Dentistry – Apparatus – Having static product shaping surface
Reexamination Certificate
1999-07-06
2001-04-24
Wilson, John J. (Department: 3732)
Dentistry
Apparatus
Having static product shaping surface
C433S139000, C433S149000
Reexamination Certificate
active
06220858
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to an apparatus for placement of fillings and, in particular, an apparatus for placement of light curable dental fillings.
BACKGROUND OF THE INVENTION
Over the past two decades, the dental profession has been urged to provide its clients with natural looking fillings for posterior teeth. Composite resins have been used to provide these natural looking fillings. Composite resins, when cured, have a natural tooth colour, can be placed in one appointment and are free of the toxin mercury.
Before placement, composite resins have a soft putty-like consistency and are generally non-compactable. Fillings formed of composite resin are cured by application of a concentrated source of light. To place a composite resin filling, a matrix is used. A matrix is a device which wraps around a prepared tooth area. It acts as a mold and limits the spread of filling materials beyond desired borders. This mold conforms ideally to the original anatomy of the interproximal tooth structure. Matrices are generally formed from stainless steel or plastic and can be circumferential or sectional. Circumferential matrices fit around the entire circumference of the tooth whereas sectional matrices fit only in one interproximal area of the tooth. Matrices are secured in place by use of wedges and/or clamps. Wedges are triangular in cross section and taper along their length. They are placed between the matrix and the adjacent tooth in order to seal the matrix against the base of the prepared tooth structure. Wedges are generally made of wood or plastic.
The placement of composite resin fillings in the interproximal area has been found to be very problematic. Since the resin is non-compactable, it is very difficult to create a firm contact point between the newly placed filling and the adjacent tooth. The contact point is the point at which the crown of one tooth contacts, or nearly contacts, the crown of an adjacent tooth. If a gap is formed at the contact point, food becomes trapped between the teeth causing gum irritation or inflammation, tooth movement and general patient dissatisfaction. When the curing light source is applied from the direction of the biting surface, this causes the resin material to be drawn away from the base of the proximal tooth preparation and towards the light. When this occurs, the seal of the composite resin at the tooth/filling margin is compromised and microscopic leakage of bacteria and saliva between the tooth and the filling material can occur. This causes sensitivity at the area of the filling and tooth decay often occurs.
The prior art has attempted to overcome these problems by provision of wedges and matrices formed of materials, such as acrylic or thermoplastic, which are transparent to the curing light for resin material used in dental fillings. These devices allow curing light to be conducted interproximally such that curing takes place between the teeth first.
The prior art transparent wedges tend to experience internal reflection of light directed therethough and, thus, have limited usefulness.
SUMMARY OF THE INVENTION
An apparatus has been invented for placement of light curable dental fillings. The apparatus includes a matrix formed of light transparent material and shaped to conform to the natural contour of a tooth in the interproximal zone. A light transparent wedge has also been invented which selectively conducts light to the base of the tooth preparation and which can be used to conduct light interproximally applied from either side of the interproximal zone.
In accordance with a broad aspect of the present invention, there is provided a dental matrix for insertion interproximally between two teeth, the matrix comprising a sheet of material transparent to the light for curing resin dental filling material, the sheet having a first side and a second side and having a selected thickness between the first side and the second side such that it can withstand the forces of being inserted interproximally and having a gum contacting edge and further having a thinned portion positioned thereon and spaced a selected distance from the gum contacting edge, the thickness of the sheet around the thinned portion being greater than the thickness of the material in the thinned portion.
A matrix according to the present invention is of a suitable thickness to be inserted interproximally between two teeth without failing, while providing close spacing at the contact area between adjacent teeth. The matrix is formed in any suitable way to have a thinned portion positioned thereon. In particular, the thinned portion is positioned on the matrix and a thicker portion extends substantially about the thinned portion. The thicker portion acts as a more durable frame for the thinner portion. In one embodiment, the matrix is formed such that its thickness tapers from the edges towards a selected point on the matrix. Alternately, a thinned area having defined edges can be formed at a selected position on the matrix. The matrix acts as a mold against which the composite resin material is pushed. The final cured filling takes the form of the matrix and a raised portion is formed on the filling corresponding to the position of the thinned portion on the matrix. Thus, where the thinned area has defined edges, the edges should be formed to graduate smoothly between the thicker region and the thinned portion such that when the filling is cured it will not have a raised portion that creates dental problems (i.e. catches dental floss). To facilitate manufacture, the matrix is formed as one part, for example, as by molding a sheet of material with a thinner portion therein. Preferably, the sheet around the thinned portion is formed to have a thickness of between about 0.05 to 0.15 mm and the thinned portion is selected to have a thickness of between about 0.03 to 0.07 mm.
The thinned portion is positioned on the matrix such that it is adjacent at the contact area between the teeth when the matrix is positioned between two teeth. Generally, the thinned portion is spaced from the gum contacting edge of the matrix with consideration as to the spacing from the gum to the contact point on an average tooth. The area of the thinned portion can be enlarged to provide for some variation in the spacing from gum to contact point in a tooth. Preferably, the gum contacting edge of the matrix is shaped to conform to the shape of the interproximal gingival margin. In particular, the edge of the matrix which is selected to be positioned against the gum is curved inwardly. Preferably, the matrix is curved such that it is generally concave to allow it to curve around the sides of the tooth and into the tooth neck, when the matrix is positioned against a tooth. The thinned portion is formed in the matrix such that an indentation is positioned on the concave side of the matrix.
The matrix of the present invention is useful with any matrix securing means. In one embodiment, the side edges of the matrix have applied thereto an adhesive material for securing the edges of the matrix to the tooth surface about which it is to be used. The adhesive is selected to be releasable from a tooth surface by application of a selected amount of force.
Other matrix securing means can be used with or without the adhesive such as, for example, wedges and/or clamps. A particularly useful wedge is, of course, also light transparent.
A light transparent wedge has been invented which enhances light transmission interproximally. Thus, in accordance with another broad aspect of the present invention, there is provided a dental wedge formed of materials transparent to the curing light for resin dental filling material, comprising: an elongate body tapering from its first end to its opposite end and being generally triangular in cross section having three sides and the first end having a convex curvature.
The convex curvature causes the first end to act as a lens. This causes light directed at the wedge to be directed through a selected focal point within the wedge and toward the sid
Hague Anthony M.
McKenna Mark H.
Bennett Jones LLP
Mercor Dental Products Inc.
Wilson John J.
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