| Resin-based dental materials are widely used in restorative dentistry for theirexcellent esthetics, stability and ease for operation. However, resin materials invivo had more biofilm and plaque accumulation than other restorative materials.Biofilm forms on the resin material surface used for the restoration of functionin the oral cavity not only lead to some infectious diseases such as secondarycaries and stomatitis, but also degrade the material and roughens its surface, andthe decrease of materials may make its surface be prone to bacterial colonization,finally induce the failure of restorative treatment even some systemic diseases.Consequently, the interest in new dental materials attracting less biofilm orreleasing antimicrobial compounds is increasing.There are two main kinds of methods for making antibacterial resin-based dentalmaterials. One is antibiotic-releasing systems and another is contact inhibitor. Itis concluded that, for dental applications, antimicrobial coating killing bacteria upon contact is more promising than antimicrobial-releasing coating.Polymerizable quaternary ammonium salts (QAS) monomers are developed bycombining the antibacterial agent quaternary ammonium and a methacryloylgroup. It can copolymerize with other monomers after curing of the resinmaterials and the antibacterial agent is covalently bonded to the polymernetwork. The immobilized agent does not leach out from the material but acts asa contact inhibitor against the bacteria which attach to the surface. Our researchgroup synthesized several antibacterial polymer monomers such as DMAE-CB,MAE-DB and MAE-HB, and tried to develop a series of antimicrobial dentalapplications based on these monomers. However, there are some problems withthe previous monomers like poor solubility and low concentration in resinmatrix, and high cytotoxic effects. In order to produce monomer with betterperformance, in this research a new kind of low-melting-point and cross-linkedQAS was synthesized, and physicochemical properties, antibacterial activity andcytotoxicity of it were tested. The experimental adhesives was prepared byincorporating the novel monomer in a commercial adhesive system Single Bond2. The antibacterial property and microtensile bond strength of experimentaladhesives were tested for evaluating possibility of the novel monomer used foracquiring antibacterial resin-based dental materials.Main methods and results:1The novel monomer was successfully synthesied based on the characterizationof DMAEMA-PMDPM salt using FTIR. DMAEMA-PMDPM salt is a kind ofionic liquid, transparent and colorless at room temperature. The monomercontains three polymerizable groups and bactericide in the molecule.2The antibacterial activities of the monomer were investigated by using thebroth dilution test on4oral pathogenic bacteria. The results showed that DMAEMA-PMDPM salt exhibited bactericidal activities against the testedbacterial. It has the best antibacterial effect to Streptococcus mutans (S. mutans),MIC/MBC is39/78μg/ml, but weaker to Candida albicans (C. albicans).Time-kill curve showed that almost all of the bacterial can be killed within120min by DMAEMA-PMDPM salt at78.8mg/ml (4*MBC).3Without any solvent or accelarator, DMAEMA-PMDPM salt monomer wasactivated for blue light photopolymerization with a small quantity ofcamphorquinone(CQ) at room temperature. Degree of conversion(DC) of themonomer was measured by FTIR. DC of monomer contained CQ(1%by weight)for20s irradiation was near to90%. Poly-QAS was water insoluble solid, buthad a limited swelling capacity in water.4The antibacterial activity of poly-QAS was determined by film contact test.Compared with control group (single bond2), poly-QAS exhibited contactinhibitory effect against S. mutans.5Cytotoxicity of DMAEMA-PMDPM salt monomer on the human gingivalfibroblast cell was determined by MTT (Methyltetrazolium test) assay. Themedian lethal concentration (LC50) was52.39μg/ml. The cytotoxicity of themonomer was less than that of Bis-GMA and DMAE-BC.6The experimental adhesive was obtained by adding different amounts ofDMAEMA-PMDPM salt monomer to commercial adhesives single bond2. Themonomer completely dispersed in resin matrix. Bond strength to dentin of eachexperimental adhesive was determined by microtensile bond strength test. Allthe experimental adhesives containing DMAEMA-PMDPM salt showed lowerbond strength compared to control adhesive, and the standard deviation (SD) oftreatment groups increased obviously.7The antibacterial activities of cured experimental adhesives’ surfaces were determined by film contact test. Three experimental adhensives containing8%,10%and12%DMAEMA-PMDPM salt monomer showed no singnificantcontact inhibitory capacity against S. mutans compared with control group(SB2).Main conclusions:DMAEMA-PMDPM salt monomer has a better solubility in resin matrix andless cytotoxicity compared with some QAS. It can increase crosslink density ofresin monomers. However, the antibacterial activity of DMAEMA-PMDPM saltis not so good. The polymer of it is readily absorbing or dissolving in waterand limited swelling capacity. A high concerntration of DMAEMA-PMDPM saltmonomer in adhensives may lead to singnificant antibacterial activity forexperimental adhensives but decrease bond strength and bond durability.Therefore, for th purpose of using DMAEMA-PMDPM salt monomer for thepreperation of antibacterial dental adhesives and composite resin, increasing theantibacterial capacity and decreasing the hydroscopic property of the novelmonomer is important, it means that molecular structure of the monomer shouldbe modified, for example by connecting a alkyl chain. If possible, this monomercould be used for producing other biomaterials such as denture base and softlining materials with antibacterial activities. It can also be used as cross-linkingmonomer and accelerator. Poly-DMAEMA-PMEDPM salt is a kind of hydrogelthat might be used as a carrier for some drugs and biological agents. |
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