• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    A General Strategy for Efficiently Constructing Multifunctional Cluster Fillers Using a Three-Fluid Nozzle Spray Drying Technique for Dental Restoration

    2022-04-24 03:23:12DanLeiYangDanWangHaoNiuRuiLiWangMeiLiuFeiMinZhangJieXinWangMeiFangZhu
    Engineering 2022年1期

    Dan-Lei Yang, Dan Wang, Hao Niu, Rui-Li Wang, Mei Liu, Fei-Min Zhang, Jie-Xin Wang,*,Mei-Fang Zhu

    a State Key Laboratory of Organic–Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China

    b Research Center of the Ministry of Education for High Gravity Engineering and Technology, Beijing University of Chemical Technology, Beijing 100029, China

    c State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, China

    d Jiangsu Key Laboratory of Oral Diseases, Department of Prosthodontics, Affiliated Hospital of Stomatology, Nanjing Medical University, Nanjing 210029, China

    Keywords:Multifunctional cluster fillers Three-fluid nozzle spray drying Mechanical properties Antibacterial activity Radiopacity Dental resin composites

    ABSTRACT Multifunctional fillers are greatly required for dental resin composites(DRCs).In this work,a spray dryer with a three-fluid nozzle was applied for the first time to construct high-performance complex nanoparticle clusters(CNCs)consisting of different functional nanofillers for dental restoration.The application of a three-fluid nozzle can effectively avoid the aggregation of different nanoparticles with opposite zeta potentials before the spray drying process in order to construct regularly shaped CNCs. For a SiO2–ZrO2 binary system,the SiO2–ZrO2 CNCs constructed using a three-fluid nozzle maintained their excellent mechanical properties ((133.3±4.7)MPa, (8.8±0.5)GPa, (371.1±13.3)MPa, and (64.5±0.7)HV for flexural strength, flexural modulus, compressive strength, and hardness of DRCs, respectively), despite the introduction of ZrO2 nanoparticles, whereas their counterparts constructed using a two-fluid nozzle showed significantly decreased mechanical properties. Furthermore, heat treatment of the SiO2–ZrO2 CNCs significantly improved the mechanical properties and radiopacity of the DRCs.The DRCs containing over 10%mass fraction ZrO2 nanoparticles can meet the requirement for radiopaque fillers.More importantly, this method can be expanded to ternary or quaternary systems. DRCs filled with SiO2–ZrO2–ZnO CNCs with a ratio of 56:10:4 displayed high antibacterial activity(antibacterial ratio>99%)in addition to excellent mechanical properties and radiopacity. Thus, the three-fluid nozzle spray drying technique holds great potential for the efficient construction of multifunctional cluster fillers for DRCs.

    1. Introduction

    The rapid development of nanotechnology is facilitating the exploration and application of nanomaterials in novel tools for a wide variety of applications, such as energy[1],catalysts[2],electronics[3,4],biomedicine[5–7],and the environment[8].In particular, the biomedical applications of nanomaterials have attracted broad attention due to the unique and advantageous properties of such materials. Nowadays, dental cavities are one of the most common oral diseases.Tooth decay results in the formation of cavities in the teeth, and the enamel cannot regenerate once it becomes worn or eroded [9]. Without effective treatment, caries can progress until the teeth are destroyed [10]. Hence, reliable and versatile restoration materials are greatly required.Resin composites have been widely used in recent years for treating dental caries due to their numerous advantages, such as esthetics, biocompatibility, mechanical properties, and operability [11].

    The main components in dental resin composites (DRCs) are organic matrices and inorganic fillers.The organic matrices,which mainly comprise polymerizable monomers and photoinitiators,can be converted from a liquid phase into a highly crosslinked polymer by being exposed to visible light [12]. Different inorganic fillers have various functions,such as enhancing mechanical properties,reducing polymerization shrinkage,altering thermal expansion behavior, and endowing DRCs with remineralization,radiopacity, and antibacterial abilities [13–16]. The type, size,shape,and structure of the inorganic fillers are the decisive factors in establishing the properties of DRCs [17–21].

    The most commonly used inorganic fillers are reinforcing fillers,such as SiO2and glasses,which are essential for nearly all commercial DRCs. These hard and chemically inert fillers are dispersed in organic matrices to provide the necessary structural reinforcement for clinical applications [22]. Although DRCs loaded with reinforcing fillers have been widely used to treat dental caries, secondary caries cannot be avoided at the tooth-restoration interfaces; this is one of the major reasons for restoration failure and results in 50%–70% failed restorations out of all restorations that are placed[23]. Therefore, antibacterial materials, such as fluorides, silver(Ag)-related fillers, and ZnO nanoparticles, have been adopted as co-fillers to give DRCs antibacterial activity [24–26]. Furthermore,dental clinics require DRCs to have radiopacity,which allows dentists to easily differentiate a restoration from a decayed tooth,evaluate voids, identify inappropriate contour in restorations, and diagnose secondary caries around the restorations [27]. Radiopacity can be achieved by incorporating an element with a relatively high atomic weight (e.g., Zr, Sr, or Ba) as the co-filler in DRCs[28]. According to the various requirements for DRCs, fillers with different functions must be embedded into DRCs to achieve multifunctional restorations. However, the direct addition of functional co-fillers may detrimentally affect the mechanical properties of DRCs due to incompatibility between the fillers and resin matrices[26,29,30].

    Aside from filler type,filler structure is a crucial factor in determining the mechanical properties of DRCs [17,31,32]. Recent research has demonstrated that nanoparticle clusters (NCs) have a superior reinforcing effect, and NCs have been applied in commercial DRCs (e.g., Filtek Z350 XT, 3 M ESPE, USA). Several methods, including coupling [33], sintering [34], and solvent evaporation[35],have been used to prepare NCs as fillers for DRCs.However,to the best of our knowledge,few of these processes have been applied to construct NCs with more than one component.

    Spray drying is an efficient and robust particle-production method that has been widely used in industrial processes [36],such as in the food [37], pharmaceutical [38], and chemical[39,40] industries. It enables the continuous and fast production of particles within a reasonable size range. In our previous work,SiO2NCs (SNCs) [41], hydroxyapatite (HAp) NCs [42], and SiO2–ZnO complex NCs (CNCs) [43] were precisely constructed using a spray dryer with a two-fluid nozzle. The DRCs filled with these NCs showed significantly enhanced properties compared with those filled with the nanoparticle counterparts.In particular,DRCs filled with the SiO2–ZnO CNCs displayed enhanced antibacterial activity while maintaining good mechanical properties [43]. However,their lack of radiopacity makes such DRCs unsuitable for clinical applications.

    Our objective in the present work is to provide a general strategy to construct multifunctional fillers for DRCs using a spray dryer with a three-fluid nozzle.The use of a three-fluid nozzle avoids the aggregation of incompatible particles before the spray drying process, which may occur with the use of a traditional two-fluid nozzle due to its single feed line and nozzle[44,45]. In general,threefluid nozzle spray drying has been applied in biomedicines, especially for microencapsulation [46–48]. Herein, we report on the use of the three-fluid nozzle spray drying process for the first time in the construction of multifunctional CNCs. ZrO2and ZnO nanoparticles were adopted as the co-fillers of SiO2nanoparticles in order to realize radiopaque and antibacterial properties in the DRCs. The filling properties of the CNCs constructed by two- and three-fluid nozzles were compared. In addition, a heat treatment process was applied to strengthen the structure of the CNCs. The relationships between the SiO2–ZrO2ratios in the heat-treated CNCs and the properties of the DRCs were investigated. The radiopacity and antibacterial activity of the DRCs filled with SiO2–ZrO2–ZnO CNCs were confirmed. The universality of threefluid nozzle spray drying was also explored.

    2. Experimental section

    2.1. Reagents and materials

    Absolute ethyl alcohol (C2H5OH), tetraethyl orthosilicate(TEOS), ammonium hydroxide (NH3·H2O), sodium hydroxide(NaOH), n-propylamine, and cyclohexane were bought from Beijing Chemical Reagent Co.,Ltd.Zirconium oxychloride octahydrate(ZrOCl2·8H2O), triethylene glycol dimethacrylate (TEGDMA),bisphenol A glycerolate dimethacrylate (Bis-GMA), zinc acetylacetonate, oleic acid, phenylcarbinol, camphorquinone (CQ), and ethyl-4-dimethylaminobenzoate (4-EDMAB) were bought from Shanghai Aladdin Biochemical Technology Co., Ltd. 3-Methacryloxypropyl trimethoxysilane (γ-MPS) was purchased from Alfa Aesar (China) Chemical Co., Ltd.

    2.2. Preparation of inorganic nanodispersions

    The SiO2nanodispersion was obtained according to the St?ber method [49]. First, deionized water (70 mL), NH3·H2O (6.4 mL),and ethanol (190 mL) were mixed and stirred at 60°C in a 1000 mL flask. Then, a mixture containing TEOS (30 mL) and ethanol (190 mL) was poured into the above flask. The reaction lasted for 3 h at 60°C.

    The ZrO2nanodispersion was prepared based on a published work [50]. In brief, 10.473 g of ZrOCl2·8H2O was dissolved in 325 mL of deionized water at room temperature. A total of 190 mL of NaOH aqueous solution(0.125 mol·L-1)was added dropwise into the above ZrOCl2solution under vigorous stirring. The mixture was then stirred at 70°C for 3 h,followed by a dialysis process to thoroughly wash the as-obtained zirconium hydroxide precursor.Finally,the precursor was heat-treated at 170°C for 10 h in a 1 L Teflon-lined stainless-steel autoclave to form the ZrO2nanodispersion.

    The preparation of the ZnO nanodispersion was based on our previous work [43]. First, 5.272 g of zinc acetylacetonate, 2.4 mL of oleic acid,and 120 mL of phenylcarbinol were mixed and stirred at 60°C for 3 h. The mixture was then heat-treated at 150°C for 10 h in a 200 mL Teflon-lined stainless-steel autoclave. The obtained suspension was centrifuged and washed with ethyl alcohol for three times, followed by an ultrasonic treatment (Scientz-IID, Ningbo Scientz Biotechnology Co., Ltd., China) to obtain the ZnO nanodispersion.

    2.3.Construction of CNCs using a spray dryer with a three-fluid nozzle

    The SiO2–ZrO2CNCs were constructed using a spray dryer with a three-fluid nozzle. SiO2and ZrO2nanodispersions with a solid content of 2% in mass fraction were simultaneously pumped into the spray dryer through two different liquid channels in the three-fluid nozzle. The aspirator level, inlet temperature, compressed air flow rate, and total feed rate were set at 100%, 100°C,600 L·h-1, and 0.4 L·h-1, respectively. For comparison, SiO2–ZrO2CNCs and SNCs were also constructed by means of a two-fluid nozzle under the same spray drying conditions.

    In order to prepare the SiO2–ZrO2–ZnO CNCs,first,the SiO2and ZnO nanodispersions(2%in mass fraction)were mixed to obtain a SiO2–ZnO dispersion.Then,the above dispersion and the ZrO2nanodispersion(2%in mass fraction) were respectively pumped into the spray dryer through the three-fluid nozzle.The aspirator level,inlet temperature, compressed air flow rate, and total feed rate were set at 100%, 100°C, 600L·h-1, and 0.4 L·h-1, respectively. Other CNCs including SiO2–ZnO–CaF2CNCs, SiO2–TiO2–CaF2CNCs, SiO2–ZnO–ZrO2–TiO2CNCs, and SiO2–ZnO–TiO2–CaF2CNCs were constructed using the same three-fluid nozzle spray drying process as described above;the distributions of the raw materials in the two channels of the three-fluid nozzle are shown in Table S1 in Appendix A.

    To confirm the influence of heat treatment on the filling properties of the SiO2–ZrO2and SiO2–ZrO2–ZnO CNCs,the CNCs were calcined in a muffle furnace (LH 30/13, Nabertherm, China) at 500°C for 3 h. All the inorganic fillers were coded, as shown in Table 1.

    2.4. Preparation of DRCs

    All the fillers were further silanized before being blended with the resin matrices (Bis-GMA and TEGDMA at a mass ratio of 1:1)and photoinitiators (CQ and 4-EDMAB at a mass ratio of 1:4, 1%in mass fraction of the matrices).The silanization process was done according to our previous work[41].All the components were premixed by hand and then thoroughly blended using a three-roll mixer(TR50M,Trilos Precision Equipment Co.,Ltd.,China).The filler content was fixed at 70% in mass fraction. The well-mixed pastes were filled into different silicone rubber molds with various shapes and photopolymerized by means of light-emitting diode(LED)light curing(SLC-VIII B,430–490 nm,Hangzhou Sifang Medical Apparatus Co., Ltd., China) for 120 s. All specimens were polished with silicon carbide papers before testing.

    2.5. Characterization of CNCs

    A transmission electron microscope (TEM; JEOL-7800, JEOL,Japan) was used to observe the nanoparticles at an accelerating voltage of 120 kV.The surface potentials of the nanoparticles were measured using a particle size and zeta potential analyzer (Nano ZS90, Malvern, UK). The morphology and size of the CNCs could be clearly seen via scanning electron microscopy (SEM; JSM-6701F, JEOL) with a 5 kV operating voltage. The crystal structures of the CNCs were confirmed by means of an X-ray diffractometer(D8 Advance, Bruker Optik GmbH, Germany). The distribution of the silicon (Si), zirconium (Zr), zinc (Zn), and oxygen (O) elements in the CNCs were observed using scanning electron microscopyenergy dispersive X-ray spectrometry (SEM-EDS) at 20 kV.

    2.6. Characterization of resin composites

    2.6.1. Mechanical properties

    According to International Organization for Standardization(ISO) 4049:2009, the flexural strength and modulus of the DRCs were determined by means of a three-point bending test using a universal testing machine (CMT6503, MTS Industrial Systems Co.,Ltd., China). Six specimens (25 mm×2 mm×2 mm) were bent in the machine with a span of 20 mm and crosshead speed of 0.75 mm·min-1, respectively. Compressive strength was also tested by the universal testing machine using cylindrical specimens(φ4 mm×6 mm,n=6)with 0.75 mm·min-1crosshead speed.Vickers microhardness was tested on the cylindrical samples(φ6 mm×4 mm, n=6) using a microhardness tester (HXD-1000TMC/LCD, Shanghai Taiming Optical Instrument Co., Ltd.,China) under a 50 g load for 10 s.

    2.6.2. Degree of conversion

    2.6.3. Radiopacity

    Disc-shaped samples(φ10 mm×1 mm)were prepared for each type of DRC and were irradiated with X-rays (70 kV, 8 mA, 0.1 s),along with a standard aluminum (Al) step-wedge having 12 steps ranging from 0.5 to 6 mm, to obtain radiographs. The optical density of each material in the radiographs was measured using an optical density meter (LS117, Shenzhen Linshang Technology Co.Ltd.,China).The radiopacity of the samples was expressed in terms of equivalent Al thickness (mm).

    2.6.4. Antibacterial activity

    The antibacterial activity of the DRCs was determined through a quantitative analysis based on American Society for Testing and Materials (ASTM) E2180–07(2012). Inoculated molten agar slurry(0.08 mL) containing approximately 106colony-forming units(CFU) of Streptococcus mutans (S. mutans) was pipetted onto the DRCs (φ20 mm×2 mm, n=3) and was then incubated at 37°C for 24 h. The surviving S. mutans after incubation was obtained by the elution of the agar slurry inoculum with Dey/Engley(D/E)neutralizing broth.The serial dilutions were spread on tryptic soy agar,and then incubated for 48 h. Finally, the bacterial colonies were counted and recorded. The S. mutans incubated without DRCs was adopted as a blank sample.The antibacterial ratio of the DRCs was calculated by Eq. (2).

    where a represents the antilog of the geometric mean of the number of bacteria recovered from the incubation period in the blank samples, and b represents the antilog of the geometric mean ofthe number of bacteria recovered from the incubation period in the experimental samples.

    Table 1 Codes of different inorganic fillers.

    2.7. Statistical analysis

    The statistical significance was evaluated with SPSS software using one-way analysis of variance(ANOVA)with Tukey’s test with a 95% confidence interval.

    She took her sons shopping. Clerks gasped14 when her sons made grunting15 sounds. And now, she knew about the other women. Sometimes her husband didn t bother to come home. Her friends quit calling her and Marianne felt a biting loneliness.

    3. Results and discussion

    Fig.1 shows a schematic diagram for the preparation process of SiO2–ZrO2CNCs by means of a spray dryer with a two-fluid nozzle and a three-fluid nozzle,respectively. The raw materials(SiO2and ZrO2nanodispersions) for the spray drying process were transparent, and the nanoparticles were well dispersed in the mediums(Figs.1(a)and (b)).A two-fluid nozzle has only one liquid channel and one gas channel (Fig. 1(d)), whereas a three-fluid nozzle includes two liquid channels (Fig. 1(g)). Therefore, the SiO2and ZrO2nanodispersions had to be mixed before being pumped into the spray dryer through the two-fluid nozzle. However, the zeta potentials of the SiO2(–31 mV) and ZrO2(+47 mV) nanoparticles are opposite. This resulted in severe aggregation of nanoparticles,the formation of an opaque nanodispersion,and even precipitation after both nanodispersions were mixed (Fig. 1(c)). As a result, the SiO2–ZrO2CNCs fabricated by the two-fluid nozzle appeared to have an irregular shape (Fig. 1(e)).

    The use of a three-fluid nozzle can avoid unwanted aggregation before the spray drying process by separating nanodispersions with opposite zeta potentials;in this case,the SiO2and ZrO2nanodispersions were simultaneously and respectively pumped into the spray dryer through different channels of the three-fluid nozzle(Fig. 1(f)). The nanodispersions were instantaneously mixed and immediately atomized into microdroplets by compressed air at the end of the nozzle.Meanwhile,the solvent was evaporated from the droplet surface by a gas stream at 100°C. The SiO2–ZrO2CNCs were thus constructed when the solvent was completely evaporated. Fig. 1(h) displays an SEM image of Si60Zr10-3. The regular shape and closely packed structure (similar to those of the SNCs[41]) demonstrate that the incorporation of ZrO2nanoparticles did not affect the morphology of the NCs.

    The mechanical properties of the DRCs filled with SNCs,Si60Zr10-2, and Si60Zr10-3 are shown in Fig. 2. Compared with the performances of the SNCs-filled DRCs, the flexural strength and compressive strength of the Si60Zr10-2-filled DRCs showed a significant decrease(of 16%and 17%, respectively), which was probably due to the irregular and relatively loose structure of Si60Zr10-2. In contrast, the Si60Zr10-3-filled DRCs exhibited good mechanical properties comparable to those of the SNC-filled DRCs, thus demonstrating that the structure of the CNCs is important for their filling properties, and that the three-fluid nozzle is suitable for spray drying components that are incompatible due to opposite zeta potentials.

    CNCs with different SiO2–ZrO2ratios were further constructed by means of the three-fluid nozzle, and were then heat-treated at 500°C for 3 h to improve their filling properties (labeled as HSi64Zr6-3, H-Si62Zr8-3, H-Si60Zr10-3, and H-Si58Zr12-3), since our previous work [51] demonstrated that the heat treatment process can strengthen the CNC structure. The morphologies of the SiO2–ZrO2CNCs are shown in Fig.3,and the corresponding size distributions are displayed in Fig.S1 in Appendix A.All the CNCs exhibited a regular shape and closely packed structure. Their average sizes increased from 1.20 to 1.89μm as the ZrO2content was increased from 6/70 to 12/70.

    Fig. 4 shows the X-ray diffraction (XRD) patterns of CNCs with different SiO2–ZrO2ratios. The broad diffraction peak at 23° indicates that the SiO2nanoparticles are amorphous,which is specified in Powder Diffraction File (PDF) card No. 29–0085. The diffraction peaks at 28.34°, 31.48°, 40.89°, and 45.51° belong to monoclinicphase ZrO2, according to PDF card No. 80–0966, and the peaks at 30°, 35°, 50.37°, and 60.19° can be ascribed to tetragonal-phase ZrO2(PDF card No. 88–1007). These findings indicate that the ZrO2nanocrystals are a mixture of tetragonal and monoclinic phases [50]. In addition, the peaks of ZrO2became stronger with the increase of ZrO2content. To confirm the distributions of SiO2and ZrO2in the CNCs, the O, Si, and Zr elements in H-Si60Zr10-3 were directly observed using SEM-EDS maps (Fig. 5). Fig. 5(a)clearly shows that all the elements are evenly distributed in HSi60Zr10-3, as is also evidenced by the even and spherical distribution of the Si and Zr elements in Fig. 5(b). These results demonstrate that the CNCs are successfully composed of ZrO2and SiO2nanoparticles with even distributions.

    Fig. 1. Schematic diagrams for the preparation process of SiO2–ZrO2 CNCs using a spray dryer equipped with a two-fluid nozzle or a three-fluid nozzle. (a) TEM image and photograph of the SiO2 nanodispersion; (b) TEM image and photograph of the ZrO2 nanodispersion; (c) TEM image and photograph of the SiO2 and ZrO2 mixture;(d)photograph of the two-fluid nozzle;(e)SEM images of Si60Zr10-2;(f)scheme of SiO2 and ZrO2 nanodispersions in the three-fluid nozzle;(g)photograph of the three-fluid nozzle; (h) SEM images of Si60Zr10-3.

    Fig. 2. (a) Flexural strength, (b) flexural modulus, (c) compressive strength, and (d) hardness of DRCs filled with SNCs, Si60Zr10-2, and Si60Zr10-3, respectively. *: p<0.05 compared with the DRCs filled with SNCs.

    Fig. 3. SEM images of (a) H-Si64Zr6-3, (b) H-Si62Zr8-3, (c) H-Si60Zr10-3, and(d) H-Si58Zr12-3.

    Fig. 4. X-ray diffraction (XRD) patterns of H-Si64Zr6-3, H-Si62Zr8-3, H-Si60Zr10-3,and H-Si58Zr12-3.

    Fig. 6 shows the mechanical properties of the DRCs containing heat-treated CNCs (H-Si60Zr10-3) and untreated CNCs (Si60Zr10-3).The heat treatment process clearly and dramatically enhanced the filling properties of the CNCs,especially in terms of the flexural modulus and hardness of the DRCs, which increased by 18% and 40% compared with those of the DRCs filled with untreated CNCs.The main reason for this increase is that the heat treatment process enhanced the interaction among the nanoparticles, resulting in a more compact structure and a densified framework in the CNCs[46], as evidenced by the fracture surfaces of the DRCs (Fig. 7).The Si60Zr10-3-filled DRCs exhibited a flat surface (Fig. 7(a)), indicating weak resistance to an externally applied force. The CNC structure cannot be clearly seen in Fig.7(a);this demonstrates that the nanoparticles in the untreated CNCs are unstable, which may result in destruction after they are extruded from the three-roll extruder.After the heat treatment process,the H-Si60Zr10-3 exhibited a stronger structure,since many complete H-Si60Zr10-3 can be seen on the cross-section of the DRCs (red circles in Fig. 7(b)). The DRCs displayed a coarse fracture surface with several curved steps,demonstrating the crack deflection caused by the addition of H-Si60Zr10-3 and the higher fracture energy of the DRCs [42]. The conversion degrees showed no significant difference between the heat-treated and untreated CNC-filled DRCs(Fig.S2 in Appendix A).

    Fig. 5. SEM-EDS maps for O, Si, and Zr in H-Si60Zr10-3. (a) Holistic element distributions; (b) element distributions in a single CNC.

    Fig.6. (a)Flexural strength,(b)flexural modulus,(c)compressive strength,and(d)hardness of the DRCs filled with Si60Zr10-3 and H-Si60Zr10-3.*:p<0.05 compared with the DRCs filled with Si60Zr10-3.

    Fig. 7. SEM images of the fracture surfaces of DRCs filled with (a) Si60Zr10-3 and(b) H-Si60Zr10-3.

    Fig. 8 gives the radiographs and radiopacity of DRCs filled with different types of fillers; the corresponding data are listed in Appendix A Table S2.Fig.8(a)shows the radiograph of the Al steps and the DRCs filled with SNCs, Si60Zr10-3, and H-Si60Zr10-3. The optical densities of the Al steps in the radiograph show a linear decline (Fig. 8(c)) with the increased thicknesses, indicating the enhanced radiopacity. The SNC-filled DRC displays the lowest radiopacity, which is only equivalent to a 0.14 mm Al step(Table S2), while the DRCs filled with Si60Zr10-3 and H-Si60Zr10-3 are equivalent to the 0.57 and 1.02 mm Al steps, respectively.These results indicate that the addition of ZrO2nanoparticles significantly improves the radiopacity of the DRCs, and that the heat treatment process for the fillers can further strengthen this property.

    DRCs loaded with H-Si64Zr6-3, H-Si62Zr8-3, H-Si60Zr10-3, and H-Si58Zr12-3 were prepared in order to explore the influence of ZrO2content on the radiopacity (Fig. 8(b)). It became evident that an increase of ZrO2content from 6%to 12%in mass fraction led to a significant increment from 0.36 to 1.3 mm of the radiopacity of the DRCs (Table S2). According to ISO 4049:2009, the radiopacity of DRCs must be equal to or higher than that of the same thickness of Al, which means that the H-Si60Zr10-3-filled DRCs and H-Si58Zr12-3-filled DRCs can meet this standard.

    S.mutans is commonly regarded as the primary pathogenic bacteria of dental caries[52,53].Plaque accumulating at the margin of DRCs may result in secondary caries, and may shorten the service life of the DRCs [54,55]. Therefore, ZnO nanoparticles (Fig. S3 in Appendix A) were introduced into the CNCs by means of a threefluid nozzle spray drying process in order to provide the DRCs with antibacterial activity. Fig. 9 shows SEM images of H-Si56Zr10Zn4-3,along with the corresponding XRD pattern and SEM-EDS maps.H-Si56Zr10Zn4-3 maintains a regular shape (Fig. 9(a)), and all the components are successfully imbedded into the CNCs (Fig. 9(b)).The element distributions of O, Si, Zr, and Zn are even (Figs. 9(c)and (d)), which is due to the good dispersion of the raw materials pumped into the spray dryer.

    Fig.8. (a,b) Radiographs and(c, d)radiopacity data of DRCs filled with different types of fillers.1: SNCs; 2:Si60Zr10-3; 3:H-Si60Zr10-3. A:H-Si64Zr6-3; B: H-Si62Zr8-3;C: HSi60Zr10-3; D: H-Si58Zr12-3. The aluminum steps were used as a reference.

    Fig. 9. (a) SEM images and (b) XRD pattern of H-Si56Zr10Zn4-3; (c, d) SEM-EDS maps for O, Si, Zr, and Zn elements in H-Si56Zr10Zn4-3.

    Fig. 10 shows the properties of the H-Si60Zr10-3-filled and HSi56Zr10Zn4-3-filled DRCs. The flexural properties, compressive strength, and degree of conversion of the H-Si56Zr10Zn4-3-filled DRCs show no significant difference in comparison with those of the H-Si60Zr10-3-filled DRCs, which demonstrates that the introduction of the ZnO nanoparticles did not destroy the advantageous structure of the CNCs. However, the hardness decreases from(64.5±0.7) to (61.7±0.2)HV. This decrease is mainly because the ZnO nanoparticles are not as hard as the SiO2and ZrO2nanoparticles.In addition,the radiopacity of the DRCs slightly increases from 1.02 to 1.08 mm (in terms of equivalent Al thickness).

    To quantitatively analyze the antibacterial activity of the HSi56Zr10Zn4-3-filled DRCs, S. mutans was adopted in this study.Fig.11 shows photographs of surviving S.mutans after being incubated for different times in the blank and experimental groups.For the blank group, the number of live S. mutans significantly increased after being incubated for 24 h (Figs. 11(a) and (b)). The number of S. mutans cultured on the H-Si60Zr10-3-filled DRCs for 24 h showed no significant difference in comparison with those cultured on the blank group,indicating that the composites loaded with the SiO2–ZrO2CNCs have no antibacterial activity.In contrast,the growth of the S.mutans incubated on the H-Si56Zr10Zn4-3-filled DRCs was obviously inhibited (Fig. 11(d)), and the antibacterial ratio exceeded 99.9%. These results demonstrate that HSi56Zr10Zn4-3 has great potential as an antibacterial filler.

    To confirm the universality of three-fluid nozzle spray drying,TiO2(Fig. S4(a) in Appendix A) and CaF2(Fig. S4(b) in Appendix A) nanoparticles—which are also commonly used dental fillers—were adopted as co-fillers of SiO2nanoparticles to construct CNCs.The zeta potentials of CaF2and TiO2nanoparticles are +55.6 and+45.2 mV, which are opposite with that of SiO2nanoparticles.Therefore, it is appropriate to use three-fluid nozzle spray drying.Various CNCs were constructed using three or four kinds of nanoparticles as building blocks, including SiO2–ZnO–CaF2CNCs(Fig. 12(a)), SiO2–TiO2–CaF2CNCs (Fig. 12(b)), SiO2–ZnO–ZrO2–TiO2CNCs (Fig. 12(c)), and SiO2–ZnO–TiO2–CaF2CNCs (Fig.12(d)). The mass ratios of the different nanoparticles are shown in Table S1.All the CNCs exhibited a regular shape,thereby demonstrating that three-fluid nozzle spray drying is a feasible and general strategy for constructing multifunctional fillers for DRCs.

    4. Conclusions

    In this study, multifunctional CNCs were successfully constructed using a spray dryer with a three-fluid nozzle for DRCs.The use of the three-fluid nozzle effectively avoided the unwanted aggregation of different nanoparticles with opposite zeta potentials before the spray drying process, thus achieving regularshaped CNCs with evenly distributed elements. For the SiO2–ZrO2binary system, the mechanical properties of the Si60Zr10-3-filled DRCs were consistent with those of SNC-filled DRCs because the regular CNC structure was maintained. The CNCs were also heat treated to reinforce their structure, thus obtaining better filling properties. Compared with the DRCs filled with untreated CNCs,the heat-treated CNC-filled DRCs exhibited significantly improved mechanical properties, particularly in terms of the flexural modulus(an increase of 18%)and hardness(an increase of 40%).In addition, increasing the ZrO2content and using the heat treatment process for the CNCs resulted in DRCs with significantly enhanced radiopacity.The heat-treated CNC-filled DRCs containing over 10%(in mass fraction) ZrO2nanoparticles meet the requirement for radiopaque fillers. For the SiO2–ZrO2–ZnO ternary system, the antibacterial ratio of the H-Si56Zr10Zn4-3-filled DRCs reached 99.9% while the mechanical properties remained stable. This method can also be extended to other ternary and even quaternary systems. Therefore, this work provides a general strategy to construct high-performance multifunctional cluster fillers for DRCs,especially when simultaneously considering the mechanical performance, radiopacity, and antibacterial activity.

    Fig. 10. (a) Flexural strength, (b) flexural modulus, (c) compressive strength, (d) hardness, (e) degree of conversion, and (f) radiopacity of H-Si60Zr10-3-filled and HSi56Zr10Zn4-3-filled DRCs. *: p<0.05 compared with the DRCs filled with H-Si60Zr10-3.

    Fig. 11. Photographs of surviving S. mutans after being incubated for different times.(a)0 h,blank group;(b) 24 h,blank group;(c)24 h,H-Si60Zr10-3-filled DRCs;(d) 24 h, H-Si56Zr10Zn4-3-filled DRCs.

    Fig.12. SEM images of(a)SiO2–ZnO–CaF2 CNCs,(b)SiO2–TiO2–CaF2 CNCs,(c)SiO2–ZnO–ZrO2–TiO2 CNCs, and (d) SiO2–ZnO–TiO2–CaF2 CNCs constructed by means of the three-fluid nozzle spray drying technique.

    Acknowledgments

    This work was financially supported by the National Key Research and Development Program of China (2016YFA0201701)and the National Natural Science Foundation of China(21878015).

    Compliance with ethics guidelines

    Dan-Lei Yang, Dan Wang, Hao Niu, Rui-Li Wang, Mei Liu,Fei-Min Zhang, Jie-Xin Wang, and Mei-Fang Zhu declare that they have no conflict of interest or financial conflicts to disclose.

    Appendix A. Supplementary data

    Supplementary data to this article can be found online at https://doi.org/10.1016/j.eng.2021.08.001.

    久久人妻av系列| 免费观看a级毛片全部| 色尼玛亚洲综合影院| 亚洲高清免费不卡视频| 日韩成人伦理影院| 日本一二三区视频观看| 搡女人真爽免费视频火全软件| 一级黄色大片毛片| 高清在线视频一区二区三区 | 国内久久婷婷六月综合欲色啪| а√天堂www在线а√下载| 欧美一区二区精品小视频在线| 精品久久久久久久人妻蜜臀av| 嘟嘟电影网在线观看| or卡值多少钱| 国内揄拍国产精品人妻在线| 亚洲欧美日韩东京热| 精品久久久久久成人av| 美女cb高潮喷水在线观看| 久久久久久大精品| 国产精品福利在线免费观看| 特级一级黄色大片| 欧美3d第一页| 午夜福利在线观看吧| 国产一区亚洲一区在线观看| 亚洲欧美精品自产自拍| 国产在线男女| 久久精品夜色国产| 性插视频无遮挡在线免费观看| 国产高清视频在线观看网站| 久久精品久久久久久噜噜老黄 | 日日干狠狠操夜夜爽| 永久网站在线| av黄色大香蕉| 禁无遮挡网站| 热99在线观看视频| 国内精品一区二区在线观看| 色尼玛亚洲综合影院| 丝袜美腿在线中文| 在线观看66精品国产| 亚洲av电影不卡..在线观看| 国产一区二区在线av高清观看| 99久久久亚洲精品蜜臀av| 中文字幕制服av| 免费观看的影片在线观看| 国国产精品蜜臀av免费| 亚洲成人精品中文字幕电影| 女同久久另类99精品国产91| 欧美变态另类bdsm刘玥| 如何舔出高潮| 日韩欧美精品免费久久| 变态另类丝袜制服| 日本黄色视频三级网站网址| 亚洲成av人片在线播放无| 国产大屁股一区二区在线视频| 秋霞在线观看毛片| 熟女人妻精品中文字幕| 国产精品国产三级国产av玫瑰| 男人舔奶头视频| 一个人看的www免费观看视频| 亚洲精华国产精华液的使用体验 | 国产成人精品久久久久久| 国产精品乱码一区二三区的特点| 亚洲人成网站高清观看| 女人被狂操c到高潮| 国产淫片久久久久久久久| 日日摸夜夜添夜夜爱| 国产一区二区在线av高清观看| 99久久精品热视频| 欧美日韩在线观看h| 插逼视频在线观看| 看免费成人av毛片| 少妇的逼水好多| 国产在线精品亚洲第一网站| 色视频www国产| av女优亚洲男人天堂| 一个人观看的视频www高清免费观看| 我要看日韩黄色一级片| 91久久精品国产一区二区三区| 丰满乱子伦码专区| 91久久精品国产一区二区三区| 亚洲成人中文字幕在线播放| 村上凉子中文字幕在线| 波多野结衣高清无吗| 91久久精品电影网| 亚洲成人精品中文字幕电影| 悠悠久久av| 国产高潮美女av| 亚洲欧美精品自产自拍| 久久精品91蜜桃| 国产熟女欧美一区二区| 成年女人看的毛片在线观看| 久久精品91蜜桃| 男的添女的下面高潮视频| 成年女人看的毛片在线观看| 你懂的网址亚洲精品在线观看 | 亚洲成av人片在线播放无| av在线亚洲专区| 日日摸夜夜添夜夜添av毛片| 亚洲在久久综合| 国产伦理片在线播放av一区 | 男人舔奶头视频| 边亲边吃奶的免费视频| 欧美精品一区二区大全| 91久久精品电影网| 亚洲中文字幕日韩| 国产伦精品一区二区三区四那| 99久久成人亚洲精品观看| 性插视频无遮挡在线免费观看| 国产不卡一卡二| 精品国内亚洲2022精品成人| 欧美成人精品欧美一级黄| 熟女人妻精品中文字幕| 免费观看的影片在线观看| 亚洲av熟女| 舔av片在线| 日韩三级伦理在线观看| 美女大奶头视频| 国产精品综合久久久久久久免费| 在线a可以看的网站| 看片在线看免费视频| 观看免费一级毛片| 亚洲人成网站在线播| 美女高潮的动态| 午夜激情欧美在线| 1024手机看黄色片| 18禁在线无遮挡免费观看视频| 国产精品精品国产色婷婷| 国产精品一区二区三区四区久久| 最新中文字幕久久久久| 一级毛片我不卡| 有码 亚洲区| av福利片在线观看| 99在线视频只有这里精品首页| 中文字幕熟女人妻在线| 狂野欧美激情性xxxx在线观看| 亚洲国产欧美在线一区| 国产精品,欧美在线| 亚洲欧洲国产日韩| 看非洲黑人一级黄片| 97人妻精品一区二区三区麻豆| 亚洲成人精品中文字幕电影| 欧美日本亚洲视频在线播放| 欧美又色又爽又黄视频| 2022亚洲国产成人精品| 神马国产精品三级电影在线观看| 人体艺术视频欧美日本| 亚洲国产精品合色在线| 大香蕉久久网| 看黄色毛片网站| 亚洲国产日韩欧美精品在线观看| 亚洲在久久综合| h日本视频在线播放| 国产黄片美女视频| 变态另类成人亚洲欧美熟女| av天堂中文字幕网| 天堂中文最新版在线下载 | 99久久精品一区二区三区| 亚洲成av人片在线播放无| 麻豆成人av视频| 久久精品国产亚洲av涩爱 | 日韩强制内射视频| 嫩草影院精品99| 精品免费久久久久久久清纯| 天美传媒精品一区二区| а√天堂www在线а√下载| 免费人成视频x8x8入口观看| 国产真实乱freesex| 校园春色视频在线观看| 午夜激情欧美在线| 美女cb高潮喷水在线观看| 在线免费观看不下载黄p国产| 亚洲欧美中文字幕日韩二区| 99热全是精品| 国产69精品久久久久777片| 人妻少妇偷人精品九色| 亚洲人与动物交配视频| 免费看日本二区| 精品久久久久久成人av| 亚洲国产精品久久男人天堂| 又爽又黄a免费视频| 国产成人精品一,二区 | av免费观看日本| 97人妻精品一区二区三区麻豆| 国产69精品久久久久777片| 啦啦啦啦在线视频资源| 99久久精品国产国产毛片| 美女cb高潮喷水在线观看| 一本一本综合久久| 日韩一区二区三区影片| 校园春色视频在线观看| 老女人水多毛片| 国产欧美日韩精品一区二区| 欧美高清成人免费视频www| 白带黄色成豆腐渣| 日本成人三级电影网站| 亚洲成人久久性| 国产伦精品一区二区三区视频9| 亚洲国产欧洲综合997久久,| 欧美性感艳星| 久久久久久大精品| av在线播放精品| 少妇猛男粗大的猛烈进出视频 | 午夜福利在线在线| 少妇人妻一区二区三区视频| 高清日韩中文字幕在线| 国产成年人精品一区二区| 精品久久国产蜜桃| 日本爱情动作片www.在线观看| 久久午夜福利片| 国产中年淑女户外野战色| 国产v大片淫在线免费观看| 亚洲美女搞黄在线观看| 国产乱人偷精品视频| 天堂av国产一区二区熟女人妻| 两性午夜刺激爽爽歪歪视频在线观看| 日韩,欧美,国产一区二区三区 | 国产精品国产高清国产av| 国产成人精品久久久久久| 免费看a级黄色片| 久久婷婷人人爽人人干人人爱| 天堂√8在线中文| 69人妻影院| 亚洲va在线va天堂va国产| 人妻系列 视频| 99久久成人亚洲精品观看| 麻豆一二三区av精品| 大香蕉久久网| 成人毛片a级毛片在线播放| 26uuu在线亚洲综合色| 又粗又硬又长又爽又黄的视频 | 久久人人爽人人片av| 国产精品蜜桃在线观看 | 熟女电影av网| 日韩av不卡免费在线播放| 哪个播放器可以免费观看大片| 国产男女内射视频| 亚洲欧美清纯卡通| 99热这里只有是精品在线观看| 亚洲第一av免费看| 国产精品不卡视频一区二区| 久久久久久久久久久免费av| 男的添女的下面高潮视频| 婷婷色麻豆天堂久久| 国产极品粉嫩免费观看在线 | 久久 成人 亚洲| 美女国产高潮福利片在线看| 蜜桃久久精品国产亚洲av| 精品久久久噜噜| 色5月婷婷丁香| 老司机影院毛片| 久久久久久久久久久久大奶| 国产一区二区三区av在线| 亚洲欧美成人综合另类久久久| 国产成人精品婷婷| 国产精品女同一区二区软件| 国产亚洲精品久久久com| 中文字幕亚洲精品专区| 亚洲精华国产精华液的使用体验| 性高湖久久久久久久久免费观看| 国产成人精品无人区| 又大又黄又爽视频免费| 中国三级夫妇交换| 视频中文字幕在线观看| 一本一本综合久久| 亚洲美女搞黄在线观看| 国产成人一区二区在线| 一级毛片黄色毛片免费观看视频| 男人操女人黄网站| 国产国拍精品亚洲av在线观看| 天堂8中文在线网| 久久久久网色| 熟妇人妻不卡中文字幕| 国产又色又爽无遮挡免| 欧美最新免费一区二区三区| 91午夜精品亚洲一区二区三区| 日韩中字成人| 有码 亚洲区| 高清不卡的av网站| 狂野欧美白嫩少妇大欣赏| av在线app专区| 国产探花极品一区二区| 国产成人精品无人区| 一区二区av电影网| 久久久久人妻精品一区果冻| videossex国产| 国产黄色视频一区二区在线观看| 欧美 日韩 精品 国产| 亚洲精华国产精华液的使用体验| 亚洲精品aⅴ在线观看| 亚洲国产精品专区欧美| 色视频在线一区二区三区| 水蜜桃什么品种好| 狠狠精品人妻久久久久久综合| 久热这里只有精品99| 99国产综合亚洲精品| 亚洲欧美精品自产自拍| 少妇人妻 视频| 国产黄片视频在线免费观看| 九色亚洲精品在线播放| 在线亚洲精品国产二区图片欧美 | 人妻少妇偷人精品九色| 高清不卡的av网站| 国国产精品蜜臀av免费| 免费观看在线日韩| 一区二区三区乱码不卡18| 精品久久久精品久久久| 建设人人有责人人尽责人人享有的| videosex国产| 男女国产视频网站| 在线观看人妻少妇| 国产熟女午夜一区二区三区 | 肉色欧美久久久久久久蜜桃| 丰满乱子伦码专区| 成人漫画全彩无遮挡| 一级a做视频免费观看| 国产免费一区二区三区四区乱码| 999精品在线视频| 在线观看免费视频网站a站| 全区人妻精品视频| 久久久久久久久大av| 一二三四中文在线观看免费高清| 人妻少妇偷人精品九色| 亚洲第一av免费看| 色网站视频免费| 成人黄色视频免费在线看| 男女边吃奶边做爰视频| 国产在视频线精品| 国产欧美日韩一区二区三区在线 | 日本色播在线视频| 国产精品女同一区二区软件| 国产精品久久久久久精品古装| 高清视频免费观看一区二区| 国产黄色免费在线视频| 日韩强制内射视频| 熟女人妻精品中文字幕| 男人添女人高潮全过程视频| 免费高清在线观看日韩| 亚洲天堂av无毛| 男女边吃奶边做爰视频| 久久99热这里只频精品6学生| 婷婷成人精品国产| 日韩,欧美,国产一区二区三区| 亚洲精品视频女| 久久久久久久久大av| 精品国产国语对白av| 久久久久久久久久久丰满| 精品少妇黑人巨大在线播放| 九九在线视频观看精品| 久久久久精品久久久久真实原创| 校园人妻丝袜中文字幕| 三上悠亚av全集在线观看| 久久久久久久久久成人| 欧美精品一区二区免费开放| 欧美少妇被猛烈插入视频| 亚洲婷婷狠狠爱综合网| 超碰97精品在线观看| 考比视频在线观看| 久久热精品热| 国产国拍精品亚洲av在线观看| 五月天丁香电影| 亚洲国产毛片av蜜桃av| 一级毛片黄色毛片免费观看视频| 国产精品国产三级国产av玫瑰| av电影中文网址| av在线app专区| 国产av精品麻豆| 日韩中字成人| 午夜免费鲁丝| 婷婷成人精品国产| 九草在线视频观看| 少妇人妻久久综合中文| 最后的刺客免费高清国语| 极品少妇高潮喷水抽搐| 久久人妻熟女aⅴ| 免费不卡的大黄色大毛片视频在线观看| 一级毛片我不卡| 久久久久久久久久久丰满| 人人妻人人澡人人爽人人夜夜| 一区二区av电影网| 一区二区三区免费毛片| 老熟女久久久| 国产免费福利视频在线观看| 国产精品免费大片| 狂野欧美激情性bbbbbb| 18+在线观看网站| 久久99蜜桃精品久久| 久久影院123| 午夜精品国产一区二区电影| 大香蕉久久网| 精品久久久久久电影网| 在线 av 中文字幕| 少妇的逼水好多| 国产精品偷伦视频观看了| 天美传媒精品一区二区| 妹子高潮喷水视频| 色5月婷婷丁香| 制服诱惑二区| 国产成人免费无遮挡视频| 久久久久久久久久久丰满| 高清午夜精品一区二区三区| av又黄又爽大尺度在线免费看| 国产老妇伦熟女老妇高清| 少妇被粗大的猛进出69影院 | 青春草视频在线免费观看| 精品国产露脸久久av麻豆| 777米奇影视久久| 人妻少妇偷人精品九色| 人人妻人人爽人人添夜夜欢视频| 男人操女人黄网站| 精品久久久精品久久久| 成人午夜精彩视频在线观看| 这个男人来自地球电影免费观看 | 观看美女的网站| 久热久热在线精品观看| 岛国毛片在线播放| 最近最新中文字幕免费大全7| 97精品久久久久久久久久精品| 免费看不卡的av| 69精品国产乱码久久久| 精品国产国语对白av| 在线观看免费视频网站a站| 精品人妻偷拍中文字幕| 观看美女的网站| 熟妇人妻不卡中文字幕| 国产免费福利视频在线观看| 91精品国产国语对白视频| 日韩视频在线欧美| 我的老师免费观看完整版| 日本猛色少妇xxxxx猛交久久| 999精品在线视频| 免费av不卡在线播放| 久久人人爽人人爽人人片va| 国产精品久久久久久精品电影小说| 人妻 亚洲 视频| 日本欧美国产在线视频| 欧美一级a爱片免费观看看| 午夜福利网站1000一区二区三区| 欧美国产精品一级二级三级| 建设人人有责人人尽责人人享有的| 久久精品人人爽人人爽视色| 免费人妻精品一区二区三区视频| 日本爱情动作片www.在线观看| av在线app专区| 日韩av不卡免费在线播放| 天堂8中文在线网| 晚上一个人看的免费电影| 成人亚洲精品一区在线观看| 18禁裸乳无遮挡动漫免费视频| 日本欧美国产在线视频| 97超碰精品成人国产| 亚洲欧洲国产日韩| 国产精品久久久久成人av| 免费人成在线观看视频色| 大香蕉久久成人网| 大片免费播放器 马上看| 中文字幕久久专区| 91午夜精品亚洲一区二区三区| 久久韩国三级中文字幕| 国产亚洲av片在线观看秒播厂| 一级爰片在线观看| 国产免费福利视频在线观看| 成人漫画全彩无遮挡| 日日啪夜夜爽| 蜜臀久久99精品久久宅男| 一本久久精品| 人人妻人人爽人人添夜夜欢视频| 美女国产视频在线观看| 韩国高清视频一区二区三区| 你懂的网址亚洲精品在线观看| 视频中文字幕在线观看| 国产淫语在线视频| 亚洲av成人精品一二三区| 国产日韩欧美视频二区| 久久人妻熟女aⅴ| av在线播放精品| 精品一品国产午夜福利视频| 日本wwww免费看| 精品久久久精品久久久| 麻豆成人av视频| 午夜久久久在线观看| 亚洲不卡免费看| 日韩av不卡免费在线播放| 最近手机中文字幕大全| 看免费成人av毛片| 国产精品人妻久久久影院| 在线观看www视频免费| 国产成人精品无人区| 大片免费播放器 马上看| 中国美白少妇内射xxxbb| 亚洲精品乱久久久久久| 久热久热在线精品观看| 婷婷色麻豆天堂久久| 日本欧美国产在线视频| 国产免费现黄频在线看| 狂野欧美激情性xxxx在线观看| 老女人水多毛片| 婷婷色综合大香蕉| 狂野欧美激情性bbbbbb| 欧美日韩一区二区视频在线观看视频在线| 天美传媒精品一区二区| 免费少妇av软件| 草草在线视频免费看| 国产乱来视频区| 日本-黄色视频高清免费观看| 久久韩国三级中文字幕| a级片在线免费高清观看视频| av免费在线看不卡| 晚上一个人看的免费电影| 亚洲一区二区三区欧美精品| 嫩草影院入口| 亚洲国产精品999| 国产成人精品婷婷| 中文字幕人妻熟人妻熟丝袜美| 一区在线观看完整版| 久久久久国产精品人妻一区二区| 国产有黄有色有爽视频| 久久青草综合色| 午夜免费观看性视频| 久久久久久伊人网av| 亚洲精品中文字幕在线视频| 日韩一本色道免费dvd| 免费观看的影片在线观看| 成年人免费黄色播放视频| 狂野欧美激情性xxxx在线观看| 在线观看一区二区三区激情| 极品人妻少妇av视频| 国产精品蜜桃在线观看| 亚洲精品久久久久久婷婷小说| 日本欧美国产在线视频| 日韩熟女老妇一区二区性免费视频| 国产日韩一区二区三区精品不卡 | av有码第一页| 久久综合国产亚洲精品| 另类亚洲欧美激情| 欧美国产精品一级二级三级| 国产日韩欧美在线精品| 亚洲av成人精品一二三区| 嘟嘟电影网在线观看| 婷婷色麻豆天堂久久| 精品人妻熟女av久视频| 国产免费福利视频在线观看| 性色avwww在线观看| 久久久久国产网址| av天堂久久9| 国产精品人妻久久久久久| 男女高潮啪啪啪动态图| 国产淫语在线视频| 国产精品人妻久久久影院| 99久久人妻综合| 国产精品秋霞免费鲁丝片| 午夜精品国产一区二区电影| 国产精品无大码| 99热全是精品| 美女大奶头黄色视频| 一本久久精品| 99视频精品全部免费 在线| 一二三四中文在线观看免费高清| 中国美白少妇内射xxxbb| 色哟哟·www| 男人添女人高潮全过程视频| 色婷婷av一区二区三区视频| 国产爽快片一区二区三区| 亚洲色图 男人天堂 中文字幕 | 又粗又硬又长又爽又黄的视频| 精品人妻一区二区三区麻豆| 亚洲美女视频黄频| 亚洲图色成人| 最新中文字幕久久久久| 超碰97精品在线观看| 搡女人真爽免费视频火全软件| 91成人精品电影| 精品国产一区二区久久| 亚洲av不卡在线观看| 国产一区二区在线观看日韩| 国产精品蜜桃在线观看| 69精品国产乱码久久久| 久热久热在线精品观看| 欧美日韩精品成人综合77777| 欧美丝袜亚洲另类| 国产一区二区三区av在线| 最近的中文字幕免费完整| 免费大片黄手机在线观看| 制服人妻中文乱码| 尾随美女入室| 久久综合国产亚洲精品| 日韩在线高清观看一区二区三区| 97在线视频观看| 蜜桃在线观看..| 91久久精品国产一区二区三区| 国产精品国产av在线观看| 欧美另类一区| av视频免费观看在线观看| 777米奇影视久久| 男女无遮挡免费网站观看| 午夜激情久久久久久久| 一级爰片在线观看| 亚洲国产欧美在线一区| 成人综合一区亚洲| 黑人高潮一二区| 精品久久久噜噜| 国产精品三级大全| 亚洲精品一二三| 色视频在线一区二区三区| 一个人看视频在线观看www免费| 91精品国产国语对白视频| 欧美最新免费一区二区三区| 一本久久精品| 成年美女黄网站色视频大全免费 | av有码第一页| 亚洲高清免费不卡视频| 国产男女超爽视频在线观看| av电影中文网址| 成人毛片60女人毛片免费| 国产精品一区www在线观看|