Objective:To explore the application prospect of a new pH-responsive tertiary amine monomer dodecylmethylaminoethyl methacrylate (DMAEM) modified resin adhesive (DMAEM@RA) in the prevention and treatment of secondary caries.Methods:Five percents DMAEM was added to the resin adhesive to synthesize DMAEM@RA for modifying. Streptococcus mutans (Sm) and Lactobacillus casei (Lc) biofilms were cultured on resin adhesive and DMAEM@RA, respectively. The culture systems were set up at pH=7.4, 6.0, 5.5, and 5.0. The antimicrobial activity of DMAEM@RA was evaluated by quantitative PCR. The effects of DMAEM@RA on biofilm thickness, bacterial amount, and extracellular polysaccharides were studied by scanning electron microscope (SEM) and extracellular polysaccharide staining. Real-time fluorescence quantitative PCR was used to study the effect of DMAEM@RA on the expression levels of cariogenic genes in Sm. Results:DMAEM@RA could significantly reduce the amount of Sm and Lc under acidic conditions, especially Lc. At pH=5.0, the logarithm value of co-cultured Sm bacteria [lg (CFU/ml)] in DMAEM@RA group (7.58±0.01) was significantly lower than that in control group (7.87±0.03) ( t=14.32, P<0.001), and the logarithm value of Lc bacteria [lg (CFU/ml)] (7.29±0.04) was also significantly lower than that in control group (7.93±0.15) ( t=6.93, P=0.002). SEM observed that the bacteria decreased and the cell fragments appeared in DMAEM@RA group. In addition, DMAEM@RA significantly reduced the biomass of extracellular polysaccharides in the dual-species biofilm under acidic conditions. At pH=5.0, the biomass of extracellular polysaccharides in DMAEM@RA group [(25.13±3.14) mm 3/mm 2] was significantly lower than that in the control group [(42.66±7.46) mm 3/mm 2] ( t=3.75, P=0.020). DMAEM@RA could significantly up-regulate the expressions of gtfB and gtfC genes in Sm under acidic conditions. At pH=5.0, gtfB and gtfC genes were significantly up-regulated by (14.64± 0.44) times and (2.99±0.20) times, respectively ( t=-42.74, P<0.001; t=-13.55, P<0.001). Conclusions:The DMAEM@RA has a good antibacterial effect under acidic conditions, demonstrating that it has a good potential to prevent the occurrence and development of secondary caries.

Endodontic and periapical lesions are prevalent infectious diseases primarily caused by bacteria and their metabolic byproducts. The most widely used treatment method today is root canal therapy, which aims to remove infectious substances from the root canal. Root canal sealers can fill areas that core filling materials cannot reach, effectively reducing the risk of reinfection through their antimicrobial properties thus improving the success rate of root canal treatment. Various strategies have been employed to enhance the antimicrobial efficacy of root canal sealers through different mechanisms such as mechanical interlocking or chemical bonding. These strategies include antibiotic modification, quaternary ammonium compounds modification, nanoparticle modification, and others. Overall, antimicrobial modification strategies are increasingly diverse, and their effectiveness in enhancing the antimicrobial properties of sealers is beyond doubt. Root canal sealers modified with quaternary ammonium compounds and nanoparticles have shown certain advantages in antibiofilm activity and have potential clinical prospects. However, whether these modified materials have long-term antimicrobial effects, whether they can perform similarly in vivo as they do in vitro, and their biocompatibility are issues that still need to be addressed. In the future, the preparation of root canal sealers with ideal multidimensional properties will require further long-term and in-depth exploration.

The oral microbiota is associated with oral diseases and digestive systemic diseases. Nevertheless, the causal relationship between them has not been completely elucidated, and colonisation of the gut by oral bacteria is not clear due to the limitations of existing research models. The aim of this study was to develop a human oral microbiota-associated (HOMA) mouse model and to investigate the ecological invasion into the gut. By transplanting human saliva into germ-free (GF) mice, a HOMA mouse model was first constructed. 16S rRNA gene sequencing was used to reveal the biogeography of oral bacteria along the cephalocaudal axis of the digestive tract. In the HOMA mice, 84.78% of the detected genus-level taxa were specific to the donor. Principal component analysis (PCA) revealed that the donor oral microbiota clustered with those of the HOMA mice and were distinct from those of specific pathogen-free (SPF) mice. In HOMA mice, OTU counts decreased from the stomach and small intestine to the distal gut. The distal gut was dominated by Streptococcus, Veillonella, Haemophilus, Fusobacterium, Trichococcus and Actinomyces. HOMA mice and human microbiota-associated (HMA) mice along with the GF mice were then cohoused. Microbial communities of cohoused mice clustered together and were significantly separated from those of HOMA mice and HMA mice. The Source Tracker analysis and network analysis revealed more significant ecological invasion from oral bacteria in the small intestines, compared to the distal gut, of cohoused mice. In conclusion, a HOMA mouse model was successfully established. By overcoming the physical and microbial barrier, oral bacteria colonised the gut and profiled the gut microbiota, especially in the small intestine.
Animals ; Bacteria ; Gastrointestinal Microbiome ; Germ-Free Life ; Humans ; Mice ; Microbiota ; RNA, Ribosomal, 16S