U.S. patent number RE37,646 [Application Number 09/226,743] was granted by the patent office on 2002-04-09 for dental implant system.
This patent grant is currently assigned to Sulzer Dental Inc.. Invention is credited to Max Zuest.
United States Patent |
RE37,646 |
Zuest |
April 9, 2002 |
Dental implant system
Abstract
A dental implant assembly is provided, as well as a system and
method for exposing an embedded implant after osseointegration has
taken place. The implant assembly comprises an implant member for
embedding in the jaw and a rest factor member for securing to the
implant member, the rest factor member having an upper rest surface
just above the tissue level for opposing an overlying portion of a
prosthesis anchored elsewhere in the jaw to form a non-retentive
rest or support for accepting down pressure from the prosthesis.
The implant member is relatively short and can be installed in
distal jaw regions without interference with the mandibular nerve.
A bore is cut out in the jaw for receiving the implant, inserting
the implant and an attached healing screw in the implant. The
implant site is closed and osseointegration takes place over an
extended period. Subsequently, the implant site is uncovered, the
healing screw is removed, and the rest factor member is secured in
the implant.
Inventors: |
Zuest; Max (San Diego, CA) |
Assignee: |
Sulzer Dental Inc. (Houston,
TX)
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Family
ID: |
27493255 |
Appl.
No.: |
09/226,743 |
Filed: |
January 7, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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861183 |
Mar 31, 1992 |
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751661 |
Aug 22, 1991 |
5254005 |
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436432 |
Nov 14, 1989 |
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Reissue of: |
102353 |
Aug 5, 1993 |
05591029 |
Jan 7, 1997 |
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Current U.S.
Class: |
433/173;
433/174 |
Current CPC
Class: |
A61C
8/0018 (20130101); A61C 8/0025 (20130101); A61C
8/0089 (20130101) |
Current International
Class: |
A61C
8/00 (20060101); A61C 008/00 () |
Field of
Search: |
;433/172,173,174 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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4238383 |
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Jul 1994 |
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DE |
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2635964 |
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Mar 1990 |
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FR |
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93/12733 |
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Jul 1993 |
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WO |
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Primary Examiner: Lewis; Ralph A.
Attorney, Agent or Firm: Bright; Patrick F.
Parent Case Text
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is a Continuation-In-Part of application Ser. No.
07/861,183 filed Mar. 31, 1992, abandoned, which was a Continuation
of application Ser. No. 07/751,661 filed Aug. 22, 1991, now U.S.
Pat. No. 5,254,005, which was a Continuation of application Ser.
No. 07/436,432 filed Nov. 14, 1989 (now abandoned).
Claims
I claim: .[.
1. A dental implant assembly for supporting as a rest factor the
distal end of a denture anchored elsewhere in the jaw,
comprising:
implant means for embedding in the distal region of the jawbone
including a first part for projecting into and osseointegrating
with the jawbone and a second part for projecting up to just above
the tissue level;
the first part being relatively thin and having a predetermined
height less than the distance between the top of a patient's
jawbone at the implant site and the underlying region of the
mandibular nerve;
the second part having an upper rest surface for supporting but not
being connected to overlying portions of a denture anchored
elsewhere in the jaw to resist biting pressure on the tissue and
bone; and
the first part comprising a thin disc-shaped member having a
downwardly projecting annular rim and a central spigot projecting
downwardly from the disc-shaped member..]. .[.
2. The assembly as claimed in claim 1, wherein said first part
comprises an implant member and the second part comprises a rest
factor releasably securable to the implant member..]..[.
3. The assembly as claimed in claim 2, including a plurality of
implant members in a range of different sizes, the members having
outer diameters in the range from about 4.25 to 6 mm..]..[.
4. The assembly as claimed in claim 2, including a plurality of
implant members in a range of different heights from 2 to 4.5
mm..]..[.
5. The assembly as claimed in claim 1 wherein the first part has a
height no greater than its diameter..]..[.
6. The assembly as claimed in claim 1, wherein the first part has a
selected diameter slightly less than the width of the alveolar
crest at the implant site..]..[.
7. The assembly as claimed in claim 6, wherein the selected
diameter is 1 mm less than the width of the alveolar
crest..]..[.
8. The assembly as claimed in claim 1, wherein the first part has a
height no greater than 4.5 mm..]..[.
9. The assembly as claimed in claim 8, wherein the first part has a
height of between 2 to 4.5 mm..]..[.
10. The assembly as claimed in claim 1, wherein the rest surface
has a shaped, cooperating area for non-retentive seating engagement
with a correspondingly shaped mating surface on an overlying
denture..]..[.
11. The assembly as claimed in claim 1, wherein the first part has
a central bore in an upper face of the disc-shaped
member..]..[.
12. The assembly as claimed in claim 11, wherein the second part
comprises a shaft portion for engagement in the central bore of the
implant member and a solid head portion projecting upwardly from
the shaft portion..]..[.
13. The assembly as claimed in claim 12, wherein the extension
portion is generally cylindrical with an upper, convex rest
surface..]..[.
14. The assembly as claimed in claim 11, wherein the bore has an
upper threaded portion and a non-threaded, lower extension portion,
the second part having a shaft portion with a corresponding
threaded upper portion and non-threaded lower portion for mating
engagement in said implant member bore..]..[.
15. The assembly as claimed in claim 14, wherein said implant
member bore and rest factor shaft portion have upper ends having
matching tapers..]..[.
16. A dental implant assembly for supporting as a rest factor the
distal end of a denture anchored elsewhere in the jaw,
comprising:
implant means for embedding in the distal region of the jawbone
including a first part for projecting into and osseointegrating
with the jawbone and a second part for projecting up to just above
the tissue level;
the first part being relatively thin and having a predetermined
height less than the distance between the top of a patient's
jawbone at the implant site and the underlying region of the
mandibular nerve;
the second part having an upper rest surface for supporting but not
being connected to overlying portions of a denture anchored
elsewhere in the jaw to resist biting pressure on the tissue and
bone;
the first part comprising a thin disc-shaped member having a
downwardly projecting annular rim; and
axially extending spaced grooves in the outer surface of the
annular rim for restricting rotation of the embedded implant..].
.[.
17. A dental implant assembly for supporting as a rest factor the
distal end of a denture anchored elsewhere in the jaw,
comprising;
implant means for embedding in the distal region of the jawbone
including a first part for projecting into and osseointegrating
with the jawbone and a second part for projecting up to just above
the tissue level;
the first part being relatively thin and having a predetermined
height less than the distance between the top of a patient's
jawbone at the implant site and the underlying region of the
mandibular nerve;
the second part having an upper rest surface for supporting but not
being connected to overlying portions of a denture anchored
elsewhere in the jaw to resist biting pressure on the tissue and
bone;
the first part comprising a generally cylindrical member having a
downwardly depending annular rim, and a central spigot projecting
downwardly from the cylindrical member, the central spigot having a
length in the range from 1 to 2 mm..]. .[.
18. A combined denture and support assembly, comprising:
a denture of more than one tooth;
an anchor securing one end of the denture to the jawbone;
support means for freely supporting a distal region of the denture
at a selected location to the rear of the first bicuspid, the
support means comprising a first part for embedding in the jawbone
at the selected location and a second part for projecting up to at
least the tissue level, the second part having an upper rest
surface for supporting but not being connected to the denture and
for accepting biting pressure from the denture; and
the first part comprising a thin disc-shaped member having a
downwardly projecting annular rim and a central spigot depending
downwardly from the disc-shaped member to define an annular cavity
between the spigot and rim..]. .[.
19. The assembly as claimed in claim 18, wherein said first part
extends no more than about 4 mm into the jawbone..]..[.
20. The assembly as claimed in claim 19, wherein said first part
has a diameter in the range from 4 mm to 6 mm..]..[.
21. The assembly as claimed in claim 18, wherein said second part
extends up to between 1/2 to 1 mm above the tissue level..]..[.
22. The assembly as claimed in claim 18, wherein the first part
comprises a flat, disc-shaped member having a downwardly projecting
peripheral rim..]..[.
23. The assembly as claimed in claim 22, wherein the first part has
a height of 2 mm and the rim projects 1 mm below the undersurface
of the disc-shaped member..].
24. A dental implant assembly for embedding in the jawbone of
.Iadd.a .Iaddend.patient, comprising:
an implant member for embedding in and osseointegrating with the
jawbone of a patient at a selected site;
an attachment member for securing to the implant member after
osseointegration;
the implant member having an
.Iadd.externally.Iaddend.-.Iadd.unthreaded .Iaddend.upper end
portion .[.with.]. .Iadd.and .Iaddend.a central bore, the
attachment member and central bore of the implant member having
interengageable securing means for releasably securing the
attachment member to the implant member, and .[.a.]. .Iadd.an
externally.Iaddend.-.Iadd.threaded .Iaddend.stem portion depending
downwardly from the upper end portion for engagement with a recess
in the jawbone of shape and dimensions matching those of the stem
portion;
.[.the stem portion having an annular indent at its lower
end;.].
the stem portion having outwardly projecting screw threads
.Iadd.wherein the spacing between adjacent threads is substantially
the same, and the height of said outwardly projecting screw
threads, is substantially the same, over the entire threaded length
of said stem portion.Iaddend.; and
the threads comprising multiple lead threads.
25. The assembly as claimed in claim 24, wherein the threads
comprise triple lead threads.
26. The assembly as claimed in claim 24, wherein the threads
comprise quadruple lead threads.
27. The assembly as claimed in claim 25, wherein the threads are of
square cross-section.
28. The assembly as claimed in claim 24, wherein the spacing
between adjacent threads is at least 1 mm and the threads run
parallel to one another.
29. The assembly as claimed in claim 28, wherein the gap between
adjacent threads is larger than the width of each individual
thread.
30. The assembly as claimed in claim 24, wherein the threads
project out to a distance of 1/2 mm from the surface of the stem
portion.
31. The assembly as claimed in claim 24, wherein the stem portion
has an upper end and a lower end and the threads start at a
position spaced below the upper end of the stem portion.
32. The assembly as claimed in claim 31, wherein the threads
terminate at a position spaced above the lower end of the stem
portion.
33. The assembly as claimed in claim 24, wherein the central bore
projects downwardly into the stem portion of the implant
member.
34. The assembly as claimed in claim 24, wherein the upper end
portion of the implant member comprises an annular ring and an
inwardly tapering rim projecting upwardly from the annular
ring.
35. The assembly as claimed in claim 24, including a wrench element
projecting from the upper end portion of said insert member for
engagement with a tool for inserting the implant member, the wrench
element having a bore aligned with the central bore of said insert
member.
36. The assembly as claimed in claim 35, wherein the wrench element
has a twelve-sided outer wrench engaging surface.
37. The assembly as claimed in claim 24, including a plurality of
implant members in a range of different heights from 2 to 13
mm..[.
38. A dental implant assembly for embedding in the jawbone of
patient, comprising:
an implant member for embedding in and osseointegrating with the
jawbone of a patient at a selected site;
an attachment member for securing to the implant member after
osseointegration;
the implant member having an upper end portion with a central bore,
the attachment member and central bore of the implant member having
interengageable securing means for releasably securing the
attachment member to the implant member, and a stem portion
depending downwardly from the upper end portion for engagement with
a recess in the jawbone of shape and dimensions matching those of
the stem portion;
the stem portion having an annular indent at its lower end; and
the attachment member comprising a rest factor member having an
upper rest surface for supporting, but not being connected to,
overlying portions of a denture anchored elsewhere in the jaw, the
rest factor member having an upper, dome-shaped portion and a
downwardly depending stem portion for engagement in said implant
member bore, the rest surface comprising the upper end of said
dome-shaped portion..]. .[.
39. The assembly as claimed in claim 38, including a plurality of
rest factor members having dome-shaped portions of different
heights in the range from 1.5 mm. to 3.5 mm..]..[.
40. The assembly as claimed in claim 39, in which said rest factor
members have total heights in the range from 2 mm. to 4.5
mm..]..[.
41. The assembly as claimed in claim 38, wherein said dome-shaped
portion has a hex indent at its upper end for engagement with a hex
tool for insertion of the rest factor member into an implant member
bore..].
42. An implant member for embedding in a patient's jawbone for
attachment to other dental devices, the member comprising:
a generally cylindrical body having an
.Iadd.externally.Iaddend.-.Iadd.unthreaded .Iaddend.upper end
portion for projecting above the
jawbone.Iadd.,.Iaddend.and.Iadd.,.Iaddend..[.a.]. .Iadd.extending
downwardly from said upper end portion, an
externally.Iaddend.-.Iadd.threaded .Iaddend.lower stem portion for
insertion in a recess prepared in a patient's jawbone;
.[.the upper end portion.]. .Iadd.said implant member
.Iaddend.having a central bore for insertion of a portion of a
dental device to be attached to the implant member; and
the lower .[.end.]. .Iadd.stem .Iaddend.portion having an outer
cylindrical surface and a plurality of multiple lead threads
projecting outwardly from the outer surface.Iadd., said multiple
lead threads extending over said outer surface and wherein the
spacing between adjacent threads is substantially the same, and the
height of said outwardly projecting threads is substantially the
same, over the entire threaded surface.Iaddend..
43. The implant member as claimed in claim 42, wherein the upper
end portion includes a cylindrical ring portion of diameter greater
than said cylindrical surface of the lower end portion, and an
inwardly tapered rim portion projecting upwardly from said ring
portion.
44. The implant member as claimed in claim 43, wherein said ring
portion has a diameter equal to the diameter of said threads.
45. The implant member as claimed in claim 43, wherein said upper
end portion has a height less than that of the lower end
portion..Iadd.
46. An implant member for embedding in a patient's jawbone for
attachment to other dental devices, the member comprising:
a body having an externally-unthreaded upper end portion and,
extending downwardly from said upper end portion, an
externally-threaded lower portion for insertion in a recess
prepared in a patient's jawbone;
said implant member having an internal site for insertion of a
portion of a dental device to be attached to the implant member;
and
said lower portion having an outer surface and multiple lead
threads projecting outwardly from said outer surface, said multiple
lead threads extending over substantially the entire length of said
externally-threaded lower portion and wherein the spacing between
adjacent threads is substantially the same, and the height of said
outwardly projecting threads, is approximately the same, over said
substantially entire length..Iaddend..Iadd.
47. The implant member as claimed in claim 46 wherein the number of
said lead threads is two, three, or four..Iaddend..Iadd.
48. The implant member as claimed in claim 46 wherein the pitch of
each of said lead threads is in the range of about 9.degree. to
about 17.degree. and the spacing between adjacent lead threads is
at least about one millimeter..Iaddend..Iadd.
49. The implant member as claimed in claim 46 wherein the gaps
between said lead threads are about twice the width of said lead
threads..Iaddend..Iadd.
50. The implant member as claimed in claim 46 wherein the length of
said implant is in the range of about two millimeters to about
thirteen millimeters and the outer diameter of said implant member
is in the range of about four millimeters to about six
millimeters..Iaddend..Iadd.
51. The implant member as claimed in claim 46 wherein said implant
is coated with a material that improves bone
adhesion..Iaddend..Iadd.
52. An implant member for embedding in a patient's jawbone for
attachment to other dental devices, the member comprising:
a body having an externally-unthreaded upper end portion and,
extending downwardly from said upper end portion, an
externally-threaded lower portion for insertion in a recess
prepared in a patient's jawbone;
said implant member having a central bore for insertion of a
portion of a dental device to be attached to the implant member;
and
said externally-threaded lower portion having an outer surface, and
at least two separate lead threads protecting outwardly from said
outer surface, said multiple lead threads extending over
substantially the entire length of said lower portion and wherein
the spacing between adjacent threads is substantially the same, and
the height of said outwardly projecting threads, is approximately
the same, over said substantially entire length..Iaddend..Iadd.
53. The implant member as claimed in claim 52 wherein the number of
said lead threads is two, three, or four..Iaddend..Iadd.
54. The implant member as claimed in claim 52 wherein the pitch of
each of said separate lead threads is in the range of about
9.degree. to about 17.degree. and the spacing between adjacent lead
threads is at least about one millimeter..Iaddend..Iadd.
55. The implant member as claimed in claim 52 wherein the gaps
between said separate lead threads are about twice the width of
said lead..Iaddend..Iadd.
56. The implant member as claimed in claim 52 wherein the length of
said implant is in the range of about two millimeters to about
thirteen millimeters and the outer diameter of said implant member
is in the range of about four millimeters to about six
millimeters..Iaddend..Iadd.
57. The implant member as claimed in claim 52 wherein said implant
is coated with a material that improves bone
adhesion..Iaddend..Iadd.
58. An implant member for embedding in a patient's jaw bone for
attachment to other dental devices, the member comprising:
a body having an externally-unthreaded upper end portion and,
extending downwardly from said upper end portion, an
externally-threaded lower portion for insertion in a recess
prepared in a patient's jawbone;
said implant member having a central bore for insertion of a
portion of a dental device to be attached to the implant member;
and
said externally-threaded lower portion having an outer surface and
at least two threads with separate leads projecting outwardly from
said outer surface, said at least two threads forming multiple lead
threads extending over substantially the entire length of said
lower portion and wherein the spacing between adjacent threads is
approximately the same, and the height of said outwardly projecting
threads, is approximately the same, over said substantially entire
length..Iaddend..Iadd.
59. The implant member as claimed in claim 58 wherein the number of
said lead threads is two, three, or four..Iaddend..Iadd.
60. The implant member as claimed in claim 58 wherein the pitch of
each of said separate lead threads is in the range of about
9.degree. to about 17.degree. and the spacing between adjacent lead
threads is at least about one millimeter..Iaddend..Iadd.
61. The implant member as claimed in claim 58 wherein the gaps
between said separate lead threads are about twice the width of
said lead..Iaddend..Iadd.
62. The implant member as claimed in claim 58 wherein the length of
said implant is in the range of about two millimeters to about
thirteen millimeters and the outer diameter of said implant member
is in the range of about four millimeters to about six
millimeters..Iaddend..Iadd.
63. The implant member as claimed in claim 58 wherein said implant
is coated with a material that improves bone adhesion..Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a dental implant system.
Dental implants are embedded in the jaw bone and serve to anchor
one or more artificial teeth or dentures. Most implant systems
involve a relatively long implant cylinder which is placed into a
custom bored hole in the jawbone, then left for several months to
allow healing and bone integration. Then the implant must be
exposed for attachment of a dental prosthetic appliance such as a
crown, denture, partial denture or bridge. This generally involves
the dentist cutting out a flap of tissue which is peeled back to
expose the implant, and secured by sutures after installing the
prosthesis. This results in a relatively large area of trauma with
a certain degree of pain to the patient and risk of post-operative
infection.
Another problem with conventional implants is their length, which
makes them difficult to implant in the distal jaw region, where
there is insufficient depth to enable their insertion without
interference with the mandibular nerve, without the assistance of a
dental surgeon to locate the precise position of the nerve and
ensure that the implant does not interfere with it. A shorter
cylindrical implant would not normally be suitable since it would
provide insufficient "hold" and would likely become loosened with
time if anchored to a denture or bridge. Also, side to side forces
on the implant lead to bone erosion and trauma. Thus, dentures or
bridges are often not anchored at the rear of the jaw. However,
this has the disadvantage that trauma to the tissue and underlying
bone beneath the denture occurs as a result of the denture
repeatedly impacting the bone, particularly with long dentures
which will tend to tilt or rotate about their attachment or anchor
points during chewing or other jaw motions. This biting pressure
can result in bone erosion or resorption down to the level of the
nerve.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved dental
implant system and method which is less likely to cause significant
tissue trauma and which reduces bone erosion as a result of denture
wear.
It is a further object of this invention to provide an improved
system and method for exposing an implant site after
osseointegration has taken place.
According to a first aspect of the present invention, a dental
implant assembly is provided which comprises a first, implant
member for implanting in the distal region of the jaw bone, and a
second member or rest factor for attachment to the implant member.
The two members have cooperating releasable securing devices for
releasably securing them together, preferably comprising a screw
threaded bore in the implant member and a corresponding threaded
portion on the rest factor member. The rest factor member projects
up to just above the level of the tissue overlying the jaw bone and
has an upper surface opposing an overlying portion of a prosthesis
anchored elsewhere in the jaw to form a rest for the prosthesis
which accepts down pressure only, and which acts as a support to
prevent or restrict bone erosion. The implant member has a selected
height less than the depth of the mandibular nerve at the implant
site, so that it can be embedded in the bone without risk of
interference with the nerve. At the same time, the implant member
is as wide as possible, and preferably has the maximum diameter
possible according to the width of the patient's alveolar ridge at
the implant site. The implant member diameter is preferably
selected to be 1 mm less than the available alveolar ridge or bone
width at the implant site. Implant members in a range of different
heights and diameters are preferably provided to meet the
requirements of a range of patients. Preferably, implant members
with heights of 2 mm, 4.5 mm, 7 mm and 10 mm are provided, to allow
for patients whose jawbone is already eroded to some extent.
Implant members with diameters ranging from about 4 mm to 6 mm may
be provided.
Since the implant member is of relatively large diameter, it has a
relatively large surface area resisting downward forces. In a
preferred embodiment of the invention, the implant member has a
generally cylindrical body with an upper end portion and downwardly
depending stem portion which engages in a corresponding recess
drilled out in the bone. Preferably, at least part of the stem
portion at the lower end of the implant member has an annular
recess forming an outer rim and central boss. This engages a
corresponding annular recess drilled out in the bone to resist
sideways movement of the implant. This will resist sideways
movement of the implant during osseointegration, and also provides
additional depth for securing the rest factor to the implant
member. A bore of corresponding shape to the undersurface of the
implant member is drilled out in the jawbone at the implant site,
so that when the implant member is positioned in the bore, the
peripheral rim will provide stabilization of the member against
lateral movement during the osseointegration period. The shape of
the undersurface of the implant provides a large area of bone to
implant contact for osseointegration, and significant resistance to
both lateral and downward forces both during and after the
osseointegration period. Preferably, at least two separate or
double lead threads are provided, and triple or quadruple threads
may be provided for added retention. Bone grows into the gaps
between threads.
The outer surface of the stem portion of the implant preferably has
threads to provide additional surface area for bone attachment.
Bone grows into the area above and below the threads to resist
loosening of the implant.
Since the rest factor is not anchored to the prosthesis, the risk
of jaw bone erosion or damage as a result of upward forces is
reduced. However, the rest factor does accept down pressure as a
result of biting pressure of the denture, and will thus reduce the
risk of trauma to the tissue and jawbone erosion as a result of
pressure. The localized contact between the rest factor and the
underlying bone via the implant member reduces or substantially
eliminates pressure trauma on the entire bone.
If desired, the upper surface of the rest factor and the opposing
portion of the prosthesis may be provided with opposing,
non-retentive mating formations, such as opposing slightly convex
and concave formations, for guiding the prosthesis against the rest
factor. However, these formations do not provide any upwards
retention of the prosthesis. A series of such rest factors may be
provided at appropriate locations in the jaw where maximum down
pressure from a denture is encountered, considerably reducing the
discomfort of denture use and reducing the risk of tissue and
jawbone damage as would result from conventionally anchored
dentures.
The rest factor may be preformed with a suitable rest surface in
incremental heights, in which case the procedure after removing the
healing screw comprises selecting an appropriate height rest factor
and securing the selected rest factor in the implant member.
The implant member may be relatively short with a relatively large
diameter, so that it can be anchored securely in the jawbone
without needing a deep bore to be drilled out. The implant member
is provided in several heights. The shortest of the implants will
be shorter and wider than conventional cylindrical implants, and
thus can be used at the back or posterior mandible of the jaw where
the nerve position prevents or restricts the use of long implants.
This implant is particularly suitable for positioning a rest factor
in the second molar area in conjunction with implant dentistry
where cantilevered bridges or anterior implants need support or in
other places where a rest factor is needed in dentistry. The
implant requires less bone to be drilled out than conventional
cylindrical implants, reducing or minimizing bone loss, and is able
to accept hundreds of pounds of down pressure from an overlying
denture or prosthesis.
After bone integration, the implant can be recovered by piercing
the tissue overlying a healing screw secured to the implant with a
pointed end of a locating guide tool, probing the implant site with
the pointed end until it engages a hole in the top of the healing
screw, inserting the pointed end into the hole, utilizing a tissue
punch centered on the guide tool to cut out a plug of tissue
directly over the implant, and subsequently removing the healing
screw.
Thus, the locating tool and tissue punch can be removed together
from the implant site, carrying with them the tissue plug to expose
the healing screw for removal with a separate tool. The implant is
then exposed for secondary healing or restoration procedures while
a minimum amount of tissue has been disturbed and little or no
suturing is required. This considerably reduces the trauma,
secondary tissue healing, discomfort to the patient, and risk of
infection.
The implant member provides osseointegration with good resistance
to loosening forces as a result of chewing. It may alternatively be
used to secure other dental devices such as an implant denture
anchor or an implant magnet abutment.
An implant locating and exposing tool may be used to recover the
implant. The tool comprises an elongate shaft having a head at one
end and a locating probe at the opposite end having a sharp end for
probing the tissue over an implant site to locate a central hole in
the top of a healing screw, and a cutter member mounted on the
elongate member with its cutting face facing in the same direction
as the locating probe, the cutter member being movable along the
elongate shaft to cut out a plug of tissue overlying a healing
screw.
Thus, the healing screw can be located and the overlying tissue
removed in one step, without having to cut out a relatively large
flap of tissue.
The healing screw may be provided with a concave upper surface so
that the locating probe will be guided towards the central
opening.
The implant system and method described above provides a rest
surface for an overlying cantilevered bridge or denture which is
anchored elsewhere in the jaw, on which the denture can rest and
which accepts down pressure from the denture, reducing tissue
trauma. Rest surfaces may be provided wherever needed, in
conjunction with the conventional implants and anchors used for
securing the denture or prosthesis in the jaw. The improved implant
recovery tool and method produces minimal trauma when exposing a
previously embedded implant for subsequent connection to either a
rest factor or to a conventional anchor or magnet abutment.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be better understood from the following
detailed description of a preferred embodiment of the invention,
taken in conjunction with the accompanying drawings, in which like
reference numerals refer to like parts, and in which:
FIG. 1 is a perspective view of the separated implant and healing
screw components of an implant assembly according to a preferred
embodiment of the invention;
FIG. 2 is a perspective view of a rest factor of the implant
assembly;
FIG. 3 is a sectional view of the implant taken on line 3--3 of
FIG. 1;
FIG. 4A is a perspective view of a preferred embodiment of the
implant locating tool according to another aspect of the
invention;
FIG. 4B is a perspective view of a healing screw removal tool;
FIG. 5 is a sectional view through a typical jawbone with a
finished implant in place and a rest factor inserted;
FIG. 6 is a jawbone section illustrating the initial drilling set
up for an implant;
FIG. 7 is a similar view illustrating the final counter-boring
operation for an implant;
FIG. 8 is a similar view with an implant and healing screw in place
and enclosed under tissue for the osseointegration period;
FIG. 9 illustrates the locating of the integrated implant under the
issue;
FIG. 10 illustrates the cutting out of a tissue plug overlying the
healing screw;
FIG. 11 illustrates the removal of the healing screw;
FIG. 12 illustrates the lower half of a patient's jaw with a full
denture anchored in place and seated on rest factors in posterior
areas on both sides;
FIG. 13 is a side view of the denture arrangement of FIG. 12;
FIG. 14 is a perspective view of the separated implant and healing
screw components of an implant assembly according to a second
embodiment of the invention;
FIG. 15 is a jawbone section illustrating the initial drilling set
up for the implant of FIG. 14;
FIG. 16 is a similar view to FIG. 15 illustrating the next step in
the drilling procedure;
FIG. 17 is a similar view illustrating the finishing step in the
boring operation;
FIG. 18 is a similar view illustrating the implant and healing
screw in place and enclosed under tissue for the osseointegration
period;
FIG. 19 is a perspective view of a rest factor according to another
embodiment of the invention;
FIG. 20 is a perspective view, partially cut away, of one example
of an implant for the rest factor of FIG. 19;
FIG. 21 is a side elevation view, partially cut away, of another
implant with triple retaining threads;
FIG. 22 is a side elevation view of a further implant with
quadruple threads;
FIG. 23 is a top plan view of FIG. 20;
FIG. 24 is a view similar to FIG. 7, showing the addition of a
shallow counter-bore;
FIG. 25 is a similar view showing the cutting of threads to receive
an implant;
FIG. 26 is a similar view showing insertion of the implant;
FIG. 27 is a similar view showing attachment of the rest
factor;
FIG. 28 is a side elevation view, partially cut away, of another
modified implant having an alternative wrench element; and
FIG. 29 is a top plan view of the implant of FIG. 28.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1-3 and 5 of the drawings illustrate an implant assembly 10
according to a preferred embodiment of the present invention, as
well as a preferred method of installing the assembly in the jaw.
As best illustrated in FIG. 5, the implant assembly 10 basically
comprises an implant 12 for insertion into a suitably prepared bore
14 in the jawbone 16, where it is secured in place by
osseointegration as is known in the field of implant dentistry, and
an extension member or rest factor 18 secured to the implant 12 and
extending up to slightly above the level 20 of the tissue or gum 21
to form a rest surface 22 for an overlying denture or bridge 24
which is anchored elsewhere in the jaw.
As best illustrated in FIGS. 1 and 3, implant 12 comprises a thin,
annular member 26 having a central spigot or downward extension 28
projecting from one of its faces and an annular peripheral rim 30
projecting from the same face. A central bore 32 extends from the
opposite face into the spigot 28, as illustrated in FIG. 4. The
bore 32 has a larger diameter upper portion 33 having internal
screw threads 34 extending along its length with a taper 37 at its
upper end for added strength to hold the threaded engagement. The
lower end of bore 32 comprises a smaller diameter lower portion 35
extending into spigot 28 for centering parts mating with implant 12
and preventing cross-threading of the threaded engagement. The
implant will be of metal or any suitably rigid material as is
normally used for dental implants, for example surgical titanium
alloy. The implant may have spaced, short grooves or indents 29 on
its outer surface for resisting rotation. These are preferably of
the order of 1 mm in length.
Also illustrated in FIG. 1 is a healing screw 70 for insertion in
the implant member during the osseointegration process. Healing
screw 70 has a relatively short head portion 72 and downwardly
depending shaft portion 73 for engagement in the bore 32 of implant
12. Portion 73 has a screw threaded larger diameter upper part 74
for threaded engagement in bore portion 33, the upper part 74
having a taper 71 at its upper end matching the taper 37 at the
upper end of the implant bore 32 for support and seating of the
screw 70 in bore 32. The lower end of portion 73 comprises a
smaller diameter, cylindrical lower part 75 for fitting into lower
portion 35. The upper end face of the head portion has a central,
tool receiving bore 76 for receiving the end of a suitable tool for
inserting the arrangement in the bore in the jawbone, and for
subsequently receiving the end of a locating or removing tool as
will be explained in more detail below. If desired, the upper end
face of screw 70 may have a concave or dish-shaped depression 79
surrounding bore 76. The bore corresponding to bore 76 is
illustrated in FIG. 11 and has a screw threaded upper portion 77
and a downwardly depending cylindrical centering extension 76
corresponding to extension 75 in FIG. 1. The threads in upper
portion 77 are of opposite hand to those of screw threaded portion
74. In the embodiment illustrated in the drawings, portion 74 has a
right hand thread while portion 77 has a left hand thread. The
healing screw may be provided in a range of sizes, but in each case
the height of the head portion is of the order of 1 mm or less.
The extension or rest factor member 18 as it appears prior to
installation in the jaw is illustrated in FIG. 2. The member
comprises a generally cylindrical boss 36 having a projecting shaft
38 at one end dimensioned for mating engagement in the bore 32 of
implant 12. Shaft 38 has an upper, larger diameter portion 39
having external screw threads for threaded engagement with the
internal screw threads 34 in the upper part 33 of bore 32, and a
lower, smaller diameter cylindrical extension 40 for fitting into
the lower part 35 of bore 32, as illustrated in FIG. 11. The upper
end of shaft 38 has a taper 41 matching the taper 37 at the upper
end of the implant bore 32. Member 18 has a curved, slightly convex
rest or support surface 42 at its upper end, and an external hex
formation 43 for securing it to a suitable tool for insertion into
the implant. The member 18 will also be of a suitable dental
material such as titanium alloy.
Member 18 may alternatively be formed with a concave support
surface (not illustrated), or with any suitably shaped upper rest
or support surface. Member 18 will be made in a range of heights to
allow the dentist to select the appropriate size rest factor for a
particular patient's tissue level. The rest factor is selected to
project only to a distance of the order of 1/2 to 1 mm above the
tissue level when installed in the jaw, and is preferably kept as
low as possible so that it acts to accept biting pressures but will
not interfere with normal jaw motions.
The implant assembly with the rest surface 42 is used to form a
rest or support surface in implant dentistry for a prosthesis
anchored elsewhere in the jaw, for example, as illustrated in FIGS.
12 and 13. The implant assembly is designed to be relatively short
or thin so that it can be installed in distal jaw regions to the
rear of line 160 in FIGS. 12 and 13, which extends between the
first and second bicuspids 161 and 162 and corresponds to the
approximate location where the mandibular nerve 163 exits the
jawbone. The mandibular nerve extends through the jawbone to the
rear of the first bicuspid, making the installation of long
implants in this region difficult or impossible without the
assistance of a dental surgeon. Thus, unsecured dentures are
common, resulting in bone erosion from biting impacts. This rest
factor assembly avoids or reduces such problems. The implant has a
relatively large diameter as compared to its height, providing good
implant to bone contact and integration, while having only a short
penetration into the jawbone. In the preferred embodiment
illustrated, the penetration into jawbone is only between 2 to 4.5
mm, depending on the patient's bone depth, and there is thus no
risk of interference with the mandibular nerve.
FIGS. 12 and 13 illustrate the assembly implanted in the jaw for
cooperation with an overlying denture anchored elsewhere. In FIGS.
12 and 13, a full denture or prosthesis 164 is illustrated, secured
to a patient's lower jaw 165 via a pair of anchors 166, 167 mounted
in the anterior regions of the patient's jaw, and seated on
implanted rest factors 168, 170 in the posterior or distal jaw
region below the former second molar at each end of the denture. In
practice, the rest factor assembly may be installed anywhere
between the region corresponding to the former second molar (line
171) and the first bicuspid (line 160). The area to the rear of the
line 171 has too many muscles for insertion of an implant. As
illustrated in FIG. 13, the rest factors may be provided or
preformed with a slightly convex or ball-shaped head 42 which
projects from around 1/2 to 1 mm above the tissue level, although
support surfaces of a different shape may be provided. The
prosthesis or denture is preferably provided with a corresponding
concave surface or depression for seating on the opposing rest
factors or surfaces 168 and 170.
Most typical denture anchors allow a limited degree of pivoting or
side-to-side motions of the denture with jaw motions so as to
reduce stress in the jaw bone areas to which the denture is
positively anchored. With relatively long partial or full dentures
which extend into the posterior jaw regions, tilting or rotation of
the denture about the anchor points with jaw or biting motions will
apply pressure or biting force to the underlying tissue and
jawbone, causing discomfort and trauma to the underlying bone and
tissue, and ultimately resulting in significant bone erosion. The
rest surface or surfaces avoid or reduce this problem by accepting
down or biting pressure from the denture. Since the rest surfaces
are not positively anchored to the denture, they will not be pulled
up or from side to side as a result of jaw motions, and will
therefore be less likely to cause bone erosion or damage. The
implant assembly is therefore intended to be used at appropriate
locations in the jaw which would otherwise be subject to
considerable down pressure and potential trauma from an implant
such as a full or partial denture or cantilevered bridge. The rest
factor surface will be shaped to ensure that it can accept down
pressure from an overlying denture in various possible
orientations, whatever the angle of the patient's jaw. The support
surface prevents excessive force on the tissue, and thus protects
the gum tissue from impacting forces which could cause soreness and
trauma. Additionally, the rest or support surface prevents or
reduces bone erosion by providing support to the distal end of the
denture and resisting biting forces.
The implant assembly is designed for implantation at any position
in the jaw where a rest factor or surface for a full or partial
denture or bridge is needed. Normally, this will be in the
posterior jaw, for example in between the first bicuspid and the
second molar area, as illustrated in FIGS. 12 and 13, but a rest
surface may also be advantageous in other areas. The dimensions of
the assembly 10 are selected according to the dimensions of the jaw
in the area where the implant is to be used. A range of implant
assemblies of different dimensions may be provided for fitting
patients having different jaw dimensions. The implant member is
designed to provide sufficient anchoring area with the jawbone when
embedded in the jaw, while not extending too deeply into the jaw
where it might otherwise interfere with the nerve. The implant
member has a relatively large diameter, larger than typical
straight cylindrical implants, but is shorter in length than such
implants, preferably having an overall length in the range from 2
mm to 4.5 mm. In one specific example, several different size
implants were provided with annular members of 4.25 mm, 5 mm, and 6
mm outer diameter, respectively. The rest factor may have a
diameter of 4 mm. The extension or spigot 28 may also be provided
in different sizes according to the position in the jaw where it is
to be embedded. Central spigots of length between 1 mm and 3 mm may
be provided. Also, the central spigot may be omitted in some cases
where very little depth is available in the jawbone for embedding
the implant. In this case, the rest factor 18 will also have no
projection 40. Rest factors having heads in a range of different
sizes are also provided, for example, 3 mm, 4 mm and 5 mm.
Generally, the overall implant assembly is very short, extending
only from 2 to 4.5 mm into the jawbone, while the implant is shaped
to have a relatively large bone to implant contact area, as best
illustrated in FIG. 5.
As can be seen in FIG. 5, after osseointegration has taken place,
there will be a relatively large area of bone to implant
integration even though the penetration into the jaw bone is very
short. The implant has first, circumferential surfaces 180, 182
which resist sideways movements of the dentures, while the second,
lower surfaces 184, 185, 186 of the outer rim 30, upper face, and
boss 28 resist vertical movements. The two surfaces combine to
provide maximum rest factor to bone contact with a relatively short
distance of penetration into the jawbone. The grooves 29 in the
outer surface will resist rotational movements of the implant.
Thus, the implant surfaces resist lateral and vertical loosening
movements, and the implant effectively becomes fully integrated
with the bone.
This implant is sufficiently short to be safely inserted even where
some bone erosion has already taken place, with the appropriate
height implant member and rest factor being selected according to
the bone depth and tissue height of the particular patient.
The method of inserting the implant 12 in the jaw will now be
described with reference to FIGS. 6-11 of the drawings. This can
easily be done by a dentist or dental surgeon. First, a bore shaped
to correspond to the shape of member 12 must be cut out. This is
done using a series of special cutting burrs. A first water cooled
burr or cutter (not illustrated in the drawings) is used to drill a
cylindrical guide hole or pilot dimple at the center of a selected
site, for example under the second molar area or at the distal end
of a cantilevered bridge. The width of the alveolar crest with
equal distance on both sides of the pilot dimple is then measured.
The largest diameter rest factor implant which will fit within the
available width while allowing at least 1/2 mm of bone on each side
of the implant is selected. An internally irrigated implant body
drill 44 of diameter matching that of the selected rest factor
implant is then selected. Burr 44, illustrated in FIG. 6, has a
smaller diameter pilot drill 46 for cutting out a cylindrical bore
48 and a larger diameter portion 50 having an end cutter 52 for
drilling out the larger diameter upper end 56 of the bore. The
cylindrical portion 50 may be provided with suitable markings or a
scale (not shown) so that the dentist can control the depth the
drilled bore. However, in the preferred version, the height of
portion 50 matches the height of implant member 12. The length of
the pilot drill 46 will correspond to the length of spigot 28 of
the implant, so that spigot 28 will fit in bore portion 48. The
dentist determines the optimum angle and drills in to the bone to a
point where the larger diameter portion 50 ends.
FIG. 7 illustrates the operation of a water cooled guided core
drill or burr 58 having a central guide or pilot tip 59 for fitting
in the previously drilled bore portion 48 to center the tool on the
bore. The tool has a cylindrical central body portion 60 having a
downwardly facing annular ring of cutting teeth 62 for drilling out
an annular groove or channel 64 around the periphery of the flat or
shoulder 66 separating counter bore 56 from the smaller diameter
bore portion 48. The length of the teeth controls the depth of
groove 64, and will be equivalent to the height of the downwardly
depending rim 30 of the implant to be received in the bore. Once
the lower face of body portion 60 hits the flat 66, drilling is
stopped.
All three cutting tools may be provided with a cage for collecting
bone as it is drilled out of the bore. The collected bone may be
used for filling any edges or spaces left after insertion of the
implant.
After the bore for receiving the implant 12 has been prepared as
described above, and debris has been cleaned out in the standard
manner, for example by irrigating the site with sterile water or
sterile saline, the implant 12 can be inserted. The healing screw
70 is initially secured to the implant.
Prior to insertion in the previously prepared bore, the internal
faces of the implant will be coated with a suitable bonding agent,
such as hydroxyl apatite. These faces may be roughened as
illustrated in FIGS. 1 and 3 to increase the bonding area and
strengthen the adhesion in the bore 14. A suitable plastic
insertion tool 67 (see FIG. 1) having a handle and a gripping end
for snap engagement over the head of the healing screw is then used
to insert the implant and attached healing screw in the bore. The
bore is drilled out to a depth such that the upper end of the
implant 12 will be at the bone level when fully inserted, as
indicated in FIG. 8, or slightly below that level if desired. For
convenience, the insertion tool is preferably a disposable,
snap-off plastic member which is supplied in a sealed, sterile
package together with the healing screw and implant, the three
parts being supplied secured together in the package for easy
handling. The insertion tool can be snapped off after the parts
have been positioned in the bore.
The tissue or gum 21 is then secured over the implant and healing
screw with conventional flap sutures 80. Since the head portion of
the healing screw projecting above the implant member is relatively
short, little or no bulge will be apparent when the tissue is sewn
up. The site is left to heal for several months to allow the
implant to osseointegrate, or bond with the surrounding bone. At
this time, a special locating tool 82, best illustrated in FIGS.
4A, 9 and 10, is used to locate the implant.
The retrieval tool 82 comprises a central shaft 84 with a head or
gripping handle 86 at one end. Handle 86 projects to one side of
the shaft as indicated. A projecting probe 88 at the opposite end
is designed for engagement in the bore 76 of healing screw. The
probe has a sharp pointed end 91. A cutter sleeve or tissue punch
92 is slidably mounted on shaft 84. Cutter sleeve 92 has a
projecting annular handle or gripping portion 94 and a lower
cutting edge 96.
The use of the retrieval tool 82 to locate the implant site will
now be explained, with reference to FIGS. 1 and 9. The approximate
area of the implant is first located, utilizing radiographic charts
and finger palpations. The pointed end 91 of the probe is then used
to pierce the tissue 21 at the approximate site of the implant, and
is then used as a probe to locate the upper face of the healing
screw. Once the screw has been found, the concave recess (if
provided) will act as a guide to direct the pointed end to the
retrieval hole or bore 76 at the center of the healing screw, as
illustrated in FIG. 9, centering the tool on the implant site.
Once the probe has entered bore 76, as illustrated in FIG. 9, the
handle 86 of the locating tool is held firmly in one hand to
support the tool upright and the tissue punch is turned in a
circular motion while pushing it down along the locating tool with
a firm pressure. The tissue punch is designed to cut out a plug 97
of tissue directly over the implant. The punch will be stopped when
it engages the outer diameter of the healing screw. The locating
retrieval tool 82 is then removed together with the tissue punch,
simultaneously pulling out the plug of tissue. If the tissue plug
does not pull out, it may be removed with forceps.
A separate healing screw removal tool 110 is then used to remove
the exposed healing screw. Tool 110 is illustrated in FIG. 4B and
11, and comprises a shaft portion 112 with a head or gripping
portion 114 at one end and a threaded portion 116 at the opposite
end for threaded engagement in the threaded, upper end portion 77
of bore 76 of the healing screw. The threaded end 116 is threaded
counter-clockwise into the healing screw, tightening the tool
inside the healing screw and at the same time unscrewing the
healing screw from the implant as illustrated in FIG. 11. The
implant is thus exposed for secondary healing or restoration
procedures.
This technique for exposing or recovery of an embedded implant
after healing and osseointegration has taken place removes only a
small plug of tissue from immediately above the implant site,
avoiding the need to cut out an enlarged flap of the tissue both to
locate the implant and to expose the healing screw for removal.
Little or no suturing will be required. Thus, considerably less
trauma to the tissue is involved, reducing the healing time and the
risk of infection. Also, the healing screw is located and the
tissue plug may be removed simultaneously with one tool,
simplifying the procedure and reducing the time involved. The
method involves the use of a specialized healing screw with a bore
in its upper surface, together with a special locating and
retrieval tool. It may be used not only for location of the implant
12 as described above, but also for locating any conventional
cylindrical implants in implant dentistry, replacing the
conventional healing screws of such implants with a healing screw
as illustrated in FIG. 1 but having a stem or shaft designed for
fitting into the implant bore. Although in the preferred embodiment
described above, the upper end of the retrieval bore 76 in the
upper face of the healing screw is screw threaded, it may
alternatively be hexagonal with the retrieval tool having a
corresponding hexagonal portion for mating engagement in the
bore.
As an additional aid in locating the embedded implant, a thread or
wire may be left projecting from the heading screw through the
suture area, so that the location may be found easily after
healing. Alternatively, the tissue overlying the implant may be
marked with a suitable dye. However, it is expected that such
markers will not normally be required, the dentist locating the
general implant site by feel before piercing the tissue with the
probe.
The same implant recovery tools may be used for any selected
implant size, since the dimensions of bore 76 in the healing screw
will be identical.
Once the healing screw has been removed and the exposed surface of
the implant suitably cleaned and prepared, the appropriate rest
factor 18 is inserted into the implant. The rest factor 18, in
addition to providing a rest surface, also acts as a secondary
tissue healing insert. The rest factor is selected with a head
height so that it will project just above the patient's tissue
level when installed. The shaft 38 of rest factor 18 is screwed
into bore 32 of implant 12, as indicated in FIG. 5, with the mating
surfaces first being coated with a suitable bonding agent.
Although the rest factor in the preferred embodiment has a head
portion preformed in a range of heights, it may alternatively be
provided with a longer extension piece which projects above the
tissue level 20 when the member 18 is fully inserted. In this case,
the dentist marks around the periphery of the selected member 18 at
the tissue height, and removes the member from the implant. A
suitable temporary cover or crown of a standard nature may be
fitted into implant 12 at this point.
The dentist then mounts the member 18 in a previously prepared cast
of the patient's jaw, and machines or cuts away the upper face of
member 18 to provide the desired rest surface 22 at the tissue
level 20, as determined by the markings made while the member was
mounted in the patient's jaw. The cut away surface may be slanted
or inclined according to the angle of the patient's tissue or gum.
This allows the height to be customized for minimal side torque.
The shape of the rest surface 22 may be of the dentists choice. For
example, it may be concave, while the denture or prosthesis with
which it is to cooperate has a corresponding convex area or bump 95
for fitting into the concave depression on the rest surface, so
that the rest factor or member 18 accepts down pressure from the
denture without any retention. However, in the preferred
embodiment, members 18 with ready-made ball-shaped or other shape
heads of various sizes in a range of tissue heights are provided to
avoid the need for machining on site by the dentist.
This procedure may be utilized to implant one or more rest factors
at any suitable location in the jaw, depending on the denture
pressure points, for example as illustrated in FIGS. 12 and 13.
FIG. 14 of the drawings illustrates an alternative embodiment of
the implant assembly which is much thinner than that of FIGS. 1-3
and 5 and which will therefore project only a minimal distance into
the jawbone, further reducing the risk of interference with the
nerve. This implant assembly is useful for providing a rest surface
at a desired location in any patient's jaw, whether or not previous
bone erosion is a factor, but is particularly useful in patients
having significant bone erosion where very little depth is
available for implants.
FIG. 14 illustrates an implant member 180 and healing screw 182 of
an implant assembly according to a second, modified embodiment of
the invention. FIG. 18 illustrates the implant member 180 and
healing screw 182 of FIG. 14 implanted in the jawbone during the
osseointegration process, while FIGS. 15-17 illustrate a modified
method of forming a bore in the jawbone for receiving the
implant.
As illustrated in FIGS. 14 and 18, implant member 180 is a flat
disc-like member having an undersurface of similar shape to the
undersurface of member 12 in the first embodiment. However, the
peripheral rim 184 and central spigot 186 are approximately the
same length in this embodiment, so that the spigot 186 does not
project downwardly below the lower end of rim 184. Preferably,
member 180 has a total height of around 2 mm while its peripheral
rim 184 projects around 1 mm below the undersurface of disc part
188. The member 180 is provided in a range of diameters, preferably
4.25 mm, 5 mm and 6 mm, for patients having varying alveolar ridge
widths. As in the first embodiment, the maximum diameter possible
implant member is selected for the patient dependent on the
available space, i.e., the alveolar ridge width. The rim 184 is
relatively thin, and in one particular example had a thickness of
the order of 0.4 mm.
The member 180 has a recess 190 in its upper surface with a taper
191 extending around the outer periphery of the recess. A central,
straight cylindrical bore 192 extends from the center of recessed
area 190 into the spigot 186, and bore 192 has screw threads 193
extending along its length. Member 180 is made of the same material
as the implant 12 of the first embodiment. As in the first
embodiment, circular or rounded indents 194 are provided on the
outer surface of member 180 to resist rotational movement after
implantation. Between six and eight equally spaced indents may be
provided, for example.
Healing screw 182 has a relatively short head portion 195 and a
downwardly depending, screw threaded shaft portion 196 for mating
engagement in the bore 192 of implant member 180, as illustrated in
FIG. 18. The undersurface of head portion 195 seats in recessed
area 190 and has a tapered annular surface portion 197 for seating
on taper 191 around the recessed area 190, for accurate seating of
the screw in bore 192. The upper surface of head 195 has a central,
tool receiving bore 198 for receiving the end of a suitable tool
for inserting the arrangement in a previously prepared bore in the
jawbone, and also for receiving the end of locating tool 82 as
described above in connection with the first embodiment of the
invention. Bore 198 is of hexagonal cross-section, and is designed
to be removed by a suitable removal tool having a hexagonal end
after location by tool 82.
The rest factor or member of the second embodiment is not
illustrated in the drawings but will be similar or equivalent to
rest factor 36 as illustrated in FIGS. 2 and 5 of the drawings
apart from its lower surface and downwardly depending shaft
portion, which will be identical to lower surface and shaft portion
of the healing screw 182 for mating engagement in the bore 192 in
implant member 180 after osseointegration is complete.
The modified method of inserting insert member 180 in the jaw will
now be described with reference to FIGS. 15-17 of the drawings.
This procedure can easily be carried out by a dentist, although a
dental surgeon may also perform the procedure if desired. After the
tissue overlying the implant site has been cut, a pilot dimple is
formed at the center of the selected site. The width of the
alveolar crest or ridge at the implant site is measured, and the
largest possible diameter implant which will fit within the
available width while leaving at least 1/2 mm of bone on each side
is selected.
A bore matching the selected implant dimensions is then accurately
drilled out using a series of three internally irrigated drilling
burrs. The first burr 210 has a straight pilot drill 212 for
drilling out a cylindrical bore 214 to a desired depth at the
implant site, as determined by stop 216, as illustrated in FIG. 15.
Preferably, bore 214 will be slightly longer than the implant
member, for example 3 mm. A second burr 218 is designed to cut out
the desired bore shape to match the shape of the undersurface of
implant member 180, as illustrated in FIG. 16. Burr 218 has a
central, non-cutting guide or spigot 220 for fitting into
previously drilled bore 214 for centering purposes, a first cutting
surface 222 for cutting down to the level of flat 224, and an
annular, downwardly projecting rim of cutting teeth 226 for cutting
out part of annular recess 228 for receiving the annular rim 184 of
the implant member. Preferably, teeth 226 are designed to cut
recess 228 to a depth of 1/2 mm. The final burr 230 is illustrated
in FIG. 17 and is designed to finish and smooth the surfaces of
recess 228. Burr 230 also has a central guide 231 and an annular
rim of finer cutting teeth 232 which cut the final 1/2 mm of the
recess to a total depth of around 1 mm, and which smooth and finish
the cut surfaces.
The finished bore of FIG. 17 is cut to very precise dimensions by
the series of cutting drills so that the implant member can be
accurately seated in the bore as illustrated in FIG. 18 after
suitable treatment of the surfaces and application of bonding
agents. The gap below spigot 186 does not affect the integration
process and will soon fill in with bone. The accurate, close
fitting of peripheral rim 184 into recess 228 provides great
stability and resistance against any sideways movement during the
three-month or more osseointegration period, so that a good
bone-to-implant bond can be produced in spite of the minimal length
of the implant.
After osseointegration is complete, the site is located and the
healing screw 182 exposed and removed as described above in
connection with the first embodiment of the invention. The rest
factor (not illustrated) is inserted into the implant member as
described in connection with the previous embodiment.
In both of the embodiments described above, the shape of the
undersurface of the implant ensures that there will be little or no
side sway either during or after the osseointegration period. This
results from the downwardly projecting peripheral rim, having inner
and outer circumferential surfaces which combine to resist any
sideways forces. This resistance to side-sway is enhanced by the
spigot 186 which also acts to resist sideways movement. The
relatively large diameter of the implant provides a large area of
downwardly facing surfaces which together resist downward forces on
the implant assembly, further increasing the stability of the
implant and acting to absorb biting pressures. The implant is
selected to be of the maximum possible diameter according to the
bone width available for implantation in a particular patient. The
indents 29, 194 will act to resist rotational movements during and
after osseointegration. The combined effect of the shape of the
undersurface of the implant and its relatively large surface area
is to produce a very stable implant with minimal penetration into
the bone.
Although the implant member is illustrated as implanted so that its
upper surface is at the bone level, it may be implanted to a lesser
depth if the patient has a large amount of bone erosion or
resorption. For example, if there is only 1 mm bone depth available
for implantation without fear of interference with the nerve, the
implant is simply installed to 1 mm in depth so that approximately
1 mm projects above the bone level. However, it will still have
sufficient holding power to remain in position since the
undersurface, and particularly the peripheral rim, will position
the implant during osseointegration and bond to the surrounding
bone to resist sideways and downwards forces. Since it is not
anchored to any overlying body, upwards forces do not have to be
resisted. Thus, sufficient bonding area is provided to resist any
loosening during normal wear.
This implant system and method may be used in any implant procedure
where a denture or prosthesis of more than one tooth is involved,
and is particularly useful in posterior areas of the jaw where the
implant depth is limited, for example the second molar area, and in
conjunction with anterior implants or cantilevered bridges. The
implant has a relatively short penetration into the bone, so that
it can be installed in regions to the rear of the first bicuspid
without fear of interference with the nerve, yet has sufficient
anchoring surface area to integrate with the bone and accept down
pressure of two to three hundred pounds from an overlying denture
or prosthesis. Since the implant is not positively anchored to the
prosthesis, it does not have to resist large upward or sideways
forces, reducing the risk of bone erosion. At the same time, the
rest factor will reduce the trauma to underlying tissue and reduce
or eliminate bone erosion from the overlying denture by accepting
the downward pressure from the denture.
The implant recovery method and tool described above will eliminate
the need to locate and expose osseointegrated implants by a
surgical flap technique. The locating tool and guided tissue punch
accurately locate the implant with minimal trauma, and remove only
a plug of tissue directly above the implant sufficient to expose
the healing screw for removal. The amount of trauma and bleeding is
reduced and the tissue around the implant site remains virtually
intact.
FIG. 19 illustrates a rest factor 250 according to another
embodiment of the invention. The rest factor 250 is generally
cylindrical and has an upper, dome-shaped portion 252 and a
downwardly depending, threaded stem portion 254. The dome portion
252 has hex bore 256 formed in its upper end for gripping by a hex
tool on installing or removing the rest factor 250, as will be
explained in more detail below. The hex bore will be relatively
small, preferably of the order of 0.050", and may be filled with a
temporary sealant after installation.
The rest factor 250 is made from a suitable metal such as titanium
alloy. The dome portion has a wear resistant titanium nitride
coating applied. Rest factors are provided in a range of different
dimensions. The dome portion is preferably provided in a range of
different heights, and in a preferred embodiment rest factors were
provided with dome portions of height 1.5 mm, 2.5 mm and 3.5 mm for
fitting patients with different gum thicknesses. The total height
of the rest factor is preferably in the range 2 mm to 4.5 mm.
FIGS. 20, 21 and 22 illustrate three alternative types of implant
for implanting in the jaw bone at a selected site to receive rest
factor 250 or other denture fitting devices Such as denture anchors
or magnetic abutments of a conventional type. The implant 260 of
FIG. 20 is relatively short and has a body of generally cylindrical
shape having an upwardly tapering upper end portion 262 and a
downwardly depending stem portion 264. A threaded bore 266 extends
downwardly from the upper end of the implant for receiving the
threaded stem portion of the rest factor 250. An eight-sided cut
268 extends through the threads, as illustrated in FIGS. 20 and 23.
The outer diameter of the implant at its upper end 270 is
dimensioned to match the outer diameter of the dome portion of the
implant at its lower end 272.
The stem portion 264 of the implant 260 has an annular recess 274
extending upwardly from its lower end to a position close to but
offset downwardly from the lower end of the recess 268. Recess 274
forms an outer annular rim 276 and a central boss 278 at the lower
end of the implant, and provides an area for bone growth and
osseointegration upwardly into the implant. Thus, the implant is
generally cup-shaped at its lower end, with a central protrusion in
the cupped area. A triple lead screw having a first lead or thread
279, a second thread 280, and a third lead or thread 282 is formed
around the outside of the stem portion 264. The threads 279, 280,
282 are preferably of square cross-section and project out a
predetermined distance from the surface of the stem portion 264.
The threads may each extend around approximately 180.degree. and
preferably do not overlap, although they may overlap in alternative
embodiments.
FIG. 21 illustrates another implant 284 which is longer than that
of FIG. 20. Again, the implant is generally cylindrical and has a
relatively thin upper annular portion 286 with a short, upwardly
projecting and tapered rim 288 and a downwardly depending stem
portion 290 of reduced diameter. A bore 292 projects downwardly
from the upper end of the implant 284 and has a threaded portion
294 for receiving the threaded stem of a rest factor member. A
ten-sided or decagon cut 296 is formed through the threads, and
preferably extends about halfway down the bore 292. In this
version, the bore 292 projects downwardly into the stem portion of
the implant, since the upper portion 286 and rim 288 are shorter
than those of implant 260.
A triple lead thread having first, second and third threads 297,
298 and 299 is formed around the outer surface of stem portion 290.
Preferably, the threads 297, 298 and 299 start at equally spaced
intervals around the periphery of the stem portion adjacent its
upper end but spaced downwardly a distance below the annular ring
portion 286. The threads extend around the stem portion towards its
lower end and terminate at a location spaced above the lower end of
the stem portion. As in the version of FIG. 20, the stem portion
290 has an annular recess 300 at its lower end forming an annular
rim 302 and central boss 304. As in the previous embodiment, the
upper end 306 of the implant is of diameter matching that of the
lower end of the rest factor.
FIG. 22 illustrates another, longer implant 310 which is similar to
that of FIG. 21, apart from the fact that the stem portion 312 is
longer and a quadruple lead screw is provided on the stem portion.
The implant of FIG. 22 is otherwise identical to that of FIG. 21
and like reference numerals have been used for like parts. The
implant has a bore identical to that of implant 284 extending
downwardly from its upper end, and an annular recess at its lower
end which is identical to the recess of implant 284. As in the
previous two embodiments, the upper end 304 of the implant has a
diameter matching that of the lower end of the dome portion of the
rest factor.
A series of four separate threads 314, 316, 318 and 320 is provided
around the periphery of the stem portion 312. The threads start at
equally spaced intervals around the periphery of the stem at a
location close to but spaced slightly below the upper end of the
stem portion, to leave a gap between the annular ring 286 and the
threads. The gap is in the range from 1 mm to 2 mm.
Although in the illustrated embodiment the implants 260 and 284
each have three threads, and the longest implant has four external
threads, any one of these implants may have two, three or four
threads. The double, triple or quadruple lead thread allows for
quick and solid engagement into a tapped bone site. The projecting
screw threads form an undercut region and bone growth and
attachment in this area increases the strength of the attachment
and resistance to loosening forces. The unique cup shaped recess
design at the lower end of the implant is also designed to increase
bone to implant surface contact and attachment area.
The pitch or angle of the thread is preferably relatively steep and
is preferably in the range from around 9.degree. to 17.degree.. The
spacing between adjacent threads is preferably at least 1 mm. It
has been found that this is the minimum spacing required to ensure
significant bone growth and osseointegration in the gaps between
threads. The threads preferably project out around 1/2 mm from the
surface of the stem portion of the implant, and they are about 1/2
mm in height. Thus, the gaps between the threads are twice as wide
as the threads themselves. This provides good blood supply to the
bone between the threads, and provides a greater bone thickness and
stronger shelf of bone between the threads.
Both the implants and the rest factor are all made in a range of
lengths and diameters to fit the size of different patient's jaws.
Implants will be provided in a range of lengths. Preferably, the
lengths are of the order of 2 mm, 4.5 mm, 7 mm, 10 mm and 13 mm.
The 2 mm length implant will be of the type illustrated in FIG. 20,
while the 4.5 mm implant will be of the type illustrated in FIG. 21
and the 7 mm, 10 mm and 13 mm implants will be as illustrated in
FIG. 22. Each of the different implants will be provided in a range
of different outer diameters, preferably 4 mm, 5 mm and 6 mm.
Preferably, the height of the tapered rim of the implant 260 or 310
is as short as possible, for example around 0.5 mm.
The implants are made of a suitable material such as titanium and
may be coated with a coating of a material for improving bone
adhesion.
The method of installing implants 260, 284 and 286 will be similar
with appropriate changes in the dimensions of the drilled bore to
accommodate the different length stem portions and numbers of
threads. The method will therefore be described for the implant 260
only, by way of example. The implantation method is similar to that
illustrated in FIGS. 6-11 and described above.
The first step in the implant procedure is to select the site in
the jaw at which the implant is to be installed. The appropriate
height and diameter implant member is selected dependent on the
bone depth, tissue height, and jaw thickness at the selected site.
The minimum bone depth required is 1 mm between the bottom end of
the installed implant and the mandibular nerve canal or maxillary
sinus space. Thus, the total bone depth required for installing the
2.5 mm implant is only 3.5 mm, while the longer implants can be
installed where a greater bone depth is available. The minimum bone
width required to place a rest factor implant is 1/2 mm each on the
lingual and facial sides of the implant, requiring a 5.0 mm total
ridge width for the 4.0 diameter implant, 6.0 mm ridge width for
the 5.0 mm diameter implant, and 7.0 mm ridge width for the 6.0 mm
implant. Based on these dimensions, the appropriate implant can be
selected.
The very short, 2.5 mm implant can be installed safely even where
some bone erosion has already taken place and even in the distal
jaw regions without risking interference with the mandibular nerve.
The design is such that the implant has a relatively large surface
area for bone to implant osseointegration, and undercut areas for
improved retention and resistance to movement in any direction.
Once the appropriate implant has been selected, a bore shaped and
dimensioned to correspond to the shape and dimensions of the
implant is cut out. This is done in a series of steps. First, a
mesio-distal incision is made through the tissue or gum 321 along
the alveolar mid-crest at the selected site, typically the area of
the second molar. A bone plateau is created which is made as flat
as possible by removing ridges or other bone irregularities. At
this point, the width of the alveolar crest can be measured to
determine the largest diameter rest factor implant which can be
fitted within the available width and still allow at least 1/2 mm
of bone on each side. The implant is placed as close as possible to
the lingual side while still allowing the 1/2 mm of bone on the
lingual side.
At this point, a pilot burr is used to drill out a pilot hole of
appropriate depth at the center of the insertion site, as
illustrated in FIG. 15 above. The pilot hole diameter will be
substantially identical to the diameter of the implant central boss
278. An appropriate depth limiting sleeve is used with the pilot
burr in order to limit the depth of the pilot hole to match the
implant height. Thus, depth limiting sleeves will be provided for
each of the four different implant heights, and the appropriate
sleeve will be selected on installation. The lower end of a
previously drilled pilot hole 322 in jawbone 323 can be seen in
FIG. 24, which illustrates a subsequent step in the procedure.
An alignment pin may be placed in the pilot hole to check for
proper alignment to the path of a prosthetic insertion and between
multiple implants.
After alignment, a spot-face drill (not illustrated) is used to
make a shallow, 360.degree. shoulder or seat 324 into the crest of
the bone. This seat is used to assist in engaging of a bone tap in
a later stage of the procedure. The drill is withdrawn several
times during site preparation to remove bone buildup between the
flutes of the drill. An implant body drill is used to drill out the
main recess 328 for receiving the implant. This drill will be
similar to drill 44 illustrated in FIG. 6, above, and will have a
diameter corresponding to that of the stem portion of the selected
implant. Thus, the drill will have a diameter equal to the implant
diameter less the thickness of the threads, or 4.0 mm in the case
of a 5.0 mm implant, for example.
In the next step of the procedure, a core drill 326 is used to cut
an annular ring or recess 330 at the bottom of recess 328 for
receiving the underside rim 272 of the implant. Drill 326 has a
central guide 332 for centering in the previously drilled pilot
hole 322, a cylindrical central body portion, and a downwardly
facing annular ring of cutting teeth 334 for drilling out an
annular groove or recess 330 for receiving the rim 272 (or 302 in
the case of the implant 284 or 310) of the implant.
A series of three guided hand taps (starting tap, intermediate tap
and finish tap) are used to make a multiple lead tapped preparation
into the drilled hole 328. It will be understood that the triple
and quadruple leads will be made in a similar manner. One of the
thread taps 336 is illustrated in FIG. 25. Each tap has a tap guide
pin 338 which engages the pilot bore to keep the tap centered on
the recess. Optionally, a tap guide template (not illustrated) may
be secured across the recess via pins secured on opposite sides of
the implant site. This can be used to provide better support for
the bone tap if the patient has spongy, cancellous bone. The tap
336 has triple lead cutting flutes 340 for forming a thread
matching that on the insert. The starting tap has a machined line
indicating the start of the double cutting edge of the bone tap.
The starting tap is positioned into the drilled recess and the
cutting flutes are engaged into the cortical bone, with the
machined line on the tap positioned perpendicular to the
longitudinal axis of the ridge. The implant site is then hand
tapped and threads 342, 343 and 345 are tapped into the recess. The
tap is backed off a quarter of a turn several times during the
process to clear bone chips. In this way, the tap is worked down to
the bottom of the drilled recess 328.
The procedure is then repeated using an intermediate tap, which
will be marked with two lines to distinguish from the other two
thread cutting taps. The lines are positioned in the same starting
position as the line on the starting tap. Finally, the procedure is
repeated with the finish tap, which will be marked with three
lines, to create a final cut of the bone thread to accept the
implant.
An octagonal wrench 344 is used to place the implant into the
prepared implant recess, as illustrated in FIG. 26. The octagonal
end of wrench 344 will engage in the octagon 268 cut through the
threads 266 and will not damage the threads in bore 266. The
implant is completely seated with the implant threads completely
engaged in the bone threads and the tapered upper portion of the
implant projecting above the level of the bone, as illustrated in
FIG. 26. If the implant is set in correctly, the stem portion 264
will have its upper end located 1/2 to 1 mm below the top of the
bone, as illustrated in FIG. 26.
A healing screw is then threaded into the implant to protect the
internal threads of the implant during the osseointegration period.
The healing screw is similar to the healing screw 70 of the first
embodiment but with a threaded stem matching bore 266 and a hex
hole in place of threaded hole 76 at the upper end of the screw.
The flap of gum 321 is sewn down over the implant site, in a
similar manner to that illustrated in FIG. 8 above, after
installation of the healing screw.
The implant is then left for a healing period to allow the bone to
osseointegrate with the surface of the implant. A healing period of
not less than 41/2 months should be used. The bone will grow over
and osseointegrate into the gaps between the threads, providing a
greater osseointegration surface area and better retention of the
implant. The cup-shaped design of the lower end of the implant,
along with the multiple lead threads, increases bone to surface
contact and helps to withstand posterior occlusal load.
Where a triple or quadruple lead thread is used, resistance to
rocking or movement of the implant is provided. With two opposing
threads, there may be some tendency for the implant to rock from
side to side. Thus, implants with three or four threads are used
for even greater resistance to rocking as a result of loads.
After the minimum period required for osseointegration, an incision
is made over the implant for access to the healing screw.
Radiographic charts and finger palpation may be used to locate the
general area of the implant. The incision may be made in a
conventional manner, but preferably a guided tissue punch 82 is
used as in the previous embodiments. The tissue is pierced with the
sharp point or probe 91 of the tissue punch, and the implant site
is probed until the point 91 locates a hex hole provided on the top
of the healing screw. The guided tissue punch 92 is then turned
down on the guide with firm pressure until it punches an opening
through the tissue or gum. The tissue punch will engage the outside
diameter of the healing screw, and will cut out a plug of tissue
directly over the center of the implant, as illustrated in FIG. 10
above.
The locating tool/tissue punch assembly is then removed,
simultaneously pulling out the cut plug of tissue. If the tissue
does not pull out with the tissue punch, forceps may be used to
remove it and expose the healing screw. A cover screw hex tool (not
illustrated) is used to engage the hex hole at the top of the cover
screw and remove the cover screw from the implant.
The implant is now exposed for attachment of the dome-shaped rest
factor 250 as illustrated in FIG. 27. The implant may alternatively
be attached to other dental devices, such as implant anchors or
magnetic abutments for dentures. The dimensions of the selected
rest factor will depend on the implant dimensions and also the
tissue height of the patient. The height of the implant should be
such that the top of the dome is at the tissue level or only
slightly above it. The dome portion of the rest factor selected
should therefore have a height substantially equal to the tissue or
gum thickness. If the gingival layer has a height substantially
greater than the largest dome portion, tissue reduction must be
used to reduce the gingiva thickness to a maximum of 3 mm at the
implant site.
Once the correct size rest factor has been selected, a hex wrench
346 having a hexagonal shaft 348 is used to engage the hex bore 256
at the upper end of the dome-shaped upper end portion 252 of the
rest factor. The rest factor is then threaded into the bore of the
implant, as illustrated in FIG. 27. The tissue is then sewn back
around the implant dome, as indicated in dotted lines in FIG. 27,
and the dome is left in place for around 4-6 weeks to allow for a
period of reduced implant loading during gingival healing. The
patient's denture should be fitted to the dome top with a soft
reline material to maintain proper occlusion during the gingival
healing period. This is done by taking a full arch reline
impression including the exposed metal tip of the rest followed to
prepare a master cast of the jaw including the exposed tip of the
dome. The denture base is relined using this cast in the normal
manner.
If a change in tissue height has occurred during the tissue healing
period, the rest factor may be unthreaded and replaced with another
rest factor of the correct dimensions.
Once the healing period is complete, the top of the dome is exposed
for a prosthesis to rest on with lateral freedom of movement. The
preferred arrangement is to use the dome as a permanent,
non-retentive rest when the patient has existing anterior retention
for a prosthesis. However, the rest factor may be used as an
attachment if required, for example if there is no existing
retentive means for the prosthesis, or lateral stability is needed
due to severely reduced ridge height. A hole is drilled into the
center of the dome to an appropriate depth, and resin is injected
into the counter-bore. When the resin starts to become firm, a post
forming part of a standard rest plate of a denture is inserted into
the bore until the bottom of the plate comes into contact with the
resin.
FIGS. 28 and 29 illustrate a modified insert 350 for use with a
rest factor 250 in an equivalent manner to that described above.
However, rather than having a multifaceted cut for receiving a
wrench in the threaded bore 352 of insert 350, an external,
twelve-sided wrench element 354 is secured to the upper end of
insert 350. Element 354 has an outer twelve-sided surface 356 for
engaging a wrench with a corresponding internal bore, and a through
bore 358 coaxial with threaded bore 352 but of larger diameter.
Element 354 is preferably formed separately from insert 350 and
then pressure bonded or welded to it. A conventional hex wrench may
also be used to engage the element 354.
Apart from threaded bore 352 and wrench element 354, insert 350 is
otherwise identical to that of FIG. 21 and like reference numerals
have been used as appropriate. It will be understood that a wrench
element 354 may also be provided on the insert of FIG. 20 or FIG.
22 in place of the multi-sided internal cut. This avoids the need
for a precision machined cut extending through the threads, where
the cut must be of precise dimensions between those of the inner
and outer diameter of the threads to avoid damaging the
threads.
The use of an implant having two or more stabilizing threads on the
outer surface of the stem embedded in the jawbone, combined with
the inverted cup shape of the lower end of the implant, provides a
stable implant which resists movement even in the case of the very
short version. Bone growth into the inverted cup and between the
threads provides a large area of bone to implant contact and
osseointegration, providing significant resistance to both lateral
and downward forces both during and after the osseointegration
period.
The non-retentive rest factor can be used to support dentures
non-retentively in the posterior area of the jaw. As a result, the
pressure applied to the lower jaw by the denture during mastication
is dramatically reduced, reducing the discomfort and bone erosion
normally resulting from denture wear. Although the implant can be
installed anywhere in the jaw for retentive or non-retentive
engagement with a denture or prosthesis, it is particularly useful
for providing support in posterior regions of the jaw where the
jawbone has become eroded. The accepted formula for cantilevered
dentition attached to anterior implants limits the extension of the
cantilever over the posterior ridge to no further than the distance
between the plane of the most anterior implant and the furthest
posterior implant. This results in a lack of support under the
molar dentition and an extraction effect on the anterior implants
during masticatory function. With the additional support provided
by one or more rest factors and implants in posterior regions of
the jaw, the extraction effect is significantly reduced or
eliminated. In addition, trauma to the ridge under occlusal load,
and the resulting bone loss, may be reduced.
Although some preferred embodiments of the present invention have
been described above by way of example only, it will be understood
by those skilled in the field that modifications may be made to the
disclosed embodiments without departing from the scope of the
invention, which is defined by the appended claims.
* * * * *