Dentistry – Orthodontics – Tool
Reexamination Certificate
2000-10-31
2002-11-05
O'Connor, Cary E. (Department: 3732)
Dentistry
Orthodontics
Tool
Reexamination Certificate
active
06474988
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a tool for use with orthodontic brackets that are directly secured to surfaces of teeth by an adhesive. More particularly, the present invention relates to a hand tool for detaching orthodontic brackets from teeth at the conclusion of treatment.
2. Description of the Related Art
Orthodontic treatment involves movement of the teeth toward positions for correct occlusion. During treatment, tiny orthodontic appliances known as brackets are connected to the teeth, and an archwire is placed in a slot of each bracket. The archwire forms a track to guide movement of the teeth to orthodontically correct positions.
Orthodontic brackets are typically made of metal, ceramic or plastic. Metal brackets are widely used and are considered by many orthodontists to have mechanical properties that are satisfactory for moving the teeth to desired positions. Unfortunately, metal brackets are not aesthetic in the mouth and often lead to comments of a “metallic mouth appearance” that can be an embarrassment to the patient.
Orthodontic brackets that are made of a plastic material are generally considered more aesthetic than metal brackets. However, some plastic brackets are stained by certain food and beverages and turn an unsightly color after a period of time. Moreover, the plastic material may slowly creep in use such that the archwire slot widens during a period of extended use and precise control of tooth movement is hindered.
Orthodontic brackets that are made of transparent or translucent ceramic materials overcome many of the problems associated with plastic brackets, since ceramic material is resistant to staining and does not deform by creep as in the case with plastic brackets.
U.S. Pat. No. 4,954,080, assigned to the assignee of the present invention, describes a color-free ceramic bracket made of polycrystalline material with a translucency that permits the natural color of the tooth to diffusely show through the bracket. An improved translucent polycrystalline ceramic bracket having a metallic archwire slot liner to enhance sliding movement of the bracket on the archwire is described in pending U.S. Pat. Nos. 5,358,402 and 5,380,196, both of which are assigned to the assignee of the present invention.
Metal brackets are typically debonded by using a peeling or prying motion. U.S. Pat. Nos. 3,986,265 and 4,248,587 describe plier-type hand instruments that are used with a prying action to remove orthodontic brackets. U.S. Pat. No. 4,553,932, assigned to the assignee of the present invention, describes a peeling-type debonding tool having a pull wire with a loop for hooking a wing of the bracket. The loop applies a pulling force to a tiewing located on an upper or lower portion of the bracket while a pair of spaced apart abutments engage the tooth on opposite sides of the bracket.
Peeling-type debonding methods are usually considered satisfactory for detaching brackets made of ductile materials such as metal. Debonding of such brackets often begins by fracturing the adhesive bond along one side of the bracket base, and then peeling or bending the base of the bracket so that the fracture propagates to remaining regions of the adhesive bond. In this manner, the debonding force is applied only to a relatively small, generally linear area at any particular point in time.
However, ceramic orthodontic brackets are relatively hard and brittle, and do not bend or flex like metal brackets during debonding. As a result, debonding occurs by fracturing the adhesive bond in all areas at essentially the same time, rather than in a propagating type of fracture as occurs when metal brackets are debonded by a peeling-type motion. Pulling on the tiewings of a ceramic bracket is not normally recommended because the ceramic material is brittle and the tiewings may break from remaining portions of the bracket.
Damage to the tooth structure may result during a debonding operation when excessive stress is applied to the tooth during attempts to lift or pry the bracket from the tooth. Tooth damage is more likely to occur when the tooth structure is weakened or has been previously damaged; however, such weakened or previously damaged tooth structure often cannot be noted by visual observation. Consequently, it is desirable that brackets are removed from the teeth with as little force as possible to minimize the risk of damage to the tooth.
It has been proposed in the past to weaken the strength of the bond between a ceramic bracket and the tooth so that debonding of the bracket is facilitated. However, such a solution is not entirely satisfactory because of the resulting increased likelihood that the bracket may unintentionally, prematurely debond during treatment. For example, a relatively weak adhesive may not have sufficient strength to resist debonding of the bracket when the bracket is subjected to relatively large forces, as when the patient bites into a relatively hard food object. In other instances, a bracket may debond due to forces exerted by the archwire, orthodontic auxiliaries or attachments coupled to the bracket. Premature debonding of orthodontic brackets represents a nuisance to both the orthodontist and the patient, since the detached bracket normally must be re-bonded or replaced with a new bracket in order for treatment to resume.
An improved ceramic bracket that overcomes the debonding problems mentioned above is described in U.S. Pat. Nos. 5,439,379 and 5,366,372. The ceramic brackets described in those references have a mesial section (i.e., a section facing toward the middle of the dental arch) and a distal section (i.e., a section facing away from the middle of the dental arch). The mesial and distal sections are spaced apart from each other by a channel that extends in a generally occlusal-gingival direction (i.e., a direction that extends from the outer tips of the teeth to the patient's gums or gingiva). The mesial and distal sections are connected to each other by a thin web of material that lies along the bottom of the channel.
The brackets that are described in U.S. Pat. Nos. 5,439,379 and 5,366,372 are debonded from the surface of the tooth at the conclusion of treatment by urging the mesial and distal sections in directions toward each other. As the sections pivot, the sections detach from underlying areas of the tooth. It is believed that such construction significantly lowers the stresses applied to the tooth surface in comparison to, for example, the stresses that are needed to debond a ceramic bracket of similar size by use of a tensile force in directions perpendicularly away from the tooth surface. As a consequence, the likelihood of injury to the enamel surface of the underlying tooth is reduced.
In certain embodiments of the brackets described in U.S. Pat. Nos. 5,439,379 and 5,366,372, a metallic archwire slot liner is fixed to the mesial and distal sections and enhances sliding motion of the brackets along the archwire. Advantageously, the archwire slot liner retains the sections together during and after a debonding operation to facilitate removing the bracket from the mouth as one coupled-together assembly.
However, brackets according to other embodiments described in U.S. Pat. Nos. 5,439,379 and 5,366,372 do not have a metallic archwire slot liner. As a consequence, it is possible for one of the sections in those embodiments to shift away from the other section and detach from the grip of the debonding tool during a debonding operation, especially in instances where the jaws of the debonding tool are not centrally located over the mesial and distal sides of the bracket. Additionally, if the practitioner uses excessive force on the handles of the debonding tool after the bracket has debonded it is possible for one or both of the sections to break into fragments that are expelled from the grip provided by the jaws of the debonding tool.
Unfortunately, it is undesirable for bracket sections and bracket fragments to become loose in the oral cavity. If such a situation occurs, debonding o
Christoff James D.
Georgakis Evangelos G.
3M Innovative Properties Company
Christoff James D.
O'Connor Cary E.
LandOfFree
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