Note: Descriptions are shown in the official language in which they were submitted.
11~5880
The invention relates to moulded dental fittings, such as dentures,
crcwns or bridges, with improved mechanical properties.
In most cases, dentures made of plastic are prepared by the pcwder-
liquid process [Ger~an Patent Specification 737,058].
In this procedure, a bead polymer based on polymethacrylates is
processed, with methacrylates, such as, for example, methyl methacrylate, to
form a paste by stirring 2 to 3 parts of powder with 1 part of liquid. A
peroxide has been added to the manomer before preparing the paste, so that
after the paste has been moulded it can be cured by heating, the monomer
being polymerised.
Because the preparation pro oess for dentures, crcwns and bridges
is easy to carry out, the powder-liquid process has become the standard
technique for preparing plastic dentures. Furthermore, it is known to im-
prove the pro oessability of dental beads in the powder-liquid prooe ss by
using polymethyl methacrylate powder or, preferably, polymethyl methacrylate
beads of a definite particle size, and it is also known to improve the pro-
oe ssing spectrum of dental beads by using beads consisting of ccpolymers of
methyl methacrylate with a major proportion of co~olymerised methacrylic
acid methyl ester as the powder, instead of polymethyl methacrylate beads.
These variations make it possible to obtain the desired rapid prooe ssability
together with the broad pro oessing spectrum which is also desired.
A disadvantage of the dentures, crowns and bridges based on poly-
methyl methacrylates and prepared by the powder-liquid process is that the
mechanical values of the raw material are not satisfactory for many struc-
tures. In particular, in many cases the toughness properties of the plastics
under load are
not sufficient for dentures, crowns and bridges. Improving the
impact strength of the plastic would have the effect of lowering
the tendency of the dentures to brcak and also therefore of
making it possLble to carry ou~ the cleaning opera~lon more
reliably.
It has been found that moulded dental fittings prepared by
the powder-liquid process, such as dentures, bridges, crowns
and orthodontic appliances, based on polymethacrylates, have
irnproved mechanical properties if polymethyl methacrylates
which have been elasticized with polyurethanes are used or co-used
as the powder.
The same also applies to synthetic teeth prepared in this
manner. Polymethyl methacrylates elasticized with polyurethanes
are also a suitable component of materials for rep~iring dentures,
bridges, crowns and orthodontic appliances.
It is known to elasticize polymethyl methacrylates by
polymerising the methyl methacrylate by the bulk polymerisation
process, whilst simultaneously shaping. However, it was not to
be expected that dentures with improved properties can be
obtained if the powder-liquid process i9 used and a polymethyl
methacrylate which contains a polyurethane as an elasticizing
component is employed as the powder.
As is generally known, dental plastics which are obtained
by the powder-liquid process are charac~erized by a particular
structure. A multi-phase system, which can be detected by
special methods, exists in the cured plastic: only some of the
original "liquid" has penetrated into the powder
particles during the initial swelling procedure. A
large; if not predominant, preportion of the liquid polyrnerises
as a plia~e in itself and fills the intermediate spaces between
the swoLlen original powder particles. The structure of
moulded fittings which consist of polymethacrylates o-r modified
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polymethyl methacrylates and which have been obtained by the
powder-liquid process is thus substantially different to that
of mouldsd fitments which consist of polymethyl methacrylates
and which have been obtained by customary shaping processes.
It is indeed also known, from German Patent Specifica-
tion 940,493, to improve the mechanical properties of moulded
fittings consisting of methyl methacrylates, by using mixtures
of different polymers or copolymers as the powder components.
For example, copolymers consisting of 80% of methyl methacrylate
and 20% of butadiene are used for improving the flexural
endurance. However, because of the butadiene content, copolymers
of this type have a poor fastness to light.
Furthe more, it is known, from German Patent
Specification 940~493, to use post-chlorinated polyvinyl
chloride as an additive in order to improve the flexural impact
strength and the flexural endurance of moulded fittings which
are based on methyl methacrylate polymers and which have been
ohtained by the power-liquid process. However, using post-
chlorinated polyvinyl chlorides as an additive has the effect
of lowering the resistance towards discolouration. Moreover,
the stability of post-chlorinated polyvinyl chlorides is not
sufficient when relatively active peroxides or relatively high
polymerisation temperatures are used.
Moulded fittings for dental purposes, such as full
and partial dentures, bridges, crowns or orthodontic appliances,
based on organic plastics can be prepared by various procedures.
Thus, for example, it is possible to convert the
plastic into the desired moulded fittings ~7ia an injection or
extrusion process.
The moulded dental fittings, e.g. dentures, bridges,
crowns or teeth, according to the invention are obtained by this
process by shaping a new class of polymer, namely polyurethane-
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elasticated polym~ethacrylates, optionally mixed with customary "injectable"
polymethyl methacrylates, by means of an injection devioe or by means of an
extrusion device.
However, a particularly versatile process for the preparation of
dentures, crcwns or bridges is the powder-liquid prooe ss. me moulded fitt-
ings according to the invention are obtained by this process by using a poly-
urethane-elasticized polymethacrylate as the powder. mese pcwders can be
obtained by converting polyurethane-elasticized polymethacrylates into so-
called "acrylate chips" via a comminuting process. However, particularly
good results are obtained when those polyurethane-elasticized polymethacry-
late powders which have been prepared by the procedure of a bead polymerisa-
tion are used.
In addition to the better prooessability comçared with the acry-
late chips, the use according to the invention of the eias~icized polymer
beads additionally has the advantage that the elasticizing co~ponent is
better protected against degradation by components in the medium of the
mouth and is generally protected against the action of components in the
medium of the mouth. In the dental ~eads, the polyurethane present as a
separate phase is enveloped by the base substanoe of the dental beads, that
is to say the polymethacrylate, and is thus protected from such action. In
addition, the dental beads are themselves also in turn embedded in a matrix
of polymethacrylate and are thus protected.
A particul æ embodlment of the proceduLe according to the inven-
tion, for the preparation of dentures, crcwns or bridges by the powder-/
liquid process consists in setting up the desired processability and the re-
quired processing spectrum by using elasticized dental beads of a definite
particle size,
588~
or by adjusting the initial swelling behaviour of the polymer
beads by using comonomers in the bead polymerisation. However,
it is very particularly advantageous to set up the characteristic
quantities of processability and processing spectrum, which are
particularly important for handling from the point of view of
dentistry, by adding non-elasticized beads. It was surprising
that the good elasticizing activity of the dental beads is not
lowered when the latter are used as a mixture with customary
dental beads. The mixing ratios most favourable technologically
must nevertheless be determined from case to case and depend on
the construction and on the function of the denture or bridge.
Polymethacrylates in the sense of the present invention
are understood as polymerisation products of methacrylic acid
esters. In most cases, methacrylic acid methyl ester is the
main component, but useful results are also obtained with poly-
functional esters of methacrylic acid, and for specific purposes,
good results are given by, for example, bis-GMA which is
chemically bis-(2-hydroxy-3-methacryloyloxypropoxyl-phenyl-
dimethylmethane or its modification products and also the
comonomers mentioned in United States Patent 3,730,g47.
Polyurethanes in the sense of the present invention are
understood as reaction products of polyols and polyisocyanates.
In particular those polyurethanes which are obtained from the
diisocyanates below are of industrial interest:
A) aliphatic (particularly alkyl) diisocyanates having a
branched carbon skeleton with 7 to 36 C atoms, for example
2,2,4- or 2,4,4-trimethyl-hexane-1,6-diisocyanate or industrial
mixtures thereof, diisocyanates derived from esters of lysine or
diisocyanates based on dimerised fatty acids, which are prepared
in a known manner by conversion of dicarboxylic acids of this
type with up to 36 C atoms into the corresponding diamines
and subsequent
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phos~cnation,
B) cycloaliphatlc (particularly cycloalkyl hydrocarbon having
4 to 6 ring members) dLisocyanates, for example cyclobutane-
1,3-diisocyanate, cyclohexane-1,3- and -1,4-cliisocyanate, 2,~-
or 2,6-diisocyanato-1-methylcyclohexane or 4,4'-diisocyanato-
dicyclohexylmethane, either in the form of the pure geometric
isomers or an industrial mixtures thereof, an~ furthermore 1~
isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclollexane (i&o-
phorone diisocyanate), and finally
C) aliphatic (partlcularly alkyl)or cycloaliphatic (particularly
cycloalkyl) diisocyanates whlch are modified by free radical
graft copolymerisation wlth vinyl monomers and which are obtained
by polymeri~ing in the presence of 100 parts of the diisocyanate
of 10 to 100 parts, preferably methyl methacrylate, with the
aid of a free radical polymerisation initiator, for example an
organic peroxide, such as benzoyl peroxide, tert.-butyl peroctoate
and the like, or an aliphatic azo compound, such as azoisobutyro-
nitrile. In addition to the diisocyanates already mentioned,
aliphatic (particularly alkyl) diisocyanates having a linear
carbon chain, for example hexamethylene diisocyanate, are also
suitable for use as the graft substrate. It has been shown that
aliphatic diisocyanates modified in this manner lead to polyurethene-
urea elastomers, wlich are soluble in monomeric methyl meth-
acrylate to give a clear solution and give clear polymers when
the refractive indices of the polymer phase and viscous phase are
correctly matched.
Isophorone diisocyanate and hexamethylene diisocyanate
or isophorone diisocyanate ~hich have been modified by graEt
copolymerisation with methyl methacrylate and have a polymer
content of up to 50%, preferably of up to 40V/o~ are preferably
used.
Suitable polyols which can be used, accordin~ to the
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ll~S880
present invention, for the preparation of the polyurethanes are longer-chain
diols with 2 terminal hydroxyl groups. Polyesters, polyethers, polyaoetals
or polycarbonates with m~lecular weights of 400 to 6,000 and a glass transi-
tion temperature <20& are preferably used.
Suitable polyesters containing hydroxyl groups are, for example,
reaction products of dihydric alcohols with dibasic carboxylic acids.
In the preparation of the polyurethanes to be used according to
the invention, the hydroxyl ccmponent and the isocyanate ccmponent are not
employed in equivalent amounts, but an excess of one or other component is
used. In particulæ, in the prepolymer process, a polyurethane prepolymer
which is free from QH groups and has NCO functional groups and which can
still contain free diisocyanate is obtained in the first stage, and this is
reacted in the second stage with the chain lengthener until the desired mole-
cular weight is reached. A residue of free NCO groups usually remains in the
product, and these are appropriately protected with the aid of a monofunc-
tional chain stopper [component (C)]. Examples of suitable chain stoppers
are lower aliphatic alcohols, such as methanol, ethanol, butanol or allyl
alcohol.
Chain lengtheners for the polyurethanes to be used according to the
invention include suitable short-chain compounds with 2 hydroxyl groups are,
for e~ample: ethylene glycol, propylene 1,2- and 1,3-glycol, butylene 1,4-,
1,3- and 2,3-glycol, penta-1,5-diol, hexane-1,6-diol, heptane-1,7-diol,
octane-1,8-diol, neopentyl-glycol, 1,4-bis-hydroxymethyl-cyclohexane, 2-methyl-
propane-1,3-diol, diethylene glycol, triethylene glycol, tetraethylene glycol,
polyethylene glycols with a molecular weight <400, dipropylene glycol, poly-
propylene glycols with a lecular weight <400 dibutylene glyool, poly-
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119~588~
butylene glycols with a molecular weight <400, 4,4'-dihydroxy-diphenylpro-
pane or hydroqL mone-bis-(20 hydroxyethyl ether).
For their prooessing by the powder-/liquid process in dentistry,
the polyurethane-elasticized polymethacrylates are mixed with a mono~er to
form a paste. Methyl methacrylate is preferably used as the monomer. Mono-
mers which contain two or more double bonds in the molecule (such as deriva-
tives of acrylic and methacrylic acid) and which thus lead to crosslinking
are added in order to increase the resistance to solvents and the abrasion
resistan oe. The following oompounds, for example, can be added as crosslink-
ing agents in amounts of about 0~1% by weight to 30% by weight, preferablyabout 1% by weight to 15~ by weight: ethylene glycol dimethacrylate, tri-
ethylene glycol dimethacrylate, butanediol dimethacrylate, triacrylformal and
the bifunctional comonomers mentioned in U.S. Patent 3,730,947.
The resulting CQmpOSitiOnS consisting of bead polymer and monomer
can be cured using initiator systems, based on peroxides or aliphatic azo
ecmpounds, which release free radicals. Examples of suitable polymerisation
initiators are diacyl peroxides, such as, for example, dibenzoyl peroxide, or
aIkylacyl peroxides, such as, for example, tertiary butyl perpivalate, option-
ally in the presenoe of ac oelerators, such as aromatic tertiary amines, for
example alkylated anilines, toluidines or xylidines. Cobalt salts or copper
salts as well as oompounds frcn the barbiturate group and sulphinic acids
and sulphones can also be used as acoe lerators.
Whilst curing at elevated temperature can be OE ried out by means
of peroxides alone, such as dibenzoyl peroxide, chlorobenzoyl peroxide,
toluyl peroxide or lauryl peroxide, or by means of free radical initiators
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~1~5880
alone, such as, for example, azoisobutyric acid nitrile or azoisobutyric acid
esters, it is neoe ssary to add acoe lerators in the case of curing at 1GW
temperatures. About 0.01% by weight to 2% by weight of polymerisation
initiator are required in the case of curing at elevated temperature. About
0.02% by weight to 5% by weight of polymerisation initiators and about 0.02%
by weight to 5% by weight of acoe lerators are required in the case of curing
at lcw temperatures.
Example 1
Dental beads are prepared, in the presen oe of a polyurethane, by a
pro oe ss for the bead polymerisation of methyl methacrylate.
MgCO3 is used as the dispersing agent in the bead polymerisation
and a mixture of lauroyl peroxide and dicyclohexyl percarbonate in the ratio
1:1 is used as the peroxidic initiator in an amount of 0.73%, relative to
methyl methacrylate used (% by weight). The methyl methacrylate aontained
9.9% of dissolved polyurethane.
The polyurethane is a "diol"-lengthened polyester-polyurethane
based on a mixture of tw~ polyester-diols A and B.
Polyester-diol A consists of a polyester based on adipic acid,
hexane-1,6-diol and neopentylglycol, with a hydroxyl number of 66.
Polyester B is a polyester based on ethylene glycol, adipic acid
and phthalic anhydride, with a hydroxyl number of 64.
Polyester A (0.35 equivalent) and polyester B (0.15 equivalent) are
reacted with isophorone diisocyanate (0.75 equivalent), and the chain is
lengthened to the extent of 85% by means of butane-1,4-diol and terminated by
means of 2-hydroxyethyl methacrylate. The polyurethane formation is
catalysed by tin dioctoate.
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11~5880
0.25% by weight of dibenzoyl peroxide are added to 15 parts by
weight of the dental beads prepared in this manner and the mixture is made
into a paste with 5.36 parts by weight of a liquid consisting of 94% by
weight of methyl methacrylate and 6% by weight of ethylene glycol dimethacry-
late. Sheets 2mm thick are pressed fram this paste and polymerisation is
then carried out.
The polymerisation is carried out as follows: the water bath is
heated to 70C in the course of 30 minutes, the temperature is kept constant
for 30 minutes, the bath is then heated to loo& and this te~perature is kept
constant for a further 30 minutes. m e cell is cooled in a water bath.
After remDving from the cell, test pieces are cut out of the sheet
without heating the sheet. The test pie oes thus obtained are subjected to
the Dynstat test according to DIN 53,452.
Test results: (in each case the mean value from 5 test pieces)
Impact strength 30.4 kp/cm2
Bending angle 12.6
Flexural strength 981 kp/cm2
Ball indentation hardness 10" 1,355 kp/cm2
60" 1,249 kp/cm2
Dental beads elasticated by polyurethanes are also used in Examples
2, 3 and 4. These dental beads differ in that different polyurethanes are
used as the elasticating agents in the bead polymerisation.
Ex2mple 2
The dental beads contain a polyurethane which is prepared using 1
equivalent of isophorane diisocyanate instead of 0.75 equivalent of iso-
phorone diisocyanate. For lengthening, the chain is lengthened to the extent
of 90% using butanediol.
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~x5880
0.5% by weight of lauroyl peroxide is added to the beads obtained
in this manner, the mixture is polymerised with a liquid consisting of 97%
by weight of methyl methacrylate and 3~ by weight of triethylene glycol
dimethacrylate and the polymer is subjected to the strength test according
to DIN 53,452:
Impact strength 32.0 kp/cm2
Bending angle 23.4
FJexural strength 1,315 kp/cm
Ball indentation hardness 10" 1,249 kp/cm
60" 1,137 kp/cm2
Example 3
The dental beads used are also obtained as described in Example l;
a polyester-polyurethane which is prepared using 1.25 equivalents of iso-
phorone diisocyanate and the chain of which is lengthen~d to the extent of
90% using butane-1,4-diol is employed as the elasticating polyurethane.
0.1% by weight of dichlorodibenzoyl peroxide is added to the beads
obtained in this manner, the mixture is polymerised with a liquid consisting
of 90~ by weight of methyl methacrylate and 10% by weight of trimethylolpro-
pane trimethacrylate and the polymer are subjected to the strength test
according to DIN 53,452:
Impact strength 49.1 kp/cm
Bending angle 16.6
Flexural strength 1,086 kp/cm
Ball indentation hardness 10" 1,360 kp/cm2
60" 1,252 kp/cm2
Example 4
The dental beads used are elasticated with a polyurethane which has
been prepared using 1.5 equivalents of
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~58t30
isophorone dilsocyanate and the chain of which has been
lengthened to the extent of 90% using butane-1,4-diol.
1% by weight of Ditoluyl peroxide i.s added to the bead
polymers obtained in this manner, is mixture polymeriscd
with a liquid consisting of 88% by weight of methyl methacrylate
and 12% by weight of butanediol dimethacrylate and the polymer
is subjected to the strength test according to DIN 53,452:
Impact strength 27.3 kp/cm2
Bending angle 16.8
Flexural strength 1,267 kp/cm2
Ball indentation hardnes~ 10" 1,517 kp/cm2
60" 1,385 kp/cm2
Example 5
1% by weight of bls-4-chloro-benzoyl peroxide is added
to 4 parts by weight of the dental beads prepared according to
Example 1 and the mixture is made lnto a paste with 3 parts by
weight of a liquid consisting of 94% by weight of methyl meth-
acrylate, 6% by weight of ethylene glycol dimethacrylate and
0.7% by weight of N,N'-dimethyl-p-toluidine. A pourable
consistency is obtaîned with this mixing ratio. A knead-
able consistency is obtained with a mixing ratio of 4.7 parts
by weight of powder and 2 parts by weight of liquid. The
polymerisation has ended after 16-17 minutes at 23C.
The test pieces described in Example 1 are subjecte~ to
the Dynstat test according to DIN 53,452. Test results:
(in each case the mean value from 5 test pieces)
Impact strength 27.4 kp/cm2
Flexural strength 1,005 kp/cm2
Bending angle 28.8
Ball indentation hardness 101' lt327 kp/cm2
60" 1,137 kp/cm2
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l~S880
ocmparison
As a control experiment, customary methyl methacrylate beads con-
taining 0.25~ by weight of dibenzoyl peroxide are polymerised with a liquid
consisting of 94% of methyl ~ethacrylate and 6% by weight of ethylene glycol
dimethacrylate and the polymer is subjected to the strength test according to
DIN 53,452:
Impact strength 19.4 kp/cm2
Bending angle 18
Flexural strength 1,059 kp/cm2
Ball indentation h ædness 10" 1,249 kp/cm2
60" 1,158 kp/cm2
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