## 1 Introduction  
In recent years, there has been an increase in adults undergoing orthodontic treatment; therefore, this therapy is no longer the simple prerogative of subjects in the development phase [1; 2]. However, there are numerous problems that still hold adults back from approaching orthodontic treatment. First and foremost is the desire to be able to wear an effective, comfortable, and discreet appliance that is a valid alternative to fixed multibracket therapy [3]. Clear aligners have proven to be a valid answer to this aesthetic demand of patients, and the literature available to date has shown that it is possible to achieve results that are now fully comparable to those obtained with fixed orthodontic treatment, without forgetting, however, that both therapies have specific and different strengths and limitations [4]. The second factor holding adult patients back from orthodontic treatment is that it takes a long time to complete. According to a study on individual preferences with regard to orthodontic treatment carried out in 2020 on a sample of 100 patients, 72% stated that orthodontic treatment was generally too long, and 50% stated that they could accept a treatment that was at most 6 months long [5; 6]. Therefore, to shorten the duration of orthodontic treatment without compromising clinical results and, at the same time, maintain high patient compliance, it would be useful to have an orthodontic acceleration system [7]. In the range of possibilities available today to speed up orthodontic treatment, clinicians can take advantage of both surgical and nonsurgical techniques. Among surgical techniques, some of the most popular are the corticotomy techniques. They are rather efficient and predictable, leading to a reduction in treatment time of up to 6-8 months, but at the same time, they are relatively invasive as they require mucoperiosteal flaps, cortical incisions, and sutures, with post-surgical discomfort that can result in pain, swelling, hemorrhages, infections, gingival recessions, etc. [8]. However, nonsurgical acceleration techniques are less invasive, among which we can include biomechanical, biological, and physical approaches as different subcategories. The latter techniques, in particular, are among the least invasive, as they often use additional devices capable of transmitting energy to the alveolar structures through ultrasound or electromagnetic radiation of infrared length [9; 10; 11; 12; 13]. Ultrasound techniques have been applied to orthodontic therapy with the idea of increasing the extent of bone remodeling and reducing the incidence of root resorption but have been shown to exhibit pulpal heat damage as a side effect [14]. The second physical technique mentioned is based on the emission of electromagnetic waves of infrared length (600-1000 nm) produced by an LED or laser source [10; 11; 12; 13], called photobiomodulation (PBM) or low-level light therapy (LLLT). This therapy can stimulate the proliferation of osteoblasts, osteoclasts, and fibroblasts of the dentoalveolar complex by activating molecular and chemical mechanisms: the photons emitted by these devices are absorbed by the mitochondria of the cells mentioned and stimulate the enzyme cytochrome C oxidase, which is part of the cell's respiratory chain [14]. This leads to an increase in the synthesis of three important molecules: endogenous ATP, the cell's main source of energy; superoxide anions O\({}_{2}{}^{-/-}\) and other reactive oxygen species (ROS), which can activate numerous intracellular signaling pathways; and nitric oxide (NO), a vasodilator molecule that allows for greater blood flow to the affected areas and, consequently, an increased supply of oxygen and nucleic acids. All this is reflected in an increased rate of bone remodeling, resulting in accelerated tooth movement [15]. Furthermore, by inhibiting the depolarization of nerve endings and reducing serum prostaglandin concentrations, PBM can also control the perception of painful stimuli associated with orthodontic treatment [16; 17]. [PERSON] et al.