Determining the optimal concentration of nanoparticles for antibacterial properties in mouthwashes containing nanoparticles of zinc oxide, titanium dioxide, hydroxyapatite and silver fluoride (in vitro study)

Abstract

Background and purpose: Streptococcus mutans is one of the main microorganisms in causing caries. Due to the change of the oral microbial flora in favor of this pathogenic microorganism in patients with orthodontic appliances, the use of antimicrobial mouthwash along with the toothbrush is necessary to maintain oral and dental hygiene. Today, chlorhexidine mouthwash is the gold standard antibacterial mouthwash. However, due to the bad taste and smell and the possibility of teeth staining in long-term use, the acceptance of this mouthwash by patients is low. The aim of this study is to investigate the antibacterial properties and biocompatibility of four types of mouthwash containing nanoparticles of zinc oxide, titanium dioxide, hydroxyapatite, silver fluoride and chlorhexidine in an in vitro study in order to find the optimal concentration of nanoparticles. Materials and methods: Mouthwashes containing nanoparticles of titanium dioxide, zinc oxide, silver fluoride and hydroxyapatite were prepared in chitosan solution in 1% acetic acid. The size of the particles was evaluated by DLS test and then their lowest inhibitory concentration (MIC) on Streptococcus mutans bacteria was obtained by microdilution method. Next, the toxicity of these mouthwashes on the fibroblast cell line was investigated with the MTT test, the IC50 value was obtained, and the biocompatibility of the mouthwashes with chlorhexidine (control group) was compared. The toxicity of mouthwashes was compared with one-way ANOVA or Kruskal Wallis test. Findings: According to the DLS test, the dimensions of silver fluoride nanoparticles are 122.9 ± 29.24, hydroxyapatite is 253.5 ± 85.30, zinc oxide is 6.99 ± 0.96, and titanium dioxide is 15.21. ± 98.36 nm. The amount of zeta potential of mouthwashes is equal to 13, 1.09, 8 and 3.8 mV, respectively. MIC concentrations for mouthwashes containing nanoparticles of titanium dioxide, zinc oxide, silver fluoride and hydroxyapatite are 15.625, 31.25, 8.7 and 31.25 µg/ml, respectively, and IC 50 concentration is 66, 100, 21.14, 50 µg/ml, and 0.004% respectively. Conclusion: The present study showed that all metal nanoparticles and hydroxyapatite have good antibacterial properties against Streptococcus mutans bacteria and in all dilutions, the toxicity of chlorhexidine is higher than the mouthwash containing nanoparticles. Therefore, the use of nanoparticles of hydroxyapatite, titanium dioxide, zinc oxide and silver fluoride dispersed in chitosan as a mouthwash is a suitable alternative to chlorhexidine.