Nickel-titanium alloy archwire with high elasticity and precise root control and preparation method thereof

Abstract

The application belongs to the technical field of archwire correction, and provides a nickel-titanium alloy archwire with high elasticity and precise root control and a preparation method thereof. The nickel-titanium alloy archwire with high elasticity and precise root control comprises an archwire body, the archwire body comprises a nickel-titanium alloy base body, Nb and Zr, and the molar ratio of Ni to Ti in the nickel-titanium alloy base body is 50.8:49.251.2:48.8. The application also provides a preparation method of the nickel-titanium alloy archwire with high elasticity and precise root control. The application solves the core problems that the elasticity and strength of the traditional nickel-titanium alloy archwire are difficult to be considered together and the root control precision is insufficient in orthodontic treatment. The elasticity recovery rate of the archwire is greater than or equal to 98%, the yield strength is increased to 850 MPa-950 MPa, and the archwire has differential surface roughness, which can meet the high elasticity demand in the initial alignment stage of teeth and realize the precise control of the tooth root position in the fine adjustment stage, is suitable for the whole period treatment of oral orthodontics, and has extremely high clinical application value.

Description

Technical Field

[0001] This invention relates to the field of orthodontic archwire technology, and in particular to a nickel-titanium alloy orthodontic archwire that combines high elasticity and precise root control, and its preparation method. Background Technology

[0002] Nickel-titanium alloys have become the core archwire material in orthodontic treatment due to their unique shape memory effect and superelasticity. Their superelasticity can provide continuous and gentle orthodontic force in the early stages of tooth alignment, avoiding damage to periodontal tissues. This is an advantage that traditional materials such as stainless steel and cobalt-chromium alloys cannot replace.

[0003] However, existing nickel-titanium alloy orthodontic archwires have two major technical challenges:

[0004] (1) It is difficult to balance elasticity and strength: In order to pursue high elasticity, most commercial nickel-titanium archwires use low-strength formulas with yield strength ≤700MPa. In the later stage of tooth alignment, the insufficient strength cannot provide enough root control force, resulting in difficulty in accurately controlling the position of the tooth root (such as tooth tilting and increased risk of tooth root resorption). If the strength is increased by increasing the nickel content, the elastic recovery rate of the archwire will decrease, which will not meet the large deformation-full recovery requirements of the initial alignment stage.

[0005] (2) Insufficient root control precision: During orthodontic treatment, low friction is beneficial for tooth sliding and alignment in the initial alignment stage; however, in the fine adjustment stage, it is necessary to appropriately increase the friction to stabilize the archwire position and achieve precise traction of the tooth roots. Traditional nickel-titanium archwires have a uniform surface roughness, generally Ra0.3-0.5μm, and the friction between the archwire and bracket is constant. Existing technologies mostly adopt a phased archwire replacement solution, such as using low-strength nickel-titanium archwires in the initial stage and high-strength stainless steel archwires in the fine stage. This approach not only increases the number of visits and treatment costs for patients, but may also cause sudden changes in orthodontic force due to differences in the mechanical properties of different materials, leading to periodontal discomfort. There are problems of low root control efficiency and prolonged treatment cycle.

[0006] Therefore, developing a nickel-titanium alloy archwire that can cover the entire orthodontic cycle while meeting the requirements of high elasticity and precise root control has become an urgent problem to be solved in the industry. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a nickel-titanium alloy orthodontic archwire that combines high elasticity and precise root control, as well as its preparation method.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution: a nickel-titanium alloy orthodontic archwire that combines high elasticity and precise root control, comprising an archwire body, wherein the archwire body comprises a nickel-titanium alloy matrix, Nb, and Zr, and the molar ratio of Ni to Ti in the nickel-titanium alloy matrix is ​​50.8:49.2. 51.2:48.8;

[0009] The Nb doping amount is 1.2% of the mass of the nickel-titanium alloy matrix. The Zr doping level is 1.8%, which is 0.5% of the mass of the nickel-titanium alloy matrix. 0.9%;

[0010] The archwire body has a circular cross-section, and its outer circumferential surface has different surface roughness Ra along the axial direction of the archwire body. The surface on the side that contacts the bottom surface of the orthodontic bracket groove has a high roughness Ra of 0.8 μm. The outer peripheral surface has a roughness of 1.2 μm, while the remaining portion has a low surface roughness Ra of 0.1 μm. 0.3μm.

[0011] Furthermore, the nickel-titanium alloy matrix is ​​also doped with Ta, and the Ta doping amount is 0.1% of the mass of the nickel-titanium alloy matrix. 0.3%.

[0012] Furthermore, the diameter of the archwire body is 0.45 mm. 0.65mm.

[0013] Furthermore, the surface on the side contacting the bottom of the orthodontic bracket groove occupies 20% of the overall axial outer circumference of the archwire body. 40%.

[0014] This invention also provides a method for preparing a nickel-titanium alloy orthodontic archwire that combines high elasticity and precise root control, specifically including the following steps:

[0015] Step 1, Alloy Melting:

[0016] According to actual needs, metal raw materials with a purity ≥ 99.95% are mixed in the above proportions and placed in a vacuum electric arc melting furnace for 3... The process involves four repeated melting processes, each lasting 8 minutes. After 12 minutes, a uniform alloy ingot was obtained.

[0017] Step 2, Hot Extrusion Molding:

[0018] Heat the alloy ingot obtained in step one to 800℃. 850℃, keep warm for 2 hours After 3 hours, hot extrusion was performed to obtain a diameter of 5mm. 8mm alloy rod;

[0019] Step 3, multiple pull-out cycles:

[0020] The alloy bar obtained in step two was subjected to multiple drawing passes at room temperature, with the deformation amount controlled at 8% per pass. 12%, followed by low-temperature annealing after each drawing until a diameter of 0.45 mm is obtained. Initial bowwire blank of 0.65mm;

[0021] Step 4, gradient heat treatment:

[0022] The initial bowwire blank obtained in step three is placed in a tubular heat treatment furnace for gradient heating treatment; finally, it is cooled to room temperature with the furnace to achieve a balance between bowwire elasticity and strength, thus obtaining the bowwire body.

[0023] Step 5, localized mechanical grinding:

[0024] The archwire body obtained in step four is subjected to axial mechanical grinding on the surface of its contact side with the bottom surface of the orthodontic bracket groove, so that the surface roughness Ra of this side reaches 0.8 μm. 1.2μm; the remaining outer surfaces of the archwire body maintain the surface condition after gradient heat treatment, with a roughness Ra of 0.1μm. The final nickel-titanium alloy orthodontic archwire product was obtained by reducing the thickness to 0.3μm.

[0025] Furthermore, the melting conditions of the vacuum arc melting furnace in step one are: vacuum degree ≤ 5 × 10⁻⁶. -3 Pa, melting current 200A 250A.

[0026] Furthermore, the hot extrusion rate in step two is 5 mm / s. 8mm / s.

[0027] Furthermore, the number of pull-out cycles in step three is 7. Nine times, low-temperature annealing conditions at 300℃ 350℃, keep warm for 30 minutes 45 minutes.

[0028] Furthermore, the gradient heating process in step four is as follows: first, the temperature is increased to 400℃ at a rate of 5℃ / min. 420℃, keep warm for 1.5 hours 2 hours; then increase the temperature to 520℃ at a rate of 3℃ / min. 550℃, keep warm for 40 minutes 60 minutes.

[0029] Furthermore, in step five, a 2000-mesh diamond grinding wheel is used during the mechanical grinding process, with a pressure of 0.1 MPa. 0.2 MPa, grinding time 10 s 15s.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. In the nickel-titanium alloy matrix of the nickel-titanium alloy orthodontic archwire of the present invention, which combines high elasticity and precise root control, the molar ratio of Ni to Ti is 50.8:49.2 The ratio is 51.2:48.8, and Nb is added to the nickel-titanium alloy matrix. Nb, as a β-stabilizing element, can be incorporated into the nickel-titanium alloy lattice, increasing the alloy's yield strength to 850 MPa. The yield strength of traditional nickel-titanium alloy archwires is typically ≤700MPa, while the yield strength of this invention's nickel-titanium alloy orthodontic archwire is 950MPa. This invention's archwire exhibits stable superelasticity in the oral environment, rapidly returning to its original shape after deformation, and maintains a yield strength of 950MPa. With an elastic recovery rate of ≥98% under a deformation of 5mm (traditional archwire ≤92%), it achieves a synergy of high elasticity and high strength, covering the entire orthodontic treatment cycle from initial alignment to fine adjustment, eliminating the need to change archwires midway, simplifying the treatment process and reducing the number of patient visits.

[0032] Meanwhile, this invention incorporates Zr doping into the nickel-titanium alloy matrix. Zr has an atomic radius close to that of Ti, allowing it to replace some Ti atoms in the crystal lattice, thus improving the alloy's plasticity and toughness and preventing the archwire from cracking during drawing and bending. Furthermore, Zr can form a ZrO2-TiO composite passivation film on the alloy surface, thereby optimizing the surface passivation film, improving the archwire's corrosion resistance and Ni ion dissolution, and maintaining good performance in the acidic environment of oral saliva.

[0033] 2. The nickel-titanium alloy matrix of the present invention may also selectively contain Ta. The addition of Ta can further enhance the density of the surface passivation film, control the corrosion rate of the archwire to below 0.005 mm / year, reduce the risk of metal ion leaching caused by corrosion, improve biosafety, and avoid problems such as oral allergies and inflammation caused by metal ion leaching.

[0034] 3. This invention utilizes a differentiated archwire surface roughness design to create a frictional difference between the outer surface of the archwire and the inner wall of the orthodontic bracket groove. This achieves "low friction for alignment and high friction for root control with directional force," eliminating the need to replace the archwire throughout the orthodontic treatment. This effectively shortens the orthodontic treatment cycle, reducing patient treatment costs and discomfort. It also significantly improves root control accuracy, with a control error ≤0.5mm, far lower than traditional archwire control errors, effectively reducing the risks of root resorption and tooth tilting, and enhancing orthodontic treatment outcomes.

[0035] During the tooth alignment stage, the surface on the non-contact side of the orthodontic bracket groove has low roughness (roughness Ra = 0.1 μm). With a thickness of 0.3μm and a coefficient of friction of 0.11~0.15, the crown can slide smoothly along the labial and buccal surfaces of the archwire with low resistance, without additional frictional resistance consuming the archwire's elasticity. At the same time, the low friction on this side ensures that there is no extra reverse torque on the labial and buccal sides, preventing crown displacement and ensuring the orthodontic sequence of crown repositioning first and root orientation second, laying the foundation for subsequent precise root control.

[0036] In the later stage of tooth alignment – ​​the initial stage of fine adjustment: After the crowns are aligned, the tooth roots are often tilted. At this time, due to the need for the archwire to fit the shape of the dental arch, a slight bending elastic rebound force will be generated in the bracket groove. Because the side of the archwire with high roughness is locked with the bottom surface of the groove with high friction, the archwire cannot slide on the bottom surface of the bracket groove. This rebound force will be transmitted through the bracket as a rotation torque around the long axis of the tooth.

[0037] Fine-tuning throughout: After the tooth root is aligned, the archwire and dental arch are fully engaged, and the high-roughness locking creates a continuous static friction constraint. When the tooth has a slight tendency to shift, the bottom surface of the bracket groove will obtain a reverse constraint force from the archwire through high friction, directly limiting the non-preset movement of the tooth root. Combined with the archwire's yield strength of 850~950MPa, the tooth root will always be fixed in the preset position in the dental arch bone groove, achieving precise root positioning. The torque generated by high friction is gentle and continuous, and will not cause tooth root resorption due to sudden changes in force.

[0038] 4. The preparation method of this invention employs a composite process of gradient heat treatment and local mechanical grinding. This invention uses a low-temperature, long-time (400℃) process. 420℃, keep warm for 1.5 hours 2h) and high temperature short time (520℃) 550℃, keep warm for 40 minutes The process employs a gradient heat treatment method (60 min). The low-temperature, long-time treatment eliminates internal stress during drawing, homogenizes the martensitic structure, and ensures superelasticity. The high-temperature, short-time treatment refines the grains, improves the archwire strength, and achieves a balance between archwire elasticity and strength. Low-temperature annealing after each drawing pass eliminates internal stress generated during drawing, preventing cracking or uneven deformation of the archwire during subsequent processing.

[0039] Simultaneously, this invention performs localized directional grinding on the archwire body using a 2000-grit diamond grinding wheel. The fine grinding particle size avoids damage to the archwire surface. By rationally controlling the grinding pressure and time, the surface roughness Ra of the side in contact with the bottom of the orthodontic bracket groove reaches 0.8 μm. 1.2μm, while not compromising the smoothness of the surface on the non-contact side of the orthodontic bracket groove and the overall mechanical properties of the archwire.

[0040] In summary, the nickel-titanium alloy orthodontic archwire of this invention uses nickel-titanium alloy as the matrix. By optimizing the molar ratio of nickel and titanium and modifying the composition by doping with specific amounts of Nb and Zr, and combining this with a composite preparation process of gradient heat treatment and localized mechanical grinding, the core problems of traditional nickel-titanium alloy archwires in orthodontic treatment—namely, the difficulty in balancing elasticity and strength and insufficient root control precision—are solved. This archwire achieves a 0 With a deformation of 5mm, the elastic recovery rate is ≥98%, and the yield strength is increased to 850MPa. With a strength of 950MPa and a differential surface roughness, the archwire can meet the high elasticity requirements of the initial tooth alignment stage and achieve precise control of the root position during the fine adjustment stage. It is suitable for the entire cycle of orthodontic treatment and has extremely high clinical application value. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the differentiated surface roughness Ra of the outer peripheral surface of the nickel-titanium alloy orthodontic archwire of the present invention, which combines high elasticity and precise root control.

[0042] Figure 2 This is a schematic diagram of the nickel-titanium alloy orthodontic archwire product of Embodiment 1 of the present invention applied to the teeth of an orthodontic patient.

[0043] Figure 3 This is a schematic diagram of the nickel-titanium alloy orthodontic archwire product of Embodiment 2 of the present invention applied to the teeth of orthodontic patients with poor periodontal conditions, and X-ray images before and after treatment.

[0044] Figure 4 This is a schematic diagram of the nickel-titanium alloy orthodontic archwire product of Embodiment 5 of the present invention applied to the teeth of patients in the mixed dentition period.

[0045] Figure 5 This is a schematic diagram of the nickel-titanium alloy orthodontic archwire product of Comparative Example 1 of the present invention applied to the teeth of an orthodontic patient. Detailed Implementation

[0046] The following specific embodiments further illustrate the detailed content and specific implementation of the present invention. In this embodiment, the Ni, Ti, Nb, Zr, and Ta raw materials used in the highly elastic and precisely controlled nickel-titanium alloy orthodontic archwire are all commercially available elemental metals with a purity ≥99.95%.

[0047] Example 1:

[0048] A nickel-titanium alloy orthodontic archwire that combines high elasticity and precise root control includes an archwire body, wherein the archwire body comprises a nickel-titanium alloy matrix, Nb and Zr, and the molar ratio of Ni to Ti is 51.0:49.0.

[0049] The Nb doping amount is 1.5% of the mass of the nickel-titanium alloy matrix, and the Zr doping amount is 0.7% of the mass of the nickel-titanium alloy matrix;

[0050] Reference Figure 1 As shown, the cross-section of the archwire body is circular, and along the axial direction of the archwire body, its outer peripheral surface has different surface roughness Ra. The surface roughness Ra of the side in contact with the bottom surface of the orthodontic bracket groove is 1.0 μm (friction coefficient is 0.35), and the surface roughness Ra of the remaining outer peripheral surface is 0.2 μm (friction coefficient is 0.13).

[0051] The surface that contacts the bottom of the orthodontic bracket groove accounts for 20% of the overall axial outer circumference of the archwire body.

[0052] In this embodiment, the diameter of the bowwire body is 0.55 mm.

[0053] The preparation method of the nickel-titanium alloy orthodontic archwire with high elasticity and precise root control in Example 1 specifically includes the following steps:

[0054] Step 1, Alloy Melting:

[0055] Ni, Ti, Nb, and Zr metal raw materials with a purity ≥ 99.95% were mixed according to the above proportions and placed in a vacuum arc melting furnace. The melting conditions of the vacuum arc melting furnace were: a vacuum degree of 3 × 10⁻⁶. -3 Under the conditions of Pa and melting current of 220A, the alloy ingot was repeatedly melted three times, with each melting time lasting 10 minutes, to obtain a uniform alloy ingot.

[0056] Step 2, Hot Extrusion Molding:

[0057] The alloy ingot obtained in step one was heated to 820℃ and held for 2.5 hours, and then hot extruded at a rate of 6.5 mm / s to obtain an alloy bar with a diameter of 6 mm.

[0058] Step 3, multiple pull-out cycles:

[0059] The alloy rods obtained in step two were drawn in 8 passes at room temperature, with the deformation amount controlled at 10% per pass. After each drawing, they were annealed at low temperature. The annealing conditions were 320℃ and 40min, until an initial bow wire blank with a diameter of 0.55mm was obtained.

[0060] Step 4, gradient heat treatment:

[0061] The initial archwire blank obtained in step three is placed in a tubular heat treatment furnace and subjected to gradient heating treatment. The gradient heating treatment process is as follows: first, the temperature is increased to 410℃ at a rate of 5℃ / min and held for 1.8h; then, the temperature is increased to 530℃ at a rate of 3℃ / min and held for 50min; finally, the temperature is cooled to room temperature with the furnace to achieve a balance between the elasticity and strength of the archwire and obtain the archwire body.

[0062] Step 5, localized mechanical grinding:

[0063] For the archwire body obtained in step four, mechanical grinding is performed axially on the surface of the side that contacts the bottom surface of the orthodontic bracket groove. During mechanical grinding, a 2000-mesh diamond grinding wheel is used, the pressure is 0.15MPa, and the grinding time is 12s, so that the surface roughness Ra of this side reaches 1.0μm and the coefficient of friction is 0.35. The remaining outer surfaces of the archwire body (the side that does not contact the bottom surface of the orthodontic bracket groove) maintain the surface state after gradient heat treatment, with a roughness Ra of 0.2μm and a coefficient of friction of 0.13, thus obtaining the final nickel-titanium alloy orthodontic archwire product.

[0064] The mechanical properties, corrosion resistance and surface properties of the product prepared in Example 1 were tested, and the test results are shown in Table 1.

[0065] The nickel-titanium alloy orthodontic archwire product in Example 1 is used in orthodontic patients with 3mm-5mm crowding during their first orthodontic visit. Figure 2 As shown, during the initial alignment stage (1-3 months), the tooth sliding rate can reach 0.8 mm / month, which is better than the traditional archwire's 0.6 mm / month; during the fine adjustment stage (4-6 months), the root positioning error is 0.4 mm, with no mucosal irritation or allergic reaction.

[0066] Example 2:

[0067] A nickel-titanium alloy orthodontic archwire that combines high elasticity and precise root control includes an archwire body, wherein the archwire body comprises a nickel-titanium alloy matrix, Nb and Zr, and the molar ratio of Ni to Ti in the nickel-titanium alloy matrix is ​​51.2:48.8.

[0068] The Nb doping amount is 1.8% of the mass of the nickel-titanium alloy matrix, and the Zr doping amount is 0.9% of the mass of the nickel-titanium alloy matrix;

[0069] The nickel-titanium alloy matrix is ​​also doped with Ta, and the amount of Ta doping is 0.2% of the mass of the nickel-titanium alloy matrix.

[0070] The cross-section of the archwire body is circular, and its outer circumferential surface has different surface roughness Ra along the axial direction of the archwire body. The surface roughness Ra of the side in contact with the bottom surface of the orthodontic bracket groove is 1.2 μm (friction coefficient 0.39), and the surface roughness Ra of the side not in contact with the bottom surface of the orthodontic bracket groove is 0.15 μm (friction coefficient 0.11).

[0071] The surface that contacts the bottom of the orthodontic bracket groove accounts for 40% of the overall axial outer circumference of the archwire body.

[0072] The diameter of the bowwire body is 0.65 mm.

[0073] The preparation method of the nickel-titanium alloy orthodontic archwire with high elasticity and precise root control in Example 2 specifically includes the following steps:

[0074] Step 1, Alloy Melting:

[0075] Metal raw materials with a purity ≥ 99.95% were mixed according to the above proportions and placed in a vacuum arc melting furnace. The melting conditions of the vacuum arc melting furnace were: a vacuum degree of 2 × 10⁻⁶. -3 Under the conditions of Pa and melting current of 200A, the alloy ingot was repeatedly melted 4 times, with each melting time lasting 12 minutes, to obtain a uniform alloy ingot.

[0076] Step 2, Hot Extrusion Molding:

[0077] The alloy ingot obtained in step one is heated to 850℃ and held for 3 hours, and then hot extruded at a rate of 8 mm / s to obtain an alloy bar with a diameter of 8 mm.

[0078] Step 3, multiple pull-out cycles:

[0079] The alloy rods obtained in step two were drawn in nine passes at room temperature, with the deformation amount controlled at 12% per pass. After drawing, they were annealed at low temperature at 350℃ for 45 minutes until an initial bow wire blank with a diameter of 0.65 mm was obtained.

[0080] Step 4, gradient heat treatment:

[0081] The initial bow wire blank obtained in step three is placed in a tubular heat treatment furnace for gradient heating treatment. The gradient heating treatment process is as follows: first, the temperature is increased to 420℃ at a rate of 5℃ / min and held for 2 hours; then, the temperature is increased to 550℃ at a rate of 3℃ / min and held for 60 minutes; finally, the temperature is cooled to room temperature with the furnace to achieve a balance between bow wire elasticity and strength.

[0082] Step 5, localized mechanical grinding:

[0083] For the archwire body obtained in step four, mechanical grinding is performed axially on the surface of the side that contacts the bottom surface of the orthodontic bracket groove. During mechanical grinding, a 2000-mesh diamond grinding wheel is used, the pressure is 0.2MPa, and the grinding time is 15s, so that the surface roughness Ra of this side reaches 1.2μm. The remaining outer surfaces of the archwire body (the side that does not contact the bottom surface of the orthodontic bracket groove) maintain the surface state after gradient heat treatment, with a roughness Ra of 0.15μm, thus obtaining the final nickel-titanium alloy orthodontic archwire product.

[0084] The mechanical properties, corrosion resistance and surface properties of the product prepared in Example 2 were tested, and the test results are shown in Table 1.

[0085] Example 3:

[0086] The difference from Example 2 is that the amount of Ta doping is 0.1% of the mass of the nickel-titanium alloy matrix.

[0087] Along the axial direction of the archwire body, its outer peripheral surface has different surface roughness Ra. The surface roughness Ra of the side in contact with the bottom surface of the orthodontic bracket groove is 1.1 μm (friction coefficient 0.37), and the surface roughness Ra of the side not in contact with the bottom surface of the orthodontic bracket groove is 0.10 μm (friction coefficient 0.12).

[0088] The preparation method is the same as that in Example 2.

[0089] The mechanical properties, corrosion resistance and surface properties of the product prepared in Example 3 were tested, and the test results are shown in Table 1.

[0090] Example 4:

[0091] The difference from Example 2 is that the amount of Ta doping is 0.3% of the mass of the nickel-titanium alloy matrix.

[0092] Along the axial direction of the archwire body, its outer peripheral surface has different surface roughness Ra. The surface roughness Ra of the side in contact with the bottom surface of the orthodontic bracket groove is 1.2 μm (friction coefficient 0.38), and the surface roughness Ra of the side not in contact with the bottom surface of the orthodontic bracket groove is 0.13 μm (friction coefficient 0.13).

[0093] The mechanical properties, corrosion resistance and surface properties of the product prepared in Example 4 were tested, and the test results are shown in Table 1.

[0094] The preparation method is the same as that in Example 2.

[0095] Examples 2, 3, and 4 all involve archwire products with added Ta, and their performance is similar. Therefore, taking Example 2 as an example, the nickel-titanium alloy orthodontic archwire product of Example 2 is applied to orthodontic patients with poor periodontal condition and a periodontal probing depth of 3-4 mm. Figure 3 As shown, there was no root resorption within 6 months of treatment (X-ray showed no change in root length), the gingival inflammation index (GI) was ≤1.0, and the biocompatibility was superior.

[0096] Example 5:

[0097] A nickel-titanium alloy orthodontic archwire that combines high elasticity and precise root control includes an archwire body, wherein the archwire body comprises a nickel-titanium alloy matrix, Nb and Zr, and the molar ratio of Ni to Ti in the nickel-titanium alloy matrix is ​​50.8:49.2.

[0098] The Nb doping amount is 1.2% of the mass of the nickel-titanium alloy matrix, and the Zr doping amount is 0.5% of the mass of the nickel-titanium alloy matrix;

[0099] The cross-section of the archwire body is circular, and along the axial direction of the archwire body, its outer circumferential surface has different surface roughness Ra. The surface roughness Ra of the side that contacts the bottom surface of the orthodontic bracket groove is 0.8 μm (friction coefficient 0.30), and the surface roughness Ra of the side that does not contact the bottom surface of the orthodontic bracket groove is 0.3 μm (friction coefficient 0.15).

[0100] The diameter of the bowwire body is 0.45 mm.

[0101] The surface that contacts the bottom of the orthodontic bracket groove occupies 30% of the overall axial outer circumference of the archwire body.

[0102] Example 5 describes a method for preparing a nickel-titanium alloy orthodontic archwire that combines high elasticity and precise root control, specifically including the following steps:

[0103] Step 1, Alloy Melting:

[0104] Metal raw materials with a purity ≥ 99.95% are mixed according to the above proportions and placed in a vacuum arc melting furnace. The melting conditions of the vacuum arc melting furnace are: a vacuum degree of 5 × 10⁻⁶. -3 Under the conditions of Pa and melting current of 250A, the alloy ingot was repeatedly melted three times, with each melting time lasting 8 minutes, to obtain a uniform alloy ingot.

[0105] Step 2, Hot Extrusion Molding:

[0106] The alloy ingot obtained in step one is heated to 800℃ and held for 2 hours, and then hot extruded at a rate of 5 mm / s to obtain an alloy bar with a diameter of 5 mm.

[0107] Step 3, multiple pull-out cycles:

[0108] The alloy rod obtained in step two was drawn in 7 passes at room temperature, with the deformation amount controlled at 8% in each pass. After drawing, it was annealed at low temperature. The annealing conditions were 300℃ and 30min, until an initial bow wire blank with a diameter of 0.45mm was obtained.

[0109] Step 4, gradient heat treatment:

[0110] The initial bow wire blank obtained in step three is placed in a tubular heat treatment furnace for gradient heating treatment. The gradient heating treatment process is as follows: first, the temperature is increased to 400℃ at a rate of 5℃ / min and held for 1.5h; then, the temperature is increased to 520℃ at a rate of 3℃ / min and held for 40min; finally, the temperature is cooled to room temperature with the furnace to achieve a balance between bow wire elasticity and strength.

[0111] Step 5, localized mechanical grinding:

[0112] For the archwire body obtained in step four, mechanical grinding is performed axially on the surface of the side that contacts the bottom surface of the orthodontic bracket groove. During mechanical grinding, a 2000-mesh diamond grinding wheel is used, the pressure is 0.1MPa, and the grinding time is 10s, so that the surface roughness Ra of this side reaches 0.8μm. The remaining outer surfaces of the archwire body (the side that does not contact the bottom surface of the orthodontic bracket groove) maintain the surface state after gradient heat treatment, with a roughness Ra of 0.3μm, thus obtaining the final nickel-titanium alloy orthodontic archwire.

[0113] The mechanical properties, corrosion resistance and surface properties of the product prepared in Example 5 were tested, and the test results are shown in Table 1.

[0114] The nickel-titanium alloy orthodontic archwire in Example 5 is an economical formula with low Nb content and no Ta, suitable for patients in the primary or mixed dentition stage. Applying the nickel-titanium alloy orthodontic archwire product of Example 5 to patients in the mixed dentition stage, such as... Figure 4 As shown, the archwire is flexible enough to meet the needs of adjusting the gaps between primary dentition teeth, and there is no archwire breakage or mucosal scratching; the production cost is reduced by 8% compared to Example 1, making it suitable for large-scale popularization.

[0115] Comparative Example 1:

[0116] Commercially available undoped nickel-titanium alloy bow wire with a Ni to Ti molar ratio of 50:50; free of Nb, Zr, and Ta doping; the bow wire has a circular cross-section with a diameter of 0.55 mm.

[0117] Preparation process of Comparative Example 1:

[0118] The difference from Example 1 is as follows:

[0119] After eight drawing passes, the wire was annealed at a single temperature (480℃ for 1 hour), and the entire surface of the bowwire was polished and ground without differentiation. The surface roughness Ra of the bowwire was 0.4 μm. Other processes were the same as in Example 1.

[0120] The mechanical properties, corrosion resistance and surface properties of the nickel-titanium alloy bowwire prepared in Comparative Example 1 were tested, and the test results are shown in Table 1.

[0121] When the nickel-titanium alloy archwire of Comparative Example 1 was applied to orthodontic patients with the same dentition crowding of 3mm-5mm as those in Example 1, the alignment period was prolonged (requiring 4 months to complete alignment), and root tilting occurred during the fine-tuning phase (error of 1.2mm), accompanied by mild Ni allergy (gingival redness and swelling). Figure 5 As shown.

[0122] Comparative Example 2:

[0123] The raw materials and proportions of the nickel-titanium alloy bow wire are the same as in Example 1;

[0124] Preparation process of Comparative Example 2:

[0125] The preparation method differs from that in Example 1 in that:

[0126] The heat treatment after multiple drawing passes adopts a single high-temperature treatment of 530℃ for 2 hours, without gradient heat treatment.

[0127] The mechanical properties (elastic recovery rate, yield strength, fracture strength), corrosion resistance (corrosion rate, Ni ion leaching amount) and surface properties of the bowwire prepared in Comparative Example 2 were tested, and the test results are shown in Table 1.

[0128] In Comparative Example 2, the archwire did not fully spring back after being bent, affecting the accuracy of the treatment.

[0129] In this invention, the mechanical properties are tested using a universal testing machine to examine the manufactured bowwire, obtaining the elastic recovery rate (0.5%). (under a deformation of 5mm), yield strength and fracture strength;

[0130] In the corrosion resistance test, the corrosion rate was tested using an electrochemical workstation Reference 600TM that simulates the oral saliva environment (pH 6.8, constant temperature 37℃); the Ni ion dissolution was detected in accordance with the sample preparation and reference sample standard of "Biological Evaluation of Medical Devices" (GB / T16886.12—2005).

[0131] In surface performance testing, roughness Ra is measured using a contact surface profilometer, and the coefficient of friction is determined using a coefficient of friction meter.

[0132] Table 1. Performance test results of the archwires prepared in Examples 1 to 5, Comparative Example 1, and Comparative Example 2:

[0133] .

[0134] The above test results show that:

[0135] (1) Composition doping significantly improves the mechanical properties and corrosion resistance of the archwire. By introducing Nb, Zr and Ta elements into the nickel-titanium alloy matrix, not only are the elastic recovery rate and yield strength of the archwire optimized, but the dissolution of Ni ions is also effectively reduced, thereby improving biosafety.

[0136] As can be seen from the comparison between Example 1 and Comparative Example 1, Example 1 of the present invention can significantly improve the elastic recovery rate and yield strength of the archwire by doping with Nb and Zr. The elastic recovery rate of Example 1 increased from 91.5% to 98.5%, and the yield strength increased from 680MPa to 900MPa. At the same time, the corrosion resistance was also significantly improved, with the corrosion rate decreasing from 0.016mm / year in Comparative Example 1 to 0.007mm / year, and the Ni ion dissolution amount decreasing to 0.03mg / L.

[0137] The archwire in Embodiment 2 of this invention is doped with Ta, and its fracture strength reaches 1320 MPa, which is 5.6% higher than that in Embodiment 1; the corrosion rate is 0.004 mm / year, which is 42.9% lower than that in Embodiment 1, making it more suitable for patients with periodontal sensitivity or acidic oral environment.

[0138] (2) The gradient heat treatment process of the present invention enables the archwire to maintain high strength while possessing excellent flexibility, which is crucial for clinical adaptability.

[0139] Compared with Comparative Example 1, the present invention, through gradient heat treatment, specifically low-temperature long-time and high-temperature short-time treatments, can improve strength while maintaining the elasticity of the archwire. In contrast, the single-temperature annealing treatment in Comparative Example 2 (480℃ for 1 hour) leads to excessive grain growth, disrupting the integrity of the martensitic structure and causing a double decrease in elasticity and strength: the elastic recovery rate is 93.2% (5.3% lower than in Example 1); the yield strength is 820 MPa (8.9% lower than in Example 1), and the archwire exhibits incomplete springback after bending, affecting the accuracy of orthodontic treatment.

[0140] (3) The differential design of the surface roughness of the archwire in this invention reduces the friction between the archwire and the bracket groove, promoting the sliding efficiency of the teeth in the initial alignment stage; while the high roughness enhances the friction in the root control stage, and the root control error is ≤0.5mm, which is much lower than the root control error of traditional archwires, ensuring the accuracy of tooth root positioning.

[0141] The archwires in Examples 1 to 5 of this invention undergo surface grinding treatment, resulting in a high surface roughness (Ra = 0.8-1.2 μm) on the side in contact with the bottom surface of the orthodontic bracket slot, and a low surface roughness (Ra = 0.1 μm-0.3 μm) on the side not in contact with the bottom surface of the orthodontic bracket slot. This avoids irritation to the labial and buccal mucosa and ensures that the root control error (tooth root positioning error) is ≤0.4 mm, far superior to the 1.2 mm of Comparative Example 1. During orthodontic treatment, there is no need to replace the nickel-titanium alloy archwire with a stainless steel archwire, allowing for the use of the same archwire throughout the entire treatment cycle.

[0142] (4) The archwire of Embodiment 5 of the present invention is doped with Nb and Zr on the basis of nickel-titanium alloy matrix, and the doping amount of Nb is 1.2%. This content reduces the cost while ensuring the basic performance of the archwire, and is suitable for price-sensitive scenarios such as children's primary dentition or mixed dentition.

[0143] The archwires of Embodiments 2, 3, and 4 of this invention are doped with Nb, Zr, and Ta on a nickel-titanium alloy matrix, wherein the Nb doping amount is 1.8%, and Ta is also doped. This type of archwire is suitable for patients with periodontal disease and patients with allergies, demonstrating the flexibility of the archwire of this invention.

[0144] In summary, the nickel-titanium alloy orthodontic archwire of this invention, which combines high elasticity and precise root control, has achieved comprehensive improvements in mechanical properties, corrosion resistance, and clinical adaptability through component optimization, process improvement, and differentiated surface roughness design, making it promising for broad applications in orthodontic treatment.

[0145] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A nickel-titanium alloy orthodontic archwire that combines high elasticity and precise root control, characterized in that: The device includes a bowwire body, which is composed of a nickel-titanium alloy matrix, Nb, and Zr, wherein the molar ratio of Ni to Ti in the nickel-titanium alloy matrix is ​​50.8:49.2 to 51.2:48.

8. The Nb doping amount is 1.2% to 1.8% of the mass of the nickel-titanium alloy matrix, and the Zr doping amount is 0.5% to 0.9% of the mass of the nickel-titanium alloy matrix. The cross-section of the archwire body is circular, and along the axial direction of the archwire body, its outer peripheral surface has different surface roughness Ra. The surface that contacts the bottom surface of the orthodontic bracket groove has high roughness Ra, with a roughness Ra of 0.8 μm to 1.2 μm, while the surface of the remaining outer peripheral surface has low roughness Ra, with a roughness Ra of 0.1 μm to 0.3 μm. The method for preparing the nickel-titanium alloy orthodontic archwire, which combines high elasticity and precise root control, specifically includes the following steps: Step 1, Alloy Melting: According to actual needs, metal raw materials with a purity of ≥99.95% are mixed in the above proportions and placed in a vacuum arc melting furnace for repeated melting 3 to 4 times, with each melting time being 8 to 12 minutes, to obtain alloy ingots with uniform composition. Step 2, hot extrusion molding: The alloy ingot obtained in step one is heated to 800℃~850℃ and held for 2h~3h, and then hot extruded to obtain alloy rods with a diameter of 5mm~8mm. Step 3, multiple pull-out cycles: The alloy rods obtained in step two are drawn in multiple passes at room temperature, with the deformation amount controlled at 8% to 12% per pass. After each drawing, they are annealed at low temperature until an initial bow wire blank with a diameter of 0.45 mm to 0.65 mm is obtained. Step 4, gradient heat treatment: The initial bowwire blank obtained in step three is placed in a tubular heat treatment furnace for gradient heating treatment; finally, it is cooled to room temperature with the furnace to achieve a balance between bowwire elasticity and strength, thus obtaining the bowwire body. The gradient heating process is as follows: first, the temperature is increased to 400℃~420℃ at a rate of 5℃ / min and held for 1.5h~2h; then, the temperature is increased to 520℃~550℃ at a rate of 3℃ / min and held for 40min~60min. Step 5, localized mechanical grinding: For the archwire body obtained in step four, mechanical grinding is performed axially on the surface of the side that contacts the bottom surface of the orthodontic bracket groove, so that the surface roughness Ra of this side reaches 0.8μm to 1.2μm; the remaining outer surfaces of the archwire body maintain the surface state after gradient heat treatment, with a roughness Ra of 0.1μm to 0.3μm, thus obtaining the final nickel-titanium alloy orthodontic archwire product.

2. The nickel-titanium alloy orthodontic archwire with high elasticity and precise root control as described in claim 1, characterized in that, The nickel-titanium alloy matrix is ​​also doped with Ta, and the amount of Ta doping is 0.1% to 0.3% of the mass of the nickel-titanium alloy matrix.

3. The nickel-titanium alloy orthodontic archwire with high elasticity and precise root control as described in claim 1, characterized in that, The diameter of the bowwire body is 0.45mm to 0.65mm.

4. The nickel-titanium alloy orthodontic archwire with high elasticity and precise root control as described in claim 1, characterized in that, In the archwire body, the surface that contacts the bottom surface of the orthodontic bracket groove accounts for 20% to 40% of the overall axial outer circumference of the archwire body.

5. The method for preparing the nickel-titanium alloy orthodontic archwire with high elasticity and precise root control as described in any one of claims 1-4, characterized in that, Specifically, the following steps are included: Step 1, Alloy Melting: According to actual needs, metal raw materials with a purity of ≥99.95% are mixed in the above proportions and placed in a vacuum arc melting furnace for repeated melting 3 to 4 times, with each melting time being 8 to 12 minutes, to obtain alloy ingots with uniform composition. Step 2, hot extrusion molding: The alloy ingot obtained in step one is heated to 800℃~850℃ and held for 2h~3h, and then hot extruded to obtain alloy rods with a diameter of 5mm~8mm. Step 3, multiple pull-out cycles: The alloy rods obtained in step two are drawn in multiple passes at room temperature, with the deformation amount controlled at 8% to 12% per pass. After each drawing, they are annealed at low temperature until an initial bow wire blank with a diameter of 0.45 mm to 0.65 mm is obtained. Step 4, gradient heat treatment: The initial bowwire blank obtained in step three is placed in a tubular heat treatment furnace for gradient heating treatment; finally, it is cooled to room temperature with the furnace to achieve a balance between bowwire elasticity and strength, thus obtaining the bowwire body. The gradient heating process is as follows: first, the temperature is increased to 400℃~420℃ at a rate of 5℃ / min and held for 1.5h~2h; then, the temperature is increased to 520℃~550℃ at a rate of 3℃ / min and held for 40min~60min. Step 5, localized mechanical grinding: For the archwire body obtained in step four, mechanical grinding is performed axially on the surface of the side that contacts the bottom surface of the orthodontic bracket groove, so that the surface roughness Ra of this side reaches 0.8μm to 1.2μm; the remaining outer surfaces of the archwire body maintain the surface state after gradient heat treatment, with a roughness Ra of 0.1μm to 0.3μm, thus obtaining the final nickel-titanium alloy orthodontic archwire product.

6. The method for preparing the nickel-titanium alloy orthodontic archwire with high elasticity and precise root control as described in claim 5, characterized in that, The melting conditions in the vacuum arc melting furnace in step one are: vacuum degree ≤ 5 × 10⁻⁶. -3 Pa, melting current 200A~250A.

7. The method for preparing the nickel-titanium alloy orthodontic archwire with high elasticity and precise root control as described in claim 5, characterized in that, The hot extrusion rate in step two is 5 mm / s to 8 mm / s.

8. The method for preparing the nickel-titanium alloy orthodontic archwire with high elasticity and precise root control as described in claim 5, characterized in that, The number of pull-out cycles in step three is 7 to 9, and the low-temperature annealing conditions are 300℃ to 350℃ and 30 min to 45 min.

9. The method for preparing the nickel-titanium alloy orthodontic archwire with high elasticity and precise root control as described in claim 5, characterized in that, In step five, a 2000-mesh diamond grinding wheel is used for mechanical grinding, with a pressure of 0.1MPa to 0.2MPa and a grinding time of 10s to 15s.

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