U.S. patent application number 09/746973 was filed with the patent office on 2001-04-26 for dental implant having a force distribution shell to reduce stress shielding.
Invention is credited to Story, Brooks J..
Application Number | 20010000486 09/746973 |
Document ID | / |
Family ID | 23315569 |
Filed Date | 2001-04-26 |
United States Patent
Application |
20010000486 |
Kind Code |
A1 |
Story, Brooks J. |
April 26, 2001 |
Dental implant having a force distribution shell to reduce stress
shielding
Abstract
A dental implant that reduces the potential for stress
shielding. The dental implant utilizes an implant body that
includes a metallic core and a shell disposed about the metallic
core. The shell is made from a material that has a lower modulus of
elasticity than the metallic core. The metallic core also is
connected to a mounting end to which a prosthetic tooth may
ultimately be attached.
Inventors: |
Story, Brooks J.; (Carlsbad,
CA) |
Correspondence
Address: |
SULZER MEDICA USA INC.
Suite 1600
3 East Greenway Plaza
Houston
TX
77046
US
|
Family ID: |
23315569 |
Appl. No.: |
09/746973 |
Filed: |
December 21, 2000 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09746973 |
Dec 21, 2000 |
|
|
|
09336322 |
Jun 18, 1999 |
|
|
|
6193516 |
|
|
|
|
Current U.S.
Class: |
433/173 ;
433/201.1 |
Current CPC
Class: |
A61C 8/0086
20130101 |
Class at
Publication: |
433/173 ;
433/201.1 |
International
Class: |
A61C 008/00 |
Claims
What is claimed is:
1. A dental implant, comprising: an implant body formed solely from
two separate materials and including a metallic core forming the
first material and a polymeric shell forming the second material,
wherein the shell has an outer surface adapted to contact bone and
has an inner surface that surrounds substantially all of the core
and attaches directly to it.
2. The dental implant of claim 1 in which the core has a body with
elongated cylindrical configuration and the inner surface of the
shell completely surrounds the entire body and directly attaches to
it.
3. The dental implant of claim 2 in which the shell has a modulus
of elasticity lower than the core.
4. The dental implant of claim 3 in which the shell is formed from
polyetheretheketone, and the core is formed from titanium or a
titanium alloy.
5. The dental implant of claim 4 in which the shell is reinforced
with carbon fiber, and the outer surface of the shell has a layer
to promote osseointegration.
6. The dental implant of claim 3 in which the shell is attached to
the core by one of resistive heating of the core, induction heating
of the core, partially melting the shell with microwave radiation,
spin welding, high temperature compression molding, ultrasonic
welding, or biocompatible adhesives.
7. The dental implant of claim 6 in which the core has a proximal
end that includes an anti-rotational mounting feature not
surrounded by the shell.
8. A dental implant, comprising: a metallic core and a polymeric
shell, wherein the implant has a cross section in which the core
has an outer surface, the shell has an inner surface that surrounds
and directly contacts substantially all of the outer surface of the
core and attaches directly to it, and the shell has an outer
surface adapted to contact bone directly.
9. The dental implant of claim 8 in which the core and shell have
an elongated cylindrical configuration, and the core has a proximal
end that includes an anti-rotational mounting feature not
surrounded by the shell.
Description
1. This is a continuation of U.S. application Ser. No. 09/336,322
filed on Jun. 18, 1999 entitled "Dental Implant Having a Force
Distribution Shell to Reduce Stress Shielding."
FIELD OF THE INVENTION
2. The present invention relates generally to prosthetic implants,
and particularly to dental implants that are designed to distribute
forces, created during mastication, to surrounding bone. This
distribution of forces reduces stress shielding of the surrounding
bone.
BACKGROUND OF THE INVENTION
3. A variety of dental implants currently are known and available.
The implants are designed for insertion into the maxilla or
mandible, e.g. jawbone, of a patient to support the mounting of a
prosthetic tooth. Generally, a cylindrical hole is formed in the
mandible or jawbone of the patient, and the implant is mounted in
the hole and allowed to undergo osseointegration.
4. A dental implant includes a generally cylindrical body designed
for placement in the cylindrical hole formed in the jawbone of a
patient. The generally cylindrical body may be threaded. The
exposed or coronal end of the dental implant includes a mounting
feature or features that aid in the mounting of a prosthetic tooth.
For example, the coronal end may include a splined interface and a
threaded bore to which an abutment and prosthetic tooth are
ultimately mounted.
5. Conventionally, the body of the dental implant has been formed
from titanium or a titanium alloy, such as Ti6Al4V. Such titanium
materials have served well in enhancing bone attachment to the
surface of the dental implant. It is believed that a stable oxide
forms on the titanium or titanium alloy, and serves as a suitable
surface for enhancing the desirable attachment between bone and the
dental implant.
6. Despite their proven record in promoting osseointegration,
titanium and titanium alloys present certain other challenges to
providing an optimal dental implant. Titanium and suitable titanium
alloys are orders of magnitude higher in stiffness than human bone,
and therefore dental implants formed from such materials absorb
most of the forces of mastication. This can lead to a phenomenon
known as Astress shielding of the surrounding bone.
7. Specifically, it has been determined that inadequate stimulation
of bone tissue over extended periods causes the bone tissue to be
resorbed by the body, an effect commonly known as Wolff?s Law. This
effect becomes apparent when bone surrounding the dental implant is
not adequately stimulated due to, for instance, absorption of a
majority of forces created during mastication by a stiff dental
implant. The lack of stimulation can cause saucerization, otherwise
known as bone die-back, which progresses around the upper portion
of an otherwise healthy dental implant. The loss of bone can lead
to destabilization and even loosening of the dental implant.
Additionally, once sufficient bone tissue has undergone resorption,
portions of the implant body become exposed, and this surface,
which is typically textured to provide high surface area, is
susceptible to infection.
8. It would be advantageous to design a dental implant able to
transmit the forces of mastication to surrounding bone tissue
without being unduly subject to degradation or breakage.
SUMMARY OF THE INVENTION
9. The present invention features a dental implant comprising an
implant body. The implant body includes a metallic core and an
anti-rotational mounting feature connected to the metallic core.
Additionally, a shell is disposed about the metallic core. The
shell has a lower modulus of elasticity than the metallic core to
facilitate transfer of force to surrounding bone tissue.
10. According to another aspect of the invention, a dental implant
is designed for implantation at an implant site in a maxilla or
mandible of a patient. The dental implant comprises a metallic core
and a shell. The shell includes a recessed opening sized to receive
at least a portion of the metallic core. The shell includes an
outer surface sized to fit within a cylindrical hole formed in the
mandible at the implant site. Additionally, the shell is formed of
a less stiff material than the metallic core to facilitate transfer
of forces from the dental implant to the surrounding bone
tissue.
11. According to a further aspect of the invention, a dental
implant is provided for implantation at an implant site which
includes a cylindrical hole formed in a mandible or maxilla of a
patient. The dental implant comprises a mounting end to which a
prosthetic tooth can be attached. Additionally, a force dissipater
is coupled to the mounting end. The force dissipater is sized for
insertion into the hole formed in the mandible. This force
dissipater effectively distributes a substantial portion of the
forces, generated during mastication, to the mandible surrounding
the force dissipater.
BRIEF DESCRIPTION OF THE DRAWINGS
12. The invention will hereafter be described with reference to the
accompanying drawings, wherein like reference numerals denote like
elements, and:
13. FIG. 1 is a front view of a conventional dental implant and
prosthetic tooth mounted in a mandible of a patient;
14. FIG. 2 is a front view similar to FIG. 1 showing an infected
area about the dental implant proximate an area of
saucerization;
15. FIG. 3 is a front view similar to FIG. 1 but showing the lack
of saucerization when the dental implant is constructed according
to the present invention;
16. FIG. 4 is a perspective view of a dental implant according to
an exemplary embodiment of the present invention;
17. FIG. 5 is an exploded view of the dental implant illustrated in
FIG. 4;
18. FIG. 6 is a cross-sectional view taken generally along line
6--6 of FIG. 4; and
19. FIG. 7 is a cross-sectional view similar to FIG. 6 but showing
an alternate embodiment of the dental implant.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
20. The stiffness of conventional dental implants can lead to
saucerization of the bone tissue surrounding the upper region of
the dental implant, as illustrated in FIG. 1. In this illustration,
a conventional titanium or titanium alloy dental implant 10 is
shown implanted within a cylindrical bore 12. Cylindrical bore 12
is formed in an appropriate area of bone tissue 14 at an implant
site 16.
21. A prosthetic tooth 18 is mounted to dental implant 10, and a
naturally occurring layer of gingival tissue 20 is disposed between
bone tissue 14 and prosthetic tooth 18. As chewing or mastication
forces act on prosthetic tooth 18, those forces are translated
through dental implant 10. However, because of the stiffness of the
titanium or titanium alloy from which dental implant 10 is formed,
most of the forces are absorbed by the implant, leading to a
reduction in stress transfer to the bone tissue 14. If the bone
tissue is inadequately stimulated for an extended period of time,
the tissue begins to be resorbed by the body. This effect is most
pronounced in the more dense cortical bone located near the surface
of the jawbone, as opposed to the spongy, or trabecular, bone in
the inner regions on the jawbone. This leads to an area of
saucerization 22 in which bone tissue actually disappears around
the portion of the dental implant proximate gingival tissue 20.
22. As illustrated in FIG. 2, continued inadequate stimulation of
the bone tissue leads to further resorption of bone tissue.
Ultimately, the depletion of bone tissue can create a pocket in the
gingival tissue which exposes the textured implant surface, making
it susceptible to infectious agents from the oral cavity.
Additionally, the dental implant may become destabilized and loose
within cylindrical bore 12. In any of these situations, failure of
the dental implant may result.
23. However, if sufficient stimulation is provided to the bone
tissue, the stress shielding phenomenon can be avoided, as
illustrated in conjunction with an exemplary embodiment of the
present invention shown in FIG. 3. In this illustrated embodiment,
a preferred dental implant 30 is designed to dissipate forces
throughout surrounding tissue. The dental implant 30 is disposed at
an implant site 32 within a cylindrical bore 34 formed in an area
of bone tissue 36.
24. A prosthetic tooth 38 and an appropriate abutment 40 are shown
mounted to dental implant 30. As described above, a layer of
gingival tissue 42 typically is disposed between bone tissue 36 and
prosthetic tooth 38. The unique design of dental implant 30
provides a reduced stiffness or flexibility of the implant that
results in sufficient bone tissue stimulation to avoid the
detrimental effects of stress shielding. As illustrated, the bone
tissue 36 remains healthy and in place along the complete length of
dental implant 30 beneath gingival tissue 42.
25. Referring also to FIGS. 4 and 5, dental implant 30 comprises an
implant body having a core 44, a mounting end 46 and a shell 48.
Preferably, core 44 and mounting end 46 are integrally connected,
and they typically are formed as a single unitary structure. Both
core 44 and mounting end 46 are formed, for example, from a
metallic material, such as titanium or a titanium alloy (e.g.
Ti6Al4V).
26. In the illustrated embodiment, core 44 is generally cylindrical
and defined by an outer surface 50. Outer surface 50, in turn, is
circular in cross-section, as illustrated best in FIG. 6. However,
although other shapes/cross-sections can be utilized. Also, core 44
is sufficiently elongated to extend into shell 48, and preferably
through a majority of the length of shell 48.
27. Mounting end 46 typically includes an annular expanded portion
52 adjacent core 44. A mounting feature 54 is connected to annular
expanded portion 52 on the side opposite core 44. Often, mounting
feature 54 is structured as an anti-rotational mechanism that
prevents rotation of prosthetic tooth 38. In the illustrated
embodiment, mounting feature 54 includes a plurality, e.g. six,
splines 56 that extend outwardly from annular expanded portion 52
in an axial direction generally opposite core 44. A gap 58 is
disposed between each adjacent pair of splines 56. Additionally,
mounting end 46 includes an axial, threaded bore 60 disposed at a
generally central location that is radially inward from splines 56.
Axial bore 60 may extend into core 44, and it facilitates the
mounting of abutment 40 and prosthetic tooth 38.
28. In the illustrated embodiment of the invention, shell 48 is
cylindrical in shape and has an outer surface 62 that is circular
in cross-section, as best illustrated in FIG. 6. Shell 48 and outer
surface 62 are sized for engagement with cylindrical bore 34 formed
in bone tissue 36. Potentially, outer surface 62 can be smooth or
textured. Additionally, outer surface may comprise a threaded
region 63 (see FIG. 4), depending on the particular dental implant
application.
29. Shell 48 also includes an axial opening 64 having a length and
cross-section formed to receive core 44. A wall 66 is effectively
created between axial opening 64 and outer surface 62. The
thickness of wall 66 is sufficient to place outer surface 62 in
general axial alignment with the radially outer surface of annular
expanded portion 52.
30. Shell 48 is made from a material that is less stiff than core
44. Specifically, the preferred material of shell 48 has a lower
modulus of elasticity than that of core 44. Preferably, the
material of shell 48 has a modulus of elasticity that is similar to
the modulus of elasticity of bone tissue 36.
31. The material of shell 48 may be a polymeric material, such as
polyetheretherketone, commonly known as PEEK. PEEK has the
characteristics of high strength, low water absorption and
biocompatibility, as well as having a modulus of elasticity much
closer to that of the surrounding bone than the typical titanium or
titanium alloy core 44. To increase the strength of a polymer, such
as PEEK, the polymer may be reinforced with a fiber or fibers, such
as a carbon fiber, to create a polymeric composite. Thus, the
polymeric material retains the desired flexibility and resiliency
that permits transfer of mastication forces to bone tissue 36
throughout the entire implant site 32, while the fibers provide
strength and thermal stability.
32. A primary example of such a composite material is carbon fiber
reinforced (CFR) PEEK. CFR PEEK material may be formed by way of a
filament winding process or a braiding process. Furthermore, the
shell 48 may be formed by creating opening 64 in a solid rod or
cylinder of PEEK reinforced with either chopped or continuous
carbon fibers depending on the desired material characteristics.
Accordingly, the desired strength of shell 48 potentially can be
adjusted by selection of both the length and orientation of the
carbon fibers throughout the PEEK material. For example, to
withstand the mastication loads exerted on dental implant 30 during
chewing, it may be desirable to use continuous fiber reinforcement
of the PEEK material.
33. Core 44 and shell 48 may be attached to one another by a
variety of methods. For example, the two components may be attached
by resistive heating of the titanium alloy (e.g. TiAl4V) core or by
induction heating of core 44. Other potential methods of attachment
include microwave radiation to partially melt the PEEK material, or
attachment by spin welding, a method by which the two components
are assembled while one or the other is spinning. If the spin rate
is sufficiently high, frictional forces at the interface between
core 44 and shell 48 cause the PEEK to melt. As the speed of
spinning is then reduced, the PEEK material of shell 48 adheres to
the metallic material of core 44 and forms a bond. Other methods of
attachment include high temperature compression molding, ultrasonic
welding and conventional, biocompatible adhesives.
34. The lower modulus material utilized in forming shell 48 should
have sufficient flexibility to permit the transfer of forces from
prosthetic tooth 38 to bone tissue 36. Effectively, outer surface
62 of shell 48 bends and moves a sufficient amount to permit the
transfer of forces to bone tissue 36. The transfer of forces
reduces or eliminates the saucerization/resorption of bone tissue
beneath gingival layer 42 that can otherwise occur.
35. In a slightly modified embodiment illustrated in FIG. 7,
surface 62 of shell 48 has been covered with an outer layer 68
designed to further promote osseointegration. Outer layer 68 may
comprise a thin layer of titanium laid over a PEEK composite shell
or substrate. The titanium layer may be placed on the PEEK material
by, for example, a technique known as vapor deposition.
36. Outer layer 68 also may comprise other materials. For example,
hydroxylapatite (HA) may be deposited as layer 68 through an
electrochemical deposition technique. Alternatively, outer layer 68
may be a coating of biologically active molecules such as proteins,
growth factors or synthetic peptides or other materials that
improve the in vivo attachment of bone tissue to the dental
implant. It will be understood that the foregoing description is of
preferred embodiments of this invention, and that the invention is
not limited to the specific forms shown. For example, a variety of
mounting end configurations may be utilized; a variety of core
materials can provide sufficient strength and stiffness; and other
materials potentially may be used in the construction of the shell.
These and other modifications may be made in the design and
arrangement of the elements without departing from the scope of the
invention as expressed in the appended claims.
* * * * *