Comparative Efficacy of Nanoparticulate and Non-nanoparticulate Agents against Cariogenic Bacteria

Objectives: To assess the inhibitory effect of nanoparticulate solutions and compare them with other antimicrobial/antiseptic compounds currently used in clinical dentistry. Also to evaluate the impact of these agents on the mineral content of dentine. Methods: The solutions tested were silver (Ag), titania (TiO₂) and silica (SiO₂) nanoparticles (NPs) as well as silver nitrate (AgNO₃), sodium hypochlorite (NaOCl), calcium hydroxide (CaOH₂), thymol and chlorhexidine. The efficacy of these solutions was tested against Streprococcus mutans (S. mutans), which is one of the most cariogenic bacterial species. Efficacy was determined by evaluating the minimum inhibitory concentration (MIC) through an agar diffusion assay and also by measuring the turbidity increase caused by the bacteria growth. Bovine dentine disks were also acquired and stored in the solutions up to 14 days. After 24h and 14 days, dentine surfaces were examined with scanning electron microscopy (SEM) to evaluate the presence of bacteria. The possible loss of minerals from the specimens' matrix after exposure to the solutions was investigated using inductively coupled plasma optical emission spectrometry (ICP-OES). Results: AgNO₃ and Ag NPs were the most effective antibacterial agents against S. mutans having MICs of 0.0025% and 0.01% w/v respectively, followed by chlorhexidine (0.13% v/v), NaOCl (0.15% v/v) and SiO₂ NPs (2.5% v/v). The remaining solutions did not demonstrate antibacterial properties. ICP examination of the solutions containing the dentine specimens showed raised levels of calcium and phosphorus in the case of chlorhexidine, SiO₂ NPs and AgNO₃, suggesting dentine demineralisation. SEM confirmed that dentine surfaces treated with NaOCl, SiO₂ NPs, Ag NPs and AgNO₃ remained bacteria free 14 days after storage. Conclusions: NaOCl, SiO₂ NPs, Ag NPs and AgNO₃ demonstrated an inhibitory effect against S. mutans and could potentially be used as constituents in dental biomaterial compounds for the control of cariogenic oral bacteria.