Background. When silver diamine fluoride (SDF) is used in conjunction with conservative caries removal in deep carious lesions, the distribution depth of silver is critical for safety and effectiveness. Objective. The purpose of this study is to determine the effect of selected caries removal on silver penetration when 38% SDF is applied to deep carious lesions in permanent teeth. Methods. Extracted permanent teeth with caries extending to the inner third of the dentin were used (N = 18). The periphery of the carious lesion was completely removed to the dentinoenamel junction (DEJ). In group A (n = 9), no further removal of carious tissue was performed, leaving necrotic dentin inner to the DEJ, whereas in group B (n = 9) superficial necrotic dentin was completely removed until leathery, slightly moist, reasonably soft dentin remained. SDF was applied for 3 minutes in both groups. Microcomputer tomography (micro-CT) and field emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (FESEM-EDS) were used to measure mineral density and silver distribution. The silver penetration depth/lesion depth (PD/LD) ratio was calculated for each sample. The Mann–Whitney U test was used to compare differences between the two groups. Results. The micro-CT analysis showed that the PD/LD ratios of group B (1.07–2.29) were marginally greater than those of group A (1.00–1.31). However, a statistically significant difference was not observed ( p value = 0.5078). When stratified by remaining dentin thickness (RDT), the PD/LD ratios of group B were still greater than those of group A only when RDT was >500 µm. The FESEM-EDS analysis indicated that silver particles precipitated throughout the entire thickness of the carious lesions. Conclusion. Applying SDF on a deep carious lesion and leaving the necrotic dentin pulpally did not affect silver penetration. However, the extent to which silver penetrates the remaining dentin beneath the lesions is dependent on the amount and characteristics of that dentin.

Objective: Presently, one of the most common oral diseases is dental caries, which is a biofilm-mediated disease. Lawsone methyl ether (LME) has shown promising antibacterial activity due to its 1,4-napthoquinone structure. Recently, a 1,2,3-triazole scaffold has been used in the structural modification of potential antimicrobial agents. To develop novel anticaries agents, the structure modification of 1,4-napthoquinone with N-substituted 1,2,3-triazole, therefore, may be a candidate. Material and Methods: LME was used as a lead compound, and three new lawsone derivatives were prepared by two-step reactions. Their antimicrobial effects against three dental caries pathogens; including S. mutans, L. casei, and A. naeslundii were investigated, using the microdilution technique (0.78-100 μg/mL). A growth curve assay was performed to assess the effects of compounds on the growth kinetics of bacteria. Moreover, the effect of synthetic lawsone derivatives on the biofilm formation of S. mutans was also evaluated by crystal violet assay. Results: Overall, S. mutans was most sensitive to lawsone derivatives (minimum inhibitory concentration (MIC)=1.56- 50 μg/mL), followed by A. naeslundii and L. casei: corresponding to their growth curves. Lawsone derivatives, at the concentration of 1/2 MIC and 1/4 MIC, inhibited 12-hour S. mutans biofilm formation by 86.0-98.0%. The inhibitory effect decreased with decreasing concentrations and increasing incubation times. Conclusion: Synthetic lawsone derivatives have an inhibitory effect on the growth of three tested cariogenic bacteria, and the biofilm formation of S. mutans. The compounds exhibited anti-cariogenic bacterial strains and satisfying antibiofilm formation effects on S. mutans.

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This study investigated the potential anticaries properties of synthetic 1,4-naphthoquinone derivatives. Synthetic 1,4-naphthoquinone derivatives (2-4) were designed and synthesized by employing lawsone methyl ether (LME, 1), a plant-derived 1,4-naphthoquinone, as a lead compound. The synthetic compounds were characterized by infrared spectroscopy, 1H-nuclear magnetic spectroscopy, 13C- nuclear magnetic spectroscopy, and high-resolution mass spectrometry. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and growth curves were determined to assess their antibacterial effects against Streptococcus mutans, Lacticaseibacillus casei, and Actinomyces naeslundii. The pH drop assay was also performed on these three bacterial species. The effect on S. mutans biofilm formation was evaluated by crystal violet assay. From the microdilution assay, 2-(prop-2-ynyloxy) naphthalene-1,4-dione (compound 2) showed potent antimicrobial activity against S. mutansand A. naeslundii(MIC of 1.56 and 3.125 µg/mL, respectively) in the same range as chlorhexidine (MIC of 1.95 and 1.95 µg/mL, respectively). The 1,4-naphthoquinone derivatives showed low antibacterial activity against L. casei. LME (compound 1) and 2-(prop-2-ynyloxy) naphthalene-1,4-dione (compound 2) inhibited pH reduction from S. mutans. The compounds at sub-MIC concentrations showed a potent inhibitory effect against S. mutans biofilm formation in a dose- and time-dependent manner. These results suggested that the synthetic 1,4-naphthoquinone derivatives are promising compounds that could be developed as a novel alternative or adjunctive anticaries therapies.