Novel Dentin Bond System Containing Quaternary Ammonium Salt And Amorphous Calcium Phosphate

Resin composites and resin-based bonding system are increasingly popularin dental clinics because of their excellent esthetic effects and direct-fillingcapabilities. However, compared to other restorative materials, compositesaccumulated more biofilms/plaques. And the polymerization shrinkage of resincomposites causes marginal microleakage, leading to the formation of channelfor dental plaque invasion. Dental plaque biofilm is on the one hand, a directresult of certain oral infectious diseases, such as secondary caries, denturestomatitis, on the other hand can cause the material aging or degradation, thusmore likely to attract bacterial accumulation. This vicious circle will ultimatelylead to restoration failing, and even impact negatively on the whole body. Dentalplaques contribute to secondary caries, which is a main reason for restorationfailure. Replacing the failed restorations consumes50-70%of the dentist’s time.Replacement dentistry costs$5billion annually in the United States. Extensivestudies have been performed to improve the fillers, resins, and polymerizationproperties. Besides composites, it is also important to develop novelantibacterial and remineralizing adhesives because composite restorations arebonded to tooth structure via adhesives. Resin composites and resin-basedbonding system with antibacterial properties can stabilize oral micro-ecologicalenvironment, improve the long-term clinical effect of the restoration andmaintain the health of the oral microbial environment.Part1Effect of quaternary ammonium and silver nanoparticle-containingadhesives on dentin bond strength and dental plaque microcosm biofilmsObjective: Antibacterial bonding agents are promising to hinder the residualand invading bacteria at the tooth–restoration interfaces. The objectives of thisstudy were to develop an antibacterial bonding agent by incorporation of quaternary ammonium dimethacrylate (QADM) and nanoparticles of silver(NAg), and to investigate the effect of QADM-NAg adhesive and primer on dentinbond strength and plaque microcosm biofilm response for the first time.Methods: Scotchbond Multi-Purpose adhesive and primer were used as control.Experimental adhesive and primer were made by adding QADM and NAg intocontrol adhesive and primer. Human dentin shear bond strengths weremeasured (n=10). A dental plaque microcosm biofilm model with human salivaas inoculum was used to investigate biofilm metabolic activity, colony-formingunit (CFU) counts, lactic acid production, and live/dead staining assay (n=6).Results: Adding QADM and NAg into adhesive and primer did not compromisethe dentin shear bond strength which ranged from30to35MPa (p>0.1).Scanning electron microscopy (SEM) examinations revealed numerous resintags, which were similar for the control and the QADM and NAg groups. AddingQADM or NAg markedly reduced the biofilm viability, compared to adhesivecontrol. QADM and NAg together in the adhesive had a much strongerantibacterial effect than using each agent alone (p<0.05). Adding QADM and NAgin both adhesive and primer had the strongest antibacterial activity, reducingmetabolic activity, CFU, and lactic acid by an order of magnitude, compared tocontrol.Significance: Without compromising dentin bond strength and resin tagformation, the QADM and NAg containing adhesive and primer achieved strongantibacterial effects against microcosm biofilms for the first time. QADM-NAgadhesive and primer are promising to combat residual bacteria in tooth cavityand invading bacteria at the margins, thereby to inhibit secondary caries. QADMand NAg incorporation may have a wide applicability to other dental bondingsystems. Part2Novel dental adhesives containing nanoparticles of silver and amorphouscalcium phosphateObjective: Antibacterial bonding agents are promising to inhibit residualbacteria in the prepared tooth cavity and invading bacteria along the margins.The release of calcium (Ca) and phosphate (PO4) ions was previously shown toremineralize tooth lesions. The objectives of this study were to incorporatenanoparticles of silver (NAg) and nanoparticles of amorphous calciumphosphate (NACP) into a bonding agent for the first time, and to investigate theeffects on dentin bond strength and dental plaque microcosm biofilm response.Methods: Scotchbond Multi-Purpose adhesive and primer were used as control.NAg were incorporated into the control primer and adhesive at0.1%by mass.NACP were mixed into adhesive at10%,20%,30%and40%. A microcosmbiofilm model with human saliva as inoculum was used on disks with primercovering the adhesive on the top of a composite. Biofilm metabolic activity,colony-forming unit (CFU) and lactic acid production were measured.Results: Human dentin shear bond strengths ranged from26to34MPa; addingNAg and NACP did not significantly decrease the bond strength (p>0.1). Bondingagents containing NAg and NACP greatly reduced the biofilm viability andmetabolic activity, compared to the control. CFU for total microorganisms, totalstreptococci, and mutans streptococci on bonding agents with NACP and NAgwere an order of magnitude less than those of control. Lactic acid production forgroups containing NACP and NAg were reduced to1/4of that of control. SEMexamination revealed the prevalence of resin tags from well-filled dentinaltubules, and numerous NACP infiltrated in the adhesive layer as well as indentinal tubules. Significance: In conclusion, microcosm biofilm viability and acid productionwere greatly reduced on bonding agents containing NAg and NACP nanoparticlesfor the first time, without compromising dentin bond strength. The method ofincorporating a remineralizing agent NACP and an antibacterial agent NAg may Part3Dental primer and adhesive containing a new antibacterial quaternaryammonium monomer dimethylaminododecyl methacrylateObjectives: The main reason for restoration failure is secondary caries causedby biofilm acids. Replacing the failed restorations accounts for50–70%of alloperative work. The objectives of this study were to incorporate a newquaternary ammonium monomer (dimethylaminododecyl methacrylate,DMADDM) and nanoparticles of silver (NAg) into a primer and an adhesive, andto investigate their effects on antibacterial and dentin bonding properties.Methods: Scotchbond Multi-Purpose (SBMP) served as control. DMADDM wassynthesized and incorporated with NAg into primer/adhesive. A dental plaquemicrocosm biofilm model with human saliva was used to investigate metabolicactivity, colony-forming units (CFU), and lactic acid. Dentin shear bond strengthswere measured.Results: Minimum inhibitory concentration (MIC) and minimum bactericidalconcentration (MBC) of the new DMADDM were orders of magnitude lower thanthose of a previous quaternary ammonium dimethacrylate (QADM). Uncuredprimer with DMADDM had much larger inhibition zones than QADM (p <0.05).Cured primer/adhesive with DMADDM-NAg greatly reduced biofilm metabolicactivity (p <0.05). Combining DMADDM with NAg in primer/adhesive resultedin less CFU than DMADDM alone (p <0.05). Lactic acid production by biofilms was reduced by20-fold via DMADDM-NAg, compared to control. Incorporationof DMADDM and NAg into primer/adhesive did not adversely affect dentin bondstrength.Significance: A new antibacterial monomer DMADDM was synthesized andincorporated into primer/adhesive for the first time. The bonding agents arepromising to combat residual bacteria in tooth cavity and invading bacteria attooth-restoration margins to inhibit caries. DMADDM and NAg are promising foruse into a wide range of dental adhesive systems and restoratives. Part4Effect of water-aging on dentin bond strength and anti-biofilm activity ofbonding agent containing new monomer dimethylaminododecyl methacrylateObjectives: The objectives of this study were to develop bonding agentcontaining a new antibacterial monomer dimethylaminododecyl methacrylate(DMADDM) as well as nanoparticles of silver (NAg) and nanoparticles ofamorphous calcium phosphate (NACP), and to investigate the effects of water-aging for6months on dentin bond strength and anti-biofilm properties for thefirst time.Methods: Four bonding agents were tested: Scotchbond Multi-Purpose (SBMP)primer and adhesive control; SBMP+5%DMADDM; SBMP+5%DMADDM+0.1%NAg; and SBMP+5%DMADDM+0.1%NAg with20%NACP in adhesive.Specimens were water-aged for1day and6months at37oC. Then the dentinshear bond strengths were measured. A dental plaque microcosm biofilm modelwas used to inoculate bacteria on water-aged specimens and to measuremetabolic activity, colony-forming units (CFU), and lactic acid production.Results: Dentin bond strength showed a35%loss in6months of water-agingfor SBMP control (mean±sd; n=10); in contrast, the new antibacterial bonding agents showed no strength loss. The DMADDM-NAg-NACP containing bondingagent imparted a strong antibacterial effect by greatly reducing biofilm viability,metabolic activity and acid production. The biofilm CFU was reduced by morethan two orders of magnitude, compared to SBMP control. Furthermore, theDMADDM-NAg-NACP bonding agent exhibited a long-term antibacterialperformance, with no significant difference between1d and6months (p>0.1).Conclusions: Incorporating DMADDM-NAg-NACP in bonding agent yieldedpotent and long-lasting antibacterial properties, and much stronger bondstrength after6months of water-aging than a commercial control. The newantibacterial bonding agent is promising to inhibit biofilms and caries at themargins. The method of DMADDM-NAg-NACP incorporation may have a wideapplicability to other adhesives, cements and composites.