Acetylation of glucosyltransferases regulates Streptococcus mutans biofilm formation and virulence

Lysine acetylation is a frequently occurring post-translational modification (PTM), emerging as an important metabolic regulatory mechanism in prokaryotes. This process is achieved enzymatically by the protein acetyltransferase (KAT) to specifically transfer the acetyl group, or non-enzymatically by direct intermediates (acetyl phosphate or acetyl-CoA). Although lysine acetylation modification of glucosyltransferases (Gtfs), the important virulence factor in Streptococcus mutans, was reported in our previous study, the KAT has not been identified. Here, we believe that the KAT ActG can acetylate Gtfs in the enzymatic mechanism. By overexpressing 15 KATs in S. mutans, the synthesized water-insoluble extracellular polysaccharides (EPS) and biofilm biomass were measured, and KAT (actG) was identified. The in-frame deletion mutant of actG was constructed to validate the function of actG. The results showed that actG could negatively regulate the water-insoluble EPS synthesis and biofilm formation. We used mass spectrometry (MS) to identify GtfB and GtfC as the possible substrates of ActG. This was also demonstrated by in vitro acetylation assays, indicating that ActG could increase the acetylation levels of GtfB and GtfC enzymatically and decrease their activities. We further found that the expression level of actG in part explained the virulence differences in clinically isolated strains. Moreover, overexpression of actG in S. mutans attenuated its cariogenicity in the rat caries model. Taken together, our study demonstrated that the KAT ActG could induce the acetylation of GtfB and GtfC enzymatically in S. mutans, providing insights into the function of lysine acetylation in bacterial virulence and pathogenicity.

Using an Optical Reflectometer to Measure Caries Lesion Activity on Enamel

Background: Specular reflection can be used to quantify dental erosion, and might also provide similar results for caries. This study assessed the possibility of using specular reflection intensity (SRI; quantitative lesion activity assessment) to measure the progression of initial enamel caries lesions. Methods: Two hundred native enamel specimens and flat ground enamel specimens (n=100 each) were subjected to a 4-species biofilm caries model during 2, 4, 6, 8, and 10 weeks (n=20 each), to induce ‘active’ enamel caries lesions. Afterwards, to induce ‘inactive’ lesions, all specimens were continuously remineralized and brushed twice daily for 2, 4, 6, 8, and 10 weeks. Change in specular reflection intensity (%SRI), visual caries detection (ICDAS) and visual caries severity assessment were performed for all active lesions and during the remineralization phase. Scanning electron microscopy (SEM) images were taken for qualitative analysis. Results: For active lesions, %SRI dropped from 100% to about 80% in native enamel, and to about 15% in polished enamel. Remineralization/brushing increased %SRI in native enamel, but not in polished enamel. The comparison with visual caries scores yielded a better linear relationship of %SRI with early enamel lesion where caries was induced for up to 6 weeks. Conclusion: The use of the optical reflectometer for the assessment of caries lesion activity seemed to work better for early caries lesions and for polished specimens.

Anti-Demineralization Effects of Dental Adhesive-Composites on Enamel–Root Dentin Junction

Oral biofilm reactor (OBR) and pH cycling (pHC) artificial caries model were employed to evaluate the anti-demineralization effects of four composite filling systems on enamel–root dentin junction. Sixty-four enamel–root dentin blocks (6 mm × 6 mm × 2 mm) each with a cylindrical cavity were randomly assigned to the pHC and OBR group, then four subgroups (n = 8) and filled with either the Beautifil II (BEF, SPRG-filler-containing) or Estelite (EST) composite after the adhesive (either Single Bond Universal (SBU) or FL Bond II (FL, SPRG-filler-containing)). The demineralization lesions of filling interface were examined by micro-computerized tomography (μCT) and swept-source-optical coherence tomography (SS-OCT). According to the degree of interface damage, the caries lesions were sorted into four types: Type A and B (no attachment loss); Type C and D (attachment loss). EST/SBU showed the worst demineralization lesion and attachment loss (100% Type D), while BEF/FL exhibited the shallowest lesion depth (p < 0.05, 145 ± 45 μm on enamel, 275 ± 35 μm on root dentin) and no attachment loss (75% Type A and 25% Type B). Using FL adhesive alone does not effectively reduce enamel demineralization. BEF plays a leading role in acid resistance. The combination of BEF and FL showed a cumulative synergistic effect on anti-demineralization.

Phage Targeting Streptococcus mutans In Vitro and In Vivo as a Caries-Preventive Modality

Dental caries is a common infectious disease worldwide. Current conventional therapies lack specific antimicrobial effects against Streptococcus mutans, a key bacterium that induces caries. A promising alternative approach is bacteriophage (phage) therapy. Recently, SMHBZ8 phage targeting S. mutans was isolated and characterized. The aim of this study was to evaluate the caries-prevention efficacy of SMHBZ8 using in vitro and in vivo caries models. Hemi-mandibles dissected from euthanized healthy mice were subjected to caries-promoting conditions in vitro. Jaws treated with phage therapy in suspension and in formulation with a sustained-release delivery system showed no carious lesions, similar to control and chlorhexidine-treated jaws. Subsequently, SMHBZ8 phage suspension also prevented carious lesion development in a murine caries model in vivo. In both models, caries lesions were analyzed clinically and radiographically by µCT scans. This study shows how SMHBZ8 phage therapy targeting S. mutans can serve as an efficient caries-prevention modality, in suspension or with a sustained-release delivery system, by in vitro and in vivo mouse models.

A Novel Dental Caries Model Replacing, Refining, and Reducing Animal Sacrifice

In vitro and in vivo models simulating the dental caries process enable the evaluation of anti-caries modalities for prevention and treatment. Animal experimentation remains important for improving human and animal health. Nonetheless, reducing animal sacrifice for research is desirable. The aim of the study was to establish a new reproducible in vitro caries model system and compare it to an in vivo model using similar conditions. Hemi-mandibles were extracted from previously euthanized healthy 10-week-old BALB/C female mice. Jaws were subjected to saliva, high-sucrose diet, and dental caries bacteria Streptococcus mutans UA159 for 5 days. Similar caries induction protocol was used in vivo in fifteen BALB/c female mice (6–7 weeks old) and compared to the in vitro model. Caries lesions were assessed clinically by photographic analysis and µCT analysis, and bacterial growth was evaluated. Under in vitro experimental conditions, carious lesions evolved within 5 days, prominently in the depth of the occlusal fissures in the control group as depicted by photographic analysis, µCT analysis, and bacterial growth. The developed in vitro caries model presented in this study may be a novel animal sparing model for caries disease studies and can be used widely to evaluate the efficacy of different antibacterial dental materials.

Core Microbiota Promotes the Development of Dental Caries

A previous longitudinal study about using microbiome as a caries indicator has successfully predicted early childhood caries (ECC) in healthy individuals, but there is no evidence to verify the composition of core microbiota and its pathogenicity in vitro and in vivo. Biofilm acidogenicity, S. mutans count, and biofilm composition were estimated by pH evaluation, colony-forming unit, and quantitative PCR, respectively. Extracellular polysaccharide production and enamel demineralization were observed by confocal laser scanning microscopy (CLSM) and transverse microradiography (TMR), respectively. A rat caries model was established for dental caries formation in vivo, and caries lesions were quantified by Keyes Scoring. We put forward that microbiota including Veillonella parvula, Fusobacterium nucleatum, Prevotella denticola, and Leptotrichia wadei served as the predictors for ECC may be the core microbiota in ECC. This study found that the core microbiota of ECC produced limited acid, but promoted growth and acidogenic ability of S. mutans. Besides, core microbiota could help to promote the development of biofilms. Moreover, the core microbiota enhanced the enamel demineralization in vitro and increased cariogenic potential in vivo. These results proved that core microbiota could promote the development of dental caries and plays an important role in the development of ECC.

Effect of Thermal Cycling Aging on the Surface Microhardness and Roughness of Resin-Infiltrated Enamel Lesions

With the widespread use of resin infiltration, its properties have drawn increasing attention. The objective of this study was to investigate the effect of resin infiltration on the surface microhardness and roughness of enamel lesions after thermal cycling aging. Tooth blocks were made from extracted premolars and placed into a control group, resin-infiltrated group or demineralized group. Before and after the aging procedure, the surface microhardness and surface roughness was measured. Before the aging procedure, the surface microhardness of the control group, resin-infiltrated group and demineralized group was 302.14 (±9.77) HV, 146.62 (±8.22) HV, and 28.85 (±2.21) HV (p 0.001), respectively. After the aging procedure, the surface microhardness of the control group, resin-infiltrated group and demineralized group decreased by 9.42%, 16.59%, and 20.75% ( p 0.001), respectively. Before the aging procedure, the surface roughness of the control group, resin-infiltrated group and demineralized group was 0.29 (±0.04) μm, 0.32 (±0.04) μm, and 0.39 (±0.07) μm (p = 0.009), respectively. After the aging procedure, the surface roughness of the control group, resin-infiltrated group and demineralized group increased by 9.85%, 8.31%, and 17.37% (p = 0.634), respectively. Resin infiltration can improve the surface microhardness and surface roughness of demineralized teeth in an artificial enamel caries model. The treatment also shows good aging resistance after thermal cycling. The infiltrant resin provided a suitable material for early enamel caries.

Caries dental: de la placa ecológica a las decisiones clínicas

Antecedentes: la caries dental ha sido estudiada desde múltiples enfoques, sin embargo, a pesar del conocimiento disponible, lograr medidas efectivas para prevenir su aparición en los individuos y las comunidades, aún parece lejano. Objetivo: integrar los cambios conceptuales actualmente aceptados para caries, con escenarios en la práctica clínica, para apoyar a los profesionales en las decisiones terapéuticas. Método: en esta revisión integrativa se consultaron PubMed, Cochrane, Science Direct, SciELO, EBSCO utilizando como palabras claves: dental caries, model, prevention, ICDAS, risk factors, risk assessment. se verificó que el objetivo de cada fuente permitiera hacer el recorrido histórico del concepto de caries identificando aspectos centrales, relacionándolos con las limitaciones para que la teoría se evidencie en la práctica clínica. Resultados: la síntesis de la literatura se presenta organizada en: evolución de la definición de la caries dental a partir del papel de las bacterias y su impacto en las decisiones clínicas, acciones para abarcar la definición actual de caries dental y acciones ajustadas al modelo ICCMS para llevarlo a la práctica. Conclusión: los cambios conceptuales en caries dental se reflejan en los diagnósticos actuales y abordajes multivariados que aun requieren fortalecer el análisis y un control efectivo de los factores de riesgo, buscando un cuidado centrado en la persona, basado en la relación entre el comportamiento de los individuos a lo largo de la vida y la dinámica de la patología, que invitan al profesional a fortalecer un abordaje preventivo para controlar la enfermedad y evitar sus secuelas discapacitantes.

Novel Nanocomposite Inhibiting Caries at the Enamel Restoration Margins in an In Vitro Saliva-Derived Biofilm Secondary Caries Model

Secondary caries often occurs at the tooth-composite margins. This study developed a novel bioactive composite containing DMAHDM (dimethylaminohexadecyl methacrylate) and NACP (nanoparticles of amorphous calcium phosphate), inhibiting caries at the enamel restoration margins in an in vitro saliva-derived biofilm secondary caries model for the first time. Four composites were tested: (1) Heliomolar nanocomposite, (2) 0% DMAHDM + 0% NACP, (3) 3% DMAHDM + 0% NACP, (D) 3% DMAHDM + 30% NACP. Saliva-derived biofilms were tested for antibacterial effects of the composites. Bovine enamel restorations were cultured with biofilms, Ca and P ion release of nanocomposite and enamel hardness at the enamel restoration margins was measured. Incorporation of DMAHDM and NACP into composite did not affect the mechanical properties (p > 0.05). The biofilms’ CFU (colony-forming units) were reduced by 2 logs via DMAHDM (p < 0.05). Ca and P ion release of the nanocomposite was increased at cariogenic low pH. Enamel hardness at the margins for DMAHDM group was 25% higher than control (p < 0.05). With DMAHDM + NACP, the enamel hardness was the greatest and about 50% higher than control (p < 0.05). Therefore, the novel composite containing DMAHDM and NACP was strongly antibacterial and inhibited enamel demineralization, resulting in enamel hardness at the margins under biofilms that approached the hardness of healthy enamel.

Evaluation of Virtual Reality Simulation of Dental Caries through Student Questionnaire

The purpose of this study was to evaluate the applicability of virtual reality simulation after experience of dental caries diagnosis for dental students before exposing to clinical pediatric practice.A pediatric patient model of a five-year-old child with primary dentition was developed and a caries model that is amenable to VR(virtual reality) diagnosis was organized and set-up. The dental student’s were allowed to use the simulated model for fifteen minutes and their experiences were evaluated using a self-reported questionnaire to evaluate presence and usability of this application.Overall, virtual presence and appearance area of the simulation were highly scored. The result indicates that the VR model has no significant difference from the actual clinical caries regardless of grade of students, gender and VR experience. If the prototype is continuously advanced, its applicability in dental education will increase.