Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-07-30
2004-12-21
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06833394
ABSTRACT:
The invention relates to dental materials which contain chromophoric xerogels as colouring component.
Dental materials are mostly reacted with coloured substances for aesthetic reasons in order to match them optically to the natural tooth substance. To this end, dyes or pigments are used as a rule. In the case of photopolymerizable dental materials the problem arises that both dyes and pigments adversely affect the full-curing depth, i.e. lead to a reduction in the full-curing depth. This effect occurs more markedly with filling composites in which the addition of fillers also leads to an additional reduction in the transparency of the material. Accordingly, a full-curing depth of at least 1.5 mm is required for restorative materials according to the international standard ISO 4049 (2000).
For colouring agents used in dental materials there is a range of basic requirements (cf. L. -A. Linden, Photocuring of polymeric dental materials and plastic composite resins”, in: Radiation curing in polymer science and technology, Vol. IV., Pub. J. P. Fouassier und J. F. Rabek, Elsevier Appl. Sci., London and New York 1993, 402 ff.), in particular colour stability over many years, stability vis-à-vis heat, for example during the consumption of hot food and chemical stability vis-à-vis oxidants or reduction agents. Furthermore dental colouring agents must not dissolve in fat or water, alcohol or other solvents, have to behave inertly vis-à-vis the other components of dental materials and must be toxicologically acceptable. For these reasons pigments are predominantly used. The pigments can generally be divided into inorganic and organic pigments. Inorganic pigments are often metal oxides or hydroxides, such as e.g. titanium dioxide or ZnO as white pigment, ferric oxide (Fe
2
O
3
) as red pigment or ferric hydroxide (FeOOH) as yellow pigment. The organic pigments can be divided inter alia into azo pigments (e.g. monoazo yellow and orange pigments, disazo pigments or &agr;-naphthol pigments) and non-azo or polycyclic pigments (e.g. phthalocyanine, quinacridon, perylene or flavanthrone pigments) (cf W. Herbst und K. Hunger, Industrielle organische Pigmente, VCH, Weinheim 1987, 4 ff).
The object of the invention is to prepare coloured dental materials with an improved full-curing depth during photopolymerization.
This object is achieved by dental materials which contain as colouring pigment a chromophoric xerogel of formula I:
(SiO
2
)
a
(SiO
1.5
-Sp-X-CG)(Me
n
O
m
)
b
(1)
in which:
Me represents a main-group metal of the 2
nd
to 3
rd
main groups or a transition metal of the 4
th
sub-group of the periodic table of elements;
n is 1 or 2, m being equal to 1 or 2 if n is equal to 1 and m being equal to 3 if n is equal to 2;
Sp is a C
1
to C
10
alkylene radical or C
2
to C
10
oxyalkylene radical with 1 to 4 oxygen atoms or is absent;
X is a compound group, such as CO—O, O—CO, CO—NH, NH—CO, O—CO—NH, NH—CO—O, NR, O or S or is absent, R being hydrogen or a C
1
to C
6
alkyl radical;
CG is a chromophore;
a is an integer from 0 to 20 and
b is an integer from 0 to 5.
X and Sp are preferably not absent at the same time.
Preferred meanings for the stated variables are:
Me Ti, Zr and/or Al;
Sp a C
1
to C
4
alkylene radical, preferably a propylene radical;
X CO—NH, NH—CO, O—CO—NH, NH—CO—O or NR;
R hydrogen or a C
1
to C
4
alkyl radical, preferably methyl;
CG a 4-nitrophenyl group, aromatic azo group, di- or triarylmethane group, xanthene group or anthraquinione group;
a 0,1,2,3,4 or 5; and/or
b 0,1,2 or 3.
By aromatic azo groups are meant groups with the general structure R
1
—N═N—R
2
, R
1
and R
2
representing aromatic radicals.
The preferred meanings can be chosen independently of each other. Particularly preferred however are naturally xerogels in which several or all variables have one of the preferred meanings.
Xerogels are solids which form from silica gels if the liquid dispersion agent is removed by evaporation, suction or pressing. They are colloidal, tight or loose, shaped or unshaped silicic acid which has a fine pore structure and thus a high adsorption capacity (cf. Ullmanns Encyklopädie der technischen Chemie, 4
th
Edition, Vol. 21, Verlag Chemie, Weinheim etc., 1982, 458 ff). Silica gels of very variable structure are accessible by the sol-gel processing of mixtures of silicic acid esters, e.g. of a tetraalkoxysilane with an organically modified trialkoxysilane, or with other metal alkoxides, such as e.g. aluminium, titanium or zirconium alkoxides (cf. C. J. Brinker and G. W. Scherer, Sol-Gel Science, Academic Press, Bostin etc. 1990, 2 ff). During the hydrolytic condensation of such mixtures in solution a Sol-phase primarily forms, which changes into a gel which consists of an inorganic heteropolysiloxane network and the solvent physically incorporated into it. By evaporating off the solvent the correspondingly compressed dry xerogel is finally obtained. According to the invention by xerogels are preferably meant xerogels in the narrower sense, i.e. xerogels which, during drying, suffer a volume contraction relative to the hydrogel.
The chromophoric xerogels according to the invention are accessible via the Sol-Gel process by hydrolytic co-condensation of tetraalkoxysilanes, e.g. tetraethoxysilane (TEOS), with chromophoric trialkoxysilanes and optionally further metal alkoxides. By chromophoric trialkoxy silanes are meant silanes which carry a chromophore as organic radical. A coloured xerogel is obtained which is called chromophoric xerogel.
Preferred further metal alkoxides are zirconium and titanium compounds, such as Zr(OC
2
H
5
)
4
, Zr(OC
3
H
7
)
4
, Zr(OC
4
H
9
)
4
, Ti(OC
2
H
5
)
4
, Ti(OC
3
H
7
)
4
and Ti(OC
4
H
9
)
4
. Preferred aluminium compounds are Al(OCH
3
)
3
, Al(OC
2
H
5
)
3
, Al(OC
3
H
7
)
3
and Al(OC
4
H
9
)
3
. The metal alkoxides are converted into the corresponding metal oxides Me
n
O
m
during hydrolytic condensation. TiO
2
(Me=Ti), ZrO
2
(Me=Zr) or Al
2
O
3
(Me=Al) are particularly suitable for the modification of silica gels.
Chromophoric trialkoxysilanes are accessible for example by the chemical reaction of propyltrialkoxysilanes functionalized in 3-position, e.g. 3-amino, 3-chloro, 3-isocyanato- or 3-mercaptotriethoxysilane, with suitably functionalized chromophoric compounds, e.g.:
Y and FG each stand for the functional groups with which the chromophoric compound or the alkyltrialkoxysilane has to be equipped in order to facilitate a reaction in the described way while the group X develops. Y and FG preferably have the meaning given above and are preferably also reacted together in the shown combinations.
During the preparation of the chromophoric xerogels by hydrolytic condensation, a preferable procedure is to react the hydrolysing silanes in the presence of a hydrolysis and condensation catalyst with the necessary amount of water and stir the resulting mixture. A mixture of TEOS and chromophoric silane is preferably used. The silanes can be present either as such or dissolved in a suitable solvent. Water is added at room temperature or with slight cooling. After the gel has formed the reaction mixture is left to stand for an extended period of time until the reaction is complete and the solvent used is then separated off by heating or evacuation. Considered as solvent are primarily aliphatic alcohols, such as e.g. ethanol or i-propanol, dialkylketones, such as acetone or methyl isobutyl ketone, ethers, such as e.g. diethylethers or tetrahydrofuran (THF), esters, such as ethyl or butyl acetate, and their mixtures. The obtained xerogels can be washed once again with an inert solvent to separate off non-reacted components and then dried until their weight is constant. If the hydrolytic condensation is carried out in the presence of reactive Zr, Ti or Al compounds, then the addition of water should be carried out stepwise at approx. 0 to 30° C. It is preferred to add the water not as such but in the form of water-containing solvents, such as e.g. aqueous ethanol, or to release it by a chemical reaction
Burtscher Peter
Moszner Norbert
Rheinberger Volker
Spange Stefan
Ivoclar Vivadent AG
Nixon & Peabody LLP
Sanders Kriellion A.
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