# Low-Level Light Therapy in Orthodontic Treatment: A Systematic Review
## 4 Discussion
### Lllt and Miniscrew Stability  
In a randomized clinical trial by [PERSON] et al. in 2020 and in a follow-up study by [PERSON] et al. in 2020, low-level light therapy was used to assess the impact of photobiomodulation (PBM) on the stability and potential loss of mini-implants (MIs), while also assessing patients' post-treatment pain experiences. At 60 days after the end of treatment, there was significantly greater stability in the laser group than in the control groups but no significant difference in pain sensation over time [54]. The MIs were placed 2 mm below the mucogingival junction on both sides of the maxilla at the region of adherent gingiva between the second premolar and the first molar. While the implants on the left side were in the control group and therefore not exposed to laser irradiation, the MIs on the right side of the maxilla were exposed to a 635 nm diode laser with a dosage of 10 J and exposure periods of 100 s per spot [54]. Light therapy was performed at different periods during orthodontic treatment: immediately and in different periods. MI stability was also measured at the same time periods. The secondary stability was found to be much higher in the right MIs compared with the left control group. Therewere no appreciable differences, however, in the level of pain measured on both sides of the jaw. Therefore, it could be concluded that 635 nm diode laser irradiation increases the secondary stability of orthodontic MIs by maintaining their total stability for as long as two months of treatment [42; 54]. Also, [PERSON] et al., in an RCT performed in 2016, studied the effects of light-emitting diode (LPT)-mediated photobiomodulation therapy on the stability of MI, as well as the rate of tooth movement during orthodontic treatment in cases of upper first premolar extraction, in which it was necessary, therefore, to retract the upper canines (Figure 3) [32; 40; 58]. The primary outcome of this study was to evaluate the effect of LPT on the rate of orthodontic tooth movement. The secondary outcome was the measurement of MI stability and interleukin-1\(\upbeta\) levels in gingival and peri-implant circular fluid after LPT [30; 40]. With a large increase in tooth movement following LPT, MI stability was dramatically increased in the LPT group in the second and third months. In conclusion, LPT might hasten tooth movement during orthodontic treatment and improve MI stability [40]. In the 2019 clinical study by [PERSON] et al., the effect of photobiomodulation (PBM) on the stability and displacement of orthodontic MIs subjected to loading was evaluated. Cone beam computed tomography images were viewed to determine the extent of MIs' head displacement. MIs in PBM groups showed less loss of stability [58]. MIs can lose stability and be moved during loading in the various phases of orthodontic treatment, debunking the beliefs that were held until a few years ago, thinking that MIs remained stable throughout the loading period. It has been established that physiological repair processes and a consequent decrease in bone density around MIs could promote their instability over time. The bone around the MIs may increase its density significantly only 3 months after implantation. For this reason, some authors suggest that several weeks of repair time is needed before applying loading to MIs. Although immediate loading protocols are widely recommended in clinical practice, the literature on this topic still remains unclear. It has been shown that the stability of MIs is subject to change during the repair process and that, after an initial decrease, stability values remain stable only after the fourth week. It has been suggested that photobiomodulation (PBM) can increase the stability of MIs. Non-ionizing light sources in the near-infrared and visible range are used in this therapy to encourage nonthermal biological activities on tissues [40; 58]. Figure 3: Stability case of MI in orthodontic treatment with extraction of the upper first premolar [40].