Note: Descriptions are shown in the official language in which they were submitted.
~69Z39
The invention relates to dental materials containing
polymerisable monomers and/or polymers suitable for dental pur-
poses, and finely-divided filler.
The term "dental material" includes, for example,
fillings for cavities, fixing cements, sealing and protect-
ive coatings, crown and bridge materials, and denture base
materials and substances for manufacturing artificial teeth
based on polymerisable monomers ~nd/or polymers.
Monomers or polymers suitable for dental purposes,
include for example, polyvinyl chloride, polystyrene and
copolymers thereof, polyamides, epoxy compounds, polyure-
thanes and, more particularly, monomeric and polymeric
acrylates and methacrylates ~cf. Ullmanns Enzyklop'adie
der Technischen Chemiej Volume 5, 1954, pages 717-721).
Artificialteeth or parts of teeth are usually
manufactured from polymethacrylates in the form of bead
.
or splinter polymers, which can normally be processed ~ ;
togather with the corresponding monomers, by heating in
moulds. Mixtures of monomeric and polymeric methacrylates
are used, for example, as denture base material and crown `~
and bridge material, the monomer in the mixture being
polymerised in the presence of the polymer. Monomers
alone are normally used as fixing cements, sealing and protect-
îve coatings, and, more recently, as filling materials.
The Eollowing description is applicable mainly,
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but not exclusively to denture base material and filling
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material, since special problems occur in these cases.
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il069;~39
~hen the conventionally-used monomeric acrylic or metha-
crylic acid esters are polymerised, considerable shrink-
age occurs. For this reason, a paste consisting of bead
polymer and monomer in the weight ratio of 2:1 was very
early used in the manu~acture of denture base material.
Even so, the contraction is still 7~. In addition,
there is a high linear thermal expansion coefficient of
81.0 x 10 /mm/mm C. By comparison, the coefficient
for a natural tooth is only about l/8th thereof, i.e.
11.4 x 10-6
Use for tooth filling and similar purposes did ~-
not become more widespread until long-chain monomers
were used,Based on bisphenol A and glycidyl methacry-
late, according to United States Specification No.
3 066 112. These monomers, somet~mes called Bis-GMA
for short, shrink to a lesser extent. In order to
reduce the shrinkage further, these monomers are some-
times mixed with about three parts by weight of inert
inorganic fillers. Accordingly, they comprise about 25%
of a binder - a cold-polymerisable monomer mixture -
and about 75% of inorganic fillers, preferably aluminium
and silicon oxides, silicate glass or calcium carbon-
ate on various forms, such as spheres and fibres. This
reduces the aforementioned contraction on polymerisation
to about 1%, which can be tolerated for all applications,
and also reduces the coefficient of thermal expansion to
about 20 - 30 x 10 6mm/ =C.
Instead of the aforementioned monomer Bis-GMA,
the binder mixture can contain other derivatives of
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bisphenol A or urethane addition derivatives, e.g.
from diisocyanates and hydroxy alkyl methacrylates.
Usually, short-chain methacrylic acid esters and/or
known cross-linking agents such as t:riethylene glycol
dimethacrylate are added in order to reduce the
viscosity.
Fillings are usually prepared by mixing two
pastes containing binders and fillers. The redox
system ~e.g. peroxide-amine) used for polymerisation
is distributed so that one paste contains the peroxide
catalyst only and the other paste contains the amine
initiator.
Before mixing, the inorganic filler may be
silanised, i.e. coated with suitable unsaturated silane
compounds, to improve the bond to the organic matrix.
These materials, which are known as "composite", are
given a filler content appropriate for the particular
application and are suitable for filling cavities in front
~ teeth, and as fixing cements, seals over fissures and means
; 20 for preventing caries, i.e. protective coatings for teeth; ~ `
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they are also used as crown and bridge materials. ~
It has been found that although these materials ;
have very good mechanical properties in general, they
polish badly and also frequently have unsatisfactory
transparency. Attempts have been made to improve the
polishing qualities by using finely-divided inorganic `
fillers having a particle size of not more than about
30~u ~cf. German Offenlegungsschrift 2 126 419).
Unfortunately, the transparency decreases
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as the particle size is reduced. The surface is initially
unhomogeneous and, after a short time, becomes rough
owing to uneven wear and may therefore become discol-
oured.
Even after the particle size of the inorganic
filler particles has been reduced to a minimum of
about 0.8 - 8 ~ and a maximum of about 3 - 20 ~ ~see
German Offenlegungsschrift 2 312 258), the teeth fil-
lings still have unsatisfactoly transparency and
polishing properties.
It is also known from German Auslegeschrift
1 928 831 and German Offenlegungsschriften 2 126 419,
2 164 668 and 2 224 683 that silicon dioxide can be -;
- added having a particle size of less than 1 ~ in pro-
portions of up to 8% of the total weight of the tooth
filling material in addition to the normal inorganic
fillers. The only purpose of adding silicon dioxide, -~
of this particle size is to thicken the monomer in
order to prevent sedimentation of the rela*ively large
particles of filler. German Offenlegungsschrift 2 164 668
states that particles smaller than 0.7 ~ must be removed
by suitable methods, since otherwise there is an excessive -
decrease in the transparency of the filling material.
Likwise, German Offenlegungsschrift 2 126 419
' states that silicon dioxide having a particle of size
of 50 - 2000 ~, used as a thickening agent, must be -;-
added in only a very small porportion - i.e. about 5 - 8%
; by weight of the total material.
Possibly, the disadvantages mentioned in the
aforementioned patent specifications when silicon
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dioxide is used having a particle size of less than 1 ~ are due to the fact
that silicon dioxide is used together with larger quantities of a filler
having a greater particle size.
It has now unexpectedly been found that ~he mechanical properties
and the polishing qualities of dental materials can be improved, without
impai~ing the transparency thereof, when an inorganic filler is used which
has a particle size of less than ~00 m~.
This invention relates to a dental material comprising a poly-
merisable monomer and/or a polymer suitable for dental purposes, selected
from polyurethanes, monomeric and polymeric acrylates and methacrylates, and
mixtures thereof, and a silanised microfine inorganic filler which is present
in a proporation of from 20 to 80% by weight of the material and has a
particle size in the range from 10 to 400 m~. Preferably, the microfine
inorganic filler has a specific surface area of less than 200 m2/g.
Preferably, at least 50% of the microfine inorganic filler particles
have a particle size in the range from 10 to 40 m~.
The present invention also provides artificial teeth, replacements
for parts of teeth and outer layers for artificial teeth and replacements for
parts of teeth which are manufactured from the material defined above.
The microfine inorganic filler thickens the polymerisable monomer of
~` the material and gives it thixotropic properties, so that the material can be
re-liquefied simply by stirring.
Advantageously, when more highly viscous monomers or monomer-polymer
mixtures are used, the microfine inorganic filler is added in smaller
quantities within the aforementioned range, so that the mixture does not
become too viscous~ Alternatively, the proportion of th0 microfine inorganic
filler can be increased, even in the case of monomers or mixtures
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~069Z3~
having a greater initial viscosity, if ~he filler
selected is such that its specific surface area is
less than 200 m2/g. Preferably, the specific surface
area of the microfine filler is between 30 and 80 m2/g.
Advantageously, the-proportion of ~he microfine
inorganic filler is in the r~nge from 20 to 80%, pre-
ferably from 40 to 75~, by weight of the material. As
already mentioned, the most favourable ranges depend
inter alia on the specific surface area of the filler
and on the viscosity of the polymerisable monomer and/or -
polymer.
Preferably, the microfine inorganic filler is
silicon dioxide and/or aluminium oxide. Alternatively,
use can be made of glass such as borosilicate glass or
lithium aluminium silicate glass or glass containing
barium oxide or lanthanum oxide or similar fillers,
provided that the particle size thereof is less
than 400 m y. Mixtures of microfine fillers can ~ ~ -
also be used; preferably the glass has a small thermal
expansion coefficient and is added in a proportion of
up to 25% by weight of the total filler content.
Preferably the microfine filler is silanised,
e.g. by processing with trimethoxy-~-3-methacryloyl-
oxypropyl)-silane. The silanisation process is usually
performed with a silane containing polymerisable organic
Y
groups. The polymerisable groups react with the po ~eris-
able mo~omer; in the organic matrix producing a strong -
bond bet:ween the organic components of the material and
the inorganic filler. However, in contrast to the previously-used
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comparatively coarse fillers, it is not absolutely
necessary to silanise the microfine inorganic fillers.
The colour of the dental material according
to the invention can be assimilated to that of natural
teeth by adding organic or inorganic pigments and/or
opacifiers. The particle size of such additives should
not be more than 400 m ~.
The invention also embraces artificial teeth and
replacements,for parts of teeth, e.g. tooth fillings,
crowns, bridges ~more particularly the outer l~ayer thereof),
veneers and similar replacements, manufactured from
a dental material according to the invention.
Owing to the presence of the microfine inorganic
filler, the dental materials can be used to manufacture
products having unusually high compressive strength, excel-
lent transparency and a very smooth homogeneous surface.
Even the naked eye can observe the difference in surface
. . .
quality between a commercial dental material, e.g. a filling
material, and a filling material containing the ~icrof~ne
inorganic filler. Under the microscope, the difference
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` is even more visible. No individual particles are
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observable in the filling material containing the micro-
fine filler ~the surface appears as a homogeneous unit)
whereas in commercial filling materials the individual
particles are visible in the form of splinters or spheres.
The microfine filler helps to eliminate the previous con-
flict between the requirements for high transparency and
for good polishing qualities. In addition, dental mat-
erials according to the invention are opalescent. This
considerably improves the cosmetic effect, since the
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~)6~39
resin layer is yellowish in transmitted light and bluish-
white in inciden~ light, in the same manner as natural
teeth. Consequently, the materials according to the
invention are particularly suitable as front-tooth
fillings.
Good results have been obtained more particularly
with the following polymerisable monomeric binders:
mono-, di- and higher esters of methacrylic acid, more
particularly Bis-GMA, if necessary with an admix-
ture of diluting monomers such as methyl methacrylate.
Other examples of monomeric binders are bis-[4-~2-
hydroxy-3-methacryloyloxypropoxy)-phenyl] -dimethyl
methane, 2,2-bis-~4-~2-hydroxy ethoxy)-phenyl]-propane
dimethacrylate and triethylene glycol dimethacrylate. ~"~
Alternatively, use-can-be made of other derivatives of
bisphenol-A or of the reaction products of hydroxy
alkyl methacrylates and isocyànates. These monomers
mostly have relatively high viscosity, which is usually
lowered by adding short-chain monomeric methacrylic
acid esters. Difunctional es*ers of acrylic or meth-
acrylic acid can be added as cross-linking agents. ~ -
The inorganic filler is the microfine filler.
Polymerisation catalysts can be added, e.g.
organic peroxides such as dibenzoyl peroxide, tertiary butyl
peroctoate or azo compounds such as 2,2 azo-bis isobutyroni-
trile ~A[BN). Use can also be made of redox systems
which are conventional for dental plastics, e.g. di-
benzoyl peroxideldimethyl-~-toluidine or dibenzoyl
peroxide/trimethyl barbituric acid. It is possible -~
to prepare a "composite" material for fillings and
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~692~9
other purposes, comprising two separately-stored
components A and B, preferably in paste form. Both
contain an organic binder system and a filler, and
in addition one contains the catalyst and the other
contains the activator. The proportion of inorganic
filler to be added can vary, depending on the
application. It can be, for example, 60 - 65% for
a composite material used for filling purposes, whereas
the organic matrix comprises 20 - 22% bis-GMA and 15-
18% ethylene glycol dimethacrylate.
The organic binder mixture may be thoroughly
mixed with the microfine inorganic filler until a paste
is produced. Subsequently, 0.5 - 2% benzoyl peroxide
may be added to the first component and 0.5 - 1% dimethyl
paratoluidine added to the second component.
A test-piece may be manufactured by taking
approximately equal quantities of paste A and B and
mixing them on a mixing block; a metal spatula can be
used, in contrast to when normal filling materials are
used. The working time of the material is about 2 minutes;
after 5 minutes the mixture has polymerised into a
solid specimen. The measured compressive strength,
` depending on the proportion of microfine filler used
and the variation in the organic matrix, is between
4000 and 6000 kg/cm2 which is even better than for
amalgam.
The transverse strength reaches values bet~een
11 and 16 kg/mm2, and the water adsorption after 2 months
is between 0.5 and 1.5%. The surface quality of a
commercial filling material and of a material manufactured
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in the aforementioned manner were compared under a
microscope after both surfaces had been polished to
a high lustre by conventional methods. It was found
that the filling material containing the microfine
filler has a homogeneous surface completely free from
pores, whereas in the case of the commercial filling
material, individual splinters or spherical particles
were visible, embedded in the matrix. Another unexpected
effect is that the microfine filling material is opal-
escent, i.e. yellowish in transmitted light and
bluish-white in incident light, and thus has optical
properties closely resembling natural enamel, which is
particularly desirable for front-tooth fillings.
The microfine filler can also be used to manu-
facture a substantially improved material for crowns,
inlays and bridges. This can be done, for example,
by dissolving a crystalline dimethacrylate of a
modified bisphenol-A in an organic solvent such as
chloroform or ether and adding the~microfine filler
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to the solution with continuous agitation. A paste
is obtained and is kneaded until the solvent has
completely evaporated. The powder is crushed in a
ball mill and a catalyst, e.g. benzoyl peroxide, is -
added. The mixture is screened, yielding a material
suitable for manufacturing crowns and bridges. ~
A crown, for example, is modelled as follows: ; ;
Powder produced in the aforementioned manner is heated
` above the melting-point of the crystalline monomer in -~
a porcelain dish, until a thinly-liquid slurry is ~
obtained which can be applied with a brush or spatula. -~ ,
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1069~39
The slurry is applied in layers to an isolated model
stump and polymerised one layer at a time, e.g. in
a stream of hot air, thus obtaining a crown having
an attractive transparency and extremely high resistance
to abrasion. Alternatively, the crown can be formed
in conventional manner in layers in a dental flask,
using a polymer/monomer paste to which a suitable
quantity of microfine filler has been added, and can
then be polymerised by heating in a water bath.
Alternatively, the microfine filler can be
mechanically mixed with a polymethyl methacrylate in
bead form and monomer can be added to form a paste which
is polymerised at elevated temperature, e.g. 100C,
under pressure in a metal mould, to form an artificial
tooth or veneer.
A tooth manufactuTed in this way had very good
opalescen~e, excellent physical properties such as :
compressive and transverse strength, and was cLearly
superior to traditional materials.
.:
The microfine filler can be ~ery uniformly dis-
tributed in the polymer by forming the monomeric methyl
methacrylate and the microfine filler into a paste ~ ~:
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which is polymerised under pressure and at elevated
temperatuTe to form a block, which is then ground ~ -
into a sp:Linter polymer. The resulting polymer is mixed
with filler and can be used in a conventional manner
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for manufacturing artificial teeth or parts of teeth,
or as a base material for dentures.
In general, the microfine filler can be used to -
make improved dental materials which have much better
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compressive strength, good polishing properties,
excellent transparency and low abrasion, and which
are opalescent, thus closely resembling natural enamel.
The dental material according to ~he invention
has given good results in the manufacture of tooth-
filling material and is also suited for manu-
facturing crowns, bridges, prefabricated veneers or
artificial teeth; in the case of crowns, bridges or
artificial teeth, at least the outer layer is made of
dental material according to the invention.
The following Examples illustrate the invention.
Example 1
61.5 g of silicon dioxide (average particle size
between 10 and 20 m ~; specific surface area 50 m2/g) -
was silanised in conventional manner with methacryl-
oxypropyl trimethyl silane and poured into a laboratory
kneading machine. 22 g of Bis-GMA and 16.5 g of ethylene
glycol dimethacrylate were added and the mixture was
kneaded into a homogeneous paste free from specks.
0.6 g of 50% benzoyl peroxide was added to 40 g of the
paste (paste A). 0.1 g of dimethyl paratoluidine was
added to another 40 g of the original paste (paste B).
If equal quantities of paste A and paste B are
mixed on a mixing block, a material is obtained suitable
for filling tooth cavities. The working time is 2 minutes,
and the material is hard after 5 minutes. A specimen
was prepared in the aforementioned manner and stored
in water at 37C for 24 hours.
The specimen and a sample for comparison,
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prepared from commercial composite material for dental -
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~:1169;~9
fillings and containing about 75% silicon dioxide
having an averag~ particle size of 30 y, was polished
with a rubber polisher for 5 m:inutes. The surfaces
of both test pieces were examined under-a microscope.
A photomicrograph of the mater:ial containing microfine
silicon dioxide showed a homogeneous, uniformly smooth
surface without pores, whereas in the case of the
commercial material, the individual particles were
clearly visible, distributed in the matrix.
The following tables show some comparative results:
Filling
material `
Commerical according
filling to the
material invention
. . .
Compressive strength after 24
hours in water, 37CCkgtcm2) 2700 4700
Transverse strength ~g~mm2~ 11.0 11.7
~ater absorption after 1
month (%) 1.0 1.4 ~ ~-
Transparency after 24 hours
in water at 37C ~) 32 80 ;
Example 2
.
20 g of 2,2 bis 4-~2-hydroxy-ethoxy)-phenyl -
propane dimethacrylate was dissolved in 50 g chloroform. -
21 g of silanised silicon dioxide having an ~average
particle size of 30 m lu and a specific surface area o~ `~
less than 80 m2/g was added to the solution. The
resulting paste was dried with continuous agitation until
the crystalline monomer had~;re-solidified and the solvent
had evaporated. The silicon dioxide was thus distributed
in the monomer in a completely homogeneous
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manner. 0.5% ben~oyl peroxide was distributed in
the powder by grinding it in a ball mill and subse-
quently scree~ing it. This mixture is stable provided
it is not heated above 42C. It was processed by
melting the powder in a porcelain dish at 50 - 60C
and applying it in layers, using a brush or spatula,
to an isolated model stump, each layer being polymerised
in a stream of hot air at approximately 150C. The
resulting crown was compared with a crown made from
a commercial material.
The cro~n containing the microfine filler was
opalescent, i.e. it appeared bluish-white in incident
light, and therefore had very nearly the same cosmetic
effect as natural ena~el. Tests on the two crowns,
by brushing them with precipitated chalk using tooth-
brushes, showed that the polymer containing microfine
silicon dioxide was much more abrasion-resistant. The
difference is illustrated by the follo~ing few comp-
arative results.
Cro~n Crown
containing manufactured
microfine from a
silicon commercial
dioxide material
Compressive strength kg/cm2 3300 1360
Transverse strength kg/mm2 11.5 6.0
Ball-~ressure hardness
kg/cm 2320 1600
~ater:abso~tion a$ter 1
month ~%~ Q.8
Example 3
lQQ g of the same microfine filler used as in
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9Z3~3
Example 1 ~except that it hat not been silanised) was
mixed with 30 g of non-coloured polymethyl methacrylate
in the fo~m of a bead polymer, and 2 g of 50% benzoyl
peroxide. A monomer mixture was prepared, comprising
35% monomeric methyl methacrylate and 35 g of a
reaction product of hydroxyethyl dimethacrylate and
hexamethylene diisocyanate The powder and the liquid
were mechanically mixed in a vibrating mixer in a
sealed container until a viscous paste was produced.
The paste was poured into a tooth mould and polymerised
at 110C for 4 minutes. The resulting artificial tooth -
had marked opalescence, i.e. appeared yellowish in ~ -~
transmitted light and blue~white and transparent in
incident light. The ball pressure hardness was 2800
kg/cm2 compared with 1400 kg/cm2 for comparable teeth
prepared on a conventional methacrylate basis. The
artificial tooth containing the microfine filler was
appreciably more resistant to monomers, chloroform and ~ -
` boiling water.
Embodiments of the invention are shown in the ~ ;
accompanying drawings, in which~
Figure 1 is a view of an artificial tooth;
Figure 2 is a cross section along the plane A~A
in Figure 1. As Figure 2 shows, the tooth has a
plastics core 1 not containing a filler and an outer
layer 2 mad~ from a dental material according to the
` invention.
~ Figure 3 shows a veneer made from dental material
`~ according to the invention.
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