WO2008119119A1

WO2008119119A1 - An orthodontic bracket

Info

Publication number: WO2008119119A1
Application number: PCT/AU2008/000450
Authority: WO
Inventors: M. Ali Darendeliler; David Armstrong
Original assignee: The University Of Sydney
Priority date: 2007-03-30
Filing date: 2008-03-28
Publication date: 2008-10-09

Abstract

An orthodontic bracket (100) comprises a face (20) and a base (10). Following the application of sufficient energy, the face can be repositioned with respect to the base.

Description

AN ORTHODONTIC BRACKET

Technical Field

An orthodontic bracket as well as a base and face for the bracket are disclosed.

Background

Orthodontic brackets are used in orthodontic treatments. They are bonded to the teeth of a patient using adhesive and feature a groove which receives a wire. Typically, a number of brackets are applied to adjacent teeth and a wire is passed through the grooves of the brackets to effect movement of teeth over a period of time. Initially a flexible wire is used and then, after a time when the teeth have become straighter, a stiff wire is passed through the bracket grooves.

As treatment progresses, it sometimes becomes desirable to adjust either the vertical position, mesio-distal position, or the tip of the groove of a bracket. This is done by debonding the bracket and rebonding a new replacement bracket in the desired position.

This need to debond brackets during treatment slows down treatment and can be costly in terms of clinical time, materials and patient inconvenience. It may also subject the tooth to increased enamel loss, which may predispose the tooth surface to demineralisation or caries.

When a bracket is debonded for repositioning, failure at the base-adhesive interface often results in adhesive remnants being firmly attached to the enamel. Removal of large amounts of adhesive remnants can be time consuming and may cause enamel surface damage. Rebonding a bracket can lead to a lower bond strength, which may lead to an increased chance of bond failure.

If the bracket is not repositioned then compensation bends need to be placed in the arch wire, which is time consuming and increases treatment time.

Summary of the Disclosure In a first aspect there is disclosed an orthodontic bracket that includes a face and a base. Following the application of sufficient energy, the face is repositionable with respect to the base.

In a second aspect there is disclosed a base for an orthodontic bracket, the base being adapted such that, following the application of sufficient energy, a face for the bracket can be repositioned with respect to the base.

In a third aspect there is disclosed a face for an orthodontic bracket, the face being adapted such that, following the application of sufficient energy, the face can be repositioned with respect to a base of the bracket.

In one form the base may include a layer of a material which is deformable following application of the sufficient energy.

In this form the base may include a substrate which remains in a solid state when the material is in a deformable state.

In one embodiment of this form the substrate may be formed from metal. The metal may be selected from nickel phosphor bronze, stainless steel, nickel titanium, titanium or gold alloy. However, it should be appreciated that the material for the substrate is not at all limited to a metal and may be formed from eg. a ceramic or polymer, etc that does not deform when the material is in a deformable state.

In another form the deformable material may comprise the base, whereby part of the base to which the face is connected deforms with the application of sufficient energy.

In one from the deformable material can comprise a polycarbonate, or a polystyrene. However, other materials can be employed including so-called smart plastics which change shape with the application of light thereto, or which have shape memory in that they can change shape in response to a temperature increase.

In this regard, the material may be of a type that deforms with the application of energy in the form of heat. Alternatively, it may deform in response to an electrical current applied thereto or therethrough, or responsive to incident electromagnetic radiation (such as UV-light), or responsive to a chemical reaction or change of chemical state, etc.

The base may include an undercut region which can provide mechanical engagement with the face The face may be repositionable to effect one of more of a vertical adjustment, a mesiodistal adjustment, a tip adjustment, or a bucco-lingual adjustment.

In one embodiment the face may also be formed from metal. The metal may again be selected from nickel phosphor bronze or stainless steel.

Brief Description of the Drawings

An embodiment of the orthodontic bracket will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure l is a top view of a base for an orthodontic bracket according to a first embodiment;

Figure 2 is an underside view of the base of Figure 1; Figure 3 is a side view of the base of Figure 1; Figure 4 is another side view of the base of Figure 1;

Figure 5 is a side view of a face for an orthodontic bracket according to the first embodiment;

Figure 6 is another side view of the face of Figure 5; Figure 7 is a top view of the face of Figure 5;

Figure 8 is an underside view of the face of Figure 5;

Figure 9 is a top view showing the base of Figure 1 assembled with the face of Figure 5;

Figure 10 is a side view of Figure 9; Figure 11 is another side view of Figure 9;

Figure 12 depicts the opposite side view of Figure 11;

Figures 13 A and 13B are respectively perspective and cross-sectional views of the substrate of Figure 1 ;

Figure 14 is a perspective view of the face shown in Figure 5; Figure 15 illustrates vertical, mesiodistal and tip adjustments;

Figure 16 is a side view of the orthodontic bracket of Figure 9 arranged on a tooth and illustrating schematically a bucco-lingual adjustment of the face with respect to the base; and

Figure 17 is a front view of the orthodontic bracket of Figure 16 arranged on a tooth and illustrating schematically a tip adjustment by rotating the face with respect to the base.

Detailed Description of Specific Embodiments

Direct bonding of orthodontic brackets was observed to be inaccurate and, without bending the archwire or repositioning the brackets to compensate for these errors, was observed to be almost impossible to achieve an acceptable occlusion. An orthodontic bracket was therefore developed for repositioning on the tooth surface without debonding, to address the inadequacies of current approaches.

Referring in this regard to Figures 1 to 4, a base 10 for such an orthodontic bracket is shown. Base 10 includes a substrate 11 formed from stainless steel.

Substrate 11 includes a recess 12 in which is housed a layer of a material which is deformable after application of sufficient heat energy in the form of polystyrene or polycarbonate 30.

Substrate 11 includes a series of projections 14 on one surface. This surface is intended to be bonded to a tooth in use and the projections provide a key for the bonding adhesive to improve bond strength.

Referring now to Figures 13A and 13B, substrate 11 is shown in further detail. It can be seen that an undercut region 32 is provided about recess 12. This undercut assists to retain the polystyrene and can provide mechanical engagement with a projection 22 of the face 20, by way of the projection becoming partially inserted into the undercut region. Depending upon the position of the face, this can increase the strength of a resulting bracket assembly.

To form base 10, the substrate 11 is first cast from stainless steel. A 0.8 mm thick sheet of polystyrene is cut to produce a piece 4mm x 4mm. The piece of polystyrene is placed onto substrate 11 overlying recess 12 and then the two are placed in an oven at 100 degrees centigrade, which is the glass transition temperature of the polystyrene. Once the polystyrene is softened, substrate 11 is removed from the oven, the polystyrene is packed into the undercut region 32 of the substrate, and the polystyrene 30 solidifies in recess 12.

Referring now to Figures 5 to 8, a face 20 for an orthodontic bracket is shown. Face 20 includes a projection 22 and tie wings 24. The tiewings define grooves 26 which have a generally square cross section. In use, these grooves receive an archwire of square cross section in a conventional manner. The tie wings can include undercuts for the placement of an O-ring to hold the archwire in place. Projection 22 is dimensioned to fit inside recess 12 of base 10 and to fit inside undercut region 32 as may be required, depending upon the position of face 20 with respect to base 10. The face 20 can also be modified to include hooking points for a tooth anchoring assembly. This can anchor the face and thus the tooth orientation with respect to eg. a user's jaw (eg. for facial reconstruction surgery). Hooks at the hooking points can be used for attachment of auxiliaries such as elastics or coil springs to move the teeth. Elastics can be used intra-arch or inter-arch. When coil springs are employed they are used inter-arch.

Face 20 is assembled to base 10 by pressing projection 22 into the polystyrene layer 30 whilst the face is being heated. The assembly is then re-introduced into the oven at 100 degrees centigrade for several minutes, removed and then allowed to cool. Upon cooling, polystyrene layer 30 hardens. The resulting assembly is an orthodontic bracket 100 and is shown in Figures 9 to 12 and 15 to 17.

Orthodontic bracket 100 fits to the teeth of a patient by bonding surface 14 to the teeth in the usual manner. During the course of orthodontic treatment, if it becomes desirable to adjust the position of groove 26, then adjustments can be effected without the need to debond the bracket. Instead, energy such as heat energy is applied to the bracket to raise the temperature of the polystyrene above its glass transition temperature. This allows deformation of the polystyrene and so the face 20 can be repositioned with respect to the base. When the polystyrene cools, it hardens and the groove 26 is fixed in its new position.

Referring to Figure 15, a bracket 100 is shown affixed to a schematic representation of a tooth 110. Whilst the polystyrene is deformable, the following adjustments can be made: • Vertical adjustment by moving the face in the direction of arrows A

• Mesiodistal adjustment by moving the face in the direction of arrows B

• Tip adjustment by rotating the face in the direction of arrows C

• A combination of any or all of the above

Referring to Figure 16 the bracket 100 is shown affixed to a tooth T. This Figure illustrates the face 20 being moved bucco-lingually from the base 10 whilst the polystyrene is deformable. This adjustment is desirable in some situations and can be achieved by twisting the wire so that a section is rotated relative to the rest of the wire whilst remaining in the same plane. It can be referred to as "torque" and moves the root buccally (buccal/labial root torque) or lingually/palatally (palatal/lingual root torque). The movement can be considered as a modification of the slot relative to the base so as to effect a change in the torque (buccal/ labial root torque or palatal/lingual root torque). The lines in Figure 16 also demonstrate that the force on the bracket base is not a 100% shear despite a force being applied parallel to the long axis of the teeth.

Referring to Figure 17 the bracket 100 is also shown affixed to a tooth T. This Figure illustrates the face 20 being rotated with respect to the base 10 whilst the polystyrene is deformable.

In the above described embodiment the intermediate material used was polystyrene or polycarbonate. Similarly, other intermediate materials could be used including poly(vinylchloride), poly(methyl methacrylate), poly(ether ketone), etc. One factor for material selection is that the glass transition temperature of the material is higher than the highest extreme temperature experienced in the mouth, which is approximately 70°C.

The intermediate material may optionally be in the form of a so-called "smart plastic" which can automatically change shape in response to energy sources such as eg. light and/or temperature and/or chemical sources. Such plastics can include molecular "switches" which can comprise photosensitive groups that are grafted onto a polymer network. In one example the resulting photosensitive polymer can have an external stress applied thereto when the bracket is first formed so that, when illuminated with ultraviolet light of a certain wavelength, the molecular switches crosslink, or bind one to another, causing a predetermined shift (eg. one of more of a vertical adjustment, a mesiodistal adjustment, a tip adjustment, an angled adjustment). In the above described embodiment the substrate and face were formed from stainless steel. Similarly, they could be formed from nickel phosphor bronze.

In other embodiments the substrate and face may be formed from materials such as plastic, ceramic or titanium based materials (aesthetic, bio-compatible and anti- allergic).

In another embodiment, the base is formed entirely from the intermediate material. In yet a further embodiment, the base and face are formed entirely from the intermediate material whereby movement of the face is caused by eg. deforming just a certain intermediate region of the material (such as through the use of a smart plastic). Any reference to prior art contained herein is not to be taken as an admission that the information forms a part of the general knowledge of a person of ordinary skill in the art.

Finally, it is to be appreciated that various alterations or additions may be made to the parts previously described without departing from the spirit or ambit of the orthodontic bracket described herein.

In the claims which follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the orthodontic bracket.

Claims

1. An orthodontic bracket comprising: a face; a base; wherein, following the application of sufficient energy, the face is repositionable with respect to the base.

2. A base for an orthodontic bracket, the base being adapted such that, following the application of sufficient energy, a face for the bracket can be repositioned with respect to the base.

3. A face for an orthodontic bracket, the face being adapted such that, following the application of sufficient energy, the face can be repositioned with respect to a base of the bracket.

4. A bracket, base or face according to any one of the preceding claims wherein the base includes a layer of a material which is deformable following the application of sufficient energy.

5. A bracket, base or face according to claim 4 wherein the deformable material is polystyrene or polycarbonate.

6. A bracket, base or face according to claim 4 or 5 wherein the base includes a substrate which remains in a solid state when the layer of material becomes deformable.

7. A bracket, base or face according to claim 6 wherein the substrate is formed from metal.

8. A bracket, base or face according to claim 7 wherein the metal is selected from nickel phosphor bronze, stainless steel, nickel titanium, titanium or gold alloy.

9. A bracket, base or face according to any one of the preceding claims wherein the base includes an undercut region which can provide mechanical engagement with the face.

10. A bracket, base or face according to any one of the preceding claims wherein the face is repositionable to effect one or more of a vertical adjustment, a mesiodistal adjustment, a tip adjustment, or a bucco-lingual adjustment.