Submicron-to-nanoscale structure characterization and organization of crystals in dentin bioapatites
The aim of this study was to ascertain the crystal morphology and to assess the ultrastructure and texture changes of sound (SD) and caries-affected dentin (CAD) after being restored with Zn-free and Zn-containing amalgam. Dentin surfaces were studied before amalgam placement and after amalgam removal by X-ray diffraction (μXRD2) and transmission electron microscopy (TEM) through selected area diffraction (SAED) and bright-field (BF) imaging. Crystals at the dentin surface were identified as hydroxyl-apatite with augmented crystallographic maturity, crystallinity and grain sizes and lower microstrain in CAD dentin after Zn-containing amalgam removal at the 310 plane. The opposite trend was followed at 002 reflection. Texture increased in CAD at both reflections after the removal of Zn-containing amalgams. Crystallinity increased in SD after amalgam restorations at 002 and 310 reflections. In CAD, crystallinity decreased after amalgam restorations at the 002 plane. Block-like and needle-like apatite crystals constituted the bulk of minerals in SD. Needle-like apatite crystals were observed in CAD surfaces before and after Zn-free amalgam restorations. Polyhedral and rounded drop-like crystals characterized the CAD surfaces before Zn-containing amalgam placement. After the restoration removal, plate-like polygons and three-dimensional agglomerated crystals were revealed. Crystallites with improved crystallographic orientation became shorter and thinner in CAD treated with Zn-containing amalgams, thus increasing mineralization and maturity.