Dentistry – Method or material for testing – treating – restoring – or... – Endodontic
Reexamination Certificate
1998-10-02
2001-05-01
Lewis, Ralph A. (Department: 3732)
Dentistry
Method or material for testing, treating, restoring, or...
Endodontic
C433S226000
Reexamination Certificate
active
06224379
ABSTRACT:
BACKGROUND OF THE INVENTION
The field of dentistry routinely requires the manipulation of a high-viscosity, adhesive material. In one application, a dimethacrylate composite is used to fill oral cavities. Dimethacrylate composite esthetic restorative materials have been the subject of considerable research since their introduction in 1962. They represent the current state of the art in the drive to develop restorative materials that have the appearance of natural teeth and do not contain mercury. Composite restorations have been shown to have good clinical performance, particularly for application in the anterior portion of the mouth, where the mechanical stresses to which the restoration is subjected are comparatively low. Posterior, load-bearing applications are generally more problematic. It has been demonstrated, however, that when properly placed, composite dental materials can produce posterior restorations with excellent longevity. Proper placement refers to placement and packing of dental restoratives in such a way that firm adhesion to the dental substructure is achieved, with a minimum number and size of voids due to air entrapment, and minimization of overall porosity.
Due to their strong adhesive properties, composite restorative materials can stick to dental instruments and be difficult to manipulate, causing the practitioner to introduce flaws and voids into a restoration that may cause a degradation of nominal mechanical and clinical properties. During a dental restorative procedure, after a composite is initially placed inside an oral cavity, a step is routinely required in which pressure is applied to the composite to remove entrapped air and to ensure adaptation and a firm bond of the composite to the cavity walls. This step is referred to as “packing,” and is fraught with difficulties caused by the extreme stickiness of the restorative materials. In general, the composite sticks to the packing tool when the tool is withdrawn from the restoration. As shown in the illustration of a restored tooth
10
in
FIG. 1
, the resulting strain on the composite
12
during the removal phase can cause air entrapment and disbanding of the composite
12
from the inner walls
14
of the cavity.
The sticking of the restorative material to the tool is known as adhesion, or adhesive “tack,” the elimination of which has been the focus of considerable efforts over the last two decades. Presently, packing tools commonly used by dental practitioners include instruments, or “pluggers,” with a variety of geometries made of materials such as plastic, Teflon®, and stainless steel, as well as injection syringes.
The development of low-viscosity, flowable composites have effectively removed the packing step from the clinical procedure. However, in order to achieve low viscosity, these composites are manufactured with a lower volume percentage of filler particles in their matrix, and therefore do not have the mechanical strength of high-viscosity composites. Flowable composites are recommended for small class III or class V cavities, but are not recommended for large cavities or for any application subject to wear.
SUMMARY OF THE INVENTION
The adhesion phenomenon associated with currently-available tools greatly limits the manipulative procedures that can ordinarily be used for packing. This invention provides a new method for effectively packing and placing high-viscosity, wear-resistant, adhesive materials, such as chemically-cured and photopolymerized dental restorative composites, with a significant reduction or elimination of adhesion between the high-viscosity, adhesive material and the packing tool. In accordance with the broad aspects of this invention, the methods are further suited to the deformation of other adhesive materials in applications where deformation without tack is desirable. Examples of such applications include processing involving paint or food.
In a method of this invention, a spinning end of a rotating instrument is used to deform an adhesive material without the adhesive material adhering to the instrument.
In a preferred embodiment, the adhesive material is a dental restorative that is applied to a tooth. Preferably, the adhesive dental restorative is applied to a cavity in the tooth and packed into the cavity with the spinning end of the rotating instrument. The dental restorative is preferably a composite of up to 50% particulate fillers in a copolymer matrix, including a dimethacrylate, for example. One preferred copolymer matrix includes a combination of bisphenol A-glycidyl methacrylate (BIS-GMA) and triethylene glycol dimethacrylate (TEG-DMA). A preferred embodiment of the instrument includes a bit rotated by a motorized, hand-held tool.
Preferably, the adhesive material is in a plastic state. The term, “plastic,” as used in its adjective sense, here, means that the material is pliant and capable of being molded. Such a material is at a temperature greater than its glass-transition temperature.
In further preferred embodiments, the instrument is rotated at a rate sufficient to generate a vibrational frequency at least as great as a critical frequency in the adhesive material. The critical frequency is the minimum vibrational frequency at which the adhesive material will not adhere to the instrument. Preferably, the spinning end of the rotating instrument has a smooth, blunted, non-circular shape and is made of a material that will not contaminate the copolymer dental-restorative composite, that material is preferably plastic.
The methods of this invention offer the advantage of a significant reduction or elimination of adhesion between the composite resin and the packing tool. As a result, restorations shaped in accordance with this invention are likely to have improved longevity due to improved placement. Further, the improved properties and greater ease of use of dental resins enables more extensive use of dental resins in dental filling operations. Finally, the ability to manipulate adhesive materials that are considered unworkable by conventional means may enable the practical utilization of new classes of dental resins with improved mechanical and thermophysical properties.
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Abedian Behrouz
Millstein Philip L.
O'Leary James P.
Racz Livia M.
Hamilton Brook Smith & Reynolds P.C.
Lewis Ralph A.
Trustees of Tufts College
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