Nilormi Biswas

Mechanical Properties of Enamel Nanocomposite

For adult Indian premolar teeth, we report for the first time ever the simultaneous evaluations of nanohardness, Youngs modulus, and fracture toughness of the enamel nanocomposite. The nanohardness and Youngs moduli were evaluated from near the beginning of the middle enamel region to within 10 μm of the dentino-enamel junction (DEJ) and in the dentin region using the nanoindentation technique. The fracture toughness from near the middle of the enamel region to near the DEJ zone was measured using the microindentation technique. The deformation was studied using scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM). The relative differences in the extents of biomineralization in the enamel and dentin regions were studied by the energy dispersive X-ray (EDS) technique. The variations of the toughness of the enamel as a function of the toughness of the protein matrix phase have been analyzed which showed that the predicted value of the toughness of the protein present in the nanocomposite was comparable to that of other bioproteins reported in the literature. Further, the work of fracture estimated from the measured value of toughness of the enamel nanocomposite agreed well with the experimental data reported in the literature.

Phase pure, high hardness, biocompatible calcium silicates with excellent anti-bacterial and biofilm inhibition efficacies for endodontic and orthopaedic applications

Here we report for the very first time the synthesis of 100% phase pure calcium silicate nanoparticles (CSNPs) of the α-wollastonite phase without using any surfactant or peptizer at the lowest ever reported calcination temperature of 850 °C. Further, the phase purity is confirmed by quantitative phase analysis. The nano-network like microstructure of the CSNPs is characterized by FTIR, Raman, XRD, FESEM, TEM, TGA, DSC etc. techniques to derive the structure property correlations. The performance efficacies of the CSNPs against gram-positive e.g., S. pyogenes and S. aureus (NCIM2127) and gram-negative e.g., E. coli (NCIM2065) bacterial strains are studied. The biocompatibility of the CSNPs is established by using the conventional mouse embryonic osteoblast cell line (MC3T3). In addition, the biofilm inhibition efficacies of two varieties of CSNPs e.g., CSNPs(W) and CSNPs(WC) are investigated. Further, the interconnection between ROS e.g., superoxide (O2.-) and hydroxyl radical (.OH) generation capabilities of CSNPs and their biofilm inhibition efficacies is clearly established for the very first time. Finally, the mechanical responses of the CSNPs at the microstructural length scale are investigated by nanoindentation. The results confirm that the α-wollastonite phases present in CSNPs(W) and CSNPs(WC) possess extraordinarily high nanohardness and Youngs moduli values. Therefore, these materials are well suited for orthopaedic and endodontic applications.

Micro-Pop-In Issues in Nanoscale Contact Deformation Resistance of Tooth Enamel

Human tooth enamel is a natural nanocomposite with a hierarchical structural architecture that spans from macroscale to nanoscale. Thus it offers the unique opportunity to study the physics of deformation at the nanoscale in a controlled manner using the novel nanoindentation technique. In spite of the wealth of literature, however, the information about the effect of loading rate on the nanoindentation behavior of human tooth enamel is far from being significant. Therefore, the major objective of the present work was to study the loading rate effect on nanoindentation behavior of enamel with a view to improve our understanding that could be used for development of better bioinspired synthetic structures for functional as well as biomedical utilities. The nanoindentation experiments were conducted at loading rates in the range of to at peak load of at room temperature with a Berkovich tip on the longitudinal section from a freshly extracted premolar tooth enamel surface from a 65-year-old Indian male. To the best of our knowledge here we report for the first time the experimental observation of the increase in intrinsic resistance against contact-induced deformation at the nanoscale with the loading rate applied to the enamel surface. The results were explained by considering the microstructural details and the shear stress underneath the nanoindenter.