Student Theses, Dissertations and Capstones

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Dentistry

Copyright Statement

All rights reserved. This publication is intended for use solely by faculty, students, and staff of Nova Southeastern University. No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, now known or later developed, including but not limited to photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author or the publisher.

Department

College of Dental Medicine

First Advisor

Toshihisa Kawai

Second Advisor

Judith Chin

Third Advisor

Sibel Antonson

Publication Date / Copyright Date

2020

Publisher

Nova Southeastern University

Abstract

BACKGROUND: Early childhood caries (ECC) is one of the most prevalent infectious diseases in childhood worldwide. It afflicts 23% of the preschoolers in the U.S. It most frequently targets children from poor socioeconomic families and racial/ethnic minority backgrounds and becomes a serious public health problem. The major pathogen of ECC is Streptococcus mutans (S. mutans). However, the occurrence of ECC is positively associated with the presence of Candida albicans (C. albicans). It is well established that Silver Diamine Fluoride (SDF), a recent Food and Drug Administration (FDA)-off labeled approved agent for arresting dental caries, exhibits a robust antibacterial effect on S. mutans associated with ECC. Very interestingly, C. albicans has been implicated as one of the major contributing factors for the high prevalence of ECC, indicating that the reduction of C. albicans colonization in the oral cavity may suppress ECC. However, it remains elusive if SDF can also mediate an antifungal effect on C. albicans. OBJECTIVE: The purpose of this study was to evaluate the effect of SDF on the growth of C. albicans and compare it to that of fluoride varnish and fluconazole, and to determine the minimum inhibitory concentration (MIC) of SDF on the growth of C. albicans. HYPOTHESIS: We hypothesized that: There are significant differences in the inhibitory effect on the growth of C. albicans among SDF, fluoride varnish, fluconazole (positive control), and Phosphate Buffered Saline (PBS: negative control) groups. Null hypothesis: There are no significant differences in the inhibitory effect on the growth of C. albicans among SDF, fluoride varnish, fluconazole (positive control), and Phosphate Buffered Saline (PBS: negative control) groups, or SDF doesn’t possess any inhibitory effect of the growth of C. albicans. MATERIALS AND METHODS: The antifungal 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%), fluconazole (25 µg/mL, positive control) and PBS (negative control) were applied to a paper disc placed on the Mueller-Hinton agar plate on which low concentration (invisible level) of C. albicans was evenly spread (1×105/plate or 1×106/plate). After incubation at 37°C in aerobic 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 fluconazole (25 µg/mL, positive control group) were tested by the exposure of C. albicans of 1 × 105 concentration in a 96-well plate to the serial dilutions of the respective reagent. After incubation at 37°C in aerobic condition for 24 hours, the relative amount of C. albicans grown in the 96-well plate was measured using a plate reader and the minimum concentration of reagent that inhibited the growth of C. albicans was determined. In the disc diffusion assay, the experiment was performed in quadruplicates and repeated three times. A general linear model (ANOVA) followed by Tukey’s HSD test 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 C. albicans growth compared to fluconazole. However, both fluoride varnish and PBS showed no inhibitory effect on the growth of C. albicans. MIC of SDF was 0.009% of its original concentration, compared to 0.6% of that for fluconazole, suggesting that SDF has antifungal effect even at lower concentration than antifungal effect mediated by fluconazole. CONCLUSION: This study, for the first time, demonstrated the inhibitory effect of SDF on the growth of C. albicans, indicating that SDF possesses antifungal property, which would be translated into the novel approach in arresting ECC associated with C. albicans. 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

Keywords

Candid Albicans, Early childhood caries, Fluoride, SDF, Infectious diseases, Socioeconomic minority, Public health issue, Pathogen

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