ENDODONTIC FILES WITH HYBRID METALLURGICAL ELASTIC CHARACTERISTICS AND IDENTIFICATION COLORS

Abstract

The invention describes an additional manufacturing method to improve the metallurgical properties of an endodontic file, which method customizes torsional and cyclic fatigue resistance behavior performance for separate files sizes. A heat-treatment file size tailored method accomplished after grinding the blank is disclosed aiming to improve the elasticity behavior of the specific file size based on its application during instrumentation protocol, also generating a colored oxidation layer on the working part surface of the file. The colored coded customized heat-treatment process will help the operator to identify the improved metallurgical properties behavior of each file, and decide the best use of such files.

Claims

1. A set of hybrid austenite/martensite NiTi endodontic files, wherein for each file size in the set a customize heat-treatment is applied to each file after grinding a blank, which files in said set exhibit different levels of flexibility and torsional resistance depending on the sizes and exhibited colors of the resulting files, wherein said set is optionally configured to attach to an engine/motor driven device, and wherein color is indicative of degree of cyclic fatigue resistance, torsional resistance or both.

2. The set of austenite/martensite NiTi endodontic files of claim 1, wherein an exhibited color is gold.

3. The set of austenite/martensite NiTi endodontic files of claim 1, wherein said exhibited colors correspond to different levels of cyclic (flexural) fatigue resistance and/or torsional fatigue resistance, wherein the exhibited colors are selected from blue, purple or gold.

4. The set of austenite/martensite NiTi endodontic files of claim 3, wherein said levels of cyclic (flexural) fatigue resistance further depend on the size of the file.

5. The set of austenite/martensite NiTi endodontic files of claim 3, wherein the levels of torsional fatigue resistance further depend on the size of the file.

6. The set of austenite/martensite NiTi endodontic files of claim 3, wherein the colors and colors shades of the entire work part are purple, blue or gold.

7. The set of austenite/martensite NiTi endodontic files of claim 1, wherein the heat treatment comprises multiple variable heat-treatment techniques that decrease the percentage of superelasticity to control memory within a file as file size increases.

8. The set of austenite/martensite NiTi endodontic files of claim 1, wherein the heat treatment is applied after grinding the blank based on the final dimensions of the file.

9. A method of manufacturing a set of austenite/martensite NiTi endodontic files, comprising: a) grinding one or more NiTi wires; b) optionally shaping the one or more NiTi wires into a blade; c) optionally grinding the proximal and distal tips of the bladed one or more NiTi wires; d) cleaning the ground bladed one or more NiTi wires by ultrasonication; e) heating the sonicated one or more NiTi wires; f) cooling said heated one or more NiTi wires; and g) assembling an endodontic file from the cooled one or more NiTi wires, wherein said endodontic file comprises a handle, smooth shaft and blade, wherein color of the resulting NiTi wire is indicative of degree of cyclic fatigue resistance, torsional fatigue resistance or both.

10. The method of claim 9, wherein the one or more NiTi wires have different diameters.

11. The method of claim 10, wherein the diameters are selected from the group consisting of about 0.8 mm, about 1.0 mm, and about 1.2 mm.

12. The method of claim 9, wherein the smooth shaft contains one or more measuring lines.

13. The method of claim 9, wherein the one or more sonicated NiTi wires are heated to between about 350° C. to about 550° C.

14. The method of claim 9, wherein the one or more sonicated NiTi wires are heated for between about 5 minutes to about 120 minutes, wherein sufficient oxidation occurs producing TiO, pure Ni and NiTi in a B2 phase on an external surface layer, and wherein, after oxidation, different phases are observed comprising TiO.sub.2, Ni and Ni.sub.3Ti beneath the Ni-rich Ni.sub.3Ti layer.

15. A method of manufacturing a set of austenite/martensite NiTi endodontic files, comprising: a) grinding one or more NiTi wires; b) cleaning the ground one or more NiTi wires by ultrasonication; c) heating the sonicated one or more NiTi wires to between about 350° C. to about 550° C. for a time sufficient to produce TiO, pure Ni and NiTi in a B2 phase on an external surface layer; d) cooling said heated one or more NiTi wires; and e) assembling an endodontic file from the cooled one or more NiTi wires, wherein said endodontic file comprises a handle, smooth shaft and blade, wherein the one or more NiTi wires have different diameters, and wherein color of the resulting NiTi wire is indicative of degree of cyclic fatigue resistance, torsional fatigue resistance or both.

16. The method of claim 15, wherein the diameters are selected from the group consisting of about 0.8 mm, about 1.0 mm, and about 1.2 mm.

17. The method of claim 15, wherein after oxidation, different phases are observed comprising TiO.sub.2, Ni and Ni.sub.3Ti beneath the Ni-rich Ni.sub.3Ti layer.

18. The method of claim 15, wherein said files in said set exhibit different levels of flexibility and torsional resistance depending on the sizes and exhibited colors of the resulting files.

19. An endodontic device produced by the method of claim 9, wherein the exhibited colors are selected from gold, purple or blue.

20. An endodontic device produced by the method of claim 15, wherein the exhibited colors are selected from purple, blue or gold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIGS. 1, 2 and 3 illustrates different heat-treatments during endodontic manufacturing presented by this invention.

[0037] FIG. 1 shows a photograph of active part, including tip and penetration guide of three (3) endodontic files resulting from heat-treatments as disclosed herein: gold (top file), blue (middle file) and purple (bottom file).

[0038] FIG. 2 shows a photograph of the measuring lines, including tops of handles with color guide, of three (3) endodontic files resulting from heat-treatments disclosed herein: gold (top file), blue (middle file) and purple (bottom file).

[0039] FIG. 3 shows a photograph of active part, including tip and penetration guide and measuring lines of three (3) endodontic files resulting from heat-treatments disclosed herein: gold (top file), blue (middle file) and purple (bottom file).

DETAILED DESCRIPTION OF THE INVENTION

[0040] Before the present composition, methods, and methodologies are described, it is to be understood that this invention is not limited to particular compositions, methods, and experimental conditions described, as such compositions, methods, and conditions may vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only in the appended claims.

[0041] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, references to “a wire” includes one or more wires, and/or compositions of the type described herein which will become apparent to those persons skilled in the art upon reading this disclosure and so forth.

[0042] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the invention, as it will be understood that modifications and variations are encompassed within the spirit and scope of the instant disclosure.

[0043] As used herein, “about,” “approximately,” “substantially” and “significantly” will be understood by a person of ordinary skill in the art and will vary in some extent depending on the context in which they are used. If there are uses of the term which are not clear to persons of ordinary skill in the art given the context in which it is used, “about” and “approximately” will mean plus or minus <10% of particular term and “substantially” and “significantly” will mean plus or minus >10% of the particular term. In embodiments, a composition may “contain,” “comprise” or “consist essentially of” a particular component or group of components, where the skilled artisan would understand the latter to mean the scope of the claim is limited to the specified materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed invention.

[0044] As used herein, “superelasticity” means an elastic (reversible) response to an applied stress, caused by a phase transformation between the austenitic and martensitic phases of a crystal.

[0045] As used herein, “endodontic file” and “endodontic device” are surgical instruments used by dentists when performing root canal treatment.

[0046] As used herein, “cyclic fatigue” means the stress, strain, and deformation induced in a material by cyclic loading.

[0047] As used herein, “torsional fatigue” means a fracture in a shaft caused by a proximal end of a shaft bound to one surface where mechanical stress is applied perpendicular to the long axis of said shaft at its distal end.

[0048] As used herein, “an engine/motor driven device” means a hand-held or mounted, mechanical instrument used to perform a variety of dental procedures (e.g., including removing decay, polishing fillings, performing cosmetic dentistry, and altering prostheses), which device may be air driven or motor driven, cordless or non-cordless.

[0049] As used herein, “controlled memory” refers to the property of an alloy that can be deformed when cold but returns to its pre-deformed (“remembered”) shape when heated.

[0050] In embodiments, raw materials are prepared, including NiTi wires (e.g., with different diameters: about 0.8 mm, about 1.0 mm and about 1.2 mm), handle, ink, stopper and package materials to make the endodontic device using a customized CNC grinder and appropriate NiTi wire to grind the flutes of the file, where to each file a particular program is applied. After grinding the flutes, the NiTi wire is turned into a blade, where the distal and proximal tip of the blade are subjected to grinding, the blade may be cleaned by ultrasonic cleaner (although other means of cleaning would be clear to the skilled artisan); where the blade is heat treated based on the operating requirement, e.g., different file and different colors, subjected to different heat treatment parameters, such as the temperature, duration and cooling period.

[0051] Existing endodontic files typically include two or more cutting edges.

[0052] A working length of a file has helical or non-helical flutes that include cutting edges. The working length is located between a proximal (shank) and distal (tip) end of a file. Endodontic files typically include two or more flutes. Generally, each flute has two cutting edges—a cutting edge and a trailing edge. A file having a triangular cross-section has three flutes and six theoretical edges. However, due to the triangular shape of the cross-section, the trailing edge of flute 1 is also the cutting edge of the flute 2, the trailing edge of the flute 2 is also the cutting edge of the flute 3, and the trailing edge of flute 3 is also the cutting edge of flute 1. Therefore, the triangular file typically has three cutting edges.

[0053] A geometric parameter of an endodontic file includes dimensions of the file's tip. The tip provides two main functions: a) the tip enlarges the canal during shaping and b) guides the file through the canal during shaping.

[0054] These two functions of the tip are accomplished by balancing various geometric parameters of the tip. Illustrative geometric parameters include the rake angle of the cutting edge, angle and radius of the tip's cutting edge and proximity of a flute end to the tip end of the file. Balancing such geometric parameters of endodontic files has not been easily achieved. For example, typically, in existing files, improved tip functionality may come at the expense of other performance characteristics of the file.

[0055] Flutes, taper, tip or any other geometric parameter of an endodontic file may be fabricated by twisting a file blank having a triangular, square, or rhomboid-shaped cross section. Another method for fabricating helical or non-helical flutes, taper, tip or other geometric parameters includes a machining process. For example, a solid file blank is moved past a rotating grinding wheel. The file blank is repeatedly indexed and moved past the grinding wheel as many times as necessary to form a file having the desired geometric parameters.

[0056] In embodiments, a file is manufactured by grinding a tube/shaft/cylinder, as the case may be.

[0057] A performance characteristic of an endodontic file may be obtained by applying a heat treatment. An illustrative heat treatment may include an annealing process. The annealing process is performed prior to forming a file blank, or performed on the blank after its formation. Annealing refers to heating an alloy to a threshold temperature and maintaining that temperature for a time sufficient to bring about a desired change in a property of the alloy.

[0058] For example, an annealing process for a NiTi file blank includes heating the blank at a threshold temperature and for a sufficient time to bring the blank to a state having a desired crystal structure between 100% austenite and 100% martensite. The crystal structure preferably includes a percentage of rhombohedral phase crystal structure. In embodiments, the rhombohedral phase is the only crystal structure. Alternatively, the crystal structure is a combination of austenite and martensite without any rhombohedral phase. In one aspect, NiTi ratios may be 56 wt % nickel and 44 wt % titanium.

[0059] A threshold temperature for inducing the desired crystalline structure may be dependent upon a particular NiTi alloy, but generally is in the range of about 250-359° C. for typical NiTi alloys, and is advantageously in the range of about 350-550° C. In one aspect, for 0.8 mm files, heat-treatment may be in the range of between about 400-450° C., for 1.0 mm/1.2 mm files, heat-treatment may be between 450-550° C. In one aspect, cooling temperatures may be as follows: for gold, between about 350-400° C., for purple between about 400-450° C., for blue between about 450-550° C. Generally, annealing time for a NiTi file blank ranges from about 5 minutes to about 120 minutes, about 30 minutes to about 60 minutes, 60 minutes to about 120 minutes, or 120 minutes.

[0060] Following an annealing process, a file blank may be cooled to room or ambient temperature, upon which it retains the desired crystal structure. After annealing, the instrument blank includes a superelastic material in a rhombohedral phase alone or in combination with austenite and/or martensite, or in a phase structure that is a combination of austenite and martensite.

[0061] After the annealing process, cutting edges are fabricated in the file blank. For example, the file blank may be twisted at low temperature (e.g., less than about 100° C.). The twisting may be performed at ambient temperature, without immersing the blank and tooling equipment into high temperature salt baths or exposing them to other high temperature methods.

[0062] Cooling may be performed by any suitable methods. For example, the heated file blanks may be cooled by placing the heated file blank in an environment at room temperature and waiting for the files to cool for a certain period of time. In embodiments, cooling critical time is between about 120 min-180 min, depending on the file size.

[0063] Illustrative heat-treat methods and apparatus are in U.S. Pat. No. 7,779,542, which is incorporated by reference herein in its entirety.

EXAMPLES

[0064] Table 1 shows examples of properties of treated blanks as described herein.

TABLE-US-00001 Temp/Temp Range Property Temp/Temp (Reacts (CF or TF Size Range Time with O.sub.2) Color resistance) 0.8 mm 400-450° C. 5 min- 400-450° C. purple CF/TF 60 min 1.0 mm 450-550° C. 60 min- 450-550° C. blue TF 120 min 400-450° C. purple TF 350-400° C. gold CF 1.2 mm 450-550° C. 60 min- 350-400° C. gold TF 120 min

[0065] Although the invention has been described with reference to the above disclosure, it will be understood that modifications and variations are encompassed within the spirit and scope of the invention. Accordingly, the invention is limited only by the following claims.