Root canal instruments

Abstract

The present invention relates to a root canal instrument having a shank (2) and a working part (4) attached to the shank (2), wherein the working part (4) is made of a nickel-titanium alloy containing 38 to 46 at% nickel, 46 to 53 at% titanium, and 5.5 to 8.8 at% copper.

Description

[Technical field]

[0001] The present invention relates to a root canal instrument for treating a root canal of a tooth and a method for manufacturing the same. Furthermore, the use of a nickel-titanium alloy for manufacturing the root canal instrument is described. [Background technology]

[0002] Root canal instruments are known from the prior art, for example from US Pat. No. 5,399,633. To perform a proper root canal treatment, the root canal instruments are required to have a certain degree of flexibility to follow the curvature of the root canal. The root canal instruments have a core that starts from the working area of ​​the root canal instrument and expands continuously conically, i.e. a rigid core, towards the shank area of ​​the root canal instrument. Particularly molar teeth have a relatively complex root canal system, and the root canal instruments are required to follow even small radii of the root canal. For this purpose, the working area of ​​the root canal instrument must be more flexible. This has traditionally been achieved by further tapering the core of the root canal instrument, but this reduces the mechanical stability of the working area, which leads to the risk of part of the working area breaking off during the root canal treatment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] German Utility Model No. 202012012526 Summary of the Invention

[0004] Therefore, an object of the present invention is to provide a dental root canal instrument having a simple yet stable structure, being easy and inexpensive to manufacture, while having improved flexibility, and in particular being able to follow even large curvatures in the root canal of a tooth, and a method for manufacturing the same.

[0005] This object will be achieved by providing a root canal instrument, a method for its manufacture and its use having the features of the independent claims. Preferred further developments of the invention are set out in the dependent claims.

[0006] The dental root canal instrument according to the invention having the features of claim 1 has the advantage that the root canal instrument is characterized by a good flexibility. As a result, when treating a root canal, even in the case of a root canal in the molar region, which is difficult to access, the root canal instrument according to the invention can be used to follow the curvature of the root canal well, without the risk of the working area of ​​the root canal instrument breaking. This means that dead or infected pulp tissue can be completely removed from the root canal with high certainty. As a result, microorganisms present in the root canal can be removed as much as possible.

[0007] According to the invention, this is achieved by providing a root canal instrument comprising a shank and a working area attached to the shank, the working area being made of a nickel-titanium alloy comprising 38-46 at% nickel, 46-53 at% titanium and 5.5-8.8 at% copper. The shape of the root canal instrument according to the invention can be designed in a conventional manner, i.e. in particular tapered from a first end of the working area connected to the shank to a second exposed end of the working area. In this case, the working area serves as a cutting area for the root canal and in particular comprises a plurality of cutting edges arranged along a core. By using a nickel-titanium alloy as defined above, the working area is nevertheless formed from a very flexible material, characterized by a high mechanical stability, i.e. a high tensile stress in particular of at least 800 MPa, as well as a high flexibility or a large Young's modulus combined with a good elongation capacity, which effectively prevents breakages occurring during the use of the root canal instrument. Due to its physical and mechanical properties, the copper-containing nickel-titanium alloy is ideally suited to form a very flexible working area for the root canal instrument.

[0008] In order to improve the fatigue strength, the nickel-titanium alloy may preferably further contain 0.05 to 0.15 at % of chromium.

[0009] According to a most preferred further development, the nickel-titanium alloy essentially comprises 40.5-43.1 at% nickel, 48.7-50.8 at% titanium, 6.3-8.4 at% copper, and 0.08-0.13 at% chromium, more specifically 42.50 at% nickel, 49.90 at% titanium, 7.50 at% copper, and 0.10 at% chromium, where "essentially" means that no other alloying metals or additives are actively added, although any small amount of metals or additives may be present in the material used in the form of impurities.

[0010] To further stabilize the alloy structure, the nickel-titanium alloy contains a maximum of 500 ppm oxygen and nitrogen, and / or a maximum of 500 ppm carbon, and / or a maximum of 50 ppm hydrogen, in accordance with ASTM F2063-15, in particular, the total content of oxygen and nitrogen is less than 500 ppm, the content of carbon is less than 500 ppm, and the content of hydrogen is less than 50 ppm.

[0011] In order to improve the bending properties of the working area, the nickel-titanium alloy is annealed within a temperature range of 350°C to 450°C. That is, the nickel-titanium alloy forming the working area is heat-treated within a temperature range of 350°C to 450°C for about 5 minutes to 4 hours, thereby optimizing the lattice structure of the alloy lattice.

[0012] Also, induction temperature treatment at a temperature of 500°C ± 20°C for 1 to 60 seconds is considered to be advantageous, which can also improve the lattice structure of the alloy lattice.

[0013] More preferably, the nickel-titanium alloy has been work hardened by 21-40%, especially 35%, prior to mechanical machining (ie, prior to machining, for example, to form the working area).

[0014] In order to improve the mechanical stability, not only in terms of bending performance but also in terms of any stretching, and to counteract breakage in the working area, especially under high torsional forces, the nickel-titanium alloy was quenched to room temperature after heat treatment or annealing. For the purposes of the present invention, quenching is understood to mean a rapid cooling from the annealing or heat treatment temperature to room temperature, i.e., about 20-25°C. This will essentially be achieved by contacting the annealed or heat treated nickel-titanium alloy with a medium kept at room temperature. The medium is essentially not limited and may include a gas, such as nitrogen or carbon dioxide, or a liquid, such as water or other inert solvent.

[0015] It is particularly advantageous to carry out the quenching in water, which, due to its high heat capacity, has been found to result in a particularly rapid cooling of the nickel-titanium alloy and further improves both the flexibility and the stretchability of the working area.

[0016] More advantageously, the root canal instrument comprises regions in the axial direction with different helix angles, each made of a nickel-titanium alloy. The regions with different shapes allow the working region to be characterized by a large tapering shape, especially in the direction of the second exposed end, while the use of a nickel-titanium alloy results in a working region characterized by a sufficiently high mechanical stability and flexibility without the risk of breakage.

[0017] Further, according to the present invention, a method for manufacturing a root canal instrument as disclosed above is also described. That is, the method according to the present invention is used to manufacture a root canal instrument according to the present invention. In this respect, the method first comprises the step of providing a nickel-titanium alloy in the form of a strand, the nickel-titanium alloy comprising 38-46 at% nickel, 46-53 at% titanium and 5.5-8.8 at% copper. In a subsequent step, the strand is machined to form a working area. The machining can include any machining method suitable for nickel alloys, in particular mechanical machining. After the working area is completed, it is attached to a shank. The shank is essentially unlimited and can be made of any metallic or plastic material, for example.

[0018] The advantages, beneficial effects and further developments explained for the root canal instrument according to the invention also apply to the method for manufacturing the root canal instrument according to the invention. Furthermore, with regard to any definitions, reference is additionally made to the above explanations.

[0019] Advantageously, with regard to improving the flexibility of the working area, the nickel-titanium alloy is annealed in a temperature range of 350°C to 450°C. As explained above, for annealing, the nickel-titanium alloy forming the working area is heat treated in a temperature range of 350°C to 450°C for a period of about 5 minutes to 4 hours, thereby optimizing the lattice structure of the alloy lattice. Advantageously, the annealing is carried out in a furnace under an oxygen atmosphere. However, variants can also include annealing in vacuum and / or in an argon atmosphere.

[0020] According to another heat treatment, the nickel-titanium alloy is heat treated by induction at a temperature of 500°C ± 20°C for 1 to 60 seconds, which also leads to an improvement of the lattice structure of the alloy lattice, but in a much shorter time. Another advantageous further development of induction heating is the localized limitation of the heat zone.

[0021] More advantageously, the nickel-titanium alloy can be work-hardened to 21-40%, in particular 35%, before cutting the strand. When the material is work-hardened, the temperature range for heat treatment can change. In this case, a work-hardening of 30% would result in an increase in temperature for heat treatment of approximately 100°C.

[0022] More preferably, the nickel-titanium alloy is quenched after annealing, which is carried out in particular with water kept at room temperature. In particular, the machined nickel-titanium alloy is brought into contact with a medium, in particular water, kept at about 20-25° C. immediately after heat treatment or tempering, i.e., after removal from the furnace, whereupon quenching of the nickel-titanium alloy takes place, so that the lattice structure is changed in such a way that, in addition to the bending performance, the mechanical stability is also improved with respect to any stretching of the working area.

[0023] Preferably, the working area is attached to the shank by pressing, welding or gating. In particular, the first two mentioned methods are particularly suitable when the shank is made of a metallic material. Gating the shank to the working area, i.e. directly at the first end of the working area, is particularly preferred when the shank is made of an injection-moldable plastic material, for example by using injection molding techniques.

[0024] Furthermore, according to the invention, the use of a nickel-titanium alloy is also described, which consists essentially of 38-46 at.-% nickel, 46-53 at.-% titanium, 5.5-8.8 at.-% copper and 0.05-0.15 at.-% chromium, the proportion of chromium being in particular 0.08-0.13 at.-%, more in particular 0.01 at.-%. The use of the nickel-titanium alloy is intended for the production of root canal instruments, which are characterized in that they have a particularly flexible and pliable working area. The embodiments and advantageous further developments of the root canal instruments according to the invention also apply to the uses according to the invention.

[0025] In the following, the invention will be explained by means of exemplary embodiments with reference to the drawings. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic side view showing a root canal instrument according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] 1 is a detailed view of a root canal instrument 1 having a shank 2 and a working region 4 connected to the shank 2 by a coupling region 3. At the distal end of the shank 2 a coupling 5 is located. The coupling 5 is used to connect to a drive or handpiece that is used by the dentist to operate the root canal instrument 1.

[0028] The working area 4 will be considered as the cutting area used to remove dead or bacterially infected pulp tissue from the root canal. The working area 4 has a first end 6 and a second end 7. The first end 6 is connected to the shank 2 at the connection area 3, while the second end 7 is exposed and has a tip. Overall, the extent of the working area 2 from the first end 6 to the second end 7 is more or less conical, and the working area 2 consists of multiple areas with different helix angles in the axial direction XX, which decrease from the first end 6 to the second end 7.

[0029] The working area 4 is made of a nickel-titanium alloy containing 38-46 at% nickel, 46-53 at% titanium and 5.5-8.8 at% copper. Furthermore, the nickel-titanium alloy may contain 0.05-0.15 at% chromium, up to 500 ppm oxygen and nitrogen, up to 500 ppm carbon and up to 50 ppm hydrogen. Due to the use of a nickel-titanium alloy, the working area 4 is characterized by particularly good bending properties and high elasticity. This allows the working area to penetrate even difficult-to-access root canals, remove tissue residues therefrom and form conical root canals. Due to the high flexibility and elasticity of the working area 4, the diameter of the working area 4 can be made very small, since the working area 4 is still characterized by high mechanical stability due to the use of a nickel-titanium alloy, such that no breakage of the working area occurs.

[0030] Preferably, the nickel-titanium alloy is annealed within a temperature range of 350 to 450° C. and then quenched with water to room temperature (about 20 to 25° C.), thereby improving stretchability and flexibility while maintaining high breaking strength. EXAMPLES

[0031] The working area of ​​the root canal instrument was manufactured from the alloys shown in Table 1 so that it could be designed as shown in Figure 1.

[0032] For this purpose, material strands were produced from the indicated alloys and were first stored at room temperature (20-25 ° C). This material was not work-hardened. The material strands were then stored in a furnace at 350-450 ° C for 30 minutes (the duration may in particular range from 5 to 60 minutes, preferably from 20 to 40 minutes). The furnace heating was carried out without passing through a temperature lamp. The heat-treated working area was then quenched in water maintained at room temperature. From the obtained alloy material, the working area of ​​the root canal instrument was produced by cutting. In Table 1, the physical and mechanical properties of the alloys used are additionally shown.

[0033] [Table 1]

[0034] The strength and elongation were measured according to ASTM F2516, 2018. The maximum tensile stress (σz) was calculated by the following formula: σz=F / S (F=force (MPa), S=cross-sectional area (mm2)).

[0035] Force (F) was measured on a tension and compression testing machine with the following parameters: Crosshead speed = 1 mm / min. Reference diameter (material) = 1.0mm and 1.2mm.

[0036] The elastic modulus was determined based on a tensile test as the slope up to the yield point of the material (the starting point of plastic deformation according to Hook's line).

[0037] As can be seen from Table 1, the alloy of Example 1 is characterized by having particularly high elongation and tensile stress, and therefore is highly elastic and flexible. Thus, the working area of ​​a root canal instrument formed from the alloy of Example 1 is also characterized by being particularly flexible. [Explanation of symbols]

[0038] 1 Root canal instruments 2 Shank 3 Combined area 4. Joints 6 1st end 7 Second end

Claims

1. 1. A root canal instrument comprising: a shank (2); and a working part (4) attached to said shank (2), said working part (4) made from a nickel-titanium alloy consisting essentially of 40.5-43.1 at% nickel, 48.7-50.8 at% titanium, 6.3-8.4 at% copper, and 0.08-0.13 at% chromium.

2. the nickel-titanium alloy consists essentially of 42.50 at.% nickel, 49.90 at.% titanium, 7.50 at.% copper, and 0.10 at.% chromium; The nickel-titanium alloy contains up to 500 ppm oxygen and nitrogen, and / or up to 500 ppm carbon, and / or up to 50 ppm hydrogen according to ASTM F2063-15; 2. A root canal instrument according to claim 1.

3. 3. The root canal instrument according to claim 1 or 2, wherein the nickel-titanium alloy is annealed within a temperature range of 350°C to 450°C, or the nickel-titanium alloy is heat treated by induction at a temperature of 500°C±20°C for 1 second to 60 seconds.

4. Root canal instrument according to claims 1 to 3, wherein the nickel-titanium alloy is work-hardened by 21 to 40%, in particular 35%.

5. 5. Root canal instrument according to claim 3 or 4, wherein the nickel-titanium alloy is quenched to room temperature after the heat treatment or tempering, in particular quenching is performed in water.

6. A method for manufacturing a root canal instrument (1) according to claims 1 to 5, comprising the steps of: providing a nickel-titanium alloy in the form of strands consisting essentially of 40.5-43.1 at.% nickel, 48.7-50.8 at.% titanium, 6.3-8.4 at.% copper, and 0.08-0.13 at.% chromium; cutting the strand to form a working area (4); connecting said working area to a shank (2); Including, A method, wherein the connection of the working area (4) to the shank (2) is effected in particular by pressing, welding or gating.

7. 7. The method of claim 6, comprising annealing the nickel-titanium alloy within a temperature range of 350° C. to 450° C., or heat treating the nickel-titanium alloy by induction at a temperature of 500° C.±20° C. for 1 second to 60 seconds.

8. A method according to claim 6 or 7, wherein the nickel-titanium alloy is work-hardened to 21-40%, in particular 35%, before machining the strand.

9. A method according to claim 7 or 8, comprising the step of quenching the heat treated or annealed nickel-titanium alloy, in particular with water, to room temperature.

10. 1. Use of a nickel-titanium alloy for the manufacture of a root canal instrument (1), the nickel-titanium alloy consisting essentially of 40.5-43.1 at.% nickel, 48.7-50.8 at.% titanium, 6.3-8.4 at.% copper, and 0.08-0.13 at.% chromium.

Images