Phenotypic heterogeneity of Streptococcus mutans in dentin

Microbiological and SEM assessment of atraumatic restorative treatment in adult dentition

OBJECTIVES

To investigate the practicability of atraumatic restorative treatment (ART) in adults in terms of marginal adaptation of restorations and microbiological changes in residual carious dentin.

MATERIALS AND METHODS

The occlusal dentin caries of 25 permanent molar teeth were removed with hand instruments. The total counts of bacteria (TCB) and the facultative anaerobic bacteria (FAB), mutans streptococci (MS), and Lactobacillus spp. (LB) counts in the affected dentin were evaluated quantitatively. The weights of the samples were measured with an electronic balance (Shimadzu, Type AX200, Japan). The cavities were restored with glass ionomer cement (Ketac^TM Molar Easymix, ESPE Dental AG, Seefeld, Germany). Twenty replicas of randomly selected ART restorations were prepared and marginal adaptation was evaluated by scanning electron microscopy (SEM). After 6 months, the same protocols were repeated. Data were analyzed with paired sample t-tests, Wilcoxon t-tests, Pearson and Spearman correlations, and chi-square tests (p<0.05).

RESULTS

In the sixth month, restoration loss and pulpitis were not observed. The mean weight of samples removed from the cavity floor was less than the baseline (0.014±0.009 and 0.023±0.013 g, respectively) (p<0.01), and the counts of total bacteria, FAB, MS, and LB significantly decreased compared to baseline (p<0.01). The frequency of marginal gaps was increased (p< 0.01).

CONCLUSIONS

ART showed that the counts of microorganisms decreased after 6 months although the marginal gap rates of restorations increased.

CLINICAL RELEVANCE

ART can be a reliable treatment approach in adults for 6 months due to the decrease in microorganism counts, although gaps exist.

Usefulness of matrix-assisted laser desorption ionization/time of flight mass spectrometry for the identification of Streptococcus mutans

This study evaluated the reliability of MALDI-TOF MS coupled with statistical tools for the identification of Streptococcus mutans in comparison with PCR-based techniques. Bacterial isolates were identified and serotyped by conventional PCR, using S. mutans species and serotype-specific primers. For bacterial identification, mass spectra data from S. mutans and other streptococci were compared with Biotyper V 3.1 database and the mass peak lists were examined by cluster and principal component (PCA) analysis. Identification of potential biomarkers was performed using UniProtKB/Swiss-Prot and UniProtKB/TrEMBL databases and BLAST tool of the NCBI database. PCR identified 100% of the isolates as S. mutans. S. mutans strains were typed as serotypes c (85.6%), e (8.6%), k (4.8%), and f (0.9%). Although only the 70% of the strains tested were identified at species level by the Biotyper database, PCA and cluster analysis of mass peaks allowed the identification of 100% S. mutans isolates and its differentiation from the other oral and non-oral streptococci. One mass peak at m/z value of 9572.73 was identified as species-specific biomarker for S. mutans. No biomarkers were identified for S. mutans serotypes. KEY POINTS: • MALDI-TOF MS coupled with statistical tools for the identification of S. mutans. • Detection of species identifying biomarkers by MALDI-TOF MS. • PCR identification and serotyping of S. mutans from saliva samples.

Self-Limiting versus Rotary Subjective Carious Tissue Removal: A Randomized Controlled Clinical Trial-2-Year Results

Background: the aim of this study was to assess the 2-year pulp survival of deep carious lesions in teeth excavated using a self-limiting protocol in a single-blind randomized controlled clinical trial. Methods: At baseline, 101 teeth with deep carious lesions in 86 patients were excavated randomly using self-limiting or control protocols. Standardized clinical examination and periapical radiographs of teeth were performed after 1- and 2-year follow-ups (REC 14/LO/0880). Results: During the 2-year period of the study, 24 teeth failed (16 and 8 at T12 and T24, respectively). Final analysis shows that 39/63 (61.9%) of teeth were deemed successful (16/33 (48.4%) and 23/30 (76.6%) in the control and experimental groups, respectively with a statistically significant difference (z score = 2.3, p = 0.021). Of teeth with severe and mild symptoms at T0, 42.9% and 36.7% respectively failed at T24 (p > 0.05). Within the self-limiting group, there was a lower success in premolars compared to molars (p < 0.05). Conclusion: after 2 years, there was a statistically significant higher pulp survival rate of teeth with deep carious lesions excavated using self-limiting protocols in patients with reversible pulpitis. Molars showed higher success than premolars in teeth excavated using the self-limiting protocol. There was no statistically significant association between the outcome and the severity of symptoms at T0 (ClinicalTrials.gov NCT03071588).

Morphological identification of Streptococcus mutans and Streptococcus sobrinus in SB-20M culture medium has efficiency comparable to proteomic identification by the MALDI-TOF mass spectrometry technique

OBJECTIVES

The objective of this study was to evaluate the efficiency of SB-20 M culture medium to perform differential morphological identification of S. mutans and S. sobrinus compared to biochemical identification and to proteomic identification by the MALDI-TOF mass spectrometry technique.

MATERIAL AND METHODS

Unstimulated saliva samples from 266 dental students were seeded on SB-20 M culture medium by the wooden spatula technique. After incubation, S. mutans and S. sobrinus colonies were identified by stereomicroscopy based on their differential morphological characteristics. Following these procedures, 135 colonies with characteristic morphology of S. mutans (89 colonies) and S. sobrinus (46 colonies) were randomly selected, submitted to biochemical identification (biotyping) and proteomic identification by the MALDI-TOF mass spectrometry technique. The results were compared using the Kappa test, with a 5% significance level.

RESULTS

All (100%) S. mutans colonies were correctly identified after culture in SB-20 M medium compared to biotyping and proteomic identification. For S. sobrinus, morphological identification in SB-20 M medium was correct for 43 colonies (93.5%) compared to biotyping and proteomic identification. However, there was no statistically significant difference when comparing the capacity to identify S. mutans and S. sobrinus of the three techniques (p < 0.001; K = 0.951).

CONCLUSIONS

It was concluded that the SB-20 M culture medium for morphological identification of S. mutans and S. sobrinus was highly reliable, being comparable to the MALDI-TOF mass spectrometry technique.

CLINICAL RELEVANCE

The efficiency evaluation of identification methods of S. mutans and S. sobrinus is clinically relevant in order to determine caries risk and activity of patients.

Killing of adherent oral microbes by a non-thermal atmospheric plasma jet

Atmospheric plasma jets are being intensively studied with respect to potential applications in medicine. The aim of this in vitro study was to test a microwave-powered non-thermal atmospheric plasma jet for its antimicrobial efficacy against adherent oral micro-organisms. Agar plates and dentin slices were inoculated with 6 log(10) c.f.u. cm(-2) of Lactobacillus casei, Streptococcus mutans and Candida albicans, with Escherichia coli as a control. Areas of 1 cm(2) on the agar plates or the complete dentin slices were irradiated with a helium plasma jet for 0.3, 0.6 or 0.9 s mm(-2), respectively. The agar plates were incubated at 37 degrees C, and dentin slices were vortexed in liquid media and suspensions were placed on agar plates. The killing efficacy of the plasma jet was assessed by counting the number of c.f.u. on the irradiated areas of the agar plates, as well as by determination of the number of c.f.u. recovered from dentin slices. A microbe-killing effect was found on the irradiated parts of the agar plates for L. casei, S. mutans, C. albicans and E. coli. The plasma-jet treatment reduced the c.f.u. by 3-4 log(10) intervals on the dentin slices in comparison to recovery rates from untreated controls. The microbe-killing effect was correlated with increasing irradiation times. Thus, non-thermal atmospheric plasma jets could be used for the disinfection of dental surfaces.