Method: Dentine discs were coated applying a 10 g l-1 Ag NPs solution. The antibacterial efficacy of the coating was tested against S. mutans and was compared to AgNO3 and chlorhexidine. The tests were performed in 24-well plates. One dentine disc was placed at the bottom of each well, which was then inoculated with a bacterial suspension (OD595=0.1). Following a 24h exposure, the bacterial growth and cell viability in the media were quantitatively assessed by measuring the turbidity, proportion of live and dead cells (Backlight™, Invitrogen Ltd), and lactate production. These three bio-assays were also employed to investigate bacterial adhesion. The integrity of the antibacterial coatings was investigated using inductively coupled plasma optical emission spectrometry (ICP-OES). The optical properties of coated dentine were assessed with a VITA Easyshade®portable dental spectrophotometer.
Result: Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) confirmed that dentine specimens were successfully coated. Both silver coatings were found to be very stable (>97%). All three bio-assays showed that Ag NPs and AgNO3 dentine coatings were equally highly bactericidal (>99.5%), while inhibiting bacterial adhesion. The chlorhexidine coating showed no antibacterial effect. The Ag NPs coating did not affect the natural colour of dentine (ΔE* =4.3), while the AgNO3coating caused severe discolouration (ΔE* =50.3).
Conclusion: Ag NPs formed a stable dentine coating with remarkable bactericidal and anti-biofilm properties. Although equally effective to Ag NPs, AgNO3 coating was not aesthetically acceptable. Thus, it is suggested that Ag NPs coating may be a viable alternative to both chlorhexidine and AgNO3, inhibiting dental plaque formation and protecting from caries.