On modeling and nanoanalysis 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 (µXRD 2 ), 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 4 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.

Submicron-to-nanoscale structure characterization and organization of crystals in dentin bioapatites

“…Both ions perform as Ca/P growth inhibitors 33 , indicating destabilization of the amorphous state 34 , favoring crystallinity at the new nucleated minerals 13 .…”

“…It has been demonstrated, previously, that Zn-containing amalgam restorations submitted to three weeks of load cycling promoted intrafibrillar mineralization of the partially mineral-depleted caries-affected dentin. These minerals were identified as calciumphosphate deposits, and crystals as HAp with augmented crystallographic maturity but with some components of lattice distortion 13 . X-ray diffraction (XRD) is one of the most powerful techniques to study the hierarchical structure of biological mineral such as teeth and bone.…”

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

“…Amalgam is being discontinued in response to global concerns about mercury in the environment, but the evidence brought by studies assessing the environmental risks is based on estimations and assumptions; therefore, no concrete conclusions can be drawn [11] .The Food and Drug Administration (FDA) and the American Dental Association (ADA) support amalgam as safe and effective material for dental restorations [12,13] . The FDA also claims that the levels of exposure to the mercury from amalgams are well below levels actually known to cause adverse effects, and notes that amalgam is a commonly used device with a low frequency of adverse events reported to the agency [14] . With a failure rate nearly double that of amalgam [15] , the increasing trend to replace amalgam with resin composite could be detrimental for patients.…”

“…Most of the times, it is not necessary to line the base of the cavity prior to condensating F o r P e e r R e v i e w 4 the amalgam, and in large cavities, dentin pins may be required as an alternative form of retention [19] . Additionally, Zn-containing amalgams submitted to mechanical stimuli have contributed to create new crystalline mineral deposits on the partially mineraldepleted subjacent substrate of the caries-affected dentin 14 . Furthermore, after thermocycling, new mineral aggregated on the carious dentin below the amalgams restoration [20] , but to know if they are crystalline or amorphous in order to infer their clinical performance, must be ascertained.…”

“…Raman spectroscopy is an analytical technique able to measure the molecular composition by providing a spectrum that contains information regarding all the chemical bonds present within the sample [23] for investigating molecular species. MicroRaman mapping technique has been a powerful method to directly analyze the dentin interface and the mineral content, and distribution, after placing the restorative and the application of mechanical [14] and thermal stimuli. Single point Raman spectra, permits to image a line profile thorough a series of point-to-point sampling.…”