Morphological and quantitative analysis of silver compounds on demineralised dentine in saliva substitutes

Abstract

Silver compounds have become popular for the treatment of arresting dental caries and dentine hypersensitivity. This study investigated the interaction of silver compounds in demineralised dentine under different conditions. Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), ion chromatography (IC) and inductively coupled plasma-mass spectroscopy (ICP-MS) were used to analyse these interactions.

A systematically-approached literature review was conducted on silver compounds in dentistry. They have been demonstrated to be effective for preventing and arresting caries, as well dentine desensitivity. The mode of action of silver compounds on carious teeth includes inhibition of demineralisation process and anti-bacterial effect.

Reaction products of Silver Diammine Fluoride (SDF) on dentine in different saliva substitutes were determined. Dentine samples were stored in deionised water (DIW), non-protein artificial saliva (NPAS), basal medium mucin (BMM), and un-stimulated whole saliva (UWS). These samples were chemically demineralised. Afterwards 38 wt-% SDF was applied. Dentine surfaces were analysed by SEM and showed different surface deposits and coatings. EDX, XPS and XRD detected metallic silver and silver compounds (predominantly AgCl) were formed and the amount was highest in NPAS group. BMM and UWS groups showed similar reactions. Sulphur was detected only in BMM and UWS groups.

Chemical composition of BMM and UWS were determined by IC. Dentine samples were pre-saturated with BMM, UWS and DIW and then chemically demineralised. Either of 42 wt-% AgNO3, 22 wt-% AgF and 38 wt-% SDF was applied. Treated samples were replaced in their respective “saliva”. The exposed surface and a cross-section of dentine was analysed by quantitative EDX. A precise linear relation of the silver standard wires (wt-%) according to EDX counts was obtained (R2 > 0.99). The amount of silver was concentrated between 0 to 60 μm in depth. BMM groups yielded the highest amount of silver for AgF and AgNO3 compounds (p < 0.06), which may be related to the greater concentration of salivary protein and chloride in BMM solution.

ICP-MS was used to quantitatively determine silver present on SDF-treated dentine. Dentine samples were pre-saturated with BMM or UWS and chemically demineralised. Afterwards 10 wt-%, 24 wt-% or 38 wt-% of SDF was applied and the treated samples were re-placed with respective “saliva” daily for 5 days. Dentine samples were then digested in 70% HNO3 and silver concentration was determined by ICP. For UWS, silver was in proportion to the application of various concentrations of SDF. However, for BMM, the higher amount of silver at 10 wt-% and 38 wt-% SDF suggests an interaction effect with excessive salivary protein and chloride.

Reaction products of silver compounds on dentine can be determined by the combined SEM-EDX, XPS and XRD techniques. Both modified SEM-EDX and ICP techniques are qualified for quantitative comparison of silver concentration between treatment groups. The interaction effects of silver with different in vitro salivary components should be considered in future investigations as this may affect the chemical reaction outcomes.