# Magnetism in Dentistry: Review and Future Perspectives
## 3 SPIONs in the Biomedicine  
Advanced strategies to improve hard tissue regeneration consists in the application of a magnetic field and magnetic nanoparticles, which have a strong influence on cell fate. The use of static and pulsed magnetic field (SFM, PMF) in regenerative medicine has been often associated to increase of bone regeneration, wound healing and also to magnetic resonance technique. The concept of magnetism in the medical field was firstly introduced in 1970 by [PERSON] and his research group [82]. Since then, numerous research advancements on different types of magnetic particles and on different ways for their use by optimizing their properties have been performed. Superparamagnetic iron oxide nanoparticles (SPIONs) are synthetic particles made up of maghemite (\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)), magnetite (Fe\({}_{3}\)O\({}_{4}\)), and hematite (\(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)) characterized by a core diameter between 10 and 100 nm and a coating for drug or protein loading, thus making SPIONs able to be carried to a specific tissue through the use of an external magnet. SPIONs are magnetisable up to a saturation value in the presence of an external magnetic field. When the application of the magnetic field is interrupted, the nanoparticles will not show residual magnetisation. This property is a function of the size of the nanoparticles and usually takes over for values of at least 10-20 nm in diameter. Below these values the system does not have the multiple domains that are instead present in all the larger magnets and on the contrary behaves like a \"single super spin\" with high magnetic susceptibility. SPIONs, for their physical, chemical, thermal, and magnetic, have been largely employed in different biomedical areas like cell labelling and cell separation; magnetic resonance imaging (MRI); tissue repair; magnetofection; hyperthermia; treatment of arthritis and drug delivery. Cell labelling with iron/paramagnetic represents a method used for in vivo cell separation and to ensure that labelled cells should be identified by MRI. In vivo cell labelling and separation techniques adopts two different approaches: attachment of magnetic nanoparticles on the external cell surface or internalization of biocompatible magnetic nanoparticles through fluid phase endocytosis, receptor mediated endocytosis or phagocytosis [83; 84; 85; 86]. A strategy for effective and specific cell marking with magnetic nanoparticles consists in modifying the surface of the nanoparticles with different kinds of specific ligands, in such a way that the cell does not only recognizes the system but internalizes it through receptor-mediated endocytosis [87]. The SPIONs, suitably functionalized with organic \begin{table}
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**Additive Manufacturing Method** & **Biomaterial** & **Type** \\ \hline \begin{tabular}{c} Vat polymerization; \\ powder bed fusion; \\ fused deposition modelling; \\ binder jetting \\ \end{tabular} & Hydroxyapatite & \begin{tabular}{c} Bioactive/non-degradable \\ ceramic \\ \end{tabular} \\ \hline \begin{tabular}{c} Vat polymerization \\ \end{tabular} & Bio glass & Bioactive ceramic \\ \hline \begin{tabular}{c} Powder bed fusion \\ \end{tabular} & Calcium silicate & Bioactive ceramic \\ \hline \begin{tabular}{c} Binder jetting; \\ vat polymerization; \\ fused deposition modelling \\ \end{tabular} & \(\beta\)-tricalcium phosphate & Bioactive/biodegradable \\ \hline \begin{tabular}{c} Powder bed fusion; \\ fused deposition modelling \\ \end{tabular} & Polycaprolactone & Biodegradable polymer \\ \hline \begin{tabular}{c} Fused deposition modelling \\ \end{tabular} & \begin{tabular}{c} Polymer-based \\ micro-nano-composites \\ \end{tabular} & Biodegradable polymer \\ \hline \
\begin{tabular}{c} Fused deposition modelling \\ \end{tabular} & Poly(lactic acid) & Biodegradable polymer \\ \hline
\begin{tabular}{c} Material jetting; \\ fused deposition modelling \\ \end{tabular} & Poly(lactic acid-co-glycolic acid) & Biodegradable polymer \\ \hline \hline \end{tabular}
\end{table}