Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-10-07
2001-05-15
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S115000, C523S220000, C524S413000, C524S558000, C526S301000, C260S998110, C260S998170
Reexamination Certificate
active
06232367
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally related to a composite resin material used for dental restoration, and more particularly to a universal composite resin material suitable for all dental restorations incorporating a self-opalescing translucent filler.
BACKGROUND OF THE INVENTION
In dentistry, practitioners use a variety of restorative materials to create crowns, veneers, direct fillings, inlays, onlays and splints. One of the major goals in restorative dentistry is to produce restorations that match the esthetics of the natural tooth. Highly esthetic tooth colored restorations were first introduced to dentistry in the 1940's with acrylic resins and silicate cements. These were direct filling restorations that were tooth colored and translucent in visible light like natural teeth. When placed in the mouth, the fillings were not easily discernible from the tooth itself. In the 1950's, dental porcelains were introduced, which provided a variety of shades and translucencies to further improve the esthetics of the restorations. These were used in restorations, such as porcelain fused to metal crowns and bridges, or in inlays, onlays and veneers. Tooth shading with porcelain restorations has been highly successful and has become state-of-art in the industry today. In the 1970's, fluorescence was incorporated into dental porcelains, which further improved the esthetics of dental restorations and made them more natural appearing, especially under fluorescent lighting conditions. More recently, in the 1990's, opalescence has been incorporated into dental porcelains to produce the natural “opal effect” present in natural teeth.
Translucency, shading, fluorescence and opalescence are optical properties that give the natural tooth its vital-looking appearance. Translucency and shading have the greatest impact on the total vitality of the tooth because they are the most readily observed. Dentin and enamel are both translucent, but enamel is more translucent, almost transparent and colorless. The color or shade of the tooth mostly comes from dentin and is transmitted through the enamel layer to the surface of the tooth. Enamel is a highly mineralized crystalline structure composed of millions of enamel rods or prisms. As light travels through the enamel, the rods scatter and transmit the rays to the tooth surface much like a fiber optic system. Enamel, though highly transparent, does not transmit light like a clear window glass. Instead, the enamel diffuses the light, rendering the enamel opalescent.
Fluorescence and opalescence are more subtle optical properties that further enhance the natural-looking, life-like appearance or “vitality” of the tooth. Fluorescence is defined as the emission of electromagnetic radiation that is caused by the flow of some form of energy into the emitting body, which ceases abruptly when the excitation ceases. In natural teeth, components of the enamel, including hydroxyapatite, fluoresce under long wavelength ultraviolet light, emitting a white visible light. This phenomenon is subtle in natural daylight but still adds further to the vitality of the tooth. In contrast, under certain lighting conditions, the lack of fluorescence in a restorative material may become alarming. Under “black light” conditions, such as that often used in discotheque-type night clubs, if a restoration does not fluoresce, the contrast between the tooth and restoration may be so great that the tooth may actually appear to be missing.
Opalescence is defined as the milky, iridescent appearance of a dense, transparent medium or colloidal system when illuminated by visible light. It is best illustrated by the mineral opal, which is a natural hydrated form of silica. The “opal effect” is a light scattering phenomenon in translucent materials that produces a blue effect in reflected light due to the scattering of short wavelength light and an orange effect in transmitted light. This effect is different from simple reflected light in translucent materials and produces the milky iridescent effect present in the natural tooth. Restorations that are not opalescent do not have the vital looking appearance of a natural tooth itself.
Without being bound by theory, the chemistry and structure of enamel may be responsible for the “opal effect.” Chemically, tooth enamel is a highly mineralized crystalline structure containing from 90% to 92% hydroxy apatite by volume. Structurally, it is composed of millions of enamel rods or prisms aligned perpendicular to the dentinoenamel junction and extending to the tooth surface. The enamel rods measure about 4-8 &mgr;m in diameter and the head or body section at the surface of the rods is about 5 &mgr;m wide. The crystallites are tightly packed in a distinct pattern or orientation that gives strength, hardness and structural identity to the enamel prisms. The particle size and crystalline orientation of the enamel prisms likely are responsible for producing the light scattering “opal effect.”
Although opalescence has been incorporated into dental porcelains, the current trend in dental restorative technology is to use composite resins for restoration, rather than the porcelains. Composite resins are a type of restorative material which are suspensions of strengthening agents, such as mineral filler particles, in a resin matrix. These materials may be dispersion-reinforced, particulate-reinforced, or hybrid composites.
Dispersion-reinforced composites include a reinforcing filler of, for example, fumed silica having a mean particle size of about 0.05 &mgr;m or less, with a filler loading of about 30%-45% by volume. Because of the small particle size and high surface area of the filler, the filler loading into the resin is limited by the ability of the resin to wet the filler. Consequently, the filler loading is limited to about 45% by volume. Due to the low loading, the filler particles are not substantially in contact with one another. Thus, the primary reinforcing mechanism of such dispersion-reinforced composites is by dislocation of flaws in the matrix around the filler. In dispersion-reinforced materials, the strength of the resin matrix contributes significantly to the total strength of the composite. In dentistry, dispersion-reinforced composite resins or microfills are typically used for cosmetic restorations due to their ability to retain surface luster. Typically, these microfill resins use free radical-polymerizable resins such as methacrylate monomers, which, after polymerization, are much weaker than the dispersed filler. Despite the dispersion reinforcement, microfill resins are structurally weak, limiting their use to low stress restorations.
One example of a dispersion-reinforced composite is HELIOMOLAR®, which is a dental composite including fumed silica particles on the order of 0.05 &mgr;m mean particle size and rare earth fluoride particle on the order of less than 0.2 &mgr;m mean particle size. HELIOMOLAR® is a radiopaque microfill-type composite available from Vivadent. The rare earth fluoride particles contribute to both flexural strength and radiopacity.
Particulate-reinforced composites typically include a reinforcing filler having an average particle size greater than about 0.6 &mgr;m and a filler loading of about 60% by volume. At these high filler loadings, the filler particles begin to contact one another and contribute substantially to the reinforcing mechanism due to the interaction of the particles with one another and to interruption of flaws by the particles themselves. These particulate-reinforced composite resins are stronger than microfill resins. As with the dispersion-reinforced composites, the resin matrix typically includes methacrylate monomers. However, the filler in particulate-reinforced composites has a greater impact on the total strength of the composite. Therefore, particulate-reinforced composites are typically used for stress bearing restorations.
Another class of dental composites, known as hybrid composites, include the features and advantages of dispersion reinfo
Angeletakis Christos
Kobashigawa Alvin I.
Kerr Corporation
Szekely Peter
Wood Herron & Evans LLP
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