Preparation And Properties Of Sr-N Co-doped TiO₂/n-HA Dental Resin Composites

Objective:In the past several decades,dental resin composite（DRC）has been an effective method for repairing decayed teeth because of its excellent esthetics and convenient operation qualities.However,in long-term dental resin restoration,the growing bacteria will create oral biofilms on the resin’s surface,particularly in the gap formatted by polymerization shrinkage,and continuously degrade the current resin composite and dental tissue nearby,causing secondary caries and treatment failure.It has been suggested that the most effective approach to modifying DRC is to add antimicrobial and remineralization agents.The creation of bacterial acids and enzymes is inhibited by removing pathogenic bacteria,while the synthesis of new minerals may allow the gaps and faults around the resin to mend.In recent years,Ti O₂-based materials have been widely studied as photocatalysts and antibacterial agents in the field of dental materials due to its excellent performance.This study prepared strontium and nitrogen co-doped titanium dioxide（Sr-N-Ti O₂）/nano hydroxyapatite（n-HA）dental resin composite,and evaluated the basic properties,antibacterial properties,remineralization ability,and biosafety of the novel dental resin composites,clarified the antibacterial mechanism,to explore the feasibility of the application in the oral clinic.Methods:1.Sol-hydrothermal method was used to create Sr-N-Ti O₂ nanoparticles.By using SEM,TEM,EDS,XPS,XRD,Raman,and UV–Vis,the phase composition and surface morphology of the produced composites were characterized.2.Sr-N-Ti O₂ and n-HA were mixed as reinforcing fillers.The resin composites were synthesized in the mass fractions of 0%,2.5%,5%,and 7.5%and were divided into control group（0%Group）,experimental groups（2.5%Group,5%Group,and 7.5%Group）.The basic properties were tested.Fourier-transform infrared spectrometer（FT-IR）was used to measured separately the spectrum of 0 s,20 s,40 s,and 60 s.The DC rates were computed by the equation.Cylindrical specimens（h=10.0 mm,d=4.0 mm）of each group were prepared to measure the curing depth（CD）.The light-curing equipment photopolymerized the composite for 20 s,starting from one side.The uncured material was removed after irradiation.A digital micrometer was used to measure the height of the cured composite.The surface of the sample was sprayed with 5 m L of deionized water to calculate the water contact angle（WCA）.3.Cylindrical specimens（h=2 mm,d=6 mm）were co-cultured with Streptococcus mutans.The plate colony counting method was used to determine the number of bacteria attached to the surface of the specimens,and the antibacterial rates（AR）were calculated.The biofilm metabolic activity was demonstrated by crystal violet staining.The FE-SEM images showed the bacterial morphology,exhibiting different degrees of damage to the cell membrane structure.The live/dead staining of bacterial biofilm on DRCs’surface was also experimented.To further clarify the photocatalytic antibacterial mechanism,DPBF and CFU with NAC methods were conducted.4.The specimens were incubated in 5 m L synthetic saliva（SBF）for 1 d,3 d,5 d,7 d,14 d,and 28 d,respectively.By using a FE-SEM with EDS,morphological surface alterations and element quantification were carried out.5.L929 cells were incubated in the extraction solution.The CCK-8 method was used to determine the relative growth rates（RGR）of 1 d,2 d,and 3 d in vitro,and its cytotoxicity level was evaluated.Results:1.Sr-N-Ti O₂ nanoparticles were successfully synthesized and identified as anatase-phase Ti O₂.The absorption of visible light was improved.2.With the same curing time,the DC rate of each group decreased with the increase in the filler ratio.With the proliferation of curing time,the DC rate of all groups showed an increasing trend.The CD also decreased with the increase in the filler ratio,ranged from 4.36±0.18 mm to5.10±0.19 mm.The WCA values of the 0%group were statistically significantly lower than that of the 5%group（P<0.01）.3.The antibacterial experiments showed that the synthesized DRC had antimicrobial properties,and the antimicrobial properties of each group gradually increased,which was verified to be derived from reactive oxygen species（ROS）.4.Mineralized nodules were observed on the surface of the experimental group under SEM.EDS results showed an increasing trend in calcium and phosphorus content,and the molar ratio of Ca/P was close to that of HA.5.The relative growth rate of mouse fibroblast L929 indicated high biocompatibility,with the cytotoxicity level being 0 or I.Conclusion:After comprehensive analysis of the above experimental results,it can be concluded that the modified Sr-N-Ti O₂ was successfully synthesized and that DRC containing Sr-N-Ti O₂ and n-HA meets clinical standards with high antibacterial properties,remineralization properties,and high biosafety,which was expected to be a promising biological material.