Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: DENTAL IMPLANT
FIELD OF THE INVENTION:
This invention relates to dental implant of the type used in the
mouth to stabilize dentures or support dental crowns and bridges.
BACKGROUND OF THE INVENTION:
Dental implants used to stabilize dentures or support dental crowns
and bridges have been known and have been used fairly extensively in the
recent
past. Such prior art devices are typically comprised of three components,
namely,
an implant component for anchoring to the bone, a transgingival component and
a separate support component. The support component usually attaches to the
transgingival component which, in turn attaches to the anchoring component at
about the level of the bone. An artificial tooth or bridge may then be
attached to
this separate support component. This support component is sometimes referred
to as an abutment portion, the transgingival component is sometimes referred
to
as an abutment portion, the transgingival component is sometimes referred to
as
an abutment connection or the transgingival collar or the transepithelial
connection
and the implant is sometimes referred to as a fixture.
An example of such a prior device may be found in Canadian Patent
No. 1,313,597. This patent describes an implant for insertion into bone
through
an epithelial and fibrous connective tissue layer to which a prosthesis may be
attached. This implant comprises a top portion for supporting a mechanical
component to which the prosthesis may be connected and a body comprising an
upper bone attachment region which tapers to a lower bone engagement region
having a porous surface. The upper bone attachment region comprises a
substantially non-porous but bioreative surface and this patent teaches that
this
results in an upper bone attachment region which is claimed to be capable of
enhancing bone attachment.
However, several problems develop with an implant of this type.
In particular, the patent teaches use of a collar 14 that is adapted to be
coupled to
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the implant 12. However the interface between the collar 14 and the implant 12
occurs at a level below the gingiva in the installed position. Further,
although the
patent teaches providing recesses 40 on the lower surface 42 of the collar 14
to
compliment projections 32 of the implant 12 to prevent rotation between the
two
components, in practice this is not effective. The attachment between the
collar
and the implant is accomplished by means of a threaded screw identified as 46
in
Figure 1. Such a screw has a natural tendency to become loose during the
vigorous stresses to which an implant of this type is subjected.
To avoid problems associated with the loosening of the threaded
screw 46, practitioners have resorted to insertion of cement into the threaded
portion to ensure a locked and non-loosening joint between the implant
component
and the support component. Unfortunately, because the interface between the
collar and the implant is below the gum level, any excess cement will be
squeezed
out at the interface and may not be noticed by the practitioner since it is
hidden
from view. Such excess accumulation of cement can create irritation of the gum
and the bone and can result in infection and/or implant failure.
In addition, all implant systems, (fixture, abutment connection,
abutment) which have this type of arrangement have a microgap between the
fixture or implant and the abutment connection or the transgingival collar at
the
level of the bone. This microgap has been called an "endotoxin generator" by
some authorities because it is a region for potential bacterial growth.
Other prior art devices include implants with threaded exteriors
which require extensive and complicated methods for preparation of the gum and
bone to accept the insert. As a result, such implants are difficult and
expensive
to insert and the surgery is most often done by specialists. In any event they
are
not practical and result in excess discomfort for the patient and unnecessary
difficulties for the dentist making the installation. For example, some
require
incising the gum to gain access to the bone; multiple drilling and reaming
steps;
installation of the implant; reattachment, by surturing or the like, of the
gum over
the implant site to promote healing; a return visit several months later to
the dental
office to have the gum again incised to allow access to the implant; insertion
and
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attachment of the abutment portion; and final attachment of the prosthesis to
the
abutment portion. The first incision into the gum can promote scarring, making
the second incision difficult.
SUM1VIARY OF THE INVENTION
What is required is an implant which may be installed in an easy
one-step method and yet which is secured to the bone and provides a firm
anchor.
Preferably such an invention would also minimize the risk of infection or
irritation
of the bone and the gingiva and would provide for easy attachment with
standard
components. Further, such an implant would not require an excessive number of
steps for installation, or excessive patient discomfort and would be quickly
and
efficiently installed in various types of installation conditions.
Therefore, according to the present invention there is an implant for
anchoring a prosthetic device in bone, said implant comprising:
(a) a one piece body having:
(i) a root portion having a surface conducive to bone ingrowth,
and having a press fitting portion;
(ii) a press fitting emergent portion having a smooth biocompatible
surface which is non-irritating to living tissue; and
(iii) a coronal portion having a keyway; and
(b) an abutment portion for insertion into said keyway, said abutment
portion including a key at one end for insertion into said keyway and a head
for
retention of said prosthetic device at the other end.
In further aspect of the present invention there is provided a method
of inserting a dental implant comprising:
incising through a gingival layer;
drilling a pilot hole, at an appropriate position into a bone located
below said gingival layer;
drilling a recess, about said pilot hole, into the bone with a second
drill bit to form a tapered recess of appropriate diameter;
positioning a one piece dental implant in the tapered recess;
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gently tapping said implant into surface engagement with said bone
wherein said step of tapping includes wedging a smooth emergent portion
against
a hard cortical bone portion and wedging a root portion coated with a material
conducive to bone ingrowth into a cancellous region of the bone;
allowing said bone to grow into said root portion; and
securing an abutment portion to said implant.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference will now be made to preferred embodiments of the
invention by reference to the attached drawings which are by way of example
only
and in which:
Figure 1 is a side view showing an implant according to the present
invention;
Figure 2 is a front view of the implant of Figure 1;
Figure 3 is a front view of an abutment portion for an implant of
Figure 1 adapted to act as an anchor for overdenture retention;
Figure 4 is a front view of an abutment portion for an implant of
Figure 1 adapted to act as an anchor for a false tooth cap;
Figure 5 is a cross-sectional view through the abutment portion
along the lines of 4-4 of Figure 4;
Figure 6 is a side view of a healing cap for use in association with
the implant of Figure 1;
Figure 7 is a view of the implant partially inserted;
Figure 8 is a view showing the implant of Figure 1 in an installed
position;
Figure 9 is a view of a drill for inserting the implant of Figure 1;
Figure 10 is a view of an implant according to a second aspect of
the present invention;
Figure 11 is a front view of a drill for inserting the implant of
Figure 10;
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Figure 12 is a side view of a third embodiment of an implant
according to the present invention;
Figure 13 is a side view of the second embodiment showing how
the abutment portion may be freed; and
Figure 14 is a side view of the second embodiment of Figure 13
showing the abutment portion coming free.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 shows a one piece body or implant 10 having a coronal
portion 12 and an apical portion 14. Beginning at the bottom of the one piece
body 10 there is shown a tapered section 16 above which is cylindrical section
18.
The tapered section 16 and the cylindrical section 18 are suitably coated with
a
material which is conducive to bone ingrowth and which is identified as 20.
These
sections 16, 18 together may be considered as a root portion. The preferred
form
of bony ingrowth material is of the type which creates a multitude of tiny
passageways. This can be accomplished, for example, by fine wire mesh screens
or the like, but the preferred form is to use discrete particles of titanium
alloy
which are bonded to the outside of the implant in a random fashion. The
preferred
method of bonding is by sintering, as will be known by those skilled in the
art.
The preferred size of particles is between 45 to 150 microns although other
sizes
may also be appropriate for bony ingrowth, as will be known to those skilled
in
the art.
The one piece implant consisting of the coronal portion 12, the
body 10, with the apical portion 14, is preferably made of titanium alloy,
Ti6A14Va, and the coating material is made of commercially pure titanium.
Above the cylindrical section 18 coated with bony ingrowth material
20 is a tapered, smooth-walled portion 22. The taper of portion 22 may be
referred to as the "fourth taper" . The smooth wall is an important aspect of
the
present invention. To avoid gum and bone infection it is important to have a
' relatively smooth nonporous surface which is biocompatible at the emergent
portion. In particular, it is preferred if the emergent region is machine
polished
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rather than highly polished. Also it is preferred if the emergent cylindrical
portion
18 and the tapered portion have an angle therebetween (shown as A in Figure 1)
which is preferably more than 168 degrees and which is most preferably about
176
degrees. The preferred length of the smooth walled portion 22 is .06 in. (1.50
m.m.). It is also preferred if the tapered portion 16 has an identical angle
of taper
of no more than 12 degrees from vertical, and most preferably about four
degrees
from vertical where vertical in this sense means the vertical side edge of the
cylindrical portion 18.
The coronal portion 12 begins with a tapered section 24 increasing
in diameter towards the end of the coronal portion 12, and which ends at a
generally horizontal top portion 28. Between tapered section 24 and the top 28
are
located two further tapered sections, identified as 25 and 26 respectively.
The
preferred total length of the coronal portion 12 is .16 in. (4.00 m.m.), of
which
the axial length of tapered section 24 is .12 in. (3 .00 m. m. ) and of each
of sections
25, 26 is .02 in. (0.50 m.m.).
Located within the coronal portion is a keyway identified as 30
which includes a tapered section 32 and a part cylindrical section 34. The
taper
on section 32 may also be referred to as the "first taper" . Located between
these
two sections is a toroidal section 36 which may be formed in a part circular
shape
with cross-section having a .O1 in. (0.30 m.m.) diameter.
Located at the top of the coronal portion 12 is a cross groove 38
which is shown more clearly in Figure 2. The purpose of this groove is to
provide
an additional keyway to resist rotation of the parts of the present invention
with
respect to each other as will be appreciated from the following description.
Turning to Figure 3, an abutment portion indicated generally as 40
is shown. The abutment portion is formed with a key 42 (also referred to as a
keyway insertion portion) for insertion into the keyway 30 of the implant 10
and
a head 42 which is in the form of a common anchor for over denture retention.
As
can be seen in Figure 3, a locking bar 46 is provided which mates with groove
38
on the coronal portion of implant 10. Also, it can be seen that a tapered
section
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indicated at 48, also referred to as a second taper, is provided on the key
for the
purpose of locking the abutment portion 40 into the implant 10.
Figure 4 is a view of a second abutment portion 50 of the type used
to act as an anchor for a single false tooth cap. The key portion 52 is
identical to
the key portion 42 of the abutment 40 and includes a locking bar 56 which is
identical to locking bar 46. The head portion 44 is in the form of a standard
anchor for a single tooth cap. Again, a tapered portion 58 is provided which
is
identical to the tapered portion 48.
Figure 5 shows a cross-sectional view along line 4-4 of Figure 4.
As will be appreciated this view is identical for abutment portions 40 and 50,
which according to the present invention have the same key portion. As can be
seen, one face of the key portion 52, 42 is flat and is indicated as 60. Also
shown
is the underside of the head 44 which is shown as 62 as well as the locking
bar
which is shown as 56. The main portion of the key is shown as represented by
the
line 52 and the taper is represented by the area shown as 58. It can now be
appreciated that the taper runs around the perimeter of the key except for at
the
plane surface 60.
It can now be appreciated how the abutment portions 40, 50 may
be securely retained in the implant 10. The first aspect is that there is a
non-
rotational feature, namely the locking bars 46, 56 and the groove 38. This
feature
prevents the rotation of the abutment portion relative to the insert, when the
abutment portion is fully inserted into the insert. It is preferred to use
this feature
to achieve secure non-rotational attachment.
It can now be appreciated that two types of locking are present
between the abutment and the implant. The taper of the portion shown as 48 and
58 is preferably less than seven degrees and more than two degrees. Most
preferably this degree of taper is about four or five degrees. This degree of
taper
is desired to take advantage of a metallurgical phenomenon known as cold
welding
which occurs between relatively smooth metal surfaces which have an
interference
fit and which are closely angled to each other. It is a feature of the present
invention that a cold weld be formed between the mating surfaces of the key
and
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the keyway. The weld can be effected by gently tapping the abutment portion
into
the implant portion. As will be appreciated, the achieve this weld the
surfaces
between which the weld is to be formed need to be carefully and properly
finished,
such as by sandblasting or the like.
The second matter of attaining secure attachment is the use of
standard dental cement. It will be understood of course that this is an
alternative
to the cold welding method outlined above. In this method the cement can be
inserted into the implant prior to the abutment portion key 52, 42 being
inserted.
The cementable abutment portions 40, 50 are about .001 in. (.035 m.m.) smaller
in radius than the keyway 30 to allow for cement space. The cement then forms
a solid bond between the metal surfaces. It is preferred in this approach to
roughen the metal surfaces by serrating or the like to ensure a good bond with
the
cement. The toroidal section 36 can now be more fully understood. Its purpose
is to provide a reservoir into which excess cement may be driven upon
insertion
of the key into the keyway. Suitable cements for the metal to metal bonding
are
composite in excess cement present, according to the present invention it will
be
forced out at an interface between the underside 62 of the head of the
abutment
portion and the top of the coronal portion, shown as 37 above the gum line and
thus will be clearly visible to the practitioner and readily removed while
still soft.
Figure 6 shows a healing cap which may be used to protect the
keyway 30 while the bone is healing and growing into the implant prior to an
abutment portion 50 or 40 being inserted. The healing cap is identified
generally
at 70 and includes a coronal portion 72 which is gently curved and a keyway
portion 74 which is intended to be press fit into the keyway 30. The keyway
portion 74 is comprised of two limbs 76 and 78 separated by a groove 80. By
means of the groove, the portion 76 and 78 may be compressed inwardly into the
keyway 30 and securely retained in position.
It will be also noted that the healing cap 70 includes an insert
portion 82 which accommodated the upper part of the coronal portion 12 of the
one piece implant. The surfaces 84, 86, 88, and 90 are intended to cover and
capture the coronal portion of the implant. By means of the inward angle of
the
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portions 84, the healing caps snaps into place over top of the coronal portion
of
the one piece implant 10. In this manner, the healing cap is securely held in
place
in addition to the compression of the keyway portions 76 and 78. Preferably
the
healing cap 70 is made of a polymer material for flexible retention in the
coronal
portion.
With references to Figures 7-9, it can now be appreciated how the
implant of the present invention may be installed. The first step is to
identify the
site into which installation is to occur. As will be understood by skilled
practitioners, the necessary ground work to prepare for installation will
involve
the obtaining and careful analysis of X-rays or other suitable imaging
techniques
to enable a full understanding of the implant site to be gained. Once the
location
has been identified then it becomes necessary to identify the appropriate
insert.
It will now be appreciated that by forming the preferred implant with a
cylindrical
section 18 above the tapered apical portion 14 the implant length can be
varied
according to site conditions. While the preferred axial length of the tapered
apical
portion 14 is .12 in. (3.00 m.m.), the cylindrical section 18 can be made .14,
.26,
.37 or .49 in. (3.50, 6.50, 9.50 or 12.5 m.m.). This can then provide to the
practitioner a range of implant depths to choose from again according to site
specifics. In general, providing there is adequate integral bone the larger
depths
are preferred.
Block et al. writing in J. Oral Maxillofac. Surg. 48: 174-178, 1990
and Stultz et al. writing in Compend. Contin. Educ. Dent., Vol XIV, No. 4, 478-
486, and Walmsley have shown that implant success is directly proportional to
implant length.
Once the proper length has been selected it is then necessary to
prepare the gingiva 92 and bone 90 for the implant 10 (see Figure 7). This is
accomplished by, after adequate anaesthetic of the patient, drilling a single
recess
89 into the installation site. It is noted that the bone 90 of the
installation site is
generally composed of a soft cancellous portion 90A and a hard cortical
portion
90B, and the gingiva 92 is generally composed of a gum 92A and the sub-gum or
derma 92B.
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According to the present invention only a single final drill bit 93
need be used as shown in Figure 9. The drill bit 93 has a tapered section 94
and
a cylindrical section 95. It will be appreciated that the shape and dimension
of
sections 94, 95 of the drill bit should closely correspond to that of the
selected
implant 10. However, it is preferable for the tapered section 94 to be just
slightly
longer than the corresponding implant, for example by .03 in (0.75 m.m.), for
ease of fit.
The cylindrical section 94 has opposed cutting edges 96 (only one
of which is shown). A tapered coronal portion 97 has one or more discrete,
protruding cutting teeth 98 thereon. The taper on the coronal portion 97 may
be
referred to as the "third taper" . Reference numeral 99 indicates another set
of
cutting edges on the tapered section 94 (which has three or four sets of such
edges,
as desired). A smaller diameter upper portion 100 of the drill 93 has a keyway
adapter 1010 at its top end for engaging a drive mechanism of a dentist's
drill (not
shown). A hollow stem or bore 102 extends through the drill 93 along its
length,
as shown. A saline coolant is delivered from the drill to an opening 103
through
the bore 102 to cool the drill bit and prevent heat build up, which heat could
damage the living cells being drilled into.
The use of the single final drill 93 is preceded by the use of a
conventional smaller pilot drill (not shown). The pilot drill also has a
hollow stem
or bore to allow internal irrigation with normal saline solution.
Additionally,
external irrigation may be used (for both drills) to cool the site being
drilled to
prevent damage to the bone tissue during the site preparation.
The drill 93 of the present invention differs from prior art systems
which use a parallel sided final drill, either with a hollow stem or with a
solid
stem (which permits external irrigation only). The tapered portion of the
surgical
site is prepared after, by a separate drill, thus allowing no control over the
length
of the midsection portion of the bone hole.
Once the recess 89 in the bone has been drilled, it will have a
tapered apical portion. Referring back to Figure 7, an implant 10 according to
the
present invention is shown being installed into the recess 89 in the bone 90
and the
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gingiva 92 after the bone has been drilled. As can be seen, the lower section
of
the recess 89 tapers slightly, preferably in an amount less than 5°,
over the depth
of .12 in. (3.00 m.m.).
Figure 8 shows the implant in the fully installed position. To attain
this position it is necessary to press the implant into the bone 90, by reason
of the
interference fit between the bone 90 and the implant 10. This is preferably
accomplished by gently tapping the coronal portion 12 of the implant to firmly
seat
the implant into the bone. Thereafter the healing cap 70 is installed and the
patient
is allowed to leave. A suitable period of a few months is allowed to elapse
and
then the patient can return for installation of an appropriate abutment
portion.
Those skilled in the art will appreciated that the two styles of abutment
portions
provided according to the present invention are conventional above the gum
line
and thus will be readily understood and used by practitioners.
At this point an important aspect of the invention can be better
appreciated, namely how the implant 10 of the present invention and the bone
90
interact. When the implant 10 is tapped into the recess 89 as shown in Figure
8,
the smooth-walled (i.e. emergent) portion 22 causes the implant to initially
be
wedged into the hard cortical portion 90B of the jaw bone 90 to stabilize the
implant in the recess 89. This wedging arises because of the taper of emergent
portion 22 and because the diameter of the emergent portion 22 is slightly
larger
than the diameter of the recess, and is not due to any surface effects between
the
cortical bone 90B and the smooth biocompatible surface on emergent portion 22.
During the ensuing months, the soft cancellous portion 90A of the jaw bone
gradually grows into the coating 20 and attaches to the cylindrical section 18
of
the implant. In the meantime, the cortical portion 90B slowly subsides away
from
the smooth biocompatible surface of the emergent portion 22. Hence, the
biocompatible surface of the emergent portion 22 only temporarily helps hold
the
implant 10 in place while the cancellous portion 90A bonds to the cylindrical
section 18. It is believed that the stress induced into (i.e. the displacement
of) the
cortical portion 90B by the taper of the emergent portion 22 is insufficient
to
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prevent the cortical portion 90B from subsiding and remoulding away from the
implant.
Figures 10 and 11 show a further embodiment of the present
invention, in which like reference numbers refer to the same components. While
achieving an interference fit between the implant and the cortical bone
section at
the emergent portion 22 of the implant 10 and the implant and the cancellous
bone
section at the root portion 14 with a wedge or taper fit yields satisfactory
results,
there is also a drawback with such a taper. More specifically such a taper
acts as
a wedge which if forced too hard during implantation by an unskilled
practitioner
can lead toa splitting or fracturing of the bone. Thus the present invention
also
contemplates an interference fit between the emergent portion and the cortical
bone
by means of a straight walled step as shown at 400 in Figure 10. The step is
dimensioned to fit, in an interference manner in the hole drilled in the bone.
The
width of the step is dimensioned to exert a significant gripping force on the
one
hand, without exceeding the typical fracture stresses for such bone on the
other.
Different degrees of step or size of interference fit would be provided for
different
patients, with older patients having more brittle bones being treated with
implants
having a narrower step than for younger patients with stronger bones. In
general
to ensure a secure fit in the cancellous region, which is generally a softer
bone,
a slightly greater step or interference fit is necessary in this region. The
step
function at the emergent portion is preferred to be between .O1 mm and 0.10 mm
and at the cancellous bone region between .O1 mm and . l5mm. Step function in
this sense refers to the amount by which the implant is bigger in outside
diameter
than the inside diameter of the bore or hole into which it is being inserted.
It will
be appreciated that forming an interference fit can be done by making the
implant
bigger than the bore into which it is inserted, by making the implant bigger
than
the drill diameter, or the drill smaller than the implant diameter. To form an
interference fit in the apical portion or root portion 14 will require forming
an
initial bore of a slightly smaller diameter than the following bore, which can
easily
be accomplished by a drill having a smaller diameter tip 410 than a trailing
section
420 as shown in Figure 11. The width of the shoulder on the drill will be such
as
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to form a good interference fit in the cancellous bone section. In some case
it may
be preferred to provide a taper at the apical end of the implant together with
a step
at the emergent portion, to minimize the risk of forming pockets or gaps
around
the apical portion 14 of the implant.
It will be appreciated that the step design will prevent the implant
from being installed in a manner which is likely to cause a bone fracture.
Further,
the depth of the implant can be more easily varied in the hole than with a
tapered
design. All that is required to press the implant into the bore more is to
overcome
friction; with a taper, deeper penetration could lead to fracturing the bone.
Thus
the stepped design is preferred in some applications.
It will be understood that this second embodiment works according
to the same principles as the previous embodiment in that the implant upon
being
implanted will press fit into the bone at the emergent portion 22 and at the
root
portion 14 to retain the implant in a secure position to allow bone ingrowth
to
occur over the straight walled root portion 18. The straight walled root
portion
will not necessarily be an interference fit, but merely closely fit to allow
bony
ingrowth to occur. Thereafter the bone adjacent to the press fit sections will
likely
subside, in part as a reaction to the unnatural stresses being imposed upon it
by the
press fitting action of the implant. As the cortical bone subsides next to the
press
fit section of the emergent portion 22, it is simultaneously growing into the
straight walled root portion, thereby forming a secure and stable attachment
to the
patient.
Figure 12 is a side view of a third embodiment of the present
invention, shown generally as 300. In Figures 12, 13 and 14, like numerals
refer
to like components as in the previous embodiment. In this embodiment, the
cylindrical section 18 is similar to that of the previous embodiments, but
rather
than tapering at 22 as in the first embodiment, or including a step as in the
second
embodiment, in the third embodiment, the smooth-walled portion, shown as 310,
is also cylindrical and of the same dimension as the root portion. This, is
certain
implant circumstances, has some clear advantages. The primary advantage is
that
by replacing the wedging taper, the potential for splitting the bone coronally
is
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reduced. Of course, the smooth-walled portion 310 is sized and shaped to
correspond to the outside diameter of the cylindrical root portion 18. In the
case
of a cylindrical root portion 18, the bore formed in the bone will be such
that a
smooth friction fit between the root and the bone is established. In this
sense, the
friction fit needs to be sufficient to secure the implant in place for initial
stabilization. Longer term stabilization, occurring through bone ingrowth,
achieves a three dimensional locking between bone and implant by reason of the
porous coating.
Another feature of the third embodiment is the extension of the
cylindrical root portion fully down the length of the implant, whereby the
lower
tapered section 16 of the previous embodiments is removed. Adequate results
have been achieved with a cylinder of between 3.55 and 3.75mm in diameter,
with
a preferred diameter of 3.64mm. The advantage of such a cylindrical geometry
is that it increases the surface area in this region (what was section 16),
over the
surface area of the taper, by about 9.6 % . By increasing the surface area, a
better
and stronger bond is possible between the bone and the porous coating. Quite
simply, the larger the surface area, the more bonding can take place. For a
drilled
bore, the maximum surface area is a true cylinder which is what this third
embodiment uses.
Another feature of the third embodiments is to slightly increase the
overall diameter of the implant, which also increases the overall
intraossesous
surface area. For example, by increasing the cross sectional diameter to
3.64mm
increases the intra osseous surface area by about 5.5 % which again gives a
better
implant by bore bond. In this regard, one of the key advantages of the third
embodiment remains its generally narrow diameter. It is believed that bone
resorption, post implantation, is influenced by how much bone mass is left
around
the implant. Thus, implants with large coronal diameters, at the location
where
the implant emerges from the bore, may tend to suffer more bone loss, because
the
larger diameter hole required. Thus, slightly increasing the diameter of the
implant root portion is desirable to increase surface area, but this must be
balanced
against the need for as small a root portion as practical, given strength and
other
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considerations. Thus, the preferred diameter is about 3.64mm for the
cylindrical
root portion (including the porous coating).
A further feature of the third embodiment is the formation of a
slight overhang 320, at the interface between the abutment portion and the
root
portion. In this manner a pair of orthodontic wire cutters can be used shown
as
312 in Figure 12, by applying force (arrows 314) below the over hang 320 as
shown in Figure 13, to pry out the abutment from the root portion (arrow 316).
In this sense the small gap between the abutment portion and the root portion
is
like a notch, into which the sharp edge of the wire cutters may be applied, as
shown. In this manner, the abutment is made more easily retrievable, and, as
soon
as the cement bond is broken, the abutment comes easily free as shown in
Figure
14.
To facilitate this feature it is preferred to radius the lower corners
of the abutment portion, as shown, to permit the wire cutters to be inserted
into
the interface and to exert and outward thrust component, isolated on the
abutment
portion, as shown. In this manner the abutment portions are made retrievable,
to
facilitate repositioning the prosthetic to accommodate bite changes and the
like
occurring in the patient. Further, the abutments may be retrieved without
disturbing the bone implant interface.
It can now be appreciated that the method of installing the third
embodiment, while generally similar, is also different from the first two
embodiments. Primarily, the third embodiment is a time saving simpler
procedure. Because the recess formed around the pilot hole is cylindrical, no
extra
drills or drilling steps are required. To implant, one simply forms the pilot
hole,
drills a cylindrical recess with a second drill, to a predetermined depth
corresponding to the depth of the cylindrical root portion, and then inserts
the
implant into the recess. Of course, the cylindrical recess is sized and shaped
to
form a frictional fit to permit initial implant stabilization of the implant
during
bone ingrowth. A healing cap may also be used as previously described.
It will be understood that the third embodiment described above
works in accordance with the same general principles as the previous
CA 02210615 1997-07-16
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embodiments, with the exception that no step or taper is required to press fit
the
implant into the cylindrical recess in the bone. The method is simpler and
less
time consuming, but otherwise the principles are the same. By reason of a
frictional fit, initial implant stabilization is achieved, in a one stage
implant
surgery. A narrow diameter bore is used, to minimize bone disruption during
surgery and to promote good bone growth post surgery. A cylindrical profile
for
the full root portion 18 and the smooth-walled emergent portion 22 maximize
surface area for bonding. Bone resorption is reduced because of the larger
bone
mass remaining post surgery, as compared to other implant profiles which show
larger diameter bone emergent portions.
It will be appreciated by those skilled in the art that the foregoing
description is in respect of preferred embodiments and that various
modifications
can be made to in the invention without departing from the broad scope of the
appended claims. Some of these modifications have been suggested above, and
others will be apparent to those skilled in the art. For example, the head
portion
44, 54 may be angled relative to the key portion 42, 52, respectively, to
allow the
location of the implant to be varied based on site conditions without
displacing the
over denture or bridge. The angle by which the head portion and the key
portion
may be angled is between 15° -35°. Also, the precise dimensions
may be
modified without changing the operation of the invention. And finally, while
the
invention has been described in association with over dentures and bridges, it
will
be appreciated that it can be used to secure other cosmetic devices, such as
artificial ears or eyes where an anchor is necessary in bone.
