Composites containing nanoparticles of amorphous calcium phosphate (NACP) remineralize tooth lesions and inhibit caries. A recent study synthesized quaternary ammonium methacrylates (QAMs) with chain lengths (CLs) of 3–18 and determined their effects on a bonding agent. This study aimed to incorporate these QAMs into NACP nanocomposites for the first time to simultaneously endow the material with antibacterial and remineralizing capabilities and to investigate the effects of the CL on the mechanical and biofilm properties. Five QAMs were synthesized: DMAPM (CL3), DMAHM (CL6), DMADDM (CL12), DMAHDM (CL16), and DMAODM (CL18). Each QAM was incorporated into a composite containing 20% NACP and 50% glass fillers. A dental plaque microcosm biofilm model was used to evaluate the antibacterial activity. The flexural strength and elastic modulus of nanocomposites with QAMs matched those of a commercial control composite (n 5 6; P . 0.1). Increasing the CL from 3 to 16 greatly enhanced the antibacterial activity of the NACP nanocomposite (P , 0.05); further increasing the CL to 18 decreased the antibacterial potency. The NACP nanocomposite with a CL of 16 exhibited biofilm metabolic activity and acid production that were 10-fold lesser than those of the control composite. The NACP nanocomposite with a CL of 16 produced 2-log decreases in the colony-forming units (CFU) of total microorganisms, total streptococci, and mutans streptococci. In conclusion, QAMs with CLs of 3–18 were synthesized and incorporated into an NACP nanocomposite for the first time to simultaneously endow the material with antibacterial and remineralization capabilities. Increasing the CL reduced the metabolic activity and acid production of biofilms and caused a 2-log decrease in CFU without compromising the mechanical properties. Nanocomposites exhibiting strong anti-biofilm activity, remineralization effects, and mechanical properties are promising materials for tooth restorations that inhibit caries.

Dental composites are commonly used restorative materials; however, secondary caries due to biofilm acids remains a major problem. The objectives of this study were (1) to develop a composite containing quaternary ammonium dimethacrylate (QADM), nanoparticles of silver (NAg), and nanoparticles of amorphous calcium phosphate (NACP), and (2) to conduct the first investigation of the mechanical properties, biofilm response and acid production vs water-ageing time from 1 day to 12 months. A 4 × 5 design was utilized, with four composites (NACP-QADM composite, NACP-NAg composite, NACP-QADM-NAg composite, and a commercial control composite), and five water-ageing time periods (1 day, and 3, 6, 9, and 12 months). After each water-ageing period, the mechanical properties of the resins were measured in a three-point flexure, and antibacterial properties were tested via a dental plaque biofilm model using human saliva as an inoculum. After 12 months of water-ageing, NACP-QADM-NAg had a flexural strength and elastic modulus matching those of the commercial control (P40.1). Incorporation of QADM or NAg into the NACP composite greatly reduced biofilm viability, metabolic activity and acid production. A composite containing both QADM and NAg possessed a stronger antibacterial capability than one with QADM or NAg alone (Po0.05). The anti-biofilm activity was maintained after 12 months of water-ageing and showed no significant decrease with increasing time (P40.1). In conclusion, the NACP-QADM-NAg composite decreased biofilm viability and lactic acid production, while matching the load-bearing capability of a commercial composite. There was no decrease in its antibacterial properties after 1 year of water-ageing. The durable antibacterial and mechanical properties indicate that NACP-QADM-NAg composites may be useful in dental restorations to combat caries.

Antibacterial dimethylaminododecyl methacrylate (DMADDM) was recently synthesized. The objectives of this study were to:(1) investigate antibacterial activity of DMADDM-containing primer on Streptococcus mutans impregnated into dentin blocks for the first time, and (2) compare the antibacterial efficacy of DMADDM with a previous quaternary ammonium dimethacrylate (QADM). Scotchbond Multi-Purpose (SBMP) bonding agent was used. DMADDM and QADM were mixed into SBMP primer. Six primers were tested:SBMP control primer P, P+2.5%DMADDM, P+5%DMADDM, P+7.5%DMADDM, P+10%DMADDM, and P+10%QADM. S. mutans were impregnated into human dentin blocks, and each primer was applied to dentin to test its ability to kill bacteria in dentinal tubules. Bacteria in dentin were collected via a sonication method, and the colony-forming units (CFU) and inhibition zones were measured. The bacterial inhibition zone of P+10%DMADDM was 10 times that of control primer (Po0.05). CFU in dentin with P+10%DMADDM was reduced by three orders of magnitude, compared with control. DMADDM had a much stronger antibacterial effect than QADM, and antibacterial efficacy increased with increasing DMADDM concentration. Dentin shear bond strengths were similar among all groups (P40.1). In conclusion, antibacterial DMADDM-containing primer was validated to kill bacteria inside dentin blocks, possessing a much stronger antibacterial potency than the previous QADM. DMADDM-containing bonding agent was effective in eradicating bacteria in dentin, and its efficacy was directly proportional to DMADDM mass fraction. Therefore, DMADDM may be promising for use in bonding agents as well as in other restorative and preventive materials to inhibit bacteria.

Dental caries are the most prevalent chronic infections in the oral cavity,and Streptococcus mutans acts as the main cariogenic bacterial species. Antibacterial quaternary ammonium compounds (QAs) have been developed to preveFnt or treat dental caries. However, there is no report on the tolerance of S.mutans to QAs.In this study, we investigated the development of S. mutans persistence induced by a novel dental caries defensive agent, dimethylaminododecyl methacrylate (DMADDM), for the first time. Typical biphasic killing kinetics for persisters were observed in both S. mutans planktonic and biofilm cultures challenged by DMADDM at concentrations of 20 and 200 μg·mL-1,respectively. The persisters tolerated six other antibiotics with different antibacterial mechanisms, while only daptomycin and vancomycin could slightly reduce the persister numbers in planktonic cultures. The distribution of persisters in DMADDM-treated biofilms was similar to that in the untreated control, except that the total biomass and biofilm height were significantly reduced.A higher exopolysaccharides (EPS):bacteria ratio was observed in DMADDM-treated biofilms. Persisters in biofilms significantly upregulated gtf gene expression, indicating an increase in the bacteria's ability to produce EPS and an elevated capability of cariogenic virulence. Carbon source metabolism was significantly reduced,as related metabolic genes were all downregulated in persisters. Concentrations of 0.1 mM, 1 mM and 10 mM of extra glucose significantly reduced the number of persisters both in planktonic and biofilm conditions. The formation of non-inheritable and multidrug tolerant persisters induced by DMADDM suggested that drug tolerance and new persistent eradication strategies should be considered for oral antibacterial agents.

Secondary caries due to biofilm acids is a primary cause of dental composite restoration failure. To date, there have been no reports of dental composites that can repel protein adsorption and inhibit bacteria attachment. The objectives of this study were to develop a protein-repellent dental composite by incorporating 2-methacryloyloxyethyl phosphorylcholine (MPC) and to investigate for the first time the effects of MPC mass fraction on protein adsorption, bacteria attachment, biofilm growth, and mechanical properties. Composites were synthesized with 0 (control), 0.75%, 1.5%, 2.25%, 3%, 4.5% and 6% of MPC by mass. A commercial composite was also tested as a control. Mechanical properties were measured in three-point flexure. Protein adsorption onto the composite was determined by the microbicinchoninic acid method. A human saliva microcosm biofilm model was used. Early attachment at 4 h, biofilm at 2 days, live/dead staining and colony-forming units (CFUs) of biofilms grown on the composites were investigated. Composites with MPC of up to 3% had mechanical properties similar to those without MPC and those of the commercial control, whereas 4.5% and 6% MPC decreased the mechanical properties (P<0.05). Increasing MPC from 0 to 3% reduced the protein adsorption on composites (P<0.05). The composite with 3% MPC had protein adsorption that was 1/12 that of the control (P<0.05). Oral bacteria early attachment and biofilm growth were also greatly reduced on the composite with 3% MPC, compared to the control (P<0.05). In conclusion, incorporation of MPC into composites at 3% greatly reduced protein adsorption, bacteria attachment and biofilm CFUs, without compromising mechanical properties. Protein-repellent composites could help to repel bacteria attachment and plaque build-up to reduce secondary caries. The protein-repellent method might be applicable to other dental materials.
Adsorption ; Biofilms ; Colony Count, Microbial ; Composite Resins ; chemistry ; Dental Plaque ; microbiology ; Methacrylates ; analysis ; Phosphorylcholine ; analogs & derivatives ; analysis ; Proteins ; chemistry