XRD Characterization of Crystallinity of Human Tooth Enamel under Influence of Mechanical Grinding

Crystallinity refers to the degree of structural order in a solid and has a big influence on hardness, density, transparency and diffusion. Even within materials that are crystalline completely, the degree of structural perfection can vary, reflecting size and elastic strain of many independent crystalline regions (grains or crystallites) of which these materials are composed. In this work it was attempted to reduce the crystallinity of human enamel using a technique of mechanical grinding (MG) with an ultra-compact FRITSCH Mini-Mill PULVERISETTE 23 machine. Variation in the crystallinity through the MG was monitored by X-ray diffraction (XRD) by broadening of the diffraction peak and examined using the Williamson-Hall plot method. Crystallites in human enamel are regularly arranged and oriented (in the [001] direction) perpendicularly to the interface of enameldentin junction. The results showed an anisotropic feature in crystallinity. Reduction of the crystallinity along the a-axis is due to the crystal strain rather than to the refinement of crystal, and vice versa along the c-axis. After 230 h of the MG, the length of crystallites decreased from 100 nm to 30 nm and width from 40 nm to 37 nm approximately.