U.S. patent application number 13/458667 was filed with the patent office on 2012-08-23 for shaded zirconium oxide articles.
This patent application is currently assigned to IVOCLAR VIVADENT AG. Invention is credited to Dmitri G. Brodkin, Ajmal Khan, Carlino Panzera.
Application Number | 20120214134 13/458667 |
Document ID | / |
Family ID | 46033179 |
Filed Date | 2012-08-23 |
United States Patent
Application |
20120214134 |
Kind Code |
A1 |
Khan; Ajmal ; et
al. |
August 23, 2012 |
Shaded Zirconium Oxide Articles
Abstract
A dental article includes yttria stabilized tetragonal zirconia
polycrystalline ceramic, and no more than about 0.15 wt. % of one
or more coloring agents of one or more of: Fe, Er, Co, Pr, Tb, Cr,
Nd, Ce, V, Eu, Ho, Ni, and Cu, oxides thereof, and combinations
thereof, whereby the dental article is provided with a color
corresponding to a natural tooth shade; and wherein the dental
article has a flexural strength of at least about 800 MPa.
Corresponding methods are also described.
Inventors: |
Khan; Ajmal; (Princeton,
NJ) ; Panzera; Carlino; (Hillsborough, NJ) ;
Brodkin; Dmitri G.; (Livingston, NJ) |
Assignee: |
IVOCLAR VIVADENT AG
Schaan
LI
|
Family ID: |
46033179 |
Appl. No.: |
13/458667 |
Filed: |
April 27, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13437998 |
Apr 3, 2012 |
|
|
|
13458667 |
|
|
|
|
11717199 |
Mar 13, 2007 |
8178012 |
|
|
13437998 |
|
|
|
|
60789610 |
Apr 6, 2006 |
|
|
|
Current U.S.
Class: |
433/201.1 ;
264/16; 264/333 |
Current CPC
Class: |
B33Y 80/00 20141201;
C04B 2235/3275 20130101; C04B 2235/6562 20130101; C04B 2235/3217
20130101; C04B 2235/608 20130101; C04B 2235/3279 20130101; C04B
2235/444 20130101; C04B 2235/6565 20130101; C04B 2235/3225
20130101; C04B 35/486 20130101; C04B 2235/405 20130101; C04B
2235/404 20130101; C04B 2235/604 20130101; C04B 2235/96 20130101;
C04B 2235/9661 20130101; C04B 2235/77 20130101; C04B 35/638
20130101; A61C 13/082 20130101; C04B 2235/3224 20130101; C04B
2235/443 20130101; C04B 2235/3229 20130101; C04B 2235/3281
20130101; C04B 2235/445 20130101; C04B 2235/72 20130101; C04B
2235/3239 20130101; C04B 35/62655 20130101; C04B 2235/40 20130101;
C04B 2235/449 20130101; C04B 2235/6026 20130101; C04B 2235/3241
20130101; C04B 2235/616 20130101 |
Class at
Publication: |
433/201.1 ;
264/333; 264/16 |
International
Class: |
A61C 8/00 20060101
A61C008/00; A61C 13/00 20060101 A61C013/00; B28B 3/00 20060101
B28B003/00 |
Claims
1. A method for creating a shaded ceramic including the steps of:
creating three or more uniquely shaded zirconia pigment powders,
each having their own characteristic hue, by combining zirconia
powder with a chemical component selected from the group consisting
of Fe, Er, Co, Pr, Tb, Cr, Nd, Ce, V, Eu, Ho, Ni, and Cu salts,
oxides, inorganic, organic, organo-metallic compounds thereof, and
combinations thereof; mixing together unpigmented zirconia powder
with one or more of said pigment powders to achieve a predetermined
shade powder; pressing said predetermined shade powder to form a
green block; drying said green block; pre-sintering said green
block.
2. A method for creating a dental ceramic comprising the method of
claim 1, wherein zirconia powder comprises yttria stabilized
tetragonal zirconia polycrystal (YTZP) powder.
3. A method for creating a dental ceramic comprising the method of
claim 1, with the further steps of milling the block to create a
desired form, and sintering said form.
4. A method for creating a dental ceramic comprising the method of
claim 1, wherein the chemical component is added in the form of an
aqueous or nonaqueous solution, emulsion, dispersion, gel or
particulate.
5. A method for creating a dental ceramic comprising the method of
claim 1, wherein three uniquely shaded pigment powders each have
their own characteristic hue in the yellow, pink and gray
ranges.
6. A shaded ceramic created by the method set forth in claim 1.
7. A dental ceramic prosthesis created by the method set forth in
claim 1.
Description
[0001] This application is a continuation application of U.S.
application Ser. No. 13/437,998, filed Apr. 3, 2012, which is a
continuation application of U.S. application Ser. No. 11/717,199,
filed Mar. 13, 2007, which claims priority under 35 U.S.C.
.sctn.119 to U.S. Patent Application Ser. No. 60/789,610 filed Apr.
6, 2006, all of which are incorporated by reference herein.
BACKGROUND
[0002] In the discussion of the state of the art that follows,
reference is made to certain structures and/or methods. However,
the following references should not be construed as an admission
that these structures and/or methods constitute prior art.
Applicant expressly reserves the right to demonstrate that such
structures and/or methods do not qualify as prior art.
[0003] Yttria Tetragonal Zirconia Polycrystalline (YTZP) materials
have emerged as a high-strength framework material for dental
prostheses (single-units up to multiple unit bridges). However due
to its inherent white color, often the esthetics of the finished
restoration is inferior to what is achievable with other
all-ceramic systems.
[0004] Currently there are two predominant commercially available
methods to deal with the stark white color of zirconia. In the one
method, the color of the zirconia is "hidden" by applying either a
layer of stain or liner. The other method entails shading the
zirconia by immersion in, or painting with, coloring solutions
while in the pre-sintered state. Coloring with a stain and/or
applying a liner involves an extra fabrication step and lowers
translucency. Shading with a coloring solution similarly requires
the extra step of dipping or painting, and extra time to dry before
sintering. Also, this method is deficient as the color of the final
sintered framework often is not uniform.
[0005] An alternative method is to use porous zirconia blocks that
are preshaded to the desired coloration. Such blocks only need to
be fired after any machining, thus eliminating the coloring with
solutions step. As the fully sintered frameworks emerge from the
furnace already shaded, the stain/liner step can be eliminated.
Additionally, the color of the sintered frameworks is
characteristically uniform, which is another advantage over the
shading with coloring solution method.
[0006] A finished dental restoration should match the color of the
patient's teeth, i.e., it should be "tooth colored". The colors of
human teeth appear to range from a light almost white-tan to a
light brown, and occupy a very specific color space. This color
space can be described by the commonly used CIE (Commission
Internationale de l'Eclariage) L*, a*, b* conventions, which
represents colors in a three-dimensional Cartesian coordinate
system. L*, or "value", is a measure of luminance or lightness, and
is represented on the vertical axis. The a*, b* coordinates, are a
measure of chromaticity and are represented on the horizontal
coordinates, with positive a* representing red and negative a*
representing green, and positive b* representing yellow and
negative b* representing blue. U.S. Pat. No. 6,030,209, which is
incorporated herein by reference, presents the CIE L*, a*, b* color
coordinates of tooth colors represented by the Vita Lumen.RTM.
shade guide system manufactured by Vita Zahnfabrik (i.e., it
presents the color space of tooth colors). Herein, "tooth color" is
taken to mean CIE L*, a*, b* color coordinates that fall within, or
very close to, this color space.
[0007] U.S. Pat. No. 6,713,421 appears to describe
yttria-stabilized zirconia dental milling blanks that are formed
with 0-1.9 wt. % coloring additives. The composition described
therein includes 0.1 to 0.50 wt. % of at least one oxide of
aluminum, gallium, germanium and indium for the purpose of lowering
the sintering temperature and increasing stability and hydrolytic
resistance in the densely sintered state. However, the addition of
aluminum oxide (alumina) to zirconia also often results in discrete
alumina inclusions distributed throughout the microstructure. This
occurs in part due to the low solubility of alumina in zirconia.
Further, it presents a particular disadvantage for dental
applications because alumina inclusions can lower the translucency
of the zirconia since the refractive index of alumina, 1.77,
differs considerably from that of tetragonal zirconia, 2.16. Thus,
it is desirable that dental zirconia is devoid of any alumina
inclusions. A means to achieve this is to minimize, or eliminate,
the alumina addition, thereby minimizing the potential for the
alumina inclusions in the final microstructure.
[0008] In U.S. Pat. No. 6,713,421 the blanks are made from powders
or granules that have been doped with the various oxides via a
solution followed by a co-precipitation method. The cited advantage
of this method is that the various oxides are distributed
homogeneously throughout the powder. However, the field of dental
restoratives requires many shades (e.g., 7 zirconia core shades as
per LAVA, 16 Vita Classic shades, etc.), and having to prepare so
many individually shaded powders or granules can be
cost-prohibitive.
[0009] Yet another disadvantage of U.S. Pat. No. 6,713,421 is that
it requires relatively large amounts of the preferred coloring
oxides, iron oxide and erbium oxide. This is revealed by the
Preparation Example 1 cited which teaches adding 0.2 wt. % iron
oxide+0.38 erbium oxide (0.58% total) to color 3YTZP. Although the
patent does not indicate if this resulted in a tooth color, it can
be inferred from U.S. Pat. No. 5,219,805, which appears to disclose
coloration of yttria-stabilized zirconia for dental bracket
applications using combinations of Fe.sub.2O.sub.3,
Er.sub.2O.sub.3, and Pr.sub.6O.sub.11, that even higher
Fe.sub.2O.sub.3 and Er.sub.2O.sub.3 concentrations are necessary to
achieve tooth coloration. For instance, according to the examples
given in U.S. Pat. No. 5,219,805, up to 1.0 mol % Er.sub.2O.sub.3
(3.0 wt. %) additive is required to achieve dental brackets "having
color tone similar to ivory-colored teeth". Additionally, up to 0.2
mol % Fe.sub.2O.sub.3 (0.25 wt. %) is required to achieve tooth
colors, which although less than the 1 mol % Er.sub.2O.sub.3
required, is a considerable amount. As such quantities are
significant, they can have a negative effect on other properties of
the resulting YTZP cores, such as on strength, weibull modulus,
hydrolytic resistance, and grain size.
[0010] Additionally, it has been observed that Er.sub.2O.sub.3
additions to 3Y-zirconia, of 0.2 wt. % or greater, results in
sintered bodies that fluoresce a dark yellow under ultraviolet (UV)
lighting. This is inappropriate for a dental framework, which under
UV, ideally, should fluoresce bluish-white to mimic that of natural
teeth. Less ideally, the framework should not fluoresce at all in
the visible light range. In the latter case fluorescence is
typically imparted to the final restoration by the overlay
porcelains. The shortcoming of an inappropriate fluorescence is
overcome by the present invention.
[0011] The prior art also shows Cr additions result in green or
brown coloration. For example, U.S. Pat. No. 3,984,524 appears to
describe olive coloration of cubic zirconia with addition of 0.1 to
2 wt. % Cr.sub.2O.sub.3, U.S. Pat. No. 4,742,030 appears to
describe green coloration of 5 mol % yttria-stabilized zirconia
with addition of 0.7 wt. % Cr.sub.2O.sub.3, and brown coloration
with addition of 0.2 wt. % Cr.sub.2O.sub.3 , respectively.
[0012] French patent publication 2,781,366 and Cales et. al.
("Colored Zirconia Ceramics for Dental Applications," Bioceramics
Vol. 11, edited by R. Z. LeGeros and J. R. LeGeros; Proceedings of
the 11th International Symposium on Ceramics in Medicine; York,
N.Y.; November 1998) appear to identify a number of colorants, and
was reportedly successful in achieving some of the Vita shades in
3YTZP by using combinations of Fe.sub.2O.sub.3, CeO.sub.2 and
Bi.sub.2O.sub.3. However, their choice of colorant oxides is a
drawback as they are required in fairly large amounts to achieve
some of the desired shades.
[0013] U.S. Pat. No. 5,656,564 appears to teach coloration of
zirconia for dental bracket applications using with combinations of
Er.sub.2O.sub.3 and Pr.sub.6O.sub.11. The sintered zirconia-based
ceramic is produced by a procedure generally including combining
constituents in solution, precipitating, calcining, pressing, and
sintering.
[0014] U.S. Pat. No. 5,011,403 appears to describe coloration of
zirconia dental brackets using combinations of one or more of
oxides of Fe, Ni and Mn added to a Zr-based powder.
[0015] U.S. Pat. No. 6,709,694 appears to describe the use of
solutions for coloring of pre-sintered zirconia dental frameworks
by immersion, painting or spraying using a metal ion coloring
solution or metal complex coloring solution that is applied to a
presintered ceramic, followed by sintering to form a translucent,
colored dental ceramic. The claimed ions or complexes are of the
rare earths elements or subgroups II and VIII, with an action time
of under two hours, and maximum pre-sintered zirconia diameter and
height of 10 and 7 mm, respectively. However, this method is not
ideal as the color of the final sintered frameworks often are not
uniform and the process requires the extra steps of applying the
solutions and drying prior to sintering.
[0016] The development of pink coloration in zirconia by Er
additions is described in (i) P. Duran, P. Recio, J. R. Jurado, C.
Pascual and C. Moure, "Preparation, Sintering, and Properties of
Translucent Er.sub.2O.sub.3-Doped Tetragonal Zirconia," J. Am.
Ceram. Soc., vol. 72, no. 11, pp. 2088-93, 1989; and (ii) M.
Yashima, T. Nagotome, T. Noma, N. Ishizawa, Y. Suzuki and M.
Yoshimura, "Effect of Dopant Species on Tetragonal
(t')-to-Monoclinic Phase Transformation of Arc-Melted
ZrO.sub.2--RO.sub.1.5 (R=Sm, Y, Er, and Sc) in Water at 200.degree.
C. and 100 MPa Pressure," J. Am. Ceram. Soc., no. 78, no. 8, pp.
2229-93, 1989. Additions of CoO, Fe.sub.2O.sub.3 and
Cr.sub.2O.sub.3 combinations to yttria-stabilized zirconia are
known to impart a blue color in the final sintered zirconia bodies,
as apparently described in Japanese patent publication 2,145,475.
Additions of one or both of the colorants, Ni oxide and Cobalt
oxide, to yttria-stabilized zirconia have been shown to result in a
purplish colored sintered body, as apparently described in U.S.
Pat. No. 5,043,316.
[0017] Japanese patent publication 3,028,161 appears to describe
the preparation of colored zirconia by the steps of: (1) mixing
zircon-based pigment with partially stabilized zirconia containing
Y.sub.2O.sub.3, MgO, etc., (2) molding and (3) sintering to provide
a colored zirconia sintered product.
[0018] Many of the aforementioned coloring additions can negatively
affect not only mechanical properties, including strength and
fracture toughness, but also isotropic shrinkage and final sintered
density. This can happen for a number of reasons including: (1)
loss of fracture toughness from a lowering of the "transformation
toughening" effect as a result of the over-stabilization of the
tetragonal phase by the additive (either chemically, or by grain
size reduction) thereby hindering the transformation from the
metastable tetragonal phase to monoclinic phase that is necessary
for the toughening to happen, (2) loss of strength due to
spontaneous microcrack formation that can result if grains grow too
large because of the additive, and, (3) loss of strength due to the
formation of strength-limiting pores in the microstructure due to
the additive. This last reason is what Shah et al. (K. C. Shah, I.
Denry and J. A. Holloway, "Physical Properties of Cerium-Doped
Tetragonal Zirconia," Abstract 0080, Journal of Dental Research,
Vol. 85, Special Issue A, 2006) attribute the significant loss of
strength, down to 275.+-.67 MPa, for 3YTZP materials that were
colored using Ce salts. Additionally, they observed that strength
decreased linearly with the concentration of the coloring additive,
Ce.
[0019] The problem of formation of coarse pores, along with grain
growth, in colored zirconia sintered compacts has also been
recently recognized in JP 2005289721.
[0020] It is also important to recognize that only certain
combinations of coloring agents in certain proportions will enable
the matching of the color of a dental article so as to match the
desired natural tooth color, e.g., A, B, C, D of the Vita classic
shade guide, and Chromoscop.RTM. universal shade guide.
[0021] Thus, it would be extremely beneficial to have pre-shaded
YTZP blocks or blanks that sinter isotropically to full density and
that yield the required variety of shades consistently and without
compromise in strength, fracture toughness, and reliability or
Weibull modulus.
SUMMARY
[0022] The present invention provides compositions and methods that
can optionally address one or more of the abovementioned
shortcomings associated with conventional technology, and provide
shaded ZrO.sub.2-based articles that sinter isotropically to full
density, and possess at least adequate strength, fracture
toughness, and a reliability or Weibull modulus >10 as required
per the ASTM Standard for biomedical grade 3YTZP. The amount of
coloring agent(s) contained in the ZrO.sub.2-based articles can be
relatively low, thereby minimizing any negative impact on the
properties of the articles due to the presence of coloring agent(s)
in the composition.
[0023] According to one aspect, the present invention provides a
dental article; wherein the article may comprise a blank or block,
a coping or framework for a dental restoration or implant, or an
abutment; the article comprising: yttria stabilized tetragonal
zirconia; and no more than about 0.15 wt. % of one or more coloring
agents comprising one or more of: Pr, Tb, Cr, Nd, Co, oxides
thereof, and combinations thereof, whereby the dental article is
provided with a color corresponding to a natural tooth shade;
wherein the dental article has a flexural strength of at least
about 800 MPa when sintered to at least 98% of its theoretical
density.
[0024] According to another aspect, the present invention provides
a dental restoration comprising: (i) a core or framework, and (ii)
an overlay. The core or framework comprising yttria stabilized
tetragonal zirconia, and no more than about 0.15 wt. % of one or
more coloring agents comprising one or more of: Pr, Tb, Cr, Nd, Co,
oxides thereof, and combinations thereof, whereby the core or
framework is provided with a tooth color corresponding to a natural
tooth shade and the core or framework has a flexural strength of at
least about 800 MPa when sintered to at least 98% of its
theoretical density. The overlay may be porcelain and can be fused
to the core or framework resulting in a final tooth-like
appearance.
[0025] According to a further aspect, the present invention
provides a method of forming a dental article, the method
comprising: providing a first uncolored powder; combining at least
one first coloring agent and a second powder thereby forming a
first pigment powder; mixing the first uncolored powder and the
first pigment powder, thereby forming a mixed powder; pressing the
mixed powder to form a pressed body; and firing the pressed body;
thereby producing a dental article comprising a color corresponding
to a predetermined natural tooth shade, and a flexural strength of
at least 800 MPa when sintered to at least 98% of its theoretical
density.
[0026] According to an additional aspect, the method described
above may further comprise: combining at least one second coloring
agent and the second powder thereby forming a second pigment
powder; mixing the first uncolored powder, the first pigment
powder, and the second pigment powder, thereby forming the mixed
powder.
[0027] According to yet an additional aspect, the method described
above may further comprise: combining at least one third coloring
agent and the second powder thereby forming a third pigment powder;
mixing the first uncolored powder, the first pigment powder, and
the second pigment powder, and the third pigment powder, thereby
forming the mixed powder.
[0028] According to another aspect, the white powders and pigment
powder combinations are made into liquid suspensions useful for
injection-molding or rapid-prototyping feedstocks, that have a
solids content of 2 to 90 wt. %. These suspensions or feedstocks
are used to form dental articles via a number of techniques
including gel casting, slip casting, freeze casting,
electrophoretic deposition, injection molding, or rapid prototyping
(also known as solid freeform fabrication). "Rapid prototyping" is
the generic term for net-shape manufacturing of materials into
complex shapes and includes, stereolithography,
photo-stereolithography, digital light processing (DLP), selective
area laser deposition, selective laser sintering (SLS),
electrophoretic deposition (EPD), robocasting, fused deposition
modeling (FDM), laminated object manufacturing (LOM), or 3-D
printing, as described in greater detail in US Patent Application
Publication No. 2005/0023710, which is incorporated hereby by
reference.
[0029] The pigment powders can be colored to the three primary
colors, i.e., yellow, pink and grey/blue, or colors that can be
effectively used in lieu of primary colors in dental color space,
i.e., brown or pinkish-mauve, in place of pink.
[0030] Additionally, we have discovered that the colorant Cr
(pinkish), can be used in combination with other potent colorants,
Pr (yellow), and Co (blueish grey), to achieve tooth colored
zirconia. Remarkably, the total colorant amount required is on the
order of only 0.035 wt. % (0.0063 mol. %).
[0031] In addition, according to the present invention, Cr has been
found to be a potent coloring additive that, surprisingly, results
in a pinkish-mauve color for sintered 3Y-TZP bodies with small Cr
additions (on the order of 0.003 wt. % (0.005 wt. %
Cr.sub.2O.sub.3)).
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0032] The following detailed description of preferred embodiments
can be read in connection with the accompanying drawing in
which:
[0033] FIG. 1 is a cross-sectional illustration of an example of a
dental article formed according to the principles of certain
embodiments of the present invention.
DETAILED DESCRIPTION
[0034] According to certain aspects of the present invention, there
is provided a sintered ceramic body which is doped with or
otherwise contains one or more coloring agents. The one or more
coloring agents are selected so as to provide the sintered ceramic
body with a desired color by incorporating a relatively small
amount of the coloring agents into the composition of the sintered
ceramic body. The relatively small amount of the addition of
coloring agents advantageously minimizes any adverse impacts that
the coloring agents might have on the properties of the sintered
ceramic body.
[0035] According to the present invention, the ceramic body can
take any suitable form, shape, or geometry. According to one
embodiment, a sintered ceramic body is provided in the form of a
dental article. Thus, the identity and amount of one or more
coloring agents incorporated into the composition of the sintered
ceramic body are chosen so as to provide the sintered ceramic body
with a final color corresponding to a desired natural tooth color
or shade. A number of different dental articles are contemplated.
For example, dental articles formed according to the principles of
the present invention can include: blocks or blanks suitable for
subsequent machining; a prefabricated shape; supports or frameworks
for a dental restorations; a coping; pontic; denture teeth; space
maintainers; tooth replacement appliance; orthodontic retainer;
denture; post jacket; facet; splint; cylinder; pin; connector;
crowns; partial crowns; veneers; onlays; inlays; bridges; fixed
partial dentures; Maryland Bridges; implant abutment. According to
an illustrative example, a dental restoration formed according to
the principles of the present invention is illustrated in FIG. 1.
As illustrated therein, a dental restoration 10 can comprise a
support or framework 20 in the form of a sintered ceramic body
having a concentration containing one or more coloring agents
according to the principles of the present invention, to which is
bonded to an overlay material 30. The support or framework 20 can
be formed of any suitable base ceramic material described herein,
such as a stabilized yttria tetragonal zirconia polycrystalline
material (YTZP), and one or more coloring agent having an identity
and an amount as described further below. The overlay 30 can
likewise be formed of any suitable overlay material, for example,
an overlay of zirconia-porcelain material can be utilized.
[0036] According to one optional aspect of the present invention,
the sintered ceramic body can comprise porous zirconia (e.g., YTZP)
blocks or blanks, which are preshaded, optionally by any of the
techniques described herein, and can optionally be processed by
CAD/CAM techniques, then finally sintered to form colored dental
frameworks of high strength. The term "blocks" and "blanks" are not
intended to limit the geometry of the articles of the present
invention. Any suitable CAD/CAM technique may be utilized in
connection with the present invention. For example, such techniques
are described in U.S. Pat. No. 7,011,522, which is incorporated
herein by reference, in its entirety. The blocks or blanks can be
in the as-pressed green state (with binder), or pre-sintered state
(with binder removed). The blocks can have a pore volume of 40 to
80%, and can be sinterable to at least 99% of theoretical density
yielding grain sizes of 0.2 to 1.5 .mu.m, at sintering temperatures
of 1150 to 1550.degree. C., average flexural strengths in excess of
800 MPa, optionally in excess of 900 MPa, and optionally in excess
of 1,000 MPa, when sintered to at least 98% of its theoretical
density, are attainable. The blocks are machinable and are
characterized by isotropic shrinkage during the sintering process
enabling their processing by CAD/CAM techniques into dental
restorations of high strength and excellent fit.
[0037] The ceramic body can comprise any suitable composition to
which one or more coloring agents can be added. According to
certain optional aspects, the base ceramic to which one or more
coloring agents is added can comprise a stabilized ceramic. For
example, the base ceramic can comprise a yttria stabilized
tetragonal zirconia polycrystalline ceramic material (YTZP), calcia
stabilized zirconia, magnesia stabilized zirconia, and/or ceria
stabilized zirconia, all of which can be obtained commercially.
[0038] The base ceramic material can be doped or combined with one
or more coloring agents. For example, the base ceramic composition
can be doped with no more than 0.15 wt. %, optionally no more than
0.10 wt. %, optionally no more than 0.08 wt. %, or optionally no
more than 0.07 wt. % of coloring agent(s) or additive(s). The
above-mentioned amounts referred to the amounts of either the
elemental, ionic, and/or oxide form of the agent(s) contained in
the sintered ceramic body. The one or more coloring agents or
additives can be selected from: Tb, V, Ce, Pr, Cr, Co, Nd, Ni, Cu,
Ho, oxides thereof, and combinations thereof. Optionally, the one
or more coloring agents can be selected from: Pr, Tb, Cr, Nd, Co,
oxides thereof, and combinations thereof. The coloring agents can
comprise: at least Pr and/or an oxide thereof; at least Pr, Cr,
and/or oxides thereof; Pr, Cr, Co and/or oxides thereof; and at
least Tb, Nd, and/or oxides thereof. Optionally, the coloring
additives can consist essentially of: Pr and/or an oxide thereof;
Pr, Cr, and/or oxides thereof; Pr, Cr, Co and/or oxides thereof;
and Tb, Nd, and/or oxides thereof.
[0039] A sintered ceramic body including a small amount of one or
more of the coloring agents, as described above can additionally
possess good physical properties, such as a high flexural strength
with a weibull modulus greater than 10. For example, a sintered
ceramic body formed according to the present invention may have an
average flexural strength in excess of 800 MPa, optionally in
excess of 900 MPa, and optionally in excess of 1,000 MPa. The
flexural strength is measured per a conventional three-point bend
test.
[0040] The resulting colors of the as-sintered articles are
suitable for dental restoration frameworks that can be overlaid
with a suitable overlay material, such as a zirconia-porcelain
system, to achieve tooth-colored shades for the finished
restoration.
[0041] The present invention is also directed to methods or
techniques for coloring sintered ceramic bodies. According to one
illustrative technique, an uncolored base ceramic powder can be
combined with one or more additional powders which contain one or
more coloring agents or additives. These additional powders can be
termed "pigments" or "pigment powders." Once these powders have
been combined, they can then be processed according to conventional
techniques to produce a finished sintered body possessing the
desired coloration, and mechanical properties.
[0042] The uncolored base ceramic powder can have any suitable
composition, such as including any of the compositions described
above for base ceramic materials (e.g., YTZP). Similarly, the one
or more coloring agents or additives can also comprise any one, or
combination of, the coloring agents or additives described above.
According to the principles of the present invention, the amount of
the one or more coloring agents contained in the pigment powders,
as well as the proportions of the uncolored base ceramic and
pigment powders, are calculated so as to provide a finished
sintered body having a desired total quantity of coloring agents
contained therein. This calculation can be performed according to
conventional techniques familiar to those skilled in the art, and
which are further elucidated by reference to the following
examples.
[0043] As pointed out in U.S. Pat. No. 6,030,209, the shading of
dental porcelain to achieve tooth colors typically relies on
blending of yellow, pink, grey/blue pigments (i.e., primary colors)
with the "white" porcelain powder to achieve the desired tooth
colors. Surprisingly, this model also seems appropriate for shading
of zirconia, as demonstrated in the following examples.
[0044] Examples 1 to 8 below illustrate how coloring formulations
can be developed via immersion of pre-sintered blanks in solutions
comprising coloring additives. Example 4 also illustrates sintered
bodies that have been provided with colors using a relatively small
amounts of coloring agent. Examples 9 toll illustrate combining
YTZP powder with one or more coloring additives by immersion of
as-received powder in solutions comprising coloring additives in
ionic or complex form. Examples 12 and 13 illustrate combining YTZP
powder with one or more coloring additives by combining YTZP powder
and one or more pigment powders that have been doped with at least
one coloring additive.
[0045] In alternative embodiments of the present invention the
doped powder is fabricated by introduction of coloring additives as
individual oxides or other precursor forms before, during, or after
one of the stages of the manufacturing of said powder such as
hydrolysis, drying, calcination, milling, or spray drying
processing steps. These precursor forms include but are not limited
to individual or complex oxides, salts, inorganic or organic and
organo-metallic compounds (and combinations thereof) added in the
form of aqueous or nonaqueos solutions, emulsions, dispersions,
gels and particulates. All concentrations that are referred to in
the examples are by weight percentage.
[0046] The salts used in the examples are all commercially
available and were obtained from Alfa Aesar, Ward Hill, Mass. The
zirconia powders that were used in the examples were the
commercially available 3Y-TZP grades, TZ-3YB-E, and TZ-3YB, from
Tosoh USA, Inc., Grove City, Ohio. The TZ-3YB-E grade contains
approximately 0.25 wt. % alumina, and the TZ-3YB grade is
essentially alumina-free. For the examples in which it was used,
the TZ-3YB grade is explicitly indicated. All other examples used
the TZ-3YB-E grade. All firing cycles were done in an air
atmosphere. The densities and flexural strengths reported for
select sintered specimens were measured by the Archimedes method,
and per ISO 6872, respectively. Color was evaluated as necessary,
both visually, by a certified dental technician, and measured on a
white background using a ColorTec-PSM.TM. spectrophotometer from
ColorTec.TM., Clinton, N.J. The color parameters were read in
reference to D65/10.degree. illuminations standard. Fluorescence in
the visible light range was evaluated using a model UVL-56
BLAK-RAY.RTM. Lamp, Longwave UV-365 nm, ultraviolet light box from
UVP, Upland, Calif.
EXAMPLE 1
[0047] Salts of Pr, Ce, Tb, V, Fe, Er, Cr, Eu, Ho, Co, Nd, Ni, and
Cu were dissolved in distilled water in the proportions shown in
Table 1. Zirconia discs, 27 mm diameter.times.2.75 mm thick, were
pressed (10 MPa, uniaxial) from TZ-3YB-E powder and subsequently
fired by heating at 1.degree. C./m to 700.degree. C., holding for 2
h (debinderization), followed by heating at 4.degree. C./m to
1100.degree. C., holding for 2 h (presintering), and then cooling
at 4.degree. C./m to ambient. The presintered density was
approximately 3.15 g/cc. Presintered zirconia discs were immersed
in the salt solutions for 10 minutes, removed and then fired by
heating at 4.degree. C./m to 150.degree. C., holding for 2h
(drying), followed by heating at 4.degree. C./m to 1500.degree. C.,
holding for 2 h (sintering), and then cooling at 4.degree. C./m to
ambient. The same firing was also given to a "control", i.e., a
presintered disc that had not been immersed in solution. The
resulting colors are listed in Table 1, and include yellow,
pinkish-mauve (where "mauve" is defined as a "moderate purple"),
pink, grey, blue and green. The control fired to a translucent
white color.
TABLE-US-00001 TABLE 1 Element Solution Color Pr 0.5% Praseodymium
(III) acetate hydrate Yellow Ce 10% Ce(III) nitrate Yellow Tb 0.05%
terbium(III) chloride hexahydrate Yellow-orange V 0.1% vanadium(IV)
fluoride Yellow Fe 1% Iron(II) chloride Yellow Er 10% Erbium (III)
chloride hexahydrate Light Pink Cr 0.05% Cr(III) chloride
hexahydrate Mauve Eu 10% Europium(III) Chloride Hydrate White Ho
10% Ho(III) chloride Yellow/pink Co 0.1% Co(II) chloride Grey Ni
0.5% Ni(II) chloride Green Cu 0.5% Cu(II) acetate Green Nd 5%
Nd(III) chloride hydrate Light blue
EXAMPLE 2
[0048] Solutions of Tb(III) chloride hexahydrate and V(IV)
fluoride, of different concentrations were prepared (Table 2).
Pre-sintered zirconia discs were immersed in the solutions and
fired as per Example 1. The results are shown in Table 2 and
demonstrate that the intensity of the color achieved, yellow, can
be controlled by the solution concentration. Specifically, one can
increase the yellow intensity by increasing solution
concentration.
TABLE-US-00002 TABLE 2 Solution Color Tb(III) chloride hexahydrate,
% 0.005 Pale yellow 0.01 medium yellow 0.05 Yellow V(IV) fluoride,
% 0.005 pale yellow 0.01 pale yellow 0.10 yellow
EXAMPLE 3
[0049] Solutions of Praseodymium (III) acetate hydrate and Cr(III)
chloride hexahydrate, of different concentrations were prepared
(Table 3). Pre-sintered zirconia discs were immersed in the
solutions and fired as per Example 1. Some discs were sintered in
the as-pre-sintered state, and were the controls. Flexural
strengths were measured for as-fired surfaces using the
3-point-bend test configuration. The results are shown in Table 3.
Again, the results show that the intensity of the color achieved,
can be controlled by the solution concentration. Additionally,
coloring with 0.01% Pr-acetate and 0.01% Cr-chloride does not
appear to adversely affect densification or flexural strength,
i.e., the densities and flexural strengths of Pr- and Cr-colored
specimens was statistically the same as for the control.
TABLE-US-00003 TABLE 3 Density Solution Color (g/cc) Flexural
Strength (MPa) % Pr(III) acetate hydrate 1 orange -- -- 0.25 dark
yellow 6.00 -- 0.10 medium yellow 6.05 1,106 .+-. 327 (n = 8) 0.05
yellow 6.08 -- 0.01 pale yellow -- -- % Cr(III) chloride
hexahydrate 0.10 dark pinkish- 6.07 1,099 .+-. 184 (n = 10) mauve
0.05 medium 6.03 -- pinkish-mauve 0.01 light pinkish- -- -- mauve
None (control) white 6.07 1,153 .+-. 261 (n = 8)
EXAMPLE 4
[0050] Three solutions were prepared by dissolving
Praseodymium(III) acetate hydrate, Chromium(III) chloride
hexahydrate, and Co(II) chloride in distilled water in the
proportions shown in Table 4. Pre-sintered zirconia discs were
immersed in the solutions and fired as per Example 1. The discs
were thinned to 0.5 mm and the surface color was evaluated. The
results are shown in Table 4 along with the calculated
concentrations of the coloring additive ions as calculated based on
the solution concentration and the assumption that during
immersion, the solution completely filled the pore volume of the
pre-sintered bodies.
TABLE-US-00004 TABLE 4 Total Concentration % % Cr(III) of Coloring
Pr(III) chloride Ions Flexural acetate hexa- % Co(II) Density
(calculated) Strength Shade hydrate hydrate chloride (g/cc) CIE L,
a, b wt. % (MPa) 1 0.025 0.025 0 6.07 81.78, 0.0026 n/a 1.12, 18.05
2 0.008 0.002 0 n/a 87.4, -0.37, 0.0007 n/a 12.36 3 0.024 0.005
0.005 6.07 .+-. 0.01 86.55, 0.0024 921 .+-. 203 0.34, 9.59 (n =
12)
[0051] Shades 1, 2 and 3 did not fluoresce under UV illumination.
Shades 1, 2 are considered appropriate core shade for some of the
Vita Classic A, C and D shades, respectively. These results show
that YTZP can be shaded via combinations of Pr, Cr and Co, to
achieve coloration that is appropriate for dental frameworks.
EXAMPLE 5
[0052] Pre-sintered 25.times.10.times.2.5 mm.sup.3 TZ-3YB bars were
machined by hand into a "shade tab" geometry using a dental
handpiece with a diamond bur. This entailed shaping one end of the
bar into a veneer that was approximately 0.6 mm in thickness. The
shaped bar was immersed for 10 minutes in the coloring solution
corresponding to Shade 1 of Table 4, and fired as per Example 1.
The as-sintered shade tabs were nearly fully dense (6.05 g/cc),
translucent, with a thickness of approximately 0.5 mm for the
veneer portion. The veneer portion was overlayed with the zirconia
porcelain, OPC 3G, Pentron Ceramics Inc., Somerset, N.J., to
achieve tooth colored shade of approximately Al of the Vita Classic
shade guide.
EXAMPLE 6
[0053] A colored shade tab prepared as per Example 5 was overlayed
with porcelain as per Example 5, to achieve a tooth colored shade
of approximately A2 of the Vita Classic guide.
EXAMPLE 7
[0054] A pre-sintered shade tab prepared as per Example 5 was
immersed for 10 minutes in the coloring solution corresponding to
Shade 3 of Table 4, and fired as per Example 1. The resulting fully
sintered specimen was overlayed with porcelain as per Example 5, to
achieve a tooth colored shade of approximately D3 of the Vita
Classic shade guide.
EXAMPLE 8
[0055] A 0.25 wt. % solution of Praseodymium (Ill) acetate hydrate
in distilled water was prepared. Pre-sintered zirconia discs, 27 mm
dia..times.2.75 mm thick, and pellets 16 mm diameter by 10 mm tall,
were prepared as per Example 1. These were immersed in the
solutions for a range of times from 10 minutes up to 144 h, and
fired as per Example 1. The resulting surface coloration was an
orangish-yellow, and was approximately same for all specimens. The
specimens were cross-sectioned revealing that the coloring depth
increased with immersion time. The cores of all the specimens were
white in color.
TABLE-US-00005 TABLE 5 Approximate Depth of immersion time
coloration (mm) 10 min 0.25 2 h 0.5 72 h 2.5 144 h 3
EXAMPLE 9
[0056] A 0.25 wt. % solution of Praseodymium(III) acetate hydrate
in distilled water was prepared. The solution was added to TZ-3YB-E
powder in a one-to-one ratio, by weight. The powder+solution
combination was stirred thoroughly and then dried by heating to
150.degree. C. and holding for 4 h. The dried powder was screened
through a 170 mesh (90 .mu.m) nylon screen, and pressed into discs
as per Example 1. The discs were debinderized by heating at
1.degree. C./m to 700.degree. C., and holding for 5 h, followed by
heating at 4 .degree. C./m to 1500.degree. C., and holding for 2 h,
to sinter the bodies, and then cooling at 1.degree. C./m to
ambient. This resulted in a dark-yellow colored body that was
colored through the thickness and had a density of 6.07 g/cc. This
example demonstrates that colored TZP blocks can be manufactured by
immersing the powder in the coloring salt solution prior to drying
followed by compaction.
EXAMPLE 10
[0057] Solutions of Praseodymium(III) acetate hydrate and
Chromium(III) chloride hexahydrate in distilled water were prepared
according to Table 6.
TABLE-US-00006 TABLE 6 Pr(III) acetate hydrate Cr(III) chloride
Solution (wt. %) hexahydrate (wt. %) Distilled Water 1 0.5 0
Balance 2 0 0.05 Balance 3 0 0 Balance
[0058] A third "solution", 100% water, served as the control. The
solutions were individually added to TZ-3YB-E powder in a 8-to-25
ratio, by weight, and the combinations were thoroughly mixed. The
resulting blends were subsequently freeze-dried for approximately
12 hours and screened through a 250 mesh (55 micron) nylon screen
to yield a free-flowing powder. Discs, 27 mm diameter by 1.2 mm
thick, were pressed from these powders as per Example 1, and fired
by heating at 1.degree. C./m to 700.degree. C., and holding for 2 h
(debinderization step), followed by heating at 4 .degree. C./m to
1500.degree. C., and holding for 2 h (sintering step), and then
cooling at 4 .degree. C./m to ambient. The results are shown in
Table 7.
TABLE-US-00007 TABLE 7 Nominal coloring dopant content (wt. %) Bend
Pr Cr Color Density Strength Solution (Pr.sub.6O.sub.11)
(Cr.sub.2O.sub.3) Visual CIE L, a, b (g/cc) (MPa) 1 0.0709 0 Yellow
82.15, 2.93, 37.12 6.09 1152 .+-. 208 (0.0856) 2 0 0.0031 Mauve
81.49, 1.67, 7.67 6.05 997 .+-. 119 (0.0046) 3 0 0 white 88.76,
-0.14, 3.69 6.07 1026 .+-. 178
[0059] These results show that doping of TZ-3YB-E with
approximately 0.07 wt. % Praseodymium(III) yields a yellow sintered
body with no compromise in density and strength. Also, they
demonstrate that doping with approximately 0.003 wt. % of Cr(III)
yields a sintered body that is pinkish-mauve in color with no
compromise in density and strength. For all cases, coloration was
uniform and was through the thickness of the sintered samples.
EXAMPLE 11
[0060] Three solutions of Praseodymium(III) acetate hydrate
+Chromium(III) chloride hexahydrate in distilled water were
prepared according to Table 8.
TABLE-US-00008 TABLE 8 Pr(III) acetate hydrate Cr(III) chloride
Solution (wt. %) hexahydrate (wt. %) Distilled Water 4 0.0625 0.025
Balance 5 0.1875 0.03125 Balance 6 0.125 0.0625 Balance
[0061] These solutions were used to process TZ-3YB-E powders into
sintered dics as per Example 10. Color and fluorescence evaluation
was done as per Example 4 on discs that had been thinned to 0.5 mm.
Visual color evaluation entailed comparing the colored discs to a
3M.TM. ESPE.TM. LAVA.TM.Frame Shade Tabs set available from
Issaquah Milling Center, Issaquah, Wash. The set consists of 0.5 mm
thick sintered zirconia specimens that had been shaded with the
3M.TM. ESPE.TM. LAVA.TM.Frame Shade Dyeing Liquids, 3M Center, St.
Paul, Minn., to the core shades: FS1, FS2, FS3, FS4, FS5, FS6 and
FS7. The results are presented in Table 9.
TABLE-US-00009 TABLE 9 Color Nominal Visual coloring dopant (vs.
content (wt. %) LAVA .TM. Pr Cr frame Density Solution
(Pr.sub.6O.sub.11) (Cr.sub.2O.sub.3) shades) CIE L, a, b (g/cc) 4
0.0089 0.0016 Close to FS2 83.99, -0.55, 6.06 (0.0107) (0.0023)
15.81 5 0.0267 0.0019 Close to FS3 85.19, -1.44, 6.06 (0.0322)
(0.0028) 21.32 6 0.0177 0.0047 Matches FS7 81.6, -0.04, 6.12
(0.0214) (0.0069) 18.85
[0062] Tooth colorations were achieved, and for all cases the
coloration was uniform and was through the thickness of the
sintered samples. Additionally, the tooth colored specimens did not
fluoresce under UV illumination. These results demonstrate that the
coloring dopants, Pr and Cr, can be used in combination to achieve
shades appropriate for achieving finished restorations that are
tooth-colored. It is noteworthy that the dopant levels required are
of very low concentrations, e.g., Pr<approximately 0.030% and
Cr<approximately 0.005%.
EXAMPLE 12
[0063] Solutions of 0.75 wt. % Praseodymium(III) acetate hydrate
and 0.25 wt. % Cr(III) chloride hexahydrate, in distilled water
were prepared. These solutions were individually mixed with
TZ-3YB-E powder, dried and screened, as per Example 10. This
yielded powders nominally doped with 0.1063% Pr and 0.0156% Cr,
respectively. The doped powders were then combined with as-received
TZ-3YB-E powder in the following properties: 8.3725%
Pr-doped+10.2564% Cr-doped+81.3711% as-received TZ-3YB-E powder,
and blended for 15 minutes using a paint shaker. (The proportions
were calculated to give the same bulk nominal Pr and Cr
concentration as Solution 4 of Table 9.) Several sintered discs
were prepared from the powders as per Example 10, and their color
was evaluated as per Example 11. Remarkably, visually, the color of
the discs was uniform when viewed at 1.times., 4.times. and
8.times. magnifications. One of the discs was thinned to 0.5 mm in
thickness and CIE L*, a*, b* color coordinates of 84.21, -0.85,
18.25, respectively, were determined. Visually this specimen
matched LAVA core shade FS2. Also, it did not fluoresce under UV
illumination. Strength was measured to be 1,161.+-.178 MPa
(n=8).
EXAMPLE 13
[0064] The doped powders of Example 12 were combined with
as-received TZ-3YB-E power in the following proportions: 16.651%
Pr-doped+30.1782% Cr-doped+53.2208% as-received TZ-3YB-E powder,
and blended for 15 minutes using a paint shaker. (These proportions
were calculated to give the same bulk nominal Pr and Cr
concentration as Solution 6 of Table 9.) Several sintered discs
were prepared from the powders as per Example 10, and their color
was evaluated as per Example 11. Like in Example 12, visually, the
color of the discs was uniform. One of the discs was thinned to 0.5
mm in thickness and CIE L*, a*, b* color coordinates of 80.64,
-0.41, 19.37, respectively, were determined. Visually this specimen
matched LAVA core shade FS7 and did not fluoresce under UV
illumination. Strength was measured to be 1,025.+-.178 MPa
(n=7).
EXAMPLE 14
[0065] Zirconia powder with a composition corresponding to Solution
6 of Table 9 is pressed into cylindrical blocks that are 2.0 cm
dia..times.4.0 cm long. This is done with a wet-bag cold isostatic
press at pressure of 200 MPa using polyurethane tooling. The blocks
are heated at 1.degree. C./m to 700.degree. C., and held for 10 h
(debinderization), followed by heating at 4.degree. C./m to
1000.degree. C., and holding for 2 h (presintering), and then
cooling at 4.degree. C./m to ambient. The green density of the
pre-sintered blocks is approximately 3.15 g/cc.
[0066] Using the laser scanner, D-250.TM. 3D Scanner, 3Shape A/S
Copenhagen, Denmark, models of a single-unit and 3-unit-bridge
preparations are scanned to create a 3D digital model which are
saved as STL files. Using these files, the dental CAD software,
DentalDesigner.TM., 3Shape A/S Copenhagen, Denmark is used to
design the corresponding frameworks. The 3D models are saved as a
STL files. These are transferred to a commercial CAM device with
the ability to enlarge 3D digital model by the appropriate
enlargement factor. Using an enlargement factor of approximately
1.243, which is inputted into the CAM software, the presintered
blocks are machined into an oversized single-unit and 3-unit-bridge
frameworks. The as-machined frameworks are sintered as per Example
10. The resultant sintered frameworks are of high density
(approximately 6.05 g/cc), translucent, and uniformly colored with
a shade closely matching LAVA FS7. The fit of the as-sintered
frameworks onto the starting models is determined to be acceptable.
This is indicative of isotropic shrinkage during the sintering
step. The as-sintered frameworks are overlayed with Noritake
Cerabien CZR Porcelain, Noritake Company, Inc., Fairlawn, N.J., to
achieve a final VITA classic shade D2. The fit of the finished
restorations to the starting models are determined to be
acceptable. Shades and fit are evaluated by a certified dental
technician.
EXAMPLE 15
[0067] Zirconia powder prepared as per Example 12 is processed into
cylindrical CAD/CAM blocks as per Example 14. The blocks are then
processed into sintered single-unit and 3-unit-bridge frameworks as
per Example 14. The resultant sintered frameworks are of high
density (approximately 6.05 g/cc), translucent, and uniformly
colored with a shade closely matching LAVA FS2. The fit of the
as-sintered frameworks onto the starting models is determined to be
acceptable. The as-sintered frameworks are overlayed with Noritake
Cerabien CZR Porcelain, Noritake Company, Inc., Fairlawn, N.J., to
achieve a final VITA classic shade A2. The fit of the finished
restorations to the starting models are determined to be
acceptable. Shades and fit were evaluated by a certified dental
technician.
[0068] Numbers expressing quantities of ingredients, constituents,
reaction conditions, and so forth used in this specification are to
be understood as being modified in all instances by the term
"about". Notwithstanding that the numerical ranges and parameters
setting forth, the broad scope of the subject matter presented
herein are approximations, the numerical values set forth are
indicated as precisely as possible. For example, any numerical
value may inherently contains certain errors resulting from the
standard deviation found in their respective measurement techniques
or in rounding off of measured values. None of the elements recited
in the appended claims should be interpreted as invoking 35 U.S.C.
.sctn.112, 6, unless the term "means" is explicitly used.
[0069] Although the present invention has been described in
connection with preferred embodiments thereof, it will be
appreciated by those skilled in the art that additions, deletions,
modifications, and substitutions not specifically described may be
made without department from the spirit and scope of the invention
as defined in the appended claims.
* * * * *