U.S. patent application number 13/444975 was filed with the patent office on 2012-10-18 for fixture.
Invention is credited to Anders HALLDIN, Stig HANSSON.
Application Number | 20120264084 13/444975 |
Document ID | / |
Family ID | 44512365 |
Filed Date | 2012-10-18 |
United States Patent
Application |
20120264084 |
Kind Code |
A1 |
HANSSON; Stig ; et
al. |
October 18, 2012 |
FIXTURE
Abstract
The present invention relates to a fixture for insertion into a
bore hole arranged in bone tissue, comprising a threaded leading
portion and a threaded trailing portion located coronally of the
leading portion.
Inventors: |
HANSSON; Stig; (ASKIM,
SE) ; HALLDIN; Anders; (Molndal, SE) |
Family ID: |
44512365 |
Appl. No.: |
13/444975 |
Filed: |
April 12, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61475329 |
Apr 14, 2011 |
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Current U.S.
Class: |
433/174 |
Current CPC
Class: |
A61C 8/0025 20130101;
A61C 8/0018 20130101 |
Class at
Publication: |
433/174 |
International
Class: |
A61C 8/00 20060101
A61C008/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 2011 |
EP |
11162464.9 |
Claims
1. A fixture for insertion into a bore hole arranged in bone
tissue, comprising a threaded leading portion and a threaded
trailing portion located coronally of the leading portion, wherein
the threading of the leading portion has at least one first thread
spiral, wherein the threading of the trailing portion has at least
one more thread spirals than the threading in the leading portion,
wherein the threading of the trailing portion and the threading of
the leading portion have the same or substantially the same lead,
wherein the profile of at least one of the thread spirals in the
trailing portion is, at least along a portion of its extension,
substantially the same as the profile of the outermost part of said
first thread spiral in the leading portion, and wherein the at
least one thread spiral in the trailing portion having
substantially the same profile as the outermost part of said first
thread spiral in the leading portion is arranged to follow the
spiral path of said first thread spiral.
2. A fixture according to claim 1, wherein the thread spiral in the
trailing portion that follows the path of said first thread spiral
in the leading portion has the same radius of curvature at the top
of the peaks as said first thread spiral.
3. A fixture according to claim 1, wherein the thread spiral in the
trailing portion that follows the path of said first thread spiral
in the leading portion has the same flank angles, respectively, as
said first thread spiral.
4. A fixture according to claim 1, wherein all thread spirals in
the trailing portion have substantially the same profile as the
outermost part of said first thread spiral in the leading
portion.
5. A fixture according to claim 1, wherein the profile of one of
the thread spirals in the trailing portion, that does not follow
the path of said first thread spiral in the leading portion, alters
along the thread.
6. A fixture according to claim 1, wherein the smallest spacing
between adjacent peaks of the threading in the trailing portion is
smaller than the smallest spacing between adjacent peaks of the
threading in the leading portion.
7. A fixture according to claim 1, wherein the number of thread
spirals in the threaded trailing portion is a multiple integer of
the number of thread spirals in the leading portion.
8. A fixture according to claim 1, wherein the threading in the
leading portion has at least a first and a second thread spiral,
and wherein one of the thread spirals in the trailing portion
follows the path of said first thread spiral in the leading
portion.
9. A fixture according to claim 1, wherein the fixture is
self-tapping.
10. A fixture according to claim 1, wherein the fixture is provided
with separate cutting means adapted for cutting a female thread in
the bone that corresponds to the profile of at least one of the
thread spirals at the trailing portion.
11. A fixture according to claim 1, wherein the depth of the
threads in the leading portion is larger than the depth of the
threads in the trailing portion.
12. A fixture according to claim 1, wherein the major diameter of
the fixture is similar in both the leading portion and the trailing
portion.
13. A fixture according to claim 1, wherein the major diameter of
the fixture is greater in the trailing portion than in the leading
portion.
14. A fixture according to claim 1, wherein the major diameter of
the fixture is increasing in the trailing portion, as seen in
apical to coronal direction.
Description
TECHNICAL FIELD
[0001] The present invention relates to a fixture for insertion
into a bore hole arranged in bone tissue, the fixture comprising a
threaded outer surface for engagement with the bone tissue.
BACKGROUND OF THE INVENTION
[0002] A frequent way today to restore a damaged limb, such as lost
tooth, is to install a fixture in the adjacent bone tissue and
replace the damaged parts. In this respect, for a successful
result, the fixture should become fully stable and correctly joined
to the bone. The term osseointegration is used for this joining
effect, the basic meaning of this term being the bone tissue growth
into the fixture surface. The two major contributors to this joint
are a mechanical joint and an organic joint. The former being
generally influenced by the macro geometry of the bore into which
the fixture is installed, and by the macro geometry of the fixture,
and is a direct effect of how well these two work together. The
latter one being a continuously evolving and developing effect,
particularly during the time immediately after installation, and
being generally influenced by how well the micro surface structure
of the fixture interacts with the bone tissue.
[0003] Due to ingrowth there will be an interlocking effect between
the bone and the fixture. Also, the mechanical joint is developed
over time since the bone tissue, under ideal conditions, may grow
into surface cavities of the fixture, and grow into voids left
between the fixture and the bore after installation.
[0004] It is furthermore relevant to obtain both a good initial
(primary) fixation and a good long-term fixation of the fixture in
bone.
[0005] There is a continuous endeavour in the industry to further
increase the stability of fixtures implanted in bone tissue and to
improve the basic conditions during the healing phase after fixture
installation. One example is the provision of the fixture surface
with different types of structures, such as micro-roughened or
blasted structures for increasing the contact surface between the
fixture and the bone.
[0006] Nevertheless, there is still room for further development of
fixtures as regards their stability in bone tissue.
SUMMARY OF THE INVENTION
[0007] An object of the present invention is to provide a dental
fixture which has a high stability during the healing phases of the
fixture. This and other objects, which will become apparent in the
following, are accomplished by means of a dental fixture as defined
in the accompanying claims.
[0008] According to a first aspect of the present invention, a
dental fixture for insertion into a bore hole arranged in bone
tissue is provided. The dental fixture comprising a threaded
leading portion and a threaded trailing portion located coronally
of the leading portion,
[0009] wherein the threading of the leading portion has at least
one first thread spiral,
[0010] wherein the threading of the trailing portion has at least
one more thread spirals than the threading in the leading
portion,
[0011] wherein the threading of the trailing portion and the
threading of the leading portion have the same or substantially the
same lead,
[0012] wherein the profile of at least one of the thread spirals in
the trailing portion is, at least along a portion of its extension,
substantially the same as the profile of the outermost part of said
first thread spiral in the leading portion, and
[0013] wherein the at least one thread spiral in the trailing
portion having substantially the same profile as the outermost part
of said first thread spiral in the leading portion is arranged to
follow the spiral path of said first thread spiral.
[0014] A dental fixture being provided in the manner described
above will provide both a good primary fixation and a good
long-term fixation of the fixture in the bone.
[0015] By profile of the thread is meant to understand the contour
or outline of the thread. Hence, for two threads to have
substantially the same profile, the characteristics defining the
outer contour of the thread should be similar to each other.
[0016] With outermost parts of a thread spiral is meant to
understand a part of the thread spiral from the top of the thread
towards the thread bottom. The amount of the thread belonging to
the outermost part may vary. It may in fact, in those cases where
the minor diameter of the macrothreaded section and the
microthreaded section is the same, be the entire thread. However,
when the minor diameter of the microthreaded section is larger than
the minor diameter of the macrothreaded section, the entire
macrothread will not be considered to be the outermost part.
Instead, the portion of the macrothread belonging to the outermost
part is the portion being situated further away from the central
axis of the implant, as compared to the distance between the
central axis of the implant and the minor diameter of the
microthreaded portion. Furthermore, there exist embodiments where
there is a curved transition between the threads, i.e. the thread
has a bottom radius. In those embodiments, the outermost part of
the macrothread is considered to be the part of the macrothread
being situated further away from the central axis of the implant
than the bottom radius portion of the microthread.
[0017] When the fixture is inserted into a bore, said first thread
of the leading portion will either create a path in the case of a
self-tapping fixture or follow a path in the case of a pre-tapped
hole through the cortical bone and into the cancellous bone. Since
one of the thread spirals in the trailing portion is synchronized
with said first thread spiral in the leading portion, the thread
spiral in the trailing portion will follow the same spiral path
through the bone.
[0018] By providing at least one of the thread spirals in the
trailing portion, i.e. the thread spiral following the path of said
first thread spiral in the leading portion, with a similar or
substantially the same geometrical profile as said first thread
spiral in the leading portion, at least along a portion of its
length, the female threading in the bone will be filled with
threads throughout the length of the fixture, or at least for the
portions where the profiles are substantially the same. Hence, the
fixture will be supported by thread spirals being in contact with
the bone throughout at least a large portion of the length of the
implant.
[0019] The thread spirals in the trailing section are primarily
engaged with the hard cortical bone once the fixture has been
inserted. By providing more thread spirals at the trailing section,
the area of the threads being engaged with the bone increases, as
compared to a section having fewer thread spirals. This may be
beneficial in terms of improving the initial stability of the
implant in the bone.
[0020] It may for certain embodiments be an advantage with not
providing the entire thread spiral with a thread having
substantially the same profile as the first thread spiral. The
potential advantage is that it provides for the possibility to e.g.
create blood chambers or condensation of the bone at selected
positions along the implant. According to one exemplary embodiment,
the thread profile is provided so that blood chambers become
positioned substantially on the coronal side of the threading. By
this, the threads will be in contact with bone on their apical
side, hence providing support for the implant when it is impacted
by forces from e.g. chewing.
[0021] According to one exemplary embodiment, the thread spiral
following the path of said first thread spiral in the leading
portion has substantially the same profile as said first thread
spiral in the leading portion along its entire length. By this, the
path of the female threading in the bone in which the thread at the
leading portion travels will be filled with threading throughout
the length of the fixture. Hence, the fixture will be supported by
thread spirals being in contact with the bone throughout the length
of the implant. This provides for a good initial stability and a
good ability to carry loads and distribute these loads to the bone
in a beneficial manner.
[0022] The thread spiral following the path of said first thread
spiral in the leading portion may, but need not be, continuous with
the first thread spiral in the leading portion. Furthermore, the
leading and trailing portions of the implant may, but need not be,
positioned adjacent each other. It is for example conceivable with
another threaded portion between the leading and trailing portion.
It is also conceivable with a non-threaded surface between the
leading and trailing portion. The non-threaded surface may e.g. be
smooth or roughened.
[0023] According to at least one exemplary embodiment, the thread
spiral in the trailing portion that follows the path of said first
thread spiral in the leading portion has the same radius of
curvature at the top of the peaks as said first thread spiral. The
radius of curvature at the top of the peaks is a geometrical
characteristic that influences the profile of the thread.
[0024] According to at least one exemplary embodiment, the thread
does not have a curvature at the top of the peak. Instead, the top
may have a straight extension.
[0025] According to at least one exemplary embodiment, the thread
spiral in the trailing portion that follows the path of said first
thread spiral in the leading portion has the same flank angles,
respectively, as said first thread spiral. The flank angles are a
geometrical characteristic that influences the profile of the
thread.
[0026] The flank angle at the apical side of the thread may be
similar to the flank angle at the coronal side of the thread. It is
however also conceivable with different flank angles at the apical
and coronal sides of the thread. The thread spiral in the trailing
portion that follows the path of said first thread spiral in the
leading portion has the same flank angles, respectively, as said
first thread spiral. Hence, in this embodiment the coronal flank
angle of the two threads is the same, and the apical flank angles
of the two threads are the same, even if there may be different
angles at the coronal and apical flanks, respectively.
[0027] According to at least one exemplary embodiment, the flanks
of the threads have a straight extension.
[0028] According to at least one exemplary embodiment, the flanks
of the threads have a curved extension. It is for example
conceivable with flanks having a concave curvature. It is also
conceivable with flanks having a convex curvature.
[0029] The different characteristics defining the profile of the
thread that have been mentioned above for different exemplary
embodiments may of course be combined in any suitable manners.
[0030] According to at least one exemplary embodiment, all thread
spirals in the trailing portion have substantially the same profile
as the outermost part of said first thread spiral in the leading
portion. In this embodiment, all threads in the trailing portion
are similar to and has the same thread profile as the at least one
thread in the leading portion.
[0031] According to another exemplary embodiment, the profile of
the thread spirals in the trailing portion are different from each
other, or from one of the other thread spirals in case of more than
two thread spirals. Characteristics of the thread spiral defining
its profile is e.g. thread height, curvature radius at the top of
the thread (if any), flank angle, flank extension, flank curvature,
thread width, transition between adjacent threads and major
diameter of the implant. By this, it is possible to e.g. provide
one thread spiral that creates a blood chamber between itself and
the bone, or a thread spiral that creates condensation of the bone
as it is being inserted.
[0032] According to at least one exemplary embodiment, the profile
of one of the thread spirals in the trailing portion, that does not
follow the path of said first thread spiral in the leading portion,
alters along the thread.
[0033] A thread spiral of the trailing portion that does not follow
the path of a thread spiral in the leading portion will cut into
the bone between the female thread path of the thread spiral or
spirals of the leading portion. The thread spirals may be either
self-tapping or enter into a pre-tapped bore. It may for certain
embodiments be beneficial if the profile alters along the tread
spiral or spirals. Characteristics of the thread spiral defining
its profile is e.g. thread height, curvature radius at the top of
the thread (if any), flank angle, flank extension, flank curvature,
thread width and major diameter of the implant. By alternating one
or more of the characteristics along the length of the thread
spiral it is possible to create e.g. blood chambers between the
thread and the bone at certain positions, and to create a tight fit
between the thread and the bone at other positions. It is also e.g.
possible to create a tight fit between the thread and the bone at
certain positions and to create a condensation of the bone at other
positions, or to create a fixture which alters between providing
blood chambers and condensation of the bone along its length.
[0034] According to one exemplary embodiment, more than one thread
spiral in the trailing portion has a different or a varying profile
along the length of the respective thread spiral. It is not
necessary that the characteristics of the thread spirals that vary,
varies in the same manner. Hence, one of the thread spirals may
e.g. be designed to create blood chambers and one of the thread
spirals may e.g. be designed to create condensation of the
bone.
[0035] According to at least one exemplary embodiment, the smallest
spacing between adjacent peaks of the threading in the trailing
portion is smaller than the smallest spacing between adjacent peaks
of the threading in the leading portion.
[0036] When measuring the axial spacing between adjacent peaks, the
smallest spacing between adjacent peaks in the trailing portion is
smaller than the smallest spacing between adjacent peaks in the
leading portion. When measuring the axial spacing between adjacent
peaks, the measurement is to be taken between the tops of the peaks
and not in the valleys.
[0037] If the thread in the leading portion has one thread spiral
and the thread in the trailing portion has two thread spirals that
are evenly distributed, the axial spacing between adjacent peaks in
the trailing portion will be substantially half the distance
between adjacent peaks in the leading portion. If the thread in the
leading portion has one thread spiral and the thread in the
trailing portion has three thread spirals that are evenly
distributed, the axial spacing between adjacent peaks in the
trailing portion will be approximately a third of the distance
between adjacent peaks in the leading portion.
[0038] However, there also exist fixtures in which the thread
spirals are not evenly distributed. There also exist fixtures being
provided with a major thread being provided with minor threads at
its top. In these cases, the distance between the major threads
should be measured separately, and the distance between minor
threads should be measured separately. Hence, one should not mix
between the two different thread types in one portion of the
fixture when measuring the smallest axial distance.
[0039] According to at least one exemplary embodiment, the number
of thread spirals in the threaded trailing portion is a multiple
integer of the number of thread spirals in the leading portion.
[0040] In order to be able to provide a thread spiral in the
trailing portion following the path of a thread spiral in the
leading portion, it is beneficial if the number of thread spirals
in the trailing portion is a multiple integer of the number of
thread spirals in the leading portion. Hence, if there is provided
one thread spiral in the leading portion, the number of thread
spirals in the trailing portion may be two, three, four and so on.
If there is provided two thread spirals in the leading portion, the
number of thread spirals in the trailing portion may be four, six,
and so on. If there is provided three thread spirals in the leading
portion, the number of thread spirals in the trailing portion may
be six, nine, and so on.
[0041] According to one exemplary embodiment, the number of thread
spirals in the threaded trailing portion is not a multiple integer
of the number of thread spirals in the leading portion. It is
possible to provide an implant in which the number of thread
spirals in the trailing portion is not a multiple integer of the
number of thread spirals in the leading portion, and in which one
of the thread spirals in the trailing portion follows the path of
one of the thread spirals in the leading portion. This is for
example conceivable if the thread spirals are not evenly
distributed, i.e. the axial distance between adjacent thread
spirals differ from one another, along the length of the
implant.
[0042] According to at least one exemplary embodiment, the
threading in the leading portion has at least a first and a second
thread spiral, and wherein one of the thread spirals in the
trailing portion follows the path of said first thread spiral in
the leading portion.
[0043] In those embodiments where the leading portion is provided
with two thread spirals, i.e. a double thread, a first thread
spiral in the trailing portion may follow the path of the first
thread spiral in the leading portion.
[0044] According to one exemplary embodiment, a second thread
spiral in the trailing portion may follow the path of the second
thread spiral in the leading portion. These two thread spirals in
the trailing and leading portion, respectively, may also have the
same profile so that the female threading in the bone is being
filled, thereby providing support for the fixture along the length
of the implant.
[0045] According to at least one exemplary embodiment, a second
thread spiral in the trailing portion does not follow the path of
the second thread spiral in the leading portion.
[0046] According to at least one exemplary embodiment, the fixture
is self-tapping. There exist different manners in how to provide an
implant with self-tapping capabilities, it is for example possible
to provide the implant with cutting means extending from the apical
end into the threaded leading portion. However, it is also possible
for an implant to be self-tapping even if it does not comprise any
cutting means.
[0047] According to at least one exemplary embodiment, the fixture
is provided with separate cutting means adapted for cutting a
female thread in the bone that corresponds to the profile of at
least one of the thread spirals at the trailing portion.
[0048] Providing separate cutting means at the trailing portion
provides for the opportunity to cut out a female thread for the
threading of the trailing portion. By this, the trailing portion
may be inserted into the bone with the amount of bone being crushed
during insertion being reduced.
[0049] The cutting means at the trailing portion may preferably
begin at the apical end of the trailing portion, and extend
coronally into the trailing portion.
[0050] According to at least one exemplary embodiment, the cutting
means provided for cutting a female thread in the bone
corresponding to the profile of the thread spirals at the trailing
portion extends over at least one turn of all thread spirals at the
trailing portion. With extending over at least one turn of all
thread spirals, it is meant to understand that it extends over an
axial length corresponding to the axial extension of one full
rotation of the thread spirals. Hence, if the thread at the
trailing portion is a double-thread, the cutting means extend over
at least both threads, if the thread is a triple-thread, the
cutting means extend over at least all three threads, and so on.
The cutting means, may, but does not need to, extend over several
rotations of each one of the thread spirals. By this, a female
thread corresponding to the thread of the trailing portion will be
cut in the bone and the bone will thereby not have to be subject to
the strong impact that could otherwise be a risk when a thread is
pressed into bone that has not been properly prepared.
[0051] According to at least one exemplary embodiment, the cutting
means provided for cutting a female thread in the bone
corresponding to the profile of the thread spirals at the trailing
portion is provided to cut a female thread corresponding to both
the outer and inner diameter of the thread at the trailing portion.
By this, a female thread corresponding to the thread of the
trailing portion will be cut in the bone and the bone will thereby
not have to be subject to the strong impact that could otherwise be
a risk when a thread is pressed into bone that has not been
properly prepared.
[0052] Furthermore, depending on the configuration of the cutting
means in relation to the profile of the thread in the trailing
portion, e.g. the shape and minor and major diameter of the cutting
means, it is possible to design fixtures in which a desired rate of
condensation of the bone occurs. Obviously, a desired rate of
condensation may be zero condensation.
[0053] According to at least one exemplary embodiment, the depth of
the threads in the leading portion is larger than the depth of the
threads in the trailing portion. A configuration according to this
embodiment has proven to be beneficial in terms of load
distribution to the bone, thereby providing for good initial and
long-term stability of the fixture.
[0054] According to at least one exemplary embodiment, the major
diameter of the fixture is similar in both the leading portion and
the trailing portion.
[0055] According to at least one exemplary embodiment, the major
diameter of the fixture is greater in the trailing portion than in
the leading portion. By providing the trailing portion with a
larger major diameter than the leading portion, a condensation of
the bone surrounding the trailing portion will occur when the
implant is inserted into the bone, in the case of a straight
cylindrical bore hole.
[0056] According to at least one exemplary embodiment, the major
diameter of the fixture is increasing in the trailing portion, as
seen in apical to coronal direction. By providing the trailing
portion with an increasing major diameter a gradually increasing
condensation of the bone surrounding the trailing portion will
occur when the implant is inserted into the bone, in the case of a
straight cylindrical bore hole.
[0057] According to at least one exemplary embodiment, the fixture
is further provided with a transition portion, provided between the
leading portion and the trailing portion, wherein the major
diameter of the fixture is increasing in the transition
portion.
[0058] According to at least one exemplary embodiment, the fixture
is further provided with a transition portion, provided between the
leading portion and the trailing portion, wherein the minor
diameter of the fixture is increasing in the transition
portion.
[0059] According to at least one exemplary embodiment, the major
and/or minor diameter of the fixture is continuously increasing in
the transition portion.
[0060] According to at least one exemplary embodiment, at least a
portion of the transition portion is provided with a threading,
wherein the threading of the transition portion continues into the
trailing portion.
[0061] According to at least one exemplary embodiment, the thread
of the transition portion is similar to the thread of the trailing
portion.
[0062] According to one exemplary embodiment, the cutting means
provided for cutting a female thread in the bone corresponding to
the profile of the thread spirals at the trailing portion, is
provided at the transition portion.
[0063] The cutting means at the transition portion may preferably
begin at the apical end of the transition portion, and extend
coronally into the transition portion.
[0064] According to at least one exemplary embodiment, the cutting
means provided for cutting a female thread in the bone
corresponding to the profile of the thread spirals at the trailing
portion extends over at least one turn of all thread spirals at the
transition portion. With extending over at least one turn of all
thread spirals, it is meant to understand that it extends over an
axial length corresponding to the axial extension of one full
rotation of the thread spirals. Hence, if the thread at the
transition portion and trailing portion is a double-thread, the
cutting means extend over at least both threads, if the thread is a
triple-thread, the cutting means extend over at least all three
threads, and so on. The cutting means, may, but does not need to,
extend over several rotations of each one of the thread
spirals.
[0065] According to one exemplary embodiment, the major diameter of
the cutting means at the transition portion or the cutting means at
the trailing portion is similar to the major diameter of the
threads at the leading portion. Hence, in this embodiment, there is
no increase of the major diameter of the fixture between the
coronal end of the leading portion and the cutting means at the
apical end of the transition portion and/or the cutting means at
the apical end of the trailing portion.
[0066] According to one exemplary embodiment, the major diameter of
the fixture is constant throughout the length of the cutting means
at the transition portion or trailing portion. According to one
exemplary embodiment, the minor diameter of the fixture is constant
throughout the length of the cutting means at the transition
portion or trailing portion. Hence, according to these exemplary
embodiments, there is no major and/or minor diameter increase at
the cutting means provided for cutting a female thread in the bone
corresponding to the thread of the trailing portion of the
fixture.
[0067] According to one exemplary embodiment, the major diameter
increases at the transition portion, coronally of the cutting
means.
[0068] According to one exemplary embodiment, the minor diameter
increases at the transition portion, coronally of the cutting
means.
[0069] Hence, according to either one or a combination of these
exemplary embodiments, a female thread corresponding to the thread
of the transition portion and/or trailing portion may be cut into
the bone by the cutting means. Thereafter, when the major and/or
minor diameter increases coronally of the cutting means, a
controlled condensation of the bone will be achieved.
[0070] According to one exemplary embodiment, the cutting means may
preferably begin at the apical end of the transition portion, and
extend coronally into the transition portion.
[0071] According to at least one exemplary embodiment, the length
of the transition portion is such that the transition portion
extends over at least one turn of the thread, preferably at least
two turns of the thread, and most preferred over at least three
turns of the thread. By one turn of the thread is meant to
understand one full rotation of each one of the thread spirals, in
case of a multi-start thread. By this, the diameter increase will
be gradual and not sudden. This is beneficial since a sudden
diameter increase may affect the surrounding bone negatively during
insertion of the fixture into the bone.
[0072] A dental implant may comprise a dental fixture and a
superstructure, such as an abutment.
[0073] A dental fixture is for use as the anchoring member of a
dental prosthesis. To this end, the dental fixture is insertable
into a pre-prepared bore hole in the bone tissue of a jawbone
(maxilla or mandible) at a site where the dental prosthesis is
required. The dental fixture is normally rotated into the bore
hole.
[0074] For screw-type dental fixtures the bore hole may be provided
with internal threads in advance or may be left un-tapped with the
dental fixture provided with a self-tapping capacity, e.g. by the
provision of one or more axially-extending cutting recesses, edges
or notches, etc in the fixture thread. For instance, an apical end
portion of the fixture may be provided with 2-4 cutting recesses,
such as 3 cutting recesses. Other number of cutting recesses are
readily conceivable.
[0075] A superstructure for connecting a prosthetic part to the
fixture may comprise an abutment, spacer or other transmusosal
component which engages to the dental fixture to bridge the gingiva
overlying the maxilla or mandible. The prosthetic part, e.g. a
crown, bridge or denture may be secured to the abutment. There are
various other forms that the superstructure can take. For instance,
the prosthetic part may be secured directly to the dental fixture.
A dental implant may thus comprise an abutment connected to the
dental fixture, or the dental fixture without an abutment.
[0076] The term "coronal" is here and throughout this application
used to indicate a direction towards a head end or trailing end of
the dental implant. For instance, in a situation where an abutment
is connected to a dental fixture, the coronal direction of the
abutment would be a direction towards the part of the abutment
being directed away from the fixture. Conversely, the term "apical"
indicates a direction towards an insertion or leading end of the
component. Thus, apical and coronal are opposite directions.
Furthermore, the terms "axial", "axial direction" or "axially" are
used throughout this application to indicate a direction taken from
the coronal end to the apical end, or vice versa. The terms
"radial", "radial direction" or "radially" indicate a direction
perpendicular to the axial direction.
[0077] A blind bore or socket may extend apically into the fixture
body from the coronal end to an end surface in-between the apical
and coronal ends of the fixture body for a superstructure to be
secured to the fixture. The socket may comprise an
internally-threaded section for screw connection of the
superstructure to the fixture. A rotational lock for the
superstructure may be provided in the socket, such as an internal
polygonal side wall, e.g. hexagonal, or alternatively one or more
protrusions from or indentation in the wall of the socket. A
section of the socket, such as the coronal section, may be tapered
towards the apical end. The tapered section is suitably arranged
coronally of the internally-threaded section.
[0078] The fixture may be used in a one stage procedure or a two
stage procedure. In a one stage procedure a healing or temporary
abutment is connected to the fixture to form the gingival tissue,
and after a healing period the healing or temporary abutment is
replaced by a permanent abutment. For a two stage procedure the
fixture is provided with a cover screw and the gingival tissue is
sutured over the fixture and cover screw, and after a healing
period the tissue is opened up and an abutment is connected to the
fixture after removal of the cover screw.
[0079] A conceivable alternative to having an abutment connected to
the fixture is to have a one-piece implant, wherein a portion of
the implant is embedded in bone tissue, while another portion of
the implant extends from the bone tissue across the gingiva.
[0080] The fixture may have a conically tapering end portion which
tapers towards the coronal end. The axial extent of this coronal
end portion is small compared to the total length of the fixture,
as an example no more than 4% of the total length, such as in the
range of 1.5%-3.7%. The coronal end portion may suitably be
provided without a threaded surface, e.g. having a smooth or a
roughened (such as blasted) surface.
[0081] The fixture may have a substantially flat coronal end
surface which is perpendicular to the longitudinal axis of the
fixture. Alternatively, the coronal end surface may have a sloped
contour relative to the longitudinal axis of the fixture, e.g. such
that when positioned within the jawbone the length of the fixture
is larger on a lingual side and shorter on a buccal side of the
fixture. Another alternative is a saddle-shaped or wave-like
coronal end surface.
[0082] The length of the dental fixture may be in the range of 5-19
mm, depending on the clinical situation. The outer diameter of the
dental fixture may suitably be in the range of 2-6 mm, such as 3-5
mm.
[0083] The fixture may be substantially cylindrical or slightly
tapering from the coronal end towards the apical end. If the
fixture has a slight tapering, the core of the fixture and the
outer periphery defined by e.g. thread tops may have the same or
different angle of taper. Furthermore, the core of the fixture may
be cylindrical while the thread tops describe a conicity or,
conversely, the core of the fixture may be tapered while the thread
tops describe a generally cylindrical geometry. Alternatively, the
fixture may comprise a combination of one or more cylindrical
and/or one or more tapering portions. Thus, one or more portions of
the fixture may have e.g. thread tops lying in a common imaginary
cylindrical surface, which cylindrical surface is parallel with the
longitudinal axis of the fixture. Alternatively or additionally,
one or more portions of the fixture may have thread tops lying in
an imaginary conical surface which in the apical direction is
tapering towards the longitudinal axis.
[0084] The externally threaded fixture may comprise one or more
thread spirals.
[0085] The term "pitch" is used to indicate the axial distance
between adjacent tops of a threading. The term "lead" is used to
indicate the distance advanced parallel to the longitudinal axis
when the fixture is turned one revolution, i.e. it corresponds to
the pitch multiplied with the number of thread spirals. For a
single thread spiral having a constant pitch, the lead is equal to
the pitch; for a double thread spiral, the lead is twice the
pitch.
[0086] The term "microthread" is used to indicate a thread having a
height which is no greater than 0.2 mm. According to at least one
example embodiment, the fixture is provided with microthreads
having a height in the range of 0.02-0.2 mm, such as 0.05-0.015 mm,
for instance 0.1 mm. The term "macrothread" is used to indicate a
thread having a height which is greater than 0.2 mm. According to
at least one example embodiment, the fixture is provided with
macrothreads having a height in the range of 0.25-0.35 mm, such as
0.3 mm.
[0087] Suitably, microthreads may be located coronally of
macrothreads. For instance, microthreads may be arranged to engage
dense cortical bone and macrothreads may be arranged to engage
porous spongious/cancellous bone. The lead of a microthread
suitably corresponds to the lead of a macrothread. The macrothread
pitch may, as an example, be 2-4 times, such as 3 times, the pitch
of the microthreads. The pitch (top-to-top spacing) at a fixture
portion provided with microthreads may be around 0.10-0.30 mm, for
instance 0.20-0.24 mm. The pitch (top-to-top spacing) at a fixture
portion provided with macrothreads may be around 0.30-0.90 mm, for
instance 0.60-0.72 mm.
[0088] Microthreads can be regarded as defined, oriented roughness.
A non-oriented roughness having smaller dimensions, for instance
obtained by blasting, etching, etc., may be superimposed on
microthreads as well as on macrothreads.
[0089] A thread profile may comprise two flanks, a top
interconnecting said two flanks, a bottom formed between two
adjacent threads, said flanks forming an acute angle v with a plane
which is perpendicular to the fixture axis and which angle v lies
in a plane containing the extension of the fixture axis, said
profile further having a height D. The top may be curved and may
have a top radius. Suitably, for 10.degree..ltoreq.v<35.degree.,
the top radius is greater than 0.4.times.D and, for
35.degree..ltoreq.v<55.degree., the top radius is greater than
0.2.times.D.
[0090] In this application, when strain is discussed, or when
different values of strain are discussed, unless explicitly
specified, the discussion may relate to tensile strain and/or
compressive strain. All strain-related numbers are presented in
absolute values.
BRIEF DESCRIPTION OF THE DRAWINGS
[0091] FIGS. 1a-1b illustrate a portion of the threading of the
leading and trailing portions, respectively, of a fixture,
according to at least one example embodiment of the present
invention.
[0092] FIGS. 2a-2b illustrate a portion of the threading of the
leading and trailing portions, respectively, of a fixture,
according to at least one other example embodiment of the present
invention.
[0093] FIGS. 3a-3b illustrate a portion of the threading of the
leading and trailing portions, respectively, of a fixture,
according to at least one other example embodiment of the present
invention.
[0094] FIG. 4 illustrates an example of an installation of a
fixture according to at least one example embodiment of the present
invention.
[0095] FIG. 5 illustrates an example of a fixture installed in bone
according to at least one example embodiment of the present
invention.
[0096] FIG. 6 illustrates an example of a fixture installed in bone
according to at least one other example embodiment of the present
invention.
[0097] FIG. 7 illustrates an example of a fixture installed in bone
according to at least one other example embodiment of the present
invention.
[0098] FIG. 8 illustrates an example of a fixture installed in bone
according to at least one other example embodiment of the present
invention.
[0099] FIG. 9 illustrate a fixture according to at least one
example embodiment of the present invention.
[0100] FIG. 10 illustrate a fixture according to at least one other
example embodiment of the present invention.
[0101] FIG. 11 illustrate a thread profile according to at least
one example embodiment of the present invention.
[0102] FIG. 12 illustrate a thread profile according to at least
one other example embodiment of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0103] FIG. 9 is a side view illustrating a fixture 10 according to
at least one example embodiment of the invention. The fixture 10 in
FIG. 9 comprises a leading portion 32 and a trailing portion 36
located coronally of the leading portion 32. Each one of said
portions present a respective outer surface being threaded for
engagement with the bone tissue, wherein thread tops 20 and thread
bottoms 22 are provided alternatingly in the axial direction of the
fixture 10. The leading portion is in this embodiment provided with
macrothreads 38 and the trailing portion is provided with
multi-start microthreads 46, which in the illustrated embodiment is
a double-thread.
[0104] At the apical end, the fixture is provided with cutting
means/cutting edges 44, of which one is shown. The fixture is also
provided with cutting means 48, of which one is shown, at the
apical end of the trailing portion. The cutting means 48 in this
embodiment extend over both thread spirals of the microthreads, so
that they may cut a corresponding female thread in the bone for
each one of the two thread spirals.
[0105] Although FIG. 9 illustrates that an apical portion 24 of the
leading portion 32 is substantially straight and is provided with
one or more cutting means 44, other alternatives are also
conceivable, e.g. a section tapering in the apical portion being
provided with cutting means, or a section tapering in the apical
portion without cutting means, or a non-tapering apical portion
without cutting means.
[0106] FIG. 9 illustrates a straight cylindrical fixture 10.
However, the fixture may also be provided with a transition zone in
which the diameter of the implant increases. Such a transition zone
may be either non-threaded, macrothreaded or microthreaded.
[0107] FIG. 10 illustrates an alternative embodiment of a fixture.
The features of the fixture in FIG. 10 being similar to the
features of the fixture in FIG. 9 will not be elaborated upon
herein. The difference between the fixture 1010 in FIG. 10 compared
to the fixture in FIG. 9 is that in this embodiment, both the
macrothreads 1038 and the microthreads 1046 are multi-start
threads. The macrothreads 1038 is a double-thread, i.e. it has two
thread starts, and the microthreads 1046 is a quadruple-thread,
i.e. it has four thread starts. The cutting means 48 in this
embodiment extend over all four thread spirals of the microthreads,
so that they may cut a corresponding female thread in the bone for
each one of the thread spirals.
[0108] FIGS. 1a-1b illustrate a detail of a fixture according to at
least one example embodiment of the invention. In particular a part
of the fixture is shown in cross-section, wherein the fixture has a
leading portion 132 and a substantially straight trailing portion
136. The leading portion 132 is provided with macrothreads 138
having thread tops 140 with a certain radius of curvature a. The
thread tops 140 are flanked by apical and coronal flank portions
142a, 142b at a certain angle .gamma. relative to a plane
perpendicular to the central fixture axis. In this case the apical
and coronal flanks 142a, 142b are illustrated as having the same
angle .gamma.. However, in alternative embodiments the apical and
coronal flank angles may differ from each other. The macrothread
138 is provided with a cutting means, such as a cutting edge 144
similar to the cutting means 44 in FIG. 9, to make a corresponding
female macrothread in the bone tissue.
[0109] Coronally of the macrothreads 138, the trailing portion 136
is provided with double-spiraled microthreads 146. The microthreads
146 have the same lead as the macrothread 138, the pitch being half
the pitch of the macrothread 138. A cutting means 148 is present at
the microthreads in the trailing portion 136 to make corresponding
female microthreads in the bone tissue, similar to what has been
described above for the cutting means 48 in FIG. 9. As can clearly
be seen in FIG. 1, the cutting means extend over both thread
spirals and are provided to cut a female thread having both
corresponding minor and major diameter as the microthreads 146. In
the illustrated embodiment, throughout the leading portion 132 and
trailing portion 136, the tops 150 of the microthreads 146 have the
same radius of curvature as the radius of curvature a of the
macrothreads 138. Also, the flank angles of the apical flank 147a
and the coronal flank 147b of the microthreads 146 correspond to
those of the macrothreads 138. The effect of this conformation to
the macrothreads 138 will now be explained.
[0110] The microthreads 146 are provided as two thread spirals,
herein referred to as a first thread spiral 146a and a second
thread spiral 146b. The first thread spiral 146a will follow the
path of the macrothreads 138. The second thread spiral 146b will
make its own path. The cutting means 144 at the macrothread 138
creates a female thread profile in the bone having the same radius
of curvature a and the flank angles .gamma. as the macrothread 138.
Thus, when the first thread spiral 146a of the microthreads 146
enters the female bone thread it can theoretically be in full
contact with the bone, since the thread tops have the same radius
of curvature a and the flanks have the same angles .gamma. as the
female bone thread. This means that the initial stability of the
fixture can be higher than if the first thread spiral of the
microthreads would not fill out the space of the female bone
thread. This is further illustrated in FIG. 5. With prior art
implants, it is the macrothreads that mainly provide the initial
stability, and only after the bone tissue has grown into the spaces
created by the microthreads, the microthreads will contribute to
the stability of the implant. With the inventive idea illustrated
in this exemplary embodiment, also the microthreads will contribute
to the initial stability of the implant, without compromising the
long-term stability of the implant.
[0111] It should be noted that while the cutting means 148 at the
microthreads 146 will make a new path for the second thread spiral
146b, it will, for the first thread spiral 46a, just enter into the
already made female bone thread created by the cutting means 144 at
the macrothread 138.
[0112] As can be seen in FIG. 1a, the fixture in this embodiment is
a straight cylindrical implant, hence, the major diameter D.sub.1
of the microthreaded section and the macrothreaded section are
similar to each other. The valleys of the microthreads are situated
further away from the central axis of the fixture, than the valleys
of the macrothreads. In other words, the minor diameter d.sub.1 of
the trailing portion is larger than the minor diameter d.sub.2 of
the leading portion. The reason for this being that the
microthreads have a lower height than the macrothreads, and they
should, at least along a portion of the implant, fill out the
female thread of the bone that the macrothread has travelled
through during insertion. The outermost part of the macrothreads is
for this embodiment the portion of the macrothreads being situated
further away from the central axis of the implant than the minor
diameter d.sub.1 of the trailing portion.
[0113] FIGS. 2a-2b illustrate a detail of a fixture according to at
least one other example embodiment of the invention. Features
similar to those disclosed in FIGS. 1a-1b has been given the same
reference numerals in FIGS. 2a-2b. In particular a part of the
fixture is shown in cross-section, wherein the fixture, similar to
the example embodiment in FIGS. 1a-1b, has a leading portion 232
and a substantially straight trailing portion 236. However, in this
embodiment, the fixture is also provided with a coronally widening
transition portion 234. In this transition zone, both the minor and
major diameter of the fixture increases. This is illustrated in
FIG. 2a where the major diameter D.sub.3 and the minor diameter
d.sub.3 at the apical end of the transition portion are smaller
than the major diameter D.sub.4 and the minor diameter d.sub.4 at
the coronal end of the transition portion, respectively. The
increased major diameter D.sub.4 and the increased minor diameter
d.sub.4 is thereafter maintained in the straight trailing portion
236. The leading portion 232 is provided with macrothreads 138
similar to those described in relation to FIGS. 1a-1b. Coronally of
the macrothreads 138, the transition portion 234 is provided. The
transition portion 234 is provided with double-spiraled
microthreads 146 which continue into the trailing portion 236. As
can be seen in FIG. 2a, the transition zone extends over several,
in the illustrated example three, turns of the double-thread spiral
The microthreads 146 have the same characteristics as the
microthreads described in relation to FIGS. 1a-1b, including also
the cutting means 148, which in this embodiment is provided at the
apical portion of the transition zone 234. The effect of this
conformation to the macrothreads 138 is the same as the effect
described in relation to FIGS. 1a-1b. As can also be seen in FIG.
2a, the major diameter of the cutting means 148 is similar to the
major diameter D.sub.1 of the leading portion. The major and minor
diameters of the cutting means are also similar to the major and
minor diameters of the first turn of the most apical non-cutting
thread spiral of the transition transition portion. It is also seen
in FIG. 2a that the increase in major and minor diameters of the
transition portion starts coronally of the cutting means 148.
Hence, there is no diameter increase at the cutting means.
[0114] The outermost part of the macrothreads is also for this
embodiment the portion of the macrothreads being situated further
away from the central axis than the minor diameter of the implant
at the transition portion and the trailing portion. Hence, for this
embodiment, the portion of the macrothreads being considered as the
outermost part differs, depending on where along the axial length
of the trailing portion and the transition portion a microthread is
positioned. However, the important aspect is that the microthread
following the path of a macrothread fills out the female thread
created in the bone, at least along a portion of its length.
[0115] The purpose of increasing the major and minor diameter of
the fixture in the transition portion and maintaining the increased
diameters in the trailing portion is that the fixture should apply
a desired static strain to the bone, once implanted. A desired
static strain applied to the bone by the fixture has proven to be
beneficial in relation to the osseointegration of the fixture.
[0116] The transition portion is in this exemplary embodiment
microthreaded, however it is also conceivable that the transition
portion is macrothreaded.
[0117] FIGS. 3a-3b illustrate a detail of a fixture according to at
least one other example embodiment of the invention. The fixture in
this embodiment has most features in common with the example
embodiment illustrated in FIGS. 2a-2b, and similar features have
been given the same reference numerals.
[0118] The illustrated fixture has a leading portion 332, a
coronally widening transition portion 234 and a substantially
straight trailing portion 236. The leading portion 332 is, similar
to the previously described embodiments, provided with a
macrothread extending from the apical end of the portion towards
the coronal end. However, in this embodiment, the leading portion
332 is also provided with a non-threaded section 360. The surface
of the non-threaded section may be either smooth or roughened.
[0119] It is important that the non-threaded section 360 has an
axial length such that the threads being provided coronally of the
non-threaded section follow the path of the threads being provided
apically of the non-threaded section. In the illustrated example
where the non-threaded section is provided between the
macrothreaded portion and the microthreaded portion, it is
important that is has an axial length such that one of the
microthreads follows the path of the macrothread. The reason for
this being that, similar to the previously described embodiments,
the initial stability of the fixture can be higher than if one of
thread spirals of the microthreads would not fill out the space of
the female bone thread created by the macrothread.
[0120] The embodiment with a non-threaded section is here
illustrated with a fixture having a transition portion 234, similar
to the transition portion of the previous embodiment. It is however
also conceivable with a non-threaded section 360 being provided on
the straight fixture illustrated in FIGS. 1a-1b. Furthermore, the
non-threaded section is in this embodiment provided at the leading
portion. It is however also conceivable that the non-threaded
section is provided on the transition portion (if present) or on
the trailing portion of the fixture.
[0121] FIG. 4 illustrates an example of an installation of the
fixture 10, illustrated in FIG. 9, according to at least one
example embodiment of the invention. The fixture 10 is
schematically illustrated as having a leading portion 32 and a
trailing portion 36. The fixture 10 is intended to be installed in
a bore hole 30 in the jawbone 62 under the gingiva 34. Surrounded
by cancellous bone 62a an apical section 30a of the bore hole 30
has a first diameter, e.g. substantially corresponding to the core
diameter of the leading portion 32. Surrounded by cortical bone 62b
a coronal section 30b of the bore hole 30 has a second diameter,
for instance corresponding to the core diameter of the trailing
portion 36. When the fixture has been installed in the bone, the
leading portion 32 will be positioned in the apical section 30a and
the trailing portion 36 will be positioned in the coronal section
30b.
[0122] In the following, different example embodiments of fixtures
being installed in bone will be illustrated.
[0123] FIG. 5 illustrate an embodiment of a fixture having a
threading and general outline according to the fixture illustrated
in FIGS. 1a-1b when it is installed in bone 62. As mentioned in
relation to FIGS. 1a-1b, every second microthread 146a follows the
path of the macrothread 138 in the bone and the microthread 146a
following the path of the macrothread 138 has the same profile
characteristics as the macrothread. As can be seen in FIG. 5, the
microthread therefore fills out the female thread in the bone 62
and the fixture becomes supported along its entire length. In the
embodiment illustrated in FIG. 5, also the other microthread 146b
has the same profile characteristics as the macrothread 138.
[0124] FIG. 6 illustrate an embodiment of a fixture having a
threading and general outline according to the fixture illustrated
in FIGS. 1a-1b and 5 when it is installed in bone 62. However, in
this example embodiment, the upper flank 647 of the microthread
646a following the path of the macrothread 138 has a different
geometry than the upper flank of the macrothread 138 along a
portion of its length. Hence, the female thread in the bone is not
entirely filled by the microthread, along a portion of the length
of the microthread. This results in the creation of blood chambers
648 between the bone and the fixture, which may have a positive
effect in the osseointegration of the fixture in the bone. It is
only along a portion of its length that the microthread following
the path of the macrothread has a different upper flank angle.
Along the remaining portions of its length it has the same
characteristics as the microthread 146a in e.g. FIG. 1.
Consequently, along these portions of the fixture's length the
female thread becomes filled by the microthread. Hence, the fixture
is well supported in the bone. The other microthread 646b is in
this embodiment similar to the microthread 146b in e.g. FIG. 1.
[0125] FIG. 7 illustrates an embodiment of a fixture installed in
the bone 62 having a threading and general outline according to the
fixture illustrated in FIG. 6. However, in this embodiment it is
the microthread 746b, that does not follow the path of the
macrothread 138, that has a different upper flank 747 profile, at
least along a portion of its length. Similarly to the embodiment
illustrated in FIG. 6, this results in the creation of blood
chambers 748 between the bone and the fixture, which may have a
positive effect regarding the osseointegration of the fixture in
the bone. The other microthread 746a is in this embodiment similar
to the microthread 146a in e.g. FIG. 1.
[0126] In the two embodiments illustrated in FIGS. 6 and 7, the
flank angle of the upper flank of the microthread has been modified
in order to create the blood chambers. It is however also
conceivable with amending other features of the threads in order to
create blood chambers. For instance, the radius of curvature at the
top of the peak may be altered, or the height of the peak may be
shortened.
[0127] FIG. 8 illustrate an embodiment of a fixture installed in
bone 62 having a threading and general outline according to the
fixture illustrated in FIGS. 1a-1b and 5. However, in this example
embodiment, the height of the microthreads 846b, that do not follow
the path of the macrothread, is provided so that the major diameter
of the fixture at the position of the microthread 846b is
increased. Hence, the female thread in the bone created by the
cutting means 144 of the macrothread 138 will not be deep enough to
accommodate the entire microthread 846b. This results in that the
bone 62 becomes condensated at the positions where the microthread
846b is pressed into it. Condensation of the bone provides a static
strain at these positions, which may have a positive effect in the
osseointegration of the fixture in the bone.
[0128] As can also be seen in FIG. 8, the cutting means 148 are
also in this embodiment similar to the cutting means 148
illustrated in e.g. FIG. 1. Hence, they do not provide for a female
thread having the same height as the microthread 846b. The reason
for this being that in order to achieve the condensation of the
bone, the female thread in the bone may not be cut to match the
shape and size of the microthread.
[0129] The increased height of the microthreads 846b, providing the
condensation of the bone, may be provided either along the entire
microthread or only along a portion of it. An increased height of
thread creates an increased major diameter of the implant at that
position of the implant. If the increased height of the thread is
only provided along a portion of the thread spiral, and this
portion is not only at the coronal end of the implant, there may
exist blood chambers at the position where the thread spiral does
not have an increased height. The reason for this being that when
the implant is inserted, the portion of the thread with increased
height will press into the bone and condensate it. Thereafter, if
the height of the thread being located coronally of the portion
with increased height has a smaller height e.g. the normal height
of the thread (the same size as for the other threads), there will
be a gap between the thread with normal height and the bone that
has been pressed away. However, if the increase in thread height
has only been slight, and thus also the condensation of the bone
has only been minor, the bone, and the female thread created in the
bone, may return to its original shape when the portion of the
thread with increased height has passed. In this case, there will
be condensation of the bone at the final position of the thread
with increased height, but there will be no blood chambers
coronally of that position. Hence, a thread with normal height
will, as for the other illustrated embodiments, fill out the female
thread in the bone.
[0130] Furthermore, in FIG. 8, it has been illustrated that it is
the microthread 846b, i.e. the microthread not following the path
of the macrothread 138, that provides the condensation in the bone
and that the other microthread 846a provides the same major
diameter as the macrothread 138. It is however also conceivable
that it is either the other microthread 846a or both microthreads
846a, 846b that is/are provided to condensate the bone.
[0131] FIG. 11 illustrate an exemplary embodiment of the thread
profile. The thread profile of the microthreads and macrothreads in
FIGS. 1-8 is illustrated as having straight flank portions that
meet each other in an acute angle. In the embodiment illustrated in
FIG. 11 the microthreads 1146 and macrothreads 1138 are also
provided with straight flank portions 1147a, 1147b and 1142a,
1142b, respectively, but the intersection between adjacent peaks is
in the form of a curved portion 1150 and 1149, respectively. Hence,
the thread has a bottom radius. The bottom radius of the
microthread is in this embodiment a characteristic that differs
between the microthread and the outermost part of the macrothread.
This is because the macrothread has straight flank angles and a
bottom radius that is situated closer to the central axis of the
implant. Hence, in this embodiment, the microthread has the same
profile as the outermost part of the macrothread, except for the
curved portion at the intersection between adjacent peaks. In use,
the microthread following the path of the macrothread will fill the
female thread created in the bone by the macrothread. The bottom
radius of the microthread will, similar to the microthread not
following the path of the macrothread, enter into the bone in a
female thread being cut by the cutting means 1148 at the
microthread 1146. Also in this embodiment the cutting means extend
over both thread spirals of a double-thread. Consequently, this
embodiment falls within the scope of the appended claims in which
it is defined that the profile of the microthread is substantially
the same as the profile of the macrothread.
[0132] FIG. 12 illustrate a further exemplary embodiment of thread
profiles. Similar to the embodiment illustrated in FIG. 11, the
microthread 1246 and the macrothread 1238 are provided with a
curved portion at the intersection between adjacent peaks, i.e. it
is provided with bottom radiuses. However, in this embodiment, the
macrothread 1238 is provided with an additional shoulder 1251 on
both its apical and coronal sides, resembling the bottom radius of
the microthread and being positioned at the same distance from the
central axis of the implant as the bottom radius of the
microthread. The upper part 1252 of the shoulder has a size and
extension being substantially the same as half the curvature at the
bottom radius of the microthread. The cutting means 1244 at the
apical end of the implant is provided with similar shoulders. The
purpose of these shoulders is to create a female thread in the bone
that has a shape which also includes the bottom radius of the
microthread. Hence, the microthread in this embodiment will in use
fill the female thread in the bone created by the cutting means at
the macrothread. The macrothread, having a similar shoulder as the
cutting means, will also fill out the female thread created in the
bone. The outermost part of the macrothread is in this embodiment
considered to be the portion of the macrothread being situated
further away from the central axis of the implant than the
shoulder.
[0133] FIGS. 5-8 illustrate different embodiments of a fixture
having the same general outline as illustrated in FIGS. 1a-1b.
However, any one of the embodiments illustrated in FIGS. 5-8 may
also be combined with the outline of the fixtures illustrated in
any one of FIGS. 2a-2b and 3a-3b, i.e. a fixture with a transition
portion in which the implant's major and minor diameters increase.
Furthermore, any of the embodiments illustrated in FIGS. 1a-8 may
be combined with any one of the thread profiled illustrated in
FIGS. 11 and 12.
[0134] The inventive implant has been described in relation to a
number of exemplary embodiments. However, further modifications are
conceivable within the scope of the appended claims.
[0135] The different embodiments of the fixture have throughout the
description been illustrated as a self-tapping fixture. However, it
is also conceivable with a fixture without any cutting means,
adapted to be inserted into a hole that has been prepared by a
thread maker or tapper that provides the female bone thread. It is
also possible with a fixture that is not provided with any cutting
means but are adapted to be inserted into a hole that has not been
pre-tapped.
[0136] The leading portion of the fixture has been illustrated as a
straight cylindrical portion. However, it is also conceivable with
slightly conical leading portions.
[0137] The macrothreaded portion has been illustrated as comprising
a thread having only one thread start. It is however also
conceivable with a thread having more than one thread
start/spiral.
[0138] The microthreaded portion has been illustrated as comprising
a thread having two thread starts. It is however also conceivable
with a thread having three or more thread starts/spirals.
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