Note: Descriptions are shown in the official language in which they were submitted.
184,916 CA~I/DPE
I
Descri ~tion
Zinc-Containing G1ass Composition
Technical Field
This invention relates to zinc-containing glass
compositions and to dental filling compositions containing
such ylass composition in the form o~ -finely divided ~iller.
Background Art
A variety of substances has been used over the years
to repair damaged teeth. The best known currently include
silver amalgams, which are frequently first encountered
at an early age as a filling for small cavities, even
in deciduous teeth. Gold alloys are a particularly
valuable filling material, used frequently when a tooth
has been considerably damaged, such as after several cavitjes
have occurred and a lot of tooth must be restored. Fre-
quently, for example, several smaller extending cavities,
e.g. in the occlusal surface, will be combined and a
restoration made with a single gold inlay or onlay. The
gold alloys have gained an excellent reputation for
strength, reliability and long life in service. However,
both the gold alloys, and the other metals, such as the
stainless steels, which have been technically successful
in dental reconstructions and crowns, do not impart a
natural tooth appearance.
Gold and other metallic-looking restorations are used
for molars and teeth which are not immediately open to
view when the wearer opens his mouth or smiles. For
anterior teeth, however, current practice is to use
3G materials closer in appearance to natural teeth. These
are known colloqu~ally as porcelain or plastic fillings.
They are composite rnaterials characterized by containing
usually predominantly inorganic materials, normally
finely divided powders, inert to the oral environment,
bound together with polymeric material. The inorganic
materials are frequen-tly ~inely-ground fused oxides,
particular1y glasses, or crystalline quartz, while the
polymer moiety ls commonly a polyacrylate. These compo-
site systems are available~ for example, as pastes whichare polymerized in situ, after having been activated, e.g.
by add;ng a catalyst to initiate a polymerization reaction,
just before being placed in the prepared tooth.
Fillings and restorations of thls kind can be made
to look much like natural teeth. In particular, the color
of the restoration can be adjusted to a shade quite close
to that of a patient's natural teeth by tinting wlth
pigments. In addition, the translucency or pearlescence
of the natural tooth can also be approximated through
adjustment of the relative refractive indices of the
materials used in the restoration. When color and re-
fractive indices are well matched, it is possible to obtain
a restoration that is barely perceptible to the glance.
However, the attainment of good color and overall appearance
is very difficult to achieve in practice. This is
particularly true when one desires also to optimize other
features of a good restoration, particularly radiopacity.
It is highly desirable for a filling or other re-
storation to be radiopaque, for it is by X-ray examination
that a dent~st determines whether or not d filling remains
sound. From radiographs a dentist determines the condi-
tion of a filling, e.g. whether it has cracked, or whether
decay is occurring at the intertace between the tooth
and the filling. Fillings and restorations which are made
of metal are readily observable in X-rays. Fillings of
the porcelain/plastic art are not observable by X-rays
unless they have radiopaque materials therein.
Currently, dental filling materials are rendered
radiopaque by incorporating barium into the inorganic
powder moiety of the filling material. The most effective
radiopaque agents are elements of high atomic number
(i.e. the "heavy elements" of the periodic table); it
is unfortunate, however, that most of these elements
are either radioactive or toxic, such as thorium or lead.
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earium is toxic also, but in certain medical uses it is
present in a for~ 50 highly insoluble that the body is
unable to metabolize enough of it to beco~ne intoxicated.
In dental applications barium glasses have been used as
components of dental restorations, on the hypothesis that
barium ions within the structure of a glassy matrix will
not be available to oral fluids (saliva, bevPrages, etc.)
and will not, therefore, pose a problem of toxicity.
Examples of the use of barium glass in dental restorations
can be found in U.S. Patents 3,801,344; 3,808,170; 3,826,778;
3,911~581; 3,959,212, 3,975,203 and 4,032,504. Unfor-
tunately, in practice, the barium glasses are not as
stable as had originally been hoped, and they have not,
therefore, found favor in the art on account of the risk
they pose of poisoning the patient (see, e.g. U.S. Patent
3,971,754). A further problem encountered with the
barium glasses is that of matching refractive indices
to that of the other components of the restoration. For
example, it would be desirable to use components with
refractive indices in the ranse of about 1.5 to 1.6 (so
as to closely match the refractive index of commonly used
organic binders) but most bar;um glasses with refract;ve
indices in this range are unsuitable for dental use
according to U.S. Patent 4,032,504 It is difficult,
therefore, to prepare restorations containing barium
glass which present an unobtrusive appearance when used
for anterior surface repair. An additional problem of
the barium glasses is their alkalinity. Typical1y, barium
glasses show alkalin~ty values of pH 9 or greater, whereas
a pH of 7 is preferred. Highly alkaline fillers appear
to degrade the siloxane coating resulting from etching
of the prepared tooth cavity and also cause rapid
decomposition of any peroxide catalyst present in the
dental restorative composition during storage.
Recent efforts in the field of dental restoration
materials have resulted in the use of fillers other than
barium-containing compounds as an X-ray detectable com-
ponent. For example, U.S. Patent 3,971,754 describes
the use of certain oxides or carbonates, particularly
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those of lanthanllm, s-trontium, tantalum and, less use~
~ully, hafnium. These sal-ts are mixed with glass-making
componen-ts at the time the glass is made, ~ielding a
lanthanum, strontium, tantalum or ha~nium glass ~hich
possesses a measure o-f radiopdcity. U.S. Patents
3,973,972 and 4,017,454 describe glass ceramics which
possess both a low coefficient of thermal expansion (an
advantage in dental f;llings) and a useful degree of
radiopacity, by virtue o~ a high content of rare earth
elements, particularly lanthanum. The rare earth
elements absorb ~ rays in the wavelength range of 0.2 -
0.3A, a range commonly available from dental X-ray
machines. However, the cost and problems with availabi-
lity of these rare earth fillers make them ~enerally
unsuitable for commercial use.
In another approach to preparing radiopaque
composites for dental use, organic halide (e.g. an alkyl
iodide) has been incorporated into plastic materials
(e.g. acrylate polymers), from which molded articles
are made (e.g. U.S. Patent 3,715,331). However, the
articles molded from such compositions lack the strength
of restorations made from glass or ceramic materials.
U.S. Patent 4,250,277 describes a glass composition
used for crosslinking polycarboxylic acid cement, wherein
the glass contains zino oxide and a large amount of boric
oxide, in addition to other ingred;ents. This glass,
however, is too water soluble to be useful in dental
restorative compositions and prosthetic devices.
U.S. Patent 4,215,033 dPscribes a composite dental
material containing a glass which in one embodiment is
described as single phase. ~lowever, this patent does not
appear to recognize that a single phase glass containing
zinc oxide can be made radiopaque. Also, the single
phase glass composition described in this patent is very
difficult to make. Furthermore, such glass does not
contain any aluminum fluoride.
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Disclosure of Invention
_____
In accordance with the present in~/ention there
is provided a novel glass and a dental -~illing cornposition co~nprising a
polymerizable resin binder and a finely divided inorganic
glass fi'ller which is X-ray opaque and single phase,
wherein said X-ray opaque inorganic glass fi'ller consists
essentially of, in percent by weight:
Zinc oxide 20 to 35%
Silica 45 ~o 65%
Boric oxide 3 to 15%
Aluminum oxide 0 to 10%
Aluminum fluorideAt least 2
Alkali metal oxide 0 to 3%
or alkaline
earth meta'l oxlde
wherein the combined weight of aluminum oxide and
aluminum fluoride is at least about 10%, and wherein said
glass exhibits an "X-ray absorption characteristic" of
at least 1/16 inch (0.16 cm)
Best Mode for Carr~in~_O t the Invention
It has been discovered that glasses containing
high levels of zinc can be prepared which possess physical
characteristics (e.g. refractive index, pH, coefficient
of expansion) making them especially suitable for use
in dentalrestorative compositions. Moreover, these
glasses have been found to be radiopaque and to be
capable of being made into dental composites which have
greater radiopacity than those made with harium, the
best known radiopacifying agent used heretofore. This
is quite surprising, considering barium has an atomic
number of 56, iodine an atomic number of 53, the
s~
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lanthanides having atomic numbers of 57 to 71, and
zinc having an ~tomic number o-f only 30. Moreover, it
has been found possible to make the n~w zinc glasses
with refractive indices in the desired range -For dental
restorative compositions. In addition, the new glasses
can be prepared at a pH close to 7. This ls a highly
desirable feature ln regard to the preparation of high
quality dental composltes. In particular, when the
glass is near neutral in p~l (i.e. ~.5 to 8), the stabi-
lity of the dental composite is significantly enhanced.Improved color stability, and reliable setting charac-
teristics after the activated ~mposite is emplaced in
the tooth being repaired. The new glasses are signi-
ficantly better than the barium ~lasses of the prior
art in this regard.
It is believed that the problems encountered with
the barium glasses are contributed to by the relatlve
alkalinity of these materials. ~arium is an alkaline
earth element in the periodic system, and, therefore,
more electropositive than zinc, which is a transition
element. The higher p~s characteristic of the barium
glasses cause decomposition of the peroxide catalysts
normally used in these formulations and thus greatly
reduce storage stability. A significant advantage of
the new glasses, which is an improvement over any known
heretofore, is that they contain an element, namely,
zinc, that has been in regular dental use for many yea,s.
Zinc oxide-containing ointments have long been used in
medicine as safe and mild antibacterial agents and zinc
oxide has long been used as a component in dental
cements or adhesives. These latter agents are used for
cementing prostheses, onlays, bridges, crowns, and the
like, to the teeth. In this use they have proved safe
and effective over many years. In other words, zinc
compounds have a long history of being safe to use in
the oral cavity, and are thus vastly preferable to use
compared with those of un~nown safety or known toxicity,
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such as compounds of barium.
The new single phase glasses used in this inYentior
have the following composition in percent by weight:
Zinc oxide (ZnO~ 20 to 35~
Silica (SiO2) 45 to 65%
Boric oxide(Bz03) 3 to 15%
Aluminum oxide(A1203) 0 to 10%
Aluminum fluoride(AlF3) At least 2%
Alkali meta'l oxide O to 3
or alkaline
earth metal oxide
wherein the combined weight of aluminum oxide and
aluminum fluoride is at least about 10%, and wherein
the glass exhibits an "X^ray absorption characteristic"
15 of at least 1/16 inch (0.16 cm). The alkali metal oxide or
alkaline earth metal oxide may be, for example, sodium
oxide, potassium oxide, lithium Gxide, calcium oxide,
magnesium oxide, or the like, or combinations thereof,
so long as the combined weight of such oxides does not
exceed about 3% of the glass, thus maintaining the pH
of the glass in the desired range o~ about 6 5 to 8
Of course, as will be recognized by those skilled in the
art, various other ingredients may also be present in
minor amounts so long as the resulting glass exhibits the
desired X-ray opacity and the desired pH. However~ it is
highly preferred to avoid the inclusion of toxic metals
such as lead, cadmium~ mercury, arsenic, etc.
A preferred embodiment of the new glass for
use in dental restoratiYes intended for anterior appli-
cations has the following composition:
Zinc oxide 25 to 28%
Silica 46 to 48%
Boric oxide 6 to 9%
Aluminum oxide 1 to 3%
Aluminum fluor~de17 to 19%
-B-
wherein the combined weight of aluminum oxide and
alllminum fluoride is not greater than about 20%,
and wherein the glass exhibits an X-ray absorption
characteristic of at least 3/32 inch (0.24 cm).
The compositions given above are ~ritten ir, terms
of the salts (e.g. oxides and fluorides) whlch are
used in preparing the Melt from which the glass is obtained
upon cooling. This is a common practice in the glass-
making art. There is, of course, no oxide, fluoride,
or other simple salt in the resultant glass. Glasses
used in this invention all possess a useful degree of
radiopacity.
The refractive index oF the glasâ may be varied,
depending upon the particular amount of each ingredient
present. It is preferred that the refractive index of
the glass Filler be substantially the same as that of the
binder resin when the glass is used in a dental filling
composition, i.e. within about 0.05, when the composition
is used in anterior applications. When the binder
resin comprises the well known BIS-GMA, the refractive
index for the glass filler is preferably 1.556 ~ 0.05.
Matching of the refractiYe indices of the glass filler
and the binder resin is less important when the composi-
tion is intended for posterior dental applications.
When BIS-GMA resin is diluted with another acrylic
resin (e.gO triethyleneglycol dimethacrylate) to
facilitate higher filler loadings to make a composition
having particular use for posterior filling applications,
the resultant resin mixture may have a refractive index
of 1.545, for example. Conse~uently, for such an
application it may be preferred to use a glass composi-
tion having a refractive index of 1.545 if close matching
of the resin and filler is desired. When it is desired
to preparP a dental filling composition which is light
curable it is important to obtain a close match of the
refractive indices of the polymerizable resin and the
~ ~racO~ a~k
ylass Filler so that complete and rapid cure of the resin
will be achieved ~/hen jt is exposed to the activating
light Of course, when the cornposition is intended for
use elsewhere in the body (i.e. where esthetics are not
a factor) and where the composition is not 1ight curable,
there is no need to attempt matching the refractive
index of the glass to the refractive index of the binder
resin.
Radiopacity, which reflects the materia1s's ability
to attenuate X-rays, is conveniently measured by com-
paring the X-ray film image density values of a disc of
the cured composite of a standard thickness, e.3. 0.040
inch (0.1 cm), with corresponding values of a known standard.
Film image density measurements are made with a suitable
densitometer, such as a Macbeth Transmission Densito-
meter, Model TD 504, with visible light filter (manu-
factured by Macbeth Div. of Kollmorgan Corp., ~lewburgh,
N.Y.) A convenient standard is a stepped aluminurn wedge,
for e~a~ple, a ten step wedge having a thickness of 1/32
inch (0.08 cm) at the thinnest step increasing to 5/16 inch (0.8 cm) at
the thickest step. One empirically determines the X-ray
film image density values corresponding to steps on the
wedge, which indicate degrees of X-ray beam attenuation
which provide, in actual practice, proper differentia-
tion between a composite restoration and the surrounding
tooth structure. A proper level of radiopacity wil1
permit one skilled in the art to differentiate between
the restoration and primary and recurrent caries in the
tooth structure, and will also ~/isualize defects in the
restoration itself. By way of illustration, using a
wedge, the glasses of this invention when tested in
this manner give values ofl/16 inch (0.16 cm) at 26% ZnO; 3/32 - l/8
inch (0.24 - 0.32 cm) at 26.5 - 28% ZnO, Typical barium glasses of
the prior art, tested under identical conditions give
values ofl/16 - 3/32 inch (0.16 - 0.24 cm). The typical "plastic" or
"porcelain" filling materials (containing quartz or
borosilicate filler) common in contemporary dental
practive give va1ues of zero. A silver amalgam gives a
values of~ 5/16 inch (0.~ cm). It will be understood, of course,
that these values are completely empirical. Using
different wedges and experimental apparatus, the actual
numbers one gets may be djfferent. For the purposes of
this invention, useful glasses exhibit an X-ray absorption
characteristic of at least 1/16 inch (0.16 cm).
Inso~ar as the preparation o~ the zinc glass is
concerned, standard techn~ques well-known in the glass-
making art are used. See, for example, The Handbook ofGlass Manufacture, Fay and Tooley, Volume I (1974).
After the mel-t has cooled, the glass is cornmlnuted to a
size that passes through a 325-mesh standard sieve (~
microns). For grinding the glass into smaller sizes a
ball mill is used, and grinding aids such as ammonium
carbonate or alcohols may be present in an amount of
approximately 0.5% based on the weight of the glass.
When making dental composite restorative, the glass
powder is then prepared for incorporating into an organic
binder matrix by treating the surface with a silane com-
pound. This is a well-known technique for rendering re-
latively polar materials, such as siliceous po~ders, more
compatible with relatively non-polar materials, such as
organic polymers.
The zinc glass is then mixed into a dental paste.
The paste may be formed of any of the polymerizable
resin systems useful in dentistry. Especially useful
resin systems comprise free-radically pol~merizable
materials such as the polyfunGtional acrylate systems.
Particularly useful in the system is BIS-GMA, a well-
known material which is the reaction product of bisphenol-
A and glycidyl methacrylate, widely used in dentistry.
Other commonly used resin binders include polyurethanes,
methyl methacrylate, and isobutyl methacrylate.
3~ The zinc glass may be used alone or it may be
blended with other suitable materials, such as inert
glass powders, ~hen mixed into the binder - depending,
for example, on the degree o~ radiopacity desired in the
final composite. Along with the glass, other
ma-ter;als may also be mixed into the paste, such as
pigments for making the restoration match the pat;ent's
natural tooth color, and reagents like hydroquinone
monomèthyl ether, as an inhibitor of premature poly-
merization of the binder. Immediately before use, and
after the dentist has preparecl the tooth for receiving
the restoration, the paste is activated by mixing into
it the appropriate amount of catalyst, such as benzoyl
peroxide. For example, the dental restorative composi-
tion may be in the form of two pastes (one paste con-
taining filler, resin binder and catalyst while the other
contains filler, resin binder and accelerator), or a
liquid resin and powdered filler system, or a paste-
liquid resin, or any other desired form. The mixed
composition is promptly emplaced in the tooth, harden-
ing in the manner characteristic of the resin binder
and catalyst system being used. For example, using the
well-known BIS-GMA/benzoyl peroxide system, the composite
becomes grossly rigid in about 5 minutes and may be
finely ground and polished, to give the finished restora-
tion, in about 10 minutes. At any time after emplace-
ment, but more particularly after significant time has
elapsed, such as many months or years afterwards, the
condition of the restoration and the adjacent tooth
structures can be determined by diagnostic dental X-rays.
Curable com,oositions which contain the no~el glass
and which are useful in other applications (e.g. medical
and dental prosthPses, pit and fissure sealants, hard
tissue cements) may be prepared in similar fashion
using polymerizable resin binders.
The invention is further illustrated by means of
the following representative examples wherein the term
"parts" rPfers to parts by weight unless otherwise
indicated.
1 ~
Example 1
Silica (47 gms), zinc oxide (26 gms)j boric oxide
(8 gms), aluminum oxide (1 grr.) and aluminum fluoride
(18 gms) are thoroughly mixed, as fine powders, in a
silica-lined crucible. The mixture is heated in a muffle
furnace at 1450F, (788C.) until the powder has become a trans-
parent melt.
The molten glass is then removed from the crucible
through a small hole in the crucible wall, by tilting
the crucible and allowing a thin stream of glass to flow
through, giving a filament of glass of aboutl/32 inch (0.08 cm)
diameter. This filament is quenched rapidly in cold water,
to give a completely clear glass (as opposed to being
opalescent). Mere air cooling of the glass is not
sufficiently rapid to prevent phase separation.
The clear glass is then ground, e.g. in a ball mill,
to a mean particle size range of 0.5 - 15 ~m.
~e~
Gamma-methacryloxy-propyltrimethoxy silane (2 gms)
is mixed with glacial acetic acid (0.033 gms) and water
(44.4 gms) in a plastic beaker. Glass powder (100 gms
for example, from Example 1) is added to the mixture,
and the system is stirred for 1.5 hours at room tempera-
ture. The glass slurry i5 dried by warming it at 140F.
(60 C.) for 24 hours, followed by heating it in an oven
for 2.5 hours at 240F. (115 C.~.
Example_3
Two pastes, A and Bj are prepared, having the
following compositions:
30 Ingredient Paste A P_ste_B
BIS-GMA resin 14.48 gm 14.67 gm
Triethylene glycol dimethacrylates 4.67 4.63
Silane-treated filler 80.0 80.0
(from Example 2)
35 Benzoyl peroxide - - - - .21
Dihydroxyethyl p-toluidine .46
.b
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Ingredient Paste A Paste B
"Tinuvir, P"~ a UV absorber .16
Phenylsalicylate glycidyl .14 .16
methacrylate adduct, a UV
absorber
Butylated hydroxytoluene - - - - .16
Bisphenol A - - - - .14
Pigments-titanium dioxide and .17 .17
iron oxides - yellow raw
sienna, burnt umber),
ottalume
TOTAL 100.00 gm 100.00 gm
The pastes are prepared as follows:
For each paste, A and B, two preliminary mixes are
made. The glass ~from Example 2) and the pigments are
mixed thoroughly to give an evenly colored powder. This
mix is the same for each paste. The resins, accelerator3
UV absorbers and inhibitor are mixed to give the mix
for paste A. The resins, catalyst, UV absorber, and
inhibitor are mixed to give the mix for paste 8. After
the two mixes, glass and resin based respectively~ have
been prepared, the procedure for preparing each paste,
A and B, is the same.
Each resin mix is added to a vessel and then the
respective glass mix is added. The two mixes are first
roughly blended together, such as by shaking, and are
then thoroughly mixed preferably by prolonged mechanical
mixing.
The resultant homogeneous pastes, A and B, are the
precursors to the dental restorations made from the
materials of this invention. Pastes A and B are kept
separate until immediately before the appropriate repair
is made in a tooth which has been prepared to receive it.
They are then mixed together thoroughly and promptly
emplaced in the manner well-known in dental art.
tra cl~ k
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xam~le 4
Using the procedure of Example 3, two pastes, A and
B, are prepared having the following comyositions:
Ingredient Paste A Paste B
. .
Dlacetyl BIS-GMA resin* 19.20 gm 19.57 gm
Silane treated filler 80.0 80.0
(from Example 2)
Benzoyl peroxide ~ .24
Dihydroxyethyl p-toluidine .47
"Tinuvin P" - a UV absorber .16 - - - -
Butylated hydroxytoluene - - - - .02
Pigments - titanium dioxide and ,17 .17
iron oxides (yellow, raw sienna,
burnt umber), ottalume
TOTAL lOO.OO gm lOO.OO gm
* CH3 Iq CH3 Iq CH3
2 CH2C~ 2- ~ C-~ O-CH2CHCH20-C - C 3 CH
O CH3 0
C-O C=O
CH3 CH3
The two pastes, when mixed together, form a very useful
dental restorative composition.
Example 5
The glass filler of Example l was ball milled to a
mean particle size of 4.5 microns and silane treated
according to the method described in Example 2. A light-
curable paste was prepared having the followin3 compo-
sitions.
Ingredient Parts
BIS-GMA resin 5.655
Triethylene glycol dimethacrylate 5.655
Triphenyl antimony .002
N,N-diethylaminoethyl methacrylate ,47
dl - camphoroquinone .048
Silane treated filler + 1.58~ by 88.0
weight "Aerosil R-972"
x~
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Ingredient Parts
Pigments - titanium dioxide, iron .17
oxides (yellow, raw sienna,
burnt umber) and ottalume
S TOTAL 100-00
The paste is prepared as follows:
The mill~d and treated filler (from Example 2),
Aerosil R-972 (colloidal silica, commercially available
from DeGussa Corporation, average particle diameter of
16 millimicrons, surface area of llO square meters/
gram) and the pigments are blended to give an evenly
co10red powder. The resins, inhibitor, accelerator
and photoinitiator are mixed in a dark area in a ~essel
excluding light. The filler blend is then added to the
mixing vessel containing the resin mix. The ~iller,
resins and other components are then thoroughly mixed
by prolonged mechanical mixing, with the entire opera-
tion carried out in the absence of light.
A commercially available "KULZER TRANSLUX" irra-
diation device with a light guiding rod is used to cure
the paste. Test samples are prepared by packing the
paste into an open-ended Teflon mold with a cylindrical
cavity. The loaded mold is then placed between 2 pieces
of clear polyester film (each 25 microns thick). Test
samples of prescribed thickness are then irradiated for
a period of exposure necessary to polymerize or cure the
resin in the paste. Barcol hardness measurements are
made on the top and bottom of the test sample to determine
the extent of polymerization. The following Barcol
hardnesses are determined on cured test samples using
two different sample thicknesses.
Hardness
l Min Post Cure l Hr. Post Cure
2 mm sample thickness 81 - top side 91 - top side
- 20 sec- exposure 64 - bottom side 82 - bottom side
3 mm sample thickness 83 - top side 86 - top side
- 20 sec. exposure 56 - bottom side 74 _ bottom side
cle r~ a r1c
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Barcol hardness values in excess of 80 are considered
outstanding. Standard, commercially available dental
restorative composites typically haYe Barcol hardness
values o-f 70 - 75 after 24 hours cure.
The filler loading levels of 88~ attained with the
zinc glass must also be considered to be extraordinary.
Conventional radiopaque barium glass permits maximum
filler loadings of 78 - 80% when using similar particle
slze distributions.
Example 6
The glass filler of Example 1 was ball milled to a
mean particle size of 1,8 microns and silane treated
according to the method described in Example 2. A
light-curable paste having the following composition was
prepared using the procedure of Example 5:
In~redient Parts
BIS-GMA resin 7.09
Triethylene glycol dimethacrylate 7.09
Triphenyl antimony .003
N,N-diethylaminoethyl methacrylate .59
dl - camphoroquinone .059
Silane treated filler + 10% by weight 85.0
"OX-50" (colloidal silica com-
mercially available from De&ussa
Corporation, average particle
diameter of 40 millimicrons,
surface area of 50 square
meters/gram)
Pigments - titanium dioxide, iron .168
oxides (yellow, raw sienna, burnt
umber) and ottalume
TOTAL 100.00
Barcol hardnesses were determined on 2 mm thick test
samples of composition cured at two different exposure
times:
-1 7-
Hard_ess
1 Min. Post Cure 1 Hr. Post Cure
20 sec. exposure 83 - top side
2~ - bottom side
30 sec. exposure 83 - top side 84 - top side
54 - bottom side 75 - bottom side
_xample _
The glass filler of Example 1 was ball milled to a
mean particle size of 4.5 - 5.0 microns. Radiopaque
impression pastes, containing the ingredients listed
below, were prepared by mixing the ingredients in a con-
ventional Ross brand mixer:
Ingredient Paste A Paste B
Low molecular weight vinyl 2000 grarns 1800 grams
siloxane polymer (2300 cps)
Filler of Example 1 1700 grams 1700 grams
(not silane treated)
Chloroplatinic acid 4.2 grams - - -
(catalyst)
Hydrogen polysiloxane - - - 70 grams
The concentration of the filler may be varied, as
desired, to produce compositions having various viscosities.
Compositions contain;ng 30 - 40% filler are of low
viscosity, while composition 5 containing 80 - 90~ filler
have a putty consistency.
