Faculty Bibliography

There are suggestions that the phylogeny of Streptococcus mutans, a member of the human indigenous biota that is transmitted mostly mother to child, might parallel the evolutionary history of its human host. The relatedness and phylogeny of plasmid-containing strains of S. mutans were examined based on chromosomal DNA fingerprints (CDF), a hypervariable region (HVR) of a 5.6-kb plasmid, the rRNA gene intergenic spacer region (IGSR), serotypes, and the genotypes of mutacin I and II. Plasmid-containing strains were studied because their genetic diversity was twice as great as that of plasmid-free strains. The CDF of S. mutans from unrelated human hosts were unique, except those from Caucasians, which were essentially identical. The evolutionary history of the IGSR, with or without the serotype and mutacin characters, clearly delineated an Asian clade. Also, a continuous association with mutacin II could be reconstructed through an evolutionary lineage with the IGSR, but not for serotype e. DNA sequences from the HVR of the plasmid produced a well-resolved phylogeny that differed from the chromosomal phylogeny, indicating that the horizontal transfer of the plasmid may have occurred multiple times. The plasmid phylogeny was more congruent with serotype e than with mutacin II evolution, suggesting a possible functional correlation. Thus, the history of this three-tiered relationship between human, bacterium, and plasmid supported both coevolution and independent evolution.

The determination of the composition of the microbial community in the oral cavity is usually based on cultivation methods; however, nearly half of the bacteria in the saliva and the dental plaque are not cultivable. In this study, we evaluated the difference in oral microbial diversity between children with severe early-childhood caries (S-ECC) and caries-free (CF) controls by means of a cultivation-independent approach called denaturing gradient gel electrophoresis (DGGE). Pooled dental plaque samples were collected from 20 children aged 2 to 8 years. Total microbial genomic DNA was isolated from those subjects, and a portion of the 16S rRNA gene locus was PCR amplified by using universal primers. We observed that the mean species richness of the bacterial population was greater in the CF children (n = 12) (42 +/- 3.7) than in the S-ECC children (n = 8) (35 +/- 4.3); the difference was statistically significant (P = 0.005). The overall diversity of plaque samples as measured by the Shannon index was 3.5 for the S-ECC group and 3.7 for the CF group (P = 0.004). Differences in DGGE profiles were distinguished on the basis of a cluster analysis. Sequence analysis of excised DGGE bands consisted of 2.7 phylotypes, on average. After adjusting for the number of observed bands, we estimated that the S-ECC group exhibited 94.5 total phylotypes and that the CF group exhibited 113.4. These results suggest that the microbial diversity and complexity of the microbial biota in dental plaque are significantly less in S-ECC children than in CF children.

For nearly a century, lactobacilli (LB) in the oral cavity have been generally associated with dental caries. Here, we characterized the LB isolated from the saliva of 6 women with active caries using genetic-based taxonomical identification methods. From each subject, 30 isolates growing on Rogosa medium and presumed to be LB were analyzed. Of the 180 isolates, 176 were further characterized by biotyping, DNA melting points, DNA chromosomal fingerprinting, genotyping, and phylogenetic cluster assessment. We found a total of 30 unique genotypes of LB in the saliva of caries-active women, with each woman harboring between 2 and 8 distinct genotypes. Although Lactobacillus vaginalis, L. fermentum, and L. salivarius were found in 4 of 6 of the subjects, results from other studies using comparable methods show an entirely different array of LB associated with caries. These collective observations lead us to surmise that LB associated with dental caries are likely exogenous and opportunistic colonizers, arising from food or other reservoirs outside the oral cavity.

BACKGROUND/AIMS: Clinical evaluation of oral microbial reduction after a standard prophylactic treatment has traditionally been based on bacterial cultivation methods. However, not all microbes in saliva or dental plaque can be cultivated. Polymerase chain reaction-based denaturing gradient gel electrophoresis (PCR-DGGE) is a cultivation-independent molecular fingerprinting technique that allows the assessment of the predominant bacterial species present in the oral cavity. This study sought to evaluate the oral microbial changes that occurred after a standard prophylactic treatment with a conventional oral care product using PCR-DGGE. METHODS: Twelve healthy adults participated in the study. Pooled plaque samples were collected at baseline, 24 h after prophylaxis (T1), and 4 days after toothbrushing with fluoride toothpaste (T4). The total microbial genomic DNA of the plaque was isolated. PCR was performed with a set of universal bacterial 16S rDNA primers. The PCR-amplified 16S rDNA fragments were separated by DGGE. The effects of the treatment and of dental brushing were assessed by comparing the PCR-DGGE fingerprinting profiles. RESULTS: The mean numbers of detected PCR amplicons were 22.3 +/- 6.1 for the baseline group, 13.0 +/- 3.1 for the T1 group, and 13.5 +/- 4.3 for the T4 group; the differences among the three groups were statistically significant (P < 0.01). The study also found a significant difference in the mean similarities of microbial profiles between the baseline and the treatment groups (P < 0.001). CONCLUSION: PCR-based DGGE has been shown to be an excellent means of rapidly and accurately assessing oral microbial changes in this clinical study

AIM: To prospectively determine the incidence of nickel-titanium rotary instrument fracture in an endodontic clinical practice setting. METHODOLOGY: Eleven second year endodontic residents, using four nickel-titanium rotary instrument systems (ProFile, ProTaper, GTRotary and K3Endo) according to the recommendations of the manufacturers, instrumented 3181 canals in 1403 teeth of 1235 patients, in a dental school post-graduate endodontic clinic, in 1 year. The incidence of instrument fracture was determined based on the number of instruments used. When fracture occurred, data were collected concerning the type, size, taper and prior use of the fractured instruments, the length and location of the fragment within the root canal and the curvature of the canal. RESULTS: The overall incidence of instrument fracture was 0.39%. The incidence of fracture for ProFile, ProTaper, GTRotary and K3Endo files was 0.28%, 0.41%, 0.39% and 0.52%, respectively. There was no statistically significant difference between instrument systems. The percentage of teeth in which instruments fractured was 1.9% (0.28% for anterior teeth, 1.56% for pre-molars and 2.74% for molars). A total of 26 instruments fractured, of which 23 had tapers of 0.06 or greater. Most of the fragments were located in the apical third of the root canal, and both the median and mode amongst the fragment lengths were 2 mm. CONCLUSIONS: The low incidence of nickel-titanium rotary instrument fracture supports the continued use of these instruments in root canal treatment

S. mutans plays a key role in dental caries. The extent to which perinatal events influence the acquisition of S. mutans is unclear. We hypothesized that several maternal factors, including the mode of delivery, influence the initial acquisition of S. mutans in infants. A prospective cohort study was conducted in 156 mother-infant pairs. The study found that maternal gestational age (p = 0.04), S. mutans level (p = 0.02), caries score (p = 0.02), sexually transmitted disease (STD) infection experience (p = 0.01), and family income (p = 0.03) had significant effects on the acquisition of S. mutans. Among infants who became infected, those delivered by Caesarean section acquired S. mutans 11.7 mos earlier than did vaginally delivered infants (p = 0.038). C-section infants harbored a single genotype of S. mutans that was identical to that of their mothers (100% fidelity). Analysis of the data demonstrated the possible perinatal influences on infants' acquisition of a member of the cariogenic microbiota, and its potential effect on caries outcome.

Using DNA subtractive hybridization, 49 unique gene segments were identified from a strain of Streptococcus mutans that was isolated from a patient with severe early childhood caries (S-ECC). Further hybridization with DNA from other S. mutans strains isolated from both caries-active and caries-free subjects yielded five unique sequences of DNA common to strains associated with S-ECC.

Polymicrobial biofilms in the human oral cavity exhibit marked diversity. PCR-based denaturing gradient gel electrophoresis (PCR-DGGE) surveys microbial diversity by displaying PCR-generated 16S rDNA fragments that migrate at different distances, reflecting the differences in the base-pair (i.e., % G+C) composition of the fragment. This study examined DGGE-generated diversity profiles of cultivable bacteria from individuals with different caries status. Initially, we developed a set of PCR-DGGE running conditions appropriate to oral bacteria. Next, we assessed migration standards from known oral bacterial reference strains. To test the methods, we profiled 20 bacterial saliva samples cultivated from young adults. The study produced a battery of species-specific 16S rDNA amplicons that could be used as a migration distance standard necessary for computer-assisted profile analysis. From the clinical samples, we found a significantly greater diversity of oral microbes in caries-free individuals compared with caries-active individuals (P = 0.01). These findings suggest thtat a portion of oral microbiota of caries-active individuals may be absent, suppressed, or replaced.

By definition, dental caries is an infectious and transmissible disease because it is caused by bacteria colonizing the tooth surfaces. Unlike most infectious diseases affecting humans, caries is the result of an imbalance of the indigenous oral biota rather than a nonindigenous, exogenous pathogen. The introduction of refined sugar into modern society's diet has tipped the balance from health to disease. New insight into the natural history of the leading cariogenic bacteria, the mutans streptococci, may contribute ways to control or prevent this infectious disease. Here, we use the host-parasite model as a platform for viewing the pathogenicity of the caries process in contrast to other infectious diseases.

BACKGROUND: Gravida's poor periodontal health is emerging as a modifiable independent risk factor for preterm delivery and low birth weight. METHODS: To test the hypothesis that oral bacteria other than periodontal pathogens are also associated with pregnancy outcomes, specific oral bacterial levels measured during pregnancy were evaluated in relation to gestational age and birth weight while controlling for demographic, medical, and dental variables. The study population consisted of 297 predominantly African- American women who were pregnant for the first time. The salivary bacterial levels evaluated were Streptococcus mutans, Streptococcus sobrinus, Streptococcus sanguinus, Lactobacillus acidophilus, Lactobacillus casei, Actinomyces naeslundii genospecies (gsp) 1 and 2, total streptococci, and total cultivable organisms. RESULTS: For 1 unit increase in log(10) A. naeslundii gsp 2 levels, there was a 60 gm decrease in birth weight (beta = -59.7 g; SE = 29.1; P = 0.04), and a 0.17 week decrease in gestational age (beta = -0.17 wk; SE = 0.09; P = 0.05). In contrast, per 1 unit increase in log(10) L. casei levels, there was a 42 gm increase in birth weight (beta = 42.2 g; SE = 19.3; P = 0.03), and a 0.13 week increase in gestational age (beta = 0.13 week; SE = 0.06; P = 0.04). CONCLUSIONS: We conclude that other oral bacterial species can also be related to pregnancy outcomes in addition to previously reported periodontal pathogens. These organism levels may not only predict poor pregnancy outcomes, but also be used as modifiable risk factors in reducing prematurity and low birth weight.