## 4 Discussion  
In terms of surgical methods, nine of the fourteen studies show favorable results in both canine retraction rate and tooth alignment rate. MOP appear to be effective according to one of the trials, obtaining a better effect when the number of perforations made was increased, although some authors consider that this effect occurs in the first weeks after MOP [21; 28; 34; 35; 37]. Piezovision and laser-assisted Hapless corticotomy are less invasive techniques than traditional alveolar corticotomy, resulting in less discomfort and inconveniences for the patient [17; 23; 25; 26; 31; 36]. In addition, they can be used in patients with thin biotypes as they do not damage soft tissues and promote their healing [38], another advantage over traditional corticotomies. However, it is important to keep in mind that (1) the effect of any surgical procedure on the overall duration of the treatment is limited by the indication for the procedure, the timing of the surgery and the skill of the practitioner and that (2) the number of appointments and chair time required to complete treatment may not decrease due to the recommended shorter intervals between check-ups. Therefore, it would be interesting to assess whether any reduction in the duration of the orthodontic treatment would exceed the additional cost of the surgery [39].  
On the other hand, regarding non-surgical methods, we have found no evidence that the use of a supplemental vibrating device accelerates tooth movement during the treatment with conventional orthodontics or aligners [15; 22; 27; 30]. However, the effect of low-level laser therapy and LED laser therapy appears to be promising, and the results obtained are generally consistent [18; 19; 24; 29; 31; 33]. In addition, a reduction in secondary pain to orthodontic treatment was found in one of the articles [33], which could be another advantage associated with the use of this type of therapy. In contrast, it is necessary to know how much radiation could be accumulated, so investigators must be careful with the doses administered in order not to exceed the biostimulating dose range or to reach the inhibition range [40]. The use of a laser in clinical practice may be interesting in those patients who do not mind having appointments several times and at short intervals and prefer not to undergo surgical procedures [6]. Still, it is difficult to establish a standardclinical protocol, as there was not enough evidence to determine either the ideal laser configuration, the utilization frequency or the time between sessions.  
To conclude, it is obvious that the number of long-term, quality studies investigating interventions to accelerate orthodontic tooth movement is very small. In most cases, only a portion of the therapy is evaluated, and so, the effects during the entire treatment are not fully evaluated. The side effects are mentioned only in some trials, and the procedures are not evaluated in terms of cost/benefit. On the other hand, perhaps we can increase the number of studies analyzed by increasing the publication time in the search so that we can obtain a larger sample for analysis and comparison of results, as well as including, in the same analysis, studies that analyze both acceleration and inhibition of movement. Therefore, long-term studies would be necessary to analyze qualitatively and quantitatively the pros and cons of each intervention, thus being able to assess which one would be the best choice for each individual patient.