ROOT CANAL INSTRUMENT

Abstract

The invention relates to a root canal instrument having a shank and a working area attached to the shank, wherein the working area 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. The invention relates to a root canal instrument having a shank and a working area attached to the shank, wherein the working area 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.

Claims

1. A root canal instrument comprising a shank and a working area attached to the shank, wherein the working area 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.

2. The root canal instrument of claim 1, wherein the nickel-titanium alloy further comprises 0.05 to 0.15 at % chromium.

3. The root canal instrument according to claim 1, wherein the nickel-titanium alloy essentially consists 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 more particularly 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 oxygen and nitrogen and/or a maximum of 500 ppm carbon and/or a maximum of 50 ppm hydrogen according to ASTM F 2063-15.

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

5. The root canal instrument according to claim 1, wherein the nickel-titanium alloy has been work-hardened by 21 to 40%, in particular 35%.

6. The root canal instrument according to claim 4, wherein the nickel-titanium alloy was quenched to room temperature following the heat treatment or tempering, wherein quenching was performed in particular in water.

7. A method for manufacturing a root canal instrument according to claim 1, comprising the steps of: providing a nickel-titanium alloy comprising 38 to 46 at % nickel, 46 to 53 at % titanium and 5.5 to 8.8 at % copper in the form of a strand, machining the strand to form a working area, and connecting the working area to a shank, wherein connection of the working area to the shank is in particular effected by pressing, welding or gating.

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

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

10. The method according to claim 8, comprising a step of quenching the heat-treated or annealed nickel-titanium alloy to room temperature, in particular using water.

11. Use of a nickel-titanium alloy essentially consisting 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, for the manufacture of a root canal instrument.

Description

[0024] In the following, the invention will be described by means of an example embodiment while reference will be made to the drawing, wherein:

[0025] FIG. 1 is a schematic lateral view of a root canal instrument according to one embodiment of the invention.

[0026] FIG. 1 shows a detailed view of a root canal instrument 1 with a shank 2 and a working area 4 connected to the shank 2 by a coupling region 3. A fitting 5 is located at a distal end of the shank 2. The fitting 5 is used to be connected to a drive or a handpiece which is used by a dentist to operate the root canal instrument 1.

[0027] The working area 4 is to be regarded as a cutting area used to remove dead or bacterially infected pulp tissue of a 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 coupling region 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, with the working area 2 comprising a plurality of regions in the axial direction X-X that are provided with different angles of twist, with the angles of twist 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. Furthermore, the nickel-titanium alloy may comprise 0.05 to 0.15 at % chromium, a maximum of 500 ppm oxygen and nitrogen, a maximum of 500 ppm carbon, and a maximum of 50 ppm hydrogen. Due to the use of the nickel-titanium alloy, the working area 4 is characterized by particularly good bending properties and high stretchability. This enables the working area to penetrate even into those root canals which are difficult to access, to remove tissue residues therefrom and to form a conical root canal. Due to high flexibility and stretchability of the working area 4, a 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 the nickel-titanium alloy, such that break-off of the working area does not occur.

[0029] Preferably, the nickel-titanium alloy is annealed within a temperature range of 350 to 450° C. and quenched with water to room temperature (about 20 to 25° C.), which can improve stretchability and flexibility while maintaining high fracture strength.

EXAMPLES

[0030] Working areas for a root canal instrument were manufactured from the alloys indicated in Table 1, which can be designed as shown in FIG. 1.

[0031] For this purpose, material strands were produced from the indicated alloys, which were first stored at room temperature (20 to 25° C.). The material was not work-hardened. Subsequently, the material strands were stored in a furnace at 350 to 450° C. for a period of 30 minutes (the period may in particular be in the range of 5 to 60 minutes and preferably in the range of 20 to 40 minutes). Furnace heating was carried out without passing a temperature ramp. Subsequently, the heat-treated working areas were quenched in water which was maintained at room temperature. From the alloy material obtained, working areas for a root canal instrument were fabricated by machining. In Table 1, the physical and mechanical properties of the alloys used will additionally be indicated.

TABLE-US-00001 TABLE 1 Example 1 Comparative example Nickel 42.50 At % 50.10 At % Titanium 49.90 At % 49.90 At % Copper 7.50 At % — Chromium 0.10 At % — Oxygen and nitrogen Max. 500 ppm 220 ppm Carbon Max. 500 ppm 320 ppm Hydrogen Max. 50 ppm 50 ppm Elongation Min. 30% 10% Tensile stress Min. 800 MPa 1100 MPa Melting point 1310° C. — E-modulus 25-35 GPa — (austenite) (60-80 GPa)

[0032] The strength and elongation were determined according to ASTM F 2516 edition 2018. The following formula was used to determine the max. tensile stress (σz):

σz=F/S (F=force in MPa, S=cross-sectional area in mm.sup.2).

[0033] The force (F) was determined on a tensile and compression testing machine using the following parameters: [0034] Crosshead speed=1 mm/min. [0035] Reference diameter (material)=1.0 mm and 1.2 mm.

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

[0037] As may be seen from Table 1, the alloy of Example 1 is characterized by having particularly high elongation and tensile stress, resulting in high stretchability and flexibility. Thus, a working area for a root canal instrument formed from the alloy of Example 1 is also characterized by particularly high flexibility.

LIST OF REFERENCE NUMBERS

[0038] 1 Root canal instrument [0039] 2 Shank [0040] 3 Coupling region [0041] 4 Fitting [0042] 6 First end [0043] 7 Second end