Root canal file having better safety and manufacturing method therefor

Abstract

Disclosed in the present invention are a root canal file having better safety and a manufacturing method therefor. Said root canal file comprises a root canal file base body and a titanium nitride layer located on the surface of the root canal file base body, the titanium nitride layer presenting a golden-yellow surface and homogeneously and compactly coating the root canal file base body. The root canal file of the present invention has good safety and practicability. The Ni-Ti shape memory alloy root canal file manufactured by means of heat-treatment nitriding technology and having the titanium nitride layer achieves good corrosion resistance, and can prevent the release of Ni ions during use so as to relieve the toxicity on human bodies. In addition, the processing and heat treatment methods used in the present invention involve simple processes.

Description

A safer root canal file and preparation method thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to application number CN202311192502.4, filed on September 15, 2023, entitled “A root canal file with better safety,” the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] The present invention relates to the field of biomedical metal products, and in particular to a root canal file with better safety and a preparation method thereof. Background Art

[0004] Endodontic disease and periapical periodontitis are common oral diseases, and root canal therapy is the primary treatment for these conditions. Root canal preparation is a key factor in determining the success of root canal treatment, and the effectiveness of root canal preparation is largely dependent on the appropriate root canal preparation instrument. However, clinical studies have demonstrated that the Ni ions contained in the Ni-Ti alloy used in nickel-titanium root canal preparation instruments are a potential allergen. The dissolution of Ni ions can cause toxic side effects such as sensitization and teratogenicity in the human body.

[0005] Given the above, applying a surface coating to nickel-titanium alloy root canal files is an effective means of preventing Ni ion dissolution. For example, Chinese patent application CN116356257A discloses a method for producing a nickel-titanium alloy root canal file, comprising: cleaning the nickel-titanium alloy root canal file; and forming a nanocoating on the outer surface of the file, wherein the nanocoating is a Ni-La composite coating.

[0006] Currently, there is still an urgent need for a root canal file with a titanium nitride layer that has a simpler preparation method, is safer and more practical.

[0007] The information in the background technology is only intended to illustrate the general background of the invention and should not be regarded as an admission or any form of suggestion that this information constitutes the prior art known to a person skilled in the art.

[0008] Summary of the Invention

[0009] To solve at least some of the technical problems in the prior art, the present invention provides an endodontic file having a titanium nitride layer and its use. Specifically, the present invention includes the following contents.

[0010] A first aspect of the present invention provides a safer root canal file with a titanium nitride layer, comprising a root canal file base and a titanium nitride layer located on the surface of the root canal file base, wherein the titanium nitride layer has a golden surface and is evenly and densely coated on the root canal file base.

[0011] In certain embodiments, the root canal file with better safety according to the present invention has a titanium nitride layer, wherein the titanium nitride layer is good and has no cracks under the fatigue test condition of 90 degrees fatigue 1500 times.

[0012] In certain embodiments, according to the root canal file with improved safety according to the present invention, the presence of the titanium nitride layer causes the nickel ion dissolution amount of the root canal file having the titanium nitride layer to be less than 0.025 μg / L over 10 days.

[0013] In certain embodiments, according to the root canal file with improved safety according to the present invention, the molar ratio of titanium metal to nickel metal in the root canal file base is 50:50 to 55:45.

[0014] In certain embodiments, the root canal file with better safety according to the present invention is obtained by forming a titanium nitride layer on the surface of the base through vacuum isothermal nitriding technology.

[0015] In certain embodiments, the root canal file with improved safety according to the present invention is prepared by the following steps:

[0016] a. Smelting titanium and nickel metals under non-oxidizing conditions, then heating them to 1200-1400°C under inert gas protection or vacuum environment, performing high-temperature refining respectively, and then cooling them to 600-1000°C for casting to obtain nickel-titanium shape memory alloy, which is then processed to obtain wire;

[0017] b. The wire is processed by root canal file, and the root canal file base is ground into the required specifications. The base is kept in a nitrogen mixed gas environment at a gas pressure of 0.005 to 0.1Mpa and a temperature of 550-600 ℃ for 0.5-5 hours. After cooling, the base is kept in an argon environment at 500-550 ℃ for 0.5-5 hours, and then furnace cooled.

[0018] In certain embodiments, the root canal file with improved safety according to the present invention further comprises the step of strengthening the nickel-titanium memory alloy or the processed root canal file, wherein the strengthening treatment refers to the step of repeatedly stretching / unloading the nickel-titanium memory alloy or the processed root canal file and performing high-temperature treatment in an inert environment.

[0019] In certain embodiments, according to the root canal file with better safety according to the present invention, the stretching deformation is 1-6%, and is repeated 5-20 times.

[0020] In certain embodiments, according to the root canal file with better safety according to the present invention, the obtained wire is processed by a root canal file processing grinder to grind out a root canal file base of the required specifications, and then kept in a nitrogen mixed gas environment with a gas pressure of 0.005 to 0.1 MPa and a temperature of 550-600°C for 0.5-5 hours, after cooling, kept in an argon environment of 500-550°C for 0.5-5 hours, and then furnace cooled; the root canal file is subjected to repeated stretching / unloading operations, and then heat-treated in an inert environment of 300-550°C for 1-10 hours; or the obtained wire is subjected to Repeat the stretching, deformation and unloading operations, and then heat-treat in an inert gas environment at 300-550°C; pass the treated wire through a root canal file processing grinder to grind out a root canal file base of the required specifications, keep it in a nitrogen mixed gas environment with a gas pressure of 0.005 to 0.1 MPa and a temperature of 550-600°C for 0.5-5 hours, cool it, keep it in an argon environment at 500-550°C for 0.5-5 hours, and then furnace cool it; repeat the stretching / unloading operation on the root canal file, and then heat-treat it in an inert gas environment at 300-550°C for 1-10 hours.

[0021] In certain embodiments, according to the root canal file with improved safety according to the present invention, the nitrogen-containing mixed gas comprises nitrogen and argon.

[0022] In certain embodiments, according to the root canal file with improved safety according to the present invention, the volume ratio of nitrogen gas to argon gas is 0.8:1 to 1:0.8.

[0023] In certain embodiments, according to the root canal file with better safety according to the present invention, the cumulative processing amount of the wire processing is controlled to be 17-60%.

[0024] A second aspect of the present invention provides a method for preparing the root canal file having a titanium nitride layer according to the present invention.

[0025] The titanium nitride layered root canal file of the present invention offers superior safety and practicality. The NiTi shape memory alloy root canal file, prepared through heat-treatment nitriding technology, exhibits excellent corrosion resistance, hindering Ni ion leakage during use and reducing harmful effects on the human body. Furthermore, the processing and heat treatment methods employed in the present invention are simple, yet maintain the original properties of the shape memory alloy while providing excellent corrosion resistance, resulting in exceptional protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is a surface view of the root canal file obtained in Example 1;

[0027] FIG2 is a surface image of the root canal file obtained in Comparative Example 2. The root canal file is locally oxidized, showing a yellowish-brown, dark purple, or blue color, indicating that the original nitride layer is destroyed in a high-temperature insulation environment without argon protection. DETAILED DESCRIPTION

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0029] It should be understood that the terms described in the present invention are only for describing particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges in the present invention, it should be understood that the upper and lower limits of the ranges and each intermediate value therebetween are specifically disclosed. Each smaller range between any stated value or intermediate value within a stated range and any other stated value or intermediate value within the stated range is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0030] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention belongs. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict with any incorporated document, the content of this specification shall prevail.

[0031] Safer root canal files

[0032] A first aspect of the present invention provides a safer root canal file, comprising a root canal file base and a titanium nitride layer located on the surface of the root canal file base, wherein the titanium nitride layer has a golden surface and is evenly and densely coated on the root canal file base.

[0033] The titanium nitride layer of the root canal file of the present invention exhibits excellent stability. Firstly, it is not easily oxidized, resulting in a uniform golden-yellow surface. Existing coatings or protective layers, however, are susceptible to oxidation, resulting in varying colors, such as partial or even complete ochre, dark purple, or blue. Secondly, the titanium nitride layer of the present invention exhibits excellent fatigue resistance, exhibiting no noticeable cracks even after 1,000 or even 1,500 cycles of fatigue at 90°C.

[0034] In the present invention, the presence of the titanium nitride layer causes the endodontic file having the titanium nitride layer to release less than 0.025 μg / L of nickel ions over 10 days, particularly less than 0.020 μg / L, for example, less than 0.010 μg / L, or even less than 0.005 μg / L. In another embodiment, the presence of the titanium nitride layer causes the endodontic file having the titanium nitride layer to release less than 0.4 μg / L of nickel ions over 1 day, particularly less than 0.3 μg / L, for example, less than 0.2 μg / L, or even less than 0.1 μg / L.

[0035] In the present invention, the molar ratio of titanium metal to nickel metal in the root canal file base is 50:50-55:45, preferably 51-54:46-48.

[0036] Preparation method

[0037] The present invention also provides a method for preparing a root canal file having a titanium nitride layer, which comprises at least the following steps: (1) a wire preparation step, (2) a titanium nitride layer step, and (3) an optional strengthening step. It should be understood by those skilled in the art that the numbers (1), (2) and (3) are only for the purpose of distinguishing different steps and do not indicate the order of the steps. As long as the purpose of the present invention can be achieved, the order of the above steps is not particularly limited. In addition, it should be understood by those skilled in the art that other steps or operations may be included before or after the above steps (1)-(3), or between any of these steps, such as to further optimize and / or improve the method of the present invention. Each step is described in detail below.

[0038] Steps for preparing wire:

[0039] The wire preparation steps of the present invention include smelting titanium metal and nickel metal under conditions that ensure that titanium is not oxidized. Next, under inert gas protection or vacuum environment, the initial temperature is raised to 1200-1400°C, high-temperature refining is performed respectively, and after standing, the temperature is lowered to 600-1000°C for casting to obtain nickel-titanium shape memory alloy, and the wire is obtained after processing.

[0040] In the present invention, the non-oxidizing conditions include an inert atmosphere environment. Smelting can be carried out in a crucible, for example. In the preparation method of the present invention, the amount of titanium metal and nickel metal used as raw materials is generally slightly higher than that of nickel metal based on the molar ratio. For example, the molar ratio of titanium metal to nickel metal is 50:50 to 55:45. Within the above range, it is easy to obtain an effect that is conducive to the nitriding reaction while maintaining the shape memory function. If the proportion of titanium metal is too high, the shape memory function is affected. On the other hand, if the proportion of nickel metal is too high, nickel is more likely to precipitate.

[0041] In the present invention, the refining temperature is generally 1200-1400°C, for example, 1250°C, 1300°C, 1350°C, etc., but is not particularly limited thereto. After refining, the temperature is lowered for pouring, and the pouring temperature is generally lowered to 600-1000°C, for example, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, etc.

[0042] Titanium nitride layer preparation steps:

[0043] The titanium nitride layer preparation steps of the present invention include processing the obtained wire material with a root canal file, grinding a root canal file base of required specifications, keeping it in a nitrogen-containing mixed gas environment with a gas pressure of 0.005 to 0.1 MPa and a temperature of 550-600°C for 0.5-5 hours, cooling it, keeping it in an argon environment of 500-550°C for 0.5-5 hours, and then furnace cooling it.

[0044] In the present invention, the wire is processed and / or ground to obtain the root canal file base. The size of the root canal file base is not limited and can be adjusted as needed. The processing can use known processing tools.

[0045] In the present invention, the nitriding step includes subjecting the root canal file substrate to a vacuum isothermal nitriding treatment in a low-pressure nitrogen-containing mixed gas for a time sufficient to form a continuous nitride layer on the surface, for example, 0.5-5 hours, preferably 1-4 hours, such as 2 hours or 3 hours. The volume ratio of nitrogen to argon in the mixed gas is not particularly limited, but is generally 0.8:1 to 1:0.8. Within this range, the generation rate or penetration effect of titanium nitride can be advantageously controlled. If the nitrogen ratio is too high, although the penetration rate is increased, the bonding strength tends to decrease, which is also not conducive to obtaining excellent fatigue resistance of the titanium nitride coating. On the other hand, if the nitrogen ratio is too low, it is not conducive to forming an effective titanium nitride coating thickness.

[0046] The present invention has found that although the titanium nitride layer obtained after the above-mentioned nitriding treatment has good integrity, it is easily oxidized. The inventors further discovered that adding a high-temperature argon treatment step after the nitriding treatment can effectively prevent the obtained titanium nitride from being oxidized. The anti-oxidation treatment includes keeping the obtained titanium nitride layer in a high-temperature argon environment for 0.5-5 hours after cooling, and then furnace cooling it to room temperature. The temperature of the anti-oxidation treatment is generally lower than that of the nitriding treatment, usually 500-550°C, such as 510°C, 520°C, 540°C, and 550°C.

[0047] Strengthening steps

[0048] The strengthening step of the present invention comprises subjecting the nickel-titanium memory alloy or the processed root canal file to repeated stretching / unloading operations and high-temperature treatment in an inert environment.

[0049] In the present invention, the stretching generally results in a deformation of 1-6%, such as 2%, 3%, 4%, 5%, etc. After stretching, unloading is required, i.e., the material recovers automatically after the tensile stress is removed. The stretching and unloading cycles may be repeated multiple times, for example, 5-20 times, such as 6, 8, 10, 12, 14, 16, and 18 times.

[0050] In the present invention, after repeated stretching and unloading operations, heat treatment is further performed in a high-temperature inert environment. The high temperature is generally 300-550°C, such as 350°C, 400°C, 450°C, 500°C, etc. The heat treatment time is generally 1-10 hours, preferably more than 5 hours, such as 6 hours, 7 hours, 8 hours, etc. The inert environment includes an inert gas environment, such as argon, helium, etc.

[0051] Example 1

[0052] This embodiment exemplifies a method for preparing an endodontic file having a surface protective titanium nitride layer, comprising the following steps:

[0053] 1. Preparation of nickel-titanium shape memory alloy

[0054] The smelting process was performed in a CaO crucible with high-temperature stability. By ensuring that Ti is not oxidized, which would cause Ti to form oxides and thus change the composition ratio, the Ni and Ti compositions were accurately maintained, resulting in a shape memory alloy with a stable NiTi phase transition temperature. The molar ratio of titanium to nickel was 52:48.

[0055] Under inert gas protection and vacuum degree guaranteed to be 10 -2 In a support environment, the initial temperature is first raised to 1200℃, and then high-temperature refining is performed for 5 minutes. After standing for 5 minutes, the temperature is lowered to 800℃ for casting. After the nickel-titanium shape memory alloy is obtained by casting, it is further processed to obtain the required wire material, and the cumulative processing amount is 30%.

[0056] 2. Preparation of surface protective titanium nitride layer

[0057] The nickel-titanium shape memory alloy wire obtained in step 1 is passed through a root canal file processing grinder to grind out a root canal file base of the required specifications. The processed root canal file base is heat-treated to obtain a root canal file with a surface protective coating. The heat treatment includes: in a mixed environment of nitrogen and argon with a gas pressure of 0.05 MPa, keeping the temperature at 550°C for 1 hour. After cooling, in an argon environment with a gas pressure of 0.05 MPa, keeping the temperature at 500°C for 1 hour, and furnace cooling for more than 4 hours to prepare the coating.

[0058] Example 2

[0059] This embodiment exemplifies a method for preparing an endodontic file having a surface protective titanium nitride layer, comprising the following steps:

[0060] 1. Preparation of nickel-titanium shape memory alloy

[0061] The smelting process was performed in a CaO crucible with high-temperature stability. By ensuring that Ti is not oxidized, which would cause Ti to form oxides and thus change the composition ratio, the Ni and Ti compositions were accurately maintained, resulting in a shape memory alloy with a stable NiTi phase transition temperature. The molar ratio of titanium to nickel was 52:48.

[0062] Under inert gas protection and vacuum degree guaranteed to be 10 -2 In a support environment, the initial temperature is first raised to 1200℃, and then high-temperature refining is performed for 5 minutes. After standing for 5 minutes, the temperature is lowered to 800℃ for casting. After the nickel-titanium shape memory alloy is obtained by casting, it is further processed to obtain the required wire material, and the cumulative processing amount is 30%.

[0063] 2. Preparation of surface protective titanium nitride layer

[0064] The nickel-titanium shape memory alloy wire obtained in step 1 is passed through a root canal file processing grinder to grind out a root canal file base of the required specifications. The processed root canal file base is heat-treated to obtain a root canal file with a surface protective coating. The heat treatment includes: in a mixed environment of nitrogen and argon with a gas pressure of 0.05 MPa, keeping the temperature at 550°C for 1 hour. After cooling, in an argon environment with a gas pressure of 0.05 MPa, keeping the temperature at 500°C for 1 hour, and furnace cooling for more than 4 hours to prepare the coating.

[0065] 3. Strengthening treatment

[0066] The resulting root canal file was stretched to 5% at room temperature and then unloaded, and this operation was repeated 10 times. Next, the file was heat-treated in an inert gas atmosphere at 400°C for 8 hours.

[0067] Example 3

[0068] This embodiment is a method for preparing a root canal file that is first strengthened and then nitrided, comprising the following steps:

[0069] 1. Preparation of nickel-titanium shape memory alloy:

[0070] The smelting process was performed in a CaO crucible with high-temperature stability. By ensuring that Ti is not oxidized, which would cause Ti to form oxides and thus change the composition ratio, the Ni and Ti compositions were accurately maintained, resulting in a shape memory alloy with a stable NiTi phase transition temperature. The molar ratio of titanium to nickel was 52:48.

[0071] Use inert gas protection and vacuum degree guaranteed to be 10 -2In a support environment, the initial temperature is first raised to 1200°C, high-temperature refining is performed for 5 minutes, and then the temperature is lowered to 800°C for casting. After the nickel-titanium memory alloy is cast, it is processed to obtain the required wire material, and the cumulative processing amount is 30%.

[0072] 2. Strengthening treatment

[0073] The obtained wire was stretched to 5% at room temperature and then unloaded, and this operation was repeated 8 times. Next, it was heat-treated in an inert gas atmosphere at 400°C for 8 hours.

[0074] 3. Preparation of surface protective titanium nitride layer

[0075] The nickel-titanium shape memory alloy wire obtained in step 2 is passed through a root canal file processing grinder to grind out a root canal file base of the required specifications. The processed root canal file base is heat-treated to obtain a root canal file with a surface protective coating. The heat treatment includes: in a mixed environment of nitrogen and argon with a gas pressure of 0.05 MPa, the temperature is kept at 550°C for 1 hour. After cooling, the coating is prepared by furnace cooling for more than 4 hours in an argon environment with a gas pressure of 0.05 MPa, the temperature is kept at 500°C for 1 hour.

[0076] Comparative Example 1

[0077] This comparative example is a method for preparing a root canal file without argon high-temperature treatment and strengthening treatment, comprising the following steps:

[0078] 1. Preparation of nickel-titanium shape memory alloy

[0079] The smelting process was performed in a CaO crucible with high-temperature stability. By ensuring that Ti is not oxidized, which would cause Ti to form oxides and thus change the composition ratio, the Ni and Ti compositions were accurately maintained, resulting in a shape memory alloy with a stable NiTi phase transition temperature. The molar ratio of titanium to nickel was 52:48.

[0080] Under inert gas protection and vacuum degree guaranteed to be 10 -2 In a support environment, the initial temperature is first raised to 1200℃, and then high-temperature refining is performed for 5 minutes. After standing for 5 minutes, the temperature is lowered to 800℃ for casting. After the nickel-titanium shape memory alloy is obtained by casting, it is further processed to obtain the required wire material, and the cumulative processing amount is 30%.

[0081] 2. Preparation of surface protective titanium nitride layer

[0082] The nickel-titanium shape memory alloy wire obtained in step 1 is passed through a root canal file processing grinder to produce a root canal file base of the desired specifications. The processed root canal file base is heat treated to produce a root canal file with a surface protective coating. The heat treatment comprises maintaining a temperature of 550°C for 1 hour in a mixture of nitrogen and argon at a pressure of 0.05 MPa. The coating is then produced after cooling.

[0083] Comparative Example 2

[0084] This comparative example is a method for preparing a root canal file without argon high-temperature treatment, comprising the following steps:

[0085] 1. Select a CaO crucible with high-temperature stability for smelting. By ensuring that Ti is not oxidized to prevent Ti from forming oxides and causing changes in the composition ratio, the Ni and Ti compositions are accurate, and a shape memory alloy with a stable NiTi phase transition temperature is obtained. The molar ratio of titanium metal to nickel metal is 52:48.

[0086] Under inert gas protection and vacuum degree guaranteed to be 10 -2 In a support environment, the initial temperature is first raised to 1200℃, and then high-temperature refining is performed for 5 minutes. After standing for 5 minutes, the temperature is lowered to 800℃ for casting. After the nickel-titanium shape memory alloy is obtained by casting, it is further processed to obtain the required wire material, and the cumulative processing amount is 30%.

[0087] 2. Preparation of surface protective titanium nitride layer

[0088] The nickel-titanium shape memory alloy wire obtained in step 1 is passed through a root canal file processing grinder to produce a root canal file base of the desired specifications. The processed root canal file base is heat treated to produce a root canal file with a surface protective coating. The heat treatment comprises maintaining a temperature of 550°C for 1 hour in a mixture of nitrogen and argon at a pressure of 0.05 MPa. The coating is then produced after cooling.

[0089] 3. Strengthening treatment

[0090] The resulting root canal file was stretched to 5% at room temperature and then unloaded, and this operation was repeated 10 times. Next, the file was heat-treated in an inert gas atmosphere at 400°C for 8 hours.

[0091] Comparative Example 3

[0092] This comparative example is a method for preparing an unreinforced root canal file, comprising the following steps:

[0093] 1. Preparation of nickel-titanium shape memory alloy

[0094] The smelting process was performed in a high-temperature stable CaO crucible. By ensuring that Ti is not oxidized and thus forming oxides that would alter the composition ratio, the Ni and Ti compositions were accurately maintained, resulting in a shape memory alloy with a stable NiTi phase transition temperature. The molar ratio of titanium to nickel was 58:42.

[0095] Under inert gas protection and vacuum degree guaranteed to be 10 -2 In a support environment, the initial temperature is first raised to 1200℃, and then high-temperature refining is performed for 5 minutes. After standing for 5 minutes, the temperature is lowered to 800℃ for casting. After the nickel-titanium shape memory alloy is obtained by casting, it is further processed to obtain the required wire material, and the cumulative processing amount is 30%.

[0096] 2. Preparation of surface protective titanium nitride layer

[0097] The nickel-titanium shape memory alloy wire obtained in step 1 is passed through a root canal file processing grinder to grind out a root canal file base of the required specifications. The processed root canal file base is heat-treated to obtain a root canal file with a surface protective coating. The heat treatment includes: in a mixed environment of nitrogen and argon with a gas pressure of 0.05 MPa, keeping the temperature at 550°C for 1 hour. After cooling, in an argon environment with a gas pressure of 0.05 MPa, keeping the temperature at 500°C for 1 hour, and furnace cooling for more than 4 hours to prepare the coating.

[0098] 3. Strengthening treatment

[0099] The obtained root canal files were tensile deformed to 5% at room temperature and then unloaded, and this operation was repeated 10 times.

[0100] Test Case

[0101] The amount of Ni ions dissolved in the leaching solution after each group of specimens were immersed for different periods of time. After immersion for 1 and 10 days, the amount of Ni ions dissolved in each Example and Comparative Example group was significantly reduced compared to the control group (NiTi group) without a titanium nitride layer. Specifically, the amount of Ni ions dissolved in each Example group was further reduced compared to the Comparative Example group, and the difference was statistically significant (all P < 0.05).

[0102] Table 1 - Test results of specimens Note: The fatigue test condition is 90 degrees fatigue 1500 times.

[0103] Although the present invention has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments. Various modifications and variations may be made to the exemplary embodiments of the present specification without departing from the scope or spirit of the present invention. The scope of the claims is to be given the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. A root canal file with better safety, characterized in that: The invention comprises a root canal file base and a titanium nitride layer located on the surface of the root canal file base, wherein the titanium nitride layer is golden yellow in surface and is evenly and densely coated on the root canal file base.

2. The root canal file with better safety according to claim 1, characterized in that: The titanium nitride layer of the root canal file is good and has no cracks under the fatigue test condition of 90 degrees fatigue 1500 times.

3. The root canal file with better safety according to claim 2, characterized in that: The presence of the titanium nitride layer makes the nickel ion dissolution amount of the root canal file lower than 0.025 μg / L in 10 days.

4. The root canal file with better safety according to claim 3, characterized in that: The molar ratio of titanium metal to nickel metal in the root canal file matrix is ​​50:50 to 55:

45.

5. The root canal file with better safety according to claim 4, characterized in that: The titanium nitride layer is formed on the surface of the substrate by vacuum isothermal nitriding technology.

6. The root canal file with better safety according to claim 5, characterized in that: It is prepared by the following steps: a. Smelting titanium metal and nickel metal under non-oxidizing conditions, then heating them to 1200-1400°C for refining under inert gas protection or vacuum environment, and then cooling them to 600-1000°C for casting to obtain nickel-titanium memory alloy, and processing them to obtain wire; b. The wire is processed by a root canal file, and the root canal file substrate of the required specifications is ground, and kept in a nitrogen mixed gas environment with a gas pressure of 0.005 to 0.1Mpa and a temperature of 550-600°C for 0.5-5 hours. After cooling, it is kept in an argon environment at 500-550°C for 0.5-5 hours, and then furnace cooled.

7. The root canal file with better safety according to claim 6, characterized in that: The nitrogen-containing mixed gas includes nitrogen and argon.

8. The root canal file with better safety according to claim 7, characterized in that: The volume ratio of the nitrogen gas to the argon gas is 0.8:1 to 1:0.

8.

9. The root canal file with better safety according to claim 8, characterized in that: The cumulative amount of wire material processing is controlled to be 17-60%.

10. The method for preparing a root canal file with better safety according to any one of claims 1 to 9.

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