Note: Descriptions are shown in the official language in which they were submitted.
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POLYMER CORE PROSTHETIC DENTAL DEVICE
WITH AN ESTHETIC SURFACE
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is continuation of U.S. Patent Application No. 11
/622,171,
filed January 11, 2006, which is a continuation-in-part of U.S. Patent
Application
No. 11/420,024, filed May 24, 2006, both of which are hereby incorporated
herein by
reference in their entirety.
BACKGROUND
1. Field of the Invention.
[0002] The present invention relates to prosthetic dental devices and, more
particularly, to methods and materials used to construct prosthetic dental
devices.
2. Description of the Related Art.
[0003] Often, it is desirable to replace lost, missing, injured or diseased
teeth using
prosthetic dental devices. Prosthetic dental devices include, for example,
implants which
are inserted into the mandible or maxilla of a patient. Other dental devices
temporarily
cover the implant until a sufficient amount of bone osseointegrates with the
implant to
support and anchor the implant during mastication. Such devices used during
this
"healing process" include provisional gingival cuffs, healing screws, healing
collars and
healing caps. Other structures include abutments which are attached to the
implant to
serve as a mount for a prosthetic tooth, and may be permanent or provisional.
[0004] Some of these dental devices may be visible, or have portions that may
be
visible, when viewing a dental patient's face. For instance, an abutment which
supports a
prosthesis can have a visible area near the gums that is not covered by the
prosthesis.
When these visible areas are made of metals or plastics that do not have the
color of
natural teeth, the dental devices provide a non-esthetically pleasing
appearance on a
person's face. To attempt to address this shortcoming in appearance, there are
dental
devices that have the color of natural teeth. These devices, however, tend to
lack
adequate strength which may result in relatively frequent replacement or
repair.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is an exploded, cross-sectional view of a prosthetic dental
device in
accordance with one embodiment with features of the present invention;
[0006] FIG. 2 is a perspective view of an abutment of the device of FIG. 1;
[0007] FIG. 3 is a cross-sectional view of the abutment taken along line III-
III on FIG.
2;
[0008] FIG. 4 is an exploded, cross-sectional view of another embodiment of a
prosthetic dental device with features in accordance with the present
invention;
[0009] FIG. 5 is a cross-sectional view of an alternative abutment in
accordance with
features of the present invention;
[0010] FIG. 6 is an exploded, fragmentary, perspective view of yet another
embodiment of a prosthetic dental device in accordance with features of the
present
invention;
[0011] FIG. 7 is a cross-sectional view of an alternative provisional device
in
accordance with features of the present invention;
[0012] FIG. 8 is a flow chart of a general exemplary process for manufacturing
a
dental prosthetic device with features of the present invention; and
[0013] FIG. 9 is a flow chart of further steps for the process of FIG. 7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] Referring to FIG. 1, a prosthetic dental device 10 is illustrated and
is used for
restoring an edentulous area in a dental patient's mouth. The prosthetic
dental device 10
has an abutment 12 threadedly mounted on an implant 14 on a person's jaw 16
during
dental surgical procedures. The jaw 16 may be the mandible or the maxilla. The
abutment 12 supports a tooth-shaped prosthesis 18 that may or may not cover
the entire
abutment 12. A prosthesis or prosthetic tooth typically includes an inner
cavity designed
to accept an abutment and an outer portion that replicates the appearance and
hardness of
a natural tooth. The prosthetic tooth may be cemented, screwed, or otherwise
fastened to
the abutment.
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[0015] Referring to FIGS. 2-3, the abutment 12 has a core or an inner portion
20 and =
an esthetic outer layer or portion 22 that may be integrally formed with a
metal retaining
screw 24 for attachment to the implant 14. The abutment 12 has a bore 26 to
provide
access to the head of the screw 24 and may be plugged with cement or other
material
once mounted on the implant 14. The inner portion 20 is not particularly
limited to any
color since it is covered, as explained below, by the esthetic outer portion
22. Thus, the
inner portion 20 may have a high strength polymer with a dark color or other
esthetically
displeasing color that is substantially different than the color of natural
teeth and different
than the color of the outer portion 22.
[0016] The outer portion 22 is made of an outer material with an esthetically
pleasing
color that is substantially the same color as natural teeth. In this example,
the illustrated
outer portion 22 covers substantially the entire inner portion 20. This may be
provided
when the prosthesis 18 is translucent and a dark colored inner portion 20 may
show
through the prosthesis. Of course, the outer portion 22 may also be provided
covering
substantially the entire inner portion 20 when it is more cost effective to do
so during
molding processes.
[0017] In order to provide an appropriate natural-tooth color for the outer
portion 22,
the outer portion is made of a polymer with a colorant. Thus, to form a strong
and stable
bond at the interface of the inner portion 20 and the outer portion 22, it is
also desirable to
form the inner portion 20 with a polymer. Optionally, the inner portion 20
and/or the
outer portion 22 may be made of a composite material including a polymer mixed
with a
reinforcing component such as particulates, fibers, and/or porous foams
described below.
[0018] Referring to FIG. 4, by another approach, a prosthetic dental device 40
has an
abutment 42 with a through-bore 44 for receiving a separate retaining screw 46
which
attaches the abutment 42 to an implant 48. The implant 48 and the abutment 42
may have
an anti-rotational and tactile connection structure, such as a hex connection
and/or splines
50 (shown in dashed lines).
[0019] The abutment 42 has an outer portion 52 that covers at least parts of
an inner
portion 54 that are most likely to be left uncovered by the prosthesis 18
(shown in
phantom line) such as by the gum line. Thus, when the prosthesis configuration
is known,
the outer portion 52 may be shaped to cover substantially only those parts of
the inner
portion 54 that will be left uncovered by the prosthesis. Alternatively, the
outer portion
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52 may have extensions 56 (as shown in dashed line), to cover more of the
inner portion =
52 including parts of the inner portion 52 covered by the prosthesis 18. The
outer portion
54 also may have a cylindrical inner portion 58 to optionally cover the
surface forming
the through-bore 44.
[0020] Referring to FIG. 5, a substantially cylindrical abutment 60 is
illustrated and
has a polymer-containing inner portion 62 of a dark, non-tooth color (such as
black)
covered by a polymer-containing, outer esthetic portion 64 that is
substantially the same
color as natural teeth (such as a white, ivory, or white-yellow shade, to name
some
possible examples). The abutment 60 has a bore 66 to provide access to an
integrally
formed retaining screw 68. The bore 66 is not coated with the material of the
outer
portion 64 in this example. The cylindrical abutment 60 of FIG.5 was used for
producing
nine test examples, and the specific composition of the inner and outer
materials for each
of the nine produced examples are described in detail below.
[0021] It will be appreciated that in addition to, or instead of, an abutment,
the
structure with an outer esthetic, polymer portion covering an inner polymer
portion, may
be provided on other pieces of a prosthetic dental device, including the
prosthesis, the
implant, and/or the retaining screw. Referring to FIG. 6, in another example,
a prosthetic
dental device 70 has a healing screw 78 with the described inner and outer
portions. The
prosthetic dental device 70 includes a threaded dental implant 72 that engages
a hole 74
in a mandible 76 or maxilla, which is created during a surgical procedure or
following
tooth extraction. The healing screw 78 includes a threaded shaft 80 extending
from a
head 82. The threaded shaft 80 engages a threaded aperture 84 of the implant
72. The
healing screw 78 prevents debris from entering, and gingival tissue from
growing into,
the aperture 84 while the mandible 76 heals during the osseointegration of the
implant 72
with the mandible 76. In this case, at least the top of the head 82 of the
healing screw 78
may have a polymer-based esthetic outer portion over a polymer-based inner
portion.
[0022] Other dental devices also may have the described inner and outer
portions
such as a gingival cuff which is meant to be placed near the gum line.
Provisional
devices used during osseointegration between the implant and the jaw bone or
while a
restoration, such as a coping or crown, is being fabricated, also may have the
described
structure. This may include a temporary healing cap or collar placed over an
abutment
integrally formed with an implant. In some embodiments, a provisional device,
such as a
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fixture mount 90 as shown in FIG. 7, may be used to place the implant into the
surgical =
site. For example, a screw shaped implant connected to the fixture mount 90
could be
threaded into the site by applying a driving tool to a polygonal recess 92 on
the fixture
mount. This fixture mount 90 would be pre-assembled to the dental implant by
the
manufacturer. An inner polymer portion 94 of the fixture mount 90 would have
adequate
material strength to withstand loads associated with driving the thread. An
outer portion
96 would provide a tooth colored covering so that the fixture mount 90 can
remain in
place during healing and provide an esthetic temporary restoration.
[0023] In any of the embodiments illustrated as described herein, both the
inner
portion and the outer portion are made of a polymer material. The polymer
material can
be a thermoplastic polymer including, without limitation, a poly(aryl ketone),
including
aromatic polyether ketones, such as polyether ether ketone (PEEK),
polymethylmethacrylate (PIVIMA), polyaryl ether ketone (PAEK), polyether
ketone
(PEK), polyether ketone ether ketone ketone (PEKEKK), polyether ketone ketone
(PEKK), and/or polyetherimide (PEI), polysulfone (PSu), and polyphenylsulfone
(PPSu), -
or a combination of thermoplastic polymers. One suitable polymer is ULTEM
polyetherimide available from General Electric Plastics, Inc. headquartered in
Pittsfield,
MA. Another suitable polymer is Radel polyphenylsulfone available from Solvay
Advanced Polymers, LLC, headquartered in Alpharetta, GA. Other sufficient PEEK
polymers include PEEK GATONETM (provided by Gharda, Inc., Mumbai, India), PEEK
450 (provided by Victrex, Inc., Lancashire, United Kingdom), and PEEK-CLASSIX
(provided by Invibio, Inc., Lancashire, United Kingdom). An acceptable PEKK
polymer
includes PEKK A1050 (provided by Polymics, Inc., State College, PA).
[0024] By one approach, and as used for the nine produced examples, at least
one of
the inner portion and the outer portion are formed of PEEK or PEKK.
Alternatively, both
the inner portion and the outer portion may be formed of the same polymer or
one portion
may be formed of PEEK while the other portion is formed of PEKK.
[0025] In order to strengthen the inner and/or outer portions, the inner and
/or outer
material may be a composite material that includes a reinforcing component.
The
reinforcing component can be particles, fibers, and/or porous foams,
including, without
limitation, carbon, alumina, zirconia, yttria-stabilized zirconia, magnesium-
stabilized
zirconia, E-glass, S-glass, calcium phosphates, alumina, titanium dioxide,
and/or calcium
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phosphates, such as hydroxyapatite or a biphasic calcium phosphate comprised
of
hydroxyapatite and tricalcium phosphate which also improve osseointegration of
the
dental device with surrounding bone. The fibers also may be other metal or
alloy-based
materials such as titanium, Ti6Al4V, Ta, stainless steel, and/or 316L
stainless steel, or
may even be made of the polymers themselves, such as PEEK, PEKK, or other
aramid
fibers such as Kevlar (provided by E.I.duPont de Nemours and Co., Wilmington,
DE).
A polymer reinforcing component may be placed in the same polymer material
forming
the bulk or matrix of the inner or outer portions.
[0026] The proportion of reinforcing component, such as ceramic particles or
fibers,
in the inner or outer composite material is equal to or less than
approximately 70% by
weight of the total inner or outer composite material, preferably between
approximately
20 to 60% and, most preferably, between approximately 30 to 50%. In one case,
the
fibers are provided at about 30%, and in another case, the fibers are provided
at about
35%. The proportion may be equal to or less than approximately 99% when, for
example,
the reinforcing component is relatively heavy, metal-based fibers or foam,
such as a Ta
foam.
[0027] The reinforcing component, also referred to as a filler material, can
include,
without limitation, spherical shapes, elongate fibers, or other shapes. In one
example, the
reinforcing component includes nanoparticles with a size range from about 1 nm
to about
100 nm, and/or microparticles with a size range from about 100 nm to about 100
m.
These fibers may have a length-to-diameter ratio in a range of about 1 to
1000. In some
cases, this ratio may be as low as about 10, 20, or 25 and as high as about
100, 150 or
1000. The length of the fibers can vary to as short as about 1 mm and as long
as about 50
mm. In a number of the nine produced examples described below, fibers were
about 1-2
mm long and had length-to-diameter ratios of about 8-16. Other examples
provide more
desirable length-to-diameter ratios of about 250 to 860, where the lengths of
the fibers are
5-6 mm.
[0028] The fibers may have a varying diameter in order to increase resistance
to wear,
and may include various types of fibers and particles including nanoparticles
that fuse to
fibers to increase the fracture toughness of the composite material or to
control the color
of the composite material. These alternative features are explained in detail
in the parent
U.S. patent application.
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[0029] As mentioned above, the outer material is substantially the same color
as =
natural teeth. The raw polymer materials PEEK-CLASSIX and ULTEM are obtained
with the colorant already mixed with the polymer. For other raw polymer
materials, the
colorant must be added to the polymer to obtain the desired natural-tooth
color. In one
example, the colorant mixed with the polymer is an inorganic material, such as
rutile
and/or titanium dioxide (TiOZ). In this case, the colorant is provided, by
total weight of
the inner or outer composite material, at about approximately less than 20%,
but
preferably approximately between 5 to 15% and, more preferably, between 7 to
12%.
For some of the nine produced examples, the colorant is provided at
approximately 10%
of the composite material weight. The colorant also is provided with a
particle size of
about 0.1 to 100 m and, more preferably, from about 0.1 to 10 m and, most
preferably,
from about 0.5 to 5 m.
[0030] Referring to FIGS. 8-9 , a method for forming 100 a prosthetic dental
device
includes providing 102 an outer material. As mentioned above, a raw polymer
material
that already has a desired esthetic color and/or is pre-mixed with a
reinforcing component
may be obtained. In this case, the raw material is provided in pellets that
may only need
milling to a desired size before the pellets are ready to be heated for
injection into a mold.
[0031] In the alternative, a compounding process may be used to heat a polymer
material 116, a separately provided colorant 118 (if present), and/or a
separately provided
reinforcing component 120 (if present) into a viscous state and mechanically
mix 124 the
heated substances into a composite material 126. Before compounding, dry pre-
blending
may be performed to better achieve good dispersion using a suitable mixer,
such as a
Sigma-type mixer, if necessary. In one embodiment, the polymer material may
possess a
desired viscous state at substantially room temperature and may not need to be
heated. It
is desirable to mix the composite material 126 until the colorant 118 and the
reinforcing
component 120 is substantially evenly distributed throughout the polymer
material.
Subsequently, the composite material 126 is extruded or pressed through an
orifice of a
die. As the composite material exits the orifice, it is cut into small, semi-
cylindrical
pieces, or pellets. This compounding process may be performed using a ZSK-25
twin
screw extruder. Alternatively, the composite material may be directly inserted
into a mold.
It will also be understood that the composite material could be formed into at
least one
block that is subsequently altered into a desired shape.
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[0032] Prior to, or contemporaneous with, the compounding process described
above,
the reinforcing component 120, or the composite material 126, may optionally
be treated
with a coupling agent 122 in order to increase molecular bonding in the
material and
between the inner and outer portions. The coupling agents, such as silane and
others, and
their use are described in detail in the parent U.S. patent application.
[0033] Pellets ready for injection molding are then transferred into an
injection
molding machine, in which the outer material, for example, and particularly
the polymer
material component, is heated to obtain a desired viscosity unless the outer
material
possesses a desired viscous state at substantially room temperature. Once the
material is
in a desired viscous state, it is injected as described below. During this
process, the
reinforcing component and colorant, if present, remains substantially
suspended within
the polymer material. The same process for providing the outer material may be
used to
provide the inner material 104 as well.
[0034] For the nine produced examples described below, an over-molding or two-
stage molding injection process (also called multi-component, transfer or
insert molding)
was used to form the prosthetic devices with an Engel 100 TL injection molding
machine.
In order to mold the inner and outer portions, the material for the inner
portion was
injected 106 into a first mold for forming the inner portion or core of an
abutment and
over a retainer screw. Once the core was sufficiently cooled and solidified,
it was
inserted into a second mold. The material for the esthetic outer portion was
then injected
108 into the second mold and over the solidified inner portion. Although the
two
materials are injected separately, a chemical bond or a mechanically
interlocking structure
may be formed between the two portions. The materials are then permitted to
cool to
form 110 of the dental device.
[0035] Alternatively, the examples may be formed by co-injection molding. In
this
process, a single mold is used and the outer material is injected 112 into the
mold first to
form the esthetic outer portion. When the outer material is injected, it forms
a fountain
flow and begins to fill and coat the outer surfaces of the mold cavity. The
inner material
is then injected 114 immediately following the outer material before can cool
and solidify.
This results in improved bonding and interlocking properties at the interface
between the
inner and outer portions. The materials then set in the mold to form 110 the
prosthetic
dental device.
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[0036] After sufficient time has elapsed, the prosthetic dental device is in a
=
substantially solid form and can be removed from the mold. Subsequent to
either
injection molding process 106 or 112, the prosthetic dental device can be
machined and
polished to reduce undesired deformities and surface roughness. Additionally,
the outer
surface of the dental device may be treated by a gas plasma cleaning process
to enhance
bonding between the prosthetic dental device and an adhesive that may be used
to attach
to a prosthesis, for example, if desired.
[0037] With this method, any number of different composite and non-composite
materials may be injected sequentially to form an integrated dental device.
Thus, the
prosthetic dental device may have other layers in addition to the inner and
outer portions
described above. The color of each layer may be selected to provide a range or
gradient
of colors in the same device. Further, the materials for each layer may be
selected to
provide different structural or chemical properties in different regions of
the prosthetic
dental device. Such extra layer or layers may be formed under the inner
portion, between
the inner and outer portions, or over the outer portion. It will be
appreciated that the -
surface finish and other optical properties, including, without limitation,
reflectance,
opacity and specularity also can be adjusted by the selection of the polymer
material, the
reinforcing component, and/or additives as mentioned herein.
EXAMPLES
[0038] Below are descriptions of nine produced examples of prosthetic dental
device
structures with inner and outer portions as described above. The compositions
of the
materials for each produced example are listed in Table I as well as described
below.
While these examples were provided for a cylindrical abutment such as that
depicted in
FIG. 5, the composition for the inner and outer portions for each example
could be used
on any of the other dental devices described herein and any other dental
device that
requires both strength for mastication and a natural-tooth color. All
percentages below
are weight percentages unless indicated otherwise.
[0039] For Examples 1-6, the outer esthetic material is made from a raw
polymer or
composite material that is already premixed with a colorant to provide a
natural tooth
color. For Examples 7-9, a separate colorant is mixed with the raw polymer or
composite
material to establish the natural-tooth color. ii
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[0041] Example 1. In this example, the inner material is a composite with
polyether
ether ketone and specifically PEEK GATONETM 5330 CF (provided by Gharda,
Inc.). The
PEEK is provided in pellets premixed with about 30 wt. % carbon fibers. More
specifically,
the carbon fibers comprise about 30% of the combined weight of the carbon
fibers and PEEK
mixed together. The inner composite material has a dark black color.
[0042] For the outer material, ULTEM 1010 polyetherimide (by GE Plastics,
Inc.) is
provided as pellets pre-mixed with colorant in its raw form. This outer
material is
substantially the same color as natural teeth and has low translucency so that
the black inner
material is substantially undetectable through the outer material.
[0043] As explained above for the process illustrated in FIGS. 8-9, the inner
composite
material was heated and injected into a first mold for forming the core of the
abutment. It
was then permitted to cool before placing the solidified core in a second
mold. The outer
material was then heated and injected into the second mold and over the inner
material where
it was permitted to cool to complete the dental abutment. Once cooled, the
abutment was
removed from the mold and machined and/or cleaned as required.
[0044] Example 2. In this example, the method of producing an abutment was the
same
method as described in Example 1, except the ULTEM 1010 polyetherimide for
the outer
material was replaced with the PEEK-CLASSIX polymer which is also
substantially the
same color as natural teeth and has low translucency. The carbon fibers in the
inner
composite material have a length of about 5-6 mm and a diameter of about 7 m
for a length-
to-diameter ratio in a range of about 715 to 860.
[0045] Example 3. In this example, the inner composite material includes the
polymer
PEEK 450 (by Victrex Inc.) provided as pellets. The PEEK was milled into a
powder and
sieved with a 200 mesh sieve. About 30 wt. % alumina fibers (A102) were then
mixed with
the PEEK in a Sigma-type mixer to provide the reinforcing component. The
alumina fibers
have a diameter of about 120 m and a length of about 1-2 mm for a length-to-
diameter ratio
of about 8 to 16. The inner composite material in powder form was then
compounded with a
ZSK-25 twin-screw extruder into composite pellets. This forms an inner
material that is
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dominantly grey with the fibers visible as light colored specks. The outer
material included
PEEK-CLASSIX polymer prepared as explained above for the outer material of
Example 2.
Thereafter, the inner and outer mixtures were heated and separately injected
into a mold
cavity to form a dental abutment as also explained above in Example 1.
[0046] Example 4. In this example, the esthetic outer material is the same as
Example 3
and is prepared in the same manner. For the inner composite material, the PEKK
A1050
polymer (by Polymics, Inc.) is mixed and compounded with about 30 wt. %
alumina fibers
(A10Z) of about the same size as the fibers of Example 3. The inner composite
material is
black with fibers showing as light colored specks. Both the inner and outer
materials were
injected as explained above for Example 1.
[0047] Exam]2le 5. In this example, the inner composite material includes PEKK
A1050
with about 30 wt. % zirconia fibers (Zr02) present as a reinforcing component.
The zirconia
fibers also have a diameter of about 120 m and a length of about 1-2 mm. The
PEKK and
zirconia fibers were mixed and compounded as described above for the inner
material of
Example 3 and formed a black substance with the zirconia fibers showing as
light colored
specks. Here, the substantially tooth-colored ULTEM 1010 was used as the
esthetic outer
material. Both the inner and outer materials were injected as explained above
for Example 1.
[0048] Example 6. In this example, the method of producing an abutment was the
same
as the method described in Example 5, except the esthetic outer material was
PEEK-
CLASSIX instead of the ULTEM 1010.
[0049] Example 7. In this example, the inner material is the black PEKK A1050
polymer without a further reinforcing component, and the outer composite
material is the
PEKK A1050 polymer mixed and compounded with 35 wt. % of E-glass fibers as the
primary reinforcing component and 10 wt. % of titanium dioxide (Ti02) as a
colorant to
provide the outer composite material with a color substantially the same as
natural teeth. The
E-glass fibers have a length of about 5-6 mm and a diameter of about 10-20 m
for length-
to-diameter ratios of about 250 to 600. Both the inner and outer materials
were injected as
explained above for Example 1.
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[0050] Example 8. In this example, a mechanically strong carbon reinforced
material is =
used to form the inner portion of a prosthetic component while a Ti02 filled
material is used
to form the outer portion. The carbon reinforced inner portion, composite
material is a dark
color, which is unattractive for a dental application, but is covered with a
white, esthetically
pleasing Ti02 filled outer, composite material. More specifically, the outer
composite
material is the same as that for Example 7, while the inner composite material
is the PEEK
GATONETM 5330 CF with pre-mixed carbon fibers instead of the PEKK A1050. Thus,
the
method for mixing and compounding the outer composite material is as explained
for
Example 7 and the method of injecting both the inner and outer materials is as
explained for
Example 1. The carbon fibers of the inner material provided a length-to-
diameter ratio of
715 to 860, while the length-to-diameter ratio of the outer material is about
250 to 600.
[0051] Example 9. In this example, the outer composite material was the same
as that
for Example 7 including the Ti02 colorant, while the inner material is the
black PEEK 450
without a further reinforcing component. Thus, the method for mixing and
compounding the
outer material is as explained for Example 7, while the method of injecting
both the inner
and outer materials is as explained for Example 1.
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WO 2007/140217 PCT/US2007/069562
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CA 02653274 2008-11-24
WO 2007/140217 PCT/US2007/069562
[0054] Referring to Table II, the inner composite material produced by the
method =
disclosed in Examples 1, 2 and 8 has a modulus of elasticity, or tensile
modulus, of about
3146 ksi. To determine the modulus of elasticity, or tensile modulus, a
specimen of the inner
and outer material was placed in tension using ASTM D-6389 Standards and the
resulting
deflection was recorded. The modulus of elasticity also can be determined by
placing a
specimen of the composite material in compression and similarly recording the
deflection.
One way the modulus of elasticity for the inner material can be increased
above 3146 ksi, if
desired, is by increasing the amount of fiber present. Alternatively, the
modulus of elasticity
may be increased by (1) increasing the fiber aspect ratio (length-to-diameter
ratio), where
applicable, (2) further improving the interface or bonding between the
reinforcing component
and polymer materials via coupling agents, and (3) improving the compounding
and molding
processes to better mix the reinforcing component within the plastic material
to achieve a
more even distribution and to decrease the inclusion of impurities and
porosities in the
composite material. Thus, one examplary desired range for the plastic modulus
of the inner
material is 3146 ksi or greater. The ways to increase the modulus of
elasticity are not limited
to the inner material and apply equally to the outer material.
[0055] Referring to Table III, the outer composite material produced by the
method
disclosed in Example 2 had an average modulus of elasticity, of about 391 ksi.
This includes
values within 28 standard deviation from the average value. Thus, in this
example, the
range of an average modulus of elasticity of about 391 ksi would include
values as low as
about 363 ksi and as high as about 419 ksi. For the outer composite material
of Example 8,
the average modulus of elasticity is about 957 ksi including a modulus as low
as about 875
ksi and as high as 1039 ksi due to a 82 standard deviation. Thus, the
desired elastic
modulus is equal to or greater than about 363 ksi (Example 2) or equal to or
greater than 875
ksi (Example 8).
[0056] With either Example 2 or Example 8, it is shown that an abutment can be
formed
with a modulus of elasticity of the inner portion greater than the modulus of
elasticity of the
outer portion. This permits the use of esthetically pleasing but relatively
weaker materials to
form the outer portion. In Example 2, the elastic modulus of the inner portion
is at least
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CA 02653274 2008-11-24
WO 2007/140217 PCT/US2007/069562
about eight times greater than that of the outer portion, while for Example 8
the elastic =
modulus of the inner portion is at least about three times greater than that
of the outer portion.
[0057] As seen in Tables II and III, the modulus of elasticity of the
composite material
generally depends on at least the polymer material, and the type and quantity
of reinforcing
components mixed within the polymer material. The modulus of elasticity also
depends on
whether the reinforcing component includes continuous or non-continuous
fibers, and
whether the fibers are oriented with the load directions. For a continuous
fiber-reinforced
composite, i.e., composites where the fiber length is much larger than the
critical fiber length,
in which the fiber is aligned in the same direction of the load, the modulus
of elasticity of the
composite, E,, is determined by Equation (1) below:
Equation (1): E, = VmE,,, + VfEf
wherein E. and Ef are the moduli of the polymer matrix and the ceramic fibers,
respectively,
and V,,, and Vf are the volumes of polymer matrix and ceramic fibers,
respectively, such that
V,n+V f=1. The critical length of the fiber is dependent on the fiber
diameter, the fiber's
ultimate strength, and the bond strength between the fiber and the plastic
matrix. For a
number of combinations, this critical length is on the order of about 1 mm.
For a continuous
fiber-reinforced composite in which the fiber is aligned in the transverse
direction to the
load, the composite modulus of elasticity is determined by Equation (2) below:
Equation (2): 1/Ec= Võ /E,n + Vf/ E f=
For discontinuous and randomly oriented fibers, the composite modulus of
elasticity is
determined by Equation (3) below:
Equation (3): E, = V,n E,n + K V fEf
in which K is a fiber efficiency parameter which depends upon the ratio of Vf
and EWE,,,. K
is usually in the range of 0.1-0.6. In any event, the upper and lower bounds
of the modulus
of elasticity for the composites composed of particulate fillers are
determined by Equations
(4) and (5) below:
Equation (4): E,, (upper) = V,,, Em + Vp Ep
(lower) = E,,, Ep/ (V,,, Ep + Vp E,n)
Equation (5): E,
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WO 2007/140217 PCT/US2007/069562
[0058] For an alternative prosthetic dental device, a composite material for
the inner or =
outer portions may include a ceramic matrix with pores, and an organic
material, such as a
thermoset plastic, contained in the pores. This alternative composite material
also is fully
described in detail in the parent application.
[0059] It will be understood that various changes in the details, materials,
and
arrangements of parts and components, which have been herein described and
illustrated in
order to explain the nature of the invention, may be made by those skilled in
the art within
the principle and scope of the invention as expressed in the appended claims.
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