Evaluation of the mechanical and structural properties of dentin tissue before and after demineralisation treatment

Dentin tissue is a biological material characterised by a complex structure which deeply influences its mechanical properties. It assumes a very important role in many fields due to its great potential. Its potential is even better harnessed as a result of its demineralisation. In fact, this treatment makes dentin more permeable and allows the release of substances trapped in the highly crystalline inorganic structure. In order to use dentin in the clinical setting, it is necessary to understand how this material is structured at the microscopic level. In particular, it is important to define how the structural variation along dental tissue is reflected in the change of its mechanical properties. In addition, demineralisation treatment results in a structural change that is also reflected in dentin mechanical response. So, the aim of the research is to analyse the structural characteristics of dentin both before and after demineralisation treatment and to study its mechanical properties as a function of its arrangement. Specifically, among the mechanical properties, focus has been placed on the analysis of the elastic modulus. Slices of dentin about 3mm thick were prepared from human dentin. The samples were divided into two main groups: untreated and demineralised. These then, based on the cutting direction relative to the tooth axis, were further divided into two subgroups: vertical and horizontal. The samples were suitably processed in order to perform structural analysis by Scanning Electron Microscope and mechanical analysis via nanoindentation. An effective demineralisation protocol tested by Raman Spectroscopy was optimised. The results obtained showed that for untreated samples there is a strong relationship of Young's modulus with respect to dentin cutting direction, which appears to be absent in demineralised samples. The latter, show a significant lowering of elastic modulus values, but the difference between the two cuts vanished. Only the vertical untreated samples showed a significant position-dependent correlation. Finally, there was no considerable dependence between the simultaneous presence of treatment and location among the four groups analysed. These findings highlight that dentin presents anisotropic behaviour and that following demineralisation this characteristic is less evident, while a significant decrease in elastic modulus is seen in conjunction with the significant structural variations.