The research has therefore focused on simple, easy-to-use-at-home, and noninvasive or painful systems that the patient could use simultaneously with aligners in complete autonomy, without having to visit the dentist (even considering the current global pandemic), for a few minutes a day, without contraindications, without pain, and with remote control by the professional. Photobiomodulation (PBM), also called low-level light therapy (LLLT), is a physical system that uses laser or LED technology to emit electromagnetic radiation in the range of red to near-infrared (wavelengths between 600 and 1000 nm), which stimulates the proliferation of osteoclasts, osteoblasts, and fibroblasts of the dentoalveolar complex, improving the extent of bone remodeling and consequently accelerating tooth movement [15; 21]. In fact, at reduced doses, these photonic radiations cause cellular stimulation through molecular and chemical mechanisms by which the photons are absorbed in the mitochondria and, in particular, by the cytochrome C oxidase of the respiratory chain. This leads to an increase in the amount of synthesized ATP, the main energy reserve of the cell; to the increased production of superoxide anions O2\({}^{-/-}\) and other species of ROS, or reactive oxygen species, capable of activating numerous intracellular signaling pathways involving nucleic acid and protein synthesis, enzyme activation, and cell cycle progression; and finally to the hyperproduction of NO (nitric oxide), a vasodilator that leads to improved blood flow in the affected areas, with a greater amount of oxygen and nucleic acids available [24]. PBM also appears to be able to control the perception of the painful stimulus associated with orthodontic treatment by inhibiting the depolarization of nerves and decreasing the concentration of serum prostaglandan [25], although the knowledge about its effectiveness on pain is still unknown [26]. In a preliminary study conducted on 19 orthodontic subjects (age range: 11-18 years) with Class I and Class II malocclusions and a Little's irregularity index (LII) \(\geq\)3 mm for a total of 28 arches, [PERSON] et al. (2016) showed that intraoral PBM with OrthopulseTM resulted in statistically significant changes in the tooth movement rate during the alignment phase of orthodontics and significantly reduced the total treatment time compared to the control group [27]. Furthermore, the current panorama related to the therapeutic options for the alignment of the teeth in an adult patient is wide, but the systems that are most successful today are those that involve the use of transparent aligners to be worn all day and to be replaced on a weekly and sometimes even fortnightly basis. Among these, the Invisalign System (Align Technology, Santa Clara, CA, USA) that enjoys a wide diffusion provides for the replacement of the aligner every 7 days, defining from the beginning of the therapy an estimate of the time necessary to achieve dental alignment. This historical prospective study aimed to improve the knowledge about the effectiveness of PBM in reducing the orthodontic treatment time in adults when OrthopulseTM and the Invisalign System are simultaneously applied. OrthopulseTM, a photobiomodulation device that generates continuous beams of near-infrared light (NIR--near-infrared) with a wavelength of 850 nm and a power of 42 mW/cm2 to produce an average energy density on the surface of the silicone impression of 9.3 J/cm2, was used for patients with PBM. The null hypothesis was that there is no difference between the PBM and control groups in the time for achieving an LII <1 mm.