Dentistry – Orthodontics – Bracket
Reexamination Certificate
2000-06-16
2001-08-28
Lucchesi, Nicholas D. (Department: 3732)
Dentistry
Orthodontics
Bracket
C433S006000, C433S017000, C433S018000, C433S020000
Reexamination Certificate
active
06280185
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention broadly relates to an appliance that is used in the oral cavity during the course of orthodontic treatment. More particularly, the present invention is directed to an orthodontic appliance that is made at least in part from a precipitation hardening martensitic stainless steel alloy.
2. Description of the Related Art
Orthodontic treatment involves movement of malpositioned teeth to orthodontically correct locations for improved occlusion and an improved aesthetic appearance. In certain types of orthodontic treatment programs, a system of appliances commonly known as “braces” is utilized by the orthodontist to effect movement of the teeth. Typically, braces include a set of tiny appliances known as brackets as well as archwires that are adapted to fit into slots of the brackets.
In many orthodontic treatment programs, a bracket is affixed directly to each of the patient's anterior, cuspid and bicuspid teeth, and buccal tubes are mounted on the patient's molar teeth. An archwire is then ligated into the slot of each bracket using short wire ties or ring-shaped elastomeric ligatures. Ends of the archwire are inserted into passages of the buccal tubes. The archwire forms a track to guide movement of the brackets and hence movement of the associated teeth to desired positions.
Orthodontic brackets are commonly made of metal, plastic or ceramic. Plastic and ceramic brackets that are made of transparent or translucent material are preferred by some patients and practitioners, because the color of the tooth may be visible through the bracket. As a result, such brackets are less noticeable in ordinary view.
However, plastic brackets are often considered unsatisfactory for one reason or another. Plastic material tends to creep and deform over a period of time when subjected to stress. As a consequence, the archwire slot of plastic brackets may widen during use to such an extent that precise control over movement of the teeth is lost. Additionally, some plastic materials tend to stain and discolor when exposed to certain foods and beverages such as mustard, spaghetti sauce, blueberries, coffee, tea and the like.
Orthodontic brackets that are made of ceramic materials are also deemed unsatisfactory by some practitioners and patients. Ceramic materials are generally considered very hard and brittle, and may wear away the enamel of opposing teeth if the brackets contact the enamel as the patient's jaws are closed. Additionally, the ceramic material may tend to fracture if the bracket is subjected to relatively large force, such as when the patient bites into a hard food object such as a peach pit. Certain ceramic brackets are well-constructed and overcome these difficulties, but are somewhat more expensive than brackets made of metallic materials.
As a result, metal brackets remain the appliances of choice for many orthodontists. Metal brackets are relatively low in cost, and yet have sufficient strength to withstand the forces typically encountered during treatment without breakage. Additionally, many practitioners have developed certain treatment techniques after many years of practice, and prefer to keep using metal brackets in their practice so that they can be assured that the teeth will move efficiently to their intended positions and the expected outcome of treatment can be reliably achieved without undue delay.
Over the years, many orthodontic appliances including brackets, buccal tubes and archwires have been made of stainless steel alloys. Examples of such stainless steel alloys include Series 300, Series 400 and 17-4 PH. Such alloys are relatively inexpensive, corrosion resistant and machinable with conventional apparatus.
Other metal alloys have also been suggested for use in orthodontic appliances. For example, U.S. Pat. Nos. 5,947,723 and 5,232,361 describe appliances made of titanium alloys. Orthodontic appliances made of beta-titanium alloys are described in U.S. Pat. No. 4,197,643 and PCT Published Application No. WO 99/45161.
Unfortunately, conventional metal brackets are not considered in general as aesthetic as plastic or ceramic brackets. Many metal brackets are easily visible in use, causing a condition known as a “tin grin” or “metal mouth” that can be a source of embarrassment to the patient. Attempts have been made in the past to make metal brackets less noticeable by reducing the overall size of the brackets, but any significant reduction in size is limited by the strength of the material.
While good results have been obtained in orthodontic treatment programs utilizing appliances made of some of the alloys mentioned above, there is a continuing need in the art for an orthodontic appliance that is made of a metallic alloy and yet is more aesthetic than existing appliances. Furthermore, there is a need in the art to improve existing orthodontic appliances in order to facilitate treatment and reduce the time that would otherwise be needed to achieve the desired results.
SUMMARY OF THE INVENTION
The present invention is directed toward an orthodontic appliance that is made of a precipitation hardening martensitic alloy. The appliance of the invention provides superior results in terms of strength, function and aesthetics in comparison to known appliances made of other alloys. The orthodontic appliance of the present invention is made of a stainless steel alloy that includes precipitates of titanium along with other elements in controlled amounts.
The precipitates of titanium in the appliance impart a significant improvement in strength and resistance to corrosion in the oral environment in comparison to the strength and corrosion resistance of conventional appliances. As an example, conventional appliances made of 17-4 PH stainless steel include precipitates containing aluminum, copper, nickel and/or iron. It has been found that iron-based alloys with precipitates of titanium provide superior resistance to corrosion in the oral environment where saliva and other fluids are present.
In one aspect, the present invention is directed toward an orthodontic appliance that is made of an iron-based alloy that includes precipitates of titanium in an amount effective to strengthen the alloy. In another aspect, the present invention is directed toward an orthodontic bracket that comprises a base, a body extending from the base and an archwire slot extending across the body. The body is made of an iron-based alloy that includes precipitates of titanium in an amount effective to strengthen the alloy.
In another aspect, the present invention is directed toward an orthodontic appliance having a body that is made of a martensitic precipitation hardening stainless steel alloy consisting essentially of, in weight percent, about 10-13% chromium, 9-12% nickel, 1-4% titanium, 0.5-2% molybdnum, 0.001-0.01% boron, and not more than about 1% manganese, not more than 1% silicon, not more than 0.04% carbon, nitrogen or phosphorous, and not more than 0.02% sulfur, with the balance being iron.
Advantageously, the orthodontic appliances of the invention can be constructed of a size significantly smaller than the size of similar appliances made of conventional orthodontic alloys. This reduced size makes the appliances more difficult to see when worn by a patient during the course of treatment, and consequently enhances the aesthetic characteristics of the appliance to a significant extent.
Additionally, the reduced size of the appliances provides many mechanical and functional advantages during the course of treatment. For example, and as explained in more detail below, the reduction in size enables the appliances to have configurations not previously possible to any practical extent. This reduction in size also allows the use of other orthodontic components that are different and/or used differently than previously known. Moreover, the smaller size of the appliance reduces the likelihood of irritation to the patient's oral tissues and unintentional contact with opposing dentition.
Optionally, the orthodontic
Hansen James D.
Kelly John S.
Palmer John J.
3M Innovative Properties Company
Christoff James D.
Lucchesi Nicholas D.
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