Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-10-07
2001-10-23
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...
C523S459000, C523S460000, C524S430000, C433S228100, C522S015000, C522S059000
Reexamination Certificate
active
06306926
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to polymerizing radiopaque compositions that include cationically active functional groups and radiopacifying fillers.
Fillers are often added to polymer resins to form composites having higher strength values than the polymer resin itself. Dental composites, for example, typically feature high filler loadings on the order of 50% by weight or higher.
Non-radiopacifying fillers such as quartz and silica have been successfully combined with free radically polymerizable components such as acrylates and methacrylates and a free radical initiator to form a useful dental composite following exposure to polymerization conditions. Such fillers also have been successfully used with cationically polymerizable components such as epoxy resins and a cationic initiator to form useful dental composites following cationic-initiated polymerization.
In many instances it is desirable to use a radiopacifying filler to create a radiopaque composite. Such composites are particularly useful in dental applications because the composite is x-ray detectable. Radiopacifying fillers have been successfully combined with free radically polymerizable components and free radical initiators to form dental composites. It would also be desirable to combine radiopacifying fillers with cationic initiators and cationically polymerizable components such as epoxy resins which undergo less shrinkage than acrylates and methacrylates upon polymerization.
SUMMARY OF THE INVENTION
Although there is a need for a radiopaque composite prepared by combining a cationic initiator, a cationically polymerizable component and a radiopacifying filler, the inventors have discovered that, unlike free radically polymerizable systems, not all polymerizable resin-filler-initiator combinations will produce a useful composite (i.e., a radiopaque composite having a Barcol hardness of at least 10 measured using a GYZJ-935 meter) upon exposure to polymerization conditions. In many cases, the inventors have discovered, the radiopacifying filler inhibits or suppresses the cationic polymerization mechanism. In some cases, the net result is a composite having a hardness value lower than the hardness value of the unfilled resin.
The inventors have now discovered that certain radiopacifying fillers, when combined with cationic initiators and cationically polymerizable components, will produce composites having a Barcol hardness of at least 10 (measured using the GYZJ-935 meter) following exposure to polymerization conditions. In some cases, this requires treating fillers that would otherwise interfere with the cationic polymerization mechanism, e.g., by heating or coating the fillers. The inventors have further identified selection criteria that can be used to screen cationic initiator-resin-radiopacifying filler combinations. The inventors have thus made it possible to prepare useful composites based upon cationic initiators, cationically polymerizable resins, and radiopacifying fillers.
Accordingly, the invention features, in a first aspect, a polymerizable composition that includes:
(a) a cationically active functional group;
(b) an initiation system capable of initiating cationic polymerization of the cationically active functional group; and
(c) a filler composition comprising a radiopacifying filler in an amount sufficient to render the polymerizable composition radiopaque. The radiopacifying filler is selected from the group consisting of metal oxides, metal halides, metal berates, metal phosphates, metal silicates, metal carbonates, metal germanates, metal tetrafluoroborates, metal hexafluorophosphates, and combinations thereof. The combinations may be in the form of physical blends or chemical compounds.
Components (a), (b), and (c) are selected such that the polymerizable composition polymerizes to form a polymerized composition having a Barcol hardness, measured according to Test Procedure A, infra, using a GYZJ-935 meter, of at least 10 within 30 minutes following initiation of the cationically active functional group at a reaction temperature of 25 C. Initiation can be determined using differential scanning calorimetry, and is manifested as an increase in enthalpy.
As used herein, a “radiopaque composition” is a composition that has the ability to diminish the path of x-rays to the same extent as an aluminum sample having the same thickness such that the density of an x-ray image of the composition is less than the density of the x-ray image of the aluminum, determined according to Procedure 7.11 of Intenational Standard ISO4049; 1988(E), “Dentistry—Resin-Based Filling Materials.”
A “cationically active functional group” is a chemical moiety that is activated in the presence of an initiator capable of initiating cationic polymerization such that it is available for reaction with other compounds bearing cationically active functional groups.
A “free radically active functional group” is a chemical moiety that is activated in the presence of an initiator capable of initiating free radical polymerization such that it is available for reaction with other compounds bearing free radically active functional groups.
A “metal oxide” is a compound that contains only a metal and oxygen.
A “metal halide” is a compound that contains, at a minimum, a metal and a halogen (e.g., chlorine, bromine, iodine, or fluorine).
A “metal borate” is a compound that contains, at a minimum, a metal, boron, and oxygen.
A “metal phosphate” is a compound that contains, at a minimum, a metal, phosphorous, and oxygen.
A “metal silicate” is a compound that contains, at a minimum, a metal, silicon, and oxygen. Thus, for example, a metal aluminosilicate containing a metal, aluminum, silicon, and oxygen would be considered a “metal silicate” for the purposes of this invention.
A “metal carbonate” is a compound that contains, at a minimum, a metal and a CO
3
group.
A “metal germanate” is a compound that contains, at a minimum, a metal, germanium, and oxygen.
A “metal tetrafluoroborate” is a compound that contains only a metal and a BF
4
group.
A “metal hexafluorophosphate” is a compound that contains only a metal and a PF
6
group.
The composition may also include a free radically polymerizable component such as an acrylic or methacrylic acid ester. Such compositions are often referred to as “hybrid” compositions. In a hybrid composition, free radical polymerization of the free radically active functional groups assists in obtaining the requisite Barcol hardness value of the composite. Nevertheless, even in hybrid compositions it is cationic polymerization of the cationically active functional group that preferably forms a polymerized composition having the requisite hardness value under the polymerization conditions described above.
In some embodiments, the polymerizable composition polymerizes to form a polymerized composition have a Barcol hardness, measured using a GYZJ-934-1 meter according to Test Procedure A, infra, of at least 10 within 30 minutes following initiation of the cationically active group.
The inventors have identified several screening tests for use in designing successful polymerizable compositions. Preferably, these tests are used in combination with each other.
One test focuses on the radiopacifying fillers themselves and is based upon isoelectric point measurements. The isoelectric point of any particular radiopacifying filler is independent of filler loading. However, the filler loading influences which values of isoelectric point are required in order to result in a successful cationic polymerization. According to this test, therefore, the filler composition is selected such that when the amount of the radiopacifying filler is at least 50% by weight of the polymerizable composition, the radiopacifying filler has an isoelectric point, measured according to Test Procedure B, infra, of no greater than 7.
Other tests focus on the interaction between the radiopacifying filler and a test polymerizable composition that includes a cationically polymerizable component and a cationic initiator. Accordin
Baker James A.
Bretscher Kathyrn R.
Craig Bradley D.
Gust Janis R.
Hayne Cheryl A.
3M Innovative Properties Company
Szekely Peter
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