Atmospheric Pressure Plasma Activation of Hydroxyapatite to Improve Fluoride Incorporation and Modulate Bacterial Biofilm

Abstract

Despite the technological progress of the last decade, dental caries is still the most frequent oral health threat in children and adults alike. Such a condition has multiple triggers and is caused mainly by enamel degradation under the acidic attack of microbial cells, which compose the biofilm of the dental plaque. The biofilm of the dental plaque is a multispecific microbial consortium that periodically develops on mammalian teeth. It can be partially removed through mechanical forces by individual brushing or in specialized oral care facilities. Inhibition of microbial attachment and biofilm formation, as well as methods to strengthen dental enamel to microbial attack, represent the key factors in caries prevention. The purpose of this study was to elaborate a cold plasma-based method in order to modulate microbial attachment and biofilm formation and to improve the retention of fluoride (F^-) in an enamel-like hydroxyapatite (HAP) model sample. Our results showed improved F retention in the HAP model, which correlated with an increased antimicrobial and antibiofilm effect. The obtained cold plasma with a dual effect exhibited through biofilm modulation and enamel strengthening through fluoridation is intended for dental application, such as preventing and treating dental caries and enamel deterioration.

Keywords: antibacterial properties; atmospheric pressure plasma; biofilm modulation; dental plaque control; enamel fluoridation; hydroxyapatite model.

Figure 1

EDX spectra of (a) HAP_i; (b) HAP_g; (c) HAP_DBDp_g.

Figure 2

SEM images of (a) HAP_i; (b) HAP_g; (c) HAP_DBDp_g.

Figure 3

XPS spectra: (a) survey spectra; (b) high-resolution spectra of the Ca2p region; (c) high-resolution spectra of the F1s region.

Figure 4

Graphic representation of microbial viability, expressed as log10 CFU (colony-forming units)/mL values, after 12 h incubation at 37 °C, on HAP specimens (one-way ANOVA, * p < 0.05, ** p < 0.001; when comparing plasma and fluoride-treated samples (HAP_DBDp, HAP_DBDp_g, and HAP_g) to untreated HAP_i sample).

Figure 5

Planktonic bacterial cells grown in the presence of the developed HAP samples expressed as optical density (Abs 600 nm) values of the cultures incubated in nutritive broth for 24 h in the presence of HAP variants (one-way ANOVA, * p < 0.05, ns = not significant; when comparing plasma and fluoride-treated samples (HAP_DBDp, HAP_DBDp_g, and HAP_g) to untreated HAP_i sample).

Figure 6

Biofilm development in the presence of HAP samples after 24 h of incubation at 37 °C. Values are expressed as log10 CFU (colony-forming units)/mL values (one-way ANOVA, * p < 0.05, ns = not significant; when comparing plasma and fluoride-treated samples (HAP_DBDp, HAP_DBDp_g, and HAP_g) to untreated HAP_i sample).

Figure 7

Plasma treatment on the HAP sample using the planar DBD source.