Orthodontic appliance

Details Orthodontic appliance Orthodontic appliance

2002-02-05

2003-11-11

O'Connor, Cary E. (Department: 3732)

Dentistry

Orthodontics

Bracket

C433S009000

Reexamination Certificate

active

06644968

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an orthodontic appliance adhered to teeth, such as a bracket, buccal tube, sheath, button or lingual attachment.
DESCRIPTION OF THE RELATED ART
Orthodontic appliances for use in orthodontic treatment been widely known, which comprise a main body capable of maintaining an archwire and a bonding base connected to the main body and capable of adhering to teeth. Those orthodontic appliances include bracket, buccal tube, sheath, button, lingual attachment and the like, and are appropriately selected according to orthodontic treatment methods.
In particular, the bracket is most ordinarily used in the following manner. The bracket is directly adhered to the patient's teeth with bonding base being inside. Archwire is mounted on the bracket thus adhered. As a result, external force is applied to malaligned teeth by the archwire, thereby correcting such malaligned teeth.
Metal brackets have conventionally been known as the ordinary bracket. Orthodontic appliances formed from transparent or white semi-transparent materials such as ceramic bracket or plastic brackets have recently been used for the purpose of improving aesthetic properties.
However, the ceramic bracket made of aluminum oxide or zirconium oxide is extremely hard in comparison with metal bracket, and is also harder than enamel of the teeth, so that there is the possibility of abrading enamel of the opposite teeth contacting the bracket when occluding. Especially, a deep bite has been a tabooing case evading the use of the ceramic bracket. To overcome such problems, U.S. Pat. No. 4,950,158 proposes a method of interposing an elastmeric cushion at a tiewing of incisal side.
In case of adhering a bracket having a slot in a main body and inlaying the archwire in the slot to perform the correction of dentition, the archwire should be slippery to the slot, because the teeth row is corrected by a restoring force of the archwire. However, the archwire is difficult to slide to the slot provided in the ceramic bracket, and friction between the bracket and the archwire is large, so that a problem occurred that it is difficult to exactly perform a desired correction of dentition. The main reason for this is assumed that since the ceramic bracket is very hard, the archwire creates biting at an end portion in the mesiodistal direction of the slot.
In view of the above problems, U.S. Pat. Nos. 5,358,402 and 5,380,196 disclose technologies, that a metal slot liner is attached to the ceramic bracket by means of, for example, brazing in order to improve the sliding property of the archwire within the slot. However, the ceramic bracket comprising inorganic materials such as aluminum oxide or zirconium oxide are difficult to bond to organic adhesives generally used for the orthodontic purposes. Therefore, it was necessary to apply a silane coupling agent to the bonding base, or weld glass frit or glass beads on the bonding base to form a mechanical lock thereon, thereby increasing bonding force to the organic adhesives. Treating the bonding base was a factor to increase production cost of the ceramic bracket.
When the bracket adhered on the teeth is debonded after orthodontic treatment, if the bracket is made of a metal, such a bracket can be debonded as if turning over the bonding base without injure the teeth. On the other hand, the ceramic bracket is harder than the metal bracket and the bonding base has an integral structure of the main body and has high rigidity. Therefore, extremely large force is required to debond the bracket, and there is the possibility of injuring enamel of the teeth. To overcome those problems, U.S. Pat. No. 5,439,379 proposes a method of crushing ceramic bracket at a central groove and debonding the same. Further, technologies of shielding a surface of a bonding base having dimples (U.S. Pat. No. 4,936,773) and a central part of a bonding base with an inert paint (U.S. Pat. No. 5,269,680) are to positively control a bonding/debonding strength.
On the other hand, the plastic bracket has a problem that the bracket is liable to deteriorate by absorbing water in the mouth during the orthodontic treatment and it is also liable to disintegrate before the completion of orthodontic treatment. In addition, the plastic bracket is liable to adsorb coloring agent contained in foods and drinks by water absorption, resulting in a further problem in deterioration of the aesthetic appreciation due to such a discoloration.
Polycarbonate brackets are widely known as such a plastic bracket. However, since such a bracket does not have sufficient strength to torque by rectangular archwires or ligation of a ligature wire, the bracket is generally reinforced with a metal insertion. For example, U.S. Pat. Nos. 4,299,569 and 5,254,002 disclose plastic brackets having a metal slot liner as the insert arranged in mesiodistal direction of the bracket. Further, U.S. Pat. Nos. 5,595,484, 5,597,302 and 5,692,898 disclose plastic brackets formed by inserting metal members having U-shaped section in a direction crossing the slot.
Polycarbonate brackets having glass fibers mixed therewith for strength improvement are also known. The glass fibers contributes to improve strength of the bracket, but there is the problem that solvent cracks tend to occur due to influences by organic solvent components of an adhesive used for orthodontic application. It has been clinically known that the glass fiber reinforces the polycarbonate bracket, but on the other hand increases internal stress in the polycarbonate when molding, and microcracks occur due to the presence of a solvent in the adhesive or water-invasion with the passage of time, and as a result, the polycarbonate bracket deteriorates as being disintegrated.
A glass bracket is known as means for overcoming the problems involved in the ceramic and plastic brackets, and U.S. Pat. No. 5,261,814 discloses a bracket in which surface layer is crystallized under compression stress to form a reinforcing layer and the inside thereof is constituted of amorphous glass comprising the following compositions: SiO
2
55 to 70%, Al
2
O
3
15 to 28%, ZnO 0 to 14%, Li
2
O
3
0 to 7%, Na
2
O 0 to 7%, K
2
O 0 to 3%, BaO 0 to 7%, MgO 0 to 7% and TiO
2
0 to 7%.
However, this bracket is expensive because it is prepared from a glass sheet by a supersonic abrading process, a diamond cutting process or the like. Further, it is technically difficult to control thickness of the surface crystallized layer, and unevenness in thickness results in decreasing transparency (devitrification) and strength.
U.S. Pat. No. 5,795,151 describes a bracket comprising a diopside crystallizing glass (glass composition: SiO
2
, MgO, Al
2
O
3
and TiO
2
). However, this bracket contains Al
2
O
3
and TiO
2
in high contents. As a result, hardness of such a crystallizing glass is higher than that of the enamel of a natural tooth and there is the possibility of abrading enamel of the opposite teeth.
U.S. Pat. No. 4,784,606 describes a bracket comprising a glass tempered by ion exchange, where Li—Al—Si glass is dipped in a molten salt bath for 2 to 24 hours at temperatures higher than a strain point of the glass but lower than a softening point thereof, thereby obtaining the glass tempered by Naion. However, there is a problem that the ion-tempered layer is thin, and the bracket is worn in an early stage and is broken by occlusion or ligating.
U.S. Pat. No. 4,784,649 describes a bracket comprising a glass of a double crystal structure for the purpose of increasing strength. This glass has a large crystal structure in the inside of the glass, and has a small and flat crystal layer on the surface thereof, but a production process thereof is complicated. Further, not only cost is high but also strength is insufficient.
Thus, the glass bracket has disadvantages that its production process is complicated, its production technique is difficult, its production cost increases, and its strength and durability are insufficient as the orthodontic appliance.
The above-described problems occur all ove

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