# Magnetism in Dentistry: Review and Future Perspectives
## 4 Magnetic Fields Effects on the Acceleration of Orthodontic Tooth Movement  
Currently, researcher's attention has been focused on accelerating methods for tooth movement, given the ever-increasing demand for shorter orthodontic treatment time. Several disadvantages (i.e., caries, gingival recession, and root resorption) are often related to long orthodontic treatment time poses [114].  
Different strategies have been approached for obtaining quicker results, with many still open questions.  
Orthodontic tooth movement occurs because of mechanical stimuli, subsequently followed by alveolar bone and periodontal ligament (PDL) remodelling. Applied force and the biological responses from the PDL modulate orthodontic tooth movement, with blood flow alterations, secretion of inflammatory cytokines, growth factors, neurotransmitters, colony-stimulating factors, and arachidonic acid metabolites [114].  
Direct electric currents, pulsed electromagnetic field, static magnetic field, resonance vibration, and low level laser represent some of the strategies adopted in this field, benefiting from \"bone bending theory\" and bioelectrical potential. It has been shown that vibrations for different duration per day accelerated tooth movements between 15% and 30% in animal experiments [114; 115; 116]. Cyclical force devices provide from 2 to 3 mm/month of tooth movement, adopting a vibration rate from 20 to 30 Hz, 20 min/day [117].  
Direct electric current techniques were tested on animals generating local responses and acceleration of bone remodelling by applying direct current to the anode at the pressure sites and cathode at the tension sites (by 7 V) [118].  
Photobiomodulation or Low Level Laser Therapy (LLLT), because of their biostimulatory effect on bone regeneration in the midpalatal suture during rapid palatal expansion or after bone fractures and extraction site [119; 120; 121] have been recently adopted in the field of acceleration of orthodontic tooth movement. Laser light stimulates osteoclast, osteoblast, and fibroblasts proliferation and hence influence bone remodelling probably by ATP production cytochrome C activation, as well as via receptor activator of NFkappaB-ligand RANK/RANKL and the macrophage colony-stimulating factor [122; 123; 124].  
Recently, magnets and pulsed electric magnetic fields (PEMFs) have been used in orthopaedic applications, i.e., for the treatment of fractures in human long bones. PEMF applications in dentistry have been limited to the ability to increase the rate of orthodontic tooth movement [125].  
It has been suggested that PEMF intervenes in the modulation of membrane permeability of intracellular cyclic adenosine monophosphate and cyclic guanosine monophosphate, allowing increased flow of calcium, sodium, and potassium ions across the cell membrane: tooth movement results accelerated due to an increase of active cells. or a static magnetic field have been shown to be successful in increasing the rate of orthodontic tooth movement in guinea pigs [126]. PEMF also induced vibrations that probably should enhance the effect of mechanical and magnetic forces on tooth movement [127]. As a result of exposure to PEMF with differing intensities, statistically significant increase and decrease of osteoclastogenesis and bone resorption areas have been observed and correlated to osteoproteger  
Figure 2: 4D paradigm: complex structures evolving over-time in predictable manner.  
(OPG), RANKL, (macrophage colony-stimulating factor (M-CSF), osteoclast numbers, and bone resorption [128].  
Another study showed that the canine exposed to PEMF moved 1.5 mm more than the control canine in 5 \(\pm\) 0.6 months [125]. Considering that each tooth can be moved 1 mm/month, this treatment resulted more efficient than the normal one.