| Objective:This study aimed to evaluate the effect of the incorporation of MgONPs as antibacterial filler into dual-cure dental resin cement on antibacterial activity,mechanical,bonding and physicochemical properties,as well as the performance subjected to a thermocycling regimen.Methods:The study was divided into two parts.1.To investigate the bacteriostatic activity of MgONPs against Streptococcus mutans(S.mutans).Different weight fraction of MgONPs were mixed with brain heart infusion broth and then cultured with S.mutans.The minimal inhibitory concentration(MIC)and minimum bactericidal concentration(MBC)of MgONPs were determined by testing the optical density(OD)and streak plating.The antibacterial effect of MgONPs on inhibitory and sub-inhibitory concentrations were studied by measuring OD values,colony forming units(CFU)counting,methyl thiazolyl tetrazolium(MTT)assay and acridine orange(AO)fluorescence staining,to evaluate the bacterial growth,metabolic activity and biofilm living status.2.To evaluate the comprehensive performances of the experimental resin cement.A series of dual-cure resin cements containing different mass fractions of MgONPs(0,2.5%,5%,7.5% and 10%)were prepared.Firstly,antibacterial activity against S.mutans was tested by CFU counting,MTT assay and acridine orange/propidium iodide(AO/PI)fluorescent staining.Next,multiple tests were conducted: 1)mechanical properties,including flexural,compressive,diametral tensile strength and microhardness;2)human dentine bonding tests,including shear bond strength and interface fracture mode analysis;3)physicochemical properties,including water sorption/solubility,film thickness and water contact angle.Moreover,a regimen of 5000 thermal cycles was conducted to evaluate the materials’ antibacterial,mechanical and bonding performance in an in vitro accelerated aging environment.A commercially available dual-cure resin cement(Meiyiting,Shandong Huge Co.)was selected as the commodity control group.Results:1.MgONPs showed effective antibacterial activity on against S.mutans(p<0.05)in a dose-dependent manner.The plankton proliferation and biofilm formation ability of S.mutans were significantly suppressed(p<0.05)when the concentration of MgONPs in the culture reached 1.0 mg/m L.The bacterial growth curve showed that MgONPs in 1.0mg/m L could completely inhibit S.mutans proliferation within a 72 h period.Bacteria presented a sub-inhibitory state when the concentration of MgONPs was 0.75 mg/m L,which showed that the plankton proliferated but had a weaker ability to form stable biofilm.MgONPs exhibited bacteriocidal activity at 2.0 mg/m L in which no bacteria growth could be observed in the streak plating test.2.The experimental resin cements displayed remarkable antibacterial activity against S.mutans when the addition of MgONPs reached 7.5 wt%(p<0.05)and the trend was dose-dependent,where the CFU,MTT as well as fluorescence signals of living bacteria biofilm were decreased.Meanwhile,MgONPs at this fraction did not significantly compromised the mechanical,bonding and physicochemical properties of the material(p>0.05).3.The bacteriostatic property of the experimental resin cements was decreased after undergoing 5000 thermocycles,and only the group with 10 wt% of MgONPs content showed a significant reduction compared with the control group(p<0.05).The CFU(p<0.0001),MTT(p<0.001)values and fluorescence signal of live bacteria were significantly higher than those in the subgroup without aging treatment.4.The dentine bonding and mechanical performances of the experimental resin cements did not significantly decline after undergoing thermocycling treatment(p<0.05),except for flexural properties.The compressive strength increased after thermocycling when MgONPs accounted for higher than 5 wt%(p<0.05).5.The fracture mode analysis showed that the mixed fracture mode accounted for the highest proportion,but the ratio of adhesive fracture increased after thermocycling treatment.6.Except for the flexural properties,the compressive properties,hardness and bonding performance of the experimental resin cement were not significantly different from those of the commercial control group(p>0.05).Conclusions:1.MgONPs at concentration of 1.0 mg/m L presented effective antibacterial activity against S.mutans by significantly suppressing the proliferation of planktonic bacteria and inhibiting the formation of stable biofilm.When the concentration reached 2.0 mg/m L,it exhibited bactericidal effect.2.MgONPs significantly enhanced antibacterial performance of the experimental resin cements without jeopardizing the mechanical,bonding and physicochemical properties when the addition reached 7.5 wt%.3.MgONPs could maintain a certain degree of stability in the experimental resin cements after undergoing aging regimen of 5000 thermocycles.However,the antibacterial activity decreased,possibly related to the partial degradation of MgONPs in aqueous solution.5.The experimental resin cements achieved similar mechanical performances and human dentine bonding performance as the commercial control did,suggesting that the resin cement had certain potential for clinical transformation.6.It can be a promising protocol to develop functional MgONPs-contained resin cements to suppress the accumulation of cariogenic bacteria and assist in controlling plaque accumulation at restoration margins.Nevertheless,it remains in need of further study to improve the stability of MgONPs in materials,in order to realize prolonged antibacterial performance. |
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