U.S. patent application number 16/394739 was filed with the patent office on 2019-08-15 for process for selectively treating the surface of dental ceramic.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Michael Jahns, Jacqueline C. Rolf, Dajana Zimmermann.
Application Number | 20190247152 16/394739 |
Document ID | / |
Family ID | 50433936 |
Filed Date | 2019-08-15 |
![](/patent/app/20190247152/US20190247152A1-20190815-D00000.png)
![](/patent/app/20190247152/US20190247152A1-20190815-D00001.png)
![](/patent/app/20190247152/US20190247152A1-20190815-M00001.png)
United States Patent
Application |
20190247152 |
Kind Code |
A1 |
Jahns; Michael ; et
al. |
August 15, 2019 |
PROCESS FOR SELECTIVELY TREATING THE SURFACE OF DENTAL CERAMIC
Abstract
The invention relates to a process for selectively treating
parts of the surface of a porous dental zirconia article, the
process comprising the steps of providing a liquid composition and
a porous 3-dimensional dental zirconia article having an outer and
inner surface, applying the liquid composition to only a part the
outer surface and/or inner surface of the porous dental zirconia
article, the liquid composition comprising a whitening agent
comprising a phosphorous containing component, the phosphorous
containing component comprising a phosphate, phosphone or phosphine
moiety, with the proviso that at least one P-O unit of the
phosphate, phosphone or phosphine moiety is dissociable or able to
otherwise interact with zirconia. The invention also relates to a
dental zirconia article obtainable or obtained by such a process
and a kit of parts comprising a container containing a certain
liquid composition and a dental zirconia mill blank useful for
producing a porous dental zirconia article.
Inventors: |
Jahns; Michael; (Gilching,
DE) ; Rolf; Jacqueline C.; (River Falls, WI) ;
Zimmermann; Dajana; (Amersee, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Family ID: |
50433936 |
Appl. No.: |
16/394739 |
Filed: |
April 25, 2019 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15128637 |
Sep 23, 2016 |
|
|
|
PCT/US2015/021247 |
Mar 18, 2015 |
|
|
|
16394739 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 41/009 20130101;
A61K 6/818 20200101; A61C 13/0006 20130101; C04B 41/5092 20130101;
A61K 6/802 20200101; A61C 7/00 20130101; A61C 13/082 20130101; A61C
19/066 20130101; C04B 41/009 20130101; C04B 41/5092 20130101; B05D
3/108 20130101; B05D 3/12 20130101; C04B 2111/00836 20130101; A61C
13/081 20130101; C04B 38/00 20130101; A61C 5/77 20170201; A61C
8/0048 20130101; C04B 41/4572 20130101; C04B 35/48 20130101; B05D
1/28 20130101; C04B 2111/80 20130101; C04B 41/85 20130101; A61C
8/0015 20130101 |
International
Class: |
A61C 8/00 20060101
A61C008/00; A61C 13/08 20060101 A61C013/08; A61K 6/02 20060101
A61K006/02; A61C 13/00 20060101 A61C013/00; B05D 3/12 20060101
B05D003/12; A61C 19/06 20060101 A61C019/06; B05D 1/28 20060101
B05D001/28; B05D 3/10 20060101 B05D003/10; A61C 5/77 20060101
A61C005/77; A61C 7/00 20060101 A61C007/00; C04B 41/85 20060101
C04B041/85; C04B 41/50 20060101 C04B041/50; C04B 41/00 20060101
C04B041/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 25, 2014 |
EP |
14161480.0 |
Claims
1. A kit of parts comprising: a container containing a liquid
composition, wherein the liquid composition comprises a whitening
agent comprising a phosphorous containing component, the
phosphorous containing component comprising a phosphate, phosphone
or phosphine moiety, wherein at least one P-O unit of the
phosphate, phosphone or phosphine moiety is dissociable or able to
interact with zirconia; a dental zirconia mill blank useful for
producing a porous dental zirconia article.
2. A kit of parts of claim 1 further comprising an instruction of
use.
3. A kit of parts of claim 1 further comprising a receptacle
containing a colouring liquid;
4. A kit of parts of claim 1 further comprising an application
device.
5. A device comprising: at least one compartment (A) containing the
liquid composition, wherein the liquid composition comprises a
whitening agent comprising a phosphorous containing component, the
phosphorous containing component comprising a phosphate, phosphone
or phosphine moiety, wherein at least one P-O unit of the
phosphate, phosphone or phosphine moiety is dissociable or able to
interact with zirconia; and at least one compartment (B) containing
a colouring liquid comprising a solvent and colouring ions; and an
instruction of use for selectively treating parts of a porous
dental zirconia article; wherein compartment (A) and compartment
(B) are separated from each other by a pre-defined break zone.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a process for selectively treating
parts of the surface of a porous dental zirconia article. The
invention also relates to a liquid composition which can be used in
such a process, wherein the composition comprises a liquid and a
whitening agent.
BACKGROUND ART
[0002] A dental ceramic can be coloured or opacified e.g. by
incorporating pigments into the ceramic material from the very
beginning or using metal salts containing solutions which are
applied on the surface of a porous dental ceramic article with the
aim to colour the dental ceramic article in its entirety. Colouring
solutions are described in a couple of documents:
[0003] WO 00/46168 (corresponding to U.S. Pat. No. 6,709,694)
refers to colouring ceramics by way of ionic or complex-containing
solutions containing defined concentrations of at least one salts
or complexes of the rare earth elements or of the elements of the
subgroups. The solution might contain additives like stabilizers,
complex builders, pigments and beating additives.
[0004] WO 2004/110959 (3M IPC) relates to a colouring solution for
ceramic framework. The solution comprises a solvent (e.g. water), a
metal salt and polyethylene glycol having a Mn in the range of
1.000 to 200.000.
[0005] WO 2008/098157 (3M IPC) relates to a colouring solution for
dental ceramic framework comprising a solvent, a colouring agent
comprising metal ions, and a complexing agent, wherein the amount
of complexing agent is sufficient to dissolve the colouring agent
in the solvent.
[0006] WO 2009/014903 (3M IPC) relates to a colouring solution for
dental ceramic articles, the solution comprising a solvent and a
colouring agent comprising rare earth element ions being present in
the solution in an amount of at least 0.05 mol/l solvent and
transition ions being present in the solution in an amount of
0.00001 to 0.05 mol/l solvent.
[0007] WO 2013/055432 (3M IPC) relates to aerogels, calcined and
crystalline articles and methods of making the same are described.
The content of this application is herewith incorporated by
reference.
[0008] WO 2013/022612 (3M IPC) relates to colouring solutions for
selectively treating the surface of dental ceramic articles. The
solution comprises a solvent being miscible with water but not
being water, an effect agent and a complexing agent.
[0009] Whitening agents are typically used to cover the metallic
surface of a metallic dental framework in order to give the final
dental restoration a more natural appearance. In certain cases, it
can, however, also be desirable to opacify e.g. the inner surface
of a ceramic framework to cover discolourations of the tooth
stump.
[0010] In this respect WO 2013/070451 (3M IPC) describes a process
for selectively treating parts of the surface of a porous dental
ceramic using a composition comprising a liquid being miscible with
water, but not being water, a whitening agent comprising nano-sized
metal oxide particles, metal ion containing components or mixtures
thereof which precipitate if the composition is adjusted to a pH
above 5.
[0011] The present invention is intended to improve the known
colouring and/or whitening processes.
SUMMARY OF THE INVENTION
[0012] In particular, it would be desirable to have a liquid
composition, which can be used to selectively treat specific parts
of the surface of porous dental ceramic in a simple and inexpensive
way.
[0013] Moreover, it would be desirable if this can be done without
a complete diffusion of the composition into the pores of
pre-sintered or porous dental ceramic, so that a defined
application of the composition can be accomplished.
[0014] At least one of these objects can be achieve by providing a
process of selectively treating parts of the surface of a porous
dental ceramic comprising the steps of
[0015] a) providing a liquid composition and a porous 3-dimensional
dental zirconia article having an outer and inner surface,
[0016] b) applying the liquid composition to only a part the outer
and/or inner surface of the porous dental zirconia article,
[0017] c) optionally drying the porous dental ceramic, and
[0018] d) optionally firing the porous dental ceramic,
the liquid composition comprising [0019] a whitening agent
comprising a phosphorous containing component, [0020] the
phosphorous containing component comprising a phosphate (PO4),
phosphone (PO3) or phosphine moiety (PO2), with the proviso that at
least one P-O unit of the phosphate, phosphone or phosphine moiety
is dissociable or able to bind to the zirconia surface of the
dental zirconia article (e.g. by forming a complex) leading to a
localized opacifying effect once the zirconia article is
sintered.
[0021] The invention is also related to a kit of parts comprising
[0022] the a receptacle containing the liquid composition described
in the present text, [0023] a dental zirconia mill blank useful for
producing a porous dental zirconia article as described the present
text, [0024] optionally an instruction of use, [0025] optionally a
receptacle containing a colouring liquid, and [0026] optionally an
application device.
[0027] A further aspect of the invention is directed to the use of
the liquid composition as described in the present text for
selectively treating parts of the surface of a porous dental
zirconia restoration.
[0028] In another aspect, the invention relates to a dental ceramic
treated with the composition or obtainable by the process described
in the present text.
Yet a further aspect of the invention is directed to a device
comprising [0029] at least one compartment (A) containing the
liquid composition as described in the present text; [0030] at
least one compartment (B) containing a colouring liquid as
described in the present text; and [0031] an instruction of use for
conducting the process as described in the present text.
compartment (A) and compartment (B) being separated from each other
by a pre-defined break zone.
[0032] FIG. 1 shows sintered zirconia discs to which liquid
compositions described in the present text have been applied.
[0033] FIG. 2 shows a device enabling the practitioner to provide
and apply a liquid composition as described in the present text
comprising in addition a colouring liquid.
[0034] Unless defined otherwise, for this description the following
terms shall have the given meaning:
[0035] The term "dental article" is to be understood as an article
which can and is to be used in the dental field. In this respect,
the dental article shall have sufficient strength. Examples include
inlays, onlays, veneers, crowns, abutments, bridges (including 2
parts, 3 parts, 4 parts, 5 parts or 6 parts bridges) and frameworks
forming the support structure for a crown or bridge.
[0036] The dental article has usually a 3-dimensional inner and
outer surface including convex and concave structures. Compared to
other articles such as pottery or paving stones, the dental article
is small and filigree. The thickness of the dental article can vary
from very thin, e.g. at the edges and rims (below 0.1 mm) to
considerably thick, e.g. in the biting area (up to 7 mm).
Typically, the dental article described in the present text
comprises or essentially consists after sintering of a
polycrystalline ceramic material comprising Yttrium stabilized
ZrO.sub.2.
[0037] Examples of dental articles include crowns (including
monolithic crowns), bridges, inlays, onlays, veneers, facings,
copings, crown and bridged framework, implants, abutments,
orthodontic appliances (e.g. brackets, buccal tubes, cleats and
buttons) and parts thereof. The surface of a tooth is considered
not to be a dental article.
[0038] A dental article should not contain components which are
detrimental to the patient's health and thus free of hazardous and
toxic components being able to migrate out of the dental
article.
[0039] "Zirconia ceramic article" shall mean a 3-dimensional
article wherein at least one the x, y, z dimension is at least 5
mm, the article being comprised of at least 80 wt.-% or at least 90
wt.-% zirconia.
[0040] "Ceramic" means an inorganic non-metallic material that is
produced by application of heat. Ceramics are usually hard, porous
and brittle and, in contrast to glasses or glass ceramics, display
an essentially purely crystalline structure.
[0041] "Monolithic dental restoration" shall mean a dental article
onto the surface of which no facing or veneer has been attached.
That is, the monolithic dental restoration is essentially comprised
out of only one material composition. However, if desired a thin
glazing layer can be applied.
[0042] A "liquid composition" is any substance which is able to
solubilise, dissolve or disperse the whitening agent. The liquid
should be sufficiently chemically stable if combined with the
whitening agent. That is, the liquid shall not be decomposed by the
other components present in the composition. Depending on the
chemical nature of the whitening agent, the liquid composition and
the white agent can be identical.
[0043] A "whitening agent" is an agent, which is able to whiten the
surface of a dental article either right after treatment of the
article with the whitening agent or after conducting a firing step
of the treated article. The whitening effect typically goes along
with an increase in opacity.
[0044] "Soluble" means that a component (solid) can be completely
dissolved within a solvent. That is, the substance is able to form
individual molecules (like glucose) or ions (like sodium chloride)
or non-settling particles (like a sol) when dispersed in water at
23.degree. C. The solution process, however, might take some time,
e.g. stirring the composition over a couple of hours (e.g. 10 or 20
h) might be required.
[0045] More specifically, according to the invention a substance or
composition is defined as "soluble", if less than 10 wt.-% or less
than 5 wt.-% or less than 2 wt.-% or less than 1 wt-% or less than
0.1 wt.-% (with respect to the whole composition) of solid
substance remains after the following procedure: [0046] a. 800 mg
of substance and 8.0 g of solvent are placed into a centrifuge test
tube of known weight. [0047] b. The test tube is closed and shaken
for 60 minutes. [0048] c. The mixture is centrifuged with
centrifugal acceleration (ac) of 9870 m/s.sup.2 for 20 min. [0049]
d. The supernatant liquid is decanted. [0050] e. The precipitate is
re-suspended with 6 g solvent. [0051] f. The test tube is shaken
for 60 min, centrifuged as described above, and the supernatant
liquid decanted again. [0052] g. Steps e) and f) are repeated one
time. [0053] h. The remaining precipitate is calcined for 12 h at
500.degree. C. (+/-3.5.degree. C.). [0054] i. After cooling to room
temperature the dry weight of the sample is determined and used for
calculating the soluble fraction.
[0055] A substance or composition is defined as "insoluble", if
more than 90 wt.-% or more than 50 wt.-% or more than 25 wt.-% or
more than 10 wt.-% (with respect to the whole composition) of
substance remains unsolved after the procedure described above.
[0056] The term "water-miscible" or "miscible with water" means
that a certain liquid is miscible with water at 23.degree. C. at
least to a high extend to provide a homogeneous solution, i.e.
without phase separation. More specifically, the water-miscible
liquid is defined as miscible with water if at least 10 g or at
least 100 g or at least 500 g or at least 750 g or least 1000 g
water-miscible liquid is soluble in 1000 g water without phase
separation. Ideally, no phase separation occurs at ambient
conditions independent from the mixing ratio (e.g. ethanol is
miscible with water in all ratios).
[0057] The term "amount sufficient to dissolve" describes the
amount of an agent needed to fully dissolve a certain substance in
a certain solvent so that a storage stable composition can be
obtained. The time needed to dissolve a substance is not
particularly limited, however, the dissolution should occur within
a reasonable time (e.g. within 10 to 48 h) using common equipment
like mechanical stirrers and heaters.
[0058] A component being described as being "dissociable" means
that the component contains at least one moiety being able to
generate ionic compounds e.g. like a salt or acid if dissolved in
water.
[0059] A solution can be classified as "storage stable", if it
remains stable over a considerable long period of time (at least 4
weeks to more than 12 months under ambient conditions). A storage
stable solution typically does not show any visible (visible to the
human eye) precipitation of the colouring agent during storage at
ambient conditions (23.degree. C., 1013 mbar) and does not show
decomposition of the solution or precipitation of single or
multiple components.
[0060] A "complex", also known as coordination compound, in
chemistry usually is used to describe molecules or ensembles formed
by the combination of ligands and metal ions. Originally, a complex
implied a reversible association of molecules, atoms, or ions
through weak chemical bonds. As applied to coordination chemistry,
this meaning has evolved. Some metal complexes are formed virtually
irreversibly and many are bound together by bonds that are quite
strong. The ions or molecules surrounding the metal are called
ligands. Ligands are generally bound to a metal ion by a
coordinative bonding (donating electrons from a lone electron pair
to the Lewis acidic metal center), and are thus said to be
coordinated to the ion. Those ligands are referred to as
"coordinating ligands".
[0061] "Localized opacifying effect" means that the opacifying
effect is only visible after sintering (to the human eye) in those
areas to which the liquid composition has been applied. "Rare earth
elements" and/or of the subgroups of the rare earth elements
include Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.
[0062] "Transition metals" comprise the metals listed in the
columns of the Periodic Table of Elements starting with the
elements Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn and the metals
listed below those elements.
[0063] Metals of the main groups comprise the metals listed in the
main groups of the Periodic Table of Elements starting with the
elements Li, Be, B, C, N, O, F and the metals listed below those
elements.
[0064] A dental ceramic or dental article is classified as
"pre-sintered" if the dental ceramic has been treated with heat
(temperature range from 900 to 1100.degree. C.) for 1 to 3 h to
such an extent that the raw breaking resistance of the dental
ceramic measured according to the "punch on three ball test" ISO
6872 is within a range of 15 to 55 MPa or 30 to 50 MPa. A
pre-sintered dental ceramic usually has a porous structure and its
density (usually 3.0 g/cm.sup.3 for an Yttrium stabilized ZrO.sub.2
ceramic) is less compared to a completely sintered dental ceramic
framework (usually 6.1 g/cm.sup.3 for an Yttrium stabilized
ZrO.sub.2 ceramic).
[0065] A dental ceramic or dental article is classified as
"absorbent", if the dental ceramic is able to absorb a certain
amount of a solvent, comparable to a sponge. The amount of solvent
which can be absorbed depends e.g. on the chemical nature of the
dental ceramic framework, the viscosity of the solvent, the
porosity and pore volume of the dental ceramic.
[0066] A "porous material" refers to a material comprising a
partial volume that is formed by voids, pores, or cells in the
technical field of ceramics. Accordingly an "open-celled" structure
of a material sometimes is referred to as "open-porous" structure,
and a "closed-celled" material structure sometimes is referred to
as a "closed-porous" structure. It may also be found that instead
of the term "cell" sometimes "pore" is used in this technical
field. The material structure categories "open-celled" and
"closed-celled" can be determined for different porosities measured
at different material samples (e.g. using a mercury "Poremaster
60-GT" from Quantachrome Inc., USA) according to DIN 66133. A
material having an open-celled or open-porous structure can be
passed through by e.g. gases.
[0067] The "average connected pore diameter" means the average size
of the open-celled pores of a material. The average connected pore
diameter can be calculated as described in the Examples
section.
[0068] "Glass" means an inorganic non-metallic amorphous material
which is thermodynamically an under-cooled and frozen melt. Glass
refers to a hard, brittle, transparent solid. Typical examples
include soda-lime glass and borosilicate glass. A glass is an
inorganic product of fusion which has been cooled to a rigid
condition without crystallizing. Most glasses contain silica as
their main component and a certain amount of glass former. The
porous ceramic dental material described in the present text does
not contain a glass.
[0069] "Glass-ceramic" means an inorganic non-metallic material
where one or more crystalline phases are surrounded by a glassy
phase so that the material comprises a glass material and a ceramic
material in a combination or mixture. It is formed as a glass, and
then made to crystallize partly by heat treatment. Glass ceramics
may refer to a mixture of lithium-, silicon-, and aluminium-oxides.
The porous dental material described in the present text does not
contain a glass-ceramic.
[0070] "Sol" refers to a continuous liquid phase containing
discrete particles having sizes in a range from 1 nm to 100 nm.
[0071] "Diafiltration" is a technique that uses ultrafiltration
membranes to completely remove, replace, or lower the concentration
of salts or solvents from solutions containing organic molecules.
The process selectively utilizes permeable (porous) membrane
filters to separate the components of solutions and suspensions
based on their molecular size.
[0072] The term "aerogel" shall mean a three-dimensional low
density (i.e., less than 20% of theoretical density) solid. An
aerogel is a porous material derived from a gel, in which the
liquid component of the gel has been replaced with a gas. The
solvent removal is often done under supercritical conditions.
During this process the network does not substantially shrink and a
highly porous, low-density material can be obtained.
[0073] "Isotropic sintering behaviour" means that the sintering of
a porous body during the sintering process occurs essentially
invariant with respect to the directions x, y and z. "Essentially
invariant" means that the difference in sintering behaviour with
respect to the directions x, y and z is in a range of not more than
+/-5% or +/-2% or +/-1%.
[0074] The term "tubular reactor" refers to the portion of a
continuous hydrothermal reactor system that is heated (i.e., the
heated zone). The tubular reactor can be in any suitable shape. The
shape of the tubular reactor is often selected based on the desired
length of the tubular reactor and the method used to heat the
tubular reactor. For example, the tubular reactor can be straight,
U-shaped, or coiled. The interior portion of the tubular reactor
can be empty or can contain baffles, balls, or other known mixing
techniques.
[0075] "Casting" means a manufacturing process by which a liquid
material (e.g. solution or dispersion) is poured into a mould,
which contains a hollow cavity of the desired shape, and then
allowed to solidify.
[0076] The term "calcining" refers to a process of heating solid
material to drive off at least 90 percent by weight of volatile
chemically bond components (e.g., organic components) (vs., for
example, drying, in which physically bonded water is driven off by
heating). Calcining is done at a temperature below a temperature
needed to conduct a pre-sintering step.
[0077] The terms "sintering" or "firing" are used interchangeably.
A pre-sintered ceramic article shrinks during a sintering step,
that is, if an adequate temperature is applied. The sintering
temperature to be applied depends on the ceramic material
chosen.
[0078] For ZrO2 based ceramics a typical sintering temperature
range is 1100.degree. C. to 1550.degree. C. Sintering typically
includes the densification of a porous material to a less porous
material (or a material having less cells) having a higher density,
in some cases sintering may also include changes of the material
phase composition (for example, a partial conversion of an
amorphous phase toward a crystalline phase). Sintering of firing
means making objects from a compressed powder by heating the
material (typically below its melting point--solid state sintering)
until its particles adhere to each other.
[0079] By "dental milling block" or "dental mill blank" is meant a
solid block (3-dim article) of material from which a dental article
can be machined. A dental milling block has typically a
geometrically defined shape. A dental milling block may have a size
of 20 mm to 30 mm in two dimensions, for example may have a
diameter in that range, and may be of a certain length in a third
dimension. A block or blank for making a single crown may have a
length of 15 mm to 30 mm, and a block or blank for making bridges
may have a length of 40 mm to 80 mm. A typical size of a block or
blank as it is used for making a single crown has a diameter of 24
mm and a length of 19 mm. Further, a typical size of a block or
blank as it is used for making bridges has a diameter of 24 mm and
a length of 58 mm. Besides the above mentioned dimensions, a dental
milling block may also have the shape of a cube, a cylinder or a
cuboid. Larger milling blocks may be advantageous if more than one
crown or bridge should be manufactured out of one blank. For these
cases, the diameter or length of a cylindric or cuboid shaped mill
blank may be in a range of 80 to 200 mm, with a thickness being in
the range of 10 to 30 mm.
[0080] By "machining" is meant milling, grinding, drilling,
cutting, carving, or substractive shaping a material by a machine.
Milling is usually faster and more cost effective than grinding. A
"machinable article" is an article having a 3-dimensional shape and
having sufficient strength to be machined.
[0081] "Density" means the ratio of mass to volume of an object.
The unit of density is typically g/cm.sup.3. The density of an
object can be calculated e.g. by determining its volume (e.g. by
calculation or applying the Archimedes principle or method) and
measuring its mass.
[0082] The volume of a sample can be determined based on the
overall outer dimensions of the sample. The density of the sample
can be calculated from the measured sample volume and the sample
mass. The total volume of the ceramic material can be calculated
from the mass of the sample and the density of the used material.
The total volume of cells in the sample is assumed to be the
remainder of the sample volume (100% minus the total volume of
material).
[0083] A "powder" means a dry, bulk solid composed of a large
number of very fine particles that may flow freely when shaken or
tilted.
[0084] A "particle" means a substance being a solid having a shape
which can be geometrically determined. Particles can typically be
analysed with respect to e.g. grain size or diameter. The mean
particle size of a powder can be obtained from the cumulative curve
of the grain size distribution and is defined as the arithmetic
average of the measured grain sizes of a certain powder mixture.
Respective measurements can be done using commercially available
granulometers (e.g. CILAS Laser Diffraction Particle Size Analysis
Instrument).
[0085] Adding an "(s)" to a term means that the term should include
the singular and plural form. E.g. the term "additive(s)" means one
additive and more additives (e.g. 2, 3, 4, etc.).
[0086] The term "comprising" includes also the more limited
expressions "consisting essentially of" and "consisting of". All
single values or values of numerical ranges are deemed to be
modified with the term "about".
[0087] "Ambient conditions" mean the conditions which the inventive
solution is usually subjected to during storage and handling.
Ambient conditions may, for example, be a pressure of 900 to 1100
mbar, a temperature of -10 to 60.degree. C. and a relative humidity
of 10 to 100%. In the laboratory ambient conditions are adjusted to
23.degree. C. and 1013 mbar.
[0088] As used herein, "a", "an", "the", "at least one" and "one or
more" are used interchangeably. The terms "comprises" or "contains"
and variations thereof do not have a limiting meaning where these
terms appear in the description and claims. Also herein, the
recitations of numerical ranges by endpoints include all numbers
subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75,
3, 3.80, 4, 5, etc.).
DETAILED DESCRIPTION
[0089] In the dental field, water-based colouring liquids are
commonly used for colouring especially zirconia based dental
framework in a pre-sintered or porous stage. This is typically
achieved by dipping the framework into a colouring solution in its
entirety. By doing so, a homogenous colour of the whole dental
framework is usually achieved.
[0090] However, if individual colouration or whitening in small
defined areas is desired, the water-based liquids of the prior art
cannot be used because the different colours typically will mix up
and diffuse into parts of the ceramic article where they are not
supposed to be present.
[0091] The liquid composition described in the present text solves
this problem by allowing a dental technician to selectively apply a
whitening agent to parts of the surface of a dental article e.g. by
using a brush.
[0092] The liquid composition is used for being applied selectively
to only parts of the surface of a dental article. That is, the
composition is only applied to parts of the surface of the dental
ceramic article but not to the whole (inner and outer) surface. In
contrast to commercially available colouring liquids, the dental
article is not dipped completely into the composition described in
the present text.
[0093] It was found that the whitening agent remains on the spot or
area of the surface where the liquid composition has been applied
to and does typically not diffuse through the rest of the material
of the porous dental article.
[0094] Thus, the invention enables the local and specific
application of a whitening agent to selective parts of the surface
of a dental article. It allows an exact whitening of individual
parts of the surface of a dental article. This may facilitate the
imitation of white spots, which can sometimes be found on natural
teeth.
[0095] If desired, the composition can also be used to apply an
opaque surface layer to the inner and/or outer surface of a
translucent dental article, especially dental frameworks or dental
monolithic ceramic restorations.
[0096] The painted features remain essentially sharp, even if the
bulk of the dental article is still wet from a previous colouring
step.
[0097] Thus, the liquid composition can also be applied to the
surface of wetted dental article(s), which have already been
coloured by using a commercially available water-based colouring
liquid, without the risk of the whitening agent spreading
indiscriminately due to diffusion.
[0098] If desired, the whitening impression produced by the liquid
composition in the material can be further adjusted by diluting the
liquid composition with a dilution liquid or simply with more
solvent.
[0099] Moreover, it was found that the liquid composition(s) remain
stable over a considerable long period of time. They typically do
not show visible (to the human eye) precipitation of the whitening
agent during storage at ambient conditions (23.degree. C., normal
pressure).
[0100] Surprisingly, it has been found that the desired opacifying
effect can only be achieved by using a whitening agent with the
phosphorous containing components described in the present text,
but not by using other components containing sulfate, nitrate,
chloride or acetate moieties.
[0101] Without wishing to be bound by a certain theory, it is
believed that upon contact of the phosphorous containing component
of the whitening agent with the zirconia of the porous dental
article, a reaction takes place, which after sintering may result
in a different crystal phase of the zirconia material.
[0102] It was found that for whitening agent(s) comprising
phosphorous containing component(s) the interaction between the
zirconia takes place in particular in the surface region. Thus, the
whitening agent essentially remains on that location to which it
has been applied and does not migrate into the remaining part of
the porous zirconia article.
[0103] Other embodiments, features and advantages of the present
invention will be apparent from the following detailed description,
drawings, and claims.
[0104] The liquid composition typically has an adequate viscosity
so that a sufficient amount of composition can be applied to the
surface of the porous dental article.
According to one embodiment, the liquid composition has a viscosity
above 10 or above 50 or above 100 mPa*s (measured at 23.degree. C.
with a shear rate of 50 s.sup.-1). The viscosity of the composition
is typically below 10,000 or below 5,000 or below 2,000 mPa*s
(measured at 23.degree. C. with a shear rate of 50 s.sup.-1).
[0105] Typical viscosity ranges include from 10 to 10,000 or from
20 to 8,000 or from 50 to 5,000 mPa*s (measured at 23.degree. C.
with a shear rate of 50 s.sup.-1).
[0106] If the viscosity of the composition is too high, the
whitening agent might not be able to enter the pores of the ceramic
material at all. On the other hand, if the viscosity of the
composition is too low, the whitening agent might diffuse through
the pores too much.
[0107] If desired, the measurement of the viscosity can be done as
follows: A viscosimeter MCR300 (from Anton Paar Comp.) is used. A
portion of the composition is placed between two steel discs with a
diameter of 8 mm and a gap of 1 mm at a temperature of 23.degree.
C. The gap is filled completely with the composition. Excess
composition is removed. The shear rate between the rotating discs
d(gamma)/dt is set constantly to 50 s.sup.-1. The measurement is
done 500 s after starting the shearing process of the
composition.
[0108] Thus, the composition is in the form of a liquid which can
be applied onto the surface of either a dry or wet, optionally
pre-coloured, porous zirconia based dental article.
[0109] If the porous zirconia article is already wetted, the
composition will solve into the geometry within minutes and
disappear from the surface.
[0110] If the liquid composition is used in excess, not all of it
will migrate into the pores of the porous zirconia based material.
The composition remaining on the surface can be wiped off, if
desired, before or after sintering without problems. In one
embodiment the composition is transparent.
[0111] A composition can be characterized as transparent within the
meaning of the invention if a beam of visible light (400 to 700 nm)
is not scattered by the solution and the solution does not appear
to be turbid. Providing a transparent composition can be desirable
in that the whitening agent being contained in the composition is
either a real solution (e.g. dissociation into ions) or a
dispersion (e.g. particle size smaller than wavelength of visible
light).
[0112] The liquid composition described in the present text
comprises a whitening agent.
The whitening agent comprises a phosphorous containing component.
The phosphorous containing component comprises a phosphate,
phosphone or phosphine moiety. The whitening agent is typically
water-soluble. The whitening agent can be a liquid or a solid (e.g.
salt).
[0113] Examples of phosphorous containing components include acids
and salts comprising one or more phosphate, phosphone or phosphine
moieties and mixtures of acids and salts thereof.
[0114] At least one P-O unit of the phosphate, phosphone or
phosphine moiety needs to be dissociable or able to otherwise
interact with zirconia, e.g. by forming a complex.
[0115] According to one embodiment, the phosphorous containing
component is characterized by formula (1):
(R1O)(R2)(R3)P.dbd.X, (1) [0116] with X being O or S, [0117] R1
being H, NH.sub.4, a metal ion (e.g. Na, K or Li) or an organic
moiety (including C1 to C4 alkyl, phenyl, acetoxy), [0118] R2 and
R3 being independently selected from R1 or OR1, [0119] with the
proviso that at least one residue R1, R2 or R3 is able to
dissociate from 0 in the liquid composition (e.g. H, NH.sub.4, Na)
or comprises an oxygen-containing functional group which can
interact with a zirconia material (e.g. carboxyl group like
OAc).
[0120] The whitening agent is typically present in the liquid
composition in the following amounts: [0121] Lower amount: at least
5 or at least 10 or at least 20 wt.-%; [0122] Higher amount: up to
60 or up to 50 or up to 40 wt.-%; [0123] Range: from 5 to 60 or
from 10 to 50 or from 20 to about 40 wt.-%; wt.-% with respect to
the amount of the liquid composition.
[0124] If the amount of whitening agent contained in the liquid
composition is too low, the effects obtained in the sintered
ceramic article might be too weak for the intended use.
[0125] If, however, the amount of whitening agent contained in the
liquid composition is too high, the composition might become too
viscous or acidic. In addition, properties of the ceramic article,
like e.g. strength, might be influenced in an undesired manner.
[0126] Specific examples of the phosphorous containing component
include H3PO4, alkaline (e.g. Li, Na, K) and ammonium salts of
H3PO4, phosphoric esters (including phosphoric esters containing
saturated or unsaturated organic moieties like phosphoric acid
monoethyl ester, phosphoric acid diethyl ester, phosphoric acid
di-propylester mono ammonium salt) and mixtures thereof.
[0127] If the whitening agent is already in a liquid stage (e.g. an
aqueous solution of a phosphorous containing component like an
aqueous phosphoric acid), the liquid composition can be identical
with the whitening agent.
[0128] Besides the whitening agent, the liquid composition may
further comprise a liquid or solvent. According to one embodiment,
the solvent is water. According to another embodiment, the solvent
is different from water. The liquid or solvent is typically
miscible with water.
[0129] According to one embodiment, the solvent may be
characterized by at least one of the following features: [0130]
molecular weight (Mw): from 18 to 1,000 g/mol or from 60 to 400
g/mol; [0131] viscosity: from 1 to 2,000 mPa*s or from 10 to 1,500
mPa*s or from 100 to 1,000 mPa*s (measured at 23.degree. C. at a
shear rate of 50 s.sup.-1); [0132] free of polymerizable groups
like (meth)acrylate groups, epoxy groups, carbon-carbon unsaturated
groups.
[0133] Mw (substance) is the average molecular weight of the
respective polymer used.
Liquids which can be used include polyalcohols including ethylene
glycol, polyethylene glycols, glycerol and mixtures thereof.
Polyethylene glycols which can be used can be represented by
formula (2)
R1O--(CH2-CH2-O)m-R1 (2)
with R1=H, Acyl, Alkyl, Aryl, Alkylaryl, Polypropylglycol,
Poly-THF, preferably H, Acetyl, Methyl, Ethyl, Propyl, Butyl,
Hexyl, Octyl, Nonyl, Decyl, Lauryl, Tridecyl, Myristyl, Palmityl,
Stearyl, Oleyl, Allyl, Phenyl, p-Alkylphenyl, Polypropyleneglycol,
Poly-THF and m=2 to 100, preferably 2 to 20, more preferably 2 to
5
[0134] The average molecular weight (Mw) of the polyethylene glycol
should be in the range of 100 to 5.000, preferably in the range of
100 to 1.000, more preferably in the range of 100 to 300.
[0135] If desired, the average molecular weight (Mw) can be
determined according to procedures known to a person skilled in the
art as described for example in Arndt/Muller,
Polymercharakterisierung, Hanse Verlag, 1996. Depending on the
molecular weight to be determined, it might be necessary to apply
different measurement methods (see below).
[0136] Most PEGs (polyethylene glycols) include molecules with a
distribution of molecular weights, i.e. they are polydisperse. The
size distribution can be characterized statistically by its weight
average molecular weight (Mw) and its number average molecular
weight (Mn), the ratio of which is called the polydispersity index
(Mw/Mn). Mw and Mn can be measured by mass spectroscopy.
[0137] Specific examples of water-miscible solvent(s), which can be
used, include polyol(s) (including polyvinyl alcohol), glycol
ether(s) (e,g, PEG 200, PEG 400, PEG 600, diethylene glycol methyl
ether, diethylene glycol ethyl ether), alcohol(s) (including
1,2-propanediol, 1,3-propanediol, ethanol, (n- and iso-)propanol,
glycerol), glycerol ether, and mixtures thereof.
In particular, the following solvents were found to be useful:
glycerol, ethylene glycol, propylene glycol and mixtures thereof.
According to one embodiment, the solvent should be able to dissolve
the whitening agent. Dissolving means that the composition does not
contain particles being visible to the human eye.
[0138] The amount of solvent used is not particularly limited
unless the result to be achieved cannot be obtained.
[0139] The liquid can be used in an amount of at least 20 or at
least 50 or at least 70 wt.-% with respect to the whole weight of
the liquid composition.
[0140] There is no particular upper amount, however, the liquid is
typically used up to an amount of up to 98 or up to 96 or up to 90
wt.-% with respect to the whole weight of the liquid
composition.
Useful ranges for the liquid include from 20 to 98 wt.-% or from 50
to 96 wt.-% or from 70 to 90 wt.-% with respect to the whole weight
of the liquid composition.
[0141] The liquid composition may also contain one or more
additive(s).
[0142] Additives which can be added to the composition include
stabilizers (such as methoxy phenol hydrochinone, Topanol A,
ascorbic acid and mixtures thereof), buffers (such as acetate or
amino buffers and mixtures thereof), preservative agents (such as
sorbic acid or benzoic acid and mixtures thereof), soluble
colourants (e.g. colourants which can be added to food) and
mixtures thereof.
[0143] Adding soluble colourants can be beneficial in order to
enhance the visibility of the composition during use, especially,
if the composition is transparent. Thus, the practitioner can
easily determine to which parts of the surface of the dental
ceramic the composition has already been applied and which parts
have not been treated yet and should remain untreated. On the other
hand the soluble colourants which are typically of organic nature
will be burnt during a later sintering step and thus not be
incorporated into the crystal structure of the dental ceramic.
[0144] Examples of soluble colourants which can be used include
Riboflavin (E101), Ponceau 4R (E124), Green S (E142).
[0145] There is no need for additive(s) to be present, however, if
they are present, they are typically present in an amount which is
not detrimental to the purpose to be achieved when applying the
composition.
[0146] If additive(s) are present, they are typically present in an
amount of 0.01 to 10 wt.-% or from 0.05 to 5 wt.-% or from 0.1 to 3
wt.-% with respect to the whole composition.
[0147] According to one embodiment, the liquid composition
comprises the respective components in the following amounts:
[0148] Whitening agent(s): from 5 to 60 or from 6 to 50 or from 7
to 40 wt.-%; [0149] Liquid(s): from 20 to 98 or from 50 to 96 or
from 70 to 90 wt.-%; [0150] Additive(s): from 0 to 10 or from 0.05
to 5 or from 0.1 to 3 wt.-%; wt.-% with respect to the amount of
the liquid composition. The liquid composition can be produced by
simply mixing the components contained therein until a homogeneous
mixture is obtained.
[0151] The liquid composition described in the present text is
applied to the surface of a porous dental article comprising or
preferably consisting essentially of zirconia.
[0152] The term "consisting essentially of" means that the major
part (e.g. greater than 80 or 85 or 90 wt.-%) of the dental ceramic
is based on ZrO2. The rest may be comprised of oxides selected from
HfO2 and stabilizers including Y2O3, CaO, MgO, CeO2 or mixtures
thereof.
[0153] The dental article to which the liquid composition is to be
applied is porous. Moreover, the dental article has an outer and an
inner surface. The outer surface typically has typically an overall
convex shape, whereas the inner surface typically has an overall
concave shape. The dental ceramic onto which the solution is
applied can be dry or wet.
[0154] "Wet" means that the ceramic material still contains a small
amount of water. However, there should be no visible spots of water
residues on the surface.
[0155] A pre-sintered or porous material sample is considered wet,
if the material has been completely dipped into water for 10 s,
removed from the water and wrapped for 10 s into a paper tissue
being able to absorb water or alternatively, if a water-based
solution has been applied to large areas of the material using e.g.
a sponge, a brush, etc.
[0156] The surface of a pre-sintered or porous material sample is
considered dry, if the material has been completely dipped into a
water-based solution for 10 s, removed from the water, wrapped for
10 s into a paper tissue being able to absorb water and placed into
an oven for 1 h at a temperature of 200.degree. C. or left to dry
open to the air for 4 h, or if no water-based solution has been
applied to the pre-sintered or porous ceramic at all.
[0157] According to one embodiment, the porous dental article is a
ZrO2 based article which is stabilized with Y2O3. The dental
article is typically in a pre-sintered stage.
Porous dental zirconia articles can be obtained e.g. by
pre-sintering a compressed zirconia powder.
[0158] Porous dental zirconia articles compositions are known to
the skilled person in the art (examples are described e.g. in WO
00/46168 A1).
[0159] Yttrium doped tetragonal stabilized zirconia powder is
sometimes also referred to as YTZP powder and commercially
available from e.g. Tosoh Comp., Japan.
[0160] The pressure to be applied is typically in the range of 150
to 200 MPa. Alternatively, the applied pressure is set so that the
pressed body reaches a certain density, e.g. in the case of a
zirconia body, a density from 2.8 to 3.2 g/cm3.
[0161] The porous zirconia article obtained according to the above
process can be characterized by at least one of the following
features:
[0162] (a) Not showing a N.sub.2 adsorption and/or desorption
isotherm with a hysteresis loop;
[0163] (b) BET surface: from 2 to 20 m.sup.2/g or from 3 to 14
m.sup.2/g;
[0164] (c) biaxial flexural strength: from 8 to 80 or from 20 to 50
MPa;
[0165] (d) x, y, z dimension: at least 5 mm or at least 10 or at
least 20 mm.
[0166] According to another embodiment, the porous dental article
is a ZrO2 based article shows a N2 adsorption and/or desorption of
isotherm type IV.
[0167] Commercially available Y-TZP ceramic materials typically
show a N2 adsorption and/or desorption of isotherm type II
(according IUPAC classification), which was found to be less
effective for producing an aesthetic dental article in an efficient
way.
Materials showing a type II isotherm are said to be macro-porous,
whereas materials showing a type IV isotherm are said to be
meso-porous.
[0168] The liquid composition is typically absorbed very quickly,
but having the effect that the diffusion of the whitening agent is
essentially limited to those areas to which the liquid composition
has been applied.
[0169] If desired, the dental ceramic article described in the
present text can be further individualized manually, e.g. using a
file, a cutter or carving tool, if desired. The material (before
sintering) is sufficiently hard to allow a precise machining but
not too hard or too strong to prevent manually individualization.
In contrast to this, commercially available zirconia materials are
often too soft and thus allow no precise carving or modelling in a
pre-sintered stage.
[0170] The zirconia material described in the present text shows a
variety of well balanced features (e.g. sufficient strength to be
machined, adequate strength to be manually individualized, reduced
wear of machining tools and/or reduced production of dust during
machining). In contrast to zirconia material described in the art,
the zirconia material described in the present text is more
translucent after sintering. A whitening composition applied to
this material will thus become better visible compared to whitening
compositions applied to less translucent or more opaque zirconia
material. The porous zirconia article shows a N2 adsorption and/or
desorption of isotherm type IV according to IUPAC
classification.
Further, the porous zirconia article typically has a Vickers
hardness from 25 to 150 or from 35 (HV 0.5) to 150 (HV 1).
[0171] According to one embodiment, the porous zirconia article
described in the present text can be characterized by at least one
of the following features: [0172] (a) showing a N.sub.2 adsorption
and/or desorption isotherm with a hysteresis loop; [0173] (b)
showing a N.sub.2 adsorption and desorption of isotherm type IV
according to IUPAC classification and a hysteresis loop; [0174] (c)
showing a N.sub.2 adsorption and desorption isotherm of type IV
with a hysteresis loop of type H1 according to IUPAC
classification; [0175] (d) showing a N.sub.2 adsorption and
desorption isotherm of type IV with a hysteresis loop of type H1
according to IUPAC classification in a p/p.sub.0 range of 0.70 to
0.95; [0176] (e) average connected pore diameter: from 10 to 100 nm
or from 10 to 80 nm or from 10 to 70 nm or from 10 to 50 nm or from
15 to 40; [0177] (f) average grain size: less than 100 nm or less
than 80 nm or less than 60 nm or from 10 to 100 or from 15 to 60
nm; [0178] (g) BET surface: from 10 to 200 m.sup.2/g or from 15 to
100 m.sup.2/g or from 16 to 60 m.sup.2/g; [0179] (h) biaxial
flexural strength: from 10 to 40 or from 15 to 30 MPa; [0180] (i)
Vickers hardness: from 25 (HV 0.5) to 150 or from 35 to 140 (HV 1).
[0181] (j) x, y, z dimension: at least 5 mm or at least 10 or at
least 20 mm.
[0182] A combination of the following features was found to be
particularly beneficial: (a) and (h), or (a) and (b) and (h), or
(b) and (c), or (c), (e), (g) and (h). If desired the above
features can be determined as described in the Example section.
[0183] The BET surface of porous zirconia materials described in
the prior art is typically within a range from 2 to 9 m.sup.2/g,
whereas the BET surface of the porous zirconia materials described
in the present text is preferably above 10 m.sup.2/g.
[0184] The average grain size of the zirconia particles in the
porous zirconia article described in the present text is small
compared to the average grain size of the material of commercially
available zirconia materials.
[0185] A small grain size can be beneficial in that it typically
leads to a more homogeneous material (from a chemical perspective),
which may also result in more homogeneous physical properties.
Useful ranges for the x, y and z dimensions include from 5 to 300
or from 8 to 200 mm.
[0186] It was found that it is beneficial for certain properties,
if the porous zirconia material has a certain average connected
pore diameter. The average connected pore diameter should be in a
particular range. It should not be too small and also not be too
large.
[0187] The porous zirconia material described in the present text
and used for providing the porous dental ceramic article has a
smaller average connected pore diameter than porous zirconia
ceramic material obtained by compacting zirconia powder, like
3Y-TZP powder from Tosoh Comp.
[0188] Due to the nano-scaled particle size and specific average
connected pore diameter of the material used for producing the
porous zirconia ceramic material of the porous dental ceramic
article, this material has a different sintering behaviour compared
to the zirconia ceramic material of dental materials which are
commercially available (e.g. LAVA.TM. Frame from 3M ESPE) and other
zirconia ceramics available on the dental market being typically
produced by compacting and pressing zirconia powder (e.g. 3Y-TZP
zirconia powder from Tosoh Comp.).
[0189] The Vickers hardness of the material is in a particular
range. If the Vickers hardness of the material is too low, the
machinability could fall off in quality (edge chipping or breaking
of the workpiece) as well as in the ease of manual reworking to
individualize the frame of a dental restoration or a monolithic
restoration as well. If the Vickers hardness of the material is too
high, the wear of the machining tools may increase in an uneconomic
range or the tool could break and destroy the workpiece. The
biaxial flexural strength of the material is typically also in a
particular range.
[0190] It was found that if the biaxial flexural strength of the
material is too low, the material tends to crack during the milling
process or during the manual finishing by a dental technician.
[0191] On the other hand, if the biaxial flexural strength of the
material is too high, the processing of the material by a milling
machine is often not possible with reasonable efforts. The milling
tool used or the milled material often tend to chip or break. In
such a case the shaping of the material had to be done by grinding,
e.g. using a Cerec.TM. grinding machine (Sirona).
[0192] The material of the porous zirconia ceramic article can be
characterized by at least one of the following features: [0193]
ZrO2 content: from 70 to 98 mol % or from 80 to 97 mol %; [0194]
HfO2 content: from 0 to 2 mol % or from 0.1 to 1.8 mol %; [0195]
Y2O3 content: from 1 to 15 mol % or from 1.5 to 10 mol % or from 2
to 5 mol %; [0196] Al2O3 content: from 0 to 1 mol % or from 0.005
to 0.5 mol % or from 0.01 to 0.1 mol %. According to a further
embodiment, the porous zirconia article has a composition being
characterized by the following features: [0197] ZrO2 content: from
90 to 98 mol %, [0198] HfO2 content: from 0 to 2 mol %, [0199] Y2O3
content: from 1 to 5 mol %, [0200] Al2O3 content: from 0 to 0.1 mol
%.
[0201] It was found that a higher Y2O3 content typically leads to
an increase of the cubic crystal phase in the zirconia ceramic
material after sintering the material to final density. A higher
content of the cubic crystal phase may contribute to a better
translucency.
[0202] According to a particular embodiment the porous zirconia
article can be characterized by the at least one or more or all of
the following features: [0203] showing a N2 adsorption of isotherm
type IV according to IUPAC classification, [0204] showing a N2
adsorption with a hysteresis loop in a p/p0 range of 0.70 to 0.95,
[0205] average connected pore diameter: from 15 to 60, [0206]
average grain size: less than 100 nm, [0207] BET surface: from 15
to 100 m.sup.2/g or from 16 to 60 m.sup.2/g, [0208] Biaxial
flexural strength: from 10 to 40 MPa, [0209] x, y, z dimension: at
least 5 mm, [0210] Vickers hardness: from 25 to 150, and [0211]
Density: from 40% to 60% of theoretical density.
[0212] The zirconia ceramic dental article described herein may
have an x, y, and z dimensions of at least 3 mm (in some
embodiments, at least 5 mm, 10 mm, 15 mm, 20 mm, or even 25 mm) and
a density of at least 98.5 (in some embodiments, 99, 99.5, 99.9, or
even at least 99.99) percent of theoretical density, wherein at
least 70 mole percent of the crystalline metal oxide is ZrO.sub.2,
and wherein the ZrO.sub.2 has an average grain size less than 400
nanometers (in some embodiments, less than 300 nanometers, 200
nanometers, 150 nanometers, 100 nanometers, or even less than 80
nanometers).
[0213] The zirconia material of the porous dental ceramic article
described in the present text can be obtained by a process
comprising the step of heat treating or calcining a zirconia
aerogel.
[0214] The zirconia aerogel can typically be characterized by at
least one of the following features: [0215] a. comprising
crystalline zirconia particles having an average primary particle
size in a range from 2 nm to 50 nm or from 2 nm to 30 nm or from 2
to 20 or from 2 to 15 nm; [0216] b. content of crystalline zirconia
particles: at least 85 mol.-%; [0217] c. having an organic content
of at least 3 wt.-% or within a range from 3 to 10 wt.-%; [0218] d.
x, y, z dimension: at least 5 or at least 8 or at least 10 or at
least 20 mm. A combination of the features [(a), (b)] or [(a), (c)]
or [(a), (b), (c)] or [(a), (b), (c), (d)] can be preferred.
[0219] The heat treatment of the zirconia aerogel for obtaining the
porous zirconia article is typically done under the following
conditions: [0220] temperature: from 900 to 1100.degree. C. or from
950 to 1090.degree. C.; from 975 to 1080.degree. C.; [0221]
atmosphere: air or inert gas (e.g. nitrogen, argon); [0222]
duration: until a density of 40 to 60% of the final density of the
material has been reached. The heat treatment or calcining can be
conducted in one or more steps. In a first heat treatment step a
binder burn-out could be performed to remove all organic additives
from previous process steps to obtain a so called "white body". In
a second heat treatment step the strength and/or the hardness of
the white-body could be adjusted to the needs of the follow up
processes like machining. In case of a machinable blank the
sintering protocol should reflect the interaction of temperature
with strength and/or hardness.
[0223] If the temperature is too low, the hardness and/or strength
of the resulting article might be too low. This can cause problems
during a later machining step, e.g. with respect to chipping.
[0224] If, on the other hand, the temperature is too high, the
hardness and/or strength of the material may become too high. This
can cause problems during a later machining step as well, e.g. with
respect to the machining tool durability.
[0225] The dwell time (that is the time during which the aerogel is
kept at that temperature) is helpful as well to tune strength
and/or hardness to the specific needs of the chosen machining
technology. The dwell time, however, can also be in a range from 0
to 24 h or from 0.1 to 5 h.
[0226] If the dwell time is too long, the dental mill blanks may
become too hard to be machined under reasonable conditions.
[0227] According to one embodiment, the porous zirconia article can
be obtained by a process comprising the steps of [0228] providing a
zirconia sol comprising crystalline metal oxide particles and a
solvent; [0229] optionally concentrating the zirconia sol to
provide a concentrated zirconia sol; [0230] mixing the sol with a
polymerizable organic matrix (e.g. adding a reactive surface
modifier to the zirconia sol and optionally an initiator being able
to polymerizable surface-modified particles of the zirconia sol);
[0231] optionally casting the zirconia sol into a mould to provide
a casted zirconia sol, [0232] curing the polymerizable organic
matrix of the zirconia sol to form a gel (sometimes also referred
to as gelation step); [0233] removing the solvent from the gel
(e.g. by first removing water, if present, from the gel via a
solvent exchange process to provide an at least partially
de-watered gel; followed by a further extraction step where the
remaining solvent is extracted e.g. via super critical extraction)
to provide the aerogel; [0234] optionally cutting the aerogel into
smaller pieces; [0235] heat-treating the aerogel to obtain a
machinable porous zirconia material or article.
[0236] The process of producing the porous ceramic zirconia
material typically starts with providing a sol of ZrO2
particles.
[0237] To the sol of ZrO2 particles a surface-modifying agent is
added, preferably a crosslinkable surface-modifying agent (e.g. a
radically reactive surface modifier).
[0238] The ZrO2 particles having been surface-modified with a
crosslinkable agent can be polymerized, if desired, to provide a
composition comprising crosslinked ZrO2 particles.
[0239] The crosslinkable surface-modifying agent can be removed
later, e.g. during a calcining and/or pre-sintering step.
[0240] If desired, the sol is casted into a mould. The mould may
have the negative shape of the dental mill block to be provided.
Due to size reduction which may be caused by heat treatments of the
material, the size of the mould is typically larger than the size
of the final dental mill blank. The shape of the mould is not
particularly limited.
[0241] The casted zirconia sol is typically treated with heat or
radiation in order to start polymerization of the reactive surface
modifier. This process usually results in a gel. If present and
desired, water may be removed from the gel, at least partially.
[0242] Remaining solvent of the above described sol/gel process is
removed, e.g. by supercritical extraction techniques resulting in
an aerogel (e.g. in block form). If desired, the aerogel may be cut
into smaller pieces, e.g. having the shape of the dental mill
blank.
[0243] According to a further embodiment, the invention is directed
to a kit of parts comprising [0244] at least one receptacle
containing the liquid composition as described in the present text;
[0245] a porous dental mill blank useful for producing the porous
dental zirconia article as described in the present text; [0246]
optionally at least one receptacle containing a colouring liquid;
[0247] optionally application and mixing appliances; [0248]
optionally an instruction of use describing the process steps to be
conducted to obtain a partially opacified dental restoration.
Examples of receptacles include bottles, wells, tubes and
vessels.
[0249] Colouring solutions for dental ceramics are meanwhile well
known in the art. Examples of colouring solutions are described in
U.S. Pat. No. 6,709,694, US 2006/0117989, WO 2009/014903, EP
application No. 11177189. The content of these references is
herewith incorporated by reference.
[0250] Theses colouring liquids typically comprise water, metal
cations selected from rare earth elements, transition metal and
mixtures thereof (including cations of Fe, Mn, Er, Pr and mixtures
thereof), and sometimes a complexing agent or further additives
like (poly)ethylene glycol. The colouring liquids are typically
used for homogeneously colouring dental ceramics and in particular
porous dental ceramic framework.
[0251] The liquid or solvent being provided in a separate
receptacle enables the practitioner to further individualize or
dilute the composition, especially with respect to its
intensity.
[0252] Examples of application appliances include brushes, sponges,
(hollow) needles, etc.
[0253] Examples of mixing appliances include mixing wells, trays,
plates, slides, etc.
[0254] Sometimes it is desirable to not only apply the liquid
composition containing a whitening agent as described in the
present text to the dental zirconia article, but also to colour the
dental zirconia article.
[0255] Experiments have shown that the whitening agent described in
the present text is typically not compatible with the metal cations
contained in a typical colouring liquid to form a storage stable
composition.
[0256] Thus, the respective liquids or compositions not only need
to be kept separate before use, but also need to be applied in
separate steps. This issue can be addressed with the device as
described below.
[0257] According to a further embodiment, the invention is thus
directed to a device comprising [0258] at least one compartment (A)
containing the liquid composition as described in the present text;
[0259] at least one compartment (B) containing a colouring liquid
as described in the present text; and [0260] an instruction of use
describing process steps to be conducted to obtain a partially
opacified dental zirconia article; compartment (A) and compartment
(B) being separated from each other by a pre-defined break
zone.
[0261] Using such a device is beneficial because it allows reducing
the application steps typically needed for obtaining a partially
coloured and opacified or whitened dental zirconia article. The
application of the whitening agent and a colouring liquid or agent
can be combined in one step.
[0262] On the one hand, the device described in the present text is
suitable to keep the respective liquids or compositions separate
during storage, and on the other hand it enables the practitioner
to mix them shortly before use.
[0263] Further, due to the pre-defined volume of the respective
compartments, the mixing ratio is defined as well resulting in a
reproducible and homogeneous mixture.
[0264] It also allows including the desired type of application
device (e.g. brush or sponge) for the composition to be
applied.
[0265] Compartment (A) and compartment (B) of the device are
arranged to allow mixing of the respective liquids or compositions
contained therein to obtain a coloured composition comprising the
whitening agent. The device may optionally contain an application
device like a brush tip or sponge tip for applying the mixture.
[0266] A suitable device is shown in FIG. 2. The device has at
least two compartments (A) and (B). Compartment (A) is for
receiving or containing the liquid composition described in the
present text. Compartment (B) is for receiving or containing a
colouring liquid as described in the present text. The compartments
are separated from each other by a pre-defined break zone (E1)
which can be opened upon asserting pressure on either of the
compartment. Upon asserting pressure on compartment (A), the
pre-defined breaking zone is opened and the composition or liquid
contained in compartment (A) flows into compartment (B). The
composition or liquid contained in compartment (B) is then mixed
with the composition or liquid which was contained in compartment
(A).
[0267] The device further comprises a pocket (C) separated from
compartment (B) by a pre-defined break zone (E2) similar to the
pre-defined break zone between compartments (A) and (B).
[0268] Upon asserting pressure on compartment (B) and optionally
also on compartment (A), the pre-defined breaking zone (E2) to the
pocket is opened and the mixture flows into the pocket (C) from
which it can be delivered or applied to the desired part(s) of the
surface of the porous dental zirconia article.
[0269] Delivery or application of the mixture (i.e. coloured liquid
composition) can be effected by a brush or sponge tip (D) which can
be contained in the pocket or which can be placed into the pocket,
if desired.
[0270] Examples of devices which can be used for providing a
coloured liquid composition obtained by mixing the liquid
composition described in the present text and a colouring liquid
are described in U.S. Pat. No. 6,105,761 (Peuker et al.) and U.S.
Pat. No. 7,097,075 (Peuker et al.). The content of these references
is herewith incorporated by reference.
[0271] Selectively applying the liquid composition to the surface
of the dental article is usually achieved by painting e.g. using a
brush. However, the composition can also be applied by using
brushes, sponges, (hollow) needles, pens, and by spraying.
[0272] The liquid composition is typically stored in a container or
receptacle before use. Suitable containers include vessels, bottles
and sealed wells
[0273] According to one embodiment the liquid composition is
applied to the surface of the dental zirconia article with a pen,
the pen comprising a housing, a brush tip, a removable cap and a
reservoir for storing the liquid composition described in the
present text.
[0274] The brush tip is typically attached or fixed to the front
end of the housing. The reservoir is typically fixed or attached to
the rear end of the housing. The removable cap is typically used
for protecting the brush tip during storage.
[0275] Using a pen may facilitate the application of the liquid
composition and will help the practitioner to save time. Further, a
pen with a cap will prevent the pen from drying out if not used.
The volume of the reservoir may be in a range from 1 ml to 10 ml or
from 2 ml to 5 ml. The reservoir may be removable or fixed to the
housing of the pen.
[0276] The brush tip typically comprises bristles. The material the
bristles are made of can be selected from artificial or natural
materials. Artificial materials include polyamides (nylon),
polyesters and mixtures thereof. Natural materials usually include
different kinds of animal hair. The brush tip may be removable or
exchangeable, too.
[0277] The length of the brush tip extending from the pen is
typically within a range from 5 to 20 mm or from 8 to 15 mm. If the
bristles are too short, application of the solution to the inside
of a dental restoration may be difficult. If, on the other hand,
the bristles are loo long, the handling of the brush itself might
become impractical for dental applications.
[0278] The thickness of the brush tip at its base is typically in
the range from 0.3 to 5 mm or from 1 to 4 mm. If the tip is too
broad, application of the solution to the inside of a dental
restoration may be difficult. If, on the other hand, the tip is too
narrow, the handling of the brush itself might become impractical
for dental applications.
[0279] Furthermore, if the length and the thickness of the brush
tip is either too low or too high, it will be difficult to apply
the solution properly, that is either too little to too much of the
solution is applied. Both may be detrimental for achieving the
desired effect.
[0280] The shape of the brush tip should be tapered and fan out, if
desired, when pressure is applied. Thus, the brush tip should have
some flexibility. A brush tip with these properties can be used to
draw thin lines and also to paint on larger areas.
[0281] A combination of a brush tip comprising bristles having a
length from 8 to 15 mm with the solution described in the present
text having a viscosity above 200 mPa*s or above 500 mPa*s
(measured at 23.degree. C.) was found to be beneficial. Such a
combination facilitates the accurate application of the solution on
the surface of the porous dental ceramic(s).
[0282] Thus, the invention may also be directed to a pen as
described in the present text comprising the liquid composition
comprising the whitening agent. Drying the surface of the dental
article to which the liquid composition has been applied is not
absolutely necessary, but can be preferred to reduce the time
needed for firing the dental article later. Drying can be effected
by simply storing the dental ceramic e.g. on a plate at ambient
conditions for a couple of hours (1 to 3 h). If, however, a high
boiling solvent is used, drying might be difficult to achieve.
[0283] The invention is also directed to a dental zirconia article
obtainable by a process as described in the present text. The
dental zirconia article may have the shape of a crown, bridge,
inlay, onlay, veneer, facing, coping, crown or bridged framework,
implant, abutment, orthodontic appliances and parts thereof.
[0284] A dental article having being treated according to the above
described process steps is different from dental ceramics which
have been treated with essentially water-based colouring or
whitening solutions of the state of the art.
[0285] Applying water-based colouring or whitening solutions to the
surface of dental ceramics typically leads to diffuse colouring or
whitening of the whole dental ceramic, whereas the inventive
composition allows for a more accurate, well defined whitening
effect.
[0286] If desired, the extent of diffusion of the composition on
the surface of the treated dental ceramic can be determined as
follows:
[0287] The width of a line drawn with the inventive composition can
be visually confirmed after sintering. More accurately, X-ray
fluorescence (XRF) measurements can be conducted in micro mapping
mode to determine the line's width, i.e. scanning the surface of
the ceramic in e.g. 0.25 mm steps and measuring only small spots of
e.g. 0.5 mm diameter.
[0288] A width of e.g. 0.5 mm of the drawn structures is considered
to meet the expectations of a dental technician in most cases for
an effect agent being applied to only selective parts of the
surface of a dental ceramic.
[0289] A typical process of producing a zirconia ceramic dental
article comprises the steps of [0290] a) providing a dental mill
blank comprising a porous zirconia material, [0291] b) placing the
dental mill blank in a machining device, [0292] c) machining the
porous zirconia material to obtain a machined porous zirconia
dental article, the machined porous zirconia dental article having
the shape of a crown, bridge, inlay, onlay, veneer, facing, coping,
crown and bridged framework, implant, abutment, orthodontic
appliances (e.g. brackets, buccal tubes, cleats and buttons) or
parts thereof, [0293] d) applying the liquid composition described
in the present text to only some parts of the outer and/or inner
surface of the machined porous zirconia dental article, in
particular to the inner surface thereof, [0294] e) optionally
drying the machined porous zirconia dental article, [0295] f)
optionally sintering the machined porous zirconia dental
article.
[0296] The process of producing the dental zirconia article may
further comprise the step of firing or sintering the porous dental
zirconia article having been treated with the liquid composition.
The firing conditions are typically dependent on the ceramic
material used.
[0297] The firing usually takes place for a ZrO.sub.2 based ceramic
at a temperature above 1300.degree. C., preferably above
1400.degree. C., more preferably above 1450.degree. C. and lasts
for at least 0.5 h, preferably for at least 1 h, more preferably
for at least 2 h.
[0298] The firing will result in a zirconia ceramic dental article,
sometime also referred to as crystalline metal oxide article.
[0299] If conducted, the firing or sintering step should be
accomplished under conditions which results in a dental ceramic
article having an acceptable tooth like colour (e.g. a colour which
fits into the Vita.TM. shade guide).
[0300] Useful sintering conditions can be characterized by one or
more of the following parameters: [0301] temperature: from 900 to
1500.degree. C. or from 1000 to 1400.degree. C. or from
1100.degree. C. to 1350.degree. C. or from 1200.degree. C. to
1400.degree. C. or from 1300.degree. C. to 1400.degree. C. or from
1320.degree. C. to 1400.degree. C. or from 1340.degree. C. to
1350.degree. C. [0302] atmosphere: air or inert gas (e.g. nitrogen,
argon); [0303] duration: until a density of 95 or 98 or 99 to 100%
of the final density of the material has been reached; [0304] dwell
time: from 1 to 24 h or from 2 to 12 h; [0305] pressure: ambient
pressure.
[0306] A furnace which can be used is the commercially available
Lava.TM. Therm (3M ESPE). During the firing process the porous
dental ceramic article is sintered to its final shape, thereby
undergoing changes with regard to dimension, density, hardness,
bending strength and/or grain size.
[0307] The dwell time (that is the time during which the article is
kept at that temperature) is not really critical. The dwell time
can be zero. The dwell time, however, can also be in a range from 0
to 24 h or from 0.1 to 5 h.
[0308] The firing temperature and dwell time (that is, the time
period during which a particular temperature is kept) are typically
correlated. A higher temperature typically requires only a short
dwell time. Thus, the dwell time, may last from 0 (e.g. if the
firing temperature is 1550.degree. C.) to 10 h (e.g. if the firing
temperature is 1100.degree. C.) or from 0.1 to 8 h.
[0309] Generally, the sintering or firing conditions are adjusted
such that the sintered dental ceramic article has a density of
equal or greater than 98% compared with the theoretically
achievable density.
[0310] After sintering, the dental article can typically be
characterized by at least one or more or all of the following
features: [0311] density: fully sintered density of at least 98.5
(in some embodiments, 99, 99.5, 99.9, or even at least 99.99)
percent of theoretical density; [0312] phase content tetragonal
phase: from 1 to 100 wt.-% or from 10 to 100 wt.-%; cubic phase:
from 30 to 100 wt.-% or from 50 to 90 wt.-%; [0313] biaxial
flexural strength: from 450 MPa to 2200 MPa, or from 500 MPa to
2000 MPa.
[0314] Thus, the present invention is also directed to a dental
zirconia article obtainable or obtained by a process as described
in the present text, the dental zirconia article having the shape
of a crown, bridge, inlay, onlay, veneer, facing, coping, crown or
bridged framework, implant, abutment, orthodontic appliances and
parts thereof.
[0315] In contrast to dental zirconia articles which are already
available, the dental zirconia article described in the present
text and obtained or obtainable by the process described in the
present text comprises opaque spots or areas of its inner and/or
outer surface.
[0316] According to a further embodiment, the process described in
the present text comprises the steps of: [0317] a) providing a
liquid composition and a porous 3-dimensional dental zirconia
article having an outer and inner surface (e.g. as described in the
present text), [0318] b) applying the liquid composition to only a
part of the inner and/or outer surface of the porous dental
zirconia article, [0319] c) optionally drying the porous dental
zirconia article, and [0320] d) optionally firing the porous dental
zirconia article, the liquid composition comprising a whitening
agent comprising at least one phosphate moiety and having a
viscosity from 10 mPa*s to 10,000 mPas*s at 23.degree. C., the
liquid composition being essentially free of the following
components: [0321] filler, [0322] colouring ions selected from
iron, erbium, praseodymium or mixtures thereof, [0323] reactive
organic monomers, the porous dental zirconia article being
characterized by the following features: [0324] showing a N2
adsorption of isotherm type IV according to IUPAC classification,
[0325] showing a N2 adsorption with a hysteresis loop in a p/p0
range of 0.70 to 0.95, [0326] average connected pore diameter: from
15 to 60 nm, [0327] average grain size: less than 100 nm, [0328]
BET surface: from 15 to 100 m.sup.2/g or from 16 to 60 m.sup.2/g,
[0329] Biaxial flexural strength: from 10 to 40 MPa, [0330] x, y, z
dimension: at least 5 mm, [0331] Density: from 40% to 60% of
theoretical density, [0332] ZrO2 content: from 90 to 98 mol %,
[0333] HfO2 content: from 0 to 2 mol %, [0334] Y2O3 content: from 1
to 5 mol %, [0335] Al2O3 content: from 0 to 0.1 mol %, the optional
firing step being conducted under the following conditions: [0336]
temperature: from 1200.degree. C. to 1400.degree. C., [0337]
atmosphere: air or inert gas, [0338] duration: until a density of
at least 95 or at least 98 of the final density of the material has
been reached, [0339] dwell time: from 1 to 24 h, [0340] pressure:
ambient pressure.
[0341] The liquid composition described in the present text does
typically not contain components which might produce a toxic,
injurious, or immunological response in living tissue or components
or additives which jeopardize the intended purpose to be achieved
with the present invention, especially in the sintered ceramic.
[0342] Thus, for examples components or additives added in an
amount which finally (e.g. after a sintering step) results in a
non-tooth-coloured article are usually not contained in the final
dental restoration. Typically, an article is characterized as tooth
coloured if it can be allocated a colour from the Vita.TM. colour
code system, known to the person skilled in the art.
[0343] Moreover, if possible, the composition should not or only
contain a small amount of ingredients which can be detrimental to
the firing equipment during the sintering process. According to a
specific embodiment, the liquid composition does not contain
reactive organic monomers (i.e. chemically reactive moieties like
double bonds, e.g. (meth)acrylates). Thus, after preparation, the
liquid composition does not exhibit chemical reactivity under
ambient conditions, i.e. components being present in the
composition do not react with each other at ambient conditions.
[0344] The liquid composition does also typically not contain
initiators suitable to start the curing reaction of reactive
monomers.
[0345] The liquid composition does typically also not contain
filler or filler particles. Thus, particles which can be removed by
filtration and/or precipitate from the composition are not
contained. According to one embodiment, the liquid composition does
not comprise nano-sized particles.
[0346] Nano-sized particles typically have a (hydrodynamic)
diameter in the range from 1 nm to 500 nm or from 2 nm to 100 nm or
from 3 nm to 20 nm. The diameter should be tailored to be
compatible with (i.e. being smaller than) the pore size of the
ceramic material to which the composition should be applied. If
desired, the (hydrodynamic) diameter of the particles can be
determined by a dynamic light scattering method.
[0347] Dynamic Light Scattering (DLS) is an analytical method using
the Brownian motion of particles in a solvent to determine their
size. Basis of the method is that smaller particles move faster
than bigger particles. A laser is used to irradiate a sample and
the light scattered by the particles is detected. Small, fast
moving particles cause quick fluctuations of the detected signal,
while bigger and slower particles cause slower fluctuations.
[0348] The DLS method determines the so called "hydrodynamic
diameter" of the dispersed particles. The moving particles possess
a shell of solvent that moves along with them through the solution.
The hydrodynamic diameter is the diameter of the solid particle
plus the solvent shell. As a result, the actual particle is always
smaller than the measured diameter. A device which can be used for
the DLS measurements is the Zetasizer.TM. Nano ZS (Malvern).
Nano-sized particles which are typically not contained are
ZrO.sub.2 or TiO.sub.2 particles.
[0349] The dental zirconia article does usually not contain glass,
glass ceramic materials, lithium disilicate ceramic materials, or
combinations thereof. Further, the producing of the dental zirconia
article described in the present text does typically also not
require the application of a hot isostatic pressing step (HIP).
EXAMPLES
[0350] Unless otherwise indicated, all parts and percentages are on
a weight basis, all water is deionized water, and all molecular
weights are weight average molecular weight. Moreover, unless
otherwise indicated all experiments were conducted at ambient
conditions (23.degree. C.; 1013 mbar).
Measurements
Method for Measuring N2 Sorption Isotherms, BET Surface Area, Pore
Volume, Average Connected Pore Diameter
[0351] The samples were run on either on a QUANTACHROME AUTOSORB-1
BET Analyzer" (Quantachrome Instruments, Boynton Beach, Fla.) or a
BELSORP-mini instrument (BEL Japan Inc., Osaka, Japan). The samples
were weighed and outgassed at 200.degree. C. for two days then
subjected to a N2 sorption process with an appropriate number and
distribution of measurement points, e.g. 55 adsorb points and 20
desorb points from a p/p.sub.0 range 1.times.10.sup.-6 to 1 and
back to 0.05 giving full isotherms. The specific surface area S was
calculated by the BET method (Details regarding calculation see
Autosorb-1 Operating Manual Ver. 1.51 IV. Theory and Discussion;
Quantachrome Instruments, Inc.). The total pore volume V.sub.liq is
derived from the amount of vapor adsorbed at a relative pressure
close to unity (p/p.sub.0 closest to 1), by assuming that the pores
are then filled with liquid adsorbate (Details regarding
calculation see Autosorb-1 Operating Manual Ver. 1.51 IV. Theory
and Discussion; Quantachrome Instruments, Inc.). The average pore
diameter (d) is calculated from the surface area (S) and the total
pore volume (V.sub.liq):
d = 4 Vliq S . ##EQU00001##
Average Grain Size
[0352] If desired, the average grain size can be determined with
the Line Intercept Analysis. FESEM micrographs with 70,000 times
magnification are used for grain size measurement. Three or four
micrographs taken from different areas of the sintered body are
used for each sample. Ten horizontal lines, which are spaced at
roughly equal intervals across the height of each micrograph, are
drawn. The numbers of grain boundary intercepts observed on each
line are counted and used to calculate the average distance between
intercepts. The average distance for each line is multiplied by
1.56 to determine the grain size and this value is averaged over
all the lines for all micrographs of each sample.
Particle Size
[0353] If desired, particle size measurements can be done using a
light scattering particle sizer equipped with a red laser having a
633 nm wavelength of light (obtainable under the trade designation
"ZETA SIZER--Nano Series, Model ZEN3600" from Malvern Instruments
Inc., Westborough, Mass.). Each sample is analyzed in a polystyrene
sample cuvette. The sample cuvette is filled with a particle
dispersion containing 1 wt.-% solids. The sample cuvette is then
placed in the instrument and equilibrated at 25.degree. C. The
automatic size-measurement procedure can then be run. The
instrument automatically adjusts the laser-beam position and
attenuator setting to obtain the best measurement of particle
size.
[0354] The method of Photon Correlation Spectroscopy (PCS) is used
by the software to calculate the particle size. PCS uses the
fluctuating light intensity to measure Brownian motion of the
particles in the liquid.
Density
[0355] If desired, the density of the pre-sintered or sintered
material can be measured by an Archimedes technique. The
measurements is made on a precision balance (identified as "AE 160"
from Mettler Instrument Corp., Hightstown, N.J.) using a density
determination kit (identified as "ME 33360" from Mettler Instrument
Corp.).
[0356] To measure the density of the pre-sintered material the
sample is first weighed in air (A). Then the sample is immersed in
water using vacuum overnight. The immersed sample is weighed in air
(B) and then weighed under water (C). The water is distilled and
deionized. One drop of a wetting agent (obtained under trade
designation "TERGITOL-TMN-6" from Dow Chemical Co., Danbury, Conn.)
is added to 250 ml of water. The density is calculated using the
formula .rho.=(A/(B-C)) .rho.0, where .rho.0 is the density of
water.
[0357] To measure the density of the sintered material the sample
is first weighed in air (A), then immersed in water (B) The water
is distilled and deionized. One drop of a wetting agent (obtained
under trade designation "TERGITOL-TMN-6" from Dow Chemical Co.,
Danbury, Conn.) is added to 250 ml of water. The density is
calculated using the formula .rho.=(A/(A-B)) .rho.0, where .rho.0
is the density of water.
[0358] The relative density can be calculated by reference to the
theoretical density (pt) of the material,
.rho.rel=(.rho./.rho.t)100.
Vickers Hardness
[0359] If desired, the Vickers hardness can be determined according
to ISO 843-4 with the following modifications: The surface of the
samples are ground using silicon carbide grinding paper (P400 and
P1200). The test forces are adjusted to the hardness level of
samples. Used test forces were between 0.2 kg and 2 kg and were
applied for 15 s each indentation. A minimum of 10 indentations is
measured to determine the average Vickers hardness. The tests can
be conducted with a hardness tester Leco M-400-G (Leco Instrumente
GmbH).
Biaxial Flexural Strength
[0360] If desired, the biaxial flexural strength can be determined
according to ISO 6872 (2008) with the following modifications: The
sample is sawn into wafers with a thickness of 1 to 2 mm using a
dry or wet cut saw The diameter of the samples should be between 12
and 20 mm. Each wafer is centred on a support of three steel balls.
The support diameter depends on the sample diameter and should have
maximum 14 mm and should be at least 1 mm smaller than the sample
diameter. The punch diameter in contact with the wafer is 3.6 mm.
The punch is pushed onto the wafer at a rate of 0.1 mm per min. A
minimum of 6 samples is measured to determine the average strength.
The tests can be conducted in an Instron 5566 universal testing
machine (Instron Deutschland GmbH).
Materials Used
Zirconia Sample A
[0361] A sol composition containing Zr oxide (91.1 wt.-%;
calculated as ZrO2), Hf oxide (1.8 wt.-%; calculated as HfO2) and Y
oxide calculated as Y2O3 (7.1 wt.-%) was prepared with a hot tube
reactor by using the respective metal acetates. The sol was
concentrated and water was partially replaced by a TFF process. The
concentrated sol was gelled by mixing the sol, an acrylic monomer,
ethanol, and a radical polymerization initiator. The gel was filled
into a mold and cured. The cured gel was removed from the mold and
immersed in pure ethanol to exchange water with ethanol in the gel.
The gel was then supercritically extracted with CO2. After that the
gel was de-bindered and pre-sintered at 1020.degree. C. A more
detailed description of the process can be found e.g. in WO
2013/055432 (3M). The obtained sample was sliced into discs
(diameter: 17 mm; thickness: 1.5 mm).
Zirconia Sample B
[0362] Bindered ZrO2 powder (TZP) was pressed into cylindric blocks
by applying a pressure of 200 MPa. The blocks were de-bindered and
pre-sintered at 900.degree. C. The obtained samples were sliced
into discs (diameter: 17 mm; thickness: 1.5 mm).
Liquid Compositions and Process of Application
[0363] All compositions are calculated to contain the same mass
percentage of whitening agent (0.425 g agent on 5 g
composition).
Inventive Example 1 (IE1)
[0364] 0.500 g of phosphoric acid (85%) is mixed with 4.500 g of
glycerol by stirring until a homogeneous solution is obtained. The
mixture was applied with a microbrush to a dry disc of porous
pre-sintered (1020.degree. C.) Zirconia Sample A. Half of the disc
is painted with the liquid. After that, the material was put into a
furnace and sintered at 1300.degree. C. for 2 hours. As a result,
dense zirconia disc with one white, opaque half was obtained (see
FIG. 1).
Inventive Example 2 (IE2)
[0365] 0.500 g of phosphoric acid (85%) was mixed with 4.500 g of
deionized water by stirring until a homogeneous solution was
obtained. The mixture was applied with a microbrush to a dry disc
of porous pre-sintered (1020.degree. C.) Zirconia Sample A. Half of
the disc was painted with the liquid. After that, the material was
put into a furnace and sintered at 1300.degree. C. for 2 hours. As
a result, dense zirconia disc with one white, opaque half was
obtained (see FIG. 1).
Comparative Example 1 (CE1)
[0366] 0.654 g of nitric acid (65%) was mixed with 4.346 g of
de-ionized water by stirring until a homogeneous solution was
obtained. The mixture was applied with a microbrush to a dry disc
of porous pre-sintered (1020.degree. C.) Zirconia Sample A. Half of
the disc was painted with the liquid. After that, the material was
put into a furnace and sintered at 1300.degree. C. for 2 hours. As
a result, dense zirconia disc with no white, opaque region was
obtained (see FIG. 1).
Comparative Example 2 (CE2)
[0367] 0.434 g of sulfuric acid (98%) was mixed with 4.566 g of
glycerol by stirring until a homogeneous solution was obtained. The
mixture was applied with a microbrush to a dry disc of porous
pre-sintered (1020.degree. C.) Zirconia Sample A. Half of the disc
was painted with the liquid. After that, the material was put into
a furnace and sintered at 1300.degree. C. for 2 hours. As a result,
dense zirconia disc with no white, opaque region was obtained (see
FIG. 1).
Comparative Example 3 (CE3)
[0368] 0.434 g of sulfuric acid (98%) was mixed with 4.566 g of
deionized water by stirring until a homogeneous solution is
obtained. The mixture was applied with a microbrush to a dry disc
of porous pre-sintered (1020.degree. C.) Zirconia Sample A. Half of
the disc was painted with the liquid. After that, the material was
put into a furnace and sintered at 1300.degree. C. for 2 hours. As
a result, dense zirconia disc with no white, opaque region was
obtained (see FIG. 1).
Comparative Example 4 (CE4)
[0369] 1.700 g of hydrochloric acid (25%) was mixed with 3.300 g of
glycerol by stirring until a homogeneous solution was obtained. The
mixture was applied with a microbrush to a dry disc of porous
pre-sintered (1020.degree. C.) Zirconia Sample A. Half of the disc
was painted with the liquid. After that, the material was put into
a furnace and sintered at 1300.degree. C. for 2 hours. As a result,
dense zirconia disc with no white, opaque region was obtained (see
FIG. 1).
Comparative Example 5 (CE5)
[0370] 1.700 g of hydrochloric acid (25%) was mixed with 3.300 g of
deionized water by stirring until a homogeneous solution was
obtained. The mixture was applied with a microbrush to a dry disc
of porous pre-sintered (1020.degree. C.) Zirconia Sample A. Half of
the disc was painted with the liquid. After that, the material was
put into a furnace and sintered at 1300.degree. C. for 2 hours. As
a result, dense zirconia disc with no white, opaque region was
obtained (see FIG. 1).
Comparative Example 6 (CE6)
[0371] 0.425 g of acetic acid (100%) was mixed with 4.575 g of
glycerol by stirring until a homogeneous solution was obtained. The
mixture was applied with a microbrush to a dry disc of porous
pre-sintered (1020.degree. C.) Zirconia Sample A. Half of the disc
was painted with the liquid. After that, the material was put into
a furnace and sintered at 1300.degree. C. for 2 hours. As a result,
dense zirconia disc with no white, opaque region was obtained (see
FIG. 1).
Comparative Example 7 (CE7)
[0372] 0.425 g of acetic acid (100%) was mixed with 4.575 g of
deionized water by stirring until a homogeneous solution was
obtained. The mixture was applied with a microbrush to a dry disc
of porous pre-sintered (1020.degree. C.) Zirconia Sample A. Half of
the disc was painted with the liquid. After that, the material was
put into a furnace and sintered at 1300.degree. C. for 2 hours. As
a result, dense zirconia disc with no white, opaque region was
obtained (see FIG. 1).
[0373] In FIG. 1 the results obtained for the Zirconia Samples A
are shown:
[0374] From left to right: samples obtained by using the following
agents: phosphoric acid (Inventive Example), nitric acid, sulfuric
acid, hydrochloric acid and acetic acid (Comparative Examples)
Upper row: solvent: glycerol; Lower row: solvent: water; The
results obtained for the Zirconia Samples A are also given in the
table below.
TABLE-US-00001 IE1 IE2 CE1 CE2 CE3 CE14 CE5 CE6 CE7 Opacifying
strong strong none none none none none none none intensity
Sharpness/ sharp sharp -- -- -- -- -- -- -- definition Result: Only
the phosphorus containing samples showed an opacifying effect that
was well defined and appeared only where the inventive composition
was applied.
Inventive Example 3 (IE3)
[0375] 0.500 g of phosphoric acid (85%) was mixed with 4.500 g of
de-ionized water by stirring until a homogeneous solution was
obtained. The mixture was applied with a microbrush to a dry disc
of porous pre-sintered Zirconia Sample B. Half of the disc was
painted with the liquid. After that, the material was put into a
furnace and sintered at 1450.degree. C. for 2 hours. As a result,
dense zirconia disc with one white, opaque half was obtained, the
opacifying effect being intense and well defined.
Inventive Example 4 (IE4)
[0376] 0.433 g of phosphoric acid, diammonium salt (98%) was mixed
with 4.566 g of de-ionized water by stirring until a homogeneous
solution was obtained. The mixture was applied with a microbrush to
a dry disc of porous pre-sintered Zirconia Sample B. Half of the
disc was painted with the liquid. After that, the material was put
into a furnace and sintered at 1450.degree. C. for 2 hours. As a
result, dense zirconia disc with one white, opaque half was
obtained, the opacifying effect being intense and well defined.
Comparative Example 8 (CE8)
[0377] 0.433 g of triethyl phosphate (98%) was mixed with 4.566 g
of de-ionized water by stirring until a homogeneous solution was
obtained. The mixture was applied with a microbrush to a dry disc
of porous pre-sintered Zirconia Sample B. Half of the disc was
painted with the liquid. After that, the material was put into a
furnace and sintered at 1450.degree. C. for 2 hours. As a result,
dense zirconia disc with one white, opaque half was obtained, the
opacifying effect being weak and blurry, because the whitening
agent had spread through the zirconia material.
[0378] The results obtained for the Zirconia Samples B are
described in the table below.
TABLE-US-00002 IE3 IE4 CE8 Opacifying intensity strong strong
medium Sharpness/ sharp sharp blurry definition
All agents led to an opacifying effect on the treated samples.
However, only the agents with functional groups that could interact
with the zirconia surface of the samples led to a well defined
opacifying effect that appeared only where the inventive
composition was applied.
* * * * *