Compositions: coating or plastic – Coating or plastic compositions – Dental
Reexamination Certificate
1999-07-15
2001-03-27
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Dental
C433S202100, C433S206000, C433S212100, C427S007000, C427S002270, C427S002290, C501S016000, C501S017000, C501S020000, C501S021000, C501S024000, C501S025000, C501S026000, C501S059000, C501S057000, C501S063000, C501S064000, C501S066000, C501S068000, C501S069000, C501S070000, C501S072000
Reexamination Certificate
active
06206958
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to porcelain compositions and more specifically to dental porcelain powder compositions for use as an initial layer on top of an alloy coping or ceramic core material in the preparation of dental restorations.
BACKGROUND OF THE INVENTION
Dental restorations, such as crowns, bridges and the like, are typically made of a metallic or porcelain core framework with one or more porcelain layers coated thereon. The porcelain layers provide strength, wear resistance and favorable aesthetics to the dental restorations. In porcelain fused-to-metal (PFM) restorations, it is important that the firing temperature of the porcelain be at least 100° C. below the solidus temperature of the alloy used as the metal framework and that the coefficient of thermal expansion of the porcelain (in the range of room temperature to 450° C.) be only very slightly less than that of the metal so that no stress cracks are produced in the porcelain layer during firing and cooling down. Ceramic cores are advantageous in the fabrication of dental restorations because concerns regarding effective concealment of the metal color do not exist. Similar to metal cores, when a ceramic core is used, any porcelain applied to the ceramic framework must possess a coefficient of thermal expansion that is slightly less than that of the ceramic to prevent failure in the porcelain due to stresses caused by thermal expansion mismatch.
U.S. Pat. No. 5,679,144 is directed to a powder composition comprising one or more feldspar frits and CeO
2
as an opacifier. The frits have a particle size distribution of d
50
of 3 to 6 microns, d
90
of 12 to 16 microns and a maximum grain size of less than 20 microns. As set forth therein, since the paste may segregate, it is supplied in ajar or box so that it can be stirred up before use if necessary. Also, due to the relatively fine particle size, pinholes or steam tearing may occur in the final restoration if moisture is not allowed to evaporate freely.
U.S. Pat. No. 4,557,691 is directed to a porcelain paste comprising a porcelain powder mixed with an aqueous colloidal dispersion of a urethane polymer. The product is sold in a syringe and may dry out in the syringe before use due to evaporation of ammonia and water.
U.S. Pat. No. 4,806,383 is directed to a method of applying opaque dental ceramic material to a metal structure that requires an additional step of dusting a ceramic powder having an average grain size of from 40 microns to 100 microns onto the applied opaque paste, firing the material, and applying additional ceramic and firing same. The large particle size affects the handling characteristics of the paste and also results in significant settling of the powder in the liquid. In addition, the dusting step requires additional time and skill to make the restoration.
There is a need to prevent settling of the powder from the liquid component in porcelain paste compositions so that the paste composition can be provided in a variety of packaging forms including syringes. It is desirable to produce a dental porcelain paste that can be applied easily in thin coats. It is advantageous that sufficient coverage of the core framework is achieved without the need for dusting of additional porcelain powder thereon.
SUMMARY OF THE INVENTION
These and other objects and advantages are accomplished by the porcelain compositions of the present invention comprising one or more glass or glass-ceramic powder components. Additionally, one or more opacifying agents, pigments, fluorescing agents and the like may be included in the composition. The amount of opacifier can be varied to create porcelains with varying opacity which can be used for different applications. The amount and type of pigments can be varied to create different shades of dental porcelain. The porcelain compositions may vary depending upon the specific thermal properties desired. The fusion temperature of the porcelain compositions is in the range of from about 750° to about 1010° C. and the coefficient of thermal expansion is in the range of from about 2 to about 18×10
−6
/° C. and more preferably in the range of from about 3 to about 16×10
−6
/° C. (measured from room temperature to 450° C.). The compositions are also characterized by the particle size of the particulate as defined by d
10
, wherein ten percent of the volume of particles is smaller than the indicated size; d
50
, wherein fifty percent of the volume of particles is smaller than the indicated size and d
90
wherein ninety percent of the volume of particles is smaller than the indicated size. For example, a d
10
equal to 1.1 microns indicates that ten percent of the volume of particles is smaller than 1.1 microns.
In one embodiment of the present invention, the porcelain has a d
50
of from about 3 to about 6 microns, and a d
90
of from about 8 to about 16 microns, and the maximum particle size of the particulate is greater than or equal to about 20 microns. Preferably, the porcelain further has a d
10
of from about 1.1 microns to about 1.8 microns. Preferably the maximum particle size is no greater than about 60 microns. Preferably, about 1.0% to 4% of the particulate is greater than about 20 microns and more preferably, about 1.5% to about 3.5% of the particulate has a particle size greater than about 20 microns. The mean diameter of the volume distribution (hereinafter referred to as the “mean particle size”) is preferably in the range of from about 3.0 microns to about 7.5 microns.
More preferably, the porcelain has a d
50
of from about 3.5 to about 5.5 microns, and a d
90
of from about 10 to about 14.5 microns, and the maximum particle size of the particulate is greater than or equal to about 20 microns. More preferably, the porcelain further has a d
10
of from about 1.15 microns to about 1.65 microns. More preferably, the maximum particle size is no greater than about 50 microns. The mean particle size is more preferably in the range of about 3.5 microns to about 6.75 microns.
In a preferred embodiment of the method of the present invention, two or more glass and/or glass-ceramic flits are milled separately. The milled flits are then mixed together resulting in a mixture having particle sizes in the desired particle range in accordance with the invention herein. Opacifiers, pigments and the like may also be added to the mixture. The mixture is then ready for application to a core material.
In another embodiment of the method of the present invention, two or more glass and/or glass-ceramic flits are mixed together. The mixture is then milled to the desired particle sizes and an opacifying agent, pigments and the like may then be added to the mixture. The average particle size of the opacifier typically ranges from about 0.2 to about 2.8 microns. The mixture is then ready for application to a core material.
In another embodiment of the method of the present invention, various oxides or precursors thereof are mixed together and melted to prepare a porcelain frit. Suitable precursors include silica, alumina, boric acid, feldspar, calcium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, lithium carbonate, and/or barium compounds. The frit is then milled to the desired particle sizes and an opacifying agent, pigments and the like may then be added to the porcelain frit to obtain an opaque porcelain frit. The mixture is then ready for application to a core material.
In yet another embodiment of the method of the present invention, one or more glass and/or glass-ceramic frit compositions are milled separately to the desired particle size. The frits are then mixed together and the mixture may be combined with an opacifying agent, pigments and the like. The mixture is then ready for application to a core material.
In still another embodiment of the method of the present invention, one or more glass and/or glass ceramic frits are milled separately. The frits are then mixed and an opacifying agent may be added thereto. The mixture is then milled to the desired pa
Brightly Richard A.
Brodkin Dmitri
Kaiser Lisa M.
Panzera Carlino
Panzera Paul
Jeneric Pentron Incorporated
Knab Ann M.
Koslow C. Melissa
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