Objective To investigate the antibacterial performance and biocompatibility of silver nanoparticles-coated root canal nickel titanium instruments(AgNPs-NiTi).Methods AgNPs-NiTi was prepared using pulse electrochemical deposition.The morphol-ogy of AgNPs-NiTi was observed using field emission scanning electron microscopy(FE-SEM),and the elemental composition and con-tent were analyzed using X-ray diffraction(XRD)and energy dispersive spectroscopy(EDS).The mechanical properties of AgNPs-NiTi were tested.After Co-culturing AgNPs-NiTi with E.faecalis,the antibacterial effect was detected by colony-forming units method.By constructing an in vitro model of E.faecalis biofilm in the root canal of teeth,the antibacterial effect of AgNPs-NiTi was observed using FE-SEM and live/dead bacterial staining.In addition,AgNPs-NiTi was co-cultured with Raw 264.7 cells,and its cytotoxicity was de-tected by CCK-8.Results The pulse electrochemical deposition was used to construct a silver nanoparticle(AgNPs)coating on NiTi instruments with no significant change in the mechanical properties.AgNPs-NiTi significantly inhibited the proliferation of E.faecalis and damaged E.faecalis biofilm in the root canal.AgNPs-NiTi had no significant influence on the proliferation of Raw264.7 cells and had no cytotoxicity.Conclusion The mechanical properties of AgNPs-NiTi are similar to those of nickel titanium instruments.AgNPs-NiTi inhibits E.faecalis proliferation with good biocompatibility.

Objective To analyze three-dimensional(3D)radiographic characterizations of bone island(BI)in jaw using cone-beam computed tomography(CBCT).Methods CBCT data from four thousand patients were selected,reconstructed and analyzed using NNT 10.0 software.The sagittal,coronal and axial planes were used to analyze the 3D radiographic characteristics of BIs,including the localization,shape,density,boundary,the relationship between BIs and tooth and bone cortex,diameter and anatomical structures and complications involved.Their relationship with gender were analyzed.Results A total of 803 people had BIs,with the prevalence rate of 20.08%,including 338 males with 389 BIs and 465 females with 526 BIs.Both males and females had a dominant BI,and the ratio between male and female was 1∶1.38,but the difference was not statistically significant(P＞0.05).The BIs of both male and female mostly occurred in the mandibular premolars and molars area,and appeared irregular in shape,dense and contact with lingual bone cortex.Mostly BIs were apical type and with unclear boundary.The mean maximum diameter of mesial/distal direction was greater than buccal/lingual direction(P＜0.05).The most commonly involved anatomy structure was the inferior alveolar neural canal,cortical infil-tration and mental foramen.Conclusion There are no significant differences between males and females in the three-dimensional image characteristics of BIs in Chinese populations.CBCT can accurately and comprehensively analyze the 3D radiographic characteris-tics of BI and its relationship with the surrounding teeth and bone.