WO2006037505A1

WO2006037505A1 - Orthodontic curved brace consisting of a sputtered shape-memory alloy

Info

Publication number: WO2006037505A1
Application number: PCT/EP2005/010378
Authority: WO
Inventors: Holger Rumpf; Christiane Zamponi; Eckhard Quandt; Bernhard Winzek; Dieter Drescher; Friedrich Sernetz; Tobias Sterzl
Original assignee: Dentaurum J.P. Winkelstroeter Kg
Priority date: 2004-10-01
Filing date: 2005-09-26
Publication date: 2006-04-13
Also published as: EP1796573A1; DE102004048379A1

Abstract

The invention relates to an orthodontic curved brace, used in orthodontics to correct the malalignment of teeth. Said brace comprises a hollow wire or hollow wire section with a thin wall consisting of a shape-memory alloy (3), the thin wall of the wire or wire section having super-elastic characteristics.

Description

Orthodontic arc of splintered shape memory alloy

The present invention relates to an orthodontic arch for use in orthodontics for the correction of malocclusions comprising a wire or a wire piece of shape memory alloy. The invention also relates to a method for producing a piece of wire for such an orthodontic arch.

In general, shape memory (FG) materials "remember" and resume their original shape when deformed at low temperature (martensite) and later heated to an austenitic high temperature phase, and often exhibit superelastic behavior This property results from the plateau occurring within a certain temperature range above a characteristic pre-stress of about a few hundred MPa in the stress-strain (hysteresis) curve, in which strain the austenite transforms into martensite, stress-induced martensite may correspond The applied voltage is twinned and thus reacts within the plateau on a deformation of the material with a constant counterforce.

Components made of shape memory alloys are particularly attractive because they have superelastic properties within certain limits. Especially in orthodontics this property is desirable where constant forces are beneficial for correcting misaligned teeth. So far, full wires of shape memory alloy are well known for this use. These wires of biocompatible alloys, in particular of NiTi, are preferably used for the above-mentioned orthodontic purposes.

However, it has been shown that in the bending test and thus in the clinical application known from tensile tests and decisive for use constant force plateau does not form. Instead, a superimposed linear-elastic contribution is observed, which gets a significant meaning especially with decreasing wire diameter. The reason for this behavior is that the inner region comprising the neutral "fiber" does not reach the tension required to reach the superelastic plateau when bending the wire, so that the different bending load of the individual fibers results in a superimposition of several nonlinear ones Loading and unloading curves, with which the force constancy or bending moment constancy of the orthodontic arches desired for the orthodontic treatment can not be achieved Thus, hardly wires with superelastic behavior can be realized in this way, which have a therapeutically desirable constant bending force plateau with relief.

The object of the invention is now to provide an orthodontic arc comprising a wire for having such properties, wherein the wire can be easily and inexpensively manufactured at least in pieces of a limited length and wherein the wire or piece of wire for the said application in orthodontics having desired superelasticity. In addition, it is the object of the invention to provide a method for producing such a wire, wherein the wire according to the application in orthodontics can be made in corresponding pieces of at least limited length.

These objects are achieved by the orthodontic arch having the characterizing features of claim 1 and the method of claim 14. Features of particular embodiments of the invention are mentioned in the respective subclaims. An essential basic idea of the invention is to make use of the achievement of the spring effect of the orthodontic arc of a hollow wire or piece of wire whose wall is relatively thin and consists of a shape memory alloy. In this case, the orthodontic arc may be formed entirely by the hollow wire or may include a portion bent from such hollow wire. It should also be mentioned explicitly that the feature "hollow wire" does not preclude filling its interior with a material that differs from the material of the wall, so that the hollow wire becomes a kind of "composite wire".

It is also essential to the invention to design the thin wall of the hollow wire in such a way that the superelastic property is achieved in the case of bending. Thus, due to the thin wall of the core originating superposition effect on the power plateau is significantly reduced not only in train, but also during bending and twisting. Using the invention, the desired constant superelastic force plateau can be approached much better in bending or in the orthodontic treatment than is the case with a solid wire. This applies all the more, the thinner the wall of the hollow wire. The outer dimensions of the wire pieces that can be used for the purposes mentioned are approximately between 0.1 mm and 2 mm, whereby the range between 0.2 mm and 1 mm is to be preferred. The wall thickness of the relatively thin-walled wall according to the invention is approximately between 1 .mu.m and 100 .mu.m, in particular between 5 .mu.m and 50 .mu.m. It is particularly advantageous to manufacture the wall of NiTi or NiTiX, wherein X is in particular Cu, Pd, Hf, Zr, Nb or Fe.

In order to minimize the risk of kinking which exists with such thin-walled hollow wires, which severely impairs the use for orthodontic applications, it is advantageous to provide the hollow wire with a filling (core) of a material, wherein the flexural elastic modulus of the core is generally smaller, in particular is at least 10 times smaller than the flexural modulus of elasticity of the superelastic material of the wall.

Furthermore, it is advantageous if the soul is surrounded by the wall positively and / or non-positively. This will be one for the mentioned areas of application suitable composite material in the manner of a composite wire of thickness between about 0.01 mm and 5 mm created. The core within the wall has a relatively low modulus of elasticity when bent between about 1 MPa and 80 GPa. It does not depend on the geometry of the cross-section of the wall. This can be round, oval or angular. Such composite wires may have, for example, a NiTi wall and a soft polymer core.

The advantages of the invention result from the fact that the wire according to the invention reaches the plateau within which the desired superelastic properties occur, in particular during a bend in a customary degree in orthodontics. Optimized conditions can be used to achieve a superelastic hysteresis at a body temperature of 37 ° C. In addition, the orthodontic arc having such a hollow wire, in particular in the case of the composite wires, is characterized by a high kink resistance and can thus be bent into almost any shape. Thus, orthodontic arches can be formed with the desired force and bending moment consistency. The invention thus contributes to increasing the success of particular orthodontic treatments, but the fields of application of the wire or the wire pieces are almost unlimited. These are precisely because of the good compatibility of the preferred material NiTi especially in medicine, where they can be used as "mitwachsende" stabilizers or fasteners.

Another important idea of the invention is to produce the shape memory alloy wall in a sputtering process. Two approaches are conceivable for producing the composite wires according to the invention using the sputtering technique: One approach is the planar sacrificial layer method, as described in DE 199 48 199 A1. The deposition of sputtered NiTi layers on the polymer films disclosed therein, however, has the disadvantage that this method does not provide all-round coating.

In contrast, the immediate all-round coating of correspondingly profiled polymeric substrates with a layer of Shape memory alloy possible. In this method, however, pay attention to the temperature resistance of the polymers used.

In order to avoid the disadvantages mentioned, according to the invention a core of sacrificial material, for example a capillary or a tube made of copper or brass, with shape memory alloy with superelastic properties, in particular with NiTi, coated all around. As described below, the core or the core of the unwanted foreign material is dissolved in an acid bath following the sputtering and subsequently the possibly required annealing treatment and replaced by a soft polymer core. This can be poured or pulled, for example, in the bore of the wire. It is advantageous if the wall of the wire piece surrounds the soul directly and in particular non-positively. As materials for the soul nylon, Perlon, silicone, polyimide, epoxy resin or dental glue are recommended. It is also possible to manufacture the core from monofilament and / or multifilament polymer threads, which in turn can also be cast in, so that the core itself forms a composite material.

The wires according to the invention are in particular in the following dimensions: The wall thicknesses of the shape memory alloy are in the range between 1 .mu.m and 100 .mu.m, the range between 5 .mu.m and 50 .mu.m being preferred. The outer dimension is in the range between 0.1 mm and 2 mm, with the range between 0.2 mm and 1 mm being preferred. The flexural modulus of elasticity of the filler is in the range between 100 kPa and 80 GPa, with the range between 100 MPa and 2 GPa being particularly preferred. The lengths of the wires to be produced are in the order of several centimeters, with the customary in orthodontics dimensions of about 10 cm to 20 cm can be easily manufactured with the proposed method. Also wire lengths of the order of a meter are conceivable. The length of the unfilled hollow wires, in particular, are not fundamentally limited during production. Hereinafter, an embodiment of the invention with reference to Figures 1 to 3 explained in more detail. Show it:

FIG. 1 four stages of the production of a composite wire suitable for an orthodontic arch,

Figure 2 is a diagram of a bending test and

Figure 3 hysteresis curves of a composite wire and a conventional wire

FIG. 1 shows, in four stages, the production of a polymer-filled hollow wire whose wall consists of shape memory alloy with superelastic behavior. In general, the deposition of the alloy takes place by means of the known physical deposition methods, preferably with the known methods of sputtering or cathode sputtering. For the production of crystalline layers is deposited either on a heated substrate at least 450 ⁰ C or it is carried out after the sputtering solution annealing at about 500-700 ⁰ C.

According to the invention, a tube with a circular, rectangular or oval cross-section is produced by sputtering technique as follows: First, a piece of wire or a capillary 1 (FIG. 1a) made of sacrificial material, for example a commercially available copper capillary, is provided as substrate (blank). This is round-coated in a following step (FIG. 1 b). For this purpose, for example, the sputtering substrate 1 is set in rotation (arrow A) and a directed coating by sputtering (arrows 2) performed. On the substrate 1, the FG alloy 3, here made of NiTi, adhere.

Subsequently (FIG. 1 c), the circularly coated sacrificial substrate is removed by using a selective solvent 4, which is located in a vessel 5. In the case of the NiTi-coated copper electrode, 30% nitric acid is used. It can be seen how the copper 6 dissolves.

The crystallization of the sputtered shape memory layer occurs before or after the selective wet chemical etching. Finally that will be soft core material introduced into the hollow wire. For this purpose, it is possible, for example, to coat a nylon or Perlonfaden 7 or an interlacing of several threads with an adhesive to introduce it into the hollow wire 3 and to let dry there. Alternatively, a two-component adhesive, such as an epoxy resin or other single-component air-curing adhesive, may be filled into the hollow wire 3 (Figure 1d).

With the method, wires according to the invention were created by a continuous deposition process of NiTi on a rotating copper capillary. After crystallization and dissolution of the copper core using nitric acid, a self-supporting NiTi capillary was created which was filled with polyamide wire. The modulus of elasticity of the soft core material was considered negligible compared to the Young's modulus of NiTi.

The super-elastic force plateau of a wire according to the invention is determined at about 37 ° C by means of a 3-point bending test (Figure 2) with a central load and a support distance of 10mm. The piece of wire to be tested is bent centrally up to 3.1 mm and the required bending force during loading and unloading is measured. The force plateau is considered to be sufficiently therapeutically desirable and constant, in particular, if, on unloading, the change in bending force in the region between the deflection at 2.0 mm and the deflection at 1.0 mm does not exceed 20% of the bending force at 2.0 mm and the bending force at 2.0 mm does not exceed 5N.

In the linear elastic range of the bending curve, the bending elastic modulus E is calculated according to the following equation, where F is the bending force [N], L is the bearing distance [mm], I is the area moment of inertia [mm ² ] and δ is the deflection [mm].

E = 1/48 ^■ [(F-L ³ ) / (I-δ)]

In Figure 3, the bending behavior (hysteresis) 8 of a composite with a rectangular NiTi tube of cross section 400 microns x 560 microns, which is filled with nylon, schematically compared to the hysteresis 9 of an orthodontic NiTi solid wire at body temperature of 37 ⁰ C shown. Plotted are the deflection in mm against the bending force in N. The load branches 10 and the unloading behavior 11 are shown. While in the case of the hysteresis 9 hardly a visible plateau can be seen, in particular in the particularly interesting unloading branch 11a, the unloading branch 11b shows a pronounced constant plateau 12.

Claims

claims

An orthodontic arch for use in orthodontics for correcting malocclusions comprising a hollow wire or a hollow piece of wire having a shape memory alloy thin wall, the thin wall of the wire or wire having superelastic properties.

2. bow according to claim 1, characterized by a nearly constant restoring force at a bend at body temperature.

3. sheet according to claim 1 or 2, characterized in that the piece of wire outer dimensions between 0, 1 mm and 2 mm, in particular between 0.2 mm and 1 mm, wherein the wall between 1 .mu.m and 100 .mu.m, in particular between 5 microns and 50 microns, strong.

4. bow according to one of the preceding claims, characterized in that the wall of the wire or piece of wire surrounds a soul of filling material, wherein the bending elastic modulus of the soul is smaller, in particular less than one tenth, of the bending elastic modulus of the wall.

5. Sheet according to one of the preceding claims, characterized in that the bending elastic modulus of the filling material is in the range between 100 kPa and 80 GPa, in particular between 100 MPa and 2 GPa ₁ .

6. bow according to one of the preceding claims, characterized in that the wall of the wire piece force and / or positively surrounding the soul.

7. bow according to one of the preceding claims, characterized in that the core of polymer, in particular nylon, Perlon, silicone, polyimide, epoxy resin or a dental adhesive, is made.

8. bow according to claim 7, characterized in that the core is made of monofilament and / or multifilament polymer threads.

9. bow according to one of the preceding claims, characterized in that the soul itself forms a composite of different materials, in particular one or more threads are cast in a polymer.

10. arc according to one of the preceding claims, characterized in that the wall consists of NiTi or NiTiX, wherein X is in particular Cu, Pd, Hf, Zr, Nb or Fe.

11. bow according to one of the preceding claims, characterized in that the soul is introduced after the manufacture of the wall in the hollow wire formed by the wall.

12. bow according to one of the preceding claims, characterized in that the soul is coated directly with the shape memory alloy.

13. Sheet according to one of the preceding claims, characterized in that in a 3-point bending test at 37 ° C with a central load and a support distance of 10 mm after a load to the deflection of 3.1 mm and subsequent discharge the measured Change in bending force in the range between the deflection at 2.0 mm and the deflection at 1, 0 mm is not more than 20% of the bending force at 2.0 mm and the bending force at 2.0 mm does not exceed 5N.

14. A method for producing a piece of wire for an orthodontic arch according to one of the preceding claims, characterized in that initially a blank (1) made of sacrificial material is provided that the blank in a deposition process, in particular in a sputtering process, with the shape memory alloy (3 ) is coated, that the blank (1) with a selective solvent (4) is removed, wherein the wall (3) remains as a hollow wire, and that the soul (7) is introduced into the hollow wire formed by the wall (3).

15. The method according to claim 14, characterized in that the blank (1) is rotated in the beam (2) to be applied for the deposition of the substrate of the shape memory alloy.