## 4 Discussion  
Vibrations are cyclic forces performing a physical stimulus that has been shown to promote bone formation through osteoblast differentiation and proliferation [28]. This phenomenon may be possible because the bone is a mechanosensitive tissue, and bone cells react to a biomechanical environment by activating molecular signaling pathways that regulate matrix production, differentiation, and proliferation [16]. Two types of frequencies are used to stimulate the alveolar bone: the LFV (\(\leq\)45 Hz) and the HFV (\(\geq\)90 Hz) [29]. This systematic review contrasted the different publications related to LFV [6; 9; 23; 26] and HFV [3; 13; 24; 25] and their osteogenic effect on the alveolar bone. The results of this work showed that LFV and HFV produce a mechanical stimulus that leads to an osteogenic effect on the alveolar bone, improves healing after dental extractions, increases bone density, and helps counteract the effects of induced osteoporosis [3; 6; 9; 13; 23; 24; 25; 26]. The studies analyzed in this review showed that LFV stimulates growth and osteogenesis in craniofacial bones, as demonstrated by [PERSON] et al., where the application of vibrations of 0.2 Hz together with an orthopedic force was able to increase the length of the premaxilla compared to the control [23]. This is because vibrations affect the sutures; histological evidence shows that the premaxillary-maximillary suture treated with cyclic loading showed a significant sutural separation with islands of new bone formation [23]. This result is consistent with that reported by [PERSON] et al., who reported that the application of LFV for a short period induces cranial growth through enlargement of the sagittal and parietotemporal sutures and an increase in cranial width; on the other hand, the same vibratory stimulus for a longer period stimulates the formation of cranial bones, thereby increasing their width [30]. These results suggest that the use of vibrations combined with orthopedic forces during interceptive orthodontics to achieve optimal therapeutic effects. At the same time, the application of LFV has been suggested as an alternative to prevent relapse after orthodontic treatment [9]. [PERSON] et al. reported that the application of LFV in two retention periods, one short (7 days) and one long (15 days) post orthodontic treatment, decreased relapse, with the 15-day period showing the lowest amount of relapse, which was caused by a decrease in RANKL and an increase in the number of bony trabeculae in the alveolar bone [9]. This is consistent with the findings by [PERSON] et al., where 30 Hz stimulation of osteoblasts decreases RANKL expression and promotes an increase in osteoblast activity, which may lead to an increase in bone mineral density [31]. This may lead to an increase in trabecular bone, cortical thickness, and tissue volume, which may contribute to a decrease in the amount of recurrence; it also coincides with the report by [PERSON] et al., who observed inhibition in tooth movement when using LFV [6]. On the other hand, the results found by [PERSON] et al. are contrary to those mentioned above since they report that the use of LFV in a retention period does not make a difference in the amount of relapse. However, the bone density was higher in the vibration group [26]. The studies analyzed in which HFV stimulation was used were those carried out by [PERSON] et al. They reported that the use of HFV presented a paradoxical effect on the alveolar bone, creating different reactions that depend on the context in which the vibrations were applied [3]. On the one hand, when there is an orthodontic force inducing a dental movement, the effect achieved is catabolic; this was consistent with the in vitro studies of [PERSON] et al., where periodontal ligament cells compressed by an acrylic disc and mechanically stimulated with HFV overexpressed the genes related to bone resorption RANKL and PGE2 [32].