DK158280B - POLYMERIZABLE TOOTH REPAIR MATERIALS AND PROCEDURES FOR PRODUCING THEM - Google Patents

Description

DK 158280 B

The present invention relates to a polymerizable tooth repair material which is stabilized against premature activation of a catalyst component and comprising at least one methacrylate monomer having 2-4 polymerizable olefinic double bonds, a free series of polymerization catalyst comprising an organic peroxide or hydroperoxide compound which, upon activation, is capable of initiating polymerization of the monomer, said catalyst being present in an amount of 0.5-5% by weight based on the weight of the monomer, and optionally a portion of preferably inorganic filler, preferably a silicon-containing material, and optionally a silane coupling agent, and a process for making such a polymerizable material.

15

Polymerizable dental materials based on the use of polymerization catalyst, e.g. free radical initiator, and monomers of the methacrylate type, such as the bisphenol A-glycyldylmethacrylate reaction product, described in U.S. Patent No. 3,066,112, and commonly referred to as BIS-GMA, provide valuable basic materials for a wide variety of dental restoration and repair treatments. , such as fillings, sealing and filling of holes, cracks and the like. Such agents are generally used in accordance with a prescribed chronology where the contact of the polymerization catalyst activator for the agent in the presence of polymerizable monomer occurs only at the time the dentist actually uses it. Agents are selected and dosages are controlled to ensure fairly rapid polymerization at such a contact to provide a solid polymer in the oral cavity. In order to facilitate handling and manipulation, the materials can be delivered to the dentist in the form of a series of viscous pastes, which allow the agents to be uniformly mixed with a minimum of effort.

As described in the prior art, the foregoing can be achieved by providing physically separated filler-containing products containing monomer / catalyst, monomer / activator, respectively.

2 DK 158280 B

vator, etc .. The commercially available products are packaged separately.

In spite of the manufacturer's precautions, it has been found in practice that undesirable polymerization of the monomeric material upon standing nevertheless occurs rather rapidly and to a disruptive extent before the time of contact with the activator material. Such undesirable polymerization is seen despite the fact that various inhibitors are included in the monomeric materials to react with randomly occurring free radicals which may cause polymerization. Polymerisates formed from such destabilized monomer materials have, without exception, poor structure, integrity, color, etc. Curing of the monomer material, a necessary consequence of prepolymerization, can further render the affected monomer completely unsuitable for dental use. Thus, the price can be prohibitive. To avoid the problem of premature polymerization, the dentist will generally cool the components of the polymer-forming material before use.

So far, there have been various relief measures to remedy the foregoing. Thus, it has been found that monomer destabilization can be effectively delayed somewhat by using a specific type of free radical catalyst, e.g. a particularly heat-stable catalyst. However, this way of dealing with things assumes that the problem is in all cases due to the effect of heat, ie. the higher temperatures accelerate or initiate the free radical-forming reaction of the catalyst. The number of straight catalysts used is significantly reduced by this method.

Other methods involve using fairly large amounts of filler, e.g. silica, to obtain appropriate storage stability. However, inorganic fillers of the type normally used in the products described may well delay the cure or polymerization of methacrylate monomer, as pointed out in the published literature. This can be clearly counteracted by the use of silane coupling or locking agents which are said to effect at least partially restored hardness or polymerizability of the monomer. It is of the utmost importance

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mercurability of the monomer. It is of the utmost importance that the effects of the agents to suppress undesirable monopoly polymerization do not appear to be significant at the time of monomer / catalyst activator contact, at which time rapid and effective polymerization.

5

Although the above is only partially representative of the relevant technology in the field, it is obvious that effective implementation of the auxiliary process can be difficult and requires careful and accurate balancing of a number of factors which in themselves can cause further problems.

In accordance with the present invention, it has been found that the described monomer stability problem is primarily related to the nature of the monomer supplied for use in the preparation of the material, rather than to a reaction which can occur between and among materials used. as additional constituents of the monomer material.

20

The present invention is based on the surprising finding that methacrylate monomer and especially the BIS-GMA monomer, which is generally commercially admixed when mixed with catalyst, especially of the peroxide and hydroper = oxide type, has limited storage resistance, and that the mixture more than often polymerizes under storage conditions before use, rendering the product unsaleable for reconstruction purposes. Such false reactivity is found even under moderate conditions, such as the conditions commonly encountered during normal storage. In a laboratory study using commercial BIS-GMA as the monomer, catalyst-containing samples thereof, which have not been treated according to the invention, give polymer after just 1 day standing at room temperature.

3 5

Although the instability is due to pollution and what the source is is an open question. It may thus have been incorporated.

DK 158280B

conducted at a time during the preparation and / or processing of the methacrylate monomer and / or precursor materials. It is particularly difficult to purify bisphenol A-aiethacrylate triane oxner materials by distillation because of their high boiling nature. Therefore, the possibility of a high-boiling contamination of the material cannot. excluded.

Whatever the reason, it has been found that the treatment of the methacrylate monomer with an ion exchange material and especially a sulfonic acid type cation exchange resin in acid form greatly reduces any tendency for the monomer to polymerize, especially when mixed with catalyst, and especially of the free radical peroxide type.

As previously discussed, the stability problem is particularly urgent with monomeric materials containing BIS-GMA, since this substance has surprisingly been found to polymerize after just 1 day at room temperature in the presence of (e.g.

2% based on monomeric cumene hydroperoxide, a heat-stable catalyst. Conversely, commercial inhibitor-2q containing methyl methacrylate containing from 1-2% benzoyl = peroxide polymerizes after a few days at 25 ° C, but exhibits significantly greater stability than would be expected in the presence of the more heat-stable cumene hydroperoxide and t hydroperoxide. Based on the 10-hour half-life 0_, the recommended temperature when using benzoyl peroxide is approx. 73 ° C and using cumen hydroperoxide and t-butyl hydro = peroxide 160 ° C and 170 ° C respectively. BIS-GMA. is, therefore, somewhat abnormal in that it undergoes premature polymerization rather quickly, even with heat-stable catalyst materials.

30

The foregoing serves not only to point out the importance of the possible disparate nature of the pollutants, but also the disparate effects caused by the pollutants on various catalyst materials. When BIS-GMA is used as the sole or most important monomer, long-term contact between the monomer and catalyst prior to treatment should be avoided, whereas a greater leeway exists with monomers such as methyl methacrylate. In the first-

DK 158280 B

in said case, the treatment with the ion exchange resin should preferably be done before contact between monomer and catalyst.

The sulfonic acid cation exchange resins are well known and are commercially available in a wide variety of forms. In particular, the sulfonated cross-linked polystyrene resins, such as those commercially available as DOWEX * 50 W-X8 in the form of beads (1.9 meq / ml / H + wet - 5.1 meq / ml dry) are particularly preferred. Other suitable (S) sulfonic acid cation exchange resins include DOWEX ^ 50W-X2, DOWE3P5OW-X4 and DOWeAow-X10 (Dow Chemical Co.), as well as Amberlitir IR 120, Amberlysr ^ 15 (Rohm & Haas) and 10 "Rexyn" 101 (H) from Fisher Chem. Co., the latter being characterized as 4/6 meq / ml - dry basis. Cation exchange resins are most effectively used to treat the monomer prior to its contact with the catalyst / i.e. as a pre-treatment. According to this method, contaminants which can be removed by cation exchange treatment, including those of cationic nature, are at least substantially removed from the monomer, ie. physically extracted from there. Impurities present in the cation exchange resin as it is commercially available can be removed therefrom by washing with acetone followed by oven drying before contacting it with the methacrylate monomer. Such contact may occur in the usual manner, e.g. by simply adding the ion-exchange beads (e.g., 16-100 mesh, preferably 20-5Q mesh) to a solution of the methacrylate monomer, stirring the mixture for the required time, and filtering to separate the beads. The contact is maintained until the contamination is substantially removed completely, which is determined by storage stability studies. In a laboratory experiment, a solution mixture of 8 parts of cation exchange resin with 52 parts of a BIS-GMA 30 containing monomer material, for example, gave one monomer product substantially free of contaminants after 24 hours of stirring. Alternatively, contamination removal of monomer may be suitably achieved by passing the monomer through a suitable column of the ion exchange resin in known manner.

Methacrylate monomer materials useful herein are well known in the art. The preferred materials include all 35

DK 158280 B

6 usually monomers having a central moiety containing at least one aromatic ring and at least two acrylic end groups. Of this type, BIS-GMA is particularly preferred and in preferred embodiments it constitutes at least approx. 50% by weight of the total 5 monomer material. The commercial product BIS-GMA is available from

CiS

Freeman Chemical Co. under the trademark NUPOL ^, is an example of suitable materials herein.

Methacrylate monomers particularly useful in this invention are those which can be illustrated by the following general formulas: [(M - A - O} - Ar] 2 - B (M - A - OCO) 2Ar

I II

(M - A) CR M-R1 (M - A - OCO - NH) 0R3 m p 2 2

III IV V

CH0 - M

CH - M '

CH2 - M VI

wherein M is methacryloyloxy, i.e. CH 2 = CiCH 2 COO-, M 'is methacryloyloxy or hydroxyl, A is alkylene of 1-3 carbon atoms such as methylene, propylene, isopropylene, hydroxyalkylene of 1-3 carbon atoms such as hydroxymethylene, 2-hydroxypropylene and acetoxyalkylene of 3-5 carbon atoms in the alkylene group such as 2-acetoxypropylene, 3-acetoxyamylene, etc., n is 1-4, preferably 1 or 2, m is 2 or 3, and 25 p is 1 or 2, provided that the sum of m and p is 4, R is hydrogen, methyl, ethyl or -AM wherein A and M have the meanings previously stated, Ar is phenylene,

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7 e.g. o-phenylene, m-phenylene or p-phenylene, alkyl-substituted phenylene, e.g. tolylene or 5-t-butyl-m-phenylene or cycloaliphatic having 6-10 carbon atoms, such as 1,3-cyclohexylene, B is p 4/5> X X R 5 wherein R and R are independently hydrogen, alkyl, f .g. C 1 -C 4, or substituted alkyl, and R 1 is alkylene of 2-12 carbon atoms such as ethylene, dodecylene, etc., or 2 2 2 -R - (OR> OR - where R is alkylene of 2 or 3 carbon atoms , Such as ethylene, propylene or isopropylene, and x is 0-5 and 3 R is phenylene, tolylene, methylene-bis-phenylene or alkyl of 2-12 carbon atoms.

Monomers · with the above formulas are well-known and common commercial products. Alternatively, they can be readily provided by conventional synthetic manufacturing methods, e.g. by reaction of a phenolic compound such as diphenolic acid, phloroglucinol or bisphenol A with glycidyl methacrylate in the presence of various tertiary amines and / or phosphines or by reaction of methacrylic acid with an epoxide containing compound such as the diglycidyl ether of a bisphenol. Some of these monomers are also prepared by reacting appropriate alcohols with methacrylic acid, methacrylyl chloride or methacrylic anhydride.

Examples of monomers by these formulas are; CH2 = C (CH3) COOCH2CH2-OCO-- COOCH2CH2OCOC (CH31 = CH2,

CH2 = C (CH3) -COO - CH2OCO-OCOC (CH3) = CH

HO CH3 CH3 OH

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8 C-ECH2OCOC (CH3) = CH2] 4, CH3CH2C-fCH2-0-pC = CH2) 3, 0H3 CH2 = C (CH3) COO (CH2) 4OCOC (CH3) = ch2, CH2 = C (CH3) COOCH2CH2OCH2CH2OCH2CH2OCOC (CH2) = ch2, CH2 = C (CH3) COOCH2CH (OH) CH2- "TO O-CH2-CH (OH) CH2OCOC (CH3) = ch2 ch2 = C (ch3) COO- (5) - c (CH2) ) 2- (5) O-COC (CH3) = CH2, CH2-C (CH3) COO-CH2CH (OH) ch2-o -W & - OCH2CH (OH) CH2OCOC (CH3) = CH2 OCH2CH (OH) OOOC (CH3) ) = ch2 Γ3

ch2 = c (CH3) coo ^ 2CH2ohero ^ iN

NHCOOCH2CH2OCOC (CH3) = CH2CHO

I J

CH2 = C (CH3) COO-CH2CH-OCCNH-CH2CH2C-CC -CH2-NHCOOC H-CH2-OCO-C (CH3) = ch2 ch3 ch3 ch3 ch3 Monomers of formulas I, IX, III and IV are preferred in connection with the practical practice of the present invention. Of these monomers, I, II and III are particularly preferred, with monomers IV being more frequently used in admixture with one or more of monomers I, II and III.

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9

Other useful methacrylate monomers suitable for use in the practice of this invention include those monomers having the following formulas wherein M and Ar have the previously defined meanings} 4 4 5 MR OAr) 2C (CH2) 2 * wherein R is isopropylene ; c 5 c (MR OAr) 9 and (MR 0) oAr wherein R is 2-hydroxypropylene, MA RbM wherein R ° is hydroxycyclopentyl or hydroxycyclo =

O Q

hexyl and A is 2-hydroxyethylene and M 2 R / wherein R is:

(A) CH

-O-irO- · GHa (B) -CH2- ~ ch2 ~ '(C) -CH2- <0> - O - <g ^ CH2- or (D) -CH2 _ <@ HCH2- These monomers are usually commercially or can be easily manufactured. Preparation details for many of these monomers are set forth in U.S. Patent Nos. 3,066,112, 3,721,644, 3,730,947, 3,770,811 and 3,774,305. A tertiary eutectic monomer mixture also suitable for use in this invention is described in U.S. Patent No. 3,539,526. All of the aforementioned patents are hereby fully considered to be incorporated in the present text.

DK 158280 B

10

It is to be understood that mixtures of two or more suitable methacrylate monomers "fall within the scope of the present invention. Depending on the choice of monomers, it is in fact often very desirable with mixtures to optimize the properties of the resulting dental material.

It is preferred that the monomeric or monomeric mixture has a viscosity of from about 100 to approx. 10,000 centipoise determined using a Brookfield vis cosimeter at 20 rpm. minute at room temperature.

10 More viscous masses are conveniently handled at higher temperatures. As indicated, preferred mixtures contain at least about 50 yeast% BIS-GMA.

Preferred aliphatic dimethacrylate monomers (also referred to as diluent monomer e) and particularly for use in admixture with BIS-GMA., As described, include: Hexamethylene = dimethacrylate (HMDMA), triethylene glycol dimethacrylate (TEGDMA) and polyethylene glycol (TEGDMA) According to a highly preferred embodiment, the monomer material comprises a mixture of equal parts BIS-GMA and HMDMA, this system having excellent stability at both room temperature and elevated temperature (37 ° C).

Free radical-forming catalysts useful herein generally comprise organic compounds which, when activated, release free radical forms capable of initiating polymerization of the monomers previously described. for the formation of solid MAS polymerizers, which, especially in the case of filler-containing systems, have good compressive strength of the order of 1757-2109 kg / cm, and preferably at least 2400 - 2812 kg / cm. Preferred materials 30 are the organic peroxides and hydroperoxides, and among them, especially benzoyl peroxide, cumene hydroperoxide and t-butyl hydroperoxide are preferred. The catalyst is usually contained in amounts of approx. 0.5-5%, preferably 1-4% and best 1-3% by weight of all monomer. A particular advantage of the invention is that

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11 high catalyst quantities are allowed within the given range without adversely affecting stability.

A further and particularly valuable feature of the invention is that filler is not necessary to achieve the storage stability and is therefore an optional component of the present products. Good stability is thus achieved in the monomer material, whether or not such material is included. When used, the amount of filler can go up to approx. 400% by weight of the monomer. However, on the basis of the polymerization (curing) retarding effects of the filler, it is generally advisable to limit the amount thereof to less than 100% and preferably below about 10%. 80% by weight of the total product.

The inorganic particulate filler used in the products of the invention includes molten silica, quartz, crystalline silica, amorphous silica, soda beads, barium glass and other X-ray impermeable glasses, glass rods, ceramic oxides, particulate silicate glass, and β-synthetic minerals, ), the latter having a negative heat expansion coefficient. It is also possible to use finely divided substances and powdered hydroxylapatite, although materials which react with silane coupling agents / are preferred. Small amounts of pigments that allow the color of the product to be adjusted to the teeth can be included. Suitable pigments include iron oxide black, cadmium-yellow and orange, fluorescent zinc oxides, titanium dioxide, etc. The filler particles usually tend to be less than about 5 microns in diameter and preferably at 30 microns. Non-filler products are particularly suitable where the dental product is intended to form a coating, tooth-side sealant for tooth-side reinserting or adhesive.

Coupling means, which may also be optionally used herein, are, as mentioned, particularly suitable when a silica agent is used.

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12 filler since they tend to at least partially counteract the polymerization inhibitory effects of the filler, thereby restoring an approximately equivalent measure of polymerizability. The beneficial effects of the coupling agents, which are silane compounds, are most obvious in connection with the compressive strength which characterizes the finished dental polymerisate.

The silane coupling agents are substances which contain at least one polymerizable double bond for reaction with the methacrylic 10 monomers. Examples of suitable coupling agents are γ-methacryloxypropyltrimethoxysilane, vinyltrichlorosilane, tris (2-methoxyethoxy) silane, tris (acetoxy) vinylsilane, 1-N- (vinyl «benzylaminoethyl) aminopropyltrimethoxysilane-3. because of the similar reactivity of the double bonds.

The coupling agent can simply be added to the filler-containing monomer material, since no prior hydrolysis is required in accordance with e.g. the acidic and alkaline hydrolysis techniques described in U.S. Patent No. 3,066,112, although such a method may be used. Thus, the filler (usually quartz) may be slurried first with an aqueous solution of the coupling agent of a concentration such that about 0.5-2% by weight of the agent is deposited on or reacted with the filler and then mixed with the monomer material. The latter process apparently results in a multiple-fold increase in the amount of silane that reacts with and / or becomes bound to the filler. The strength properties of the dental polymerisates prepared with the present agents prove superior, whichever method is used.

Formation of the dental polymerisate in the oral cavity is accomplished by mixing the present material, usually in the form of a paste-like consistency with an activator-containing material which may be added filler of

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13 the said type. Suitable activators include substituted thioureas, e.g. acetylthiourea, N, N-dimethylparatoluidine and para-toluenesulfinic acid. Polymerization and subsequent curing occurs rapidly / but over a reasonable period of time for / the dentist being given the opportunity to quickly treat the area subjected to dental repair with the agent. The resulting polymerate has good strength, especially compressive strength, and has no detectable tendency to crack, crack or otherwise be damaged. The polymer is completely non-toxic and tends to give low molecular weight or other substances that could cause gum irritation and thus appears in everyone. essential considerations inactive to the effects of fluids found in the oral cavity.

The polymerizable dental products prepared and prepared as described herein are stable for months at room temperature, with no evidence of premature polymerization. In addition, good stability exists at elevated temperature, with certain preferred products exhibiting good long-term stability at a temperature of the order of 37 ° C.

It is to be understood that the contamination problem described may be more or less pronounced depending on the type of methacrylate monomer used, as well as the catalyst material. Thus, an improved level of stability can be achieved in a given case with a combination of slightly or even highly contaminated monomer and relatively stable catalyst material. The importance of the catalyst in this regard is not fully clarified, X to the extent that the contamination contributes to the dissociative reaction of the catalyst and, consequently, free radical formation, provides the treatment described herein and the products designed therewith for the stability improvement described. Since materials which are capable of affecting the catalyst are thus in many or in them

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14 most cases are suitable for accurate chemical identification, it is not necessarily known what types of materials can function thus; however, such materials may be included in methacrylate monomers here and as described herein due to the process of monomer preparation or other treatment. In particular, BIS-GMA is a more dramatic example of a commercially available material which, as the present applicant has demonstrated, contains such destabilizing contaminants.

Purification treatment of the monomer, including that which has been or is in contact with the catalyst, must be carried out before the formation of free radicals in appreciable amounts, i. amounts sufficient to initiate a rate of polymerization which forms sufficient polymer in a relatively short time. By "short time" is meant a shorter period than that which was usually considered associated with requirements for holding time here. For the most part, the polymerizable material is usually used by the dentist within a few weeks of purchase.

20 Monomer destabilization will not be a problem for the present products, as they are stable under the storage conditions normally expected beyond the period of time the dentist has them. Considering that the polymerizable material is likely to be cooled by the dentist before use, it will be in order with even longer shelf life. Mixing of monomer and catalyst by the manufacturer will further and, of course, take place as planned and necessarily shortly before sale. However, if a sufficiently long storage time and / or high temperature occurs, gelling will certainly occur in the monomer material. Even the presence of a small amount of free radical will eventually cause gelling.

In the present text, it is intended that the term 15

DK 15 S 2 8 O B

"before the formation of free radicals" or "before the formation of free radicals in appreciable quantities" shall have a meaning consistent with the foregoing and shall be understood by reference thereto. Thus, treating a pre-formed mixture of catalyst and monomer in accordance with one embodiment of the invention prior to the formation of a significant amount of free radicals merely means that any free radical forms present at this time of treatment will not be sufficient for to effect gel formation of the monomer material within the described holding time requirements.

The stability of commercial BIS-GMA and methyl methacrylate (MMA) in the presence of organic peroxide and hydroperoxide * catalysts is compared as follows: 15 portions of ΜΜΆ (Rohm and Haas product containing 10 ppm methyl ether of the hydroquinone, MEHQ1 are mixed with catalyst to produce 2% solutions of benzoyl * peroxide (BP), cumene hydroperoxide (CHP) and t-butyl hydroperoxide (TBH) respectively, the solutions being allowed to stand at ambient temperature (20-25 ° C).

Portions of BIS-GMA (Freeman Chemical Co. product obtained under the trademark "NUPOL" \ are similarly prepared to produce 2% solutions, respectively, of the same catalyst materials and allowed to stand at 20-25 ° C. The results obtained are given in the following table:

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16

Table '1.

Gel time (days)

catalyst

Monomer BP TBH CHP

5 BIS-GMA (a) .3 2 MMA 3 (al (a) (a) no gelling after 9 days when the experiment ended.

Surprisingly, it turns out that BIS-GMA is more stable with TBH, a less heat-stable catalyst, ie. BP in comparison with either TBH or CHP. As previously stated, both TBH and CHP are recommended for use at temperatures substantially higher than for BP and would be expected when TBH or CHP dissolve in the monomers to achieve greater polymerization stability than BP. The data presented for 15 MMA is more in line with what would normally be expected, which underlines the rather abnormal stability trajectory of BIS-GMA in the presence of free radical catalyst. Gel time denotes the day when you first see that gelling takes place.

The following examples are intended to illustrate and in no way limit the present invention.

All parts and percentages are parts by weight and percentages.

Example 1.

To 52 parts of a homogeneous mixture of equal parts BIS-GMA 25 (NUPOL 46-4005 Charge No. 124,793} and hexamethylene dimethacrylate (HMDMA), from Sartomer Chemicals, lot No. PB 844, add 8 parts acetone wash and oven-dried DOWEX ® 50 WX 8 ion exchange beads (1.9 MEQ / nil, H + form) The mixture is stirred for 24 hours and then filtered through a sintered glass filter

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17 for removing the beads. To the monomer solution is added 0.026 parts of MEHQ to replace any inhibitor lost in the ion exchange treatment.

Portions of the monomer solution thus treated are used to prepare solutions containing 2% BP and 4% CHP, respectively. After standing at room temperature for 6 months, these solutions showed no polymer formation and the experiment was terminated at this time. The stability of the BIS-GMA product is substantially improved compared to the 2-day gel time of BIS-GMA in Table 1 for a 2% CHP solution. The substantially improved stability of the BIS-GMA / HMDMA monomer product in this example is all the more surprising when you consider the high (4%) concentration of CHP.

Example 2.

To 25 parts of the monomer product obtained by the ion exchange treatment of Example 1 is added first 5%, based on monomer, silane coupling agent and then 75 parts of amorphous silica. The product is stable (no gelling is seen) 20 for over 1 year at room temperature.

Example 3

The aged product obtained from Example 2 is mixed with a similar amount of a similar product, but CHP is omitted and 2% acetylthiourea is added as reducing agent.

25 A quick and complete cure occurs.

Other monomer materials tested as described in the previous examples with similar stabilization results are as follows with parts listed in parentheses:

Claims (5)

5 BIS-GMA (71) 1TEGDMA (29) ^ polyethylene glycol dimethacrylate 2 triethylene glycol dimethacrylate. 10 Patent Claims. A polymerizable tooth repair material stabilized against premature activation of a catalyst component comprising at least one methacrylate monomer having 2-4 polymerizable olefinic double bonds, a free radical forming polymerization catalyst comprising an organic peroxide or hydroperoxide compound, upon activation is capable of initiating polymerisaton of said monomer, said catalyst being present in an amount of 0.5-5% by weight based on the weight of the monomer, and optionally a particulate, inorganic filler, and optionally a silane coupling agent, characterized by prior to its contact with said catalyst, the monomer has been treated with a sulfonic acid type cation exchange resin in free acid form. Material according to claim 1, characterized in that at least approx. 50% by weight of said methacrylate monomers is the reaction product of bisphenol A and glycidylmethacrylate, that there is a silicon-containing filler present in an amount of less than 80% by weight based on the total weight of the material and the silane coupling agent present in an amount of 3-6% by weight based on the weight of the monomer. DK 158280 B A material according to claim 2, characterized in that said methacrylate monomer comprises an approximately 1: 1 mixture of the reaction product of bisphenol A and g1yc in dimethyl methacrylate and hexamethylene dimethacrylate, and the silane coupling agent is present in an amount of approx. 5% by weight. A process for preparing a polymerizable material according to claim 1, wherein a methacrylate monomer material of αe containing at least one methacrylate monomer of 2-4 polymerizable olefinic double bonds is mixed with a polymerization catalyst comprising an organic peroxide or hydroperoxide compound see which liberates free radicals and which, upon activation, are capable of initiating polymerization of the monomer, using the catalyst in an amount of 0.5-5% by weight based on the weight of the monomer, and optionally a particulate, inorganic filler, preferably a silicon-containing filler, and optionally a silicon coupling agent, characterized in that prior to the monomer's contact with the catalyst, it is treated with a sulfonic acid type cation exchange resin in free acid form. Process according to claim 4, characterized in that the treatment comprises stirring a solution of the methacrylic monomer with the cation exchange resin in the form of beads, or passing the solution through a column of the cation exchange resin until a substantially pollution-free monomer material is obtained. as determined by storage stability experiments.