfort.  
The area was measured by NIH image analyzer (National Institute of Health, Rockville, MD, USA). Basically, images of the aphtha and the periodontal probe, which was used to set the measure through the NIH image program, was obtained by Canon EOS 450 camera, lens of 100 mm (Canon Italia S.p.A, Cernusco Sul Naviglio, Milan, Italy). The images were acquired in a standard condition of illumination, exposition, distance, and tilt angle.  
The pain was evaluated by the visual analogue scale (VAS) (Figure 1), asking the patients to draw a line along a 10-cm horizontal that best describes their pain, with the extremes of the lines representing no pain and the worst pain possible. The VAS was then scored by measuring the distance between the patient's line and the no-pain anchor.  
Evaluations were performed immediately before the irradiation and 24 and 48 h after.  
Patients based their evaluation on compliance with the following questions: what was your subjective experience of eating today? What was your subjective experience of drinking today? What was your subjective experience of brushing your teeth today?