Dentistry – Orthodontics – Bracket
Reexamination Certificate
2000-07-21
2001-10-23
Wilson, John J. (Department: 3732)
Dentistry
Orthodontics
Bracket
Reexamination Certificate
active
06305932
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an orthodontic element and a manufacturing method therefor, and in particular relates to an orthodontic element and a method therefor where the element is furnished with a liner provided inside an archwire slot, in order to improve the slippage and shiftability of archwire engaged in orthodontic brackets made of ceramics.
2. Description of the Related Art
In orthodontic clinical treatment, small implements called brackets are attached to the teeth of the patient. In the past, these brackets were mainly made of metal, but in recent years materials such as plastics and ceramics have been developed in order to improve the aesthetic appearance, and now brackets using ceramics have come into use.
The form of use of these brackets is to attach the brackets to the teeth by adhesion, and in order to impart external force to these brackets intended to straighten the teeth, metal archwire is passed through archwire slots provided in the brackets and the archwire and brackets are suitably tied.
However, ceramic brackets particularly in the case of polycrystalline ceramic brackets have the problem of poor slippage on the metal archwire compared to metal brackets.
That is, many polycrystalline ceramics are made by processing their archwire slots with such as diamond blades so that crystal particles are scarified on the processed surface by such slot processing, making the surfaces rough so that the archwire would not slip.
There exists technology intended to improve the slippage of metal archwire on these types of ceramic brackets, as described for example in U.S. Pat. Nos. 5,358,402 and 5,380,196.
This publication describes that it is possible to turn the friction between the archwire slots and the metal archwire into the friction of metal on metal by furnishing metal liners in the slots provided in the brackets.
Further, U.S. Pat. No. 4,988,293 describes that the strength will be reinforced by providing polycrystalline outer coating layers on brackets comprising monocrystalline alumina, which is very fragile.
In addition to the problems above, ceramic brackets are themselves very hard, so that the metal archwire tends to create friction particularly at mesiodistal ends of the slots. Consequently, there is the problem of archwire slippage being worse at the extreme ends than with metal brackets.
This is equivalent to saying that the bracket is hard to slide on the archwire, with the result that tooth alignment does not proceed, and this leads to the problem of longer periods orthodontic treatment.
In the state of affairs, the structure of the ceramics bracket disclosed in U.S. Pat. Nos. 5,358,402 and 5,380,196, because it uses a metal liner, was a step back aesthetically even though slippage improved. Further, with a structure combining ceramics and metal, joining the ceramics and metal is technologically difficult, and brackets having metal liners had the problem of high cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to improve the slippage of metal archwire and ceramic brackets, together with offering an aesthetically superior orthodontic element and a method for manufacturing it easily.
An orthodontic element according to the present invention is an orthodontic element comprising: a bracket comprising polycrystalline ceramics, in which an archwire engages; and a glass liner provided in an archwire slot formed in said bracket in order to engage the archwire.
In the orthodontic element pertaining to the present invention, said glass liner may be colored, both mesiodistal end surfaces of said archwire slot may be constructed so as to have bevel portions, and the corner radius at the slot bottom surface (the radius of curvature of the R shaped entry angles of the bottom of said archwire slot) are constructed to be 0.03 mm or over.
A method for producing an orthodontic element, comprises the steps of: inserting a glass rod in a slot of a bracket, comprising polycrystalline ceramics whose slot is somewhat larger than the archwire slot required; after the inserting step, melting said glass so that said glass covers the slot internal walls; and forming said glass covering said slot internal walls as a glass liner by processing to a shape nearly along said slot internal walls.
In the method for producing the orthodontic element, hot press processing is used as the processing during the period in which said glass is melted. In the method for producing the orthodontic element, cutting processing is used as the processing after said glass is melted. In the method for producing the orthodontic element, concave portions larger than said slot are previously furnished at both mesiodistal ends of said slot, and when said glass is melted, the glass flows into said concave portions.
Following the orthodontic element pertaining to the present invention, it is an orthodontic element constructed so that archwire engages in a bracket comprising polycrystalline ceramics, and since it is furnished with a glass liner in the archwire slot formed in the bracket for the purpose of engaging the archwire, there is no lowering of slippage between the metal archwire and the bracket, and it is superior aesthetically. Also, by furnishing the glass liner, the strength of the archwire slot portion is increased because glass has a lower stress intensity factor than ceramics, and in particular the fracture toughness is increased when torque is imparted to the bracket by the metal angular archwire (square and rectangular wire).
In the orthodontic element of the present invention, following the structure where the glass liner is colored makes it easy to discriminate the glass liner, for example making it possible to avoid errors by having different colors on respective teeth, and making it easy to determine the positions on tooth surfaces by color.
In the orthodontic element of the present invention, following the structure where both mesiodistal end surfaces of the archwire slot have bevel portions makes it possible to avoid excess friction and gnawing between the archwire and the mesiodistal ends of the archwire slot.
In the orthodontic element of the present invention with the corner radius (R
0
) at slot bottom surface being constructed to be 0.03 mm or over, when torque is imparted to the archwire, its stress disperses along the archwire slot surface without being concentrated in any one part thereby raising the fracture toughness of the orthodontic element.
Following the method of manufacturing the orthodontic element pertaining to the present invention, it is a method of making orthodontic elements using brackets comprising polycrystalline ceramics, and after glass rod is insert in a slot of the bracket whose slot is somewhat larger than the archwire slot required, said glass is melted so as cover the slot internal walls by capillary action so that the glass and ceramics are chemically bonded, and said glass covering said slot internal walls is formed as a glass liner by processing to a shape nearly along said slot internal walls, so as to be able easily to manufacture an orthodontic element that is aesthetically superior without lowering the slippage between the metal archwire and the bracket.
Also, within the method of manufacturing said orthodontic element pertaining to the present invention, forming of the liner is very easy with the method using hot press forming for processing during the glass is melted, making it a manufacturing method suitable for mass production.
Also, within the method of manufacturing said orthodontic element pertaining to the present invention, forming of the liner can be done individually as required with the method using grinding process after the glass is melted.
Also, within the method of manufacturing said orthodontic element pertaining to the present invention, it is possible to previously furnish concave portions larger than said slot at both ends of said slot, so when said glass is melted the glass flows into said concave portions so as to easily form a liner having round
Bumgarner Melba
Kenyon & Kenyon
Tomy Incorporated
Wilson John J.
LandOfFree
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