Abstract
Objective
The objective of this study was to use the newly synthesized poly(quaternary ammonium salt) (PQAS)-containing polyacid to formulate the light-curable glass-ionomer cements and study the effect of the PQAS on the compressive strength and antibacterial activity of the formed cements.
Materials and methods
The functional QAS and their constructed PQAS were synthesized, characterized and formulated into the experimental high-strength cements. Compressive strength (CS) and Streptococcus mutans viability were used to evaluate the mechanical strength and antibacterial activity of the cements. Fuji II LC cement was used as control. The specimens were conditioned in distilled water at 37 °C for 24 h prior to testing. The effects of the substitute chain length, loading as well as grafting ratio of the QAS and aging on CS and S. mutans viability were investigated.
Results
All the PQAS-containing cements showed a significant antibacterial activity, accompanying with an initial CS reduction. The effects of the chain length, loading and grafting ratio of the QAS were significant. Increasing chain length, loading, grafting ratio significantly enhanced antibacterial activity but reduced the initial CS. Under the same substitute chain length, the cements containing QAS bromide were found to be more antibacterial than those containing QAS chloride although the CS values of the cements were not statistically different from each other, suggesting that we can use QAS bromide directly without converting bromide to chloride. The experimental cement showed less CS reduction and higher antibacterial activity than Fuji II LC. The long-term aging study suggests that the cements may have a long-lasting antibacterial function.
Conclusions
This study developed a novel antibacterial glass-ionomer cement. Within the limitations of this study, it appears that the experimental cement is a clinically attractive dental restorative due to its high mechanical strength and antibacterial function.
1
Introduction
Long-lasting restoratives and restoration are clinically attractive because they can reduce patients’ pain and expense as well as the number of their visits to dental offices . It is known that both restorative materials and oral bacteria are mainly responsible for the restoration failure . Secondary caries is found to be the main reason to the restoration failure of either composite resins or glass-ionomer cements (GICs) . Secondary caries that often occurs at the interface between the restoration and the cavity preparation is mainly caused by demineralization of tooth structure due to invasion of plaque bacteria (acid-producing bacteria) such as Streptococcus mutans ( S. mutans ) in the presence of fermentable carbohydrates . Among all the dental restoratives, GICs are found to be the most cariostatic and somehow antibacterial due to release of fluoride, which is believed to help reduce demineralization, enhance remineralization and inhibit microbial growth . However, annual clinical surveys found that secondary caries was still the main reason for GIC failure , indicating that the fluoride-release from GICs is not potent enough to inhibit bacterial growth or combat bacterial destruction. Although numerous efforts have been made on improving antibacterial activities of dental restoratives, most of them have been focused on release or slow-release of various incorporated low molecular weight (MW) antibacterial agents such as antibiotics, zinc ions, silver ions, iodine and chlorhexidine (CHX) .
Polymers containing quaternary ammonium (QAS) or phosphonium salt (QPS) groups have been studied extensively as an important antimicrobial material and used for a variety of applications due to their potent antimicrobial activities . These polymers are found to be capable of killing bacteria that are resistant to other types of cationic antibacterials . The examples of polyQAS or PQAS used as antibacterials for dental restoratives include incorporation of a methacryloyloxydodecyl pyridinium bromide (MDPB) as an antibacterial monomer into composite resins , use of DMAE-CB as a component for antibacterial bonding agents , and incorporation of quaternary ammonium polyethylenimine (PEI) nanoparticles into composite resins . All these studies found that PQAS did exhibit significant antibacterial activities. So far there have been no reports on using PQAS as an antibacterial agent for GICs.
The objective of this study was to use the newly synthesized poly(quaternary ammonium salt) (PQAS)-containing polyacid to formulate the light-curable glass-ionomer cements and study the effect of the PQAS on the compressive strength and antibacterial activity of the formed cements.
2
Materials and methods
2.1
Materials
2-Dimethylaminoethanol (DMAE), bromoethane, bromohexane, bromodecane, bromdodecane, bromotetradecane, bromohexadecane, dipentaerythritol, 2-bromoisobutyryl bromide (BIBB), acrylic acid (AA), itaconic acid (IA), 2,2′-azobisisobutyronitrile (AIBN), triethylamine (TEA), CuBr, N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA), dl-camphoroquinone (CQ), 2-(dimethylamino)ethyl methacrylate (DMAEMA), pyridine, tert-butyl acrylate (t-BA), glycidyl methacrylate (GM), hydrochloric acid (HCl, 37%), N,N′-dicyclohexylcarbodiimide (DCC), pyridine, diethyl ether, dioxane, N,N-dimethylformamide (DMF), methanol (MeOH), ethyl acetate (EA), hexane and tetrahydrofuran (THF) were used as received from VWR International Inc (Bristol, CT) without further purifications. Light-cured glass-ionomer cement Fuji II LC and Fuji II LC glass powders were used as received from GC America Inc (Alsip, IL).
2.2
Synthesis and characterization
2.2.1
Synthesis of the quaternary ammonium salt (QAS)
The hydroxyl group-containing quaternary ammonium salt (QAS) was synthesized following the procedures described elsewhere with a slight modification . Briefly, to a flask containing DMAE (0.056 mol) in methanol (100 ml), bromohexane (0.062 mol) was added. The reaction was run at room temperature overnight. After most of methanol was removed, the mixture was washed with hexane 3 times. The formed 2-dimethyl-2-hexyl-1-hydroxyethyl ammonium bromide (or namely B6) was purified by dissolving in methanol and washing with hexane several times before drying in a vacuum oven. The synthesis scheme is shown in Fig. 1 A .
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