## 6 Discussion
Concerning mini-screw displacement, no statistically significant difference was found. The results of that study were not in accordance with ours, favouring the use of PBMt to increase mini-screw stability. In fact, they used two types of lasers. According to the same authors, the 660-nm wavelength laser was used immediately after the insertion of the mini-screw to enhance the healing of damaged tissue and to promote the initial inflammatory reaction. In the following days, the 808 nm wavelength laser was subsequently used because it had already been shown that PBMt boosts mini-screw bone healing during the intermediate postoperative period [32]. Another study by [PERSON] et al. [33] used a diode laser at an 808 nm wavelength with an irradiance of 800 mW/cm\({}^{2}\) for a one-month period of PBMt. It measured the stability of the mini-screws for two months and found an increase after 30 to 60 days. These results proved the theory stating that better outcomes are obtained when a longer follow-up is carried out. The same result was obtained by [PERSON] et al. [34] at a 910 nm laser wavelength with an average power not exceeding 0.7 W for 60s, by [PERSON] et al. [35] in another study using a diode laser at a 635 nm wavelength, 100 mW and 20 J/cm\({}^{2}\), and by [PERSON] et al. [36] using a LED at an irradiance of 20 mW/cm\({}^{2}\). In the literature, a large variability clearly exists among lasers, wavelengths, and energy densities [37]. In our study, an 810-nm diode laser wavelength at a power density of 1.2 W/cm\({}^{2}\), a total energy of 50 joules, and an energy density with movement of 8.3 J/cm\({}^{2}\) delivered with a Gaussian optical fibre beam profile were used. According to the literature, the use of PBMt in patients involves almost exclusively the red and near infrared portion of the electromagnetic spectrum (650 nm-1100 nm). This range of wavelengths, known as the optical window, is where the effective tissue penetration of light is maximized [31]. The effective tissue penetration of light and the specific wavelength of light absorbed by photo-acceptors are two of the major parameters to be considered in light therapy [16]. As discussed earlier, PBMt possesses an anti-inflammatory effect that can increase blood flow, stimulate metabolic activities, and accelerate the healing process [14]. In fact, [PERSON] et al. reported in their study high levels of interleukins-8 for non-irradiated mini-screws after 24 h, 48 h, and 72 h of implantation [38]. [PERSON] et al. also concluded that PBMt applied during the early healing phase positively modulates the whole procedure and can improve mini-screw stability after one to two months [33]. This could explain why, in our study, the ISQ values of irradiated mini-screws were stable between T1 and T2. On the other hand, results similar to ours were obtained by [PERSON] et al. [39] and by a meta-analysis conducted by [PERSON] et al. [40] to conclude on this subject. In fact, after analysing all the clinical trials that studied the effect of PBMt on orthodontic mini-screws, they found that the existing data are inconclusive, and that further high-quality human studies are required to obtain scientifically convincing and clinically applicable conclusions. According to this meta-analysis, the study designs of several studies were not highly satisfactory. In fact, it has been demonstrated that the effect of PBMt is related to the treatment protocol, which is why unsuitable protocols may decrease the treatment efficacy. In addition, the wide variety of diode laser wavelengths assessed is characterized by a Gaussian beam profile delivery and the obtained results were inconsistent due to a lack of standardization in the applied laser protocols and techniques. According to the Arndt Schulz curve, when the power density of the laser light is insufficient or is applied for a short period of time, no effect is found on the tissue. Likewise, when using a high energy density or when the time of exposure is long, an inhibitory effect takes place.