Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to the technical
field of ceramo-metallic dental reconstructions. It re-
lates more particularly to the composition of ceramic
glass employed to produce various types of dental recon-
structions, such as crowns, inlays, bridges, and the like.
Dental reconstructions of this type are usuallyproduced from a series of ceramic layers covering a metal
coping, for example laid on the stump of a tooth reduced
after shaping with the drill. This series of ceramic
layers consists of 3 basal opacifying layer, two inter-
mediate layers known under the terms of "dentine'' and
"incisal"~ and a transparent surface layer intended to
resemble the gleam of the enamel of the natural tooth.
The subject of the present invention is aimed
more especially at the basal ceramic layer for opaci-
fying the metal coping of such a dental reconstruction.
As its name indicates, such a layer is mainly
intended to hide the metallic appearance of the supporting
coping. It is therefore essential to give it good opaci-
fying properties. However, this is not enough. In fact,to obtain good mechanical strength and good fracture
toughness of the prosthesis, it is essential to ensure
perfect bonding of the opaque ceramic layer to the metal
coping. The various solutions proposed hitherto do not
produce a satisfactory adhesion in practice.
The aim of the present invention was precisely to
develop an opaque dental ceramic which, in addition to
its improved adhesive properties, is endowed with an out-
standing opacifying power. This layer according to the
~e
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invention moreover has, after being baked, a rough surface
quality responsible for good light scatter, which makes it
possible to avoid any unpleasant reflection effect of the
prosthesis which, for this reason, would not truly restore
the appearance of the natural tooth.
It should be noted, moreover, that, as a result of
the better opacifying power, the dental ceramic according
to the invention can be applied as a thinner layer, which
leaves more space available for applying the following
coats, nhich thus become easier to mold by the prosthetist.
Furthermore, the opaque dental ceramic composition
according to the invention has been adapted to conform in
expansion with its adjacent layers, and in particular with
;ts metal support. This compatibility is further consid-
erably facilitated by its better opacity, which permits itto be deposited as a thinner layer.
The present invention which makes it possible to
reconcile, on the one hand, the adhesion and, on the other
hand, the opacity of this type of ceramic layer, springs
from the parent concept based on separating into two
distinct layers the single opaque layer usually employed
in the prior art. The first undercoat, called "opaque
slip", in direct contact with the reinforcement, is in-
tended to contribute good adhesion to the metal, while
the other layer, referred to as "opaque", has been designed
to contribute the sufficient degree of opacity.
In accordance with the ?resent invention, the
basal ceramic layer for opacifying the metal coping of a
ceramo-metallic dental reconstruction consists of an
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undercoat of opaque slip obtained from a glass frit high
in fluxes and in particular in ~23' covered with an
opaque layer obtained from a glass frit high in opacifying
metal oxides and contain;ng approximately 30% by weight of
refractory particles with a particle size of between approxi-
mately 40 microns and approximately 100 microns.
Other features and advantages of the present in-
vention will become apparent from the reading of the de-
tailed description which follows, relying particularly on
individual examples of application, which are given simply
as illustrations.
The glass frit which is high in fluxes and inten-
ded to form the undercoat of opaque slip in contact with
the metal coping, advantageously contains approximately 8
to approximately 14 X by weight, and preferably from
approximately 9 to approximately 11 X by weight, of 8203.
It is precisely this high content of boron oxide which
makes it possible to improve the metal adhesion capacity
of this undercoat of opaque slip. It should be noted,
however, that ~23 contents above approximately 14 %
by weight would result in glass frits which cannot be
used in practice, since they would become too readily
melted. In fact, an undercoat of opaque slip must not
have melting temperatures which are too low, since its
melting temperature must in any event remain above those
of the following top layers which are laid down and subse-
quently heat-stabilized.
Insofar as the opaque layer as such is concerned,
this of course contains opacifying agents such as tin
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oxide, titanium oxide and zirconium oxide, in a high con-
centration. However, the opacifying capacity of this
layer is considerably increased by the presence of a high
proportion (of the order of 30 ~ by weight) of relatively
large refractory particles, that is to say with a particle
size of between approximately 40 and approximately 100 mi-
crons. The presence of these refractory particles of
relatively large sizes produces, after baking, a roughness
in the surface of this opaque layer wh;ch contributes an
effect of light scatter through the more translucent upper
layers and thus improves the effect of tooth "depth".
Two examples of composition of glass frits inten-
ded for producing an undercoat of opaque slip and an opaque
layer are given below by way of illustration.
Example of overall composition of opaque slip:
A glass frit of this type, which is high in fluxes
and has produced satisfactory results in practice, corres-
ponds, for example, to the following composition:
SiO246 to 48 % by weight
Al20310 to 12 % by weight
CaO1 to 1.5 % by weight
MgOO.S to 1.5 % by weight
K2010 to 11 % by we;ght
Na206 to 9 % by weight
3239 to 11 X by weight
Zr21.5 to 2% by weight
SnO26 to 8 X by weight
TiO20.5 to 1 % by weight.
Preferably, such a glass frit has an average
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particle size of approximately 12 microns.
Example of overall composition of opaque layer:
A glass frit high in opacifying metal oxides,
which is employed in a satisfactory manner in practice to
produce an opaque layer according to the invention, corres-
ponds, for example, to the following overall composition:
SiO2 42 to 46 X by weight
Alz03 14 to 18 % by weight
C30 0.8 to 1.7 % by weight
MgO 9.5 to 1.5 % by weight
~zO 11 to 13 % by weight
Na20 3 to 6% by weight
B203 5 to 8 % by weight
Zr2 3 to 5% by weight
SnO2 11 to 14 X by weight
TiO2 0 5 to 3 % by weight.
The above glass frit high in opacifying metal
oxides advantageously has a mean particle size which is
slightly greater, for example approximately 36 microns,
while retaining the presence of a fraction of the order
of 30 X by weight of particles ranging from approximately
40 to approximately 100 microns, favoring the refractory
particles. This refractory particle fraction contains a
proportion of opacifying metal oxides which is always
greater than 25 X by weight, that is to say that these
particles have a higher content of opacifying agents than
the remainder of the composition.
The glass frits required for producing the layers
according to the present invention are prepared in a
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,~,
conventional manner, from powdered mixtures of the re-
quired components such as determined earlier. Such a
powdered mixture is, for example, heated for one hour at
a temperature of the order of 1500C, which, on melting,pro-
duces a homogenization, followed~ for example, by quenchingto produce the frit which can subsequently be subjected
to a grinding or granulation operation.
This grinding operation is carried out in a con-
trolled manner to obtain the particle sizes required in
accordance with the present invention.
The present application also relates to glass
frits required for producing the ceramic layers called
"opaque slip" or "opaque", which are distinguished by a
composition containing:
10 to 30 X by weight of active products,
60 to 80 X by weight of a propellant gas,
10 to 30 X by weight of a solvent with a vaporiza-
tion temperature of between
approximately 40 and approxi-
mately 80C, and
4 to 6 X by weight of a glue.
The propellant gas may consist, for example, of
one or more chlorofluorinated hydrocarbons (Freo ~).
The mixture of glue and solvent may consist, for example,
of officinal collodion dissolved in ethyl acetate. The
solvent may advantageously also consist of a chlorinated
hydrocarbon, for example CH2Cl2, and the glue may also
consist of an acrylic or, preferably, cyanoacrylic, glue.
A composition of this kind is thus suitable for
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be;ng packaged in a dispenser bottle of the aerosol type.
This glass frit composition may thus be presented
as such, to be ready for direct use. Simple spraying on
the metal coping with the aid of an aerosol can thus makes
it possible to produce thin layers of opaque slip or of
opaque composition.
These layers are then fixed in a conventional
manner by baking, for example in the course of a heat
treatment at a temperature of the order of 80U to 850C for
7 to 8 minutes. It shoul~ also be noted that as a result
of the particular compositions of the ceramics vhich are
the subject of the present invention, it is thus possible
to lower fairly substantially the baking temperature for
fixing these layers. In fact, in the prior art such a
baking temperature was never lower than approximately
950C. Moreover, the combination of the basal layer con-
sisting of the layer of opaque slip and of the opaque
layer may be applied so as to produce a layer with a mean
thickness of approximately 80 microns. In the conventional
prior art involving application with a brush, it was im-
possible, strictly speaking, to attain thicknesses below
approximately 120 microns.
The heat treatment for fixing the layer of opaque
slip and the opaque layer generally requires two succes-
sive bakings. However, when the glass frits required toproduce the opaque slip and opaque layers are deposited
with the aid of an aerosol composition containing, for
example, a cyanoacrylic glue, it is possible to fix the
combination of the opaque layers and of the successive
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layers during the same baking. Immediately after the
spraying, the propellant gas and the solvents disappear
rapidly and the glue acts as a fixer for the layers on the
reinforcement. The solvent or the plasticizer sprayed
when the successive layers, of dentine, incisal and trans-
parent compositions, are deposited is chosen such that it
does not dissolve a glue of this type. Consequently, the
basal layers are not affected by the deposition of the
following layers, and it is thus poss;ble to fix all the
ceramic layers during a single baking, which represents
a considerable saving in time. ~t should also be noted
that the lowest temperatures for baking the basal layers
are thus brought close to those of the other layers and,
in fact, make it possible to envisage a single baking of
the ~hole of the ceramo-metallic prosthesis.
Naturallv, the present invention is not restricted
in any way to the examples of embodiment described above,
but it is perfectly possible, without departing from the
scope of the present invention thereby, to envisage a
2~ number of alternative embodiments thereof.
