Dentistry – Orthodontics – Bracket
Reexamination Certificate
1999-09-07
2001-05-08
Wilson, John J. (Department: 3732)
Dentistry
Orthodontics
Bracket
Reexamination Certificate
active
06227849
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to orthodontic appliances, and more particularly concerns unitary metal injection molded orthodontic brackets made of a nickel free metal alloy in order to alleviate nickel allergy reactions experienced by a small fraction of the population.
2. Description of Related Art
Orthodontic appliances, such as brackets, buccal tubes and the like, are typically applied to teeth by adhering the appliances to the surface of the teeth. Such appliances typically include archwire portions for receiving an archwire and ligature elastic bands to provide corrective forces to straighten and reposition the teeth. The orthodontic appliances include a base portion adapted to conform to the shape of the teeth to which they are applied. The orthodontic appliances are subjected to tension and other stresses that can cause weakening of the bonds of the appliances to the teeth, and distortions in the structure of the appliances. The appliances are also subjected to cleaning that can erode the adhesion between the appliances and the teeth to which they are bonded, and are further stressed by normal mastication, so that it is not uncommon for such appliances to break away from teeth after bonding.
While orthodontic brackets are frequently made of plastic, their strength can be increased by forming at least portions of them from metal. The metal portions are typically small, and can be made by metal injection molding as a unitary metal part that is bonded or welded to be integral with the bracket. Such bonding or welding is also subject to structural instability. One known orthodontic bracket that is metal injection molded to have a basic monoblock unitary construction includes a base with raised posts adapted for abutting the surface of the teeth. However, the posts are shaped into mushroom shaped buttons by cold working, which can distort the microstructure and mechanical properties of the raised posts that are involved with bonding to teeth. Cold working of such structures can also be relatively expensive and complicated. It would therefore be desirable to form a unitary orthodontic bracket by metal injection molding to provide greater definition of the complicated geometry of the bracket as well as a well-defined base pattern to provide for better adhesion to a tooth, and to make the bracket structurally more sound.
The metal alloys used for making orthodontic brackets typically include nickel, which provides the brackets with improved hardness. However, allergies to nickel are quite common, so that it would be desirable to form the bracket of an alloy composition that is formulated to qualify as nickel-free, containing less than 1% nickel, in order to alleviate allergic reactions to nickel. The present invention meets these needs.
SUMMARY OF THE INVENTION
Briefly, and in general terms, the present invention provides for an improved unitary metal injection molded orthodontic appliance that provides greater definition of the complicated geometry of the bracket as well as a well-defined base pattern that provides for better adhesion to a tooth, and makes the bracket structurally more sound. In addition, by making the unitary orthodontic appliance by metal injection molding, no secondary operations are required during the manufacturing process. The metal alloy composition of the orthodontic appliance is preferably a Stellite cobalt chromium alloy that is formulated to be substantially nickel-free, containing less than 1% nickel, in order to alleviate allergic reactions experienced by a small fraction of the population to nickel. While nickel improved hardness of the bracket, the trace element of carbon in conjunction with the elements of cobalt, chromium and molybdenum in the proposed alloy for the bracket also has significant effect on the hardness of the alloy.
In one preferred aspect, the invention accordingly provides for a unitary metal injection molded orthodontic bracket for straightening teeth. The orthodontic bracket comprises a unitary metal injection molded body including a bonding base adapted to adhere to a tooth surface, and an archwire slot adapted for receiving an archwire. The body is formed from a metal alloy having a composition consisting essentially of cobalt, chromium, and molybdenum, with nickel being present in an amount less than 1% by weight. In a currently preferred embodiment, the composition consists essentially of 59-69% by weight cobalt, 26-30% by weight chromium, 4-8% by weight molybdenum, and 2% or less by weight trace elements. The body also preferably includes a plurality of tiewings, and the bonding base has a bonding base pattern in the form of a plurality of rectangular or square pockets that are approximately 0.005 to 0.015 inch in size.
In another currently preferred embodiment, the unitary metal injection molded orthodontic appliance comprises a unitary metal injection molded body having a bonding base and a facebow tube for receiving wires for anchorage and straightening of the tooth. The body has a surface defining a primary archwire slot for receiving an archwire for anchorage and straightening of the tooth, and the body is formed from a metal alloy having a composition consisting essentially of cobalt, chromium, and molybdenum, with nickel being present in an amount less than 1% by weight. In a currently preferred embodiment, the composition consists essentially of 59-69% by weight cobalt, 26-30% by weight chromium, 4-8% by weight molybdenum, and 2% or less by weight trace elements. In another currently preferred aspect, the primary archwire slot includes an auxiliary archwire slot for receiving the archwire. The body also preferably includes a plurality of tiewings, and the bonding base has a bonding base pattern in the form of a plurality of rectangular or square pockets that are approximately 0.005 to 0.015 inch in size. In this embodiment, the orthodontic appliance is preferably adapted for application to first and second molar teeth, and is preferably a buccal tube bracket The facebow tube can have a round aperture for receiving a cylindrical wire, or a rectangular aperture for receiving an archwire.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.
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Brehm Lindsay W.
Huff Stephen M.
Kucheria Chhattar S.
Bumgarner Melba
Fulwider Patton Lee & Utecht LLP
Ortho Organizers, Inc.
Wilson John J.
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