Enamel bionic dental ceramic repair material for indirect repair as well as preparation method and application thereof

Abstract

The invention relates to an enamel bionic dental ceramic repair material for indirect repair as well as a preparation method and application of the enamel bionic dental ceramic repair material, firstly, an ultra-long hydroxyapatite nanowire is synthesized, or the ultra-long hydroxyapatite nanowire is subjected to silicon dioxide or silicon dioxide-zirconium oxide coating modification, and a nano-scale crystal structure form of enamel is simulated; secondly, coupling the nanowires by utilizing amphiphilic molecules gamma-methacryloxy propyl trimethoxy silane or 10-methacryloxy decyl phosphoric acid dihydrogen acid, and inducing the nanowires to be compactly and parallelly arranged, so as to form an enamel-like micron-sized glaze column structure. And then, immersing the nanowire aggregate with the glaze-column-like structure into resin monomer liquid, and realizing ordered and crossed macroscopic arrangement of the glaze-column-like structure under the action of centrifugal strong shearing force. Finally, excessive organic matrixes are removed, the material is compact and solidified under the high-pressure condition of cold sintering, efficient and large-scale enamel-like block construction is achieved, and the material is applied to indirect repair of oral clinical tooth defects.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biological materials, in particular to an enamel biomimetic dental ceramic repair material for indirect repair, a preparation method and application thereof. BACKGROUND

[0002] At present, in the process of oral clinical diagnosis and treatment, tooth defects caused by caries, trauma and other reasons can only be filled with artificial repair materials to replace the missing tooth tissue. The composition, structure and performance of the repair materials such as metal, ceramic and composite resin used in clinical are quite different from those of tooth tissue, which may cause interface damage between tooth tissue and repair material, mismatch of biological compatibility and mechanical properties. For example, metal materials are not aesthetic, and some metal ions produced by corrosion also have potential safety problems; ceramic materials are brittle and have too high hardness, which can easily cause abrasion of the adjacent teeth; composite resin materials have poor wear resistance and are easy to wear, and the polymerization shrinkage during curing can easily lead to interface micro-leakage, thereby causing secondary caries. And with the development of modern society, the demand for aesthetic repair and minimally invasive repair in oral repair is increasing, and the application of ceramic, composite resin and other tooth-colored repair materials is becoming more and more widely. However, although this kind of material has been widely used in clinical and its performance is constantly improved. Resin-based ceramic (resin penetration into ceramic framework structure and composite resin filler modification) has been developed to overcome some defects of ceramic repair materials, but there are still problems in the clinical repair durability.

[0003] Oral medicine workers and material scientists have been looking for an ideal repair material, hoping that such repair material can have composition, structure and morphology matched with natural tooth tissue. The research of tooth tissue biomimetic material is one of the key scientific problems in the development of oral medicine, and the research of tooth biomimetic repair material will inevitably bring about the change of tooth repair technology and concept, leading the development of oral medicine.

[0004] The construction of enamel-like bulk material is just started. The Institute of Solid State Chemistry of Chinese Academy of Sciences obtains macroscopic orientation of HA nanowires (HANW) by 3D printing, combines resin infiltration and cold isostatic pressing to construct the enamel-like bulk material. Beijing University of Aeronautics and Astronautics and Peking University obtain macroscopically oriented, amorphous intergranular layer (AIP) on the surface of hydroxyapatite (HA) nanowires (HA@ZrOAIP, HA@Mg / Fe AIP) assembly by freeze-casting technology, and obtain 3D enamel-like bulk material with excellent mechanical properties by isostatic pressing technology under the mediation of polyvinyl alcohol adhesive. The HANW obtained by the current 3D enamel material is only arranged in a single direction, and the HA of the enamel is only arranged in parallel on the surface, and is staggered inside; in addition, the HANW arrangement has no typical enamel column structure, but only parallel and dense arrangement, and lacks the bionics of enamel interstitial structure; in terms of performance, the current research focuses on the improvement of mechanical properties, and ignores the optical performance.

[0005] In view of the above defects, the inventor of the present application has finally obtained the present application after a long period of research and practice. SUMMARY

[0006] The present application aims to solve the problem that the materials used for the current dental defect repair, including metals, ceramics and composite resins, etc., have large differences in composition, structure and performance from dental tissues, which may cause interface damage between dental tissues and repair materials, mismatch of biological compatibility and mechanical properties, and provides a dental enamel bionic dental ceramic repair material for indirect repair, a preparation method and application thereof.

[0007] In order to achieve the above-mentioned purpose, the present application discloses a preparation method of a dental enamel bionic dental ceramic repair material for indirect repair, comprising the following steps:

[0008] S1, preparing ultra-long hydroxyapatite nanowires and surface modified products thereof as a basic material, modifying the ultra-long hydroxyapatite nanowires to obtain modified ultra-long hydroxyapatite nanowires;

[0009] S2, arranging the modified ultra-long hydroxyapatite nanowires obtained in step S1 in parallel and densely into a micron-level bundle structure with a diameter of up to microns;

[0010] S3, soaking the micron-level bundle structure of the modified ultra-long hydroxyapatite nanowires obtained in step S2 in a resin monomer containing an initiator, and further arranging and assembling into a macroscopically ordered structure;

[0011] S4, using cold welding technology, the modified super-long hydroxyapatite nanowires with macroscopic order structure obtained in step S3 are extruded through a plurality of resin matrixes and solidified to form a tooth enamel biomimetic dental ceramic restoration material.

[0012] In the step S1, the method for preparing the hydroxyapatite nanowires comprises the following steps:

[0013] S11, a 300 mL sodium oleate methanol emulsion is obtained by mixing a 7% NaOH aqueous solution by mass volume ratio and a 20% methanol+35% oleic acid aqueous solution by volume ratio under magnetic stirring;

[0014] S12, an 80 mL aqueous solution containing 2.22 g of CaCl2 is slowly added to the mixture obtained in step S11;

[0015] S13, an 120 mL aqueous solution containing 6.24 g of NaH2PO4·2H2O is slowly added to the mixed solution obtained in step S12, and then the obtained suspension is moved into a high-pressure reaction kettle, and is reacted at 180℃ for 24 h under magnetic stirring. The hydroxyapatite nanowires suspended in the slurry are washed with anhydrous ethanol and deionized water respectively, and are freeze-dried to obtain a white powder sample, i.e., the hydroxyapatite nanowires.

[0016] In the step S1, the method for modifying the super-long hydroxyapatite nanowires comprises surface silica modification and surface silica-zirconia coating modification.

[0017] The specific method for the surface silica modification of the super-long hydroxyapatite nanowires is as follows: under magnetic stirring, 50 mL of deionized water and 6 mL of ammonia water are added to a 200 mL ethanol suspension containing 2 mg mL -1 of hydroxyapatite nanowires, and then 2 mL of tetraethyl orthosilicate is added. After stirring for 6 hours, centrifugal collection is performed, and the obtained sample is sequentially washed with anhydrous ethanol and deionized water, and is freeze-dried to obtain a white powder sample, i.e., the super-long hydroxyapatite nanowires-silica shell core structure.

[0018] The specific method for modifying the surface of ultralong hydroxyapatite nanowires with a silica-zirconia coating is as follows: Take 0.12 g of the above-mentioned ultralong hydroxyapatite nanowire-silica core-shell structure and disperse it in 50 mL of deionized water. Add 0.6057 g of tris(hydroxymethyl)aminomethane and 340 mL of HCl with a concentration of 12 mol / L to maintain the pH of the mixed solution at 7.5. After the mixed solution is ultrasonically dispersed evenly, add 0.0192 g of zirconium chloride octahydrate, stir at room temperature, and then incubate the mixed solution in a water bath at 60 °C for 6 hours. After washing three times with deionized water, freeze dry and sinter at 300 °C for 2 hours to obtain the silica-zirconia core-shell structure on the surface of ultralong hydroxyapatite nanowires.

[0019] In step S2, the modified ultralong hydroxyapatite nanowires are arranged in parallel and densely into a bundle structure with a diameter of up to micrometers, specifically including the following steps:

[0020] S21, using surfactant-induced self-assembly of nanowires to obtain a slurry.

[0021] S22, the slurry obtained in step S21 is placed in a syringe and continuously spun into a coagulation bath rotating at 30 r / min at a speed of 0.5 mL / min. After standing for 5 minutes, the precipitate bundles are filtered, repeatedly washed, and freeze-dried to obtain nanowire aggregates, characterized by parallel and densely arranged nanowire aggregates with diameters up to the micrometer level.

[0022] In step S21, the surfactant is γ-methacryloyloxypropyltrimethoxysilane or 10-methacryloyloxydecylphosphodihydrogen acid.

[0023] In step S4, the specific process is as follows: The micron-sized bundled ultralong hydroxyapatite nanowires obtained in step S2 are immersed in an ethanol solution containing bisphenol A-dimethacrylate glycidyl ester, dimethacrylate carbamate, and initiator monomers. The mixture is stirred at 300 r / min for 12 h. The precipitate is then collected and transferred to a centrifuge tube. The mixture is centrifuged at 20000 r / min for 30 min. The mixture of ultralong hydroxyapatite nanowires and resin matrix is ​​transferred as a whole to a mold with a microporous filter membrane at the bottom. The mixture is then processed in a cold sintering press, pre-pressed to 50 MPa to remove air, heated to 90°C, and gradually pressurized to 300 MPa. The mixture is held at the temperature and pressure for 30 min and polymerized in situ to obtain a blocky enamel-like dental restoration material.

[0024] The present invention also discloses a biomimetic dental ceramic restorative material for indirect restoration of tooth enamel prepared by the above preparation method and its application in minimally invasive restoration of tooth defects.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. Because enamel-like biomimetic materials have a similar composition and structure to natural tooth enamel, they may experience tooth decay similar to that of natural teeth during service. This invention proposes the following innovative approach compared to current technologies. This invention is the first to synthesize a unique modified structure of ultra-long hydroxyapatite nanowires, namely, hydroxyapatite nanowires with a silica (SiO2) coating, specifically synthesizing an "ultra-long hydroxyapatite nanowire-silica core-shell structure (HANW@SiO2)," and hydroxyapatite nanowires with a surface silica (SiO2)-zirconia (ZrO2) coating, specifically synthesizing an "ultra-long hydroxyapatite nanowire-silica-zirconia core-shell structure (HAWN@SiO2-ZrO2)." These modified structures are beneficial for improving the caries resistance and mechanical properties of enamel-like materials, which is one of the technological innovations of this invention compared to current enamel-like biomimetic materials.

[0027] 2. Currently, it is quite difficult to mimic the micron-level key structure of natural tooth enamel—enamel prisms—at the micron level using biomimetic materials for tooth enamel. To overcome this technical challenge, this invention proposes for the first time the use of amphiphilic molecules γ-methacryloyloxypropyltrimethoxysilane (KH570) and 10-methacryloyloxydecylphosphodihydrogen acid (MDP) coupled with ultralong hydroxyapatite nanowires and their modified forms. Utilizing the self-assembly between molecules and based on rotational centrifugal precipitation, parallel and dense arrangement of nanowires from the nanometer to the micrometer scale is achieved, mimicking the micron-level structure of tooth enamel.

[0028] 3. Current technologies for constructing biomimetic materials for tooth enamel face technical bottlenecks in achieving the macroscopically ordered arrangement of ultra-long hydroxyapatite nanowires. This is manifested in the single orientation of the arrangement, failing to mimic the staggered arrangement of hydroxyapatite crystals in natural tooth enamel. Furthermore, macroscopic sorting techniques are complex and have low engineering sophistication, such as liquid nitrogen cryogenic casting. This invention solves the aforementioned macroscopic arrangement problem of nanowires, exhibiting high repeatability and engineering sophistication, making it suitable for widespread application. This invention, for the first time, utilizes the mass difference of nanowire aggregates in an ethanol solution containing bisphenol A-dimethacrylate (Bis-GMA), urethane dimethacrylate (UDMA), and initiator monomers. Under the action of centrifugal force, the layered ordered deposition of nanowire aggregates is achieved, mimicking the macroscopic structure of tooth enamel. The synthesized enamel-like material possesses the semi-permeability and frictional properties of natural tooth enamel, as well as good mechanical properties. Attached Figure Description

[0029] Figure 1Characterization of ultralong HA nanowires: a) X-ray diffraction (XRD) patterns of the prepared ultralong HA nanowires and standard HA crystals; b) Fourier transform infrared (FTIR) spectrum of the ultralong HA nanowires; c1 and c2 are at different magnifications; d) Transmission electron microscopy (TEM) image of the ultralong HA nanowires; d1 and d2 are THE patterns at different magnifications; and the inset of d2 is an electron diffraction pattern showing the orientation of the HA crystals.

[0030] Figure 2 The images show a comparison of SEM and TEM images of ultralong hydroxyapatite nanowire-silica core-shell structure (HANW@SiO2) and ultralong hydroxyapatite nanowire (HANW). In the images, A is the SEM image of HANW, B is the SEM image of HANW@SiO2, E is the TEM image of HANW, and F is the TEM image of HANW@SiO2.

[0031] Figure 3 Based on SiO2-coated HA nanowires (HANW@SiO2), a zirconium oxide (ZrO2) coating was applied to its surface to construct HA nanowires with a ZrO2 coating (HANW@SiO2-ZrO2). Among them, a is a SEM image of HANW@SiO2-ZrO2, b is a TEM image of the cross section of HANW@SiO2-ZrO2, and c is a SEM elemental mapping image (Ca, P, O, Si and Zr elements) of HANW@SiO2-ZrO2.

[0032] Figure 4 To characterize HA nanowires before and after MDP functionalization, D shows a SEM image of MDP-functionalized HA nanowires aggregated into micron-sized parallel bundles, E is a magnified version of the "D" image, F is a TEM image of the cross-section of the bundled nanowires, and G, H, and I are comparisons of XRD, FTIR, and XPS images of HA nanowires before and after MDP functionalization, respectively.

[0033] Figure 5 The synthesis of enamel-like repair blocks is shown in Figure b, which is a SEM image and optical photograph of the cross-sectional structure of the enamel-like composite material before pressure curing; Figure c is a SEM image and optical photograph of the cross-sectional structure of the enamel-like composite material after pressure curing; and Figure d is a SEM image of the cross-sectional structure of four groups of enamel-like materials synthesized by assembling with Bis-GMA / anhydrous ethanol as a matrix in different ratios ((d1) 0.50g / 5mL group, (d2) 0.75g / 5mL group, (d3) 1.00g / 5mL group, (d4) 1.25g / 5mL group).

[0034] Figure 6The structure and morphology of natural glaze and the glaze-like composite material (ELRMs) optimized in Example 5 are shown, where (a1-a5) are SEM images of natural glaze: (a1-a3) cross-section, (a4-a5) longitudinal section, (b1-b 10 Electron microscopy images of enamel-like composite materials: (b1-b3, b6-b8) SEM images, (b4, b5, b9, b... 10 TEM image.

[0035] Figure 7 Optical properties of the optimized enamel-like composites (ELRMs), 3M P60 resin, 3M Ultra-Tough Porcelain, Vita Elastic Porcelain, natural enamel, and dentin in Example 5: a) visible light transmittance; b) fluorescence excitation spectrum under ultraviolet irradiation at a wavelength of 365 nm; c) optical photograph of the material under ultraviolet irradiation at a wavelength of 365 nm.

[0036] Figure 8 The mechanical properties of ELRMs, 3M P60 resin, 3M Elastic Ceramic, Vita Elastic Ceramic, enamel and dentin are given, where a is Vickers hardness, b is tensile strength, c is compressive strength, d is compressive modulus, and e is coefficient of friction. The values ​​are expressed as mean ± SD, where ns is the coefficient of friction. P>0.05, *P<0.05, **P<0.01, ***P<0.001, ****P<0.0001.

[0037] Figure 9 For the clinical application potential assessment of the enamel-like composite material (ELRMs) optimized in Example 5, where a is an optical photograph of the high inlay cut from ELRMs and (b) optical photographs and SEM images of ELRMs before and after acid etching: (b1) optical photograph, (b2, b3) SEM images before acid etching, (b4, b5) SEM images after acid etching.

[0038] Figure 10 The morphology of the enamel-like composite material synthesized in Example 6 is compared with that of natural tooth enamel. A shows scanning electron microscope (SEM) images of natural tooth enamel (a, b) and the enamel-like composite material (c–f); B shows transmission electron microscope (TEM) images of ultrathin sections of the enamel-like composite material, (a) showing hydroxyapatite nanowire bundles (high-contrast area, indicated by yellow arrows) and polymeric silanes (low-contrast area, indicated by white arrows). (b) The hydroxyapatite nanowire bundles are arranged in different directions: at a certain angle or perpendicularly (indicated by red arrows) (b1), parallel (indicated by yellow double arrows) (b2), or cross-connected (c)); C shows images of the enamel-like composite material before (a) and after (b) acid etching.

[0039] Figure 11This paper compares the mechanical properties of the enamel-like composite material, Tetric N-Ceram (a resin composite material from Ivoire), P60 (a resin composite material from 3M), and Charisma (a resin composite material from Heraeus) synthesized using the technology system of Example 6. In the figures, A represents Vickers hardness, B represents radial tensile strength, C represents compressive strength, D is a schematic diagram of the experiment, E represents the coefficient of friction, F represents the Z-axis depth, and G represents the scanning electron microscope morphology of the wear trajectory surfaces of enamel (a, b) and enamel-like composite materials (c, d). Figures b and d are magnified views of figures a and c, respectively. Data are expressed as mean ± standard deviation. *P < 0.05. (ns, no significant difference;)

[0040] Figure 12 The enamel-like material structure constructed by the technical system of Example 7 includes SEM images of natural tooth enamel cross sections (A, B, C), SEM images of enamel-like material cross sections (D, E, F, G), and TEM images of 100nm ultrathin sections of enamel-like material (H, I).

[0041] Figure 13 The SEM results of the acid resistance of the enamel-like material after Example 7 are shown below. (A,B) SEM image before acid etching, (C,D) SEM image after acid etching, (A,C) HANW ELM, (B,D) HANW@SiO2ELM.

[0042] Figure 14 Multiscale structural characterization of natural tooth enamel and the optimized enamel-like material (HASZ BBEM) of Example 8: A is a schematic diagram of biomimetic tooth enamel at the nano, micro, and macro levels; (BE) scanning electron microscope images of natural tooth enamel; (FH and JL) scanning electron microscope images of HASZ BBEM and (I and M) transmission electron microscope images of ultrathin sections of HASZ BBEM; (N and O) macroscopic optical images of HASZ BBEM (N) and HA BBEM (O); (P) transmission electron microscope elemental mapping images of calcium, phosphorus, oxygen, zirconium, silicon, and carbon elements in the cross section of HASZ BBEM.

[0043] Figure 15To optimize the mechanical properties of the enamel-like material (HASZ BBEM), Figure a shows the nanoindentation force curves of the enamel, HA BBEM, and HASZ BBEM; Figure b shows the nanohardness and Young's modulus of the HA BBEM and HASZ BBEM; Figure c shows the Vickers hardness of the enamel, HA BBEM, HASZ BBEM, intrinsic material, 3M P60, and 3M LAVA; Figure d shows the pre-tensile strength of the HA BBEM, HASZ BBEM, 3M P60, and 3M LAVA; Figure e shows the coefficient of friction of the enamel, HA BBEM, HASZ BBEM, intrinsic material, 3M P60, and 3M LAVA; Figure f shows the compressive strength of the HA BBEM, HASZ BBEM, 3M P60, and 3M LAVA; Figure g shows the compressive modulus of the HA BBEM, HASZ BBEM, 3M P60, and 3M LAVA; Figure h shows the optimization of the enamel-like material (HASZ BBEM) in Example 8. SEM images of the BBEM cross section, magnified step by step from left to right;

[0044] Figure 16 To optimize the acid resistance of the enamel-like material (HASZ BBEM), A represents HA BBEM and B represents digital images of HASZ BBEM before and after acid etching. SEM images of HA BBEM (C,E) and HASZ BBEM (D,F) before (C,D) and after (E,F) acid etching are also shown. Detailed Implementation

[0045] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings.

[0046] Example 1

[0047] Synthesis of ultralong hydroxyapatite nanowires (HANW):

[0048] First, under magnetic stirring, 90 mL of deionized water, 40 mL of methanol, and 70 mL of oleic acid were mixed. Second, 100 mL of aqueous solution containing 7.00 g of NaOH was slowly added dropwise to the mixture, and the mixture was stirred for 30 minutes. Third, 80 mL of aqueous solution containing 2.22 g of CaCl2 was slowly added to the mixture, and the mixture was stirred for 30 minutes. Fourth, 120 mL of aqueous solution containing 6.24 g of NaH2PO4·2H2O was slowly added to the mixture, and the mixture was stirred for another 30 minutes. The resulting suspension was then transferred to a 1 L polytetrafluoroethylene-lined high-pressure reactor and heated at 180 °C for 26 hours while simultaneously being magnetically stirred at 100 r / min. Finally, the HA nanowires suspended in the slurry were washed five times with anhydrous ethanol and deionized water, respectively, and then freeze-dried for 48 hours to obtain a white powder sample, which was then sealed and stored in a desiccant oven.

[0049] Characterization methods for synthesized hydroxyapatite nanowires: Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were used to characterize the composition and crystal structure of the samples; scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the morphology of the samples. Figure 1 ).

[0050] Example 2

[0051] Synthesis of ultralong hydroxyapatite nanowires with silica surface coating, namely, ultralong hydroxyapatite nanowire-silica core-shell structure (HANW@SiO2).

[0052] First, HANM was synthesized according to Example 1.

[0053] Then, under magnetic stirring, 50 mL of deionized water and 6 mL of ammonia (28%) were added to 200 mL of solution containing 2 mg / mL of ammonia. -1 The HANWs were ultrasonically treated in an ethanol suspension for 1 h. Then, 2 mL of tetraethyl orthosilicate (TEOS) was added with stirring at room temperature. After stirring for 6 h, the sample was collected by centrifugation, washed 5 times with anhydrous ethanol and 3 times with deionized water, and freeze-dried for 48 h to obtain a white powder sample, which was then sealed and stored in a desiccant oven. Figure 2 ).

[0054] Example 3

[0055] Hydroxyapatite nanowires with a surface coating of silica (SiO2)-zirconia (ZrO2) are synthesized as "ultralong hydroxyapatite nanowires-silica-zirconia core-shell structure (HAWN@SiO2-ZrO2)".

[0056] A hydroxyapatite nanowire@silica@zirconia core-shell structure was synthesized using an in-situ hydrolysis method involving zirconium ions. 0.12 g of HA@SiO2 was dispersed in 50 mL of deionized water, and 0.6057 g of tris(hydroxymethyl)aminomethane (Tris) and 340 mL of HCl (12 mol / L) were added to maintain the pH of the solution at 7.5. The solution was sonicated for 20 min to ensure uniform dispersion of the nanowires. Then, 0.0192 g of zirconium oxychloride octahydrate (H16Cl2O9Zr) was added, and the mixture was stirred at room temperature for 30 min to allow zirconium ions to be fully adsorbed onto the nanowire surface. The solution was then incubated in a water bath at 60 °C for 6 hours, washed three times with deionized water, freeze-dried, and sintered at 300 °C for 2 hours to obtain the HANW@SiO2@ZrO2 core-shell structure. The crystal structure and composition of the synthesized material were analyzed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR); the morphology was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Figure 3 ).

[0057] Example 4

[0058] 10-Methacryloxydecylphosphodihydrogen acid (MDP) coupled with NANW induces its self-assembly to form a dense, parallel, micron-sized enamel-like columnar structure.

[0059] 10-Methacryloxydecylphosphodihydrogen acid (MDP) coupling: A certain amount of dried HANW is dispersed in 10 mL of 10 wt% MDP anhydrous ethanol solution, and reacted for 12 hours in the dark with high-speed stirring. The mixture is then allowed to settle and the slurry is collected. The second step is wet spinning: The collected slurry is placed in a 1 mL syringe and continuously spun into a coagulation bath (ethanol:water = 9:1, volume) rotating at 0.5 mL / min, and allowed to stand for 5 minutes. The precipitate bundles are filtered, collected, repeatedly washed, and freeze-dried. Aggregates of nanowires are obtained. These are characterized by parallel, densely packed nanowire aggregates with diameters reaching the micrometer scale.

[0060] The bonding between MDP and hydroxyapatite nanowires was characterized using FTIR, XPS, and high-frequency infrared C / S measurements. The self-assembly of hydroxyapatite nanowires with the assistance of MDP was characterized using SEM. Figure 4 ).

[0061] Example 5

[0062] Synthesis of MDP-coupled HANW-based enamel-like fast materials:

[0063] 0.2 g of nanowires were immersed in an ethanol solution containing 0.5-1.0 g of bisphenol A-dimethacrylate (Bis-GMA), 0.5 g of urethane dimethacrylate (UDMA), and initiator monomers (5-10 μg benzoyl peroxide / 1-2 μg lithium phenyl-2,4,6-trimethylbenzoyl phosphite (BPO / LAP)). The mixture was stirred at 300 rpm for 12 h. The precipitate was then collected and transferred to a centrifuge tube, which was centrifuged at 20,000 rpm for 30 min. The shear force generated by the liquid flow caused the nanowires to settle layer by layer, forming a unique structure with ordered intralayer structure and interlayer crossover at a certain angle. Figure 5 After removing the supernatant, place the precipitate in a vacuum drying oven at room temperature to allow the ethanol to evaporate completely.

[0064] The aforementioned nanowire and resin matrix mixture was transferred integrally into a mold with a microporous membrane (pore size <1μm) at the bottom and processed in a cold sintering press. Pre-compression to 50MPa was performed to remove air, followed by heating to 90℃ and gradually increasing the pressure to 300MPa (50MPa / 5min, gradually increasing to 300MPa / 30min). The mixture was held at this temperature and pressure for 30min for in-situ polymerization, yielding a blocky, enamel-like dental restorative material. Its structure was characterized using SEM and TEM. Figure 5 , Figure 6 ).

[0065] I. Optical performance evaluation of the optimized enamel-like material in Example 5:

[0066] Using natural tooth enamel, dentin, and commercial restorative materials (3M Filtek) TM P60 Posterior Restorative System, 3M TM Lava TM Using the Ultimate Restorative (Vita Enamic) as a control, the optical properties of a group of materials selected in 2.3.4 were characterized.

[0067] The transmittance of visible light in the wavelength range of 380–800 nm was measured using a UV-Vis-NIR spectrophotometer through a 6 mm diameter aperture, and the spectral data were recorded at 1 nm intervals. The fluorescence excitation effect was measured using a steady-state / transient fluorescence spectrometer, which measured the fluorescence wavelength and intensity of the sample surface when irradiated with 365 nm ultraviolet light. The color of each group of samples was observed and photographed under 365 nm ultraviolet light irradiation.

[0068] The results showed that ELRMs had significantly higher visible light transmittance in the 380-800 nm wavelength range than other clinical restorative materials, most closely resembling enamel, and even slightly surpassing it. Under the same intensity of 365 nm ultraviolet light irradiation, the peak fluorescence wavelength of ELRMs was the same as that of enamel, at 440 nm, and their peak fluorescence intensity was 338,000. This indicates that ELRMs possess optical properties close to those of natural enamel. Enamel-like materials exhibit optical properties closer to natural enamel than 3M P60 resin, 3M Ultra-Tough Porcelain, Vita Elastic Porcelain, and dentin. Figure 7 ).

[0069] II. Evaluation of the mechanical properties of the optimized enamel-like material in Example 5:

[0070] 1. Microhardness test

[0071] Using natural tooth enamel, dentin, and commercial restorative materials (3M Filtek) TMP60 Posterior Restorative System (hereinafter referred to as "3M P60 resin"), 3M TM Lava TM Ultimate Restorative (hereinafter referred to as "3M Resilience Porcelain") and Vita Enamic (hereinafter referred to as "Vita Resilience Porcelain") were used as controls.

[0072] Collect the extracted third molars and cut them into enamel and dentin sheets with a thickness of 2mm using a low-speed precision diamond cutter. Use CAD / CAM to cut 3M high-strength porcelain and Vita flexible porcelain into 10mm diameter, 2mm thick circular pieces. Polish the selected 10mm diameter, 2mm thick circular 3D enamel blocks and all the above materials with silicon carbide paper (Nos. 600-3000) before use.

[0073] The hardness of six groups of samples was measured using a microhardness tester. Each group consisted of five samples, and five sites with an interval of more than 10 micrometers were repeatedly measured on each sample. During the measurement, a Knoop diamond cutter with a load of 100.0g was applied to the sample surface for 15s to obtain indentations. The indentation range was calculated to obtain the results.

[0074] 2. Tensile strength test

[0075] Using 3M P60 resin, 3M Ultra Tough Ceramic, and Vita Elastic Ceramic as controls, the tensile strength of a group of materials selected in 2.3.4 was evaluated, with 5 samples selected from each group.

[0076] 3M P60 resin was cured into sheet-like blocks 1 mm thick, 20 mm long, and 20 mm wide. The 3M P60 resin, 3M Ultra-Tough Ceramic, Vita Elastic Ceramic, and the enamel-like material selected in section 2.3.4 were then cut using a low-speed diamond cutter into pieces with a cross-sectional area of ​​approximately 1 × 1 mm. 2 The strip material was subjected to a tensile test using a universal testing machine. The strip was fixed along its long axis onto a self-curing resin mold, and the cross-sectional length and width were measured using calipers (accuracy controlled to 0.01 mm). The material was secured to the universal testing machine with stainless steel wire. Before the test, no additional tension was applied to either end of the material. The tensile rate was set to 1 mm / min until the material fractured. The universal testing machine automatically recorded the tensile fracture load and calculated the tensile strength using the following formula:

[0077] σt=p / (b×d)

[0078] In the formula, σt is the tensile strength (MPa); p is the maximum load (N); b is the specimen width (mm); and d is the specimen thickness (mm).

[0079] 3. Compression strength and compression modulus test

[0080] Using 3M P60 resin, 3M Ultra Tough Ceramic, and Vita Elastic Ceramic as controls, the compressive strength and compressive modulus of the selected enamel-like composite materials were evaluated, with 5 samples selected for each group.

[0081] 3M P60 resin was placed in a cylindrical mold with a diameter of 3mm and a thickness of 2mm, cured in layers, and then removed. 3M Ultra-Tough Ceramic and Vita Elastic Ceramic were CAD / CAM shaped into cylinders with a diameter of 3mm and a thickness of 2mm. The enamel-like composite material selected in section 2.3.4 was cut into cylinders with a diameter of 3mm and a thickness of 2mm using a UV picosecond laser cutter.

[0082] The compressive load was tested using a universal testing machine. Before testing, the sample diameter and thickness were measured with vernier calipers, with an accuracy controlled to 0.01 mm. The compression rate was set to 1 mm / min until the material fractured. The universal testing machine automatically recorded the compressive load and calculated the compressive strength using the following formula:

[0083]

[0084] In the formula, CS is the compressive strength (MPa); F is the maximum load (N); and d is the specimen diameter (mm).

[0085] Use Origin 2021 software to plot the stress-strain curves and calculate the compressive modulus.

[0086] Friction and wear test

[0087] Using natural enamel, dentin, 3M P60 resin, 3M Tough Porcelain, and Vita Elastic Porcelain as controls, friction and wear tests were conducted on the selected enamel-like composite materials to evaluate their friction performance. Five samples were selected from each group.

[0088] The preparation methods for samples of natural enamel, dentin, 3M P60 resin, 3M Ultra-Tough Porcelain, Vita Elastic Porcelain, and enamel-like materials were the same as above. The tribological properties of the samples were tested using a tribological testing machine. The grinding material was set as a 6.33 mm diameter stainless steel ball to simulate oral chewing conditions. The frictional load was set to 30 N, the sliding distance to 2 mm, and the linear velocity to 1 mm / s. The tribological tests were conducted in an artificial saliva environment. The coefficient of friction was recorded, and the tribological traces were observed and analyzed using SEM.

[0089] The results are as follows: 3M P60 resin, 3M Elastic Porcelain, Vita Elastic Porcelain, enamel, and dentin were used as controls to evaluate the mechanical properties of ELRMs. Figure 8As shown in Figure a, the Vickers hardness of ELRMs (197.69±7.13) was lower than that of enamel (357.20±17.78) and Vita elastic porcelain (260.97±10.58), but higher than that of 3M P60 resin (85.31±2.13), 3M high-toughness porcelain (130.66±3.39), and dentin (78.96±7.46) (P<0.05). The tensile strength of ELRMs (29.82±4.98 MPa) was not significantly different from that of 3M P60 resin (26.53±5.95 MPa) and 3M high-toughness porcelain (33.23±4.84 MPa) (p>0.05), but significantly higher than that of Vita elastic porcelain (9.336±1.89 MPa) (p<0.05). Figure 8 b). The compressive strength of ELRM (439.55±18.85 MPa) was higher than that of 3M P60 resin (400.78±20.86 MPa), but lower than that of 3M Elastic Ceramic (502.22±8.20 MPa) and Vita Elastic Ceramic (602.22±12.69 MPa) (p<0.05). Figure 8 c). The compressive modulus of ELRMs (12.65±0.38MPa) was lower than that of 3M P60 resin (16.14±0.26MPa), 3M Ultra-Tough Ceramic (18.19±0.07MPa), and Vita Elastic Ceramic (502.22±8.20MPa) (P<0.05). Figure 8 d). The coefficient of friction of ELRM was 0.190±0.014, which was not statistically different from 3M High-Toughness Porcelain (0.215±0.031), enamel (0.204±0.0359), and dentin (0.227±0.034) (P>0.05), but was significantly different from 3M P60 resin (0.441±0.028) and Vita Elastic Porcelain (0.484±0.023) (P<0.05). Figure 8 e).

[0090] III. Evaluation of the Clinical Application Potential of the Optimized Tooth-like Enamel Material in Example 5

[0091] The selected enamel-like composite materials were cut into inlays, and their morphology was observed and photographed to record the appearance.

[0092] After polishing the circular enamel-like composite material, one side was etched with 37% phosphoric acid etching agent for 30 seconds. After rinsing with deionized water and drying, the surface morphology before and after etching was observed with the naked eye and photographed. Then, the surface morphology before and after etching was observed with SEM.

[0093] The results showed that the synthesized ELRMs were machinable, and the inlays made from them exhibited good translucency and closely resembled the morphology of natural teeth. Since the inorganic components were the same as enamel, the ELRMs could be etched with phosphoric acid like enamel to improve their bonding properties. We etched the lower half of the ELRMs sample with a 37% phosphoric acid etchant for 1 minute and then compared the two parts. Figure 9 The b1 result shows that the lower half, after acid etching, is chalky white, resembling an acid-etched enamel surface. (SEM image) Figure 9 As shown in b2~b5), compared to before acid etching, some of the hydroxyapatite exposed by grinding in the material dissolved, forming micropores and roughening the surface of the ELRMs. Figure 9 ).

[0094] Example 6

[0095] KH570 coupled with HANW-mediated self-assembly, a synthetic enamel-like material.

[0096] 10g of KH570, initiator (0.1g camphor benzoate (CQ), 0.1g ethyl 4-dimethylaminobenzoate (EDMAB), 0.05g benzoyl peroxide (BPO)) were mixed in a polytetrafluoroethylene beaker and stirred vigorously (500 rpm) for two hours on a magnetic stirrer until the solid components were completely dissolved, resulting in a yellow solution. Then, 0.2g of hydroxyapatite nanowires were added to the solution, and the mixture was stirred vigorously (500 rpm) to evenly disperse the nanowires. The entire process was carried out in darkness. The mixture was then transferred to a high-speed centrifuge and centrifuged at 10,000 rpm for 10 minutes. The supernatant was then poured off, yielding a precipitate. The precipitate was transferred to a vacuum filtration apparatus for filtration. A 10mm diameter Buchner funnel was connected to the other end of the vacuum filtration drying chamber, and the precipitate was placed on a double layer of filter paper. Open the vacuum filtration drying oven and perform filtration until most of the organic components in the precipitate are extracted.

[0097] The KH570-coupled self-assembled nanowire aggregates were transferred as a whole to a mold with a microporous membrane (pore size <1μm) at the bottom and processed in a cold sintering press. The pressure was pre-pressurized to 50MPa to remove air, then heated to 90℃, and gradually increased to 300MPa (50MPa / 5min, gradually increasing to 300MPa / 30min). The pressure was maintained for 30min for in-situ polymerization. Finally, the material was removed and further polymerized under a curing lamp. The final product, an enamel-like dental restorative block, was obtained. A blocky enamel-like dental restorative material was obtained. Its structure was characterized using SEM and TEM. Figure 10 )

[0098] Mechanical properties of the enamel-like material obtained by the technical system of Example 6.

[0099] 1. Microhardness test:

[0100] Samples were prepared according to the requirements for dental restorative materials in ISO 4049-2019. Enamellable-like restorative materials were prepared into small round discs, 10 mm in diameter and 2 mm thick, in triplicate. A control group consisted of five samples, three per group. In addition to natural enamel and dentin, three commercially available posterior filling resins were selected: Tetric N-cream, Karisma, and 3M P60. These were injected into cylinders with a diameter of 10 mm and a depth of 3 mm for curing. All samples were polished to 2500 grit according to the requirements for natural enamel and dentin.

[0101] Testing was conducted according to the testing requirements for dental restorative materials in ISO 4049-2019. Samples were tested using a microhardness tester by applying a Knoop diamond indenter with a load of 300.0 g to the sample surface for 15 seconds to obtain an indentation. Multiple measurements were repeated for each sample at intervals of at least 10 micrometers. The extent of the indentation was determined using a reflection microscope within the microhardness tester. The software then automatically calculated the results, averaging at least five sample data points.

[0102] Radial tensile strength (DTS) test and compressive strength (CS) test

[0103] Sample preparation was performed according to the requirements of ISO 4049-2019 for dental restorative materials. In the DTS test, all samples were prepared as cylindrical specimens with a diameter of 6 mm and a height of 2 mm. In the CS test, samples were prepared as specimens with a diameter of 5 mm and a height of 5 mm. Before testing, the samples were removed from the mold and stored in deionized water for one day. The control group consisted of three commercial resins: Tetric N-cream, Karisma, and 3M P60, prepared in molds to the same size as the samples.

[0104] Testing was conducted according to the testing requirements for dental restorative materials in ISO 4049-2019. The instrument used for testing was a universal testing machine (AGS-X, Shimadzu Corporation, Japan). In the radial tensile strength (DTS) test, the instrument compression rate was 0.5 mm / min, and the results were measured using the following formula:

[0105] DTS=2F / πdh

[0106] Here, DTS is radial tensile strength, measured in MPa (megapascals), F is maximum load force, measured in Newtons (N), d is the diameter of the sample, and h is the height of the sample, measured in millimeters (mm).

[0107] In the compressive strength (CS) test, the instrument compresses at a rate of 1 mm / min. The results are measured using the following formula:

[0108] CS = 4F / (πd^2)

[0109] Here, F is the maximum load force in Newtons (N), d is the diameter of the sample, and h is the height of the sample in millimeters (mm). All dimensions are measured using digital vernier calipers with an accuracy controlled to 0.01 mm.

[0110] Friction and wear test

[0111] Samples were subjected to the same microhardness test. The control group consisted of natural tooth enamel and dentin, as well as three commercial resins: Tetric N-cream, Karisma, and 3M P60.

[0112] The tests were conducted using a tribological testing machine (MFT-5000, Aitek, USA). The test material was a 6.33mm diameter stainless steel ball, and the load was 3N. The sliding wear distance was set to 3mm, and the linear velocity was 1mm / s. The entire test was performed in artificial saliva with a pH of 7 to simulate the oral cavity environment. The artificial saliva was changed after each sample replacement. The coefficient of friction and wear depth were obtained using Rtec software. After the reciprocating sliding test, the tribological wear traces were analyzed using SEM.

[0113] The results are as follows ( Figure 11 ):

[0114] The synthetic enamel-like restorative material has a higher hardness than several other commercial posterior filling resins (Tetric N-cream, Caresma, 3M P60) and exceeds the hardness of dentin, but is not as hard as natural tooth enamel.

[0115] The radial tensile strength results showed no statistically significant difference between the synthesized enamel-like restorative material and the posterior tooth resins Tetric N-cream and Caresma (P>0.05), but the DTS values ​​were lower than 3M P60, which was significantly different (P<0.05).

[0116] The compressive strength test showed no statistically significant difference between the synthesized enamel-like repair material and Tetric N-cream and 3M P60 (P>0.05), but a statistically significant difference compared with Karisma (P<0.05).

[0117] Regarding tribological properties, there were no statistically significant differences between the experimental samples and enamel, Tetric N-cream, and 3M P60 (P > 0.05), but a significant statistical difference compared to Caresma (P < 0.05). The coefficient of friction and wear showed no statistically significant difference between the experimental samples and natural enamel (P > 0.05), but a significant statistical difference compared to several other commercial resins (P < 0.05). After the abrasion test, natural enamel showed obvious grooves but no peeling; the experimental samples showed some peeling in certain areas, but the grooves were not as pronounced as in natural enamel. Dentin had the greatest depth and experienced the most severe wear.

[0118] Example 7

[0119] Ultralong hydroxyapatite nanowires (HANW@SiO2) with silica surface coating are used to construct tooth enamel-like materials.

[0120] First, ultralong hydroxyapatite nanowires with a silica surface coating were synthesized according to the method in Example 2, namely, ultralong hydroxyapatite nanowires-silica core-shell structure (HANW@SiO2).

[0121] Secondly, following Example 3, silane coupling and self-assembly induction were performed on HANW@SiO2 nanowires. Specifically, 30 ml of anhydrous ethanol, 10 ml of deionized water, and 10 ml of KH-570 were added to a beaker under magnetic stirring. After stirring until homogeneous, the pH of the mixed solution was adjusted to the range of 4-5 by adding hydrochloric acid solution and sodium hydroxide solution. Then, 0.2 g of HANW@SiO2 core-shell structure powder was added to the mixed solution. After stirring for 24 hours, the product was collected by centrifugation. The product was washed three times with anhydrous ethanol and deionized water, respectively, to obtain the HANW@SiO2 core-shell structure functionalized on the KH-570 surface. The binding between KH-570 and the HANW@SiO2 core-shell structure was characterized by Fourier transform infrared spectroscopy (FTIR).

[0122] Next, 0.5 g of Bis-GMA was added to 7 ml of anhydrous ethanol and stirred until evenly dispersed. Then, 0.2 g of HANW@SiO2, which was surface-functionalized by KH-570, was added. The mixture was stirred at 300 rpm for 24 hours. Then, 5 mg of benzoyl peroxide (BPO) was added, and the mixture was stirred for another hour. Finally, the mixture was centrifuged at 20,000 rpm for 30 minutes. After removing the supernatant, the product was collected, and the precipitate was placed in a vacuum drying oven at room temperature until the ethanol had completely evaporated.

[0123] Finally, the nanowire and resin matrix mixture was transferred as a whole into a mold with a microporous membrane (pore size <1μm) at the bottom and processed in a cold sintering press. The pressure was pre-pressed to 50MPa to remove air, the temperature was raised to 90℃, and the pressure was gradually increased to 300MPa (50MPa / 5min, gradually increasing to 300MPa / 30min). The pressure was maintained for 30min for in-situ polymerization to obtain a blocky enamel-like dental restorative material. Its structure was characterized using SEM and TEM. Figure 12 The SEM image showing the cross-section of the synthetic material reveals that the nanowires are aggregated in an array, generally arranged along the same direction, yet exhibiting anisotropy due to differences in their orientation. Macroscopically, these ordered nanowires appear as layered stacks, similar to the arrangement of enamel prisms in tooth enamel.

[0124] Performance and advantages of the enamel-like material obtained by the technical system of Example 7:

[0125] 1. Acid resistance test

[0126] Natural tooth enamel, HANW nanowire-synthesized enamel-like materials, and HANW@SiO2 core-shell structure-synthesized enamel-like materials were used as control groups. Natural tooth enamel, HANW@SiO2, and HANW@SiO2 were cut into blocks with a height of 1 mm, a length of 3 mm, and a width of 3 mm using a low-speed precision diamond abrasive cutter. Five samples were collected from each group. After polishing and ultrasonic cleaning, the samples were immersed in 1 mm of 6 wt% citric acid solution for one minute. Then, 1 mm of deionized water was added and the samples were immersed for another minute. This process was repeated twice. The supernatant was then diluted 10 times and analyzed for various ion concentrations using ion mass spectrometry. After gradient demineralization, the morphological changes of the samples were analyzed using SEM.

[0127] The results showed that after acid etching, the Ca2+ concentration in the supernatant of the enamel-like material synthesized with the HANW@SiO2 core-shell structure was 1.046±0.104 mg / L, significantly lower than the Ca2+ concentration in the supernatant of HANW ELM (4.392±0.468 mg / L, p<0.001) and the Ca2+ concentration in the supernatant of tooth enamel (9.280±0.826 mg / L, p<0.001). SEM image of HANW ELM (…). Figure 11 As shown in A, C), the HANW ELM surface became rougher after the acid etching experiment. However, the SEM images of HANW@SiO2 show that the surface maintained relative integrity after acid etching compared to before etching. Figure 13 Therefore, the enamel-like material constructed with HANW@SiO2 exhibits good acid resistance and anti-caries properties.

[0128] Example 8

[0129] Hydroxyapatite nanowires with a surface coating of silica (SiO2)-zirconia (ZrO2), i.e., "ultra-long hydroxyapatite nanowires-silica-zirconia core-shell structure (HAWN@SiO2-ZrO2) constructing an enamel-like material (HASZ BBEM)".

[0130] First, following the method described in Example 3, ultralong hydroxyapatite nanowires with a silica-zirconia core-shell structure (HAWN@SiO2-ZrO2) were synthesized.

[0131] Next, following Example 3, HAWN@SiO2-ZrO2 nanowires were coupled with MDP to induce self-assembly. 0.5 g of MDP was dissolved in 5 mL of anhydrous ethanol, magnetically stirred until homogeneous, and then 0.1 g of hydroxyapatite nanowires were added. The mixture was stirred at 100 rpm for 4 h, allowed to stand for 4 h, and then centrifuged at 3500 rpm for 20 min. The supernatant was discarded. Anhydrous ethanol was added, mixed thoroughly, and centrifuged at 3500 rpm for 20 min. The supernatant was discarded, and the mixture was washed three times. The nanowires at the bottom of the centrifuge tube were then collected and dried in a 50°C incubator for 12 h. The dried nanowires were obtained.

[0132] Next, Bis-GMA and TEGDMA were mixed at a mass ratio of 2:1. Subsequently, MDP-modified HA@SiO2@ZrO2NW powder (0.5 g) was mixed with (Bis-GMA + TEGDMA) at a mass ratio of 1:9, and stirred again for 24 hours. During this period, BOP (1 wt%) and LAP (0.2 wt%) were added according to the mass ratio of the resin matrix. The resulting mixture was centrifuged at 20,000 rpm for 30 minutes, and then the supernatant was removed, and the precipitate was collected.

[0133] Finally, the nanowire and resin matrix mixture was transferred as a whole into a mold with a microporous membrane (pore size <1μm) at the bottom and processed in a cold sintering press. The pressure was pre-pressed to 50MPa to remove air, the temperature was raised to 90℃, and the pressure was gradually increased to 300MPa (50MPa / 5min, gradually increasing to 300MPa / 30min). The pressure was maintained for 30min for in-situ polymerization to obtain a blocky enamel-like dental restorative material. Its structure was characterized using SEM and TEM. Figure 14 ).

[0134] Performance and advantages of the enamel-like material (HA BBEM) obtained by the technical system in Example 8:

[0135] 1. Evaluation of mechanical properties:

[0136] (1) Nanoindentation experiment

[0137] Natural tooth enamel, HA BBEM, was used as a control. All the above samples were cut into 2mm thick circular pieces using a low-speed precision diamond cutter and polished with silicon carbide sandpaper (Nos. 600-3000) before use.

[0138] Three groups of samples were tested using a nanoindenter, with three indentations on each sample, spaced at least 10 μm apart. During the test, the indenter load was 1 mN, and the holding time was 15 s to obtain indentations. The results were calculated from the indentations, and the Young's modulus was calculated from the load-displacement curve.

[0139] (2) Microhardness test

[0140] Made with natural tooth enamel, dentin, and commercial resin material 3MFiltek TM P60 Posterior Restorative System (3MP60), Commercial Resin-Based Ceramic 3M TM Lava TM Ultimate Restorative (3M) and HA BBEM were used as controls. Five samples were selected for each group. Natural tooth enamel, dentin, HA BBEM, and HASZ BBEM were cut into 2mm thick circular pieces using a low-speed precision diamond cutter. 3M Ultimate Restorative was cut into 10mm diameter and 2mm thick circular pieces using CAD / CAM. 3MP60 was cured into 10mm diameter and 2mm thick circular pieces. All materials were polished with silicon carbide paper (Nos. 600-3000) and then tested with a microhardness tester. Five sites were measured repeatedly for each sample, with an interval of more than 10µm between each site. During the measurement, the load was set to 100.0g and the holding time was set to 15s to obtain indentations. The indentation range was calculated, and the results were obtained.

[0141] (3) Compressive strength and compressive modulus

[0142] 3MP60, 3M Ultra-Tough Ceramic, and HA BBEM were used as controls. Five samples were selected for each group. 3MP60 resin was placed in a mold with a diameter of 3mm and a height of 2mm, cured in layers, and then removed. 3M Ultra-Tough Ceramic was cut into cylinders with a diameter of 3mm and a height of 2mm using CAD / CAM. HA BBEM and HASZ BBEM were cut into cylinders with a diameter of 3mm and a height of 2mm using a UV picosecond laser cutter. The size error of all samples was controlled within 0.1mm. Compression tests were performed on all samples using a universal testing machine. The compression rate was set to 1mm / min, the compression load was measured, the compressive strength was calculated using the following formula, and the compressive modulus was calculated based on the load-displacement curve:

[0143] CS = 5F / πd²

[0144] Among them, CS is the compressive strength (MPa); F is the maximum load (N); d is the specimen diameter (mm).

[0145] (4) Friction and wear experiment

[0146] Taking natural tooth enamel, dentin, 3MP60, 3M Beautifil II, and HA BBEM as controls. Each group contains five samples. The preparation method of all samples is the same as shown in 2.3.5.2. A friction and wear testing machine is used to test the samples. The friction load is set to 30 N, the sliding distance is 2 mm, the linear speed is 1 mm / s, and the friction time is 30 minutes. Record the friction coefficient and analyze the friction marks by SEM.

[0147] (5) Tensile experiment

[0148] Taking 3MP60, 3M Beautifil II, and HA BBEM as controls. Five samples are selected for each group. Cut the 3MP60 resin sheet, 3M Beautifil II, HA BBEM, and HASZ BBEM into strips with a width of 1 mm, a thickness of 1.5 mm, and a length of 10 mm using a low-speed precision diamond saw, and control the error within 0.05 mm. Conduct a tensile test using a universal testing machine. Fix the above strip materials along the long axis on a self-curing resin mold. Ligate and fix the materials on the universal testing machine with stainless steel wires, set the tensile rate to 1 mm / minute until the material breaks, and the universal testing machine automatically records the tensile fracture load, and calculate the tensile strength using the following formula:

[0149] σt = p / (b * d)

[0150] σt is the tensile strength (MPa); p is the maximum load (N); b is the specimen width (mm); d is the specimen thickness (mm).

[0151] Acid resistance

[0152] After polishing the disc-shaped enamel-like composite material, etch one side with 37% phosphoric acid etchant for 30 s, rinse it with deionized water and dry it, observe it with the naked eye and take pictures for recording, and then observe the surface morphology before and after etching by SEM.

[0153] The results are as follows( Figure 15 ):

[0154] The nano-hardness of HASZ BBEM is 2.10 GPa, which is much higher than 1.58 GPa of HA BBEM. However, both are significantly lower than 406 GPa of tooth enamel. The order of plastic deformation is: enamel < HASZ BBEM < HA BBEM. Therefore, compared with the HANW biomimetic enamel material: (1) The HASZ BBEM biomimetic enamel material shows enhanced indentation resistance; (2) It produces less plastic deformation.

[0155] The Vickers hardness of HASZ BBEM (213.48±9.07) is lower than that of enamel (367.65±7.30), but higher than that of 3MP60 (120.59±5.26), 3M Lava (144.35±5.51), HABBEM (147.97±6.39), and dentin (82.4±5.55) (p<0.05). Therefore, HASZ BBEM exhibits a significantly improved hardness.

[0156] The compressive strength of HASZ BBEM (424.45±28.38MPa) was similar to that of 3M P60 (409.29±23.57MPa) (p>0.05), higher than that of HABBEM (352.34±12.69MPa), and lower than that of 3M Lava (502.22±8.20MPa) (p<0.05).

[0157] The tensile strength of HASZ BBEM (31.54±1.91MPa) was similar to that of HA BBEM (33.20±2.05MPa) (p>0.05), but both were significantly different from those of 3M P60 (40.17±1.51MPa) and 3M Lava (63.32±2.43MPa) (P<0.05). Cross-sectional SEM images of HASZ BBEM showed that some nanowires had broken, while most of the nanowires remained intact and slid along the nanowires.

[0158] The coefficient of friction of HASZ BBEM was 0.1680±0.018, which was significantly different from that of 3M Lava (0.2214±0.0142), dentin (0.4402±0.0224), 3M P60 (0.3741±0.0190) and HA biomimetic enamel material (0.2607±0.0212) (p<0.05), but still somewhat different from that of tooth enamel (0.1190±0.0194) (p<0.05).

[0159] After acid etching and rinsing, the HA BBEM surface became rougher and chalky white. SEM images showed that the resin matrix on the HA BBEM surface had been exfoliated, exposing a large number of hydroxyapatite nanowires. In contrast, this phenomenon was not observed in HASZ BBEM, which maintained surface integrity. Figure 16 ).

[0160] The above description is merely a preferred embodiment of the present invention and is illustrative rather than restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, all of which will fall within the protection scope of the present invention.

Claims

1. A method for preparing a biomimetic dental ceramic restorative material for indirect restoration of tooth enamel, characterized in that, Includes the following steps: S1, prepare ultra-long hydroxyapatite nanowires as the base material, or modify ultra-long hydroxyapatite nanowires to obtain modified ultra-long hydroxyapatite nanowires. S2, the ultralong hydroxyapatite nanowires or their surface-modified products obtained in step S1 are arranged in parallel and densely into a bundle structure with a diameter of up to micrometers. S3, the nanowire aggregates with micron-sized bundle structure obtained in step S2 are impregnated in resin monomers containing initiators and further arranged and assembled into a macroscopic ordered structure. S4. The aggregates of macroscopically ordered ultralong hydroxyapatite nanowires or their modified forms obtained in step S3 are subjected to cold sintering technology to extrude excess resin matrix and then solidify to obtain a biomimetic dental ceramic restoration material for enamel.

2. The method for preparing a biomimetic dental ceramic restorative material for indirect restoration of tooth enamel as described in claim 1, characterized in that, In step S1, the preparation method of ultralong hydroxyapatite nanowires includes the following steps: S11, a 7% (w / v) NaOH aqueous solution and a 20% (v / v) methanol + 35% (v / v) oleic acid aqueous solution are magnetically stirred and mixed evenly to obtain 300 mL of sodium oleate methanol emulsion. S12, slowly add 80 mL of aqueous solution containing 2.22 g CaCl2 to the mixture obtained in step S11; S13, 120 mL of aqueous solution containing 6.24 g NaH2PO4·2H2O was slowly added to the mixed solution obtained in step S12. Subsequently, the resulting suspension was transferred to a high-pressure reactor and reacted at 180 °C for 24 h under magnetic stirring. The slurry was washed with anhydrous ethanol and deionized water respectively, and then freeze-dried to obtain a white powder sample, namely ultralong hydroxyapatite nanowires.

3. The method for preparing a biomimetic dental ceramic restorative material for indirect restoration of tooth enamel as described in claim 1, characterized in that, In step S1, the modification method for ultralong hydroxyapatite nanowires includes surface silica modification or surface silica-zirconia coating modification.

4. The method for preparing a biomimetic dental ceramic restorative material for indirect restoration of tooth enamel as described in claim 3, characterized in that, The specific method for modifying the surface of the ultralong hydroxyapatite nanowires with silica is as follows: Under magnetic stirring, 50 mL of deionized water and 6 mL of ammonia water are added to 200 mL of a solution containing 2 mg / mL of silica. -1 The ultralong hydroxyapatite nanowires were added to an ethanol suspension, and then 2 mL of tetraethyl orthosilicate was added. After stirring for 6 hours, the mixture was collected by centrifugation, washed with anhydrous ethanol and deionized water respectively, and then freeze-dried to obtain a white powder sample, which yielded the ultralong hydroxyapatite nanowire-silica core-shell structure.

5. The method for preparing a biomimetic dental ceramic restorative material for indirect restoration of tooth enamel as described in claim 3, characterized in that, The specific method for modifying the silica-zirconia coating on the surface of the hydroxyapatite nanowires is as follows: Take 0.12 g of the above-mentioned ultralong hydroxyapatite nanowire-silica core-shell structure and disperse it in 50 mL of deionized water. Add 0.6057 g of tris(hydroxymethyl)aminomethane and 340 mL of HCl with a concentration of 12 mol / L to maintain the pH of the mixed solution at 7.

5. After the mixed solution is ultrasonically dispersed evenly, add 0.0192 g of zirconium chloride octahydrate, stir at room temperature, and then bathe the mixed solution in a water bath at 60 °C for 6 hours. After washing three times with deionized water, freeze dry and sinter at 300 °C for 2 hours to obtain the silica-zirconia core-shell structure on the surface of the ultralong hydroxyapatite nanowires.

6. The method for preparing a biomimetic dental ceramic restorative material for indirect restoration of tooth enamel as described in claim 1, characterized in that, In step S2, the modified ultralong hydroxyapatite nanowires are arranged in parallel and densely into a bundle structure with a diameter of up to micrometers, specifically including the following steps: S21, using surfactant-induced self-assembly of nanowires to obtain a slurry. S22, the slurry obtained in step S21 is placed in a syringe and continuously spun into a coagulation bath rotating at 30 r / min at a speed of 0.5 mL / min. After standing for 5 minutes, the precipitate bundles are filtered, repeatedly washed, and freeze-dried to obtain nanowire aggregates, characterized by parallel and densely arranged nanowire aggregates with diameters up to the micrometer level.

7. The method for preparing a biomimetic dental ceramic restorative material for indirect restoration of tooth enamel as described in claim 6, characterized in that, In step S21, the surfactant is γ-methacryloyloxypropyltrimethoxysilane or 10-methacryloyloxydecylphosphodihydrogen acid.

8. The method for preparing a biomimetic dental ceramic restorative material for indirect restoration of tooth enamel as described in claim 1, characterized in that, In step S4, the specific process is as follows: The micron-sized bundled ultralong hydroxyapatite nanowires obtained in step S2 are immersed in an ethanol solution containing bisphenol A-dimethacrylate glycidyl ester, dimethacrylate carbamate, and initiator monomers. The mixture is stirred at 300 r / min for 12 h. The precipitate is then collected and transferred to a centrifuge tube. The mixture is centrifuged at 20000 r / min for 30 min. The mixture of ultralong hydroxyapatite nanowires and resin matrix is ​​transferred as a whole to a mold with a microporous filter membrane at the bottom. The mixture is then processed in a cold sintering press, pre-pressed to 50 MPa to remove air, heated to 90°C, and gradually pressurized to 300 MPa. The mixture is held at the temperature and pressure for 30 min and polymerized in situ to obtain a blocky enamel-like dental restoration material.

9. A biomimetic dental ceramic restorative material for indirect restoration of tooth enamel, prepared by the method described in any one of claims 1 to 8.

10. The application of a biomimetic dental ceramic restorative material for indirect restoration as described in claim 9 in minimally invasive restoration of tooth defects.

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