Abstract:
A polyvinylsolixane catalyst paste which comprises up to 20,000 ppm of finely divided platinum black which functions to adsorb hydrogen gas generated in the reaction of said catalyst paste when mixed with a base paste containing hydrofunctional polydimethylsiloxane, said base paste further containing a hydrophilic surfactant.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 932,246, filed Nov. 19, 1986 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The liberation of small quantities of hydrogen gas from RTV addition cured polyvinylsiloxane elastomers, due to the reaction between the platinum catalyst and hydrofunctional polydimethylsiloxane, is a recognized problem. The evolution of the hydrogen gas results in the formation of pores in the model formed from the impression, producing an undesirable pitted surface. 
     In the U.S. Pat. No. 4,273,902, issued June 16, 1981, and assigned to G-C Dental Industrial Corp., of Tokyo, this problem is well described and a solution is claimed using 0.5 ppm or more finely divided palladium and/or a finely divided palladium alloy containing 10% by weight or more of palladium, without inhibiting the addition reaction. In Column 3, line 33 et seq., various other elemental metals are cited, including platinum, but are stated to be inferior to palladium and fail to eliminate the undesirable pores in the surface of the resulting model. 
     The adsorption of hydrogen by palladium is variously quoted as 502, 935 and even 2952 times its own volume, J. W. Mellor, Inorganic Chemistry Vol XVII 1947, page 616 et seq., while the adsorption of hydrogen by platinum black is quoted as 310 volumes in Vol. XVI. It therefore becomes apparent that these adsorption variabilities arise from differences in the available surface areas of the finely divided metals, but are not significant in the case of the polyvinylsiloxane elastomer application, since if sufficiently finely divided and present in adequate concentration, the adsorption saturation level will never be reached. 
     Another problem associated with polyvinylsiloxane dental impression materials is their extremely hydrophobic characteristics which lead to comparatively large bubble shaped artifacts in the surface of such impressions. 
     SUMMARY OF THE INVENTION 
     Accordingly, it has been discovered that when samples of extremely finely divided platinum black were obtained with the highest possible surface area, specifically 24 M 2  /gram, and were compared with equal weight percent concentrations of palladium black, by incorporation in identical polyvinylsiloxane elastomer pastes they were found to be equally and completely effective, down to a concentration level of about 0.2 ppm by weight. An effective concentration range for the platinum black is about 0.2 to 20,000 ppm by weight. The size range for the platinum black should be as small as possible. A preferred size range for the platinum black is from about 18 to 28 Angstrom Units. 
     The use of platinum black in conjunction with the present invention is in controlling or preventing outgassing in all addition cured polyvinylsiloxane elastomers which are primarily used in making dental impressions. 
     The platinum black is used to adsorb gaseous hydrogen generated during the curing reaction, and generally at a concentration level of about 0.2 to 20,000 ppm. A preferred concentration range is from about 0.001 to 0.01 weight percent (i.e., 1,000 to 10,000 ppm). The platinum black is added or blended with the catalyst paste in any convenient manner such as illustrated in U.S. Pat. No. 4,273,902 which is incorporated herein by reference. 
     It has also been discovered that in a preferred embodiment of the invention that the extremely hydrophobic characterisitcs of polyvinylsiloxane dental impression materials, which lead to comparatively large bubble shaped artifacts in the surface of such impressions, can be overcome by the incorporation of relatively small quantities of selected surfactants. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Both base and catalyst pastes contain vinyl polydimethyl siloxane and silica or other similar inert filler(s) and the base paste contains a moiety of hydrofunctionalpolydimethylsiloxane whereas the catalyst contains both a chloroplatinic acid catalyst complex and platinum black, to adsorb any gaseous hydrogen formed during mixing of the pastes and curing of the impression. 
     A cured impression is produced by mixing the base paste and catalyst such as that illustrated by Example I, in a 1:1 or other suitable ratio to form a homogeneous plastic mass which is applied over the dentition and adjacent gingival tissue and allowed to cure during a time frame of several minutes prior to mouth removal. Models were made from impressions taken with the platinum black containing impression materials immediately after mouth removal and found to be free of pores in all cases at or above the 0.005 weight percent platinum level. 
     Impressions and resulting molds or models formed using the concept of the present invention result in a surface smoothness which is significantly better than those formed without the use of platinum black. 
     Another problem associated with polyvinylsiloxane dental impression materials of this invention is their extremely hydrophobic characteristics which lead to comparatively large bubble shaped artifacts in the surface of such impressions. 
     U.S. Pat. No. 4,600,751 teaches the controlled release of bioactive agents, and serves to demonstrate the synthesis of silicone based prepolymers which are extremely hydrophilic. 
     In dentistry, impression materials, particularly for making crown and bridge impressions, require a high degree of dimensional stability to facilitate the production of extremely accurate prostheses, for which the techniques of U.S. Pat. No. 4,600,751 would be totally unsuitable because high water sorption is consistent with swelling and distortion of these polymers. Furthermore there are, other definite advantages to dental impressions with low water sorption, such as ease of disinfection and sterilization. 
     With respect to the problem associated with the hydrophobic characteristics of the dental impression materials of the present invention is has been found possible to utilize several species of hydrophilic compounds as low concentration additives to conventional, extremely hydrophobic, addition-cured polyvinylsiloxane dental impression materials to impart truly hydrophilic surface characteristics to these materials. This results in the prevention of comparitively large bubble shaped artifacts in the surface of these impressions, due to the effects of surface tension at a strongly hydrophobic/hydrophilic interfere causing a film of moisture to form water droplets. 
     In a preferred embodiment of this invention, any one or more of the following surfactant type compounds are added to conventional addition-cured polyvinylsiloxane dental impression materials in relatively low concentrations of about 1.0% to 10.0% by weight. 
     
         ______________________________________                      CAS NO.                      WHERECOMPOUND NAME              KNOWN______________________________________n-Dodecyl, Tetradecyl, Hexadecyl Alcohol                      68551-12-2EthoxylatePolyethylene Glycol Monolaurate                      9004-81-3Polyethylene Glycol DilauratePolyethylene Glycol MonoleatePolyethylene Glycol DioleatePolyethylene Glycol MonotallatePolyethylene Glycol DitallateSorbitan MonolaurateSorbitan MonoleateSorbitan TrioleateSorbitan MonotallateSorbitan TritallatePolyethylene Glycol Glycerol CocoeateCaprylic TriglyceridePolyoxyethylene Tridecyl Alcohol                      24938-91-8Polyoxyethylene Lauryl Ether                      5274-68-0Nonylphenoxypoly (ethyleneoxy) ethanol                      9016-45-9Polyoxyethylene Sorbitan MonolaurateSorbitan Monolaurate Polyoxyethylene Polysorbate                      9005-64-5Polyoxyethylene Oleyl Alcohol______________________________________ 
    
     The above listing of suitable surfactants is not exhaustive, but serves to illustrate twenty representative examples of the manny chemical permutations possible with the family of Polyol fatty acid ester and ethoxylated ester type surfactants useful for this invention. 
     The effectiveness of these surfactant additives is readily apparent in their ability to reduce the aqueous contact angle with cured or uncured addition-cured polyvinylsiloxane dental impression materials from the range of 95°-110° down to 30° or less. Upon contact of the dental impression materials with the dentition and gingiva any moisture present on the surface of these oral tissues is readily miscible with the surfactant moiety available at the surface of the impression material, which provides uniform wetting of the interface between the impression material and the oral tissues, thereby dramatically reducing surface tension. 
     The following example illustrates one embodiment of the present invention. The concentrations are in weight percent unless otherwise stated. 
     EXAMPLE I 
     Embodiments of Platinum Black for gaseous adsorption 
     
         __________________________________________________________________________BASE PASTE          CATALYST PASTE(VERY HEAVY VISCOSITY)           WT %               (VERY HEAVY VISCOSITY)                               WT %__________________________________________________________________________Vinyl Polydimethylsiloxane           20% Vinyl Polydimethysiloxane                               20%Hydropolydimethyl Siloxane            3% *Cyclic Vinyl Siloxane                               0.4%Silica Filler   70% **Chloroplatinic Acid Complex                               1.0%Liquid Petroleum or other            7% Liquid Petroleum or other                                7%inert plasticizer   inert plasticizer               Silica or other inert filler                               71.6%__________________________________________________________________________ 
    
     The following illustrates suitable compositional ranges for the components of the base and catalyst paste. 
     
         ______________________________________               CATALYSTBASE PASTE  WT %    PASTE        WT %______________________________________Vinyl Polydimethyl-       10-60   Vinyl Polydi-                            10-60siloxane            methylsiloxaneHydropolydimethyl       1-10    Cyclic Vinyl 0-2Siloxane            SiloxaneSilica Filler       20-80   Chloroplatinic                            0.1-5.0               Acid ComplexLiquid Petroleum       0-15    Platinum Black                            0.2-20,000 ppm               Plasticizer  0-15               Filler       20-80______________________________________ 
    
     The following illustrates suitable compositional ranges for a cured dental impression material of the present invention. 
     
         ______________________________________VERY HEAVY VISCOSITYMATERIAL (PUTTY)        WT %______________________________________Vinyl Polydimethylsiloxane                   10-60Cyclic Vinyl Siloxane   0-1Hydropolydimethyl Siloxane                   0.5-5.0Filler                  20-80Chloroplatinic Acid Complex                   0.05-2.5Platinum Black          0.1-10,000                             ppmPlasticizer             0-15Surfactant (optional but preferred)                   2-10______________________________________ *Available under the tradename PSW 2204 from Petrarch Silicones of Bristol, PA. **Available under the tradename PSW 2206 from Petrarch Silicones of Bristol, PA. 
    
     Embodiments using surfactants to confer hydrophilic characteristics: 
     EXAMPLE 2 
     
         ______________________________________Low viscosity Catalyst paste with surfactant                       WT %______________________________________Vinyl functional polydimethylsiloxane                       51.785Silaceous Filler            43.0n-Dodecyl, Tetradecyl, Hexadecyl Alcohol Ethoxylate                       4.0Pigment                     1.0Cyclic vinyl functional prepolymer                       0.2Chloroplatinic acid catalyst complex                       0.01Platinum Black              0.005                       100.00______________________________________ 
    
     Excellent hydrophilic surface characteristics, but unpleasant taste. 
     EXAMPLE 3 
     
         ______________________________________Low viscosity Base paste with surfactant______________________________________Vinyl functional polydimethlsiloxane                   46.0Silaceous Filler        42.0Hydrofunctional Polydimethylsiloxane                   7.0Pigment                 2.0Nonylphenoxypoly(ethyleneoxy)ethanol                   3.0                   100.0______________________________________ 
    
     Excellent hydrophilic surface characteristics and acceptable taste. 
     EXAMPLE 4 
     
         ______________________________________Low viscosity Base paste with surfactant______________________________________Vinyl functional polydimethylsiloxane                       46.0Silaceous Filler            41.0Hydrofunctional polydimethylsiloxane                       7.0n-Dodecyl, Tetradecyl, Hexadecyl Alcohol Ethoxylate                       4.0Pigment                     2.0                       100.00______________________________________ 
    
     Excellent hydrophilic surface characteristics, but unpleasant taste. 
     Although the above examples are restricted to low viscosity polyvinylsiloxane dental impression materials the same family of Polyol fatty acid ester and ethoxylated ester type surfactant can be used as additives in the regular and heavy, even putty viscosities of the same type of material with equally effective results. 
     The following illustrates suitable compositional ranges for the components of the base and catalyst pastes of Examples 2 through 4. 
     
         __________________________________________________________________________BASE PASTES   WT %             CATALYST PASTES                            WT %__________________________________________________________________________Vinyl polydimethylsiloxane         25-75             Vinyl Polydimethylsiloxane                            25-75Hydropolydimethyl siloxane          1-12             Cyclic Vinyl Siloxane                            0.5Silaceous Filler(s)         25-75             Silaceous Filler(s)                            25-72Surfactant(s)  1-10             Surfactant(s)  1-10Pigment(s)    0.5 Pigment(s)     0.5             Chloroplatinic Acid Complex                            0.1-5.0             Platinum Black 0.2-20,000                                  ppm__________________________________________________________________________ 
    
     The following illustrates suitable compositional ranges for a cured dental impression material of Examples 2 through 4 of the present invention: 
     
         ______________________________________LOW VISCOSITY MATERIAL (LIGHTBODY OR WASH)           WT %______________________________________Vinylpolydimethylsiloxane                   25-75Hydro polydimethylsiloxane                   0.5-5.0Cyclic Vinyl siloxane   0-1Silaceous Filler(s)     25-75Surfactant(s)           1-10Pigment(s)              0-5Chloraplatinic Acid Complex                   0.05-2.5Platinum Black          0.01-10,000                             ppm______________________________________ 
    
     The following is a preferred embodiment of the present invention which exhibits the desired properties with respect to controlling outgassing and hydrophilic characteristics: 
     
         ______________________________________                    WT %______________________________________LOW VISCOSITY BASEPASTE WITH SURFACTANTVinyl functional polydimethylsiloxane (4000 cps)                      46.0Calcium Silicate Filler    42.0Hydrofunctional polydimethylsiloxane                      7.0Nonylphenoxypoly (ethyleneoxy) ethanol                      3.0Cobalt Blue Pigment        2.0                      100.00LOW VISCOSITY CATALYSTPASTE WITH PLATINUMVinyl functional polydimethylsiloxane (4000 cps)                      54.73Calcium Silicate Filler    43.98Cobalt Blue Pigment        1.0Cyclic Vinyl functional prepolymer                      0.27Chloroplatinic Acid Catalyst complex                      0.01Platinum Black (24 M.sup.2 /gm)                      0.01                      100.00______________________________________ 
    
     The following is a typical method used in preparing the compounds of the present invention. Other methods and compounds, such as those set forth in the above mentioned U.S. Pat. No. 4,273,902 may also be used in conjunction with this invention and are incorporated herein by reference. 
     BASE PLATE 
     Blend together in a double planetary mixer the three liquid components, Vinyl functional polydimethylsiloxane, Hydrofunctional polydimethylsiloxane and Nonylphenoxypoly(ethyleneoxy)ethanol. Add pigment, and then reblend to evenly disperse the pigment, filler is then added and mixed until thoroughly homogenous to form a low viscosity fluid paste. The resulting paste is then rollmilled to maximize homogeneity followed by packaging as desired. 
     CATALYST PASTE 
     Preblends are made of the Chloroplatinic acid complex with a portion of the Vinyl functional polydimethylsiloxane and of the Platinum Black with a portion of the Calcium Silicate filler. Blend together the three liquid components, Catalyst complex preblend, balance of Vinyl functional polydimethylsiloxane and Cyclic Vinyl prepolymer. Add pigment, reblend to disperse, then add Platinum Black preblend, followed by balance of the filler and mix until throughly homogenous. Rollmill to maximize homogeneity and then package as desired. 
     While the invention has been described in detail with respect to specific embodiments thereof, it will be understood by those skilled in the art that variations and modifications may be made without departing from the essential features thereof.