摘要目的:探索pH响应性新型叔胺单体（DMAEM）改性树脂粘接剂（DMAEM@RA）防治继发龋的应用前景。方法:按粘接剂改性的方法，向树脂粘接剂中添加5%DMAEM，改性合成DMAEM@RA。以变异链球菌（Sm）和干酪乳杆菌（Lc）双菌种生物膜为研究模型，分别在树脂粘接剂（对照组）和DMAEM@RA（DMAEM@RA组）上进行培养。分别设置pH值为7.4、6.0、5.5和5.0的培养体系。通过定量PCR分析菌量，通过扫描电镜和胞外多糖染色分析DMAEM@RA对双菌种生物膜表型、菌量及胞外多糖的影响。实时荧光定量PCR研究DMAEM@RA对Sm致龋毒力基因的影响。结果:DMAEM@RA在酸性条件下可显著降低Sm和Lc的菌量，特别是Lc。pH=5.0时，DMAEM@RA组共培养Sm菌量对数值［lg（CFU/ml）］（7.58 ±0.01）显著低于对照组（7.87 ±0.03）（ t=14.32， P<0.001），Lc菌量对数值［lg（CFU/ml）］（7.29 ±0.04）亦显著低于对照组（7.93 ±0.15）（ t=6.93， P=0.002）。扫描电镜下也可观察到DMAEM@RA组菌量减少，同时有细胞碎片出现。此外，DMAEM@RA可在酸性条件下显著减少双菌种生物膜的胞外多糖生物量，pH=5.0时DMAEM@RA组胞外多糖生物量值［（25.13± 3.14）mm 3/mm 2］显著低于对照组［（42.66 ±7.46）mm 3/mm 2］（ t=3.75， P=0.020）。DMAEM@RA可在酸性条件下显著上调Sm的gtfB、gtfC基因表达，pH=5.0时gtfB、gtfC基因分别显著上调（14.64 ±0.44）和（2.99 ±0.20）倍（ t=-42.74， P<0.001； t=-13.55， P<0.001）。 结论:DMAEM@RA在酸性条件下有较好的抑菌作用，具有防治继发龋发生发展的良好潜力。

abstractsObjective: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.