Student Theses, Dissertations and Capstones

Document Type

Thesis - NSU Access Only

Degree Name

Master of Science (M.S.) in Dentistry

Copyright Statement

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Department

College of Dental Medicine

First Advisor

Judith Chin

Date of original Performance / Presentation

January 2023

Publication Date / Copyright Date

1-1-2023

Abstract

BACKGROUND: Severe early childhood caries (S-ECC) is a particularly aggressive form of dental caries associated with a history of maternal malnutrition and illness, tooth developmental defect excessive exposure to carbohydrates, and early infection by cariogenic microorganisms, predominantly mutans streptococci (MS) and lactobacilli. Evidence based on decades of studies indicates that MS and lactobacilli are involved in the initiation of dental caries Lactobacilli are associated with disease progression, as well as serving as an indirect indicator of the content of fermentable carbohydrate. Recent studies have demonstrated that the microbiota of children with S-ECC differs significantly from that of their caries-free counterparts and that lactobacilli comprise a significant portion of the cariogenic biota. Studies have shown that silver diamine fluoride (SDF) is an effective agent to arrest and prevent dental caries due to its mineralizing and antibacterial properties. While plenty of studies have investigated the mineralizing properties, there are few studies that have examined its antibacterial effect on oral biofilm. The mechanism of SDF in arresting ECC in relation to Lactobacillus acidophilus is not investigated yet. OBJECTIVE: The purpose of this study was to evaluate the effect of SDF on the growth of Lactobacillus acidophilus and compare it to that of Chlorhexidine and to determine the minimum inhibitory concentration (MIC) of SDF on the growth of L. acidophilus HYPOTHESIS: We hypothesized that: There are significant differences in the inhibitory effect on the growth of L. acidophilus among SDF, Chlorhexidine (positive control), Fluoride varnish and Phosphate Buffered Saline (PBS: negative control) groups. Null hypothesis: There are no significant differences in the inhibitory effect on the growth of L. acidophilus among SDF, Fluoride varnish, Chlorhexidine (positive control), and Phosphate Buffered Saline (PBS: negative control) groups. MATERIALS AND METHODS: The antibacterial effect of the tested groups was determined using both disk diffusion assay and minimum inhibitory concentration (MIC) assay. In the disc diffusion assay, SDF (38%), fluoride varnish (5%), Chlorhexidine (0.12%, positive control) and PBS (negative control) were applied to a paper disc placed on the deMan, Rogosa, and Sharpe Agar (MRSA) plate on which low concentration (invisible level) of L.acidophilus was evenly spread (1×106 CFU/ml) After incubation at 37°C in anaerobic condition for 24 hours, the diameter of the inhibition zone around each disc was measured with a digital caliper. In MIC assay, the minimum inhibitory concentration of SDF (38%) and Chlorhexidine (0.12%, positive control group) were tested by the exposure of L. acidophilus of 1 × 106 CFU/ml concentration in a 96-well plate to the serial dilutions of the respective reagent. After incubation at 37°C in anaerobic condition for 24 hours, the relative amount of L. acidophilus grown in the 96-well plate was measured using a plate reader and the minimum concentration of reagent that inhibited the growth of L. acidophilus was determined. In the disc diffusion assay, the experiment was performed in quadruplicates and repeated three times. A general linear model (ANOVA) was employed for statistical analysis. In MIC assay, the minimum inhibitory concentration percentage of each material’s original concentration was calculated. RESULTS: SDF (38%) demonstrated a significantly higher inhibitory effect (P < .001) against L. acidophilus growth compared to Chlorhexidine. However, fluoride varnish showed slight inhibitory effect and PBS showed no inhibitory effect on the growth of L. acidophilus. MIC of SDF was 0.003% of its original concentration, compared to 0.0001% of that for Chlorhexidine suggesting that chlorhexidine has more effect even at lower concentration than antibacterial effect mediated by SDF. CONCLUSION: This study, for the first time, demonstrated the inhibitory effect of SDF on the growth of L. acidophilus, indicating that SDF possesses antibacterial property, which would be translated into the novel approach in arresting ECC associated with L. acidophilus. This study allows a better understanding of the SDF effect in arresting ECC and discovers a new beneficial mechanism of SDF, in addition to its known mechanisms.

Disciplines

Dentistry

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