WO2000007516A2

WO2000007516A2 - Orthodontic devices

Info

Publication number: WO2000007516A2
Application number: PCT/GB1999/002543
Authority: WO
Inventors: Antony Walter Anson
Original assignee: Anson Medical Ltd.
Priority date: 1998-08-03
Filing date: 1999-08-03
Publication date: 2000-02-17
Also published as: AU5183399A; GB9816803D0; WO2000007516A3

Abstract

The use of diamond-like carbon as an abrasion resistant barrier coating to inhibit the leaching of toxic components from an orthodontic device into the mouth of a user. An orthodontic device comprising means for attaching the device to a user's teeth and a tensioning element in contact with said means wherein at least one of said means and said tensioning element has a surface finish of from RA=0.01 νm to RA=0.5 νm.

Description

ORTHODONTIC DEVICES

This disclosure relates to improvements to orthodontic teeth correction devices that are used to correct misaligned or unevenly spaced teeth. In particular, it relates to the use of diamond-like carbon as a coating on orthodontic devices, and the provision of specific surface finishes. Various forms of arch-wires, torsion springs and tensioning devices will benefit from these improvements based upon the use of a diffusion barrier and abrasion resistant coating to reduce potential device wear and to prevent the leaching of toxic materials from the prostheses to the organism.

Orthodontic arch wires apply corrective forces to teeth that are misaligned or that protrude. The wires may be constructed of stainless-steel or other metal alloys that have suitable elastic recovery properties such as nickel-titanium or nickel-titanium-copper-chromium, super elastic alloy. The arch wire is attached at the rear of the teeth by a fixation bracket.

The wire is guided and retained by a series of brackets attached to the teeth, generally by adhesive means.

The super elastic alloys have an advantage over other metal alloys when used as arch-wires because of their elastic properties; the material is elastically extensible, the range of elastic recovery being larger than other commonly used metal alloys.

For orthodontic applications the flexural characteristic of the alloy will accommodate considerable amounts of elastic-tension relaxation but, because of extended elastic properties, the super-elastic materials will continue to produce corrective forces, this means a reduced number of visits to an orthodontist to re-tension the arch-wires. Arch-wires are fixed to the rear teeth using brackets or other established forms of mechanical fixation. The wires are guided around the teeth by small captive brackets that have an open or closed eyelet arrangement within which the wire resides. However, when the wire is tensioned and the teeth are caused to move due to said tensioning force, the corrective movement facilitated by teeth relaxing under tension also means the length of the arch-wires reduces as tension reduces. Archwire movement is relative to the teeth and fixing brackets. Friction between the archwire and bracket, due to high point-contact forces, can cause an indentation to occur in the archwire where it makes contact with the fixing brackets. The developing notch or indentation in the wire has the effect of locking the wire in place, effectively preventing or limiting further movement between archwire and teeth.

A method of preventing the archwire notching effect is to coat the archwire with an abrasion resistant material that is both hard and with suitable lubricious qualities to enable the archwire to slide across or through its captive bracket.

A suitable coating material and preferred embodiment is Diamond-Like-Carbon. This amorphous carbon material, applied by plasma chemical vapour deposition (PCVD) techniques, is pure carbon applied to a suitable substrate in a thickness range of between 10 A (angstrom) and 3μm (micron). In practice, the thinnest layer of DLC applied is 250 A, preferably 500 A. The preferred thickness coating is lμm. The dense, homogeneous carbon coating can also act as a diffusion barrier, preventing leaching of toxic substances from the arch-wire such as nickel or chrome. Equally, the diffusion barrier can protect the arch-wires from degradation due to contact with saliva and other body fluids.

An orthodontic archwire of circular, square or rectangular section has a coating of diamondlike carbon, preferably with a thickness of between 500 A to 3μm. Equally, other teeth correction devices such as torsion devices to untwist teeth which have developed with an abnormal rotation or devices that can normalise unequal spacing between teeth, may benefit from DLC coating. However, in the case of the torsion or direct linear movement devices, abrasion resistance is of secondary consideration, of primary interest is the diffusion barrier characteristic derived from the diamond-like film coating.

In one aspect of the present invention, there is provided an orthodontic device comprising means for attaching the device to a user's teeth and a tensioning element in contact with said means wherein at least one of said means and said tensioning element has a surface finish of from RA=0.01μm to RA=0.5μm.

It has been discovered that, surprisingly, when either the tensioning wires or the retention brackets are given a specific surface finish, the resulting device functions much better than existing devices. The surface finish is measured on the RA scale, which is the standard scale known in the art, and is a measure of the distance from the peak to trough of indentations on the surface of the device.

Embodiments of the present invention will be described by way of example with reference to the drawings :-

Fig. 1 shows in plan, teeth [6] in the upper jaw with an archwire [5] in tension, fixed at the rear teeth by means of a fixation bracket [7] . The archwire is guided around the teeth by brackets [8] which maintain the spatial relationship of teeth to archwire.

Fig. 2 shows in section, a tooth [4] with a guiding bracket [2] and archwire [1] held inside the guiding bracket eyelet. Due to tension, the archwire on entry and exit pushes against the guiding bracket leading or trailing edge [3]. Fig. 3 shows schematically an arch wire [10] with indentations [9] and [11] caused by point contact force due to the arch wire under tension being in firm contact with the guiding bracket leading trailing edges.

Claims

1. The use of diamond-like carbon as an abrasion resistant barrier coating to inhibit the leaching of toxic components from an orthodontic device into the mouth of a user.

2. The use as claimed in claim 1 wherein the orthodontic device is formed from a shape memory alloy.

3. The use as claimed in claim 1 or 2, wherein the orthodontic device is formed from nickel-titanium alloy.

4. An orthodontic device comprising means for attaching the device to a user's teeth and a tensioning element in contact with said means wherein at least one of said means and said tensioning element has a surface finish of from RA=0.01╬╝m to RA=0.5╬╝m.

5. An orthodontic device as claimed in claim 4 wherein said surface finish is RA=0.1╬╝m.

6. An orthodontic device as claimed in claim 4 or 5, wherein at least one of said means and said tensioning element has been coated with diamond-like carbon.

7. A device as claimed in claim 6 wherein the thickness of said coating is from 25╬╕A to 3╬╝m.

8. A device as claimed in claim 7, wherein said thickness is l╬╝m.

9. A device as claimed in any of claims 4 to 8, wherein the tension element is formed from a shape memory alloy.