Ex vivo detection and characterization of remineralized carious dentin, by nanoindentation and single point Raman spectroscopy, after amalgam restoration

Abstract

The aim of this study was to assess the mechanical and chemical performance of sound and caries-affected dentin (CAD), after Zn-free vs containing amalgam restorations placement and thermocycling. Dentin surfaces were studied by Atomic Force Microscopy (AFM) analysis for surface morphological characterization (including fibril diameter assessment), nano-indentation (to measure nano-hardness-Hi and modulus of Young-Ei), and single point Raman spectroscopy for chemical analysis. Measurements were performed before amalgam placement, after amalgam removal, and after 3 months of thermocycling (100,000cy/5 ºC and 55 ºC). Restorations increased both Hi and Ei at intertubular dentin of CAD. The highest values of Hi were achieved at intertubular dentin after restoring with Zn-containing amalgams. Remineralization of dentin was attributed to the increase of both amorphous and crystalline new mineral, as lower degrees of crystal imperfections in junction with crystal disorders, and improvement in structural stability of collagen were found. Higher presence of minerals were also confirmed after the decrease of fluoridated apatite and the increase of the total water content. Proteoglycans, lipids, and proteins, augmented in both sound and CAD, providing support for the mineral growing. The increase of bands assigned to vibration of carbonate calcium phosphate contributed to a decrease of crystallinity.