U.S. patent application number 12/266318 was filed with the patent office on 2010-05-06 for expandable bone implant.
Invention is credited to Jeffrey A. BASSETT, Matthew LOMICKA, Srilakshmi VISHNUBHOTLA.
Application Number | 20100114314 12/266318 |
Document ID | / |
Family ID | 41436417 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100114314 |
Kind Code |
A1 |
LOMICKA; Matthew ; et
al. |
May 6, 2010 |
EXPANDABLE BONE IMPLANT
Abstract
An expendable bone implant has a first member with a coronal end
portion configured for supporting a prosthesis. A second member is
at least partially porous, engages the first member, and is
configured to expand outwardly upon a longitudinal force being
applied to at least one of the first and second members. This
anchors the implant in bone before mastication forces are applied
to the implant.
Inventors: |
LOMICKA; Matthew; (Vista,
CA) ; VISHNUBHOTLA; Srilakshmi; (San Diego, CA)
; BASSETT; Jeffrey A.; (Vista, CA) |
Correspondence
Address: |
FITCH EVEN TABIN & FLANNERY
120 SOUTH LASALLE STREET, SUITE 1600
CHICAGO
IL
60603-3406
US
|
Family ID: |
41436417 |
Appl. No.: |
12/266318 |
Filed: |
November 6, 2008 |
Current U.S.
Class: |
623/16.11 ;
128/898; 623/11.11 |
Current CPC
Class: |
A61C 8/0037 20130101;
A61C 2008/0046 20130101; A61C 8/0033 20130101 |
Class at
Publication: |
623/16.11 ;
623/11.11; 128/898 |
International
Class: |
A61F 2/28 20060101
A61F002/28; A61F 2/02 20060101 A61F002/02; A61B 19/00 20060101
A61B019/00 |
Claims
1. An implant comprising: a first member having a coronal end
portion configured for supporting a prosthesis; and a second
member, being at least partially porous, engaging the first member,
and configured to expand outwardly upon a longitudinal force
applied to at least one of the first and second members to anchor
the implant in bone before mastication forces are applied to the
implant.
2. The implant of claim 1 wherein the second member includes porous
metal.
3. The implant of claim 1 wherein the second member includes
tantalum.
4. The implant of claim 1 wherein the implant is a dental
implant.
5. The implant of claim 1 wherein the second member is initially
secured to the first member only by a loose press-fit that permits
the second member to be separated from the first member by
hand.
6. The implant of claim 1 wherein the second member is initially
separate from the first member for placement in a bore in bone
before the first member is assembled to the second member.
7. The implant of claim 1 wherein the second member has a cavity,
and wherein the first member has an apical end portion configured
for insertion into the cavity.
8. The implant of claim 7 wherein the cavity defines an inner
diameter of the second member, and wherein the apical end portion
has an outer diameter that is greater than the inner diameter so
that inserting the apical end portion into the cavity expands the
second member radially outward.
9. The implant of claim 7 wherein the apical end portion is tapered
inwardly as it extends apically for being disposed within the
cavity.
10. The implant of claim 7 wherein the apical end portion comprises
threads for engaging the second member.
11. The implant of claim 1 wherein the first member has an apical
end portion and the second member is generally cup shaped for at
least generally covering the apical end portion of the first
member.
12. The implant of claim 1, wherein the second member has a
generally cylindrical wall with a thickness of about 0.020 inches
to about 0.040 inches.
13. The implant of claim 1, wherein the second member has a modulus
of elasticity that is less than a modulus of elasticity of the
first member.
14. The implant of claim 1 wherein the second member has sufficient
strength to cut into bone during expansion of the second
member.
15. The implant of claim 1 wherein the second member has a
compressive strength in a range from about 50 MPa to 90 MPa.
16. The implant of claim 1 wherein the second member has a
stiffness of about 3 Gpa or less.
17. The implant of claim 1 wherein the first member comprises a
body defining a generally longitudinal cavity and at least one
opening on the body providing generally radial access to the
longitudinal cavity, and wherein the second member is at least
partially disposed within the longitudinal cavity and being
configured to expand radially into the at least one opening.
18. The implant of claim 17 wherein each at least one opening forms
a generally longitudinally extending slot so that the second member
expands to form a generally longitudinally and radially extending
rib through each slot for engaging bone.
19. The implant of claim 17 further comprising a plurality of slots
uniformly spaced around the body.
20. The implant of claim 17 wherein the first member has an apical
end surface, and wherein the slot formed by each at least one
opening longitudinally extends to the apical end surface.
21. The implant of claim 17 wherein the body has a cylindrical wall
defining the cavity and the at least one opening, and wherein the
wall has a thickness at least in the vicinity of the at least one
opening of about 0.010 inches or less.
22. The implant of claim 17 wherein the slot formed by each at
least one opening generally extends at least a majority of the
length of the first member.
23. The implant of claim 17 further configured to be placed in a
hole with a bottom in bone, and wherein the second member has a
sidewall and wherein the first member has a driving end configured
for receiving a driving tool so that impacting the driving end with
the driving tool compacts the second member between the first
member and the bottom of the hole to expand the sidewall generally
radially outward.
24. The implant of claim 17 further configured to be placed in a
hole with a bottom in bone, and wherein the second member has a
sidewall and a driving end configured for receiving a driving tool
so that impacting the driving end with the driving tool compacts
the second member between the driving tool and the bottom of the
hole to expand the sidewall generally radially outward.
25. The implant of claim 1 wherein the first member has a
longitudinal cavity, and wherein the second member has a sidewall
tapered inwardly as it extends coronally for locating the second
member within the longitudinal cavity.
26. The implant of claim 1 further comprising a third apical member
adjustably engaging the first member, the second member being
clamped between the first and third members so that adjusting the
first and third members towards each other longitudinally
compresses the second member and expands the second member
generally radially outward.
27. The implant of claim 26 wherein the first and third members are
threaded to each other.
28. The implant of claim 1 wherein the second member is generally
non-circular and has a longitudinal cavity for receiving the first
member, and wherein rotating the first member within the second
member causes the second member to expand generally radially
outward.
29. The implant of claim 28 wherein the first member and second
member are elliptical or oval.
30. A method of anchoring a bone implant in a bore in bone
comprising: providing a first member with a distal end portion and
a second member defining a cavity and being at least partially
porous; inserting the second member into the bore; and expanding at
least a portion of the second member radially outward and toward
the bone by driving the distal end portion of the first member into
the cavity of the second member.
31. The method of claim 30 wherein the cavity defines an inner
diameter of the second member, and wherein an outer diameter of the
first member is greater than the inner diameter of the second
member.
32. The method of claim 30 wherein the second member includes
tantalum.
33. The method of claim 30 wherein the second member is placed in
the bore before placing the first member in the cavity of the
second member.
34. The method of claim 30 wherein the implant is a dental
implant.
35. The method of claim 30 wherein the second member comprises a
cylindrical wall about 0.020 to about 0.040 inches thick.
36. A method of anchoring a bone implant in a bore in bone
comprising: providing a bone implant having an inner porous member
and an exterior shell member defining a longitudinal cavity and at
least one generally radial opening from the cavity; placing the
inner porous member at least partially within the longitudinal
cavity of the exterior shell member; placing the implant in the
bore; and expanding the porous member to extrude through the at
least one generally radial opening of the shell member to engage
bone.
37. The method of claim 36 wherein the at least one opening
comprises a plurality of generally longitudinally extending slots
so that expanding the porous member forms ribs that extend
generally radially outward from the shell member and extend
generally longitudinally along the shell member.
38. The method of claim 36 wherein the porous member extends
apically from the shell member.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an implant for insertion
into bone and, in particular, an expandable bone implant having
improved osseointegration features.
BACKGROUND OF THE INVENTION
[0002] One type of bone implant is a dental implant or endosseous
root form implant which is surgically implanted into a patient's
upper or lower jaw to directly or indirectly anchor and support
prosthetic devices, such as an artificial tooth. The implants are
usually placed at one or more edentulous sites in a patient's
dentition at which the patient's original teeth have been lost or
damaged in order to restore the patient's chewing function. In many
cases, the implant anchors a dental abutment, which in turn
provides an interface between the implant and a dental restoration.
The restoration is typically a porcelain crown fashioned according
to known methods.
[0003] The implant is usually either threaded or press-fit into a
bore which is drilled into the patient's mandible or maxilla at the
edentulous site. The implant is inserted by applying a force to the
coronal end of the implant in an insertion direction.
[0004] A patient typically prefers to leave after initial surgery
with some type of restoration mounted on the implant, which
transfers occlusive loads to the implant. Also, it has been shown
that in many instances, healing of both soft and hard tissue is
improved if the implant is loaded after surgery through a
restoration. While the implant rarely receives the full load of
occlusion during this healing phase and even with the restoration,
the loading is sufficient to displace the implant. Thus, threads
are used to achieve initial stability. Before biologic integration
has time to take place, the thread resists tension, twisting or
bending loads the implant might be subjected to.
[0005] The surgical procedure for inserting the threaded implants,
however, can be complicated and requires that the threaded implants
be turned into place, which further requires the use of special
tools and inserts. The torque needed to place the implant into the
jaw can be high and may require tapping of the bore on the jaw,
which adds yet another step to the surgical procedure where tapping
typically is not desired. Also with threaded implants, it is often
difficult to achieve optimal esthetics because the geometry of the
thread establishes a fixed relationship between the final vertical
and rotational orientation of the implant such that a vertical
adjustment of the implant requires a rotational adjustment and
vice-versa. Thus, a prosthetic held at an ideal rotational
orientation by the implant may not have the ideal vertical
position.
[0006] Alternatively, although a press fit implant has a much
simpler surgical procedure, the current press fit designs provide
very little initial stability and are not well suited for early and
immediate loading procedures that are currently used in
dentistry.
[0007] The body of the dental implant has commonly been formed of
titanium metal or titanium alloys. Titanium metals and alloys may
act to enhance bone attachment to the surface of the dental
implant. However, the titanium metals and alloys are orders of
magnitude higher in stiffness than human bone and as a result
absorb much of the mastication forces introduced in the mouth. This
absorption of the forces by the titanium dental implants can result
in inadequate stimulation of the surrounding bone tissue in the
jaw, which over extended periods of time can cause the bone tissue
to be resorbed by the body resulting in saucerization of the bone,
or bone die-back. Over time, this bone die-back can cause the
dental implant to loosen within its hole and even cause infection
to the area. Accordingly, a press-fit implant is desired that
provides sufficient initial stability while also providing improved
osseointegration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is an exploded, side perspective view of a first
embodiment of an implant according to the present invention;
[0009] FIG. 2 is a side elevational view of the implant of FIG.
1;
[0010] FIG. 3 is a side elevational view of an osteotome according
to the present invention and having the implant of FIG. 2 attached
at its distal end;
[0011] FIG. 4 is an exploded, side perspective view of a second
embodiment of an implant according to the present invention;
[0012] FIG. 5 is a side elevational view of the implant of FIG.
4;
[0013] FIG. 6 is a side elevational view of the implant of FIG. 4
showing a porous component expanded through slots in a shell
component;
[0014] FIG. 7 is a top view of the implant of FIG. 6;
[0015] FIG. 8 is an upper, cross-sectional view of a third
embodiment of an implant according to the present invention;
[0016] FIG. 9 is an exploded, side perspective view of a fourth
embodiment of an implant according to the present invention;
[0017] FIG. 10 is a side cross-sectional view of a fifth embodiment
of an implant according to the present invention;
[0018] FIG. 11 is a side, exploded view of a sixth embodiment of an
implant according to the invention and shown on a bore in bone;
and
[0019] FIG. 12 is an enlarged fragmentary view of a porous tantalum
portion for any of the embodiments herein and in accordance with
the present invention.
DETAILED DESCRIPTION
[0020] Referring to FIGS. 1-2, an implant 10 is provided for
insertion into a surgical site such as a bore on bone, and in the
particular examples here, into a mandible or maxilla. The implant
10 is used to support an abutment, and a prosthesis is mounted on
the abutment. While two-stage endosseous implants are shown that
terminate at the alveolar ridge, it will be understood that the
implants may alternatively be single-stage implants with an
integrally formed transgingival region or a one-piece implant with
an integral abutment.
[0021] Implant 10, as well as other implants described herein, are
press-fit implants and forego the use of threads as the main
mechanism to engage bone. This permits these implants to be placed
at a desired depth in bone by using a longitudinal driving force
without the need to rotate the implant and while still forming
sufficient initial stability to withstand mastication forces.
[0022] More specifically, implant 10 has a first, relatively rigid
member or component 12, and a second, expandable, porous member or
component 14 that is at least partially porous. The rigid member 12
is positioned coronally of the porous member 14 and has a coronal
or proximal end portion 16 to directly or indirectly support a
prosthesis. The porous member 14 engages an apical or distal end
portion 18 of the rigid member 12 when it is placed in a bore in
bone. With this structure, a longitudinal force may be applied to
the rigid member 12 so that the rigid member 12 impacts against the
porous member. This driving force causes the porous member 14 to
expand radially outward (and apically) into the surrounding bone of
the surgical site. Thus, this expansion occurs before mastication
takes place so that the implant 10 is well settled and generally
will not expand further during full load mastication.
[0023] The rigid member 12 is formed of a relatively strong, hard
metal such as titanium. The porous material forming the porous
member 14 is particularly suited to form an immediate strong,
stable interference fit with surrounding bone while improving
osseointegration of the bone into the porous member 14. The porous
member 14, in one form is a porous tantalum portion 40 (shown on
FIG. 12), which is a highly porous biomaterial useful as a bone
substitute and/or cell and tissue receptive material. An example of
such a material is produced using Trabecular Metal.TM. technology
generally available from Zimmer, Inc., of Warsaw, Ind. Trabecular
Metal.TM. is a trademark of Zimmer Technology, Inc. Such a material
may be formed from a reticulated vitreous carbon foam substrate
which is infiltrated and coated with a biocompatible metal, such as
tantalum, etc., by a chemical vapor deposition ("CVD") process in
the manner disclosed in detail in U.S. Pat. No. 5,282,861, the
disclosure of which is fully incorporated herein by reference.
Other metals such as niobium, or alloys of tantalum and niobium
with one another or with other metals may also be used.
[0024] As shown in FIG. 12, porous tantalum structure 40 includes a
large plurality of ligaments 42 defining open spaces 44
therebetween, with each ligament 42 generally including a carbon
core 46 covered by a thin film of metal 48 such as tantalum, for
example. The open spaces 44 between ligaments 42 form a matrix of
continuous channels having no dead ends, such that growth of
cancellous bone through porous tantalum structure 40 is
uninhibited. The porous tantalum may include up to 75%-85% or more
void space therein. Thus, porous tantalum is a lightweight, strong
porous structure which is substantially uniform and consistent in
composition, and closely resembles the structure of natural
cancellous bone, thereby providing a matrix into which cancellous
bone may grow to anchor implant 10 into the surrounding bone of a
patient's jaw which increases stability. The rough exterior surface
of such porous metal portion has a relatively high friction
coefficient with adjacent bone forming the bore that receives the
implant to further increase initial stability as alluded to above.
This structure can produce superior aesthetic results by
restricting movement of the implant. These implants can be placed
without supplementary surgical procedures, such as bone grafting,
and can be placed in areas where traditional implants have been
less successful, such as with reduced or decayed alveolar
sections.
[0025] Porous tantalum structure 40 may be made in a variety of
densities in order to selectively tailor the structure for
particular applications. In particular, as discussed in the
above-incorporated U.S. Pat. No. 5,282,861, the porous tantalum may
be fabricated to virtually any desired porosity and pore size,
whether uniform or varying, and can thus be matched with the
surrounding natural bone in order to provide an improved matrix for
bone in-growth and mineralization. This includes a gradation of
pore size on a single implant such that pores are larger on an
apical end to match cancellous bone and smaller on a coronal end to
match cortical bone, or even to receive soft tissue ingrowth. Also,
the porous tantalum could be made denser with fewer pores in areas
of high mechanical stress. Instead of smaller pores in the
tantalum, this can also be accomplished by filling all or some of
the pores with a solid material which is described in further
detail below.
[0026] To provide additional initial mechanical strength and
stability to the porous structure 14, the porous structure 14 may
be infiltrated with filler material such as a non-resorbable
polymer or a resorbable polymer. Examples of non-resorbable
polymers for infiltration of the porous structure 14 may include a
polyaryl ether ketone (PAEK) such as polyether ketone ketone
(PEKK), polyether ether ketone (PEEK), polyether ketone ether
ketone ketone (PEKEKK), polymethyl methacrylate (PMMA),
polyetherimide, polysulfone, and polyphenolsulfone. Examples of
resorbable polymers may include poly lactic acid (PLA), poly
glycolic acid (PGA), poly lactic co-glycolic acid (PLGA),
polyhydroxybutyrate (PHB), polyhydroxyvalerate (PHV), and
copolymers thereof, polycaprolactone, polyanhydrides, and
polyorthoesters. The resorbable material would resorb as the bone
grows in and replaces it, which maintains the strength and
stability of the implant.
[0027] Regarding the initial stability, as the porous member 14 is
inserted into the bore in bone, the porous material will bite into
the bone by grating, chipping and/or flaking bone pieces off of the
sidewalls of the bore in which the implant device is being placed.
When the implant is press-fit into the bore rather than threaded
into the bore, this "rasping" action may form slight recesses or
indents within the bore sidewall in which the implant device sits.
This restricts rotational or twisting motion of the implant device
within the bore since the implant device does not have the
clearance to rotate out of the indents and within the bore.
[0028] The rasping action also accelerates osseointegration onto
the implant device and into the pores of the porous material due to
the bone compaction into the pores. First, the grating of the bone
structure causes the bone to bleed which stimulates bone growth by
instigating production of beneficial cells such as osteoblasts and
osteoclasts. Second, the bone pieces that fall into the pores on
the porous material assist with bone remodeling. In the process of
bone remodeling, osteoblast cells use the bone pieces as
scaffolding and create new bone material around the bone pieces.
Meanwhile osteoclast cells remove the bone pieces through
resorption by breaking down bone and releasing minerals, such as
calcium, from the bone pieces and back into the blood stream. The
osteoblast cells will continue to replace the grated bone pieces
from the pores and around the implant device with new and healthy
bone within and surrounding the extraction site. The composite of
in-grown bone and porous tantalum has elastic properties much
closer to bone than a solid metal implant, creating a loading
environment that is conducive to maintaining bone near the implant.
Thus, with the porous material, the porous member 14, and in turn
the implant 10, has increased resistance to twisting or rotation,
allows for immediate or very early loading, and increases long-term
stability due to the improved osseointegration. Such an implant
with ingrown bone has stability greater than a comparably sized
implant with only on-grown bone.
[0029] The properties of the porous material also enable expansion
of the porous member 14 to anchor the porous member 14 into the
surrounding bone. To expand the porous material for any of the
implants described herein, the modulus of elasticity (i.e., the
amount of deformation in the elastic region of the stress/strain
curve when a given stress is applied) of the porous material, or at
least that portion of the porous member that will expand, should be
about 3 Gpa or less.
[0030] As the porous material of any of the implants described
herein expands radially against the bone, the porous material cuts
into the bone. This occurs because the outer surface of the porous
material can be made to have trabeculi or sharp protrusions of
metal that extend from the outer surface. These trabeculi are
formed when a "cell" of the porous tantalum is cut leaving only a
portion of each strut that make up a porous tantalum "cell." It is
believed that the trabeculi, when compressed against the bone
surface, cut into the bone because the porous tantalum metal can
withstand greater stress than many types of bone tissue. The result
of this digging in or rasping action with the cut struts further
increases the initial stability of the implant in the surgical site
in addition to the uncut struts described above.
[0031] To provide this cutting action as the porous member for any
of the implants described herein expands, the compressive strength
of the porous metal should be from about 50 to about 90 MPa, which
is relatively higher than the compressive strength of cancellous
bone which is about 10 to about 50 MPa. The area of contact between
each trabeculi and the bone will be very small due to the geometry
of the trabeculi as described above. This will result in high
stress (load/area) when even moderate loads are applied. Since the
amount of stress the porous tantalum metal can achieve prior to
yield is higher than the surrounding bone tissue, the porous
material will dig into the bone.
[0032] Referring again to FIGS. 1-2, in one form, the rigid member
12 is generally bullet-shaped with a cylindrical outer surface 20
that terminates in the apical end portion 18 which is rounded. The
outer surface 20 can be smooth but may be roughened or otherwise
treated to promote bone growth or restrict bacterial growth. The
coronal end portion 16 of the rigid member 12 is open to an inner
longitudinal cavity 22 for receiving a driving device such as an
osteotome 24 (shown in FIG. 3) and/or for receiving fasteners to
secure an abutment to the implant 10. The longitudinal cavity 22
may have a circular cross-section for the purpose of receiving a
longitudinal force from the driving tool. The longitudinal cavity
22, however, may also have a non-circular cross-section, or have a
non-circular portion, such as polygonal, to receive an abutment, a
fastener holding an abutment, or to limit rotation of the driving
tool relative to the implant 10 for convenience while inserting the
implant 10 in the bore.
[0033] The porous member 14 is generally cup-shaped and forms a
coronally accessible, longitudinally extending, interior cavity 26.
The porous member 14 has a generally cylindrical wall 28 as well as
a rounded apical end portion 30 that cooperatively defines the
cavity 26. The apical end portion 30 has a shape that corresponds
to the shape of apical end portion 18. To facilitate expansion, the
wall 28 should not be too thick, and in one aspect, has a thickness
from about 0.020 inches to about 0.040 inches.
[0034] The apical end portion 18 is configured to be inserted into
the cavity 26 to expand the porous member 14. Thus, in one form, an
inner diameter d of the porous member 14 and defined by the cavity
26 may be slightly smaller than an outer diameter D of the rigid
member 12. Since the modulus of elasticity of the porous member 14
is significantly less than the modulus of elasticity of the rigid
member 12, urging the rigid member 12 apically into the cavity 26
will expand the porous member 14 generally radially outward and
against the bone in the bore.
[0035] To place the implant 10 in a bore in bone, first, the
practitioner uses a tool, which may be the same osteotome 24 or a
separate tool, received in the cavity 26 to press the initially
separate porous member 14 into the bore by applying a longitudinal
force on the tool. Thus, the porous member 14 is placed in the bore
before placing the rigid member 12 in the bore. Once the porous
member 14 is in place, the practitioner uses the osteotome 24 to
engage the rigid member 12 to create a longitudinal force and press
or tap the rigid member 12 into the bore and subsequently into the
cavity 26 of the porous member 14. As mentioned above, this action
will expand the porous member 14 radially outward as well as
compress the apical end portion 30 of the porous member 14 between
the rigid member 12 and a bottom of the bore (similar to the bottom
64 of the bore 60 shown in FIG. 11). This forces the porous member
14 to cut into the adjacent bone defining the bore and create
initial stability in multiple directions as described above. Once
the apical end portion 18 is fully inserted into the cavity 26, the
rigid member 12 forms a core for the porous member 14, and the
porous member 14 at least generally covers the apical end portion
18.
[0036] In an alternative aspect, however, the rigid member 12 and
the porous member 14 can be assembled together before insertion
into the bore, and even preassembled by the manufacturer or
supplier before the implant 10 is received by the practitioner. In
this case, the porous member 14 is at least partially mounted on
the apical end portion 18 of the rigid member 12 before the two
members 12 and 14 are placed in a bore in bone. If the implant 10
is assembled first before it is inserted into the bore, the rigid
member 12 may be driven into the porous member 14 a sufficient
depth just to retain the porous member 14 on the rigid member 12
without significantly expanding the porous member 14. Once the
implant 10 is placed into the bore, then the osteotome 24 can be
pressed with a longitudinal force sufficient to expand the porous
member 14 radially outward and into the bone.
[0037] As another option, the porous member 14 can be secured to
the rigid member 12 by a loose press-fit that permits the porous
member 14 to be separated from the rigid member 12 easily, such as
by hand. In other words, the apical end portion 18 of the rigid
member 12 is dimensioned to easily slip in and out of cavity 26. In
this case, the diameters d and D of the cavity 26 and rigid member
12 are sufficiently close to form an interference fit that holds
the members 12 and 14 together without significant expansion until
the implant is inserted and assembled in the bore in the bone. Once
inserted, significant force may be applied to the osteotome 24 in
multiple directions to press the porous member 14 against the
surrounding bone forming the bore.
[0038] While an interference fit between the rigid member 12 and
porous member 14 is mentioned, it will be understood that
adhesives, welding, and/or heat may be used to additionally or
alternatively connect the two parts together, especially when the
implant 10 is to be preassembled.
[0039] It will also be appreciated that the porous member 14 may
alternatively extend over most, or substantially all, of the
coronal-apical length of the implant 10, or the porous member 14
may only cover certain sections of the rigid member 12 instead of
only cupping the apical end 18 of rigid member 12. Thus, it may be
cylindrical, and the rigid member 12 may or may not extend all the
way through the porous member 14 to form an apical end of the
implant 10. Also, the apical end portion 30 of the porous member 14
may be provided in varying desired thicknesses (in the
coronal-apical direction) to provide different porous lengths
extending apically from the apical end portion 18 of the rigid
member 12. Otherwise, the total assembled length of implant 10 may
be provided in different desired dimensions by varying the length
of rigid member 12.
[0040] Alternatively, a wide portion 32 (shown in dashed line on
FIGS. 1-2) of the rigid member 12 may be provided to additionally
engage a coronally facing, annular surface 34 of the porous member
14. Specifically, the wide portion 32 has a diameter larger than a
diameter of the apical end portion 18 to form an apically facing,
annular shoulder 38 extending radially outward from the apical end
portion 18. The shoulder 38 engages the surface 34 when the rigid
member 12 is pressed apically against the porous member 14. In this
case, when the practitioner impacts the driving tool 24
longitudinally on the apical end portion or driving end 16 of the
rigid member 12, the wall or sidewall 28 of the porous member 14 is
compacted between the shoulder 38 of the rigid member 12 and the
bottom of the bore (similar to bottom 64 shown in FIG. 11) in which
it is disposed. This causes the sidewall 28 to bulge or expand
radially outward to contact, and cut into, surrounding bone.
[0041] While the wide portion 32 is shown to extend to the coronal
end portion 16 of the rigid member 12, it will be understood that
instead, the wide portion 32 may extend coronally from shoulder 38
any coronal-apical distance along the length of the rigid member 12
that is sufficient to transfer adequate force to the porous member
14. In one example, the wide portion 32 is in the form of a
relatively thin flange 36 (as shown in dashed line in FIG. 2).
[0042] Referring to FIG. 11, in another alternative basic form, an
implant 50 has a rigid member 52 that engages a porous member 54 at
least partially made of the porous material as described above and
as with the implant 10. Here, however, the porous member 54 does
not have a main cavity. Instead, the porous member 54 has a
coronally facing surface 56 for engaging an apical end portion 58
of the rigid member 52. As with implant 10, either the members 52
and 54 are placed separately into the bore 60 as shown in FIG. 11,
or the members 52 and 54 are assembled before insertion into a bore
60 in bone 62. In the former case, the porous member 54 is placed
in the bore 60, and the rigid member 52 is then placed in the bore
60 and pressed or tapped in a longitudinal direction (as
represented by arrow `A` on FIG. 11) until the rigid member 52
engages the porous member 54 so that the porous member 54 is
compacted between a bottom 64 of the bore 60 and the rigid member
52. This causes a sidewall 66 of the porous member 54 to bulge or
expand radially outward to engage the surrounding bone. The porous
member 54 also is pressed apically to cut into the bone on the
bottom 64 of the bore 60.
[0043] If the members 52 and 54 are to be preassembled before
insertion into the bore 60, the members 52 and 54 may be attached
to each other by interlocking structure on the apical end portion
58 and surface 56 or by other ways such as fasteners, adhesives,
welding, heat, and so forth. Otherwise, once the implant 50 is
placed in the bore 60 the procedure is the same as if the members
52 and 54 were initially separate. Instead of being completely
porous, porous member 54 may have a core of a different solid
material or have its pores filled with a different material as
described above as long as it does not significantly interfere with
the required compression of the porous member 54 for its radial
expansion.
[0044] Referring now to FIG. 8, as yet another alternative form, an
implant 70 has a similar structure to implant 10 including a rigid
member 72 and a porous member 74 with a longitudinal cavity 76 for
receiving the rigid member 72. Except here, the rigid member 72, or
at least an apical end portion 78 of the rigid member 72 that
extends into cavity 76, and the porous member 74 have transverse
cross sections that are non-circular. While other shapes are
contemplated (such as polygonal, other shapes with flat sides,
other irregular curved shapes, or combinations of the two), in the
illustrated form, the cross sections of the apical end portion 78
and the porous member 74 are oval or elliptical. So configured,
once the apical end portion 78 extends within the cavity 76 in a
corresponding orientation as that of the porous member 74 (i.e.,
where the major axes of both cross sections extend generally in the
same direction), the rigid member 72 may be rotated relative to the
porous member 74, as illustrated by arrows X. The porous member 74
is sufficiently thin such that the rotation of the rigid member 72
causes the major diameter of the apical end portion 78 to be forced
toward or into the minor diameter of the porous member 74, which
causes the porous member 74 to bulge or expand radially outward (as
shown by bulges 80) to engage the surrounding bone.
[0045] Referring to FIG. 9, an implant 90 has further alternative
features that may also be applied to implant 10. The implant 90, as
with implant 10, comprises a rigid member 92 and a porous member 94
with a cavity 96 for receiving an apical end portion 98 of the
rigid member 92. Here, however, the apical end portion 98 can
further include threads 91 for screwing the rigid member 92 into
the cavity 96. The cavity 96 may or may not have a threaded portion
93 for engaging the threads 91. Whether or not the apical end
portion 98 is threaded, the apical end portion 98 may be tapered
such that the apical end portion 98 is sloped inward as it extends
apically. The taper 95 helps to locate the apical end portion 98 in
the cavity 96 and to expand the porous member 94 when the tapered
apical end portion 98 has diameters that are larger than the inner
diameter defining the cavity 96 as the taper 95 at the apical end
portion 98 extends coronally. To expand the porous member 94 once
placed in a bore in bone, the rigid member 92 is driven
longitudinally and apically, albeit by rotating the rigid member
92, into the porous member 94 to expand the porous member 94
generally radially outward and onto the surrounding bone. In this
case, a coronal cavity 97 on rigid member 92 may be non-circular to
receive a rotational force from a driving tool.
[0046] Referring to FIG. 10, in another form, an implant 100 has
three pieces instead of two. The implant 100 includes a first,
coronal, shell or rigid member 102; a second, porous member 104
made of the same material as porous member 14; and a third, apical,
core member 106 threaded to the shell member 102. The porous member
104 is cylindrical and is mounted around a core portion 108 of the
core member 106. The porous member 104 is clamped between an
annular ledge 110 extending radially outward from the core portion
108 on the core member 106 and an annular, apical end surface 112
formed by the shell member 102.
[0047] The core portion 108 is threaded and fits into an interiorly
threaded bore 114 defined by the shell member 102 and that is
apically accessible. The core portion 108 has a coronal-apical
length sufficient to extend through the porous member 104 and
protrude coronally from the porous member 104 to engage the
threaded bore 114. The shell member 102 has a coronally accessible
cavity 116 for receiving a driving tool for rotating the shell
member 102 to thread the shell member 102 onto the core member 106.
This rotation adjusts the shell member 102 and core member 106
toward each other to longitudinally compress the porous member 104
between the surface 112 and shoulder 110, causing the porous member
104 to bulge or expand radially outward, as indicated by arrows B,
to engage the surrounding bone. The threaded bore 114 is
sufficiently deep to accommodate the insertion length of the core
portion 108.
[0048] Alternative configurations are apparent such as where the
core portion is on the coronal member rather than the apical
member, the porous member extends additionally or alternatively on
other sections of the coronal-apical length of the implant 100,
and/or the core member and shell member are attached to each by
other than threads such as a press-fit or by fasteners.
[0049] Referring to FIGS. 4-7, in a different form, an implant 200
is similar to implant 10 in that it has a first, coronal, rigid or
shell member 202 and a second, porous member 204 made of similar
materials as that mentioned above for implant 10. Here, however,
shell member 202 forms an outer shell to cover at least a part of
the second, porous member 204, and rather than being cup-shaped
with an interior cavity, the porous member 204 is a relatively
solid piece as with porous member 54 on implant 50. The porous
member 204 is at least partially porous, but in the illustrated
embodiment substantially porous, or alternatively may have a core
of a different material or the porous material may be injected to
form a core with a different filler material as mentioned
previously.
[0050] The shell member 202 has a body 206 that defines a
longitudinal or axial cavity 208 open at an apical or distal end
portion 210 of the shell member 202. The porous member 204 is at
least partially disposed within the longitudinal cavity 208 when
assembled together, and in the illustrated form, extends apically
from the shell member 202 to form the apical end 212 of the implant
200. The porous member 204 may also have a sidewall 214 that tapers
inwardly as it extends coronally to assist with locating the porous
member in cavity 208 and expanding radially outward when pressed to
the shell member 202.
[0051] The longitudinal cavity 208 extends at least along the
apical end portion 210 but may alternatively extend the entire
length of the shell member 202 so that the longitudinal cavity 208
forms a coronally accessible hole 216 for receiving a driving tool
24 (FIG. 3). In this case, the interior surface 218 (shown in
dashed line) defining the longitudinal cavity 208 has a jog or
annular shoulder 220 to engage a coronal surface 222 of the porous
member 204. With this configuration, the shell member 202 will
engage the porous member 204 at the shoulder 220 to impact the
porous member 204 as the shell member 202 is tapped or driven
apically on the porous member 204. Otherwise, with the longitudinal
cavity 208 open the entire length of the shell member 202, the
driving tool may additionally or alternatively impact the porous
member 204 directly as explained in greater detail below.
[0052] Alternatively, an interior wall 224 (shown in dashed line)
divides the longitudinal cavity 208 from the coronal hole 216 that
receives the driving tool. In this case, the apical surface 226 of
the interior wall 224 engages the porous member 204.
[0053] The body 206 of the shell member 202 also has at least one
opening 227 providing generally radial access to the longitudinal
cavity 208 to permit the porous member 204 to extrude radially
outward and through the openings to engage bone. In one form, the
openings are generally longitudinally extending slots 228 extending
along the apical end portion 210 to an apical end surface 230 of
the shell member 202. In the illustrated form, a plurality of
longitudinal slots 228 are uniformly spaced around the body 206.
Here, six slots 228 are provided but any desired number of slots
may be used. The height of the slots 228 may vary, either uniformly
or from each other, and may extend at least a majority of the
length of the body 206 or even substantially the entire length of
the body 206 if desired. In the illustrated form, the porous member
204 extends longitudinally within longitudinal cavity 208 for a
length at least sufficient to engage the entire length of the slots
228 as shown in FIG. 5.
[0054] In order to permit the porous member 204 to expand or
extrude through the slots 228, or at least into the slots 228 and
to the exterior of the shell member 202, the body 206 is made of a
cylindrical wall 232 that defines the slots 228 and that has a
thickness at least in the vicinity of the slots 228 of about 0.010
inches or less. So configured, the porous member 204 need only
expand 0.010 inches or more to engage bone. The body 206 should not
bend significantly if at all. In one form, the body 206 may be made
of titanium and has a stiffness of about 110 GPa compared to the 3
GPa of the porous member 204 and as described above for porous
member 14. Expanding or extruding the porous member 204 through the
slots 228 will form an outwardly and radially extending porous rib
234 (as shown on FIG. 6) at each slot 228 for engaging surrounding
bone. Each rib 234 generally runs longitudinally along the shell
member 202 to correspond to the shape of the slot 228.
[0055] With the structure of implant 200 described, the porous
member 204 can be separately placed in a bore in bone (such as the
bore 60 shown in FIG. 11), and the shell member 202 is placed
subsequently in the bore and onto the porous member 204. In another
form, however, the porous member 204 is placed in the longitudinal
cavity 208 before the implant 200 is placed in the bore in bone. In
either case, the porous member 204 may be secured within the
longitudinal cavity 208 by an interference fit, or alternatively,
the porous member 204 merely initially has a loose press-fit within
the longitudinal cavity 208. In the latter case, and when the
porous member 204 is provided in different coronal-apical lengths,
for example, the practitioner can replace the porous member 204
from the shell member 202 until a porous member 204 of an adequate
coronal-apical length is selected.
[0056] Once the porous member 204 is mounted on the shell member
202, the osteotome 24 or other driving tool is mounted on the
driving end of the shell member 202 or more specifically, in the
coronal hole 216 on the shell member 202 to place the implant 200
within the bore in the bone (such as that shown in FIG. 11). As the
osteotome 24 is driven or tapped in an insertion direction, the
osteotome 24 engages the interior wall 224, if present, and/or a
coronal end surface 236 of the shell member 202. It will be
understood that the interior surface 218 of the shell member 202
may also have shoulders or ledges to receive the driving member or
osteotome 24 for driving the shell member 202 apically.
[0057] Once the porous member 204 is seated on a bottom of the bore
in the bone, further impacting the driving tool on the driving end
of the shell member 202 with a longitudinal force compacts the
porous member 204 between the shell member 202 and the bottom of
the bore. This, in turn, causes the sidewall 214 of the porous
member 204 to expand radially outward and extrude into or through
the slots 228 to form the ribs 234 to engage surrounding bone (as
shown in FIG. 6).
[0058] For the alternative configuration where the longitudinal
cavity 208 extends the length of the shell member 202 and the
interior wall 224 is not present, the driving tool 24 may directly
engage the driving end or coronal surface 222 of the porous member
204. In this case, the driving tool engages the coronal end surface
236 of the shell member 202, engages a shelf or shoulder on the
interior surface 218, or has an interference fit with the interior
surface 218 for initial placement of the implant 200 in the bore in
bone. Once so disposed, further impact of the driving tool on the
driving end (or in this case, the porous member 204) compacts the
porous member 204 between the driving tool and the bottom of the
bore. This expands the sidewall 214 of the porous member 204
radially outward and into or through the slots 228 to form the ribs
234.
[0059] The expanded porous ribs 234 cut into the bone as described
above and anchors the implant 200 in the bore in which it is
disposed to provide stable initial stability to receive immediate
mastication forces. Since the ribs 234 extend into the cortical
bone, such configuration provides the implant 200 an additional
torsional stability. The porous nature of the material forming the
ribs 234 also aids in enhancing the speed of osseointegration of
the implant 200 with the bone as described above.
[0060] The above described press-fit dental implants may be
conventionally machined or cut using Electrical Discharge Machining
(EDM). The above described press-fit dental implants may also be
made by using the net-shape manufacturing process as owned by
Zimmer Trabecular Metal Technologies, Inc.
[0061] While this invention may have been described as having a
preferred design, the present invention can be further modified
within the spirit and scope of this disclosure. This application is
therefore intended to cover any variations, uses, or adaptations of
the invention using its general principles. Further, this
application is intended to cover such departures from the present
disclosure as come within known or customary practice in the art to
which this invention pertains and which fall within the limits of
the appended claims.
* * * * *