Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED POLYVINYLSILOXANE IMPRESSION MATERIAL
BACKGROUND OF THE INVENTION
This invention is directed to improvements in room temperature polymerizable
polyorganosiloxanes having good dimensional stability upon curing or hardening
and
having improved flow characteristics. More particularly, this invention is
directed to
improvements in compositions that are generally of the type comprising two
components,
one component comprising organopolysiloxanes having vinyl groups, capable of
undergoing addition reactions with organopolysiloxanes having silicone-bonded
hydrogen
atoms. The second component comprises a catalyst capable of promoting the
addition of
hydrogen atoms bonded to silicone atoms across the vinyl groups. In one
embodiment, the
inventive material has a high tear strength, low viscosity and is highly
hydrophilic.
A major field for the use of certain of these room temperature curable
polyorganosiloxane compositions is dentistry. Such materials are typically
employed as
impression materials for securing an analog representation of oral hard and
soft tissue to
support subsequent elaboration of crowns, bridges, dentures and other oral
prostheses. For
dental use, extraordinary fidelity of structural reproduction is required in
order to ensure
good fidelity of oral prosthetic fit and the like. In this regard, changes in
the dimensions of
the impression material during curing are to be avoided. Moreover, the surface
of the
reproductions or oral prosthetics and the like must be exceptionally free from
irregularities,
blemishes, pits, and other imperfections. This is so because castings and
prostheses derived
from such impressions must have good surface qualities and be free from pits
and
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irregularities in order to have proper fit, to achieve good adhesion, and to
avoid irritation of
sensitive mouth structures. These polyorganosiloxanes will also be useful in
other fields
where detailed reproductions are important such as in the science of
metrology, laboratory
processing of SEM and even jewelry fabrication and the like.
In employing polyorganosiloxanes as dental impression materials, a number of
difficulties have arisen. First of all, tear strength tends to be low. It is
necessary, in
effectively taking an impression, to be able to easily remove the impression,
from the
dentition without tearing, particularly at thin marginal areas, to preserve
fine detail. In the
past, fillers of various types have been added to improve tear strength. Such
additions may
result in some improvement, on the order of about 10%, but such improvements
have
proved inadequate.
Paradiso in WO 93/17654 describes improving tear strength by incorporating
multi-functional, including quadri-functional, polysiloxane components into
the impression
material, to add increased cross-linking to the resulting cured impression
material matrix,
particularly along the length of the linear vinyl end-stopped polysiloxane
principal
component. The Paradiso composition comprises SiOH groups capped off with
Me3Si
units that form pendants from the molecule. These pendants provide only
mechanical or
physical interlinking between the linear polysiloxane chains. This solution is
deficient,
being non-chemical and low in cross-linking density.
Voigt et al in EP 0 522 341 Al describes very short processing times of 35-45
seconds for forming dentition bite registration devices, utilizing a "QM"
resin as a means of
speeding and increasing cross-linking. These resins comprise as Q, the quadri-
functional
SiO4/2 and as M, building blocks such as monofunctional units R3SiO1/2 wherein
R is
vinyl, methyl, ethyl or phenyl, or similar tri or bi-functional units. Voigt
notes that an
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elastomer with small elastic deformation having a higher tenacity and hardness
results.
However, such material lacks flexibility, having a low strain value, and is
unsuitable for
impression taking. The increased cross-linking rate of the QM resin also
results in very
limited processing times that are unsatisfactory.
The other major, well-known difficulties with polyorganosiloxane impression
materials are caused by its inherent hydrophobic character. Such
characteristics make
reproduction of hard and soft oral tissue difficult since the oral cavity
environment is wet
and often contaminated with saliva or blood. The hydrophobicity of the
impression
material can result in loss of surface detail often at critical surfaces of
the dentition.
A number of improvements of polyorganosiloxane impression materials focus
upon adding a surfactant component to the dental impression material in order
to reduce the
hydrophobic nature of the polysiloxanes and make the composition more
hydrophilic.
Thus, Bryan et al in US 4,657,959 describes adding an ethoxylated nonionic
surface active
agent containing siloxane or perfluoroalkyl solubilizing groups to achieve a
three minute
water contact angle below about 65 . While surfactants including hydrocarbyl
groups, for
rendering the surfactant soluble or dispersible in silicone prepolymer, are
mentioned,
including ethyleneoxy groups, the results achieved appeared to be less than
optimal.
As stated above, all silicone material are known to have highly hydrophobic
properties. Therefore, these materials are usually not able to wet the surface
of the teeth
properly, especially under moist conditions. Hydrophilic properties can be
achieved in a
silicone with the addition of dipoler surfactants. These additives are usually
not soluble in
the silicone matrix, but rather form an emulsion together with the silicon
system. The
rheological properties of such materials are characterized by a typical non-
Newtonian flow
behavior with a high yield stress and a highly sheer stress-dependent
viscosity. Non-dipolar
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surfactants include for example, polyether modified silicones, and do not
build proper
micelles. The resulting emulsions are therefore not stable and tend to
separate. However,
the resulting multiple phase systems have a high yield stress which avoids the
flow on the
tooth surface when no or low stress is applied. Hydrophilic silicones
therefore usually have
poor flow characteristics under low stress.
Conventional "light bodies" formed from a two component system are usually
applied in one of two forms. The first is a handmixed form in the case when
the two
components have to be mixed by hand. Second is an automixed form when the two
components have to be released through a static mixer out of a cartridge. In
both cases, the
mixablility of the two components are strongly influenced by the rheological
properties of
the individual components making up the light body. Especially in the most
common
automixed form, the force to release the material out of the cartridge is
influenced by the
yield stress of the pastes.
Because of the rheological sub-structures, most conventional hydrophilic
silicones
have high yield stresses. To take advantage of low forces for releasing the
material, large
static mixers have to be employed. This leads to a high rate of waste because
much of the
material often remains in the mixer. Therefore, it is desired to achieve a low
yield stress of
both the single paste component and the mix in order to minimize the force
which is
necessary to remove the paste from the cartridge.
With conventional light body formulations a high stress has to be applied to
cbtain
a flow of the impression material into the sulcus and into the other details
of the
preparation. Low viscosity type materials ("light bodies") are therefore
always used in
combination with a high viscosity type material in the so called "putty/wash"
technique or
in the "double mix" technique. To improve the mixablility of the putties, the
viscosity of
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these products must be low. Even in the case where machine mixed heavy bodies
are used
the stress for releasing is limited by the technical properties of the
machine. Higher
viscosities lead to longer release times. In cases where these so-called soft
putties or heavy
bodies are used together with low viscosity silicones, the high yield stress
and the highly
stressed viscosity of the light body causes problem because it is impossible
to generate
sufficient pressure by the unset soft putty or heavy body during the taking of
the
impression. Therefore, a flow into the details of the preparation is not
guaranteed. This
problem is even more evident when the low viscosity material has a high yield
stress.
In addition, the hydrophilic components to improve the wetting properties of
the
silicone tend to create a new problem. This problem is a stability problem of
the cross
linking SiH-components against moisture because these functional groups are
sensitive
against hydrolysis reactions especially under basic conditions. Therefore, it
is a preferred
embodiment of the present invention to add a water absorbing inorganic filler
such as
calcium sulfate hemihydrate, anhydrous calcium sulfate, calcium chloride, and
the like and
adsorbing compounds such as zeoliths, molecular sieves and other similar
adsorbing and
absorbing compounds.
It is known in the art that a low viscosity can be obtained by the use of a
short chain
dimethylvinylsiyl terminated polydimethylsiloxane in combination with either a
low filler
content or no filler at all. These materials usually have a very low
mechanical strength such
as a low tear strength making them too weak for use as a dental impression
material. In
cases where the viscosity is too low, the material tends to drop from the
teeth and the fillers
separate after certain periods of time.
In sum, polyorganosiloxane impression materials still need improvement in
viscosity, tear strength and wettability in order to provide improved use of
these
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compositions for taking impressions of oral hard and soft tissues such that
adequate working time, tear strength and wettability are provided.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a two component
polymerizable polyorganosiloxane composition, one component including a
catalyst for polymerization, said composition being for making a dental
impression,
comprising: (a) a first QM resin, containing vinyl groups and having a
viscosity of
from about 5,000 to about 7,000 mPa; (b) a second QM resin, containing vinyl
groups and having a viscosity of from about 45,000 to about 60,000 mPa;
(c) optionally, a linear vinyl terminated polydimethyl-siloxane fluid, forming
with
said QM resins a dispersion having a vinyl content of about 0.16 to 0.24 m-
mole/g;
(d) an organohydrogen polysiloxane for cross-linking said vinyl groups; (e) an
organoplatinum catalyst complex for accelerating polymerization of said
components; (f) silanated fumed silica; (g) a retarder component in sufficient
amount for temporarily delaying the onset of said polymerization; (h) a
filler;
(i) optionally, calcium sulfate; (j) optionally, a surfactant that imparts
wettability to
said composition, wherein said composition surface contact angle with water is
less than 50 after three minutes; wherein said QM resin (a) comprises from
about
15 to about 65 percent by weight of said dispersions, and said second QM resin
(b) comprises from about 5 to about 45 percent by weight of said dispersions.
In another aspect, the invention provides a method to making a
dental impression, in a wet environment, of oral hard and soft tissues,
comprising:
mixing a two component polymerizable polyorganosiloxane composition, one
component including a polymerization catalyst comprising, (a) a first QM
resin,
containing vinyl groups and having a viscosity of from about 5,000 to about
7,000 mPa; (b) a second QM resin, containing vinyl groups and having a
viscosity
of from about 45,000 to about 60,000 mPa; (c) optionally, a linear vinyl
terminated
polydimethyl-siloxane fluid, forming with said QM resins a dispersion having a
vinyl content of about 0.16 to 0.24 m-mole/g; (d) an organohydrogen
polysiloxane
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for cross-linking said vinyl groups; (e) an organoplatinum catalyst complex
for
accelerating polymerization of said components; (f) silanated fumed silica;
(g) a
retarder component in sufficient amount for temporarily delaying the onset of
said
polymerization; (h) a filler; and (i) optionally, a surfactant that imparts
wettability to
said composition, wherein said composition surface contact angle with water is
less than 500 after three minutes; wherein said QM resin (a) comprises from
about
to about 65 percent by weight of said dispersions, and said second QM resin
(b) comprises from about 5 to about 45 percent by weight of said dispersions;
placing said mixture into contact with said tissues; allowing said mixture to
harden
10 into said impression; and removing said impression from said tissues.
The new polyvinylsiloxane impression materials are useful in low
and high viscosity impression compositions to record hard and soft tissues in
the
mouth. The new impression material is a platinum-catalyzed, vinylpoly-siloxane
material, preferably a two component polymerizable organosiloxane composition,
15 one component including a catalyst for polymerization, comprising:
(a) a QM resin, containing vinyl groups;
(b) a linear vinyl terminated polydimethylsiloxane fluid, forming with
said QM resin a dispersion having a vinyl content of about 0.16 to 0.24 m-
mole/g;
(c) an organohydrogen polysiloxane for cross-linking said vinyl
groups;
(d) an organoplatinum catalyst complex for accelerating
polymerization of said components;
(e) a retarder component in sufficient amount for temporarily
delaying the onset of said polymerization;
(f) a filler; and
(g) a surfactant that imparts wettability to said composition, wherein
said composition surface contact angle with water is less than 50 after three
minutes.
6a
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Preferably, the dispersion of (a) and (b) has a viscosity of about
5,000-60,000 cps. The dispersion of (a) and (b) may comprise a plurality of
dispersion components having desired viscosities and QM resin contents.
Preferably, the QM resin-containing dispersions comprise a first dispersion
component having a viscosity of about 5,000-7,000
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cps and a second dispersion component having a viscosity of about 45,000-
60,000 cps, said
QM resin comprising about 20-25 weight % of each dispersion.
A preferred QM resin comprises a polyorganosiloxane comprising units of Si04/2
and units of R1R22 SiOl/2 wherein
R1 is unsaturated, preferably vinyl and
R2 is alkyl, aryl, etc., such as methyl, ethyl, phenyl, etc. More preferably,
the QM resin
comprises the formula:
CH2
CH
CH3 - Si - CH3
?H3 c C
I H3
H2C=CH-ISi-O-Si-O-Si- CH=CH2
CH3 0 CH3
CH3 - 11 - CH3
CH
II
CH2
The retarder component of the composition is a low molecular weight, vinyl
functional fluid that is a linear or cyclic polysiloxane in an amount of at
least about 0.030
weight percent of said composition. Preferably, the retarder component
comprises: a fluid
1,3-divinyl, tetramethyldisiloxane, in an amount of about 0.030 to 0.12 weight
percent of
said composition.
The filler component of the invention comprises about 15 to about 45 weight
percent of said composition and preferably includes a filler mixture of about
20 to about 40
weight percent.
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A key component of the composition of the invention is the surfactant for
imparting
wettability, preferably comprising an HLB of about 8-11 and a pH of about 6-8.
A most
preferred surfactant is a nonionic surfactant, nonylphenoxy poly(ethyleneoxy)
ethanol
having an HLB of about 10.8.
For compositions of the invention of relatively high viscosity, the
composition
includes an emulsifying plasticizer that imparts desired handling and flow
properties to the
catalyst complex, to match those of the second component, wherein a suitable
composition
for taking a dental impression may conveniently be formed. Preferably, the
plasticizer
comprises an alkylphthalate at about 0.5 to 2.0% by weight of said catalyst
component and
is, most preferably, octyl benzyl phthalate.
After polymerization, the compositions of the invention include a tear
strength of
270-300 PSI (1.86-2.06 MPa) and a contact angle with water of less than about
50 at three
minutes. For the lower viscosity impression material of the invention, tear
strength will be
somewhat lower at about 200 PSI (1.38 MPa) which is still substantially
improved over the
prior art.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a graph showing Wetting Contact Angle, in degrees, as a function
of
Time, in minutes.
Figure 2 is a graph showing Impression Material Viscosity as a function of
Time,
in minutes.
Figure 3 is a graph showing the difference in the charcteristics of the base
and
catalyst components of the present invention.
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Figure 4 is a graph showing the thixotropy of a base paste according to the
invention by a time sweep measured with an oscillation rheometer.
Figure 5 is a graph representing the development of viscosity during the
setting
reaction of the material accorindg to the invention by a time sweep with
an oscillation rheometer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The polymerizable polysiloxane compositions of the instant invention comprise,
in
general: an organopolysiloxane having at least about two vinyl groups per
molecule, further
including, dispersed therein, a quadri-functional vinyl polysiloxane resin; an
organohydrogen-polysiloxane having at least about two hydrogen atoms bonded to
at least
two silicone atoms per molecule; a catalyst for accelerating the addition of
the silicone
atoms bonded to the hydrogen atoms to the polysiloxane vinyl groups; a filler;
a low
molecular weight retarder composition for delaying onset of polymerization;
and an
emulsifying surfactant that imparts wettability to said impression material.
The composition of the invention is preferably divided into two components. A
first component, which is conveniently referred to as a "Base Paste", contains
the
vinylorganopolysiloxanes dispersion, the organo-hydrogen-polysiloxane, a
portion of the
filler and the surfactant. The second component of this two-part composition
is referred to
as a "Catalyst Paste" and comprises a second portion of the vinyl
polysiloxanes, together
with the catalyst for accelerating the addition reaction a scavenging agent
for hydrogen
released during polymerization and usually, additional quantities of fillers
and pigments.
Where high viscosity impression materials are desired, an emulsifying
plasticizer may be
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added to the catalyst paste component such that the working viscosities of its
two
components are compatible and have desired flow characteristics.
A wide variety of organopolysiloxanes having at least about two vinyl groups
per
molecule are known for inclusion in the dental polysiloxane compositions of
the invention
to form the dispersion including a quadri-functional vinyl polysiloxane. Each
of these
materials may be included in greater or lesser degree in accordance with the
practice of the
instant invention. Preferred for use herein are linear vinyl terminated
polydivinylsiloxanes
preferably a divinyl polydimethylsiloxane. Such polymers are sold having
varying average
molecular weights with concomitant variations in viscosity. It is preferred
that these
materials be selected to have a viscosity appropriate for the conditions to be
experienced by
the resulting silicone material.
The dispersions of interest have a viscosity range of 5,000-60,000 cps. In
practice,
it is convenient to employ a blend of the dispersing polymers having differing
viscosities
and physical properties to provide compositions having a desired
thixotropicity and
viscosity.
The dispersions of interest are preferably formed in two viscosity ranges: (1)
a first
dispersion having a viscosity of about 5000-7000 cps; and (2) a second
dispersion having a
viscosity of about 45,000-65,000 cps. While it is convenient to provide
polysiloxane
oligomers for this purpose having methyl substituents, other substituents may
also be
included in the compositions in accordance with this invention. Thus, alkyl,
aryl, halogen,
and other substituents may be included in greater or lesser degree as part of
the vinyl
polysiloxanes which are useful. Those of ordinary skill in the art will be
able to determine
which polysiloxane materials are preferred for any particular utility from the
foregoing
considerations.
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The quadri-functional polysiloxanes, designated and known in the art as QM
resins,
provide improved tear strength to the polymerized impression composition, by
increasing
its resulting polymerized crosslink density. As is known, the QM resin is made
up of. Q
units of quadri-functional SiO4/2; and M units, such as R1R22SiO1/2 wherein R1
is
unsaturated, preferably vinyl and R2 is alkyl, aryl or the like, such as
methyl, ethyl or
phenyl. In a preferred composition R1 is vinyl and both R2 are methyl. A most
preferred
composition is represented by the formula:
CH2
CH
CH3 - Si - CH3
CH3 CH3
H2C=CH-ISi-O-Si-O-Si- CH=CH2
I
CH3 0 CH3
CH3 - ~i - CH3
CH
11
CH2
The QM resin provides a vinyl concentration in the dispersions with the vinyl-
terminated polydivinylsiloxanes of at least about 0.16 m-mole/g. Preferably
the vinyl
concentration is 0.16-0.24 m-mole/g. The amount of QM resin is preferably
about 20-25%
by weight of the dispersion. Such dispersions are sold by Bayer Corp., Silicon
Division of
Pittsburg, Pennsylvania. Other QM resin formulations may be used, including
those that
are "neat" or dispersed in carriers other than the preferred fluid
polydivinylsiloxane.
A key element of the invention is a retarder component that delays onset of
polymerization of the QM resin/dispersion such that sufficient working times
to employ the
composition are provided. It functions, as it is consumed, to offset what
would otherwise
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be a too rapid polymerization. The preferred retarder fluid in the preferred
impression
material of interest is 1,3 divinyltetramethyldisiloxane at a sufficient
concentration level to
perform its retarding functions, which is in at least about 0.03 weight
percent of the
composition, preferably within a range of about 0.03 to 0.12 weight percent.
This preferred
amount is in contrast with the lower amounts of 0.0015-0.020 weight percent
typically
employed in PVS systems to stabilize compositions. Other suitable retarders
are any low
molecular weight, vinyl functional material that would be initially consumed
in the
polymerization, to delay hardening suitably and as desired, including linear
and cyclic
polysiloxanes.
The organohydrogen-polysiloxanes useful in the practice of the present
inventions
are well-known to those of ordinary skill in the art. It is required only that
polysiloxanes
having hydrogen atoms directly bonded to silicone atoms be employed, and that
they have
suitable viscosities and other physical properties. Substituents in the
molecules such as
alkyl (especially methyl), aryl, halogen, and others may be employed as well.
It is
necessary only that such substituents not interfere with the platinum-
catalyzed addition
reaction. It is preferred that molecules be employed having at least two
silicone-bonded
hydrogen atoms per molecule. Polymethylhydrogensiloxane is preferred, having a
viscosity range of about 35-45 cps.
The catalysts which are useful for catalyzing the reaction of the silicone
atoms
(bonded to hydrogen atoms) to the vinyl groups of the vinyl polysiloxane
molecules are
preferably based upon platinum. In this regard, it is preferred to employ a
platinum
compound such as chloroplatinic acid, preferably in admixture or complex with
one or
more vinyl materials, especially vinylpolysiloxanes. While such materials have
been found
to be preferred, other catalysts are also useful. Thus, platinum metal
together with other
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noble metals including palladium, rhodium, and the like and their respective
complexes and
salts are also useful. In view of the toxicological acceptability of platinum,
however, it is
greatly to be preferred for dental use.
The compositions of the present invention also include a filler, preferably a
mixture
of hydrophobic fillers. A wide variety of inorganic, hydrophobic fillers may
be employed
such as silicas, aluminas, magnesias, titanias, inorganic salts, metallic
oxides and glasses. It
is preferred, however, that forms of silicone dioxides be employed. In
accordance with the
present invention, it has been found to be preferable to employ mixtures of
silicone
dioxides, including those derived form: crystalline silicone dioxide, such as
pulverized
quartz (4-6p); amorphous silicone dioxides, such as a diatomaceous earth (4-
7i); and
TM
silanated fumed silica, such as Cab-o-Sil TS-530 (160-240 m2/g), manufactured
by Cabot
Corporation. The sizes and surface areas of the foregoing materials are
controlled to
control the viscosity and thixotropicity of the resulting compositions. Some
or all of the
foregoing hydrophobic fillers may be superficially treated with one or more
silanating or
"keying" agents, as known to those of ordinary skill in the art. Such
silanating may be
accomplished through use of known halogenated silanes or silazides. The
fillers are
present, preferably, in amounts of from about 15 to about 45 weight percent of
the
composition, forming an impression composition that is polymer rich and, thus,
having
improved flow properties. The fillers, more preferably, are about 35-40 weight
percent of
the composition. A preferred filler mixture for a higher viscosity formulation
includes 14-
24 weight percent crystalline silicone dioxide, 3-6 weight percent amorphous
silicone
dioxide and 4-8 weight percent silanated fumed silicone dioxide. A most
preferred filler is
about 19% cristobalite at about 4-6g particle diameter, about 4% diatomaceous
earth at
about 4-711 particle diameter and about 6% silanated fumed silica at about 160-
240 m2/g.
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A chemical system may be employed to diminish the presence or degree of
hydrogen outgassing which may be typically generated as a result of the vinyl
polymerization. The composition thus may comprise a finely divided platinum
metal that
scavenges for and takes up such hydrogen. The Pt metal may be deposited upon a
substantially insoluble salt having a surface area of between about 0.1 and
40mZ/g.
Suitable salts are barium sulphate, barium carbonate and calcium carbonate of
suitable
particle sizes. Other substrates include diatomaceous earth, activated
alumina, activated
carbon and others. The inorganic salts are especially preferred to lend
improved stability to
the resulting materials incorporating them . Dispersed upon the salts is about
0.2 to 2 parts
per million of platinum metal, based upon the weight of the catalyst
component. It has been
found that employment of the platinum metal dispersed upon inorganic salt
particles
substantially eliminates or diminishes hydrogen outgassing during curing of
dental
silicones.
An important improvement of the invention is inclusion in the composition of a
surfactant that imparts wettability to said composition, as indicated by a
surface contact
angle with water at three minutes of less than 50 . An unexpected result of
the selection of
surfactant provides a major clinical advantage in that the wetting contact
angle of less than
50 is achieved in less than about two minutes, decreasing and remaining below
50
throughout the working time of the composition, in contrast with prior art
polyvinylsiloxanes and surfactant formulations that require more time to wet
out. This
higher wetting rate of the composition of the invention is particularly
advantageous during
the impression taking process and is shown in the Drawings.
Referring to Figure 1, the Wetting Contact Angle, in degrees, as a function of
Time, in minutes, is shown for the polyvinyl siloxane composition of the
invention, in
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comparison with prior art compositions. Curve A is the composition of the
invention
showing a wetting contact angle of about 50 at two minutes after mixing of
the base and
catalyst components. Figure 1 demonstrates that good wettability is achieved
early and
improves at a fast rate over the about 3.5 minutes of useful working life of
the impression
taking material. Curves B and C are, respectively, polyether and conventional
polyvinyl
siloxane impression materials of the prior art. Figure 2 shows Impression
Material
Viscosity as a function of Time for composition of the invention, Curve A, and
the two
prior art compositions B and C noted above. It shows the progression of the
polymerization
process from mixing and, in combination with Figure 1, demonstrates that the
improved
wettability of the composition of the invention occurs during the critical
working time for
the impression material, an important advantages over other known systems.
The surfactant of the invention may be of cationic, anionic, amphoteric or
nonionic
type. A key criteria for selection is that the Hydrophobic Liphophilic Balance
(HLB) value
(described by Gower., "Handbook of Industrial Surfactants", 1993) must be in
the range of
8-11. As is well-known, the higher the HLB the more hydrophobic is the
substance. In
addition, the pH of the surfactant must be in the 6-8 range to prevent side
reactions that may
be detrimental the polymerization of the impression. A preferred surfactant is
nonionic,
having an HLB value of 10.8 comprising nonylphenoxypoly(ethyleneoxy) ethanol,
sold by
Rhone-Poulenc of Cranbury, NJ as Igepal CO-530. In comparison it is noted
above with
respect to Bryan et al, in US '959 that Igepal CO-630, having an HLB of 13.0,
differing in
structure from CO-530 wherein the number of repeating units in CO-630 is 9 and
those of
CO-530 is 6, is not effective, demonstrating the criticality of the HLB
limitation. The
amount of surfactant used to render the composition hydrophilic is based on
the rate of
wetting. The desired contact angle at three (3) minutes is less than about W.
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The composition of the invention may include plasticizers for the higher
viscosity
material that beneficially alter the handling and flow properties of the
impression material,
particularly the catalyst component. A preferred emulsifying plasticizer is
octyl benzyl
phthalate. Other phthalates are useful. The plasticizer composite is not
necessary for lower
viscosity wash type impression materials.
The selection of QM resin dispersion viscosity depends upon the overall
impression material characteristics desired. To give higher viscosity handling
characteristics
more of the 60,000 cps component is employed. For a low viscosity type, more
of the
6,000 cps component is employed to increase flow. In addition to the QM resin
dispersion
characteristics filler selection affects overall viscosity characteristics.
Using a higher
loading of low surface area fillers, such as cristobalite, gives more flow to
a low viscosity
type impression material. Using a higher loading of high surface area fillers,
such as
diatomaceous earth, reduces flow and gives more body to a high viscosity type
impression
material. The use of an emulsifying plasticizer makes the composition more
thixotropic,
which is useful for a high viscosity material. However, a plasticizer is
generally not used in
the low viscosity material since high flow is desired.
The composition of the invention may include various pigments to achieve a
preferred color. Such pigments are well known and include titanium dioxide as
well as
many others.
The two component compositions prepared in accordance with the instant
invertion
are employed in the same way that conventional impression materials have been
employed.
Thus, appropriately equal portions of base paste and catalyst paste are mixed
together
thoroughly and applied to the oral dentition or other region for a period of
time sufficient
for the polymerizations or hardening of the composition. Once the composition
has been
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substantially hardened, it is removed from the mouth or other surface and used
for the
elaboration of casts and the like from which representations of the casting
surface are
subsequently prepared.
As will be appreciated by those of ordinary skill in the art, it is important
that dental
silicone materials be capable of being stored for reasonably long periods of
time and at
reasonable storage temperature in order to maximize their commercial utility.
Accordingly,
it is necessary that such materials not suffer from decreased physical
properties or
substantial changes in working time or hardening time upon such storage. In
this regard,
accelerated storage tests employing high ambient temperatures are now capable
of
determining the shelf stability of such materials.
Certain embodiments of the present invention are described below. Numerous
other compositions and formulations may be prepared within the spirit of the
invention.
The following examples are not to be construed as limiting and are offered by
way of
illustration.
Example 1
A two component composition of the invention is formulated in a Base Paste and
Catalyst
Paste components. Mixing of each component's ingredients is done in a double
planetary
mixer having a mixing pot heated with circulating water at 45C-50 C and under
65 mm
mercury vacuum.
BASE PASTE COMPONENT
In making the Base Paste, the mixing pot is first charged with all
organohydrogen
polysiloxane and incrementally thereafter, with QM dispersion and filler
component, with
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mixing continuing until a uniform mixture is achieved. The finished Base Paste
is
discharged into a storage container.
CATALYST PASTE COMPONENT
The Catalyst Paste component is formulated and mixed under conditions and in
equipment as described above. The platinum catalyst, 1,3
divinyldimethyldisiloxane, QM
resin dispersions, fillers and pigments are added incrementally to the mixing
pot and mixing
carried out until a uniformly mixed mass is achieved. The compounded Catalyst
Paste is
then discharged into a storage container.
The composition of each component is indicated in the table below, wherein
amounts are in weight percent of the component.
BASE CATALYST
Organohydrogen Polysiloxane 9.00 0.00
(5000-7000 cps) QM resin dispersion 19.62 23.95
(45000-60000 cps) QM resin dispersion 34.59 42.89
Cristobalite 19.01 19.06
Diatomaceious earth 6.53 6.41
Cab-O-Sil TS-530 6.53 6.00
Pigments Predispersed in Divinyl Polysiloxane 0.65 0.25
Titanium Oxide Pigment TM 0.07 0.07
Surfactant (Igepal CO-530) 4.00 0.00
Plasticizer 0.00 0.50
Platinum Catalyst 0.00 0.64
1,3-Divinyldimethyidisiloxane 0.00 0.07
Finely divided Platinum metal
on Calcium Carbonate 0.00 0.16
100.00 100.00
Example 2
A two component composition of the invention is made by first making a Base
Paste and then a Catalyst Paste as described in Example 1, having the
composition indicated
in the table below.
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BASE CATALYST
Organohydrogen Polysiloxane 9.00 0.00
(5000-7000 cps) QM resin dispersion 20.18 31.71
(45000-60000 cps) QM resin dispersion 35.61 35.23
Cristobalite 19.74 20.67
Diatomaceious earth 4.30 4.28
Cab-O-Sil TS-530 6.45 6.42
Pigments Predispersed in Divinyl Polysiloxane 0.65 0.25
Titanium Oxide Pigment 0.07 0.07
Surfactant (Igepal CO-530) 4.00 0.00
Plasticizer 0.00 0.50
Platinum Catalyst 0.00 0.64
1,3-Divinyldimethyidisiloxane 0.00 0.07
Finely divided Platinum metal
on Calcium Carbonate 0.00 0.16
100.00 100.00
Example 3
A two component composition of the invention is made by first making a Base
Paste and then a Catalyst Paste as described in Example 1, having the
composition indicated
in the table below.
BASE CATALYST
Organohydrogen Polysiloxane 10.00 0.00
(5000-7000 cps) QM resin dispersion 14.73 26.91
(45000-60000 cps) QM resin dispersion 43.80 43.80
Cristobalite 17.00 17.40
Diatomaceious earth 5.00 5.00
Cab-O-Sil TS-530 5.00 5.00
Pigments Predispersed in Divinyl Polysiloxane 0.40 0.50
Titanium Oxide Pigment 0.07 0.07
Surfactant (Igepal CO-530) 4.00 0.00
Plasticizer 0.00 0.50
Platinum Catalyst 0.00 0.65
1,3-Divinyldimethyidisiloxane 0.00 0.07
Finely divided Platinum metal
on Calcium Carbonate 0.00 0.10
100.00 100.00
Example 4
A two component composition of the invention is made by first making a Base
Paste and then a Catalyst Paste as described in Example 1, having the
composition indicated
in the table below.
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BASE CATALYST
Organohydrogen Polysiloxane 10.00 0.00
(5000-7000 cps) QM resin dispersion 19.40 32.37
(45000-60000 cps) QM resin dispersion 36.03 36.03
Cristobalite 20.00 20.00
Diatomaceious earth 5.00 5.00
Cab-O-Sil TS-530 5.00 5.00
Pigments Predispersed in Divinyl Polysiloxane 1.50 0.00
Titanium Oxide Pigment 0.07 0.07
Surfactant (Igepal CO-530) 3.00 0.00
Plasticizer 0.00 0.50
Platinum Catalyst 0.00 1.00
1,3-Divinyldimethyidisiloxane 0.00 0.03
Finely divided Platinum metal on Calcium Carbonate 0.00 0.00
100.00 100.00
Example 5
A two component composition of the invention is made by first making a Base
Paste and then a Catalyst Paste as described in Example 1, having the
composition indicated
in the table below.
BASE CATALYST
Organohydrogen Polysiloxane 11.00 0.00
(5000-7000 cps) QM resin dispersion 14.36 28.44
(45000-60000 cps) QM resin dispersion 43.07 42.64
Cristobalite 17.00 17.19
Diatomaceious earth 5.00 4.95
Cab-O-Sil TS-530 5.00 4.95
Pigments Predispersed in Divinyl Polysiloxane 1.50 0.00
Titanium Oxide Pigment 0.07 0.07
Surfactant (Igepal CO-530) 3.00 0.00
Plasticizer 0.00 0.49
Platinum Catalyst 0.00 1.13
1,3-Divinyldimethyidisiloxane 0.00 0.06
Finely divided Platinum metal on Calcium Carbonate 0.00 0.09
100.00 100.00
Example 6
A two component composition of the invention is made by first making a Base
Paste and then a Catalyst Paste as described in Example 1, having the
composition indicated
in the table below.
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BASE CATALYST
Organohydrogen Polysiloxane 9.52 0.00
(5000-7000 cps) QM resin dispersion 11.19 27.91
(45000-60000 cps) QM resin dispersion 38.07 38.21
C ristobaiite 22.84 21.21
Diatomaceious earth 5.71 5.73
Cab-O-Sil TS-530 5.71 5.73
Pigments Predispersed in Divinyl Polysiloxane 1.58 0.00
Titanium Oxide Pigment TM 0.13 0.13
Surfactant (Tergitol 15-S-3) 4.76 0.00
Plasticizer 0.48 0.48
Platinum Catalyst 0.00 0.48
1,3-Divinyldimethyidisiloxane 0.00 0.05
Finely divided Platinum metal on Calcium Carbonate 0.00 0.08
100.00 100.00
Example 7
A two component composition of the invention is made by first mating a Base
Paste and then a Catalyst Paste as described in Example 1, having the
composition indicated
in the table below.
BASE CATALYST
Organohydrogen Polysiloxane 9.52 0.00
(5000-7000 cps) QM resin dispersion 11.19 27.91
(45000-60000 cps) QM resin dispersion 38.07 38.21
Cristobalite 22.84 21.21
Diatomaceious earth 5.71 5.73
Cab-O-Sil TS-530 5.71 5.73
Pigments Predispersed in Divinyl Polysiloxane 1.58 0.00
Titanium Oxide Pigment TM 0.13 0.13
Surfactant (Igepal CO-630) 4.76 0.00
Plasticizer 0.48 0.48
Platinum Catalyst 0.00 0.48
1,3-Divinyldimethyidisiloxane 0.00 0.05
Finely divided Platinum metal on Calcium Carbonate 0.00 0.08
100.00 100.00
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Example 8
A two component composition of the invention is made by first making a Base
Paste and then a Catalyst Paste as described in Example 1, having the
composition indicated
in the table below.
BASE CATALYST
Organohydrogen Polysiloxane 9.52 0.00
(5000-7000 cps) QM resin dispersion 11.19 27.91
(45000-60000 cps) QM resin dispersion 38.07 38.21
Cristobalite 22.84 21.21
Diatomaceious earth 5.71 5.73
Cab-O-Sil TS-530 5.71 5.73
Pigments Predispersed in Divinyl Polysiloxane 1.58 0.00
Titanium Oxide Pigment 0.13 0.13
Surfactant (Igepal CO-210) 4.76 0.00
Plasticizer 0.48 0.48
Platinum Catalyst 0.00 0.48
1,3-Divinyldimethyidisiloxane 0.00 0.05
Finely divided Platinum metal on Calcium Carbonate 0.00 0.08
100.00 100.00
Example 9
A two component composition of the invention is made by first making a Base
Paste and then a Catalyst Paste as described in Example 1, having the
composition indicated
in the table below.
BASE CATALYST
Organohydrogen Polysiloxane 9.52 0.00
(5000-7000 cps) QM resin dispersion 11.19 27.91
(45000-60000 cps) QM resin dispersion 38.07 38.21
Cristobalite 22.84 21.21
Diatomaceious earth 5.71 5.73
Cab-O-Sil TS-530 5.71 5.73
Pigments Predispersed in Divinyl Polysiloxane 1.58 0.00
Titanium Oxide Pigment 0.13 0.13
Surfactant (Igepal CO-430) 4.76 0.00
Plasticizer 0.48 0.48
Platinum Catalyst 0.00 0.48
1,3-Divinyldimethyidisiloxane 0.00 0.05
Finely divided Platinum metal on Calcium Carbonate 0.00 0.08
100.00 100.00
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Example 10
A two component composition of the invention is made by first making a Base
Paste and then a Catalyst Paste as described in Example 1, having the
composition indicated
in the table below.
BASE CATALYST
Organohydrogen Polysiloxane 9.52 0.00
(5000-7000 cps) QM resin dispersion 11.19 27.91
(45000-60000 cps) QM resin dispersion 38.07 38.21
Cristobalite 22.84 21.21
Diatomaceious earth 5.71 5.73
Cab-O-Sil TS-530 5.71 5.73
Pigments Predispersed in Divinyl Polysiloxane 1.58 0.00
Titanium Oxide Pigment 0.13 0.13
Surfactant (Igepal CO-530) 4.76 0.00
Plasticizer 0.48 0.48
Platinum Catalyst 0.00 0.48
1,3-Divinyldimethyidisiloxane 0.00 0.05
Finely divided Platinum metal
on Calcium Carbonate 0.00 0.08
100.00 100.00
Example 11
A representative sample of each of the above described Examples, of 10 grams,
is
mixed in equal parts and the properties of the mixture and resulting
polymerized
composition tested. The table below reports the results said measurements. The
first five
properties reported are tested in accord with ADA Specification 19: Non-
Aqueous
Elastomer Impression Materials (1976, as amended in 19a of 1982).
The following procedure was used to provide tensile tear strength, percent
elongation, and modulus of elasticity of the Examples.
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Equal parts of the base and catalyst components are mixed and the samples or
specimen is placed in a specimen mold having an I-shaped cavity that is 1.5 mm
thick, 20
mm x 11 mm, with top arms of 8 mm depth and center I portion 5 mm wide. The
filled
mold is clamped between two stainless steel plates and the assembly is placed
in a 32 C
water bath. At six minutes from start of mix, the assembly is removed from the
bath. The
mold is unclamped, the specimen is removed from the mold and any flash is
removed from
the specimen. At 10 minutes from start of mix the specimen is clamped into the
specimen
TM
test grips of an Instron Model 1123 in the extension mode. The Instron is
attached to a
Microcon II micropressor that has been programmed to calculate the tear
strength [psi],%
elongation, and modulus of elasticity. At 11 minutes, the specimen is stressed
by the
Instron at a rate of 10 mm/min. until the specimen reaches peak failure. (The
maximum
load is set to 5 kg.) This is repeated for five specimens and then
statistically evaluated
results are reported, as shown in Table I.
Wetting contact angles are measured for each Example as follows. One gram (1g)
of base and one gram (lg) of catalyst paste are mixed together until uniform (-
'30 seconds).
A one-half gram (0.5g) of mixed paste is placed between two sheets of
polyethylene
TM
(Dentsilk) and pressed flat using a glass plate, about 2-3 mm thick. The
specimen is
allowed to stand undisturbed until set (-15 minutes). The polyethylene sheets
are removed,
being careful not to touch the surface of the specimen, and the specimen
placed on the table
of a gynometer, a well known device for measuring contact angles. The eyepiece
recticle is
adjusted to the horizontal and vertical planes of the specimen surface and
stop watch is
started as a drop of water is dropped onto the specimen surface. At 1.5
minutes to 3.5
minutes, the inside contact angle, in degrees, of the water/specimen interface
is measured
using the gynometer scale, recorded for the specimen and reported in Table I
hereinbelow.
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TABLE I: PROPERTIES OF EXAMPLES
Examples
Property 1 2 3 4 5 6 7 8 9 10
Work Time (min) 3 3 3 2 3 4.25 2.50 3.33 3.18 2.50
Set Time (min) 6 6. 6 4 6 9 5 7 7 5.75
% Deformation 0.5 0.25 0.45 0.3 1.9 4.25 1.75 2.25 23 1.65
% Strain 2.75 3.15 3.25 2.75 3.5 NA NA NA NA NA
Consistency (mm) 33 34 36 32 38 33 29 32 31 30
Contact Angle with 30 35 38 37 42 28 52 56 42 31
water at 3 min. ( )
Tear Strength PSI 277 277 295 289 216 NA NA NA NA NA
Examples 1-3 are preferred compositions. Example 1 is suitable for dispensing
from a tube and hand mixing. Example 2 is most preferred for cartridge
dispensing and
static-mixing. Example 3 describes a composition of the invention that is
suitable for
forming a lower viscosity composition suitable for either tube or cartridge
dispensing.
The composition of Example 4, having a high viscosity, exhibited severe
gassing,
having a higher hydride concentration and no degassing component. Example 5,
having a
low viscosity, demonstrated good syringe consistency but had a high percent
deformation
and percent strain while tear strength was lower. This composition had a high
hydride, low
surfactant, low retarder and low catalyst concentration. Compositions of
Examples 6, 8 and
9 did not polymerize properly. The composition of Example 6 had too low
retarder and
catalyst contents. The surfactant was also too high an HLB and too acid. The
composition
of Example 7 lacked wetting capability having a surface contact angle
exceeding desirable
limits. Examples 8 and 9 both were too low in retarder and catalyst
concentrations The
composition of Example 10 exceeded desired percent deformation.
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Example 12
A two component composition of the invention, having the composition indicated
below, is made as described in Example 1. A higher content of lower viscosity
QM resin
dispersion is utilized to form a low viscosity-wash formulation. Also
additional surfactant
is employed while no plasticizer is necessary.
BASE CATALYST
Organohydrogen Polysiloxane 8.0 --
(5000-7000 cps) QM resin dispersion 28.7 39.6
(45000-60000 cps) QM resin dispersion 12.3 16.7
Cristobalite 32.0 39.6
Diatomaceious earth -- --
Cab-O-Sil TS-530 3 3
Pigments Predispersed in Divinyl Polysiloxane 1 --
Titanium Oxide Pigment -- --
Surfactant (Igepal CO-530) 7.5 --
Plasticizer -- --
Platinum Catalyst -- 0.36
1,3-Divinyldimethyidisiloxane -- 0.11
Finely divided Platinum metal
on Calcium Carbonate -- 0.60
Dried Calcium Sulfate 5.0 --
Organic Pigments 2.5 --
Total 100.00 100.00
Example 13
A two component composition, having the composition indicated below, is made
as
described in Example 1. The resulting formulation is a low viscosity wash
impression
material.
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BASE CATALYST
Organohydrogen Polysiloxane 9.0 0
(5000-7000 cps) QM resin dispersion 13.2 29.6
(45000-60000 cps) QM resin dispersion 47.27 47.27
Cristobalite 14.0 14.0
Diatomaceious earth 4 4
Cab-O-Sil TS-530 4 4
Pigments Predispersed in Divinyl Polysiloxane 1 --
Titanium Oxide Pigment 0.035 0.035
Surfactant (Igepal CO-530) 5 --
Plasticizer -- --
Platinum Catalyst -- 0.28
1,3-Divinyldimethyidisiloxane -- 0.014
Finely divided Platinum metal
on Calcium Carbonate -- 0.8
Dried Calcium Sulfate -- --
Organic Pigments 2.5 --
Total 100.00 100.00
Example 14
A two component composition, having the composition indicated below is made
as described in Example 1. The resulting formulation is a low viscosity wash
impression
material.
BASE CATALYST
Organohydrogen Polysiloxane 7.5 0
(5000-7000 cps) QM resin dispersion 35.56 44.89
(45000-60000 cps) QM resin dispersion 11.84 14.97
Cristobalite 29 31.63
Diatomaceious earth 0 --
Cab-O-Sil TS-530 3 3
Pigments Predispersed in Divinyl Polysiloxane 0.9 --
Titanium Oxide Pigment --
Surfactant (Igepal CO-530) 5 --
Plasticizer -- --
Platinum Catalyst -- 0.55
1,3-Divinyldimethyidisiloxane -- 0.056
Finely divided Platinum metal
on Calcium Carbonate -- 0.5
Dried Calcium Sulfate 5 5
Organic Pigments 2.2 0
Total 100.00 100.00
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Example 15
The testing procedures of in Example 11 were applied to representative samples
of
the formulations of Examples 12-14. Table II below reports the results of the
measurements.
TABLE II
Examples
Property 12 13 14
Work Time (min) 2.92 3.33 3.50
Set Time (min) 5.67 7.25 7.00
% Deformation 0.45 1.85 1.20
% Strain 3.9 6.0 4.2
Consistency (mm) 40 41 40
Contact Angle with water 33 50 40
at 3 min. ( )
Tear Strength (PSI) 200 188 220
The dental impression material according another embodiment of the invention
is
a two component system on the basis of addition curing silicones as follows:
from about 45 to 55 percent by weight based upon 100 percent by weight
of the impression material of a base paste. The base paste includes:
al. from about 1 to about 10 percent by weight based upon 100 percent by
weight of the base paste of a linear dimethylvinyl terminated
polydimethylsiloxane,
a2. from about 8 to about 20 percent by weight based upon 100 percent by
weight of the base paste of linear dimethyl-(H-methyl)-siloxane
copolymers with trimethylsilyl or dimethylhydrosilyl termination,
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a3. from about 15 to about 25 percent by weight based upon 100 percent by
weight of the base paste of dimethylvinylsilyl terminated
polydimethylsiloxane containing 15-25 % by weight highly dispersed Si02,
a4. from about 50 to about 60 percent by weight based upon 100 percent by
weight of the base paste of low molecular weight QM-resins optionally
containing functional groups reactive in the hydrosilylation reaction and
ethoxy groups and being homogeneously soluble in al and including
Si04/2, R01/2, and R3SiO1/2 in which R represents n-alkyl, phenyl or
vinyl and has an alkoxy group content from less than 4 mmol/g,
a5. a scavenger for adsorption of water from both the ingredients and the
environment,
a6. from about 0 to about 10 percent by weight based upon 100 percent by
weight of the base paste of linear dimethyl-(vinylmethyl)-siloxane
copolymers with dimethylvinylsilyl terminations,
a7. dipolar surfactant to improve wetting properties,
a8. and optionally, pigments.
The impression material also includes from about 45 to about 55 percent by
weight of a
catalyst paste which includes:
bl. from about 1 to about 5 percent by weight based upon 100 percent by
weight of the catalyst paste of linear dimethylvinyl terminated
polydimethylsiloxanes,
b2. from about 30 to about 35 percent by weight based upon 100 percent by
weight of the catalyst paste of dimethylvinylsilyl terminated
polydimethylsiloxanes containing 20-35 % highly disperse Si02
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W. from about 55 to about 70 percent by weight based upon 100 percent by
weight of the catalyst paste of low molecular weight QM-resins
optionally containing functional groups reactive in the hydrosilylation
reaction and ethoxy groups and being homogeneously soluble in al and
comprises Si04/2, ROl/2, and R3SiO1/2 in which R represents
n-alkyl, phenyl or vinyl and has an alkoxy group content from less
than 4 mmol/g
M. from about 0 to about 10 percent by weight based upon 100 percent by
weight of the catalyst paste of linear dimethyl-(vinylmethyl)-siloxane
copolymers with dimethylvinylsilyl termination's,
b5. from about 0.5 to about 1.5 percent by weight based upon 100 percent
by weight of the catalyst paste of Pt-catalyst prepared from H2PtC16
and tetramethyldivinyldisiloxane
b6. short chained dimethylvinylsilyl terminated polydimethylsiloxanes (n=0-
5).
b7.1-12-adsorbent; and optionally
b8.pigments.
All "%" and "percent" are by weight. A low viscosity type dental impression
material is
provided having the flow characteristics under clinical conditions combined
witha high
tear strength to maintain the subgingival undercuts. "Low" viscosity as used
herein
means that of type 3 accordingly to ISO 4823. These characteristics are
demonstrated by
the following physical parameter:
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Viscosity:
h[200 Pa]= 5.0 - 15.0 Pas for single pastes
h[200 Pa]- 15.0- 25.0 Pas for the mix
and a yield stress of: 0[0-10 Pa] less than about 5.0 Pa
contact angle: less than about 45
tear strength: greater than about 1.5 MPa
Wherein al and bl are characterised as vinyl terminated dimethyl polysiloxanes
according to the formula
Me Me Me Me
Si Si
\/ O
n
specified with a viscosity in the range of 0.2-200 Pas at 200C and vinyl
content
of 0.01-0.5 mval/g. The letter "n" represents an integer of from 50 to about
1300,
although this is not an absolute limitation of the invention.
The component a2 is characterised as an organpolysiloxane according to the
formula
Me-, Si O'-~- Si -~' Si O--~- Si---- Me
Me M Me M Me H Me Me
M
n
having at least three Si-bonded hydrogen atoms per molecule. Suitably, this
organopolysiloxanes contain 2.0-8.5 mval/g of active SiH-units.
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The components a3 and b2 are characterised as an aerosil containing
organopolysiloxane terminated with dimethylvinylsilyl endgroups. Examples are
those
prepared according to DE-A 2,535,334.
The components a4 and b3 are characterised in that they contain
tetrafunctional
Si04/2 as Q-moieties and monofnctional R3SiO1/2 as M-units, in which R can be
alkyl
aryl or alkenyl most preferably methyl or vinyl. Moreover, trifunctional
RSi03/2
(silsesquioxane-units or T-units) and R2SiO2/2 as D-units can be present
wherein the
content of these QM-units has to be higher than about 10%.
Component a5 is selected from water absorbing inorganic fillers such as
calcium
sulphate hemihydrate, anhydrous calcium sulphate calcium chloride and the
like, and
absorbing compounds as zeoliths type a molecular sieves and other similar
absorbing and
adsorbing compounds. A zeolith type A in a content of from about 0.5 to about
10% by
weight of the base paste is one preferred scavenger.
The components a6 and b6 are characterised as the product of a
copolymerization reaction of dimethyl-dihalogenosilanes or
dimethyldialkoxysilanes
with methylvinyl dihalogenosilanes or methylvinyl dialkoxysilanes leading to a
copolymer according to the formula
RD'S' 0--'S' 0~Si o---'Si_----R
Me Me Me M Me "R Me Me
m
n
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with wherein R is as above preferably a vinyl giving a vinyl content of 0.5-
3.0 mval/g,
and a viscosity of r)(200C)=200 mPas - 10,000 mPas. One preferred R group is
(CH2)3-
O-[CH2CH2-O]x-CH3 where x is an integer of from about 2 to about 10.
Component a7 is characterised as nonylphenoxy poly-(ethyleneoxy)-ethanol, and
b5 is characterised as the product of the reaction of hydrous chloroplatinic
acid with
tetramethyldivinyldisiloxane.
Component b7 is characterised as highly disperse platinum or palladium on
charcoal, calciumsulfate, alumina or zeoliths.
A combination of ingredients according to the invention combines a very high
tear strength together with highly hydrophilic properties and good flow and
wetting
characteristics.
The combination of ingredients according to the invention promotes low
consistency of both the single paste and the mix. The base pastes according to
the
invention show a non Newtonian flow behaviour with a stress dependent
viscosity and a
thixotropic effect. Even with a high content of surfactant (Examples A, B and
D below)
the yield stress of the base paste, resulting by rheological substructures, is
much lower as
in the case of usual light body formulations (Example F).
In the disucssion to follow reference will be made to Figures 3-4 as were
briefly
discussed hereinabove. In Figure 3, the x-axis shows the frequency omega in
1/s, and the
two y-axis show the shear stress G'(left y-axis) in Pascal (Pa) and the
viscosity n' in
Pascal seconds (Pas) (left y-axis). In Figure 4, the x-axis is time in seconds
(s). The y-
axis is again the shear strees G in Pa on the left y-axis. On the right y-
axis, there are two
parameters, the viscosity n' in kPas and the loss angle. The shear modulus G'
of a fluid
system is split into two parts. The storage modulus G' represents the elastic
properties of
33
CA 02369903 2010-02-01
64053-450
the system, whereas the loss modulus G" represents the viscous properties. The
loss
angle, delta, represents the angle between G' and G" in the triangle developed
by the axis,
G' and G". Figure 5 has the same x and y axis as Figure 4.
Furthermore, in Figure 3, the letter "A" represents the shear modulus G ; the
letter "B" represents delta or the loss angle between G' and G"; and "C"
represents n', the
viscosity in Pas. In Figure 4, the small circle graphical information
represents delta; the
letter "V" in a circle represents the viscosity; the astrics represent the
shear stress G; the
small squares represent the storage modulous G ; and the diamond shape
represents
information for the loss modulous G".
In Figure 5, the graphical representations are the same as those in Figure 4.
The catalyst paste according to the invention even with an aerosil content of
10
% shows nearly Newtonian flow characteristics with constant viscosity of 10.0
Pas and
no yield stress or thixotropic effect. The rheological properties of the
single pastes
according to the invention have been measured by a frequency sweep with an
oscillation
TM
rheometer (CS-50 Fa. Bohlin). Fig. 3 shows the difference between the non
Newtonian
flow characteristics of the Base and the quasi-Newtonian behaviour of the
Catalyst.
The thixotropy of a base paste according to the invention can be shown by a
time
sweep measured with oscillation rheometer under non-disordering conditions.
The
sample was placed on the plate of a cone/plate measuring system. After
lowering the
upper plate a boost stress of 200 Pa was applied on the material for a period
of 5 sec. to
disturb the rheological substructure responsible for the yield stress. The
relaxation of the
elastic properties was measured by oscillation with a frequency of 1 Hz and a
deformation of 0.0005 radian in periods of 10 sec. As can be seen in the graph
of Fig. 4
at the beginning of the measurement the loss modulus (G") is higher than the
storage
34
CA 02369903 2001-10-04
WO 00/61075 PCT/US00/06040
modulus (G') and the paste behaves as a liquid. After the relaxation time of
ca. 600
seconds (sec.) the substructure is rebuilt and the material shows elastic
behaviour. By
side of the typical relaxation time the gel point, when G"=G' is
characteristic for the
thixotropic behaviour of non Newtonian fluids. The time tg(usm) for reaching
this gel
point is at least 90 sec. for a base paste according to the invention.
Because of the thixotropy of the base paste even with a yield stress and a
highly
stress dependent viscosity the material according to invention behaves like
liquid that
flows on the surface immediately after mixing by releasing out of the
cartridge. When the
two components are mixed by release through a static mixer the flow behaviour
is mainly
characterised by the catalyst paste, because immediately after mixing the
rheological
substructures in the base paste, responsible for the yield stress and the
stress dependent
viscosity, are disturbed by the shear stress of mixing.
The material according to the invention has been developed preferably for the
application as a dental cartridge material. Because of the rheological
properties of the
material according to the invention only very low forces are necessary to
release the
material out of the cartridge. Therefore very small static mixers can be used
to release the
material according to invention out of the cartridge, resulting in a minimal
rate of waste
and a large reduction of costs for the user. By "low viscosity" herein, it is
meant that
according to ISO 4823.
To investigate the development of viscosity during the setting reaction of the
material according to the invention a sample (Example B) was measured in a
time sweep
with an oscillation-rheometer (Fig. 5). The material was released out of a
cartridge (as
used in dental applications) immediately on the plate of a cone/plate
measuring system
and the measurement was started 10 sec. after release. The first value of
viscosity was
CA 02369903 2001-10-04
WO 00/61075 PCTIUSOO/06040
registrated 15 sec. after release. The measurement was carried out under non
disordering
conditions with a frequency of 1 Hz, a deformation of 0.001 radians and a
measuring
period of 10 sec. Under these conditions the rheological substructures are not
disturbed
by the torque of the oscillation (as it can be shown in a amplitude sweep of
both single
pastes). As shown in Fig. 5 the viscosity rises very fast in the first period
of the reaction.
This effect can by explained by relaxation of the shear stress caused by the
release out of
the cartridge (thixotropic effect). At the beginning of the setting reaction
the loss angles
is higher than about 45 . That means at this time the material has no yield
stress. As a
liquid the material is able to flow on the surface of the teeth at low shear
stress even
under the influence from gravity, when it is syringed out of the cartridge.
Important for the kinetics of the setting reaction is at first the gel time tg
(set
material) and second the setting time tc. The gel time tg (set material) is
reached when
the loss angle 6=arctan(G"/G') has the maximum value. In cases when there is
no
maximum for the loss angle (when 6>45 ) the gel time is reached when the loss
angle
passes 45 (G'=G"). The setting time is reached when the storage modulus G'
has
reached its plateau.
In the examples A and B according to the invention the formed network is
partly
interpenetrated by the existing network of QM-resins. This allows additional
network
strength. These QM-resins are characterised in that they contain
tetrafunctional Si04/2 as
Q-moieties and monofunctional R3SiO1/2 as M-units, in which R can be alkyl,
aryl or
alkenyl most preferably methyl or vinyl. Moreover, trifunctional RSi03/2
(silsesquioxane-units or T-units) and R2Si02/2 as D-units can be present. The
content of
these QM-resins is preferably higher than about 10 %. A lower content as in
the case of
Example E is not sufficient to increase the tear strength.
36
CA 02369903 2001-10-04
WO 00/61075 PCT/US00/06040
Alternative to the use of a high QM-resin content as in Examples A and B,
highly
functional vinyl-silicones are used in Example D. In this material according
to the
invention the high tear strength is a result of a high content of reactive
vinyl groups in
both components. In usual addition curing silicones these reactive
functionalities are only
placed at the end of long chained polydimethyl siloxanes. In the material
according to the
invention additional vinyl groups are placed on the chain of these polymers.
These
additional functionalities lead to a higher network density combined with
reinforced
mechanical strength. In this case a high content of QM-resins is not
necessary.
Adding a filler to reinforce the mechanical strength is not necessary in the
case
of a material according to the invention. The fillers used are only necessary
to adjust the
rheological properties and to adsorb moisture from the surfactant or
environment. Even
with a filler content of less than 15 % by weight the material according to
the invention
(Examples A, B and D) has a higher tear strength than conventional highly
filled light
bodies (filler content greater than 40 % by weight, Example F). In combination
with a
high strain in compression the improved mechanical strength is able to
maintain the
subgingival undercuts.
To improve the wetting properties a high amount of surfactant has been added
to
the material according to the invention in order to achieve a very low contact
angle to
water. The surfactants are the same as earlier described. Surprisingly these
high amounts
of surfactant lead to only a very low yield stress of less than 5 Pa in the
case of the base
paste (Examples A, B and D). Conventional light bodies (Example F) have higher
yield
stresses with even lower content of surfactant. As it is seen in Fig. 3 this
low yield stress
of the base paste does not lead to a yield stress of the syringed material. It
is caused by a
37
CA 02369903 2001-10-04
WO 00/61075 PCT/USOO/06040
rheological substructure, which is disturbed by shear stress during releasing
out of the
cartridge.
In another embodiment of the invention, an impression material is provided and
incorporates the QM-resin for higher crosslinking and improved tear strength.
In
addition, a surfactant, such as Igepal CO-530 is provided to improve wetting.
The
inprovements lead to direct improvements in the impression detail and also
leads to less
tearing of the impression. The material has the consistency and final
stiffness of the set
material, which is desired for a high voscosity, tray impression material. As
will be
demonstrated hereinbelow, the material may be provided with either fast or
regular
(relatively slower) set characteristic. Table A below shows an example of the
base
material, a fast set example and a regular set example. It is understood that
the amounts
of each material may vary over a range of up to about 99 percent or more from
those
provided. Table B provides comparative examples.
38
Image
CA 02369903 2010-02-01
= 64053-450
TABLE B
TABLE B TEST FAST SET REGULAR SET CORRECTIVES DIMENSION
_ __ HEAVY HEAVY HEAVY HEAVY
WORK TIME _ 1120" 2'15" 30" 3130"
SET TIME 2'40" 4'20" 1'00" 6'30"
MIX CONSISTENCY 32 32 23 28
(mm)
% 3'mrt 5'mrt 6'mrt 6'mrt
COMPRESSION SET 0.50 0.40 0.20 0.45
% STRAIN 1.30 1.30 2.40 3.60
WATER CONTACT 43 43 90 100
ANGLE
TEAR STRENGTH 303 300 183 207
(PSI)
% ELONGATION 34 30 90 76
DETAIL 20 micron 20 micron 20 micron 20 micron
REPRODUCTION
Other examples of inventive materials contain the following components by
weight
percent.
CA 02369903 2001-10-04
WO 00/61075 PCT/USOO/06040
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41
CA 02369903 2001-10-04
WO 00/61075 PCT/US00/06040
In Table C, the designators MONOPHASE, LV-RS, LV-FS, XLV-RS, XLV-FS,
RIGID-RS and RIGID-FS provide an indication as to the viscosity and setting
time of the
compositions. The "MONOPHASE" product is a material that would be useful for
both
tray and syringe type applications. LV-RS is a low viscosity, regular set
product, and
LV-FS is a low viscosity fast set product. XLV-RS and XLV-FS are extra low
viscosity
and are regular set and fast set, respectively. RIGID-RS and RIGID-FS are
regular set
and fast set respectively, composition having a viscosity greater than the
other
composition in Table C. By low viscosity and "set" these terms are meant to be
relative
to each other.
It has been found that dried calcium sulphate, when present in the base paste
portion of the composition, provides improved stability of the base paste.
Preferred ranges of such components, according to the invention, are as
follows:
TABLE D
PREFERRED
RANGES
Organohydrogen Polysiloxane 7-10%
(5,000-7,000 mpa's) QM Resin Dispersion 15-65
(45,000-60,000 mpa's) QM Resin Dispersion 5-46
Divinyl Polydimethylsiloxane 0-18
Cristobalite 10-45
Diatomacelous Earth 0-20
Silanated Fumed Silica 2.5-10
Dried Calcium Sulfate 0-10
Pigments 0-4
Surfactant (Igepal CO-530) 0-8
Platinum Catalyst .25-2.0
1,3-Divinyldimethyldisiloxane .01-.10
Finely divided platinum metal on Calcium Carbonate 0.2-100 ppm
42
CA 02369903 2001-10-04
WO 00/61075 PCT/USO0/06040
Further Examples (all %'s are by weight):
Example A
component A: 53.0 % dimethylvinyl terminated
polydimethylsiloxane containing QM-resins.
20.0 % dimethylvinyl terminated
polydimethylsiloxanes containing high
disperse Si02
5.0 % crosslinking H-Silicones (SiH-content
7.5 mval/g)
10.0 % chain elongating H-Silicones (SiH-
content 2.6 mval/g)
5.0 % zeolith type A
0.5 % titandioxide
6.5 % surfactant
(nonylphenoxypolyethylenoxyethanol)
component B: 66.5 % dimethylvinyl terminated
polydimethylsiloxane containing QM-resins.
32.68 % dimethylvinyl terminated
olydimethylsiloxanes containing high
disperse Si02
0.5 % Pt-catalyst
0.05 % divinyltetramethyldisiloxane
0.07 % Pt/CaCO3
0.20 % Pigment
Example B
component A: 53.0 % dimethylvinyl terminated
polydimethylsiloxane containing QM-resins.
43
CA 02369903 2001-10-04
WO 00/61075 PCT/USOO/06040
20.0 % dimethylvinyl terminated
polydimethylsiloxanes containing high
disperse Si02
15.0 % crosslinking H-Silicones (SiH-content
4.3 mval/g)
5.0 % zeolith type A
0.5 % titandioxide
6.5 % surfactant
(nonylphenoxypolyethylenoxyethanol)
component B: 66.5 % dimethylvinyl terminated
polydimethylsiloxane containing QM-resins.
32.68 % dimethylvinyl terminated
polydimethylsiloxanes containing high
disperse Si02
0.5 % Pt-catalyst
0.05 % divinyltetramethyldisiloxane
0.07 % Pt/CaCO3
0.20 % Pigment
Example C
component A: 16.5 % dimethylvinyl terminated
polydimethylsiloxanes
30.0 % dimethylvinyl terminated
polydimethylsiloxane containing QM-resins.
20.0 % dimethylvinyl terminated
polydimethylsiloxanes containing high
disperse Si02
15.0 % crosslinking H-Silicones (SiH-content
4.3 mval/g)
5.0 % zeolith type A
0.5 % titandioxide
44
CA 02369903 2010-02-01
64053-450
6.0 % surfactant
(nonylphenoxypolyethylenoxyethanol)
TM
6.5 % hydrophilic modifier (Fa. Wacker)
component B: 36.1 % dimethylvinyl terminated
polydimethylsiloxanes
30.0 % dimethylvinyl terminated
polydimethylsiloxane containing QM-resins.
32.68 % dimethylvinyl terminated
polydimethylsiloxanes containing high
disperse SiO2
0.5 % Pt-catalyst
0.4 % short chained dimethylvinyl terminated
polydimethyl-(vinylmethyl)-siloxanes
0.07 % Pt/CaCO3
0.43 % Pigment
Example D
component A: 33.5 % dimethylvinyl terminated
polydimethylsiloxanes
15.0 % dimethylvinyl terminated
polydimethylsiloxane containing QM-resins.
22.50 % dimethylvinyl terminated
polydimethylsiloxanes containing high
disperse SiO2
11.0 % crosslinking H-Silicones (SiH-content
7.5 mvallg)
6.0 % dimethylvinyl terminated dimethyl-
(methylvinyl)-siloxane copolymers
(viscosity 5.0 Pas)
5.0 % zeolith type A
1.0 % titandioxide
CA 02369903 2001-10-04
WO 00/61075 PCTIUSOO/06040
6.0 % surfactant
(nonylphenoxypolyethylenoxyethanol)
0.2 % spearmint oil
component B: 54.03 % dimethylvinyl terminated
polydimethylsiloxanes
10.0 % dimethylvinyl terminated
polydimethylsiloxane containing QM-resins.
32.90 % dimethylvinyl terminated
polydimethylsiloxanes containing high
disperse Si02
1.0 % Pt-catalyst
0.10 % divinyltetramethyldisiloxane
1.0 % dimethylvinyl terminated dimethyl-
(methylvinyl)-siloxane copolymers
(viscosity 0.2 Pas)
0.07 % Pt/CaCO3
0.40 % Pigment
Example E
component A: 44.6 % dimethylvinyl terminated
polydimethylsiloxanes
10.0 % dimethylvinyl terminated
polydimethylsiloxane containing QM-resins.
20.0 % dimethylvinyl terminated
polydimethylsiloxanes containing high
disperse Si02
15.0 % crosslinking H-Silicones (SiH-content
4.3 mval/g)
5.0 % zeolith type A
0.2 % titandioxide
5.0 % surfactant
(nonylphenoxypolyethylenoxyethanol)
0.2 % spearmint oil
46
CA 02369903 2001-10-04
WO 00/61075 PCT/US00/06040
component B: 57.25 % dimethylvinyl terminated
polydimethylsiloxanes
10.0 % dimethylvinyl terminated
polydimethylsiloxane containing
methylsilesquisiloxane resins.
32.00 % dimethylvinyl terminated
polydimethylsiloxanes containing high
disperse SiO2
0.4 % Pt-catalyst
0.03 % divinyltetramethyldisiloxane
0.07 % Pt/CaCO3
0.25 % Pigment
Example F
component A: 39.1 % dimethylvinyl terminated
polydimethylsiloxanes
10.0 % dimethylvinyl terminated
polydimethylsiloxanes containing high
disperse SiO2
8.4 % crosslinking H-Silicones (SiH-content
4.3 mval/g)
5.0 % calcium sulphate hemihydrate
7.0 % diatomaceous earth
25.0 % quartz powder
0.2 % titandioxide
0.2 % spearmint oil
0.11 % pigment
5.0 % surfactant
(nonylphenoxypolyethylenoxyethanol)
47
CA 02369903 2001-10-04
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component B: 51.0 % dimethylvinyl terminated
polydimethylsiloxanes.
10.0 % dimethylvinyl terminated
polydimethylsiloxanes containing high
disperse SiO2
7.0 % diatomaceous earth
29.25 % quartz powder
2.0 % plastisizer
0.4 % Pt-catalyst
0.03 % divinyltetramethyldisiloxane
0.07 % Pt/CaCO3
1.0 % titandioxide
Determination of rheological parameters for the examples according to the
invention was as follows.
The rheological properties of systems consisting of an insoluble solid filler
and
two or more non-mixable liquid phases are characterised by rheological
substructures as
micelles built up by the surfactant and filler particles. The viscosity of
these systems
especially of emulsions therefore is highly dependent on the shear stress. The
viscosity
was measured in a creep test with a shear stress of 200 Pa in the case of the
single pastes
and the mix. The instrument was an Oscillation/Rotation-Rheometer (CS-50Fa.
Bohlin)
in a rotation mode. Important for this parameter is that measurement is
carried out under
constant flow conditions, otherwise the measured value has no physical
relevance. The
shear stress of 200 Pa is much higher than the yield stress of base pastes
according to the
invention. Rheological substructures of the pastes are disturbed under these
conditions.
48
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Under non-destructive conditions the viscosities especially of the base pastes
are much
higher.
In pastes containing a surfactant (base-pastes) a rheological substructure is
built up
by the dipolar molecules of the surfactant. At a stress below the yield
stress, these
micelles together with the filler build up a solid structure. The system
behaves quasi-
elastically characterised by linear shear-stress/stress-modulus relation. When
the shear
stress increases the viscosity of the material reaches a maximum and the yield
stress is
passed over, the substructures are disturbed and the system behaves as a non-
Newtonian
fluid. The yield stress has been measured with a shear stress slope of 0-100
Pa in a time
of 120 seconds. It is noted that this parameter is strongly dependent on the
stress/time
slope, a steeper slope will result in a lower yield stress. Because of this,
the rheological
parameters of such systems are usually measured under definite stress
situations.
Most often the reorganization of the disturbed substructures is combined with
a
relaxation time. In such thixotropic systems even the stress history of the
system has to
be taken into account by the measurement of all rheological parameters.
Therefore the
material is put on the plate of a cone/plate measuring system 20 minutes (min)
before
measuring the yield stress. The viscosity is measured in the creep test
immediately after
putting the material on the measuring system in the case of the single pastes
and after a
period of 30 sec in the case of the mixed material
The setting time tc is measured in a time sweep on a Rotation/Oscillation-
Rheometer (CS-50 Fa. Bohlin) in the oscillation mode. The measurement has to
be
carried out under non-destructive conditions. These conditions can be realised
by
measuring inside of the linear viscoelastic range of both the set and unset
material.
Optimal conditions for the setting reaction of addition curing silicones are a
frequency of
49
CA 02369903 2001-10-04
WO 00/61075 PCT/US00/06040
1 Hz and a deformation of 0.001. The setting time is read when the shear
modulus
G*=G'+G" has reached the plateau. The setting time has clinical relevance for
the
dentist because this period of time is identical with the minimal removal
time.
The physical parameters of the examples according to the invention (A, B and
D)
are shown in Table III together with three examples which are not according to
the
invention (C, E and F).
TABLE III: physical parameters
Example Example Example Example Example Example Example
A B C D E F
viscosity A 10.4 Pas 10.1 Pas 8.18 Pas 7.37 Pas 2.39 Pas 42.2 Pas
B 13.3 Pas 13.3 Pas 10.4 Pas 9.01 Pas 8.15 Pas 67.2 Pas
mix 21.2 Pas 21.1 Pas 16.8 Pas 76.8 Pas
yield stress (base) 2.13 Pa 2.63 Pa 2.61 Pa 3.44 Pa
contact angle to water 42.7 38.3 44.8 43.7 40.2 ca. 45
strain in compression 8.0 % 6.43 % 7.33 % 5.23 % 6.93 % 3.5-5.0 %
tear strength 1.61 1.74 0.85 1.54 0.68 1.5-3.0
MPa MPa MPa MPa
working time (ADA 19) 106 s 140s 120 s 104 s 153 s 120-150s
compression set 0.30% 0.25 % 0.15 % 0.33 % 0.28 % <0.5 %
(ADA 19)
setting time t, 300s 300s 305s 325s < 300 s
In formulation F the high tear strength is a result of the high filler
content. The
viscosities of both the single pastes and the mix are high, therefore the flow
characteristics are insufficient to obtain optimal impressions.
In formulation E the low viscosity is obtained by dispensing the filler. The
flow
characteristic on the tooth surface is very good. The example shows good
wetting
characteristics as a result of the low contact angle, but because of the very
low tear
strength the formulation tears off from the undercuts.
In example C the flow characteristics and the contact angle have been
optimised,
as in formulation E the tear strength is to low to avoid a tear off from the
undercuts.
CA 02369903 2001-10-04
WO 00/61075 PCT/US00/06040
The content of the reinforcing QM-resins is not high enough to improve the
mechanical strength.
The examples A, B and D according to the invention have very low viscosities
of
both the single pastes and the mix. Combined with a low contact angle these
rheological
characteristics lead to an optimised flow of the paste on the surface of the
teeth and into
the sulcus. A high tear strength could be achieved by a high network density
in the case
of example C or by the use of a high content of QM-resins in the case of
example A.
TABLE IV shows the gel times tg(unset material) for the base pastes according
to
the invention measured by a time sweep as explained above.
TABLE IV
Example A Example B Example C Example D Example E Example F
min. viscosity rj* 39 Pas 35 Pas 11 Pas 45 Pas 16 Pas 140 Pas
gel time tg(usm) 101 s 101 s * 30s 11 s 24.5
* The base-paste of Example C shows a very long gel time in the time sweep.
This
formulation has a very week rheological substructure which is disturbed under
the
measuring conditions (1.0 Hz, 0.0005 radian). It tends to separate under the
influence
from gravity. Therefore the measurement of the thixotropic effects are without
any
physical relevance.
Together with the gel time the min. viscosity 11 * after disturbing the
rheological
structure is important for the flow characteristics of the material. Only in
the examples
according to the invention (Example A, B and D) a long gel time is combined
with a low
viscosity.
51
