Note: Descriptions are shown in the official language in which they were submitted.
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Light-polymerizable dental composition containing an inhibitor
The present invention relates to a light-polymerizable dental composition
comprising a
specific inhibitor. Moreover, the present invention also relates to the use of
specific
fullerene compounds in a dental composition.
Light-polymerizable dental compositions comprise a polymerizable monomer, a
light-
sensitive polymerization initiator, and optionally further components such as
an organic
or inorganic filler or an organic or inorganic pigment. It is known to use a
stabilizer for
preventing a composition containing polymerizable acrylates and/or
methacrylates
from spontaneous polymerization. 2,6-Di-tert-butyl-4-cresol (BHT),
hydroquinone or
hydroquinonemonomethylether (HQME) are known as free radical savengers for
dental
compositions.
Light curing polymerisable dental compositions are usually applied in the
presence of
substantial irradiation of the environment particularity radiation generated
by operating
lamps. In order to insure suffciently long working times, international
standards require
that a dental dental composite remains stable under an illumination of 10.000
tux for 60
seconds (ISO 4049). Dental pit and fissure sealants are required to remain
stable
under an illumination of 8000 tux for 25 seconds (ISO 6874) and light
activated water-
based cements are required to remain stable under an illumination of 8000 tux
for 30
seconds (ISO 99917-2).
From SU 3,34845 it is known that 2,2,6,6-tetramethylpiperidinyl-1-oxide
(TEMPO) may
be used to inhibit the polymerisation of acrylate. Moreover, it is known to
use
galvinoxyl radicals, hydroxy-TEMPO and 2,2-diphenyl-1-picrylhydrazyl radicals
as
anaerobic polymerization inhibitors (US 5,468,789).
The effect of TEMPO as polymerization inhibitor in polymerizable dental
compositions
and its influence on the depth of curing is known for light curing restorative
materials
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from W.D. Cook, P.M. Standish, Austr. Dent. J., 28 (1983) 307. Moreover, US
5,847,025 discloses the use of TEMPO and other stable radiclas such as 2,2-
Diphenyl-
1-picrylhydrazyl radicals, galvinoxyl radicals and triphenylmethyl radicals
for reducing
the light sensitivity of a dental light-curing composite material.
Although many attempts have been made to lengthen the working times under the
conditions of a dental practice by choosing a combination of an initiator and
an
inhibitor, only minor reductions of light sensitivity are obtained without
increasing the
working times.
Therefore, it is the problem of the present invention to provide a dental
composition,
which has a sufFiciently long working time while still providing an acceptable
light
sensitivity of the composition and whereby the mechanical properties and the
color
shading of the dental material are not deteriorated.
This problem is solved according to claim 1 with a light-polymerizable dental
composition comprising
(i) a polymerizable monomer component,
(ii) a light-sensitive polymerization initiator,
(iii) an inhibitor,
(iv) optionally a filler and/or pigment, and
(v) optionally a solvent
whereby the inhibitor is a substituted fullerene compound present in an amount
suitable for improving light stability of the dental composition.
It was found that when a substituted fullerene such as 1,2-(dimethoxymethano)-
fullerene is added to a dental composition, surprisingly the stability of the
composition
under an irradiation with 10,000 lux is about 90 seconds. This is more than
twice as
much as the stability observed with a comparable composition that only
comprises
BHT as stabilizer which shows a stability under an irradiation with 10,000 lux
of only 40
seconds . At the same time, the mechanical properties and the storage
stability of the
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dental composition remain excellent in the presence of the inhibitor of the
present
invention.
The dental composition of the present invention comprises an inhibitor which
is a
substituted fullerene compound. The inhibitor may contain one or more
substituted
fullerene compounds. The substituted fullerene compoundd is preferably soluble
in the
composition, in particular in the polymerisable monomer. Preferably, the
inhibitor is
selected from the group of substituted Cso, Coo, C,2, C~6, C,B, or C84
fullerenes. A
substituted fullerene compound according to the invention is derived from an
unsubstituted fullerene compound by addition or insertion of substituents to
the
fullerene cage. The substituents added or inserted to the fulleren cage may be
further
modified in order to provide the desired substituted fullerene compound used
in the
dental compositions of the invention. The substituents are preferably able to
render
the fullerene compound soluble in the composition, in particular in the
polymerisable
monomer. Moreover, the substituents preferably contribute to the electronic
properties
of the inhibitor as a radical scavenger. Finally, the substituents preferably
are able to
modify the fullerene cage such that any chromophores absorbing in the range of
visible
light are destroyed.
One or more substituents may be present on the fullerene cage whereby it is
preferred
that at least two substituents are present. In case at least two substituents
are present
on the fullerene cage , the substituents may be the same or different. The
substituents
of the substituted fullerenes are preferably selected from the group of
substituted or
unsubstituted C,_2o-alkyl groups, C,_2o-alkoxy groups, C,_2o-alkyl-C,_ZO-
alkoxy groups, C,_
2o-alkylthio groups, C,_2o-alkylthio-C,_2o alkyl groups, C,_2oalkylamino
groups, C,_Zo
alkoxy-poly-C,_6-alkyleneoxy groups or C,_ZO-aryl groups. In case the
substituents of
the fullerene cage are substituted, such substituents may be selected form the
group
of substituents given as substituents for the fullerene cage. Moreover, such
substituents may be selected from the group consisting of hydroxyl groups,
amino
groups, thiol groups.. In a specific embodiment, one or more substituents of
the
fullerene cage are substitued with a polymerizable group. The polymerizable
group
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may be selected from acryloyl, C,_2°-alkylacryloyl, or C,_Z°-
alkenyl groups.
The substituted fullerenes are added to the dental composition in an amount
ranging
from 0.001 to 3.0% by weight, preferably in an amount of from 0.01 to 1.0% by
weight
and most preferably in an amount of from 0.01 to 0.2% by weight.
The dental composition of the present invention comprises a light-
polymerizable
monomer component. The light-polymerizable monomer component contains one or
more monomer compounds. In case the monomer component contains two or more
monomer compounds, the monomer compounds may differ with regard to the
molecular weight and/or the number of polymerizable moieties. In a preferred
embodiment, a macromonomer and a reactive diluent are used in the
polymerizable
monomer component.
The monomer compound to be used in the monomer component of the dental
composition of the present invention preferably has at least one polymerizable
group
and is a mono- or polyfunctional (meth)acrylate or a macromonomer. Preferable
monomers are 2,2-Bis-[p-(2-hydroxy-3-methacryloyloxypropoxy)-phenyl]-propane,
7,
7,9-trimethyl-4,13-dioxo-3,14-dioxa-5,12-diazahexadecan-1,16-diol
methacrylate,
dipentaerthrytrolpentamethacrylate monophosphate, a,c~-methacryloyl terminated
epoxide-amine macromonomers, a,w-methacryloyl terminated epoxidecarboxylic
acid
macromonomers, a,w-methacryloyl terminated epoxide-phenol macromonomers.
Specifically, reference is made to the macromonomers disclosed in U.S. Patent
application serial number 08/359,217 filed December 19, 1994.
Reactive diluents are mono(meth) acrylates and polyfunctional (meth)
acrylates, such
as polyalkylenoxide di-(meth)acrylates or poly(meth)acrylates, urethane
di(meth)
acrylates or poly(meth)acrylates, vinyl-, vinylen- or vinyliden-, acrylate- or
methacrylate
substituted spiroorthoesters, spiroorthocarbonates or bicycloorthoesters.
Preferred
reactive diluents are diethyleneglycol dimethacrylate, triethyleneglycol
dimethacrylate,
3,(4),8,(9)dimethacryloyloxymethyltricyclodecane, dioxolan bismethacrylate,
glycerol
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trimethacrylate, and furfuryl methacrylate.
The polymerizable monomer component may be present in the dental composition
of
the present invention in an amount of from 1 to 99 percent by weight,
preferably in an
amount of from 10 to 60 percent by weight.
The dental composition of the present invention comprises a light-sensitive
polymerization initiator. Suitable initiators are benzophenone, benzoin or
derivatives
therof. Preferred initiators are a-diketones such as 9,10-phenanthrene
quinone,
diacetyl, furyl, anisyl, 4,4'-dichlorobenzil and 4,4'-dialkoxybenzil.
Particularity preferred
is camphorquinone. The initiators may be used in combination with an amine as
activator. Examples for such activators are N,N-dimethyl-p-toluidine, N,N-
dihydroxyethyl-p-toluidine, and N-(2-cyanoethyl)-N-methylaniline.
The initiator may be present in the dental composition of the present
invention in an
amount of 0.001 to 2 percent by weight, preferably in an amount of from 0.5 to
1
percent by weight.
The dental composition of the present invention optionally comprises a filler.
The filler
may be an inorganic fillers such as La203, Zr02, BiP04, CaW04, BaW04, SrF2,
Bi203,
glasses. The filler may also be or an organic fillers, such as a polymer
granulate.
Moreover, the filler may be a combination of organic and inorganic fillers.
The filler may
be present in the dental composition of the present invention in an amount of
20 to 85
percent by weight. Preferably in case of a composite the filler is present in
an amount
of from 50 to 85 percent by weight, and in case of a sealer the filler is
preferably
present in an amount of from 20 to 50 percent by weight.
The dental composition of the present invention optionally comprises a
pigment.
Examples of pigments which may be incorporated into a composition of the
present
invention are titanium oxides and iron oxides.
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The dental composition of the present invention optionally comprises a
solvent.
Suitable solvents for use in a dental composition according to the invention
are
acetone, methylethyl ketone, and ethanol.
A preferred dental composition according to the invention is a composite
comprising
from
15 to 50 percent by weight of a polymerizable monomer component,
0.1 to 3.0 percent by weight of a light-sensitive polymerization initiator,
0.01 to 1 percent by weight of an inhibitor, and
50 to 85 percent by weight of a filler and/or pigment.
A preferred dental composition according to the invention is a sealer
comprising from
50 to 80 percent by weight of a polymerizable monomer component,
0.1 to 3.0 percent by weight of a light-sensitive polymerization initiator,
0.01 to 1.0 percent by weight of an inhibitor,
optionally 20 to 50 percent by weight of a filler and/or pigment, and
optionally 0 to 10 percent by weight of a solvent.
The dental composition according to the present invention may be prepared by
mixing
the components of the composition.
The invention will now be further illustrated by the following example and
comparative
example.
Example 1
19,814 g Urethane dimethacrylate, 1.239 g trimethylolpropane trimethacrylate,
3.715
g diethyleneglycol dimethacrylate, 0.075 g camphorquinone, 0.087 g
dimethylaminoethylbenzoicacid ethylester, 0.025 g (0.113 mmol) BHT and 0.025 g
(0.031 mmol) 1,2-(dimethoxymethano)-fullerene (Fluka) were homogeneously
mixed.
To this resin mixture, 75.020 g of a strontium alumofluorosilicate glass was
added and
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homogeneously mixed to provide a dental composition. The properties of the
dental
composition were measured and the properties are summarized in Table 1. The
light
sensitivity to ambient light was also measured. The results are shown in
Figure 1.
Example 2
19.854 g Urethane dimethacrylate, 1.241 g trimethylolpropane trimethacrylate,
3.723
g diethyleneglycol dimethacrylate, 0.075 g camphorquinone, 0.087 g
dimethylaminoethylbenzoicacid ethylester and 0.020 g (0.025 mmol)
1,2-(Dimethoxymethano)-fullerene (Fluka) were mixed homogeneously. To this
resin
mixture 75.000 g of a strontiumalumofluoro silicate glass was added and mixed
homogeneously. The sensitivity to ambient light of this composite is 110
seconds.
Comparative Example 1
19.056 g Urethane dimethacrylate, 1.191 g trimethylolpropane trimethacrylate,
3.573 g diethyleneglycol dimethacrlyate, 0,072 g camphorquinone, 0.084 g
dimethylaminoethylbenzoicacid ethylester and 0.024 g BHT were homegeneously
mixed. To the resin mixture, 76.000 g of a strontium alumofluorosilicate glass
were
added and homogeneously mixed. The properties of the dental composition were
measured and the properties are summarized in Table 1. The light sensitivity
to
ambient light was also measured. The results are shown in Figure 1.
Comparative Example 2
19.711 g Urethane dimethacrylate, 1.232 g trimethylolpropane trimethacrylate,
3.696
g diethyleneglycol dimethacrylate, 0.074 g camphorquinone, 0.087 g
dimethylaminoethyl benzoic acid ethylester, 0,025 g (0.113 mmol) BHT and 0.025
g
(0.035 mmol) buckminsterfullerene Cso (Fluka) were homogeneously mixed. To
this
resin mixture 75.150 g of a strontium alumofluorosilicate glass was added and
homogeneously mixed.. It was found that the stability of the composition was
about the
same as the stability of the composition of comparative example 1.
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Table 1 Properties of dental composites of example 1 and of comparative
example 1
Example Comp. 1 Example 1
Sensitivity to ambient light, sec 40 90
ISO 4049
(10000 lux)
Compressive strength MPa 276.0 t 267.1 t 7.0
6.2
Flexural strength, ISO 4049 MPa 82.5 t 81.0 t 5.6
7.4
E-modulus MPa 7562 t 7150 t 336
169
~
1
d0
.- _ ._.-__.... .. ~
_~. .
c.
m _
~ _..........-. .-- .....,..~
60
E
~o
~ ._.....,.......__..._
40
-. -~_..-.___._.................._._._....____-__-_.
c
0
o
z
~
s
s
io
Timo
[w~
~ BHT
~ 1,2-(Oimethoxymothono)-fullenan, BNT
Figure 1 Sensitivity to ambient light of composites comprising BHT or 1,2-
(Dimethoxymethano)-fullerene and BHT vs. storage time at 23°C (w=weeks)
