SILICONE COMPOSITION FOR THE PREPARATION OF DENTAL IMPRESSIONS

Abstract: Silicone compositions, appropriate for dental impressions, curable by a polycondensation reaction catalyzed by a tin II compound. The improvement consists in using tin catalyst stabilized by an amine, which provides the composition with a long useful life (shelf life), before utilization/cure. The compositions advantageously replace the ones from the prior art, polyaddition cured, providing articles with better finishing and uniform surface. The process for preparing the composition and the cure to obtain formed articles are also described.

Description: SILICONE COMPOSITION FOR THE PREPARATION OF DENTAL IMPRESSIONS The present invention relates to a dental composition based on polysiloxane, which rapidly cures by a condensation reaction at ambient temperature, comprising: (a) an organopolysiloxane containing at least 2 (two) hydroxyl groups in the molecule, of the general formula (b) a Di- , Tri-, or tetraalkyloxide silane, partially ** hydrolyzed or not, of formula ' SiR R, n X (4-n) wherein R = methoxy, ethoxy, propoxy, butoxy R,= Alkyl and n = 2-4 (c) a novel curing catalyst to accelerate curing at ambient temperatures by a condensation reaction, of the general formula Sn(OCOR 1 ) 2 , wherein R, = alkyl, and, optionally (d) filler material for the formation of a desired composition comprising talc, paraffin, pyrogenic silica. -2- calciu carbonate, quartz, water, starch and pigments. The present invention relates to a hydroxysilicone composition with a combination of cross-linking agent/ catalyst which polymerizes through a condensation reaction, and is useful for the accurate molding of teeth. This two- component system comprises two pastes, or a paste and a low-viscosity liquid which, after being mixed, vulcanize at ambient temperature, i.e., the paste of the first component containing hydroxysilane polymerizes after being mixed with the cross-linking agent/catalyst within 2-5 minutes at ambient temperature to provide an elastomeric article. Si li cone compositions for dental impressions are well known and widely used. In general, they comprise dime hy lpolysiloxane with vinyl terminal groups, a catalyst based in platinum compounds and filler material, and are available at various consistencies, from non-fluid pastes to fluids. The second member also consists of pastes or fluids comprising si lane terminal groups or internal silane functionality for cross-linking and elastomer formation. These two members are mixed prior to use and cure at ambient temperature within 2—5 minutes as a result of a polyaddition reaction of the type =Si-CH=CH 2 + HSi≡ — — > ≤ Si-CH 2 -CH 2 -Si≡ The disadvantage of dental impressions obtained by polyaddition reactions and based on vinyl-si licone is the -3- re lease o ' f hydrogen gas which, after the introduction of the filler material in the composition, causes imperfections on the surface of the finished article. The hydrogen gas is formed by reaction of the vinyl groups of dimethylpolysiloxane with the non- reacted Si-H groups of the cross-linking agent, since they are in excess, and the hydrogen gas formation is brought about by the mouth moisture, by the subsequent application of plaster and by the platinum catalyst. The damaged surface of plaster has a large number of small craters, thus impairing the quality of the finished article. German "Of fenlegunsschrif t" No. 2926405 describes a process to avoid these disadvantages. In this process, palladium or palladium alloys of high commercial value are incorporated to the system, using the known hydrogen absorption by palladium. Other works describe the incorporation of aluminum silicate zeolites containing finely divided palladium, to remove the released hydrogen gas. However, these operations are very costly, time consuming and require special care when pitting and dimensional instability are to be avoided in the finished article. The corrosion of the articles, as well as their dimensional deformation, caused by silicone compositions cross-linkable by polyaddition, whose preparation processes have been known for many years, can be avoided and, at the same time, linear contraction (shrinkage) can be reduced to a minimum by using curable compositions in a poly condensation reaction of the type Sniv ≡Si-OH + RO-Si= ■_> ≡≡SSii--OO--SSii≤≤ + + R ROOHH t These compositions consist of two pastes, or a paste and a fluid, i.e., one base paste comprising hydroxyl silicone fluid with filler material and a cross-linking agent/catalyst paste or fluid containing tetraal yloxide silane with organic tin compounds as catalysts. U. S. patents 4,360,354 and 4,1-37,249 describe the use of tin IV compounds as active catalysts for the promotion of condensation of the hydroxi-terminated dimethylpolysiloxane fluid. Diorganopolysiloxanes capped with hydroxyl terminal groups may be cross-linked by a mixture containing a reaction product of esters of silicic acids with or-ganic tin IV compounds of the general formula R 2 Sn(OCOR 1 ) 2 wherein R is an alkyl radical and R' is a monovalent hydrocarbon radical. These cross-linking agents/catalysts are based on well known stable tin IV compounds. Catalyst materials for the condensation of hydroxypolysiloxanes , and tetraalkyloxide si lanes based on tin II compounds are less known. The oxi dative instability of the tin II compounds with chemical structure such as Sn(OCOR 1 ) 2 wherein R* is a monovalent hydrocarbon radical, render them unsuitable polycondensation catalysts for dental compositions, since a long shelf life is a necessity for these products. -5- Repeated exposure to air and moisture of the catalytic compounds of tin II causes a chemical decomposition into substances which no longer catalyse, nor cause polycondensa- tion of polysiloxanes containing hydroxyl groups. The simple combination of tin II compounds with tetraalkyloxisilanes also inactivates the cat_alyst, even without exposure to air and or humidity. According to this invention, and contrary to the above stated, it was noted that tin II compounds such as tin bis (2-ethylhexoate) , when stabilized with tertiary amines such as tris-isooctyl amine and formulated with tetraalkyloxide silanes result in stable and useful fluids for rapid cross- linking of hydroxypolysiloxanes ." The tin II compound becomes unexpectedly stable to oxidative decomposition by addition of small quantities of te tiary amines. According to this invention, the stability deficiency of the tin II active catalyst was overcome in a simple manner, using a stabilizing agent for tin II, such as tertiary amines in general and, more specifically, longer chain alkyl tertiary amines, and preferably, tris-isooctyl- amine together with di- , tri- and tetraalkyloxide silanes and, most preferably, tetraethoxysilane. It was also found that the addition of the tertiary amine as stabilizer for tin II has no harmful effects on the curing mechanism, neither does it increase the curing time during the poly- condensation reaction between the hydroxypolydimethylsiloxane and the alkyloxisilane. Therefore, this invention relates, in particular, to dental compositions based on polysiloxanes curable at ambient temperature and cross-linkable by poly condensation reaction, containing: (a) organopolysiloxanes with two or more hydroxyl groups per molecule of the general formula (b) tetraalkoxysi lanes of the general formula Si(R) 4 wherein R= methoxy, ethoxy, propoxy, butoxy (c) a catalyst consisting of a tin II compound of the general formula Sn(OCOR 1 ) 2 wherein R = monovalent hydrocarbon, and stabilized from oxidative decomposition by a primary, secondary or tertiary amine of the general formula wherein R_= alkyl; p= 1,2 or 3; q= 2, 1 or 0, respectively, (d) filler material and, if desired, other additives, such as pigments or similar. The hydroxysilicone compositions according to this invention are useful for the production of dental molds , such molds accurately reproducing tooth details through dental plaster molds. The preparation of the mold consists of a thorough mixing of the base component with the cross-linking agent/ catalyst component, subsequent introduction of this mixture into the oral cavity, where solidification occurs, and the removal of the cured mold from the oral cavity. The dental model is then obtained by filling the mold with plaster which, after curing, accurately reproduces the teeth forms. The materials constituting said compositions are: (a) silicone fluids containing hydroxyl functionality, (b) fillers, (c) cross-linking agent, (d) tin II catalyst, stabilized, with amines, and (e) others, like pigments, colorants, flavors and fragrances . The silicone fluid (a) is a dimethylpolysiloxane with hydroxyl terminal groups or internal hydroxyl functionality, with viscosity between 50 cst to several million cst, at 25°C, depending on the desired consistency of the composition. The filler (b) may be quartz, calcium carbonate, metal silicates, precipitated or pyrogenic silica, talc, , vaseline or paraffin, starches or similar. The cross- linking agent (c) is a di- , tri- or tetra- alkyloxisilane , particularly polydimethylsiloxane, which has alkyloxide functionality on at least two silicon atoms per molecule. Ethyl orto-and/or polysilicates are particularly useful. The ethyl polysilicates may have a Si0 2 content of up to 40%. Siloxane copolymers of various molecular weights and trialkyloxisilyl or dialkyloxisyl terminal groups are well known. The catalyst (d) is a tin II compound prepared from tin bis (2-ethylhexoate) stabilized with tertiary amine such as tri-isooctylamine. This stabilized tin II catalyst was unknown up to the present time. The stabilized catalyst may be used in a fluid condition or formulated with inert fillers to produce a paste. Colorants and pigments are used for differentiation between the base paste and the catalyst and as a control of the mixture uniformity. Inorganic and organic pigments are preferred. β The following 'examples are given as an illustration with no intention of limiting the invention. The amounts indicated are in parts per weight or percentage. Example 1 The base paste was prepared by mixing 19% polydimethyl- siloxane with hydroxyl terminal groups, with a viscosity of 20000 cst at 25°C; 16.6% micronized talc; 7.6% calcium carbonate; 2% pyrogenic silica with a specific surface of 2 at least 50 /g; 6.7% paraffin wax; 34% micronized quartz powder; 12% corn starch; 0.4% distilled water and 1.7% colorant, in a laboratory kneader. The cross-linking agent/catalyst was prepared mixing 45% ethyl polysilicate with a 35% SiO- content, 45% tin bis (2-ethylhexoate) , and 10% tri-isooctylamine. Thus, 17 g of paste were then manually mixed with 15 drops of cross-linking agent/catalyst during 30 seconds, and the mixture was applied to a dental molding frame and inserted into the oral cavity of a person. Two minutes after the insertion into' the oral cavity, the dental molding frame was removed and the mixture was elastic and with a 40 Shore A hardness. After 3 minutes, hardness increased to 60 Shore A. After washing of the mold, a plaster suspension was prepared, mixing 100 parts of hydrated calcium sulfate with 30 parts of water, and the suspension thus obtained was inserted into the mold. After 40 minutes, the plaster was removed from the mold. The model thus obtained was a perfect replica of the teeth, and the model surface was smooth, with no craters and corrosion-free. The cross-linking agent/catalyst was put into a closed glass bottle and placed in an oven, kept at a constant temperature of 45°C+2°C, during 8 months. After this period of time, the procedure of this example was repeated, only modified by the fact that the cross-linking agent/catalyst aged in the oven was used and the evolution of the Shore A hardness did not change significantly. Example 2 The base paste was prepared as described in example 1. A cross-linking agent/catalyst paste was prepared mixing 39.6 parts of 35% ethyl polysilicate, 39.6 parts of tin bis (ethylhexoate) , and 8.8 parts tri-isooctylamine and 10.6% of hydrophobic pyrogenic silica, and 1.4 of an inorganic pigment. - 10- Th us , 17 g of base pas te were manually mixed with 0 . 4 g of cross- linking agent/catalyst paste during 30 seconds and a homogeneous colour mixture was obtained. The mixture was applied to a dental mold frame and inserted into the oral cavity of a person . The mold hardness evolu- tion was equal to that of example 1 , and the quality of the plas ter dental replica, prepared as described in example 1 , was perfect . The model surface was totally smooth and presented no signs of corrosion or craters . The cross-linking agent/catalyst paste was placed into a toothpaste type tube and kept in an oven at a cons tant temperature of 45°C +_ 2<?c during 8 months . After this period, the procedure of this example was repeated , using the cross- linking agent/catalyst paste aged in the oven . The shore A hardness evolution did not change significantly . Example 3 The cross- linking agent/catalyst fluid was prepared mixing 50 parts of ethyl polysi licate with 35% SiO- content , with 50 parts of tin bis ( 2-ethylhexoate ) , with no amine stabili zing agent . The cross-linking agent/catalys t fluid thus prepared was placed in a closed glass bottle and kept at ambient temperature during one month . After this period of time the base paste was prepared according to examp le 1 , and 17 grams of the base paste were mixed with 15 drops of the cross-linking agent/catalyst fluid aged at ambient temperature , as s tated in this example . The mixture was applied to a dental molding frame and introduced into the oral cavity of a person . Fi fteen minutes -11- after the introduction into the oral cavity there was no sign of siginificant hardening of the mixture. The only difference in relation to procedure 1 was the lack of tri-isooctylamine as stabilizer of the cross-linking agent/ catalyst system. The examples given' above ilustrate this invention and several modifications may be introduced without limiting the spirit of the present invention. Summarizing, this invention refers essentially to a composition for dental molds that cross- links by poly- condensation reaction at ambient temperature, the composi¬ tion comprising: » (a) an organopolysiloxane with. at least two hydroxyl groups per molecule with a viscosity, at 25°C, of 50 cst up to 2,000,000 cst, preferably between 1000 cst and 200,000 cst and, most preferably, about 20,000 cst; (b) a cross-linking agent consisting of di- , tri- or tetra-alkyloxysiloxane or organopolysiloxane with at least two alkyloxide groups per molecule, most preferably ethyl orto-and/or polysilicate; (c) a catalyst to accelerate the condensation reaction consisting of a tin II compound, preferably tin bis(2-ethyl- hexoate) stabilized with a primary, secondary or tertiary amine, preferably a tertiary amine with long aliphatic chain and, most preferably, tri-isooctylamine; (d) (b) and (c) above may be combined for the forma¬ tion of a one-part cross- linking agent/catalyst system which remains fluid; and -12- (e) hydrophobic pyrogenic or precipitated silica, paraffin wax, calcium carbonate, quartz, water, corn starch and pigments or other known filler materials ,or carriers. In use: (1) (a) and (e) ar _e combined to form a base paste. ( 2 ) ( d) and ( c) may be combined for the formation of a .cross- linking agent/catalyst paste . ( 3) the paste obtained in ( 2) above or (d) may be combined with the paste obtained in ( 1) above for the forma¬ tion of a mixture that cross-links (hardens ) within 2 to 5 minutes , forming a useful elastomer for dental impressions .

Claims: -13- Claims 1. In a silicone composition for dental impressions, comprising (a) an organopolysiloxane with at least two hydroxyl groups in the molecule, of the general formula (b) a di- , tri- or tetraalkyloxisilane , partially hydro li zed or not, of the ' general formula Si R n R 1- (4-n) Wherein R is C,-C 4 alkyloxi R. is alkyl n = 2-4 (c) optionally, a filler material, the improvement comprising further including (d) 2 to 10 weight %, based on components (a), (b) and (c) , of a curing catalyst for the composition, by conden ¬ sation reaction, of the general formula Sn(OCOR 1 ) 2 -14- wherein R, is a monovalent hydrocarbon, and (e) a stabilizer, to prevent the catalyst oxidative decomposition, comprising a primary, secondary or tertiary amine of the general formula wherein R- is alkyl and p is 1, 2 or 3 and q is, respectively, 2, 1 or 0. 2. Composition, according to claim 1, wherein the organopolysiloxane has a viscosity, at 25°C, of about 50 cst to about 2,000,000 cst. , 3. Composition, according to claim 1, wherein the organopolysiloxane has a viscosity, at 25°C, of about 1,000 cst to about 200,000 cst and, preferably, 20,000 cst. 4. Composition, according to claim 1, wherein the alky lαxi si lane cross-linking agent is ethyl ortho- or polysilicate. 5. Composition, according to claim 1, wherein the curing catalyst is tin bis (2-ethyl exoate) . 6. Composition, according to claim 1, wherein the catalyst stabilizer is tri-isooctylamine. 7. Composition, according to claim 1, wherein the filler material is one or more of the following: hydrophobic pyrogenic or precipitated silica, paraffin wax, calcium carbonate, quartz, water', corn starch and/or pigments. -15- 8. Process for producing silicone composition for dental impressions, comprising intimately mixing the polycondensation reaction catalyst with the stabilizer described in claim 1 and the tetraalkyloxisilane separately mixing the hydroxi terminated organopolysiloxane and the filler material and keeping both components separately until their utilization. • 9. Process for producing a molding article, by poly¬ condensation reaction of the type: Sn ΞSi-OH + RO-Si - ≡Si-O-Si≡ + ROH f wherein the curing catalyst is an organometallic compound . of tin of the general formula Sn(OCOR.) 2 sta-bilized by a primary, secondary or tertiary amina of the general formula (R 2 ) NH , wherein R,, R 2 , p and q are as above defined; at ambient pressure and temperature conditions. 10. Process, according to claim 9, wherein the catalyst is tin bis ( 2— eth lhexoate) . 11. Process, according to claim 9, wherein the stabilizer is tri-isooctylamine. 12. Elastomeric article formed from a silicone composition condensation- curable obtained by the process of one of claims 9 to 11.

Inventors: MAKIYAMA TOSHIKO, REIDL BERND MARTIN, MAKIYAMA, TOSHIKO, REIDL, BERND, MARTIN
Applicants: UNION CARBIDE CORP, UNION CARBIDE CORPORATION
Application year: 1985
Main classification: A61K6
IPC codes: A61K6, C08K5