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Advisory Committee Chair

Noel K Childers

Advisory Committee Members

Amjad Javed

Gary R Cutter

John D Ruby

Document Type

Thesis

Date of Award

2012

Degree Name by School

Master of Science in Dentistry (MScD) School of Dentistry

Abstract

Mutans streptococci (MS), e.g., Streptococcus mutans (Sm) and Streptococcus sobrinus (Ss), are associated with dental caries. Quantification of MS has been shown to predict caries risk. A new technology using PCR may streamline quantification compared to traditional culture methods. Purpose: To use real-time quantitative PCR (qPCR) and standard plate counting (SPC) for detection and quantification of levels of Sm, Ss and total streptococci (TS) in clinical samples from high-caries-risk children with no regular access to dental care and to study correlation of these bacterial levels and ratios to caries prevalence. Methods: Saliva and plaque samples were collected from school-aged children for SYBR Green based qPCR using primers specific for Sm, Ss and TS from DNA extracted compared to SPC. UA159 genomic DNA was used as standard from which "copy number" (CN/ml) of MS and TS was computed. Samples were also processed and quantified for "colony forming unit" (CFU/ml) of MS and TS using traditional plate culture. Calibrated examiners performed oral examinations (DMFT/DMFS/dmft/dmfs). Pearson's analysis and T-test assessed correlations between level of Sm and ratio of Sm to TS to caries using SAS V9.2. Results: Fifty-eight subjects (mean age=9.8 years, DMFS/dmfs=7.0) had samples collected. By qPCR Sm was detected in 98.1% of samples while SPC was 72.9%. Ss was only found in 4 qPCR samples. Mean qPCR CN/ml of samples were: Sm (2.54x106), Ss (5.27x102) and TS (2.34x109). Mean SPC CFU/ml of samples were: Sm (0.94x106), Ss (0) and TS (0.01x109). Significant correlations were found between level of Sm and ratio of Sm/TS from oral samples to prevalence of dental caries. Conclusion: levels of Sm and ratio of Sm/TS by qPCR and SPC were correlated to dental caries. Correlations between mean levels of Sm and ratio of Sm/TS to caries experience from qPCR are comparable to SPC. Given the similar correlations found, the more streamlined method of qPCR is a suitable outcome measure in epidemiological studies.

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Dentistry Commons

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