On modeling and nano-analysis of caries-affected dentin surfaces restored with Zn-containing amalgam and in vitro oral function

Abstract

The aim of this research was to assess the influence of mechanical loading on the ability of Zn-free vs Zn-containing amalgams to promote remineralization at the dentin interface. Sound (SD) and caries-affected dentin surfaces (CAD) were restored using Zn-free or Zn-containing dental amalgams. Mid-coronal dentin surfaces were studied by 1) Atomic Force Microscopy (AFM) analysis (including plot and phase imaging, nanoindentation test (modulus of Young (Ei), nano-roughness measurements, and fibril diameter assessment), 2) Raman spectroscopy/cluster analysis, 3) X-ray diffraction (μXRD2), 4) field emission electron microscope (FESEM) and energy-dispersive analysis (EDX), for morphological, mechanical, and physico-chemical characterization. Analyses were performed before amalgam placement and after amalgam removal, at 24 hours and 3 weeks of load cycling. Zn-free and Zn-containing amalgams restorations promoted an increase in the modulus of Young of CAD surfaces, after three weeks of load cycling; at this time, Zn-containing amalgams attained higher Ei than Zn-free restorations. Zn-containing amalgams induced tubular occlusion after load cycling, in both sound and CAD. Zn free-amalgams promoted remineralization of both intertubular and peritubular dentin in CAD substrata. These minerals were identified as calciumphosphate deposits, and crystals as hydroxyl-apatite with augmented crystallographic maturity but with some components of lattice distortion. Crosslinking of collagen diminished and secondary structure of collagen increased in CAD substrate restored with Zn-containing amalgam after 3 w of load cycling, indicating an advanced preservation, molecular organization and orientation of collagen fibrils after load cycling. Plot and phase images permitted to observe the topographical changes which were promoted by the mineral deposits; in general, the indexes related to higher remineralization gave rise to a decrease of nano-roughness and an augmentation of the bandwidth of the collagen fibrils. Zn-containing amalgam restorations submitted to mechanical stimuli promote remineralization of the partially mineral-depleted subjacent substrate at the caries-affected dentin.