Note: Descriptions are shown in the official language in which they were submitted.
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A METHOD FOR THE MANUFACTURE OF A PRIM:tN(~ MATERI~L
The invention relates to a method for the manufacture of a
priming material for the o~erlayinq or coating of a metallic
tooth crown or bridge, and also to a priming material which
contains a matrix-forming glass powder and an opacifier.
When manufacturing metal tooth crowns and bridges which are faced
with plastics or ceramic material, it is necessary to overlay ~he
metal framework with a priming material - a ~called opaquer -
in order that the dark metallic ground is covered and the metal
does not gleam through. Without such an opaquer the colour of
the finished facing, which is to match the colour of the
remainder of the denture as closely as possible, cannot be
exactly reproduced.
Known from DE-PS 33 32 179 are priming materials for dental
purposes based on polymerizable methacrylic acid esters which
contain a mixture of titanium dioxide and zirconium dioxide as
pigment, in which a considerable titanium dioxide content, namely
of up to 50 wt. %, is provided. The priming materials of ~he
examples contain 25 wt.-~ titanium dioxide. They are used to
cover metal frameworks for crowns with plastics facings.
The prior art cited in column 2 of this published document,
namely Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd
edition, New York (1970), Volume 22, 651-653, reveals that the
use of zirconium dioxide as ceramic opacifier and as pigment or
opacifiex for ceramic glazes and enamels was known. There is no
suggestion however that zirconium dioxide be used as an additive
for a metal ceramic opaquer, i.e. for a ceramic, in particular
glass ceramic priming material for the overla~ing of metal crowns
or bridges, where it must be borne in mind that such an opaquer
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must satisfy special requirements. For example, such an opaquer
must be deposited on a crown in thin layers of at most 0.5 mm and
then be capable of being stoved, the crown to be completaly
covered by the brightly gleaming opaquer layer after stoving.
DE-PS 37 43 609 describes a light-permeable glass ceramic which
comprises fine crystals of calcium phosphate which are uniformly
dispersed in a glass matrix based on SiO2-A102-ZrO2. It is
important as bio-material and has advantageous thermal,
electrical and mechanical properties. The glass ceramic is
transparent or semi-transparent. Zirconium dioxide is added as
nucleation or germination agent. The glass ceramic can be used
as adhesive or binder for ceramic mass materials or metals.
There is no reference in this publication to the use of a
zirconium dioxide-containing glass ceramic as opaquer for the
dental sector. What is essential, quite to the contrary, is the
light permeability of the glass ceramic, ~or which reason this
publication teaches precisely the opposite oE what one skilled
in the art expects from an opaquer.
EP-PS 119 062 discloses pasty materials made from porcelain
powder and water with added ceramic particles of a par~icle size
below O.3~. The materials can be used as opaquer for crowns
with porcelain facings.
Known from DE-OS 3 902 771 is a stovable silicatic material for
the manufacture of dentures which serves as connection material
and for the masking of the metallic colour alloy surface. The
object to be achieved should be to provide a silicat~ic material
which consists of a readily flowing base melt and a proportion
of opaquer, the composition and expansion coefficient of which
are set in such a way that it is stovable onto a dental
prosthesis section which can be manufactured from noble metal
alloys of th0 silver/palladium type or from dental non-metal
alloys of the base t~pes nickel/ chromium and cobalt/chromium,
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and forms a gap-free connection to a dental plastics material
after its silanization. The silicatic material proposed here is
distinguished by a high titanium dioxide content (15.0 - 16.5
wt.-%) and relatively small zirconium dioxide contents (4 to 5
wt.-%).
The disadvantages of the opaquers of DE-PS 33 32 179, EP-PS 119
062 and DE-OS 39 02 771 are lack of covering power and adhesion.
In the crown edges sector in particular, the skoving of the known
opaquers is followed by unwanted discolorations which seriously
impair the cosmetics of the succeed;ng facings. This is also
true of the opaquers known to one skilled in the art which have
been commercially available for some time.
~5 The object of the invention is to make available a method for the
manufacture of a priming material for dental purposes, namely for
the overla~ing or coating of dental metal frameworks prior to
facing and also a priming material in particular for ceramics
facings with improved covering power and adhesion, the adhesion
of which both to metal and to the facing ceramic is excellent,
which can be easily applied and stoved and which, particularly
; in the area of the crown edges, reliably covers the metal. The
discolorations occurring above all with NE alloys (non-noble
metal alloys) are also to be avoided after the stoving.
It was now surprisingly discover~d that by adding larger
quantities of zirconium dioxide as opacifier to glass powders one
obtains mixtures from which opa~uers can be manufactured which
have outstanding properties and guarantee a good covering of the
3~ metal framework and good adhesion to the metal and to the facing.
~lthough the said prior art reveals that zirconium dioxid~ was
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known as an opacifier for ceramic glazes, the use of larger
quantities of zlrconium dioxide as primarily ~hesole opacifier
addition to glass powders for the manufacture of an opaquer is
neither known nor suggested. It was, rather, surprising that in
the case of compositions which are free from larger proportions
of titanium dioxide and/or other opacifiers and contain zirconium
oxide as opacifier additi~e to glass powders one obtains opa~uers
which are distinguished by outstanding properties, especially
outstanding covering power and adhesion.
The method according to the invenkion comprises the
use of a mixture which contains a matrix forming glass powder
which is mixed with 10 to 60 wt.-% zirconium dioxide as
opacifier. The composition is free from larger proportions of
titanium dioxide and/or other opacifiers, i.e. the mixture of
glass powder and zirconium dioxide is to contain, at most, 0 to
5 wt.-% titanium dioxide and/or other opacifier.
The glass preferably consists primarily of the oxides o~
sodium, potassium, calcium, barium, boron, aluminium and/or
silicon with a small proportion of titanium, the TiO2 optionally
present being melted in the glass and functioning, not as an
opacifier, but as a germination agent for the crystallization of
leucite. Oxides of cerium and optionally of P and Zr may also
be contained in the glass. The glass preferably contains as main
constituents SiO2, Al203 and K2O, preferably in respective amounts
of 40 to 70 wt.-%, 10 to 25 wt.-% and 8 to 28 wt.-%. Other
glasses can also be used.
To manufacture the glass, the oxide mixture is melted, quenched
in water and worked up in a manner known per se into a fine glass
powder.
In detail, for example, the molten oxide mixture is quenched in
water and ground up in a ball mill. The glass powder is then
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tempered at ca. 900 degrees C, sintering together to form a block
which is quenched in water while still glowing. A granulate
forms which is ground up in an alcohol/water mixture in the ball
mill. The result is a slip which is dried and then passed
through a screen.
This glass powder is mixed with zirconium dioxide. The mixture
is manufactured in the ratio of, at most, 9 parts glass per part
zirconium dioxide. Preferred mixture ratios lie between 4:1 and
1:1.5.
To manufacture the ready-to-use opaquer, the powder mixture is
mixed with a liquid. For example, the powder can be admixed with
distilled water on a ceramic plate to produce an opaquer.
However, other liquids such as glycerin or glycol can also be
used for the admixing process.
In a particularly preferred embodiment, 3 parts by weight glass
are mixed with 2 parts by weight zirconium dioxide and
homogenized with a further 2 parts by weight glycerin on a triple
roll mill.
For application as priming material, the resultant paste is
deposited on a crown with a brush and stoved at temperatures of
between 800 and 1000 degrees C. The result is a covering white
layer which displays no discolorations even at the metal edges,
is distinguished by a high covering power and offers good
adhesion between metal and ceramic. The crown is then faced with
ceramic by conventional methods.
Colour pigments can optionally be added to the powder mixture in
order to endow the stoved opaquer with a tooth colour-like
colour. The colouring substances can also be added during
homogenization, however.
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It is also possible to add other known ceramic powders to the
glass powder in order to vary the coefficient of thermal
expansion (CTE). The CTE value is known to be an important
parameter in metal ceramic facing work and must suit the alloy
which is to be faced.
The zirconium dioxide particles have an average particle size of
1 ~m + 0.2. The zirconium dioxide particles also have a specific
surface of about 1 to 20 mZ/g and a purity o 99% +/- 1.
The following examples explain the invention.
Example ~
Manufacture of a melt A with high CTE:
glass of the following composition was melted in the usual way:
5.95 wt.-% Na20
13.86 wt.-% K20
3.48 wt.-% CaO
1.64 wt.-% BaO
1.36 wt.-% B203
16.09 wt.-% Al203
0.37 wt.-% TiO2
57.25 wt.-% SiO2.
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This glass was quenched in water and ground up in a ball mill
until the average granulation was ca. 80 to lOO um.
The glass powder was then tempered for an hour at 900 degrees C,
sintering together to produce a block which was quenched in water
while still glowing. The resultant granulate was ground up to
an average granulation of below 20 ~ in an alcohol/ water
mixture (1:1) in the ball mill. The grinding time depends on the
size and type of the ball mill.
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For example
200 g coarse glass powder
800 g porcelain balls with 9 mm diameter
100 g distilled water
100 g alcohol
were allowed to run on rolls for 8 hours in a 1-1 porcelain drum.
The resulting slip was dried at 100 degrees C and passed through
a 60-um screen to avoid agglutinated lumps.
60 g of this melt were mixed with 40 g zirconium dioxide with an
average granulation of 1 ~ which is marketed by Magnesium
Elektron under the trade mark "Zirkonoxid SC15".
This mixture was blended with 40 g glycerin to form a paste and
homogenized on a salve triple roll. The homogenized paste was
painted onto a nickel/chromium alloy with a brush and then stoved
at 960 degrees C with a 2-minute holding time. The
result was a covering white matt layer of very good adhesive~
strength which could then be overlaid with ceramic dental
materials. The coating also displayed no discolorations even at
the metal edges.
Samples were burned in order to check the strength and the CTE.
The following values were measured:
Bending strength 143 +/- 11 N/mmZ
Flexural modulus 73000 +/- 6000 N/mm
CTE 100 - 500 degrees C 14.4 x 10 /K
Example 2
Using the melt A referred to in Example 1, a paste was
manufactured according to the following formulation and
homogenized as in Example 1:
g melt A
g zirconium dioxide SC15
g ceramic colour 23264 *
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g ceramic colour 26077 **.
0.5 g ceramic colour 14-R-481 ***
2 g SiO2, BET surface 200 ~/- 25 (Aerosil 200 [R] Degussa)
g glycerin.
- * orange-yellow, based on Zr and V oxide (Degussa)
** yellow-brown, based on Zr, Cr, Fe, Al oxide (Degussa)
*** dark brown, based on Si, Co, Ni, Zn, Fe, Cr, Mn oxide
(Ferro)
A creamy paste was obtained which could be spread well with the
brush. After burning on a nickel/chromium alloy at 960 degrees
C a covering, tooth-coloured layer was obtained the colour of
15 which is the same all over.
Bending strength 161 +/- 23 N/mm
Flexural modulus 67000 ~/- 2000 N/mm
CTE 100 - 500 degrees C 15 x 10 /K.
Example 3
An Ivoclar ceramic powder, usual for metal ceramics, for melt
configuration with a CTE 100-600 degrees C of 13.5 x 106/K, a
25 glass point of 585 degrees C and a dilatometer softening point
of 600 degrees C was ground wet to an average grain size o < 20
r, dried and deagglomerated by screening as described in Example
1. This powder was named GM-DS.
3~ The following mixture was manufactured:
35 g melt A from Example 1
25 g GM-DS
21 g zirconium dioxide SC15
35 14 g ceramic colour 23264
g ceramic colour 26077
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The mixture was intimately m}xed in a ball mill. It was
processed by mixing 1 g of this mixture with water and
depositing on a nickel/chromium alloy with a brush. The
appearance was the same as in Example 2, except that a glossier
surface was obtained. Testing of the CTE value between 100 and
500 degrees C gave a result of 14.5 x 106/K, which shows that
the CTE value can be varied by adding other ceramic materials.
Example 4 (comparative examPle with ~L~a~L~
In order to compare the covering power with other opacifiers, the
following mixture was manufactured and processed as described in
Example 1:
60 g melt A from Example 1
25 g annealed tin dioxide
17 g ceramic colour 23264
11 g ceramic colour 26077
45 g glycerin
Processing of this mixture produced an inadequately covering
layer in which the black oxides of the nickel/chromium alloy
falsified the colour. Because of the high tin dioxide content,
the burning temperature of this mixture was already at 1100
degrees C, which is at the upper limit for the stoving alloys
usual in dental engineering. The mixture also became discoloured
when stored in the light.
Example 5 (comparison with various opacifiers!
In order to compare the covering power wi~h titanium dioxide, a
special glass had to be melted and worked up as indicated in
Example 1 for melt A. The melt~ named melt B, had the following
composition:
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7.12 g Na20
11.82 g K20
3.2 g CaO
1.51 g BaO
1.25 g B203
14.5 g A1203
0.34 g TiO2
59.35 g SiO2
10 The following mixture was manufactured as in Example 1:
70 g melt B
30 g opacifier
15 40 g glycerin
The following table contains the opacifiers used and the test
results for the processing on nickel/chromium alloys:
Opacifier Processing Covering Discoloration
consistency power upon stoving
Titanium
25 diOxide AD good very good dark grey
Titanium
dioxide R-KB-2 good very good grey/brown
Titanium
dioxide RN-56 good very good grey/brown
Precipitated
30 tin oxide pasty inadequate white
Zirconium ~nn
~ dioxide > 1 ~¢ liquid inadequate white
ffh~ Zirconium
silicate pasty inadequate white
The discolorations in the case of the samples with titan.ium
dioxide were uneven and clearly more marked towards the mei~.al
edge, so that this discoloration was unacceptable after stoving.
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The samples with tin oxide, zirconium dioxide > 1 ~ and
zirconium silicate had an inadequate co~ering power and were
likewise not acceptable.
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