# Magnetism in Dentistry: Review and Future Perspectives
## 3 SPIONs in the Biomedicine
In fact, by applying the external magnetic field it will be possible to target the drug delivered to a specific site, thus reducing the doses to be administered and the potential harmful side effects [93, 94, 95]. Properly designed carriers can be applied in numerous pharmaceutical fields, for oral administration, for sustained release, for drug targeting at specific sites, and for parenteral administration of anticancer drugs. For such application, the size, the surface chemistry, and charge of the magnetic particles are very crucial, as they have the effect on the circulation time in the blood and the bioavailability of the particles within the body [96]. The introduction of SPIONs in tissue engineering approaches, in particular for bone regeneration, has been recently implemented. Efficient scaffold fixation could be obtained adopting magnetic scaffolds and magnetic forces, thus providing a smart solution for the treatment of wide bone defects. Conventionally, fixation is ensured by external systems, such as intramedullary nails, plates and screws which require a constant control and multiple surgical interventions. To this purpose, the application of a magnetic scaffold highlighting a saturation value of 17 emu/g represents an innovative magnetic fixation approach [97]. Magnetic force-based tubular and sheet-like structures have been also proposed for tissue engineering purposes adopting magnetite NPs and magnetic force [98; 99]. Magnetic force mechanical conditioning bioreactors for tissue engineering have been also suggested [100], highlighting the possibility to have a control on cell function through the application of an external magnetic field by binding MNPs on cells surface [101]. Magnetic scaffolds may produce higher magnetic field gradients, thus providing significant magnetic attractive forces. A superparamagnetic material, used for magnetic scaffold design and development, may reach appropriate magnetisation values for ferrofluid or MNPs adhesion when applying an external magnetic field [102], but it may also be magnetically \"turned off\" by removing the applied magnetic field, thus providing magnetic gradients suitable for the attraction of cells or other bioagents linked to MNPs. The possibility of obtaining magnetic nanocomposite scaffolds with the addition of superparamagnetic PVP-coated Fe\({}_{3}\)O\({}_{4}\) nanoparticles in a PCL matrix has been also considered [103], also highlighting the possibility of adopting the obtained structures as fixed station, whose magnetisation can be switched on and off by means of an external magnetic field. The long-term effects of iron-oxide-based phases such as magnetite or maghemite in human body remain unclear [103; 104]. Surface-modification methods have been adopted for the design of biocompatible layers consisting of on particle surface, thus avoiding eventual toxicity problems [105]. Biocompatible bioersorbable superparamagnetic-like phase (FeHA) has been proposed by doping hydroxyapatite with Fe\({}^{3+}\)/Fe\({}^{2+}\) ions. [106]. PCL/FeHA nanocomposite substrates were characterized and designed using different polymer-to-particle weight ratios, showing that the synergistic contribution of surface chemistry and topography may be responsible for the overall features of the proposed structure: enhancement of the hydrophilic character, cell attachment, and proliferation [107]. However, the different ductility of the polymer matrix and the inorganic nanofillers should be always considered in a scaffold design process since eventual weakness in a biocompatible structure may be the result of a discontinuities in the stress transfer and production of stress concentration at the nanoparticle/matrix interface at specific concentration amount of inorganic nanofillers.