Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-04-20
2004-11-16
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...
C522S908000, C523S117000, C106S035000, C433S228100
Reexamination Certificate
active
06818682
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a dental composition that exhibits long-term stability, on the order of greater than 12 months, and can be conveniently formulated as in a paste-paste or paste-liquid system. In one embodiment, the composition contains, among other components, at least one polyacid and at least one redox catalyst. At least one of the polyacid and redox catalyst exist in a disperse phase.
BACKGROUND
In general, a dental composition such as glass ionomer cements comprise ionic polymers and reactive glasses. The mixing of the two components in an aqueous environment initiates a setting reaction. Glass ionomer cements find utility in dental and medical applications, where the cements are used on, e.g., tooth and bone structures. Conventional glass ionomer cements have been supplied as a two-part powder-liquid system, where an ionic polymer (typically polyacrylic acid) is dissolved in water and a reactive glass (typically an acid-reactive glass) is in powder form. See, e.g. Robert G. Craig,
Restorative Dental Materials
, 9
th
edition (1993) at page 197.
One advancement over the conventional glass ionomer cements is the hybrid ionomer cement, also known as resin modified ionomer cement. It contains, among other components, at least one polymerizable compound and polymerization initiators. The hybrid ionomer cement typically has liquid and powder components. The liquid component can contain an ionic polymer such as polyacrylic acid (the acid may be functionalized with ethylenically unsaturated moieties), a polymerizable compound, water, and optional redox catalysts, which functions as part of the initiating system. The powder component can contain basic-reactive glass and redox catalysts, such as oxidizing and reducing agents.
It has been recognized by those skilled in the art that a powder-liquid system, such as those of conventional or hybrid glass ionomer cement, can present drawbacks. For example, extra skill and time may be required to dispense proportionate amounts of the powder and the liquid and mixing them to form the cement.
To overcome the disadvantages of the powder-liquid system, some skilled in the art have investigated alternative systems. For example, U.S. Pat. No. 6,136,885 (Rusin et al.) discloses a ionomer cement system comprising (a) an organic composition having a liquid ingredient that is free of water, and (b) an aqueous composition having a liquid ingredient comprising water.
In U.S. Pat. No. 5,154,762 (Mitra et al.), a dental cement contains water, acid-reactive filler, water-miscible acidic polymer, ethylenically-unsaturated moiety, photoinitiator, water-soluble reducing agent, and water-soluble oxidizing agent. Two part paste-paste cements were disclosed at column 2, lines 58 to 66.
While the foregoing dental compositions may have been us compositions are sought.
SUMMARY
In brief summary, in one embodiment, the present invention provides a dental composition comprising (a) a part A comprising at least one polyacid and at least one polymerizable component and (b) a part B comprising water. The composition further comprises an oxidizing agent, a reducing agent (both being part of a redox catalyst system), and reactive fillers in at least one of part A or part B. One uniqueness of the present invention is that at least one of the following components exist in a disperse phase: the polyacid, the oxidizing agent, and the reducing agent.
In use, when parts A and B are mixed together to form the inventive composition, the reactive filler, the polyacid, and the oxidizing agent become chemically reactive. Upon mixing, parts A and B are at least partially miscible with one another. Parts A and B can be supplied in paste-paste form or paste-liquid form.
The inventive composition has shelf stability on the order of months, typically at least 12 months. The inventors have discovered that such long-term stability can be achieved when at least one of the following components is in the disperse phase: the polyacid and the redox catalyst.
The term “disperse phase” means generally a two-phase system where one phase contains discrete particles distributed throughout a bulk substance, the particles being the disperse phase, and the bulk substance being the continuous phase. In one inventive embodiment, the continuous phase is the polymerizable component and at least a portion of the polyacid and/or redox catalyst exists as the discrete particles. By “disperse phase,” it is also meant that not necessarily the entire polyacid and/or redox catalyst need to be insoluble in the polymerizable component. Some of the polyacid and/or redox catalyst can be soluble therein. The dispersed particles are generally less than about 60 micrometers in average diameter.
One skilled in the art can determine whether the polyacid and/or the redox catalysts exist in a disperse phase by using any number of separation techniques, such as centrifugation or filtration. In these techniques, if there is a disperse phase, it will phase separate out of the bulk substance, either catching on the filter paper in the case of filtration or phase separate and settle out in the case of centrifugation. The separation test method should be performed when the polyacid and/or redox catalyst is the presence of a polymerizable component. That is, the other components of the inventive dental composition, such as the filler, should not be part of the system during testing to determine the presence of a disperse phase.
Although numerous references have disclosed the use of polyacid and redox catalyst in ionomer cement compositions, the inventors are not aware of any reference that disclose or suggest using either one in a disperse phase. The inventors have been able to formulate resin modified ionomer cement compositions having stability exceeding 12 months.
The inventors have further discovered an alternative approach to achieving long-term stability in the dental composition. This approach uses a particular monoacid that is dissolved in the polymerizable component. The monoacid, as the name implies, contains acid functionality, but does not contain hydroxyl functionality, particularly primary or secondary hydroxyl groups. When using this approach it is not necessary to have the polyacid or the redox catalyst in a disperse phase.
Instabilities may exist in conventional and resin modified ionomer cement systems. For example, in some systems, peroxide oxidizing agents can react with compounds having acid functionality when both are solubilized, i.e., dissolved in some carrier, such as water, hydroxylic solvents, or short chain hydroxylic monomers all of which are widely used in glass ionomer cements. Oxidizing agents and reducing agents can react in the presence of water and initiate the setting of the polymerizable component unless the agents are first encapsulated. The polyacid can react with reactive fillers, especially with fluoroaluminosilicate (FAS) glass in the presence of water. The polyacid can react many reducing agents, such as amines and/or sulfinates, to induce premature free radical polymerization. Thus, the inventors have devised a unique solution to the instabilities that may be present in a dental composition by deliberately putting the polyacid and/or the redox catalyst in a disperse phase or by using a particular type of monoacid dissolved in the polymerizable component.
The inventive dental composition can be used in various applications, such as dental adhesives, artificial crowns, anterior or posterior fillings, casting materials, cavity liners, cements, coating compositions, mill blanks, adhesives and cements for affixing orthodontic brackets and appliances, endodontic cements, restoratives, prostheses, and sealants. The composition is especially suited for use as a cement. The composition can be placed in the mouth and cured in situ. Alternatively, it can be fabricated in a prosthesis outside the mouth and subsequently adhered in place in the mouth.
DETAILED DESCRIPTION OF THE INVENTION
The inventive dental composition can be formulated as a one- or a two-component
Falsafi Afshin
Konings Mark S.
Oxman Joel D.
Rusin Richard P.
Winters Edward J.
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