Development And In Vitro Study Of Novel Orthodontic Adhesive Containing AgNPs Fibers

Objective:Enamel demineralization is a common complication of orthodontic treatment and significantly impacts aesthetics.This study used gelatin(Gel)and polycaprolactone(PCL)as raw materials,and PCL-Gel-AgNPs composite fibers were synthesized by electrospinning.After making it into staple fibers and adding them to traditional orthodontic adhesives in different proportions,we evaluated the antimicrobial,biocompatible,and mechanical properties of the new adhesives.Therefore,this experiment aims to synthesize a new adhesive to prevent enamel demineralization during orthodontic treatment.Methods:(1)PCL-Gel-AgNPs composite fibers were prepared using the electrostatic spinning technique.The physicochemical characteristics of the composite fibers,such as spatial structure,loading of AgNPs,and loading form of AgNPs,were assessed by scanning electron microscopy observation,X-ray diffraction analysis,and infrared spectroscopy analysis.(2)An agar diffusion test was applied to compare the in vitro antibacterial performance of the fibers with different loading of AgNPs against Streptococcus mutans.(3)Cell proliferation of L929 cells cultured on the surface of the composite fibers membrane for 1,3,and 5 days was assessed using the CCK-8 cytotoxicity assay.(4)After making the PCL-Gel-AgNPs composite fibers into staple fibers,the length of the staple fibers was assessed by scanning electron microscopy.Transbond XT orthodontic adhesive was added by mass at 0%,1%,3%,and 5%.After co-cultivation of Streptococcus mutans and the new adhesive for a certain period,the antibacterial performance of the new adhesive was assessed by applying colony-forming unit counts and staining for live/ dead bacteria.The duration of the antibacterial effect was evaluated by the MTT method.(5)Biocompatibility of new adhesives assessed by CCK-8 cytotoxicity assay.(6)The new adhesive’s polymerization degree was assessed by conversion rate determination.The new adhesive was used to bond brackets on isolated premolar teeth,aged to simulate the intraoral environment.A shear bond strength test was carried out to analyze whether the mechanical properties of the new adhesive met clinical standards(n =10).An adhesive residual index(ARI)assessment was performed to investigate the bracket debonding interface(n =1 0).Results:(1)SEM showed a decreasing trend of the average diameter of the fibers when 1%,5%,10%,and 15% nanosilver were added,and their average diameters were 0.95 μm,0.94μm,0.84 μm,and 0.83 μm,respectively,with a normal distribution.The surface of each group of fibers was smooth,without beading and adhesion.XRD patterns showed characteristic absorption peaks of silver nanoparticles,which confirmed the presence of AgNPs in the fibers.FT-IR spectra indicated that AgNPs were bound to the composite fibers in a physically mixed manner.(2)Agar diffusion experiment on composite fibers membranes revealed no significant formation of the antibacterial ring in nanofibers membranes without adding AgNPs.As the AgNPs content increased,the inhibition ring around the fibers membrane gradually increased.(3)The CCK-8 cell proliferation assay showed that the cells exhibited better proliferation and differentiation on each fiber membrane.After 5 days of culture,there was no significant difference in the OD value of L929 cells on the surface of the composite fiber membrane with different AgNPs content(P > 0.05).(4)The CFU counting experiment of the new adhesive demonstrated that the number of colonies decreased to different degrees by adding antibacterial fibers.The living/dead bacterial staining image showed that a biofilm of live bacteria covered the Transbond XT control group.The total number of live bacteria gradually decreased with increasing content of the composite antibacterial fiber.The surface of the adhesive containing 5% fibers had many red-stained dead bacteria.The MTT biofilm activity assay showed that after 4 weeks of immersion,the adhesives in the 3% PCL-Gel-AgNPs group and the 5% PCL-Gel-AgNPs group still had antibacterial properties.(5)The relative cell viability of HOK cells on the surface of the four groups of adhesives was higher than 70%,and there was no significant difference between the cell viability of each experimental group and the negative control group(P > 0.05).(6)The adhesive conversion experiment confirmed that the conversion rate of the new adhesive was slightly reduced after the addition of PCL-Gel-AgNPs staple fiber.Still,there was no significant difference in the conversion rate between the groups compared with Transbond XT(P > 0.05).The shear bond strength experiment showed that the increase of antibacterial fibers had no significant effect on the SBS value of the adhesive(P > 0.05).The scores of each group in the ARI index analysis were mainly distributed between 1 and 2,indicating that most of the bond failure occurred between the adhesives.Conclusion:This study prepared composite PCL-Gel-AgNPs fibers.Bio-compatibility results showed that the composite fibers had no cytotoxicity,and the agar diffusion test showed good antibacterial activity.After combining PCL-Gel-AgNPs staple fibers with traditional orthodontic adhesive,it exerts good antibacterial properties without affecting the bonding performance and biological safety,which provides a new idea for preventing demineralization in clinical orthodontics.