The rnc Gene Promotes Exopolysaccharide Synthesis and Represses the vicRKX Gene Expressions via MicroRNA-Size Small RNAs in Streptococcus mutans.

Dental caries is a biofilm-dependent disease that largely relies on the ability of Streptococcus mutans to synthesize exopolysaccharides. Although the rnc gene is suggested to be involved in virulence mechanisms in many other bacteria, the information regarding it in S. mutans is very limited. Here, using deletion or overexpression mutant assay, we demonstrated that rnc in S. mutans significantly positively regulated exopolysaccharide synthesis and further altered biofilm formation. Meanwhile, the cariogenecity of S. mutans was decreased by deletion of rnc in a specific pathogen-free (SPF) rat model. Interestingly, analyzing the expression at mRNA level, we found the downstream vic locus was repressed by rnc in S. mutans. Using deep sequencing and bioinformatics analysis, for the first time, three putative microRNA-size small RNAs (msRNAs) targeting vicRKX were predicted in S. mutans. The expression levels of these msRNAs were negatively correlated with vicRKX but positively correlated with rnc, indicating rnc probably repressed vicRKX expression through msRNAs at the post-transcriptional level. In all, the results present that rnc has a potential role in the regulation of exopolysaccharide synthesis and can affect vicRKX expressions via post-transcriptional repression in S. mutans. This study provides an alternative avenue for further research aimed at preventing caries.

Cone-beam computed tomography study of root and canal morphology of mandibular premolars in a western Chinese population.

BACKGROUND: Traditional radiography is limited in its ability to give reliable information on the number and morphology of root canals. The application of cone-beam computed tomography (CBCT) provides a non-invasive three-dimensional confirmatory diagnosis as a complement to conventional radiography. The aim of this study was to evaluate the root and canal morphology of mandibular premolars in a western Chinese population using CBCT scanning. METHODS: The sample included 149 CBCT images comprising 178 mandibular first premolars and 178 second premolars. The tooth position, number of roots and canals, and canal configuration according to Vertucci's classification were recorded. RESULTS: The results showed that 98% of mandibular first premolars had one root and 2% had two roots; 87.1% had one canal, 11.2% had two canals and 0.6% had three canals. The prevalence of C-shaped canals was 1.1%. All mandibular second premolars had one root; 97.2% had one canal and 2.2% had two canals. The prevalence of C-shaped canals was 0.6%. CONCLUSIONS: The prevalence of multiple canals in mandibular first premolars was mainly of Type V, and mandibular second premolars had a low rate of canal variation in this western Chinese population. Root canal bifurcation occurred at the middle or apical third in most bicanal mandibular premolars. CBCT scanning can be used in the management of mandibular premolars with complex canal morphology.

The effect of a manual instrumentation technique on five types of premolar root canal geometry assessed by microcomputed tomography and three-dimensional reconstruction.

BACKGROUND: Together with diagnosis and treatment planning, a good knowledge of the root canal system and its frequent variations is a necessity for successful root canal therapy. The selection of instrumentation techniques for variants in internal anatomy of teeth has significant effects on the shaping ability and cleaning effectiveness. The aim of this study was to reveal the differences made by including variations in the internal anatomy of premolars into the study protocol for investigation of a single instrumentation technique (hand ProTaper instruments) assessed by microcomputed tomography and three-dimensional reconstruction. METHODS: Five single-root premolars, whose root canal systems were classified into one of five types, were scanned with micro-CT before and after preparation with a hand ProTaper instrument. Instrumentation characteristics were measured quantitatively in 3-D using a customized application framework based on MeVisLab. Numeric values were obtained for canal surface area, volume, volume changes, percentage of untouched surface, dentin wall thickness, and the thickness of dentin removed. Preparation errors were also evaluated using a color-coded reconstruction. RESULTS: Canal volumes and surface areas were increased after instrumentation. Prepared canals of all five types were straightened, with transportation toward the inner aspects of S-shaped or multiple curves. However, a ledge was formed at the apical third curve of the type II canal system and a wide range in the percentage of unchanged canal surfaces (27.4-83.0%) was recorded. The dentin walls were more than 0.3 mm thick except in a 1 mm zone from the apical surface and the hazardous area of the type II canal system after preparation with an F3 instrument. CONCLUSIONS: The 3-D color-coded images showed different morphological changes in the five types of root canal systems shaped with the same hand instrumentation technique. Premolars are among the most complex teeth for root canal treatment and instrumentation techniques for the root canal systems of premolars should be selected individually depending on the 3-D canal configuration of each tooth. Further study is needed to demonstrate the differences made by including variations in the internal anatomy of teeth into the study protocol of clinical RCT for identifying the best preparation technique.

[Prevalence of tooth erosion of 5-year-old and 12-year-old children in Xuzhou city].

OBJECTIVE: To investigate the prevalence of tooth erosion of Xuzhou city's children. METHODS: The stratified, cluster and random sampling methods were performed. The prevalence of tooth erosion of 1,219 5-year-old children and 786 12-year-old children in Xuzhou city were examined by one qualified dentist. The results of clinical examination were recorded by schedule table. The risk factors of tooth erosion were investigated by questionnaire and analyzed by Logistic regression model. RESULTS: In 5-year-old children group, the prevalence of tooth erosion was 10.91%. In 12-year-old children group, the prevalence of tooth erosion was 22.14%. The ranking of tooth erosion were mostly class 1 and class 2. The tooth erosions of class 3 and above were rare. The odds rations for tooth erosion were: Acidic fruits, 1.120; acidophilous milk, 1.062; sport drinks, 1.159; carbonated drinks, 1.151; fruit juice, 1.187; drinking acidic drinks or acidophilous milk before sleeping, 6.102; gastroesophageal reflux disease, 2.311; vitamin C, 1.565; supply chalybeate, 1.598. CONCLUSION: The prevalence of tooth erosions in Xuzhou is extensive. Oral health education and drink and food guidance should be strengthened. The amount and frequency of intake of acidic food and drink should be reduced to promote oral health.

[Comparative effects of essential oil-containing mouthrinse on reduction of plaque and gingivitis].

PURPOSE: The purpose of this study was to determine the efficacy of reducing plaque and gingivitis when used as an adjunct to normal oral hygiene routine and regular professional care. METHODS: Eighty-two adult subjects were enrolled into a 6-month, double-blind, controlled parallel-designed clinical study. After being scaled and polished, they were randomized into two groups: essential oil-containing mouthrinse group and placebo mouthrinse group. Everyone rinsed twice a day for 6 months with 20 mL mouthrinse. The subjects were provided with a soft nylon toothbrush and fluoride toothpaste and were asked not to use any other mouthrinse during the study. At baseline and at 3- and 6-month, subjects were evaluated for supragingival plaque and gingivitis. SPSS 13.0 software package was used for statistical analysis(student's t test). RESULTS: At 3- month, the essential oil-containing mouthrinse significantly produced a 9.02% inhibition of supragingival plaque development and a 11.88% inhibition of gingivitis development compared with the control group. At 6-month, the essential oil-containing mouthrinse significantly produced a 16.98% inhibition of supragingival plaque development and a 21.47% inhibition of gingivitis development compared with the control group. CONCLUSION: The essential oil-containing mouthrinse demonstrates a significant reduction in dental plaque, gingivitis and enhances overall gingival health compared with using placebo rinse.

[Prevalence of deciduous tooth caries in 780 children aged 5 years].

OBJECTIVE: The aim of this survey was to obtain some information about the prevalence of deciduous tooth caries of 5-year-old children in Sichuan province. METHODS: Based on World Health Organization and national oral health survey standards, dental caries prevalence and treatment needs were investigated randomly in selected children of Sichuan province in 2005. And the differences between this survey result and the dental caries prevalence of 5-year-old children of Sichuan province in 1995 were compared. RESULTS: The prevalence rate of deciduous tooth caries of 5-year-old children in Sichuan province was 58.72%. The mean number of dmft of 5-year-old was 2.77. The filling rate was only 2.32%. The prevalence rate and mean dmft of deciduous tooth caries showed no significant difference between different area and gender; but the children came from city showed significant higher filling rate than those from countryside, so did the female children compared with the male children. Compared these results with the dental caries of 5-year-old children in Sichuan province in 1995, the prevalence rate and mean dmft of deciduous tooth caries in Sichuan province in 2005 had no significant difference, but the filling rate decreased significantly. CONCLUSION: The deciduous tooth caries prevalence rate of 5-year-old children is still relatively high in Sichuan province; there remains a proportion of active untreated decays. The dental health care education to the parents and teachers should be emphasized. In order to get the earlier diagnosis and treatment, regular examination and prevention method should be conducted.