Curable compositions

A curable composition is provided, comprising a monofunctional (meth)arcylate monomer, a poly functional (meth)acrylate monomer, a (meth)acrylate monomer containing an acidic group and at least one (meth)acryloyloxyl group in its molecule, a monofunctional (meth)acrylamide monomer, and a trialkylboron and/or a partial oxide thereof. The composition has improved low-temperature curability at approximately room temperature and water-resistant adherence, and excellent adhesiveness to tooth substances including enamel and dentin and dental alloys, and gives no adverse influence of stimulation to dental pulp. Most preferably, the composition is used as a bonding agent for dental composite resins.

TECHNICAL FIELD 
This invention relates to an acrylate composition. More particularly, it 
relates to a curable composition useful for dental bonding agents 
(adhesives) and the like, which has improved low-temperature curability at 
room temperature and water-resistant adherence, excellent adhesiveness to 
tooth substances such as enamel and dentin and dental alloys, and no 
adverse influence including stimulation for dental pulp. 
BACKGROUND ART 
A number of bonding agents have been proposed for orthodontic and 
restorative treatments which typical are catalyzed compositions comprises 
a radical-polymerizable monomer such as a (meth)acrylate vinyl monomer. 
For example, Japanese Patent Application Kokai No. 60-44508 proposes a 
curable composition comprising an acrylate or methacrylate vinyl monomer, 
an aromatic carboxylic acid or an anhydride thereof containing an 
acryloyloxyl or methacryloyloxyl group, an amine, and a sulfinic acid or a 
salt thereof. Japanese Patent Application Kokai No. 53-39331 discloses a 
bonding agent comprising an acrylate or methacrylate ester which is liquid 
at room temperature, an amine, a sulfinic acid or a salt thereof, and a 
peroxide. Nihon Shika Hoken (Japanese Dental and Hygienic Journal), 28, 
270 (1985) reports a bonding agent comprising methyl methacrylate, 4-META, 
and tributylboran (TBB). 
However, conventional adhesives and curable compositions have problems that 
they have to be treated by etchants such as phosphoric acid and citric 
acid in order to obtain improved adherence to dental substances, and that 
it is difficult to obtain sufficient adherence to dentin particularly if 
an etching treatment is not carried out to dentin at all, and that an 
opening in dentin tube is caused by the etching treatment resulting in 
stimulation to dental pulp. 
Therefore, the above-mentioned problems can be solved by the present 
invention. An object of the present invention is to provide a curable 
composition having improved curability at room temperature and 
water-resistant adherence. Another object of the present invention is to 
provide a curable composition having improved adherence to tooth 
substances such as enamel and dentin and dental alloys, particularly 
dentin. A further object of the present invention is to provide a curable 
composition which can be used as a dental adhesive to bond composite 
resins for tooth restoration without any adverse influence including 
stimulation of dental pulp. 
DISCLOSURE OF THE INVENTION 
According to the present invention, there is provided a curable composition 
comprising (A) a monofunctional (meth)acrylate monomer, (B) a 
polyfunctional (meth)acrylate monomer, (C) a (meth)acrylate monomer 
containing an acidic group and at least one acryloyloxyl or 
methacryloyloxyl group in its molecule, (D) a monofunctional 
(meth)acrylamide monomer of the general formula (I): 
##STR1## 
wherein R is H or CH.sub.3, and (E) a trialkylboron and/or a partial oxide 
thereof. 
The present invention is hereinafter discribed in detail. 
The monofunctional (meth)acrylate monomer (A) used in the curable 
composition of the present invention may contain in its molecule a 
functional group other than an acidic group. Examples of the 
monofunctional (meth)acrylate monomer include (meth)acrylates containing a 
hydrocarbon group such as methyl (meth)acrylate, ethyl (meth)acrylate, 
butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 
dddecyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, 
benzyl (meth)acrylate, and isobornyl (meth)acrylate; (meth)acrylates 
containing a hydroxyl group such as 2-hydroxyethyl (meth)acrylate and 
2-hydroxypropyl (meth)acrylate; (meth)acrylates containing an ethylene 
glycol unit such as ethylene glycol monomethyl ether (meth)acrylate, 
ethylene glycol monoethyl ether (meth)acrylate, ethylene glycol 
monododecyl ether (meth)acrylate, diethylene glycol monomethyl ether 
(meth)crylate, polyethylene glycol monomethyl ether (meth)acrylate, and 
polyethylene glycol monoethyl ether (meth)acrylate; (meth)acrylates 
containing a fluorine-substituted group such as trifluoroethyl 
(meth)acrylate, and perfluorooctyl (meth)acrylate; silane (meth)acrylates 
such as .gamma.-(meth)acryloyloxypropyltrimethoxysilane, and 
.gamma.-(meth)acryloyloxypropyltri(trimethylsiloxy)silane; and 
tetrahydrofurfuryl (meth)acrylate. They may be used alone or in admixture 
of two or more. 
Preferred are alkyl (meth)acrylates such as methyl acrylate and 
methacrylate, ethyl (meth)acrylate, hexyl (meth)acrylate, and dodecyl 
(meth)acrylate, and hydroxylcontaining (meth)acrylates such as 
2-hydroxyethyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate. Most 
preferably, methyl methacrylate, n-hexyl methacrylate, 2-hydroxyethyl 
methacrylate and 2-hydroxypropyl methacrylate monomers and a mixture 
thereof are used. 
Examples of the polyfunctional acrylate or methacrylate monomer (B) used in 
the curable composition include poly(meth)acrylates of alkane polyols such 
as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 
butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 
hexylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 
glycerin tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate; and 
poly(meth)acrylates of (poly)oxyalkane polyols such as diethylene glycol 
di(meth)acrylate, dipropylene glycol di(meth)acrylate, triethylene glycol 
di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dibutylene glycol 
di(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; epoxy 
(meth)acrylates of the general formula (II): 
##STR2## 
wherein R is H or CH.sub.3, 
n is 0 or a positive integer, and 
R.sup.1 is --(CH.sub.2).sub.2 --, --(CH.sub.2).sub.4 --, 
##STR3## 
cycloaliphatic or aromatic di(meth)acrylates of the general formula (III): 
wherein R is H or CH.sub.3, and 
##STR4## 
cycloaliphatic di(meth)acrylates of the general formula (IV): 
##STR5## 
wherein R is H or CH.sub.3, and 
##STR6## 
polyfunctional acrylates and methacrylates containing at least one urethane 
bond in their molecule. An example of the polyfunctional (meth)acrylates 
is an adduct of 1 mol of diisocyanate and 2 mol of a hydroxy 
groupcontaining (meth)acrylates such as 2-hydroxyethyl (meth)acrylates. 
The diisocyanates may be used aliphatic, cycloaliphatic or aromatic 
diisocyanate. Examples of the diisocyanates include hexamethylene 
diisocyanate, lysindiisocyanate, 
2,2(4),4-trimethylhexamethylenediisocyanate, 
dicyclohexyldimethylmethane-P,P'-diisocyanate, isophorondiisocyanate, 
trilendiisocyanate, xylilenediisocyanate, diphenylmethanediisocyanate, and 
naphthalenediisocyanate. Further examples of the diisocyanate include 
##STR7## 
wherein R is H or CH.sub.3, 
##STR8## 
wherein R is H or CH.sub.3, 
##STR9## 
wherein R is H or CH.sub.3, 
##STR10## 
wherein R is H or CH.sub.3, 
##STR11## 
wherein R is H or CH.sub.3, 
##STR12## 
wherein R is H or CH.sub.3, 
##STR13## 
wherein R is H or CH.sub.3, 
##STR14## 
wherein R is H or CH.sub.3, and 
##STR15## 
wherein R is H or CH.sub.3. 
Other examples of monomers (B) include the polyfunctional (meth)acrylates 
of the general formula (V): 
##STR16## 
wherein R is H or CH.sub.3, R.sup.4 is a divalent aromatic residue which 
has at least one aromatic ring and may have an oxygen or sulfur atom in 
tis molecule, and n and m are positive integers. Examples of the 
polyfunctional (meth)acrylates of the general formula (V) include 
##STR17## 
wherein R is H or CH.sub.3, and m+n=2 to 20, 
##STR18## 
wherein R is H or CH.sub.3, and m+n=2 to 20, 
##STR19## 
wherein R is H or CH.sub.3, and m+n=2 to 20, 
##STR20## 
wherein R is H or CH.sub.3, and m+n=2 to 20, 
##STR21## 
wherein R is H or CH.sub.3, and m+n=2 to 20, 
##STR22## 
wherein R is H or CH.sub.3, and m+n=2 to 20. 
Among these polyfunctional (meth)acrylate monomers, preferred are the 
monomers of alkane polyol poly(methacrylate. (poly)oxyalkanepolyol 
poly(meth)acrylate, epoxy(meth)acrylate, aliphatic or cycloaliphatic 
(meth)acrylate containing at least one urethane bond in its molecule, and 
(poly)oxyalkanepolyol poly(meth)acrylate having aromatic rings. Most 
preferred monomers are ethyleneglycol di(meth)acrylate, neopentylglycol 
(meth)acrylate, diethyleneglycol di(meth)acrylate, triethylene glycol 
di(meth)acrylate, 
##STR23## 
wherein R is H or CH.sub.3, 
##STR24## 
wherein R is H or CH.sub.3, 
##STR25## 
wherein R is H or CH.sub.3, 
##STR26## 
wherein R is H or CH.sub.3, and m+n=2 to 10, and 
##STR27## 
wherein R is H or CH.sub.3, and m+n=2 to 10. 
They may be used alone or in admixture of two or more. 
In the curable composition according to the present invention, the 
(meth)acrylate monomer containing an acidic group and at least one 
(meth)acryloyloxyl group in its molecule (C) includes (C.sub.1) aromatic 
polycarboxylic acids having at leaqst one (meth)acryloyloxyl group per 
molecule or anhydrides thereof and (C.sub.2) partial esters of phosphoric 
or sulfonic acid having at least one (meth)acyloyloxyl group per molecule, 
such as monoesters and diesters of phosphoric acid and mixtures thereof, 
and monoesters of sulfonic acid. 
Examples of the aromatic polycarboxylic acid having at least one 
(meth)acryloyloxyl group per molecure (C.sub.1) are 
(meth)acryloyloxyl-containing aromatic polycarboxylic acids or anhydrides 
thereof having the structure wherein an alkane polyol has at least two 
hydroxyl groups per molecule and may contain an oxygen atom, at least one 
of its hydroxyl groups forms an ester with (meth)acrylic acid and at least 
one of its hydroxyl groups forms an ester with one carboxyl group of an 
aromatic polycarboxylic acid having at least three carboxyl groups. 
The preferred aromatic polycarboxylic acids containing at least three 
carboxyl groups are aromatic polycarboxylic acids in which at least two of 
the carboxyl groups are attached to the adjoining carbon atom on the 
aromatic nucleus. Examples of the aromatic polycarboxylic acids are 
hemimellitic acid, trimellitic acid, prehnitic acid, mellophanic acid, and 
pyromellitic acid. 
The (meth)acryloyloxyl-containing aromatic polycarboxylic acids or 
anhydrides thereof include 4-(meth)acryloyloxymethoxycarbonylphthalic acid 
or an anhydride thereof, 4-(meth)acryloyloxyethoxy-carbonylphthalic acid 
or an anhydride thereof, 4-(meth)acryloyloxybutoxycarbonylphthalic acid or 
an anhydride thereof, 
##STR28## 
wherein R is H or CH.sub.3, and n is an integer of from 6 to 12, 
##STR29## 
wherein R is H or CH.sub.3, and n is an integer of from 2 to 50, 
##STR30## 
wherein R is H or CH.sub.3, and n is an integer of from 1 to 50, 
4-[2-hydroxy-3-(meth)acryloyoxypropoxycarbonyl]phthalic acid or an acid 
anhydride thereof, 2,3-bis(3,4-dicarboxybenzoyloxy)propylmethacrylate 
2,3-bis(3,4-dicarboxybenzoyloxy)propylmethacrylate or an acid anhydride 
thereof, and 2-(3,4-dicarboxylbenzoyloxy)-1,3-dimethacryloyoxypropane or 
an acid anhydride thereof. 
The partial esters of phosphoric or sulfonic acid having at least one 
(meth)acryloyloxyl group per molecule (C.sub.2) include monoesters and 
diesters of sulfonic acid, for example, 2-(meth)acryloyloxyehtylphenyl 
acid phosphate, bis-[2-(meth)acryloyl-oxyethyl]acid phosphate, 
bis[3-(meth)acryloxypropyl]acid phosphate, 2-(meth)acryloyloxyethylphenyl 
phosphonate, 
##STR31## 
Among these (meth)acrylate monomers containing an acidic group and at least 
one (meth)acryloyloxyl group in its molecule (C), preferred are aromatic 
polycarboxylic acids having at least one (meth)acryloyloxyl group per 
molecule or acid anhydrides thereof (C.sub.1). More preferred are 
4-(meth)acryloyloxy-ethoxycarbonylphthalic acid or its acid anhydride. 
Most preferably, 4-(meth)acryloyloxyethoxycarbonylphthalic acid anhydride 
is used because of improved adherence to tooth and water-durability. 
In the curable composition of the present invention, a monofunctional 
(meth)acrylate monomer (D) of the general formula (I) is used. Examples of 
the monofunctional (meth)acrylamide monomer are 
3-(meth)acryloylaminosalicylic acid, 4-(meth)acryloyl-aminosalicylic acid, 
5-(meth)acryloylaminosalicylic acid, 
3-hydroxy-2-(meth)acryloylaminobenzoic acid, 
3-hydroxy-4-(meth)acryloylaminobenzoic acid, 
3-hydroxy-5-(meth)acryloylaminobenzoic acid, 
3-hydroxy-6-(meth)acryloylaminobenzoic acid, 
4-hydroxy-2-(meth)acrylaminobenzoic acid, and 
4-hydroxy-3-(meth)acryloylaminobenzoic acid. They may be used alone or in 
admixture of two or more. Among these monofunctional (meth)acrylate 
monomer, preferred are 3-(meth)acryloylaminosalicylic acid, 
4-(meth)acryloylaminosalicylic acid, and 5-(meth)acryloylaminosalicylic 
acid. Most preferably, 4-(meth)acryloylaminosalicylic acid and 
5-(meth)acryloylaminosalicylic acid are used alone or in admixture. 
The curable composition of the present invention further comprises (E) a 
trialkylboron or its partial oxide. Examples of the trialkylboron include 
triethylboron, tripropylboron, triisopropylboron, tri-n-butylboron, 
tri-n-amylboron, triisoamylboron, tri-sec-amylboron, and partial oxides of 
these trialkylborons in which the trialkylborons are partially oxidized. 
Preferably, tri-n-butylboron and its partial oxides are used. 
In the curable composition of the present invention, the proportion of the 
monofunctional (meth)acrylate monomer (A) and the polyfunctional 
(meth)acrylate monomer (B) blended therein is not particularly limited. 
Better results are obtained when the curable composition generally 
contains 5 to 95% by weight of the monofunctional (meth)acrylate monomer 
(A) and 95 to 5% by weight of the polyfunctional (meth)acrylate monomer 
(B), preferably 10 to 95% by weight of the monofunctional (meth)acrylate 
monomer (A) and 90 to 5% by weight of the polyfunctional (meth)acrylate 
monomer (B), and most preferably 25 to 90% by weight of the monofunctional 
(meth)acrylate monomer (A) and 75 to 10% by weight of the polyfunctional 
(meth)acrylate monomer (B), because adhesiveness to dentin and 
water-durability exhibit improved, particularly adhesiveness and 
water-durability to non-etched dentin. 
In the curable composition of the present invention, the proportion of the 
acidic group-containing (meth)acrylate monomer (C) blended therein 
generally ranges from 1 to 50 parts by weight, preferably from 3 to 30 
parts by weight, most preferably from 5 to 15 parts by weight per 100 
parts by weight of the total of the monofunctional (meth)acrylate monomer 
(A) and the polyfunctional (meth)acrylate monomer (B) blended therein. 
In the curable composition of the present invention, the proportion of the 
monofunctional (meth)acrylamide monomer (D) of the general formula (I) 
blended therein generally ranges from 0.1 to 50 parts by weight, 
preferably from 0.3 to 30 parts by weight, most preferably from 1 to 15 
parts by weight per 100 parts by weight of the total of the monofunctional 
(meth)acrylate monomer (A) and the polyfunctional (meth)acrylate monomer 
(B) blended therein. 
In the curable composition of the present invention, the proportion of the 
trialkylboron or its partial oxide (E) blended therein generally ranges 
from 2 to 100 parts by weight, preferably from 5 to 70 parts by weight, 
most preferably from 5 to 50 parts by weight per 100 parts by weight of 
the total of the monofunctional (meth)acrylate monomer (A), the 
polyfunctional (meth)acrylate monomer (B), the acidic group-containing 
(meth)acrylate monomer (C) and the monofunctional (meth)acrylamide monomer 
(D) of the general formula (I) blended therein. 
The curable composition of the present invention may contain any desired 
additives in addition to the abovementioned essential components, for 
example, other polymerizable monomers, organic solvents, powder inorganic 
fillers, organic polymers, and polymerization retarders. 
Examples of the other polymerizable monomers include vinyl halogenides such 
as vinyl chloride and vinyl bromide; vinyl esters such as vinyl acetate 
and vinyl propyonate; vinyl ethers such as methylvinyl ether, ethylvinyl 
ether and isobutylvinyl ether; alkenyl benzenes such as styrene, 
vinyltoluene, .alpha.-methylstyrene, chloromethylstyrene and stilbene. 
Examples of the organic solvents include ethyl alcohol, acetone, ethyl 
acetate, diethyl ether, tetrahydrofuran, N,N-dimethyl acetoamide, N-methyl 
pyrorydone and dimethyl sulfoxide. 
Examples of the powder inorganic fillers include kaolin, talc, clay, 
calcium carbonate, silica, silicaalumina, titanium oxide, calcium 
phosphate, ground glass, and ground quartz. 
Examples of the organic polymers include wax, ethylene-vinyl acetate 
copolymers, and polymethylacrylate, polymetylmethacrylate, and copolymers 
thereof. These fillers or additives may be blended in any desired 
proportion. 
The curable composition of the present invention is prepared by mixing each 
of the above-mentioned components (A), (B), (C), (D) and (E), and may also 
contain other optional components. In this case, the proportion of each of 
the above-mentioned components (A), (B), (C), (D) and (E) may be adjusted 
as desired. In order to get good procedure at the use, a part of them is 
dissolved in an organic solvent, mixed the solution with the other 
components and applied it to dental surface before curing leading to 
polymerized-curing the compositions, or each of the components is 
separately applied to the surface leading to polymerized-curing the 
compositions. Since the trialkylboron or its partial oxide (E) starts 
polymerization reaction with the (meth)acrylate monomers (A), (B) and (C) 
and the (meth)acrylamide monomer (D) within several seconds to several ten 
minutes after their mixing, the trialkylboron (E) is kept separate from 
the above-mentioned components (A), (B), (C) and (D) and mixed with the 
latter components immediately before use. 
BEST MODE FOR CARRYING OUT THE INVENTION 
Examples of the present invention are presented below by way of 
illustration and not by way of limitation. 
Evaluation of the curable composition of the present invention is described 
below together with examples of preparing the photo-curable composite 
resin used in Examples and Comparative Examples. The abbreviations used 
herein have the following meanings. 
MMA: methyl methacrylate, 
HMA: n-hexyl methacrylate, 
HEMA: 2-hydroxyethyl methacrylate, 
HEPA: 2-hydroxypropyl methacrylate, 
DPEMA: 
##STR32## 
2.6E: 
##STR33## 
RDMA: 
##STR34## 
UDMA: 
##STR35## 
4-META: 
##STR36## 
4-MET: 
##STR37## 
4-MASA: 
##STR38## 
5-MASA: 
##STR39## 
TBB-0: partial oxide of tri-n-butylboron 
BPO: benzoyl peroxide 
DEPT: diethanol p-toluidine 
PTSNa: sodium p-toluenesulfonate 
HQME: hydroquinone monomethylether 
1. Evaluation of adhesiveness 
The enamel or dentin surface of a bovine anterior tooth on its labial face 
was fully polished with #600 emery paper to smoothen the surface. The 
enamel was etched for 30 seconds with an aqueous solution of 65% by weight 
of phosphoric acid. After thorough rinsing, the etched surface was dried 
by air blowing. A piece of adhesive tape of about 13 mm by 13 mm having a 
circular opening of 5 mm in diameter was attached to the etched surface. 
The bonding agent described in Examples or Comparative Examples was 
applied to the surface in the opening, and lightly air blown. A 
cylindrical mold of polytetrafluoroethylene having a diameter of 5 mm and 
a height of 2 mm was mated with the circular opening in the adhesive tape 
and filled with the photo-polymerizable composite resin described later. 
The composite resin filling was covered on the surface with a cellophane 
sheet, and exposed for 30 seconds to visible light from a visible light 
source, Translux (manufactured by Kulzer) to cure the composite resin. An 
acryl resin bar was bonded to the surface of the cured composite resin 
with an adhesive, Super-Bond C&B (manufactured by Sun Medical K.K.) to 
form a bond test specimen. The specimen was allowed to stand for 30 
minutes at room temperature, immersed for 24 hours in water at a 
temperature of 37.degree. C., allowed to stand for 10 minutes in air at a 
temperature of 23.degree. C., and then subjected to a tensile test at a 
temperature of 23.degree. C. and a pulling rate of 2 mm/min to measure a 
bonding force. After the bond test, the rupture surface exhibited bovine 
tooth rupture, cohesive rupture of the composite resin, or interfacial 
rupture between the composite resin and the dentin. 
2. Preparation of photo-curable composite resin 
A composition was prepared by milling 7.5 grams of triethylene glycol 
dimethacrylate, 7.5 grams of 1,3-bis -(methacryloxyethoxy)benzene, 15 
grams of an adduct of 1 mol of 2,2,4-trimethylhexamethylenediamine 
diisocyanate and 2 mol of 2-hydroxyethyl methacrylate, 40 grams of a 
composite filler synthesized by the following method, 30 grams of finely 
divided silica (RM-50, Nihon Aerosil K.K.), and 4 mg of hydroquinone 
monomethyl ether in a two-roll mill at 35.degree. C. A photo-curable 
composite resin was prepared by combining 10 grams of the composition with 
45 mg of camphorquinone and 45 mg of 4-diethylaminobenzoic acid and fully 
admixing the mixture with a spatula. 
3. Preparation of composite filler 
A solution of 0.1 gram benzoyl peroxide in 10 grams of trimethylolpropane 
trimethacrylate was placed in an agate mortar. Finely divided silica 
(Aerosil R972, Nihon Aerosil K.K., average particle size of 16 m.mu.) was 
added to the solution in increments while mixing. As silica was added, the 
viscosity of the mixture gradually increased. When the mixture became 
somewhat crumby, it was transferred to a small-size rubber roll mill. 
Finely divided silica was further added until a total amount of 9.5 grams 
was reached. The resulting paste was removed from the mill and het cured 
for 10 minutes in a press at a mold temperature of 110.degree. C. under a 
pressure of 150 to 200 kg/cm.sup.2. The cured product was ground in a ball 
mill so as to pass a 230 mesh screen, obtaining 18.0 grams of a composite 
filler. The filler had an average particle size of 11 .mu.m.