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Silicate cements are produced, as known, by the dentist from a two
component system: a mixing liquid, generally a buffered aqueous
orthophosphoric acid, and as a powder component, an aluminum fluorsilicate
glass (see e.g., Materials for the Practicing Dentist, p. 58-60; The C. V.
Mosely Co., St. Louis, 1969).
In addition to silicate cements, amalgams and plastics are also used as
permanent filling materials. The former, however, are not used for
esthetic reasons where they are visible, and the plastics, though they
could achieve a certain portion of the market in recent years, still meet
great resistance because of the risk of discoloration. Additionally, as a
rule, they are harmful to the pulpa, like the ordinary silicate cements,
and can therefore only be treated by observing expensive and
time-consuming precautions.
There has been no lack of attempts to improve the properties of the
silicate cements (see e.g., German Offenlegungsschrift (DOS) 1,802,313 and
1,941,480).
A disadvantage of the silicate cements is that they are harmful to the
pulpa and relatively soluble in the mouth region. The former weakness is
naturally particularly serious; it necessitates the application of cavity
lacquers or underfillings, procedures which are time-consuming and in many
cases, unreliable.
The object of the invention is to improve the properties, particularly the
physiological compatability of the silicate cements, without reducing the
other advantages, particularly their esthetic appearance and the
relatively high compressive strength.
SUMMARY OF THE INVENTION
This invention relates to dental cements. More particularly, this invention
relates to dental cements prepared by mixing a silicate powder with an
aqueous solution of polymers of unsaturated alpha, beta-dicarboxylic
acids.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The object of this invention is achieved by using as a mixing liquid,
aqueous solutions of polymers of unsaturated alpha, beta-dicarboxylic
acids as a liquid component, instead of the usual phosphoric acid.
As in all cements, the mixing liquid according to the invention is used for
a two-component silicate cement.
The liquid component is an aqueous solution of polymers of ethylenically
unsaturated alpha, beta-dicarboxylic acids. Preferred are the polymers of
unsaturated alpha, beta-dicarboxylic acids with 4 or 5 carbon atoms.
Polymaleic acid has proved to be particularly successful, but polyitaconic
acid is also suitable. Also useful are copolymers of the two above
mentioned acids, as well as their copolymers with other ethylenically
unsaturated carboxylic acids, particularly acrylic acid. Polymers of other
carboxylic acids, for example, polyacrylic acids, can also be used as an
addition to the polycarboxylic acids in an amount of about 0.1 to 50% of
said polycarboxylic acids.
The polymeric acids are used in aqueous, at least 20%, solutions. In
general, a concentration of 65% will not be exceeded, otherwise gelling
might easily occur or the solutions may become too viscous. The preferred
concentration range is between 35% and 65%, particularly between 40% and
50%.
The polycarboxylic acids, particularly polymaleic acid, can be easily
obtained according to known methods in solid form, for example, by further
concentration of concentrated solutions by freeze-drying or by
precipitation from aqueous solutions with non-solvents.
The solutions of the polycarboxylic acids should be used with a viscosity
of at least 0.5 poise; solutions with viscosities of over 3000 poise,
preferably over 600 poise, are generally not suitable, since they are
difficult to handle and the stirred cements show a tendency of forming
"cobwebs". A preferred viscosity range is between 2 and 200
poise/25.degree. C., particularly between 5 and 100 poise/25.degree. C.
The production of the polyacids used according to the invention is known:
(see e.g. DOS 1,944,756; 1,570,708; 1,645,100; German Pat. No. 1,162,083;
J. L. Lang et al., J. of Polymer Science, A 1, 1123(1963); C. S. Marvel et
al., J. of Organic Chemistry 24, 599 (1959).
The common silicate powders can be used, that is, the inorganic glasses as
they are found in commercial silicate cement powders for dental purposes
in ground and sifted form in corresponding tooth-like colors (see e.g.
Skinner Phillips, The Science of Dental Materials, Fifth Edition, W. B.
Saunders Co. (1960) p. 244 ff). The glasses in question can be called
aluminum-fluorosilicate-glasses. They are usually produced from mixtures
of aluminum-oxide and silica with the addition of fluxes like calcium
fluoride or cryolite.
After heating to about 1400.degree. C., the glasses are ground in ball
mills and sifted. By adding pigments, tooth-like colors are obtained,
preferably powders with different pigment additions are produced to meet
all requirements.
The two components, that is, the silicate powder and the polycarboxylic
acid solution, are mixed on a support, for example, a glass plate or a
block of hardened paper. The setting starts after a few minutes; in the
tooth, the mixture will usually harden after 5 minutes at most. Setting
times, and, to a certain extent, the strength of the end product are
determined partly by the ratio of powder to liquid. As a rule, a weight
ratio (powder/liquid) of not less than 1:1 will be selected to achieve a
pleasant consistency, and a mixing ratio of 4:1 will not be exceeded. A
preferred mixing ratio of powder and liquid is between 1.5:1 and 2.5:1.
An optimum consistency is obtained according to the regulations of American
Dental Association specification No. 9, par. 4.3.2.
In recent years, it has become increasingly customary to sell
dental-preparations pre-dosed in so-called shaking caps. Liquid and powder
are kept in separate compartments and combined immediately before use by
suitable devices and subsequently mixed mechanically.
This pre-dosing is also applicable to the mixing liquid according to the
invention. In a special embodiment, the system can be divided into
silicate-cement powder, solid polydicarboxylic acid and water, instead of
the usual division into liquid and powder, that is, in the present case,
into silicate cement powder and polydicarboxylic acid solution. This
system has the advantage that it makes the dosing more reliable and the
mixing easier since the relatively viscous solutions are avoided. In this
system, the powder/polymer ratio is 1.5:1 to 20:1 and preferably between
2.3:1 and 12.5:1.
These systems can furthermore be so varied that the solid components, that
is, silicate cement powder and polydicarboxylic acid, are premixed and
packed pre-dosed as a powder mixture, since the solid substances do not
react with each other. The second component is then water, if necessary,
with the usual bacteriostatic additions, etc.
The cements produced with the mixing liquid according to the invention,
unlike the known silicate cements and filling materials based on plastics,
are not harmful to the pulpa. They are esthetically pleasant and thus
superior to amalgams. Their solubility is favorable, that is, they are
relatively insoluble under mouth conditions.
It could not be expected that the physiological properties of the silicate
cements could be improved decisively by the use of aqueous solutions of
polymers of unsaturated alpha, beta-dicarboxylic acids without losing the
advantages of the silicate cements.
The mixing liquid, according to the invention, can also be used for all
other common dental cements.
In the following Examples, the addition of pigments customary for the
production of tooth-like colors will not be mentioned specifically, since
it corresponds to the state-of-the-art.
EXAMPLE 1
Polymaleic acid, suitable for dental-medical purposes, and produced
according to the method of DOS 1,944,756, is mixed with water to a
concentration of 48% by weight (the solution has a viscosity of 10.5
poise/25.degree. C.). The powder used is a commercial silicate cement
(Syntrex).
The powder and liquid are mixed in a weight ratio of 1.9:1 to obtain a
paste that is well suitable for clinical purposes. The paste is introduced
in known manner into prepared tooth cavities. The mixture hardens after a
few minutes and has, in the set state, a transparency corresponding to the
natural tooth.
EXAMPLE 2
The liquid of Example 1 is mixed with the silicate cement powder known
under the name Achatit in a powder-liquid ratio of 1.6:1. The mixture
yields esthetically pleasant permanent fillings in teeth.
EXAMPLE 3
A silicate cement powder, produced in known manner, which contains per
analysis 39.5% SiO.sub.2, 28.1% Al.sub.2 O.sub.3, 6.1% Ca, 15.2% F, 6.6%
Na and 4.0% P.sub.2 O.sub.5, is mixed with the liquid mentioned in Example
1 in a weight ratio of 2.4:1. The cement mixture is particularly suitable
for the production of fillings in the molar region and has a high
compressive strength.
EXAMPLE 4
A 58% solution of polymaleic acid, produced according to DOS 1,570,708 and
by subsequent hydrolysis, is made into a paste with 2.1 parts of the
powder of Example 1 and is used as a permanent filling material.
EXAMPLE 5
Polymaleic acid, produced according to DOS 1,645,100, is used as a 47%
aqueous solution and mixed with 1.4 parts of the powder of Example 2.
EXAMPLE 6
A 54% aqueous solution of polyitaconic acid, produced according to DOS
1,944,756, is mixed with 2 parts silicate cement powder (Syntrex). The
paste is introduced into a tooth cavity and hardens after a few minutes.
EXAMPLE 7
The aqueous solution of polymaleic acid of Example 1 is filled in portions
of 80 mg into foil bags consisting of plastic coated aluminum, and sealed.
The foil bags are inserted into the cover part of two-component containers
as described in DOS 1,910,885. 155 mg of a commercial silicate cement
powder are filled into each container part provided as a mixing chamber.
When such a filled capsule is used, as described in DOS 1,910,885, we
obtain by means of a mechanical shaking device, a paste of optimum
consistency, which is highly suitable for tooth fillings.
COMPARISON TESTS
The comparison tests were carried out according to the regulations of ADA,
specification No. 9, par. 4.3. Mixtures of standard consistency were
processed and molded bodies were tested for compressive strength.
RESULTS
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Compressive
Mixing Strength
Powder Mixing Liquid Ratio (kg/sq cm)
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Syntrex
According to invention;
Example 1 1.9:1 1,590
Syntrex
Syntrex 2.4:1 1,620
Achatit
According to invention;
Example 2 1.6:1 1,580
Achatit
Achatit 2.4:1 1,570
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As it can be seen, the compressive strength is about as good as in the
known preparations, while the fillings prepared with the mixing liquid
according to the invention, unlike the silicate cements, are completely
harmless to the pulpa.
Instead of the polydicarboxylic acids used in the Examples, other polymers
of unsaturated alpha, beta-dicarboxylic acids, as well as copolymers, can
also be used. Particularly suitable are copolymers of maleic acid and
itaconic acid, where the maleic acid portion can be relatively high, e.g.,
80 mole percent. Also suitable are copolymers of unsaturated alpha,
beta-dicarboxylic acids with unsaturated monocarboxylic acids,
particularly acrylic acid or methacrylic acid. Here too, copolymers which
have a relatively high content of dicarboxylic acid units deserve
preference. Particularly suitable are copolymers which contain primarily
maleic acid, in addition to acrylic acid or methacrylic acid, particularly
copolymers which contain more than 90 mole percent maleic acid.
Suitable also are polymers or copolymers of the above mentioned type, which
contain additionally small amounts, that is, not more than 10 mole
percent, of monomers free of carboxyl groups. Particularly suitable are
copolymers with methacrylic esters (the ester moiety can be alkyl,
preferably 1 to 4 C-atoms), acrylic amide, methacrylic amide, as well as
derivatives substituted on nitrogen.
Various changes and modifications can be made in the composition of this
invention without departing from the spirit and the scope thereof. The
various embodiments of the invention disclosed herein serve to further
illustrate the invention, but are not intended to limit it.
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