Antibacterial composite resin-based filling material for filling root canal in dental pulp department

Abstract

The invention relates to the technical field of oral medical materials, and discloses an antibacterial composite resin-based filling material for root canal filling in the dental pulp department. The material is prepared from ethyl dicarbamate dimethacrylate, a diluting monomer, 10-methacryloyloxydecyl dihydrogen phosphate, chlorhexidine, an amino modified fumed silica carrier, an inorganic filler and an initiator. In the preparation process, chlorhexidine alkali and an acidic functional monomer are subjected to in-situ reaction to generate a hydrophobic compound, and interface chemical anchoring is formed on the surface of the amino carrier through static heat curing. By constructing a'carrier-antibacterial agent-resin 'ternary assembly structure, the problems that a hydrophilic antibacterial agent is poor in dispersion and easy to dissolve out are solved, and meanwhile, a dynamic ionic bond network is utilized to dissipate polymerization shrinkage stress, so that the edge sealing property and long-acting antibacterial ability of the material are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of oral medical materials technology, and in particular to antibacterial composite resin-based filling materials for root canal filling in endodontics. Background Technology

[0002] Root canal treatment is currently the most effective method for treating pulpitis and periapical periodontitis. Its core goal is to thoroughly remove infectious material from the root canal system through mechanical preparation and chemical irrigation, and to use filling materials to tightly seal the root canal space to prevent reinfection. However, due to the complexity of the root canal anatomy, it is difficult to completely remove bacteria from the lateral branches, accessory canals, and deep dentinal tubules in clinical practice. Residual bacteria (such as Enterococcus faecalis) often become the main cause of root canal treatment failure. Therefore, endowing root canal filling materials with long-lasting antibacterial activity is of great significance for inhibiting the growth of residual bacteria and improving the success rate of treatment.

[0003] While current resin-based root canal filling materials offer superior adhesion and workability compared to traditional zinc oxide eugenol paste, they lack inherent antibacterial properties. To address this issue, researchers have attempted to directly add inorganic or organic antibacterial agents (such as chlorhexidine salts) to the resin matrix. However, this simple physical blending modification faces significant technical bottlenecks in practical applications. Commonly used chlorhexidine salts (such as chlorhexidine acetate and chlorhexidine gluconate) are highly hydrophilic, while dental resin matrices (such as ethyl carbamate and dimethacrylate) are typically hydrophobic. This polarity difference makes it difficult for antibacterial agents to dissolve and disperse in the resin, leading to agglomeration. This phase separation not only results in uneven distribution of the antibacterial agent but also disrupts the cross-linked network structure of the cured resin, causing a decrease in the material's mechanical strength and wear resistance.

[0004] Furthermore, the active release of traditional physical hybrid antibacterial materials mainly relies on the passive diffusion and dissolution of drug molecules. This mechanism often leads to an explosive release of the drug in the early stages of implantation, and high concentrations of the drug may cause irritation or cytotoxicity to the periapical tissue. In the later stages, as the drug is depleted, a porous structure remains inside the material, and the antibacterial properties rapidly decline, failing to meet the clinical need for root canal filling materials to maintain long-term antibacterial effects for several years or even decades in a moist environment.

[0005] On the other hand, methacrylate resins undergo volume shrinkage during free radical polymerization and curing. This polymerization shrinkage generates tensile stress at the interface between the material and the root canal wall. When this shrinkage stress exceeds the interfacial bond strength, it leads to marginal microleakage. Microleakage not only compromises the seal of the root canal but also provides channels and spaces for bacterial invasion and reproduction, thus negating the material's antibacterial effect. How to effectively reduce the polymerization shrinkage stress of the resin while ensuring high dispersion and long-term stability of the antibacterial agent is a key technical challenge that urgently needs to be addressed in the development of high-performance root canal filling materials. Summary of the Invention

[0006] The technical problem solved by this invention is that the hydrophilic antibacterial agent in the existing root canal filling resin material has poor dispersion stability in the hydrophobic resin matrix and is prone to agglomeration and precipitation. In addition, the traditional physically mixed antibacterial agent is easy to dissolve, resulting in insufficient long-term effect and reduced biosafety. At the same time, the volume shrinkage stress generated during the resin polymerization process is difficult to release effectively, resulting in a decrease in edge sealing.

[0007] To address the above problems, the present invention provides the following technical solution: In a first aspect, the present invention provides an antibacterial composite resin-based filling material for root canal filling in endodontics, made from raw materials comprising the following parts by weight: 15 to 25 parts of ethyl dicarboxylate dimethacrylate, 5 to 15 parts of diluted monomer, 2 to 5 parts of 10-methacryloyloxydecyl phosphate dihydrogen ester, 0.5 to 3 parts of chlorhexidine base, 1 to 4 parts of amino-modified fumed silica carrier, 60 to 80 parts of inorganic filler, and 0.1 to 1 part of initiator system; In this process, chlorhexidine base is dissolved in a resin matrix composed of ethyl dicarboxylate, diluent monomer, and 10-methacryloyloxydecyl phosphate dihydrogen ester, and is anchored in situ at the interface with the amino-modified fumed silica carrier through acid-base interaction.

[0008] By employing the above technical solution, this invention utilizes the chemical interaction between acidic functional monomers, alkaline antibacterial agents, and aminated inorganic carriers to construct a resin network with dynamic response characteristics. The specific mechanism of action is as follows: First, this invention utilizes an in-situ acid-base reaction between 10-methacryloyloxydecyl phosphate dihydrogen ester and chlorhexidine base to improve the lipophilicity of the antibacterial agent. The biguanide group in the chlorhexidine base molecule acts as a proton acceptor, and 10-methacryloyloxydecyl phosphate dihydrogen ester acts as a proton donor; the two react to form an ionic complex. The reaction process is shown below: 2 ROP(O)(OH)2+CHX→[ROP(O)(OH)O - ]2·[CHXH2] 2+; In the formula, R represents 10-methacryloyloxydecyl, CHX represents the chlorhexidine base skeleton, and P(O) represents a phosphorus-oxygen double bond.

[0009] During this process, phosphate ester molecules with long carbon chain alkyl tails are electrostatically wrapped around the protonated chlorhexidine molecule, transforming the originally hydrophilic chlorhexidine into a hydrophobic ionic complex. This structural transformation reduces the interfacial energy difference between the antibacterial agent and the hydrophobic resin matrix (such as ethyl carbamate dimethacrylate), enabling the antibacterial agent to achieve molecular-level dispersion in the resin matrix and avoiding the aggregation phenomenon caused by poor compatibility of conventional chlorhexidine salts in the resin.

[0010] Secondly, this invention achieves non-leaching, long-lasting antibacterial action by adsorbing and anchoring the aforementioned ionic complex onto an amino-modified fumed silica support. During the maturation stage of material preparation, residual phosphate groups or P=O bonds in the ionic complex chemically adsorb onto the amino groups on the support surface, forming a ternary assembly structure of amino support-phosphate ester monomer-chlorhexidine (SiO2-NH2···HO-P(O)(OR)-O). - ··· + (H-CHX). This multiple non-covalent bonding restricts the diffusion and migration of chlorhexidine molecules, preventing their precipitation during long-term storage. Simultaneously, after resin curing, this structure reduces drug dissolution in the moist root canal environment, lowers the risk of irritation to periapical tissues, and imparts contact antibacterial properties to the material surface.

[0011] Finally, this invention utilizes the formed ionic bond network to dissipate polymerization shrinkage stress. Unlike traditional resins that rely solely on covalent crosslinking, the resin network of this invention contains a large number of phosphate ester-amino ionic bond nodes. When internal stress is generated during resin polymerization shrinkage, the relatively low bond energy ionic bond nodes can undergo reversible breakage and recombination, allowing for microscopic slip adjustment of polymer chain segments. This mechanism converts the elastic energy generated by polymerization shrinkage into heat energy for dissipation, reducing curing shrinkage stress and helping to maintain the edge seal between the filling material and the root canal wall.

[0012] Preferably, the raw materials are in the following weight proportions: 15 to 21 parts of ethyl dicarboxylate dimethacrylate, 5 to 15 parts of diluent monomer, 3 to 4 parts of 10-methacryloyloxydecyl phosphate dihydrogen ester, 1 to 2 parts of chlorhexidine base, 1.5 to 2.5 parts of amino-modified fumed silica carrier, and 61 to 74 parts of inorganic filler.

[0013] By adopting the above technical solution, the ratio of acidic functional monomers to alkaline antibacterial agents is controlled within a range close to the stoichiometric ratio, which can promote the dissolution and conversion of chlorhexidine alkali, while reducing the impact of excessive acidic monomer residue on the water absorption of the resin, thus balancing the physical and mechanical properties and antibacterial properties of the material.

[0014] Preferably, the diluent monomer is triethylene glycol dimethacrylate; the inorganic filler is barium silane glass powder; and the initiator system includes a photoinitiator, a co-initiator, and a polymerization inhibitor.

[0015] By adopting the above technical solution, triethylene glycol dimethacrylate is used to adjust the viscosity of the resin system and improve the handling feel; barium silane glass powder provides X-ray blocking properties, making it easier for clinical patients to check the filling quality through imaging methods.

[0016] Preferably, the amino-modified fumed silica support is prepared by a method comprising the following steps: S1, dispersing hydrophilic fumed silica in an aqueous ethanol solution, adjusting the pH to acidic, and ultrasonically dispersing to obtain a suspension; S2, adding γ-aminopropyltriethoxysilane to the suspension, and refluxing at 60°C to 70°C; S3, centrifuging, washing, drying, grinding, and sieving the reaction product to obtain the amino-modified fumed silica support.

[0017] By employing the above technical solution, the hydrolysis rate of γ-aminopropyltriethoxysilane can be controlled in an acidic alcohol-water system, promoting its grafting onto the hydroxyl groups on the surface of fumed silica in the form of monomolecules or oligomers, thus reducing excessive self-condensation of the silane itself. This facilitates the formation of uniformly distributed amino active sites on the carrier surface, improving its anchoring efficiency to the antibacterial agent complex.

[0018] Preferably, in step S1, the volume ratio of anhydrous ethanol to water in the ethanol-water solution is 95:5, and the pH value is adjusted to 4.5 to 5.5; in step S2, the mass ratio of the hydrophilic fumed silica to γ-aminopropyltriethoxysilane is 10:2 to 10:3.

[0019] By adopting the above technical solution, the solvent ratio and pH environment help maintain the balance between hydrolysis and condensation of silane coupling agent; the specific raw material mass ratio ensures the effective coverage of silane on the surface of hydrophilic fumed silica, making the carrier change from hydrophilic to hydrophobic, improving its dispersion uniformity in the resin matrix, and introducing sufficient amino functional groups for subsequent reactions.

[0020] Secondly, the present invention provides a method for preparing an antibacterial composite resin-based filling material for root canal filling in endodontics, comprising the following steps: (1) Mix ethyl dicarboxylate, diluent monomer and 10-methacryloyloxydecyl phosphate dihydrogen ester evenly to obtain resin matrix; (2) Add chlorhexidine base to the resin matrix and stir until completely dissolved; (3) Add amino-modified fumed silica carrier and disperse it at high speed to obtain a mixture; (4) The mixture obtained in step (3) is subjected to static thermal curing treatment so that chlorhexidine base, 10-methacryloyloxydecyl phosphate dihydrogen ester and amino-modified fumed silica carrier complete the interface assembly. (5) After the curing is completed, add the inorganic filler and initiator system, and vacuum stir to degas, and the product is obtained.

[0021] By adopting the above technical solution, this invention employs a step-by-step assembly process strategy, ensuring an ordered chemical bond between the antibacterial agent and the carrier, rather than a simple physical mixture. The specific process mechanism is as follows: First, in steps (1) and (2), a resin environment rich in acidic monomers is constructed first, and then basic chlorhexidine is added. This sequence ensures that the chlorhexidine base can preferentially contact 10-methacryloyloxydecyl phosphate dihydrogen ester and undergo a neutralization reaction, thereby completing the in-situ hydrophobic modification of the drug molecule and transforming it from a solid powder into a homogeneous resin solution.

[0022] Secondly, steps (3) and (4) are the core of this method. After adding the amino support, a large amount of inorganic filler was not added immediately, but a static thermal curing process was set up. This is because the interfacial assembly of macromolecules requires time to overcome steric barriers. During the thermal curing process, the system gains thermal energy, which causes the hydrophobicated chlorhexidine-phosphate complex to migrate to the surface of the amino support and adjust the molecular orientation so that the phosphate group and amino group form a stable ionic bond. If this step is omitted and all fillers are mixed directly, the drug complex will be randomly distributed and unable to form an effective anchor, resulting in a decrease in subsequent dispersion stability.

[0023] Finally, in step (5), a large amount of inorganic filler is added. At this point, the drug has been anchored. The addition of a large amount of filler will not destroy the already formed carrier-drug assembly structure, thus ensuring that the final material has both excellent mechanical properties and antibacterial stability.

[0024] Preferably, in step (4), the temperature of the static heat curing treatment is 45°C to 55°C, and the curing time is 12 hours to 24 hours.

[0025] By adopting the above technical solution, this temperature range provides suitable activation energy, promotes the movement and rearrangement of molecular chain segments, accelerates the formation of interfacial ionic bonds, and at the same time, this temperature is much lower than the decomposition temperature of the thermal initiator, avoiding prepolymerization of the resin during storage; sufficient curing time ensures that the interfacial assembly reaction reaches thermodynamic equilibrium, ensuring the stability of product quality between batches.

[0026] Preferably, in step (2), the stirring temperature is 35°C to 45°C; in step (3), the high-speed dispersion speed is 1000 rpm to 2000 rpm.

[0027] By adopting the above technical solutions, gentle heating helps to reduce the viscosity of the resin matrix, accelerate the dissolution rate of chlorhexidine base, and prevent drug decomposition caused by high temperature; high-speed shear force can effectively break up the aggregates of fumed silica, expose more surface amino active sites, and improve the specific surface area utilization of the carrier.

[0028] Preferably, in step (5), the vacuum degree of the vacuum stirring is -0.08MPa to -0.1MPa, and the temperature is 40℃ to 50℃.

[0029] By adopting the above technical solution, the high vacuum environment can effectively remove air bubbles entrained during the mixing process and volatile impurities that may remain in the raw materials, preventing microporous defects from appearing inside the cured material, thereby ensuring the compactness and mechanical strength of the filling material.

[0030] Preferably, in step (1), the diluent monomer is triethylene glycol dimethacrylate; in step (5), the initiator system comprises camphorquinone, ethyl 4-dimethylaminobenzoate, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and 2,6-di-tert-butyl-p-cresol.

[0031] By adopting the above technical solution, the composite initiation system combined with the use of polymerization inhibitors not only broadens the photocuring wavelength response range of the material and improves the deep curing efficiency, but also ensures the environmental light stability of the material during operation.

[0032] In summary, the present invention has at least one of the following beneficial technical effects: 1. This invention utilizes an in-situ acid-base neutralization reaction between 10-methacryloyloxydecyl phosphate dihydrogen ester (10-MDP) and chlorhexidine base to generate a hydrophobic ionic complex, overcoming the problem of incompatibility between traditional chlorhexidine salts and hydrophobic resin matrices. Combined with the carrier effect of amino-modified fumed silica, this achieves molecular-level uniform dispersion of the antibacterial agent within the resin system, resulting in excellent light transmittance and effectively preventing abnormal viscosity increases due to drug aggregation and precipitation during long-term storage.

[0033] 2. This invention constructs a ternary interface system of "carrier-drug-resin," utilizing the strong ionic interaction between phosphate groups and amino groups on the carrier surface to firmly anchor chlorhexidine molecules to the surface of the inorganic filler. This interfacial assembly structure restricts the free migration of drug molecules, minimizing their loss through solvent diffusion. This not only endows the material with durable contact antibacterial capabilities under aging conditions but also ensures good biocompatibility due to its extremely low dissolution rate.

[0034] 3. This invention utilizes the dynamic ionic bond network formed between amino-modified silica and the resin matrix to replace the rigid covalent bond connection between the traditional filler and the matrix. During the photocuring polymerization process, this non-covalent interface can effectively dissipate the internal stress generated by volume shrinkage through microscopic dissociation and recombination. While maintaining the high mechanical strength of the material, it significantly reduces the polymerization shrinkage stress, thereby ensuring the edge sealing between the filling material and the root canal wall. Attached Figure Description

[0035] Figure 1 This is a comparison of the ultraviolet-visible transmittance spectra of the resin solutions in each group in Test Example 1 of the present invention within the wavelength range of 400–800 nm. Figure 2 The cumulative dissolution kinetics curves of chlorhexidine in artificial saliva in Test Example 2 of the present invention are compared; wherein, (a) is a comparison of the overall release trends of the examples and the comparative examples; (b) is an enlarged view of the trace release characteristics of Examples 1 to 5; Figure 3 This is a comparison graph showing the real-time change curves of polymerization shrinkage stress with curing time in Test Example 3 of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. It should be understood that reagents not specifically described in the following embodiments and comparative examples are all commercially available analytical grade or higher products.

[0037] Preparation Example 1: This preparation example provides a method for preparing an amino-modified fumed silica support, comprising the following steps: (1) Slowly add 10g of hydrophilic fumed silica to a mixed solvent of 200mL of anhydrous ethanol and deionized water, wherein the volume ratio of anhydrous ethanol to deionized water is 95:5, and mechanically stir and disperse for 15 minutes. (2) Add acetic acid to the dispersion to adjust the pH of the solution to 5.0, and then sonicate for 30 minutes under ultrasonic power of 300W to obtain a uniform silica suspension; (3) Transfer the suspension to a three-necked flask equipped with a reflux condenser, and slowly add 2.5 g of γ-aminopropyltriethoxysilane under magnetic stirring. After the addition is complete, raise the temperature to 65°C and maintain the reflux reaction for 7 hours. (4) After the reaction is complete, the product is centrifuged and the precipitate is washed three times with anhydrous ethanol to remove unreacted silane monomers. (5) The washed solid was placed in a vacuum drying oven and dried at 105°C for 12 hours. It was then ground and passed through a 200-mesh sieve to obtain an amino-modified fumed silica carrier.

[0038] Preparation Example 2: This preparation example provides a method for preparing an amino-modified fumed silica support, comprising the following steps: (1) Slowly add 10g of hydrophilic fumed silica to a mixed solvent of 200mL of anhydrous ethanol and deionized water, wherein the volume ratio of anhydrous ethanol to deionized water is 95:5, and mechanically stir and disperse for 15 minutes. (2) Add acetic acid to the dispersion to adjust the pH of the solution to 4.5, and then sonicate for 30 minutes under ultrasonic power of 300W to obtain a uniform silica suspension; (3) Transfer the suspension to a three-necked flask equipped with a reflux condenser, and slowly add 2g of γ-aminopropyltriethoxysilane under magnetic stirring. After the addition is complete, raise the temperature to 60°C and maintain the reflux reaction for 6 hours. (4) After the reaction is complete, the product is centrifuged and the precipitate is washed three times with anhydrous ethanol to remove unreacted silane monomers. (5) The washed solid was placed in a vacuum drying oven and dried at 100°C for 12 hours. It was then ground and passed through a 200-mesh sieve to obtain an amino-modified fumed silica carrier.

[0039] Preparation Example 3: This preparation example provides a method for preparing an amino-modified fumed silica support, comprising the following steps: (1) Slowly add 10g of hydrophilic fumed silica to a mixed solvent of 200mL of anhydrous ethanol and deionized water, wherein the volume ratio of anhydrous ethanol to deionized water is 95:5, and mechanically stir and disperse for 15 minutes. (2) Add acetic acid to the dispersion to adjust the pH of the solution to 5.5, and then sonicate for 30 minutes under ultrasonic power of 300W to obtain a uniform silica suspension; (3) Transfer the suspension to a three-necked flask equipped with a reflux condenser, and slowly add 3g of γ-aminopropyltriethoxysilane under magnetic stirring. After the addition is complete, raise the temperature to 70°C and maintain the reflux reaction for 8 hours. (4) After the reaction is complete, the product is centrifuged and the precipitate is washed three times with anhydrous ethanol to remove unreacted silane monomers. (5) The washed solid was placed in a vacuum drying oven and dried at 110°C for 12 hours. It was then ground and passed through a 200-mesh sieve to obtain an amino-modified fumed silica carrier.

[0040] Example 1: This embodiment provides a method for preparing an antibacterial composite resin-based filling material for root canal filling, including the following steps: (1) Under light-protected conditions, 21g of ethyl diaminocarbamate dimethacrylate (UDMA), 9g of triethylene glycol dimethacrylate (TEGDMA) and 3g of 10-methacryloyloxydecyl phosphate dihydrogen ester (10-MDP) were added to a vacuum mixer and stirred at 300 rpm for 10 minutes at 40°C until the resin matrix was obtained. (2) Add 1g of chlorhexidine base to the resin matrix and continue stirring at 40°C for 20 minutes until the chlorhexidine base is completely dissolved to obtain a clear and transparent resin solution containing antibacterial agent. (3) Add 2g of the amino-modified fumed silica carrier prepared in Example 1 to the above solution and stir for 15 minutes under high-speed dispersion at 1500rpm to make the carrier uniformly dispersed. (4) Seal the mixture and place it in a constant temperature oven at 50°C for static curing treatment for 24 hours to achieve in-situ anchoring of the drug at the interface by utilizing acid-base interaction. (5) After the curing is completed, wait for the material to cool to room temperature, and add 63.4g of barium silane glass powder, 0.2g of camphorquinone (CQ), 0.2g of ethyl 4-dimethylaminobenzoate (EDMAB), 0.1g of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and 0.1g of 2,6-di-tert-butyl-p-cresol (BHT) to the mixture. (6) Under the conditions of vacuum degree -0.09MPa and temperature 45℃, stir and mix at a speed of 60rpm for 30 minutes to fully remove air bubbles, and the general-purpose antibacterial composite resin material for root canal filling is obtained.

[0041] Example 2: This embodiment provides a method for preparing an antibacterial composite resin-based filling material for root canal filling, including the following steps: (1) Under light-protected conditions, 15g of ethyl diaminocarbamate dimethacrylate (UDMA), 5g of triethylene glycol dimethacrylate (TEGDMA) and 3g of 10-methacryloyloxydecyl phosphate dihydrogen ester (10-MDP) were added to a vacuum mixer and stirred at 300 rpm for 10 minutes at 40°C until the resin matrix was obtained. (2) Add 1g of chlorhexidine base to the resin matrix and continue stirring at 40°C for 20 minutes until the chlorhexidine base is completely dissolved to obtain a clear and transparent resin solution containing antibacterial agent. (3) Add 2g of the amino-modified fumed silica carrier prepared in Example 2 to the above solution and stir for 15 minutes under high-speed dispersion at 1500rpm to make the carrier uniformly dispersed. (4) Seal the mixture and place it in a constant temperature oven at 50°C for static curing treatment for 24 hours to achieve in-situ anchoring of the drug at the interface by utilizing acid-base interaction. (5) After the curing is completed, wait for the material to cool to room temperature, and add 73.4g of barium silane glass powder, 0.2g of camphorquinone (CQ), 0.2g of ethyl 4-dimethylaminobenzoate (EDMAB), 0.1g of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and 0.1g of 2,6-di-tert-butyl-p-cresol (BHT) to the mixture. (6) Under the conditions of vacuum degree -0.09MPa and temperature 45℃, stir and mix at a speed of 60rpm for 40 minutes to fully remove air bubbles, and the antibacterial composite resin material for root canal filling is obtained.

[0042] Example 3: This embodiment provides a method for preparing an antibacterial composite resin-based filling material for root canal filling, including the following steps: (1) Under light-protected conditions, 15g of ethyl diaminocarbamate dimethacrylate (UDMA), 15g of triethylene glycol dimethacrylate (TEGDMA) and 3g of 10-methacryloyloxydecyl phosphate dihydrogen ester (10-MDP) were added to a vacuum mixer and stirred at 300 rpm for 10 minutes at 40°C until the resin matrix was obtained. (2) Add 1g of chlorhexidine base to the resin matrix and continue stirring at 40°C for 20 minutes until the chlorhexidine base is completely dissolved to obtain a clear and transparent resin solution containing antibacterial agent. (3) Add 1.5g of the amino-modified fumed silica support prepared in Example 3 to the above solution and stir for 15 minutes under high-speed dispersion conditions of 1500rpm to make the support uniformly dispersed. (4) Seal the mixture and place it in a constant temperature oven at 50°C for static curing treatment for 24 hours to achieve in-situ anchoring of the drug at the interface by utilizing acid-base interaction. (5) After the curing is completed, wait for the material to cool to room temperature, and add 63.9g of barium silane glass powder, 0.2g of camphorquinone (CQ), 0.2g of ethyl 4-dimethylaminobenzoate (EDMAB), 0.1g of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and 0.1g of 2,6-di-tert-butyl-p-cresol (BHT) to the mixture. (6) Under the conditions of vacuum degree -0.09MPa and temperature 45℃, stir and mix at a speed of 60rpm for 30 minutes to fully remove air bubbles, and a high-flowability antibacterial composite resin material for root canal filling is obtained.

[0043] Example 4: This embodiment provides a method for preparing an antibacterial composite resin-based filling material for root canal filling, including the following steps: (1) Under light-protected conditions, 20g of ethyl diaminocarbamate dimethacrylate (UDMA), 9g of triethylene glycol dimethacrylate (TEGDMA) and 4g of 10-methacryloyloxydecyl phosphate dihydrogen ester (10-MDP) were added to a vacuum mixer and stirred at 300 rpm for 10 minutes at 40°C until the resin matrix was obtained. (2) Add 2g of chlorhexidine base to the resin matrix and continue stirring at 40°C for 30 minutes until the chlorhexidine base is completely dissolved to obtain a clear and transparent resin solution containing antibacterial agent. (3) Add 2.5g of the amino-modified fumed silica carrier prepared in Example 1 to the above solution and stir for 20 minutes under high-speed dispersion at 1500rpm to make the carrier uniformly dispersed. (4) Seal the mixture and place it in a constant temperature oven at 50°C for static curing treatment for 24 hours to achieve in-situ anchoring of the drug at the interface by utilizing acid-base interaction. (5) After the curing is completed, wait for the material to cool to room temperature, and add 61.9g of barium silane glass powder, 0.2g of camphorquinone (CQ), 0.2g of ethyl 4-dimethylaminobenzoate (EDMAB), 0.1g of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and 0.1g of 2,6-di-tert-butyl-p-cresol (BHT) to the mixture. (6) Under the conditions of vacuum degree -0.09MPa and temperature 45℃, stir and mix at a speed of 60rpm for 30 minutes to fully remove air bubbles, and the antibacterial composite resin material for root canal filling with high antibacterial properties is obtained.

[0044] Example 5: This embodiment provides a method for preparing an antibacterial composite resin-based filling material for root canal filling, including the following steps: (1) Under light-protected conditions, 21g of ethyl diaminocarbamate dimethacrylate (UDMA), 9g of triethylene glycol dimethacrylate (TEGDMA) and 3g of 10-methacryloyloxydecyl phosphate dihydrogen ester (10-MDP) were added to a vacuum mixer and stirred at 300 rpm for 10 minutes at 40°C until the resin matrix was obtained. (2) Add 1g of chlorhexidine base to the resin matrix and continue stirring at 40°C for 20 minutes until the chlorhexidine base is completely dissolved to obtain a clear and transparent resin solution containing antibacterial agent. (3) Add 2g of the amino-modified fumed silica carrier prepared in Example 1 to the above solution and stir for 15 minutes under high-speed dispersion at 1500rpm to make the carrier uniformly dispersed. (4) Seal the mixture and place it in a constant temperature oven at 50°C for static curing treatment for 12 hours to achieve in-situ anchoring of the drug at the interface by utilizing acid-base interaction. (5) After the curing is completed, wait for the material to cool to room temperature, and add 63.4g of barium silane glass powder, 0.2g of camphorquinone (CQ), 0.2g of ethyl 4-dimethylaminobenzoate (EDMAB), 0.1g of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and 0.1g of 2,6-di-tert-butyl-p-cresol (BHT) to the mixture. (6) Under the conditions of vacuum degree -0.09MPa and temperature 45℃, stir and mix at a speed of 60rpm for 30 minutes to fully remove air bubbles, and the antibacterial composite resin-based filling material for root canal filling is obtained.

[0045] Comparative Example 1: Compared with Example 1, the difference is that 1g of chlorhexidine base in step (2) is replaced with an equal mass of chlorhexidine acetate, and the rest are the same.

[0046] Comparative Example 2: Compared with Example 1, the difference is that 10-methacryloyloxydecyl phosphate dihydrogen ester (10-MDP) is not added in step (1), but is replaced with an equal mass of triethylene glycol dimethacrylate (TEGDMA), and the rest are the same.

[0047] Comparative Example 3: Compared with Example 1, the difference is that the amino-modified fumed silica support in step (3) is replaced with an equal mass of fumed silica (i.e., conventional hydrophobic fumed silica, type R972) surface-treated with γ-methacryloyloxypropyltrimethoxysilane (MPS), and all other aspects are the same.

[0048] Comparative Example 4: Compared with Example 1, the difference is that the amino-modified fumed silica support in step (3) is replaced with an equal mass of unmodified hydrophilic fumed silica, and the rest are the same.

[0049] Comparative Example 5: Compared with Example 1, the difference is that chlorhexidine base is not added in step (2), but an equal mass of resin matrix (UDMA / TEGDMA mixture) is added, and the rest are the same.

[0050] Test Example 1: The experimental steps are as follows: (1) Resin mixtures without inorganic fillers were prepared according to the resin matrix preparation steps described in Example 1, Comparative Example 1 and Comparative Example 2. Group A corresponds to Example 1 (containing UDMA, TEGDMA, 10-MDP and chlorhexidine base), Group B corresponds to Comparative Example 1 (chlorhexidine base is replaced with chlorhexidine acetate), and Group C corresponds to Comparative Example 2 (containing only UDMA, TEGDMA and chlorhexidine base, without 10-MDP).

[0051] (2) Inject the three prepared resin solutions into quartz cuvettes with an optical path of 10 mm, ensuring that no air bubbles remain. Use the pure resin matrix (UDMA / TEGDMA mixture) from the same batch without any added antibacterial agents as a reference sample for baseline correction.

[0052] (3) Use a UV-Vis spectrophotometer to perform spectral scanning at 25°C. The scanning range is set to 400nm to 800nm, the scanning speed is medium, the sampling interval is 1nm, and the transmittance data at each wavelength is recorded.

[0053] (4) After the spectral test is completed, seal the cuvette containing the sample, place it in front of the black background plate, and let it stand for 24 hours under the standard D65 light source.

[0054] (5) After standing, observe and record the appearance of the solution again, focusing on whether there is turbidity, flocculent precipitation or stratification, and re-measure its transmittance at 600nm to quantify stability.

[0055] The test results are shown in Table 1.

[0056] Table 1. Test data on optical transmittance and static stability of resin solutions with different formulations:

[0057] According to Table 1 and Figure 1Data analysis showed that group A maintained a high transmittance of over 91% across the entire visible light spectrum, and the value showed no significant fluctuation (from 92.8% to 92.5%) after standing for 24 hours, maintaining a clear and transparent appearance. This indicates that chlorhexidine base and 10-MDP underwent a complete chemical reaction in the resin matrix. The dihydrogen phosphate ion in the 10-MDP molecule acted as a proton donor, undergoing acid-base neutralization with the biguanide group in the chlorhexidine molecule. The resulting (MDP)2-CHX ion complex utilized the hydrophobic properties of the long carbon chain of the MDP molecule to shield the original polar core of chlorhexidine. This molecular-level modification allowed the antibacterial agent to dissolve in the hydrophobic UDMA / TEGDMA resin matrix in a thermodynamically stable state, without forming aggregates sufficient to produce light scattering.

[0058] In contrast, group B exhibited extremely low transmittance (14.3%–22.4%), and after 24 hours, the transmittance further decreased to 8.2% accompanied by precipitation. This is because chlorhexidine acetate is a hydrophilic salt with a high lattice energy, making it unable to be dissociated by the weakly polar methacrylate monomer. Even in the presence of 10-MDP in the system, due to the competitive steric hindrance effect of acetate ions and differences in solubility, a lipid-soluble complex could not be effectively formed, resulting in the drug being suspended in the resin as micron-sized crystals, leading to severe phase separation and light scattering.

[0059] Group C performed the worst, with a transmittance of less than 12%. In the absence of 10-MDP as an acidic ligand, chlorhexidine, as a rigid polycyclic organic base, exhibits a significant difference in solubility parameters compared to the resin monomer. Physical mixing cannot overcome intermolecular repulsion, leading to rapid drug aggregation and precipitation.

[0060] In summary, only the in-situ acid-base assembly strategy used in Example 1 can achieve molecular-level dispersion of the antibacterial agent in the resin matrix, which provides a chemical basis for the curing uniformity and mechanical property stability of the subsequent materials.

[0061] Test Example 2: The experimental steps are as follows: (1) Take the uncured resin slurry prepared in Examples 1-5 and Comparative Examples 1-2 respectively, and fill it into a stainless steel mold with a diameter of 10 mm and a thickness of 1 mm. Cover with a polyester film to isolate oxygen, and use a light curing lamp (light intensity 1200 mW / cm²). 2 The samples were irradiated on both sides for 40 seconds each to obtain cured disc samples. Five parallel samples were prepared for each group. The surface was gently wiped with an ethanol cotton ball to remove the unpolymerized monomer layer, and then stored in a desiccator in the dark for 24 hours before use.

[0062] (2) Each group of samples was suspended in a brown sealed glass bottle containing 10 mL of artificial saliva (pH 6.8, containing phosphate buffer). The samples were completely submerged without touching the bottle wall and placed in a constant temperature shaking chamber at 37°C, where they were continuously shaken at a speed of 60 rpm to simulate the liquid flow environment in the oral cavity.

[0063] (3) Samples were taken at the time points of day 1, day 7, day 30 and day 60 of soaking. Each time a sample was taken, 1 mL of soaking solution was taken as the test solution and 1 mL of fresh artificial saliva was immediately added to the original bottle to maintain a constant volume of dissolution medium and the conditions of the trough.

[0064] (4) The sample solution was quantitatively analyzed by high performance liquid chromatography (HPLC). The chromatographic conditions were set as follows: C18 reversed-phase column (4.6 mm × 150 mm, 5 μm), mobile phase was acetonitrile: 0.1% phosphoric acid aqueous solution (volume ratio 40:60), flow rate was 1 mL / min, detection wavelength was 254 nm, and column temperature was 30 °C.

[0065] (5) Using the external standard method, the drug concentration in the soaking solution at each time point is calculated based on the standard curve drawn from the chlorhexidine standard, and the cumulative release concentration at each time point is calculated by combining the dilution factor and the cumulative effect formula.

[0066] The test results are shown in Table 2.

[0067] Table 2. Cumulative release concentration (ppm) of chlorhexidine in artificial saliva for each group of samples:

[0068] According to Table 2 and Figure 2 Data analysis showed that Comparative Example 1 exhibited an extremely high drug dissolution rate. Because chlorhexidine acetate, as a hydrophilic small-molecule salt, cannot form chemical bonds with the hydrophobic resin matrix, it rapidly diffuses outwards with the infiltration of water molecules under osmotic pressure. Although Comparative Example 2 used a chlorhexidine base, due to the lack of acidic anchoring by 10-MDP, the drug molecules were only physically suspended in the gaps between the polymer network, undergoing Brownian motion migration over time, resulting in continuous dissolution (reaching 19.55 ppm after 60 days).

[0069] In contrast, the cumulative release amounts of Examples 1-4 remained below 0.3 ppm over 60 days, close to the HPLC detection limit. This result confirms the effectiveness of the interfacial competitive anchoring mechanism. Chlorhexidine molecules are first protonated and encapsulated by 10-MDP to form a hydrophobic complex, and then firmly adsorbed onto the surface of nano-silica through ionic bonding between phosphate groups and amino groups on the carrier surface. This ternary assembly structure of "carrier-drug-resin" greatly restricts the freedom of the antibacterial agent molecules, preventing them from migrating with the solvent.

[0070] Furthermore, the release amount in Example 5 (cured for 12 hours) (0.56 ppm) was slightly higher than that in Example 1 (cured for 24 hours, 0.18 ppm), indicating that the static curing process at 50°C is crucial for completing interfacial assembly. Insufficient curing time resulted in some drug failing to fully penetrate the ionic bond network on the carrier surface, leading to trace amounts of free release. In summary, the material prepared by this invention achieves non-dissolution antibacterial properties, ensuring both biosafety and long-term retention of the antibacterial components within the material.

[0071] Test Example 3: The experimental steps are as follows: (1) Polymerization shrinkage stress test: The shrinkage stress was measured using a cantilever beam shrinkage stress tester. The resin slurry to be tested was filled between the upper and lower surface-treated glass rods of the instrument to form a cylindrical sample with a diameter of 5 mm and a height of 0.8 mm. The lower glass rod was connected to a force sensor (range 50 N, accuracy 0.1 N), and the upper part was fixed. A light intensity of 800 mW / cm² was used. 2 The LED curing lamp illuminates the sample through a lower glass rod for 40 seconds. The data acquisition system records the axial shrinkage force change in real time at a frequency of 10Hz from the start of illumination to 5 minutes after the end of illumination. The shrinkage stress value (MPa) is calculated based on the cross-sectional area of ​​the sample. Five parallel samples are tested in each group, and the average value of the maximum peak stress is taken.

[0072] (2) Volume shrinkage rate test: Based on Archimedes' principle, the density of the material before and after curing was measured using an electronic densitometer. First, the mass of the uncured resin slurry in air and its buoyant mass in n-hexane (as an auxiliary liquid to avoid water swelling) were weighed, and the uncured density was calculated. Then, a cured disc with a diameter of 10 mm and a thickness of 2 mm was prepared (lighting parameters as above), and its mass in air and its buoyant mass in deionized water were measured, and the density after curing was calculated.

[0073] (3) Volume shrinkage rate (VS%) is calculated according to the formula (1 - uncured density / cured density) × 100%. Record the data and analyze the correlation between stress and shrinkage rate.

[0074] The test results are shown in Table 3.

[0075] Table 3. Test results of peak polymerization shrinkage stress and volume shrinkage rate of each group of resin materials:

[0076] According to Table 3 and Figure 3The data from Comparative Example 3 (conventional hydrophobic silica treated with MPS silanization) showed the highest polymerization shrinkage stress (3.12 MPa). This is because MPS rigidly connects the inorganic filler to the organic resin matrix through covalent bonds, restricting the movement of polymer chain segments. During rapid photocuring, the internal stress generated by volume shrinkage cannot be released through interfacial slip, resulting in a high concentration of stress at the filler-matrix interface. Although its volume shrinkage rate (2.92%) is within the normal range, the extremely high stress / shrinkage ratio (1.07) indicates that a large amount of destructive energy has accumulated inside the material, which can easily lead to marginal microleakage or dental microcracks in clinical practice.

[0077] Conversely, the polymerization shrinkage stress in Examples 1-4 was significantly reduced, all controlled below 1 MPa, with Example 1 showing only 0.85 MPa. This result verifies the dynamic ionic bond stress dissipation mechanism. In the system of this invention, a "PO" bond is formed between the amino groups on the support surface and the phosphate ester groups (MDP) in the resin matrix. - H + -N” ionic bond network. This non-covalent bond is reversible and dynamic. When polymerization shrinkage generates tensile stress, the ionic bond nodes can undergo local dissociation and recombination (i.e., sacrificial bond effect), allowing polymer chain segments to slide and rearrange at the microscale on the filler surface, thereby converting elastic energy into heat energy for dissipation without destroying the overall continuity of the material.

[0078] Furthermore, Comparative Example 2 (no MDP, no bonding) exhibited a stress value of 1.65 MPa, falling between rigid and ionic bonds, and also showed the highest volume shrinkage (3.45%). This indicates that while simply removing interfacial bonds reduces rigid constraints, it prevents the filler from effectively occupying volume to resist shrinkage, increases interfacial defects, and results in the worst overall mechanical properties. Example 5 (insufficient curing) showed a slightly higher stress value (1.05 MPa) than Example 1, further demonstrating the crucial role of a well-developed ionic assembly structure in stress dissipation.

[0079] Test Example 4: The experimental steps are as follows: (1) Select 60 recently extracted, caries-free, and crack-free single-rooted premolars, remove the crowns, and retain a root length of about 12 mm. Use a machine-made nickel-titanium root canal file with irrigation solution (2.5% sodium hypochlorite and 17% EDTA) to prepare the root canals up to F3, and then use paper points to dry the moisture in the root canals.

[0080] (2) The samples were randomly divided into 10 groups (corresponding to Examples 1-5 and Comparative Examples 1-5), with 6 teeth in each group. According to the formulation instructions of each group, the resin sealant was introduced into the root canal, the appropriate master gutta-percha point was inserted, and after removing excess material, it was cured by vertically irradiating it from the coronal side for 40 seconds.

[0081] (3) The filled sample was placed in a constant temperature chamber at 37°C and 100% humidity for 24 hours to ensure complete curing. Then, a hot and cold cycle aging treatment was carried out: the sample was alternately immersed in water baths at 5°C and 55°C, with each bath lasting 30 seconds and a transition time of 10 seconds, for a total of 5000 cycles, simulating the temperature change stress in the oral cavity for about half a year.

[0082] (4) After aging, apply two layers of nail polish to the root surface (except for the 1mm area around the apical foramen) to seal the openings of the lateral canals and dentinal tubules, ensuring that the dye can only penetrate from the apical filling interface. After the nail polish dries, immerse the sample in a 2% methylene blue solution and let it stand at 37°C for 48 hours.

[0083] (5) Remove the sample, rinse the surface dye thoroughly with running water, and scrape off the nail polish. Place the root sample in liquid nitrogen to freeze and embrittle, and then grind it into fine powder using a ball mill.

[0084] (6) Weigh an equal amount of tooth powder (0.5g), add 5mL of 65% nitric acid solution, and sonicate for 2 hours to dissolve the dye. Centrifuge and collect the supernatant. Measure the absorbance (OD value) at 660nm using a UV-Vis spectrophotometer. Use an unfilled tooth root powder extract that has been treated in the same way as a blank control.

[0085] The test results are shown in Table 4.

[0086] Table 4. Microleakage dye extraction absorbance (OD value) of each group of samples after thermal cycling aging:

[0087] According to the data in Table 4, the dye extraction OD values ​​of Examples 1–5 (0.036–0.061) were significantly lower than those of all comparative examples (0.123–0.209), indicating that the material of the present invention can still maintain excellent root canal margin sealing after undergoing harsh thermal cycling aging. This result is related to the low shrinkage stress characteristics verified in Test Example 3 above. Because the dynamic ionic bond network effectively dissipates the internal stress generated by polymerization shrinkage, it prevents the material from peeling off from the dentin wall, thereby blocking the formation of microleakage channels.

[0088] Comparative Example 1 (chlorhexidine acetate group) exhibited the highest microleakage value (0.209). This is because the hydrophilicity of acetate causes the material to absorb water and swell, and the phase separation caused by drug crystal precipitation disrupts the continuity of the resin matrix and the interfacial bonding force, making it easy for the dye to penetrate along the interface. Although Comparative Example 3 (rigid bonding group) has high mechanical strength, its OD value (0.143) is still much higher than that of the example group. This confirms that excessively high polymerization shrinkage stress can lead to microcracks at the bonding interface, and even with the use of adhesives, rigid materials are more prone to interfacial fatigue failure during alternating thermal expansion and contraction.

[0089] Furthermore, Example 2 (high filler content) achieved the lowest microleakage value (0.036), indicating that increasing the inorganic filler content helps reduce the coefficient of thermal expansion and further improves dimensional stability. Example 5 (short curing) showed a slightly higher microleakage value, again highlighting the importance of adequate interfacial assembly for forming a dense and stable material structure. In summary, this invention significantly improves the long-term sealing reliability of root canal fillings.

[0090] Test Example 5: The experimental steps are as follows: (1) According to ISO 4049 standard, prepare strip-shaped samples with dimensions of 25mm × 2mm × 2mm. Inject each group of uncured resin slurry into a stainless steel split mold, cover the upper and lower surfaces with polyester film, and press the glass plate to extrude excess material. Use light intensity of 1200mW / cm². 2 An LED curing lamp is used, closely attached to the surface of the glass plate, to irradiate the sample in three overlapping sections along its length, with each section irradiated for 40 seconds to ensure uniform curing of the entire sample. Ten parallel samples are prepared for each formulation.

[0091] (2) After curing, carefully demold the sample and gently sand the edges of the sample with 600-grit silicon carbide sandpaper to remove burrs, taking care to maintain the integrity of the sample's geometric dimensions. Use a digital vernier caliper to accurately measure the width and thickness of the center of each sample to an accuracy of 0.01 mm.

[0092] (3) The prepared sample was placed in deionized water at 37°C and immersed for 24 hours to simulate the oral cavity environment and eliminate the post-curing effect in the early stage of polymerization.

[0093] (4) Remove the sample, wipe off the surface moisture, and immediately place it on the three-point bending test fixture of the universal testing machine. Set the span to 20 mm and the indenter diameter to 2 mm. Apply vertical downward pressure at a loading speed of 1 mm / min until the sample breaks.

[0094] (5) The system automatically records the load-displacement curve and the maximum breaking load (F). According to the formula σ=3FL / (2bh) 2Calculate the bending strength (MPa), and calculate the bending modulus (GPa) based on the slope of the linear portion of the load-displacement curve, where L is the span, b is the specimen width, and h is the specimen thickness.

[0095] The test results are shown in Table 5.

[0096] Table 5. Results of three-point flexural strength and elastic modulus tests for each group of resin materials:

[0097] According to the data in Table 5, the flexural strength of Example 1 reached 112.4 MPa, which is slightly lower than that of Comparative Example 3 (128.5 MPa) using rigid covalent bonds, but still far exceeds the minimum requirement (80 MPa) for dental polymer-based filling materials in ISO 4049 standard. This result indicates that although the dynamic ionic bond interface of "carrier-drug-resin" constructed in this invention has a certain stress dissipation capacity, it can still provide sufficient interfacial transfer efficiency under macroscopic mechanical loads. The ionic bond clusters act as physical cross-linking points between molecular chains, effectively hindering crack propagation.

[0098] Comparing the modulus data, the elastic modulus of Example 1 (8.4 GPa) is lower than that of Comparative Example 3 (11.5 GPa). This moderate reduction in modulus is beneficial, as it imparts better toughness and a deformation capacity that better matches dentin (modulus of approximately 14–18 GPa), helping to buffer chewing pressure and reduce interfacial stress concentration.

[0099] Conversely, the strength of Comparative Example 1 was only 45.6 MPa. This was due to the formation of numerous microscopic defects and stress concentration points by chlorhexidine acetate crystals in the resin matrix, leading to brittle fracture under low loads. Data from Comparative Example 2 (68.9 MPa) confirmed that, in the absence of interfacial chemical bonding, inorganic fillers could not provide reinforcement and instead became a weak phase in the matrix. The strength of Example 5 (98.2 MPa) decreased slightly, indicating that insufficient curing resulted in inadequate interfacial bonding density, affecting the effective transfer of load between the organic and inorganic phases. In summary, this invention, through an in-situ acid-base assembly strategy, maintains high mechanical strength while ensuring excellent antibacterial properties and low shrinkage stress, achieving a balance between functionality and structure.

[0100] Test Example 6: The experimental steps are as follows: (1) Preparation of cured resin discs (10 mm in diameter and 2 mm in thickness) for Example 1, Comparative Example 1 (chlorhexidine acetate group) and Comparative Example 5 (blank control group). Each group of samples was divided into two batches: the first batch was the fresh preparation group, which was disinfected with ethanol after preparation and used for testing immediately; the second batch was the aging group, which was placed in deionized water at 37°C for 60 days. During this period, the soaking solution was changed once a week to simulate the fluid exchange and drug loss process in the oral cavity. After aging, the discs were taken out, dried and disinfected for later use.

[0101] (2) Resuscitation of frozen Streptococcus mutans ( Streptococcus mutans (ATCC 25175), inoculated into brain heart and brain infusion (BHI) broth and cultured anaerobically at 37°C for 24 hours. Cells were collected by centrifugation, washed and resuspended with sterile phosphate-buffered saline (PBS), and the bacterial concentration was adjusted to 1.0 × 10⁻⁶. 6 CFU / mL.

[0102] (3) Place each group of samples in a sterile petri dish, and add 0.1 mL of the above standard bacterial suspension to the surface of the sample. Cover with a layer of sterile polyethylene film (9 mm in diameter) to ensure that the bacterial suspension is evenly spread and fully contacts the material surface, while preventing the bacterial suspension from evaporating. Incubate the petri dishes in a constant temperature incubator at 37°C and relative humidity above 90% for 24 hours.

[0103] (4) After the culture is completed, take out the sample and the covering film and put them into a sterile test tube containing 10 mL of neutralizing agent (D / E neutralizing broth). Vortex vigorously for 2 minutes to wash away the adhering bacteria. Take the eluent and perform serial dilutions, spread it on BHI agar plates, and anaerobic incubate at 37°C for 48 hours before counting the colonies (CFU).

[0104] (5) Data calculation: Record the number of viable bacteria in each group and calculate the antibacterial rate according to the formula R=(AB) / A×100%, where A is the average number of recovered colonies in comparative example 5 and B is the average number of recovered colonies in the experimental group.

[0105] The test results are shown in Table 6.

[0106] Table 6. Results of antimicrobial performance tests on the surface of freshly prepared and aged materials after 60 days against Streptococcus mutans:

[0107] According to the data in Table 6, both Example 1 and Comparative Example 1 exhibited strong bactericidal effects against Streptococcus mutans (antibacterial rate >99.99%) in their freshly prepared state, indicating that the chlorhexidine component in both systems possesses biological activity. However, after 60 days of water immersion aging treatment, the performance of the two systems showed a fundamental divergence.

[0108] The antibacterial rate of Comparative Example 1 significantly decreased to 43.22% after aging. Combined with data from Test Example 2 (dissolution kinetics), this indicates that chlorhexidine acetate, physically mixed in a free state within the resin matrix, dissolves in large quantities under the influence of the concentration gradient and water permeation. Once the surface drug is completely released, the material loses its antibacterial barrier, allowing bacteria to colonize extensively on the surface. This release-type antibacterial mode cannot meet the requirements for long-term in vivo service of root canal filling materials.

[0109] Conversely, Example 1 maintained an extremely high antibacterial rate of 99.98% after 60 days of aging. This result verifies the contact antibacterial properties conferred by the interfacial competitive anchoring mechanism. In this invention, chlorhexidine molecules are firmly anchored to the surface of the nano-silica carrier through ionic bonds and are uniformly dispersed in the resin matrix along with the carrier. Even after prolonged water bath immersion, the drug molecules do not dissociate or migrate. When bacteria come into contact with the material surface, the positively charged active groups (guanidino groups) of chlorhexidine exposed at the interface directly disrupt the bacterial cell membrane, leading to bacterial death, without the drug itself being consumed. This non-dissolution, contact bactericidal mechanism ensures the stability and durability of the material's antibacterial performance throughout its entire life cycle.

[0110] Test Example 7: The experimental steps are as follows: (1) Take the uncured resin slurry prepared in Example 1 and Comparative Example 4 and put it into black light-proof syringes. Prepare 10 samples in each group, of which 5 are used for initial testing (Day 0), and the other 5 are placed in a 50°C constant temperature drying oven for accelerated thermal aging treatment. The aging period is set to 14 days. According to the Arrhenius equation, this condition is equivalent to storage at room temperature (23°C) for about 12 months.

[0111] (2) At the test time points (Day 0 and Day 14), the samples were removed and placed in a constant temperature environment of 25°C for 2 hours to equilibrate. The rheological parameters of the slurry were determined using a rotational rheometer (equipped with a 20mm cone plate rotor and a cone angle of 1°). The shear rate was set from 0.1 s⁻¹. -1 Scan to 100s -1 The shear rate was recorded as 10 s. -1 The apparent viscosity value (Pa·s) at that time.

[0112] (3) Subjective evaluation of extrusion properties. Install a needle on the syringe, manually extrude the slurry, and observe under a magnifying glass whether the extrudate is continuous, whether the surface is smooth, and whether there are visible particle agglomeration or liquid phase separation (bleeding).

[0113] (4) Calculate the viscosity growth rate using the formula: Δη=(η 14d -η 0d ) / η 0d×100%.

[0114] The test results are shown in Table 7.

[0115] According to the data in Table 7, after a simulated year of accelerated thermal aging, Example 1 showed a viscosity increase of only 3.20%, and the extruded properties remained fine and uniform. This confirms the excellent colloidal stability of the "carrier-drug-resin" ternary assembly system. In Example 1, 10-MDP molecules were anchored to the silica surface by ionic bonds, with their long carbon chains (hydrophobic ends) extending outwards, forming a dense steric hindrance layer around the inorganic filler. This steric hindrance effect effectively counteracted the van der Waals forces between filler particles, preventing secondary aggregation of nanoparticles under intensified Brownian motion (high temperature conditions). Simultaneously, stable interfacial chemical bonding prevented the release and recrystallization of antibacterial agent molecules, maintaining the constant rheological properties of the slurry.

[0116] In contrast, Comparative Example 4 exhibited storage instability, with a viscosity increase rate as high as 61.87%, accompanied by a noticeable grainy texture. This is because the unmodified silica surface is rich in hydrophilic silanol groups (Si-OH), which have extremely poor thermodynamic compatibility with the hydrophobic resin matrix (UDMA / TEGDMA). During static and thermal aging, in order to reduce the total surface energy of the system, the high-energy surface nanofillers tend to approach each other, forming large agglomerates through hydrogen bonding between surface hydroxyl groups. This disordered filler network structure hinders the flow of resin segments, leading to a dramatic increase in macroscopic viscosity. Furthermore, the formation of agglomerates disrupts the homogeneity of the material, resulting in visible coarse particles during extrusion, which will affect clinical handling performance and the mechanical strength of the final cured product. Therefore, the surface assembly technology of this invention not only endows the material with functionality but is also a key technical means to ensure the quality stability of the product throughout its shelf life.

[0117] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An antibacterial composite resin-based filling material for root canal filling in endodontics, characterized in that, Made from the following ingredients in parts by weight: 15-25 parts of ethyl carbamate and dimethacrylate; Dilute the monomer to 5-15 parts; 2-5 parts of 10-methacryloyloxydecyl phosphate dihydrogen ester; Chlorhexidine base 0.5–3 parts; 1-4 parts of amino-modified fumed silica carrier; 60-80 parts of inorganic filler; Initiator system: 0.1–1 part; The chlorhexidine base is dissolved in a resin matrix composed of ethyl dicarboxylate, diluent monomer, and 10-methacryloyloxydecyl phosphate dihydrogen ester, and is anchored in situ at the interface with the amino-modified fumed silica carrier through acid-base interaction.

2. The antibacterial composite resin-based filling material for root canal filling in dental endodontics according to claim 1, characterized in that, The weight parts of the raw materials are: 15-21 parts of ethyl carbamate dimethacrylate; Dilute the monomer to 5-15 parts; 3-4 parts of 10-methacryloyloxydecyl phosphate dihydrogen ester; Chlorhexidine base 1-2 parts; 1.5–2.5 parts of amino-modified fumed silica carrier; 61-74 parts of inorganic filler.

3. The antibacterial composite resin-based filling material for root canal filling in dental endodontics according to claim 1, characterized in that, The diluent monomer is triethylene glycol dimethacrylate; the inorganic filler is barium silanide glass powder; the initiator system includes a photoinitiator, a co-initiator, and a polymerization inhibitor.

4. The antibacterial composite resin-based filling material for root canal filling in dental endodontics according to claim 1, characterized in that, The amino-modified fumed silica support is prepared by a method comprising the following steps: S1. Disperse hydrophilic fumed silica in an ethanol-water solution, adjust the pH to acidic, and then ultrasonically disperse to obtain a suspension; S2. Add γ-aminopropyltriethoxysilane to the suspension and heat to 60-70℃ for reflux reaction; S3. The reaction product is centrifuged, washed, dried, ground and sieved to obtain the amino-modified fumed silica support.

5. The antibacterial composite resin-based filling material for root canal filling in dental endodontics according to claim 4, characterized in that, In step S1, the volume ratio of anhydrous ethanol to water in the ethanol-water solution is 95:5, and the pH value is adjusted to 4.5-5.5; in step S2, the mass ratio of the hydrophilic fumed silica to γ-aminopropyltriethoxysilane is 10:(2-3).

6. A method for preparing an antibacterial composite resin-based filling material for root canal filling in dental endodontics as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Mix ethyl dicarboxylate, diluent monomer and 10-methacryloyloxydecyl phosphate dihydrogen ester evenly to obtain resin matrix; (2) Add chlorhexidine base to the resin matrix and stir until completely dissolved; (3) Add amino-modified fumed silica carrier and disperse it at high speed to obtain a mixture; (4) The mixture obtained in step (3) is subjected to static thermal curing treatment so that chlorhexidine base, 10-methacryloyloxydecyl phosphate dihydrogen ester and amino-modified fumed silica carrier complete the interface assembly. (5) After the curing is completed, add the inorganic filler and initiator system, and vacuum stir to degas, and the product is obtained.

7. The preparation method according to claim 6, characterized in that, In step (4), the temperature of the static heat curing treatment is 45-55°C and the curing time is 12-24 hours.

8. The preparation method according to claim 6, characterized in that, In step (2), the stirring temperature is 35-45℃; in step (3), the high-speed dispersion speed is 1000-2000 rpm.

9. The preparation method according to claim 6, characterized in that, In step (5), the vacuum degree of the vacuum stirring is -0.08MPa to -0.1MPa, and the temperature is 40 to 50℃.

10. The preparation method according to claim 6, characterized in that, In step (1), the diluent monomer is triethylene glycol dimethacrylate; in step (5), the initiator system comprises camphorquinone, ethyl 4-dimethylaminobenzoate, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and 2,6-di-tert-butyl-p-cresol.

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