WO2005094715A1

WO2005094715A1 - Coated orthodontic bracket

Info

Publication number: WO2005094715A1
Application number: PCT/SE2004/000524
Authority: WO
Inventors: Göran STEEN
Original assignee: Gestenco International Ab
Priority date: 2004-04-02
Filing date: 2004-04-02
Publication date: 2005-10-13

Abstract

An orthodontic bracket having a bracket body (2) of plastic material and having a first surface that is an attachment surface (3) for attaching said bracket to a tooth and a second surface that is an engagement surface (4) adapted to cooperate with an orthodontic appliance such as an archwire (5). The engagement surface has a coating (13) comprising a ceramic material and said coating has a thickness of from 0.05 to 10.0 µm, preferably from 0.5 to 8.0 µm and most preferably from 1.0 to 5.0 µm.

Description

Coated Orthodontic Bracket

TECHNICAL AREA

The invention pertains to an improved orthodontic bracket having a bracket body of plastic material and having a first surface that is an attachment surface for attaching said bracket to a tooth and a second surface that is an engagement surface adapted to cooperate with an orthodontic appliance such as an archwire.

BACKGROUND

Orthodontic appliances such as brackets have been made from a number of different materials. When designing an orthodontic bracket, it is desired that the properties of the chosen material are such as to provide an optimum combination of strength and durability of the material, bondability to teeth, resiliency, brittleness, cost, aesthetic qualities, structural stability and ease of manufacture and maintenance.

Orthodontic brackets have historically been manufactured from various types of metals. Metal brackets exhibit excellent strength characteristics, but are expensive and complicated to manufacture. Further, they are generally perceived as less aesthetically acceptable than modern brackets made from plastic materials or ceramics.

An advantage with plastic brackets is that they can be made transparent or can be made to closely match the colour of the teeth. Moreover, plastic brackets are biocompatible, resilient and non-abrasive and are less likely to cause damage to the teeth than harder materials such as ceramics and metal. In addition, plastic brackets are comparatively inexpensive to manufacture and offer the possibility of making complicated structures with simple production methods. However, the plastic materials are soft and deformable and exhibit poor durability. Moreover, when exposed to substances in drink and food, plastic brackets are subject to aging and discolouration. Hence, plastic brackets are less suitable for use in long-term treatment or for treatment requiring a material that can withstand high mechanical tension.

Ceramic brackets are less subjected to staining and have a better-lasting aesthetic appearance than plastic brackets. In addition, ceramics are strong and more durable than plastics. However, ceramic materials are brittle and hard and may cause damage when in contact with teeth or when removed from the teeth. Further, ceramic brackets have drawbacks with regard to their bonding properties and abrasiveness in contact with teeth and dental appliances such as archwires.

It has been proposed to increase the strength of plastic brackets by incorporating organic or inorganic fillers such as colloidal oxides and inorganic fibres and/or whiskers. Such reinforced bracket bodies are disclosed in US 5,078,596 and in US 5,707,231. US 5,078,596 also discloses the possibility of supplementing the internal reinforcement with a protective coating. Although such reinforced plastic brackets offer higher strength, some of the advantages of a plastic structure are lost at the same time.

Accordingly, there still exists a need for an improved plastic bracket, having greater strength and stain resistance than previously known plastic brackets in combination with high resiliency, bondability and low abrasiveness.

DISCLOSURE OF INVENTION

In accordance with the invention, an orthodontic bracket is offered having a bracket body of plastic material and having a first surface that is an attachment surface for attaching said bracket to a tooth and a second surface adapted to cooperate with an orthodontic appliance such as an archwire. The bracket according to the invention is primarily distinguished in that the engagement surface has a coating comprising a ceramic material and in that said coating has a thickness of from 0.05 to 10.0 μm, preferably from 0.5 to 8.0 μm and most preferably from 1.0 to 5.0 μm.

The extremely thin coating in accordance with the invention gives the bracket surprisingly high strength, durability and resistance to staining and discolouration without substantially negatively affecting the bondability and resilience of the plastic bracket body. Moreover, the contact surface between the orthodontic bracket and an orthodontic appliance shows considerably lower friction than has previously been possible to achieve, particularly for ceramic brackets. One problem encountered in tooth correction treatment is that when using orthodontic brackets cooperating with an archwire, the slot in the bracket accommodating the archwire exerts high friction on the archwire. However, with an orthodontic bracket in accordance with the invention, the risk of damaging or breaking the archwire is greatly reduced due to the low friction between the bracket and the archwire. Moreover, there is also a reduced risk of damaging the root of a treated tooth since the low-friction brackets in accordance with the invention require less applied force in order to move the tooth.

Hence, the orthodontic bracket in accordance with the invention combines the advantages of a plastic bracket with the advantages of a ceramic bracket.

The coating preferably comprises a ceramic material such as aluminum oxide, silica, aluminum hydroxide, wollastonite, spinel, titanium oxide, magnesioum oxide, zirconium oxide and mixtures thereof.

The coating is preferably made by a Physical Vapour Deposition (PVD) technique. PVD is the common name of a family of coating methods including sputtering and evaporation. These coating methods offer a way of producing thin, strong, even and smooth coatings.

The coating can be applied in a uniform layer of uniform thickness. Alternatively, the coating can be applied only to selected parts of the orthodontic bracket and/or with different thickness in different areas of the coating. It may be desirable to provide parts of the bracket that are exposed to more severe wear conditions with a thicker layer of coating material than other, less exposed parts of the bracket. By selectively coating critical parts of the bracket with a thicker layer of inorganic or ceramic polymer coating, optimum strength can be achieved in those parts while maintaining high resiliency and low brittleness in the remaining part of the bracket.

The bracket body is preferably made from a plastic material such as polycarbonate, polysulphone, polyetherketone (PEEK), polyethylene terephthalate (PETG), polyacrylates and mixtures thereof. The bracket body may contain reinforcement material such as glass fibres and ceramic and/or inorganic fillers preferably in an amount of 10-20 % by weight of the bracket body.

Further, the coating offers a possibility of adjusting the colour of the brackets to match the colour of the wearer's teeth.

DESCRIPTION OF FIGURES

The invention will be described in more detail in the following with reference to the embodiments shown on the appended drawings, in which:

Fig. 1 shows a top view of an orthodontic bracket according to a first embodiment of the invention, Fig. 2 shows the orthodontic bracket in Fig. 1 with an applied archwire,

Fig. 3 shows a cross-section through the orthodontic bracket in Fig. 1 taken along the line Ill-Ill, and

Fig. 4 shows an orthodontic bracket according to a second embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

The orthodontic bracket 1 shown in Figs. 1 -3 has a bracket body 2 with a slightly curved attachment surface 3 adapted for attachment to a tooth and an engagement surface 4 for engagement with an archwire 5. The engagement surface 4 is provided with four wings or hooks 6, 7, 8, 9, arranged in opposing pairs on each side of a central groove or slot 10. The wings are arranged to cooperate with locking loops 11 (only one shown in Fig. 1 ) to lock the archwire 4 in a central groove 10 on the engagement surface 4.

The bracket body is preferably made of a polymer matrix chosen from high- strength polymers such as polycarbonate, polysulphone, polyetherketone (PEEK), polyethylene terephthalate (PETG), polyacrylates and mixtures thereof. A preferred material for the bracket body is polyethylene terephthalate/polycarbonate containing reinforcing glass fibres. The bracket body 1 has a thin coating 13 in the comprising a ceramic material chosen among aluminum oxide (AI₂O₃), silica, aluminum hydroxide, wollastonite, spinel, titanium oxide, magnesioum oxide, zirconium oxide and mixtures thereof. The coating 13 has a thickness of from 0.1 to 10.0 μm, preferably from 0.5 to 8.0 μm and most preferably from 1.0 to 5.0 μm. Such coatings are preferably applied by means of a Physical Vapour Deposition (PVD) method.

The coating 13 improves the hardness, durability and wear resistance of the bracket and shows surprisingly low friction against the materials commonly used in orthodontic appliances. Moreover, the coating protects the bracket against staining and aging due to the chemical influence from tobacco and ingested food-stuffs and drinks. The coating 13 covers only the engagement surface 4, leaving the attachment surface 3 free of coating material. In this manner, the coating 13 does not affect the bonding characteristics of the plastic material in the bracket body 1. Furthermore, although the very thin coating 13 increases the strength of the bracket body 2, it does not severely affect the resiliency of the bracket body 2. Hence, the coated bracket maintains a high degree of resiliency while exhibiting many of the advantages of a ceramic bracket. Thus, although the bracket is strong and durable, it is less likely to cause trauma to the teeth for instance when the patient happens to bite on the bracket. Further, the coated plastic bracket in accordance with the invention is less abrasive and can be manufactured more easily and at a lower cost than a corresponding ceramic bracket.

The bracket 1 can have a substantially uniform coating 13 with a uniform thickness. Alternatively, the thickness of the coating may differ between different parts of the coating 13. It may, for instance, be advantageous to apply a coating 13 of a somewhat greater thickness to those areas of the bracket that are most subjected to abrasive forces. Hence, the central channel 10 and/or the parts of the wings 6-8 engaging with the locking loop 11 may have a coating of greater thickness than the remaining parts of the engagement surface 3. Accordingly, in parts where a higher resistance to wear is desired, the coating 13 preferably has a thickness of from 5.0 to 10.0 μm while in parts of the engagement surface where basically only stain resistance and a somewhat higher rigidity is needed, the coating 13 preferably has a thickness of from 0.05 to 5.0 μm.

The bracket 1 shown in Fig. 4 is of a different type from that shown in Figs. 1- 3. The bracket 1 has bracket body 2 with a slightly curved attachment surface 3, and an engagement surface 4 having a groove 10 for an archwire (not shown in Fig. 4). The archwire is fastened to the bracket 1 by means of a locking clasp 14 which is movable around a hinge 15 placed on one side of the groove 10 and is arranged to cooperate with locking members 17 located on the opposite side of the groove.

The bracket 1 in Fig. 4 has a thin coating 13 of the same kind as the coating 13 shown in Figs. 1 -3. As previously discussed, the coating 13 can be of uniform thickness or can have a greater thickness in those areas of the brackets that will be most exposed to wear. For instance, the surface of the groove 10 and the parts of the locking clasp 14 that will be in contact with the archwire when the bracket is mounted on a tooth can have a thicker coating than the outwardly facing parts of the engagement surface 4.

The invention is not restricted to the embodiments described herein. Hence, further modifications and variations are conceivable within the scope of the appended claims.

Claims

1. An orthodontic bracket having a bracket body (2) of plastic material and having a first surface that is an attachment surface (3) for attaching said bracket to a tooth and a second surface that is an engagement surface (4) adapted to cooperate with an orthodontic appliance such as an archwire (5), characterized in that the engagement surface has a coating (13) comprising a ceramic material and in that said coating has a thickness of from 0.05 to 10.0 μm, preferably from 0.5 to 8.0 μm and most preferably from 1.0 to 5.0 μm.

2. An orthodontic bracket according to claim 1, characterized in that the bracket body (2) comprises a polymer matrix chosen from polycarbonate, polysulphone, polyetherketone (PEEK), polyethylene terephthalate (PETG), polyacrylates and mixtures thereof.

3. An orthodontic bracket according to claim 2, characterized in that the bracket body (2) comprises reinforcement material such as glass fibres, ceramic fillers, inorganic fillers and mixtures thereof.

4. An orthodontic bracket according to claim 1, 2 or 3, characterized in that the coating (12) comprises ceramic material chosen among aluminum oxide, silica, aluminum hydroxide, wollastonite, spinel, titanium oxide, magnesioum oxide, zirconium oxide and mixtures thereof.

5. An orthodontic bracket according to any one of the preceding claims, characterized in that the coating (13) has different thickness in different areas.

6. An orthodontic bracket according to any one of the preceding claims, characterized in that the coating has been applied to the bracket body (2) by means of a Physical Vapour Deposition (PVD) method.

7. An orthodontic bracket according to any one of the preceding claims, characterized in that the bracket body (2) comprises a polycarbonate or polyethylene terephthalate/polycarbonate matrix containing reinforcing glass fibres.

8. An orthodontic bracket according to any one of the preceding claims, characterized in that the bracket body (2) comprises a polymer matrix containing 10-20 % by weight of a reinforcing filler.