root canal instruments

Abstract

The invention relates to an endodontic instrument (1) comprising a handle (2) and a working area (4) fastened to the handle (2), wherein the working area (4) consists of a nickel-titanium alloy comprising 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 an endodontic instrument for treating a tooth root canal and a method for preparing the same. In addition, the invention also describes a use of a nickel-titanium alloy for preparing an endodontic instrument. Background Art

[0002] Endodontic instruments are known from the prior art, for example from DE 202012012526 U1. Endodontic instruments must possess a certain degree of flexibility to conform to the bends and curvatures of the root canal and to perform the corresponding root canal treatment. To this end, endodontic instruments have a core, i.e., a solid core of material, starting from the working area of ​​the instrument, which continuously tapers toward the shank area of ​​the instrument. Molars, in particular, have relatively complex root canal systems, where endodontic instruments must also conform to the small radii of the root canals. To this end, the working area of ​​endodontic instruments must be even more flexible. Previously, this was achieved by further tapering the core of the instrument. However, this resulted in reduced mechanical stability of the working area and, as a result, a certain risk of breaking a portion of the working area during the root canal treatment. Summary of the Invention

[0003] The object of the present invention is therefore to provide a dental endodontic instrument and a method for producing the same, which, while having a simple and stable construction and simple, cost-effective producibility, has improved flexibility and can in particular also conform to the high degree of curvature of the root canal of a tooth.

[0004] This object is achieved by an endodontic instrument, a method for its production and its use having the features of the independent claims. The dependent claims provide preferred developments of the invention.

[0005] The dental endodontic instrument according to the present invention, having the features of claim 1, has the advantage of being characterized by excellent flexibility. Thus, when treating root canals, even in difficult-to-access molar root canals, the endodontic instrument according to the present invention can perfectly follow the curvature and meandering of the root canal without risking breaking the working area of ​​the instrument. Consequently, necrotic or infected pulp tissue can be completely removed from the root canal with high safety, thereby minimizing the microbial presence in the root canal.

[0006] According to the present invention, this is achieved by an endodontic instrument comprising a shaft and a working region fastened to the shaft, wherein the working region is composed of a nickel-titanium alloy comprising 38 to 46 at% nickel, 46 to 53 at% titanium, and 5.5 to 8.8 at% copper. The geometry of the endodontic instrument according to the present invention can be conventionally designed, in particular, extending conically from a first end of the working region connected to the shaft to a second, exposed end of the working region. The working region serves as a cutting region for the root canal and, in particular, comprises a plurality of cutting sections arranged along the core. By using a nickel-titanium alloy as defined above, the working region is formed from a highly flexible material that, while exhibiting good ductility, is characterized by high mechanical stability, in particular a high tensile stress of at least 800 MPa, and high bendability or a large Young's modulus, thereby effectively preventing breakage during use of the endodontic instrument. Due to their physical and mechanical properties, nickel-titanium alloys containing copper are optimally suited for forming highly flexible working regions for endodontic instruments.

[0007] In order to improve fatigue strength, the nickel-titanium alloy may also preferably include 0.05 to 0.15 At % of chromium.

[0008] According to a particularly preferred refinement, the nickel-titanium alloy consists essentially of 40.5 to 43.1 At% nickel, 48.7 to 50.8 At% titanium, 6.3 to 8.4 At% copper, and 0.08 to 0.13 At% chromium, and in particular of 42.50 At% nickel, 49.90 At% titanium, 7.50 At% copper, and 0.10 At% chromium. "Essentially" here means that no other alloying metals or additives are actively added, although possibly very small amounts of metals or additives may be present as impurities in the material used.

[0009] To further stabilize the alloy structure, nickel-titanium alloys include a maximum of 500 ppm of oxygen and nitrogen and / or a maximum of 500 ppm of carbon and / or a maximum of 50 ppm of hydrogen according to ASTM F 2063-15. 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.

[0010] In order to improve the bendability of the working area, the nickel-titanium alloy is annealed in a temperature range of 350° C. to 450° C. This means that 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.

[0011] It has proven advantageous to perform a heat treatment by induction at a temperature of 500° C.±20° C. for 1 to 60 seconds. This can also lead to an improvement in the lattice structure of the alloy.

[0012] It is further advantageous if the nickel-titanium alloy is work-hardened to 21% to 40%, in particular 35%, before machining, ie, for example, before machining to form the working region.

[0013] In order to improve the mechanical stability in terms of ductility in addition to bendability, thereby in particular preventing the working area from breaking under high torsional forces, the nickel-titanium alloy is quenched to room temperature after heat treatment or annealing. In the sense of the present invention, quenching is understood to mean quenching from the annealing temperature or heat treatment temperature to room temperature, i.e., approximately 20° C. to 25° C. This is achieved in particular by contacting the annealed or heat-treated nickel-titanium alloy with a medium that is kept at room temperature. The medium is not particularly limited and can include gases such as nitrogen or carbon dioxide, or liquids such as water and other inert solvents.

[0014] It is particularly advantageous to carry out the quenching in water. It has been shown that water, due to its high heat capacity, leads to particularly rapid cooling of the nickel-titanium alloy, thereby further improving the flexibility and ductility of the working area.

[0015] Furthermore, it is advantageous if the endodontic instrument comprises regions in the axial direction that have different torsion angles and each consist of a nickel-titanium alloy. Due to their differently configured geometric shapes, a working region can be formed that is characterized by a particularly strong tapering shape toward the exposed second end, but which, due to the use of nickel-titanium alloy, is characterized by sufficiently high mechanical stability and flexibility without the risk of breaking.

[0016] Furthermore, according to the present invention, a method for producing an endodontic instrument as disclosed above is described. In other words, the method according to the present invention is used to produce an endodontic instrument according to the present invention. The method first comprises the following steps: a nickel-titanium alloy is provided in the form of a strip, wherein the nickel-titanium alloy comprises 38 to 46 At % nickel, 46 to 53 At % titanium and 5.5 to 8.8 At % copper. In a subsequent method step, the strip is processed to form a working region. Processing can include various processing methods suitable for nickel alloys and, in particular, mechanical processing. After the working region has been completed, it is connected to the handle. The handle is not specifically restricted here and can also consist of a metal material or a plastic, for example.

[0017] The advantages, advantageous effects and improvements described for the endodontic instrument according to the invention also apply to the method according to the invention for producing an endodontic instrument.

[0018] Advantageously, to improve the bendability of the working region, the nickel-titanium alloy is annealed at a temperature range of 350°C to 450°C. As already described above, for annealing, the nickel-titanium alloy forming the working region is heat-treated at a temperature range of 350°C to 450°C for a period of approximately 5 minutes to 4 hours, thereby optimizing the lattice structure of the alloy. Annealing is advantageously performed in a furnace under an oxygen atmosphere. A variant may also include annealing in a vacuum and / or under an argon atmosphere.

[0019] According to an alternative heat treatment concept, the nickel-titanium alloy is heat treated by induction at a temperature of 500° C. ±20° C. for 1 to 60 seconds, which also improves the lattice structure of the alloy lattice, but saves significantly more time. Another advantageous development of induction heating is to locally limit the hot zone.

[0020] It is further advantageous if the nickel-titanium alloy is work-hardened to 21 to 40%, in particular 35%, before forming the strip. If the material is work-hardened, the temperature range for the heat treatment can vary. In this case, a 30% work-hardening would result in a temperature increase of approximately 100°C during the heat treatment.

[0021] It is also advantageous to quench the nickel-titanium alloy after annealing, in particular using water kept at room temperature. In particular, the processed nickel-titanium alloy is brought into contact with a medium kept at approximately 20° C. to 25° C., such as water, immediately after heat treatment or annealing, i.e., for example, after removal from the furnace. The nickel-titanium alloy is quenched, which changes the lattice structure, thereby improving the mechanical stability in terms of ductility in the working area in addition to its flexibility.

[0022] The working area is preferably connected to the handle by extrusion, welding, or injection molding. These two methods are particularly suitable when the handle is made of a metal material. When the handle is made of an injection-moldable plastic material, the handle is typically directly injection-molded onto the working area, i.e., onto the first end of the working area. Injection molding technology is used, for example.

[0023] Furthermore, the present invention describes the use of a nickel-titanium alloy consisting essentially of 38 to 46 at% nickel, 46 to 53 at% titanium, 5.5 to 8.8 at% copper, and 0.05 to 0.15 at% chromium, the chromium content being in particular 0.08 to 0.13 at% and even in particular 0.01 at%. This use provides for the production of endodontic instruments using the nickel-titanium alloy, which are thus characterized by a particularly flexible and bendable working area. The embodiments and advantageous developments of the endodontic instrument according to the invention also apply to the use according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be described below with reference to embodiments in conjunction with the accompanying drawings, in which:

[0025] Figure 1 A schematic side view of an endodontic instrument according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0026] Figure 1 The endodontic instrument 1 is shown in detail and comprises a handle 2 and a working area 4 connected to the handle 2 via a connecting area 3. A connecting piece 5 is provided at the distal end of the handle 2. The connecting piece 5 serves here for connection to a driver or a grip with which the dentist can operate the endodontic instrument 1.

[0027] The working area 4 is considered the cutting area, which is used to remove necrotic 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 in the connection area 3, while the second end 7 is exposed and has a pointed tip. Overall, the working area 2 has a generally conical profile from the first end 6 to the second end 7. The working area 2 includes multiple regions with different torsion angles in the axial direction XX, with the torsion angle decreasing from the first end 6 to the second end 7.

[0028] The working area 4 is made of a nickel-titanium alloy comprising 38 to 46 At% nickel, 46 to 53 At% titanium and 5.5 to 8.8 At% copper. In addition, the nickel-titanium alloy may comprise 0.05 to 0.15 At% chromium, a maximum of 500 ppm of oxygen and nitrogen, a maximum of 500 ppm of carbon and a maximum of 50 ppm of hydrogen. Due to the use of nickel-titanium alloy, the working area 4 is characterized by particularly good flexibility and high ductility. This allows the working area itself to be advanced into root canals that are difficult to access in order to remove tissue residues therefrom and to construct a tapered root canal. Due to the high flexibility and ductility of the working area 4, the diameter of the working area 4 can be constructed to be very small, because the working area 4, despite the use of nickel-titanium alloy, is still characterized by high mechanical stability, so that no breakage of the working area occurs.

[0029] Preferably, the nickel-titanium alloy is annealed in a temperature range of 350° C. to 450° C. and quenched with water to room temperature (about 20° C. to 25° C.), thereby improving ductility and bendability while maintaining high fracture strength.

[0030] Example

[0031] The alloys given in Table 1 are used to prepare and construct the root canal instruments. Figure 1 The working area is shown.

[0032] To this end, a material strip is produced from the alloy given and initially stored at room temperature (20°C to 25°C). The material is not cold-hardened. The material strip is then stored in a furnace at 350°C to 450°C for 30 minutes (this duration can particularly be between 5 and 60 minutes, and preferably between 20 and 40 minutes). Heating in the furnace is performed without a temperature ramp. The heat-treated working area is then quenched in room-temperature water. The alloy material thus obtained is used to produce the working area for endodontic instruments by machining. Table 1 also shows the physical and mechanical properties of the alloys used.

[0033] Table 1

[0034] Example 1 Comparative Example 1 nickel 42.50At% 50.10At% titanium 49.90At% 49.90At% copper 7.50At% chromium 0.10At% oxygen and nitrogen Maximum 500ppm 220ppm carbon Maximum 500ppm 320ppm hydrogen Maximum 50ppm 50ppm Extension Minimum 30% 10％ tensile stress Minimum 800MPa 1100MPa Melting point 1310℃ - Elastic modulus (austenite) 25-35GPa (60-80GPa) -

[0035] Strength and ductility are determined according to the 2018 edition of ASTM F 2516. To determine the maximum tensile stress (σ z ) using the following formula: z =F / S (F = force (in MPa), S = cross-sectional area (in mm 2 )).

[0036] The force (F) is determined on a tensile and compression testing machine with the following parameters:

[0037] Crosshead speed = 1 mm / min.

[0038] Reference diameter (material) = 1.0 mm and 1.2 mm.

[0039] The modulus of elasticity is determined by means of a tensile test as the slope up to the yield point of the material (onset of plastic deformation according to the Hooke's curve).

[0040] As can be seen from Table 1, the alloy of Example 1 is characterized by particularly high ductility and tensile stress, resulting in high bendability and ductility. Therefore, the working area for endodontic instruments formed from the alloy of Example 1 is also characterized by particularly high flexibility.

[0041] Reference Signs List

[0042] 1. Root canal instruments

[0043] 2 handles

[0044] 3 Connection area

[0045] 4 Work Area

[0046] 5 Connectors

[0047] 6 First end

[0048] 7 Second end.

Claims

1. An endodontic instrument comprising a handle (2) and a working area (4) fastened to the handle (2), wherein the working area (4) is composed of a nickel-titanium alloy, the nickel-titanium alloy consisting essentially of 40.5 to 43.1 At% nickel, 48.7 to 50.8 At% titanium, 6.3 to 8.4 At% copper and 0.08 to 0.13 At% chromium.

2. The endodontic instrument of claim 1 , wherein the nickel-titanium alloy consists essentially of 42.50 At % nickel, 49.90 At % titanium, 7.50 At % copper, and 0.10 At % chromium, and / or wherein the nickel-titanium alloy comprises a maximum of 500 ppm of oxygen and nitrogen and / or a maximum of 500 ppm of carbon and / or a maximum of 50 ppm of hydrogen according to ASTM F 2063-15.

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

4. The endodontic instrument according to claim 1 or 2, wherein the nickel-titanium alloy is work-hardened to 21% to 40%.

5. The endodontic instrument of claim 4, wherein the nickel-titanium alloy is work hardened to 35%.

6. The endodontic instrument according to claim 3, wherein the nickel-titanium alloy is quenched to room temperature after the heat treatment or after the annealing, wherein the quenching is performed in water.

7. A method for preparing an endodontic instrument (1) according to any one of the preceding claims, comprising the steps of: - providing a nickel-titanium alloy in the form of a rod, the nickel-titanium alloy consisting essentially of 40.5 to 43.1 At % nickel, 48.7 to 50.8 At % titanium, 6.3 to 8.4 At % copper and 0.08 to 0.13 At % chromium, - machining the strip to form a working area (4), and - connecting the working area to the handle (2), wherein the connection of the working area (4) to the handle (2) is performed by extrusion, welding or injection molding.

8. The method according to claim 7, wherein the method comprises the following steps: The nickel-titanium alloy is annealed at a temperature ranging from 350° C. to 450° C., or the nickel-titanium alloy is heat-treated at a temperature of 500° C.±20° C. for 1 second to 60 seconds by induction.

9. A method according to claim 7 or 8, wherein the nickel titanium alloy is work hardened to 21 to 40% prior to machining the strip.

10. The method of claim 9, wherein the nickel-titanium alloy is work hardened to 35% prior to machining the strip.

11. The method according to claim 8, wherein the method comprises the following steps: The heat treated or annealed nickel titanium alloy is quenched to room temperature.

12. The method according to claim 11, wherein the method comprises the following steps: The heat treated or annealed nickel titanium alloy is quenched to room temperature using water.

13. Use of a nickel-titanium alloy for preparing an endodontic instrument (1), the nickel-titanium alloy consisting essentially of 40.5 to 43.1 At% nickel, 48.7 to 50.8 At% titanium, 6.3 to 8.4 At% copper and 0.08 to 0.13 At% chromium.

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