Note: Descriptions are shown in the official language in which they were submitted.
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D~T~L I~IPL~T
This invention relates to dental implants and
more particularly to post stem dental implants or
supportin~ artificial teeth.
B~CI~Gr~OUND OF TH~ V~NTIO~
One type of dental implant has a post stem
integrally attached througll a short neck to a head for
receivin~ a c~ental appliance, such as an artificial
tooth. The post is inserted into a relatively aeep
socket or os~eotomy formed in the alveolar bone so ~hat
the neck extends throu~h the gingiva while the head
protrudes abGve the surface of the ~ums. Typically,
post stems have uneven outer surfaces for fixation
within the alveolar bone through tissue ingrowth. ~n
example of a dental implant having a post stem with an
undulatin~ surface i3 found in U.S. Patent IJo. ~,195,409.
~ s a means of providin~ immediate
immobilization of a dental implant within the alveolar
bone, it is common practice to slightly undersize the
socket and to force the stem thereinto. Unfortunately,
the success rate of post stem dental implants has been
less than would be desirable. The porous alveolar bone
is particularly subject to deterioration, and i~ is
believed that bone c]amage incurred by forcing an
oversized stem into a narrow socket may accelerate bone
deterioration. I~ence, while forcin~ an oversize stem
into a narrow socket may provide immecliate
immobilization, the fixation through tissue ingro~l~h,
necessary for long-term stability, may not occur.
Subsequent bone deterioration may actually result in
loosening of the implant, and if this occurs, the
implant may have to be removed.
~ nother cause of failure of post stem implants
is the imprecision of the clrilling operations ~hich form
the socket. Frequently, post stems are tapered for
insertion into tapered soc~ets. Such sockets are j~
~Z:17367,
com~only formed by a succession of drillin~s with
several clrill bits o~ clifferent diameters. This process
is slow and may result in burninc3 of the bone tissue and
other trauma. Frequently, due to imprecise ~rillinc3,
tlle result of the sueeessive drillin~s is not the
desired undersized soeket, but an oversized socket in
whieh the implant fits loosely. ~n implant which is not
immediately immobilized usually shifts ~hen subjected to
the stresses of mastieation eausing failure of ~he
implant.
The need eontinues for dental prostheses which
may be implantecl with minimal disruption to the alveolar
bone into whieh they are inserted and whieh have no
mobility in the socket immediately after implantation.
SUI~I~P~Y OF TJIE I~EI~TIOM
~ clental implant and methocl of insertion
provide for immediate loel;in~ and immobilization of the
implant into a preparecl socl;et. The implant has a head,
a neck and a stem, ineluding an intermecliate se~ment
havin~ an ~Ineven outer surface with radial extremities
that lie alon~ the contour of a ri~ht eireular eone and
a terminal segment havinc~ an outer surfaee with radial
extremities that e~tend beyond the eontour of the ri~h~
eireular eone. ~ soe~et is clrilled into the alveolar
bone with a drill bit matehecl in taper to the
intermediate se~ment, that is, the bit has ecl~es whieh
lie alonc3 the ri~ht eireular eone. The implant is
pressed into the prepared soeXet until its end se~ment
deforms the alveolar bone at the deep end of the soel;et
lockin~ the implant in plaee with the radial e~tremities
of the intermediate se~ment in firm surface contaet with
the siclewall of the soelcet fully immobilizin~ the
implant.
BRIEF DESCRIPTION OF THE Dr~WIMGS
-
FIGURE 1 is a perspeetive view of a post t~pe
dental implant embodyinc3 various features of the
invention;
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FIGURE 2 is an enlar~ed elevation view of the
post stem of the implant of FIGUR~ 1 rotated 30 with
respect to FIGURE l;
FIGURE 3 is an elevation view of the implant of
FIGURE 1 implanted in an osteotomy formed in the
mandible;
FIGURE ~ is an elevation view of a tapered
drill bit for forming the osteotomy that receives the
post of the i~plant;
FIGUR~ 5 is a perspective view of a try-in
device for use in implanting the dental implant of
FIGURE l; and
FIGUP~F, 6 is a perspective view of an
alternative embodiment of the dental implant of FIGUR~ 1.
DET~IL~D D~5CRIPTION OF TEIE PR~FER~ED ~MBODIl1ENTS
Illustratcd in FIGUR~J 1 i5 a dental im~lant 20
having a post stem 22 integrally attached through a
short nec~ portion 2~ to a head 26 or receiving a
dental appliance 28 (FIG 2). The implant is shown in
the uprigllt orientation and will be described herein
according to its implantation in the mandible in this
upright orientation, understanding that the implant is
inverted if it is implanted in the maxillia. The
precise configuration o the implant 20 varies according
to the location of insertion within the mouth, and the
em~odiment of FIGURE 1 is particularly designed for
supporting an artificial molar 28.
The head 26 has a configuration adapted ~or
receiving a standard dental appliance, and herein, the
head is in the shape of a truncated cone tapering
towards its upper end. Preferably the head is no
greater than 7 mm high so that it will accept any dental
appliance without in situ reduction of the head. The
nec}; 2~, which extends through the gingiva 25 when the
implant 20 is surgically inserted, consists of a groove
27 between the head 26 and the post 22.
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~ s a means to provide for fixation of the stem
22 within the alveolar bone 32 throu~h tissue ingrowth,
the post 22 has an unAulating configuration from end to
end providing a plurality of annular ridges 34
alternating with a plurality of annular grooves 36. ~t
least four and up to twelve ridges 34 are provided
depending, in part, on the length of the post 22. It is
intended that after the implant 20 is inserted into an
osteotomy or soc]cet 38, tissue will grow into the
~rooves 36 preventin~ displacement of the stem 22 by
interfering with the rid~es 34.
In the illustrated embodiment (see FIG. 2), the
surfaces of the ridges 34 and grooves 36 in an axial
direction are curved, and the concave radius of
curvature Rl of the grooves 36 is substantially greater
than the convex radius of curvature R2 of the ridges 34
whereby the grooves have a width (I~Jl) about twenty-five
to about one hundred and fifty percent greater than the
width (1~2) of the ridges in the axial direction.
~lthough, this repreesents the preferred embodiment, in
certain instances the raAii (Rl, R2) ancl/or the widths
~ 2) of the rid~es and grooves will be similar. The
diameter Dl of the post 22 at the depth of each groove
35 is between about 50 and about 80 percent of the
diameter D2 of the stem at the peaks of next lower
adjacent ridge 34.
The post 22 has a generally tapered
configuration for insertion into a tapered socket 3~3
that narrows towards its deep end 39. The post has a
terminal segment 41 opposite the head 26 and an
intermeAiate segment 43 between the terminal segmenc and
the nec]c 24. The ridges 34 in the intermediate segment
43, successively decrease in diameter towards the
terminal end. To provide for contact of the ridges 34
with a uniformly tapered socket, the ridges (with the
exception of the terminal end ridge 34z) have diameters
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such that they are mutually tangential to the contour of
a right circular cone 44, (represented in dot-dash in
FIGUR~ 2) which can be drawn along the post tapering
toward the terminal end. The side of this cone tapers
towards its axis 45 at an angle ~ of between about 2.5
and about 10.
In accordance with the present invention, the
terminal segment 41 has an outer surface with radial
extremities that extend radially outward beyond the
contour of the right circular cone 44 along which the
radial extremities of the surface of the intermediate
segment 43 lie. Thereby, when the post 22 is pressed
into a socket 3~ in the alveolar bone that has the
configuration of a truncated portion of the riqht
circular cone 44, the terminal segment 41 deforms the
alveolar bone at the deep end 39 of the socket, and the
intermediate segment is in firm surface contact with the
sidewall of the socket, whereby the implant 20 is locked
into and fully immobilized in the socket.
The terminal segment 41 comprises the terminal
ridge 34z which has a diameter greater than the diameter
which would make the terminal ridge tangential to the
right circular cone 44, and generally the diameter of
the terminal ridge is between about .04 and about .12mm
greater than the diameter that would make the terminal
ridge tangential to the cone. The post 22 is adapted
for insertion into a socket 38 formed with the
configuration of a truncated portion of the right
circular cone 44 to a depth which permi~s full insertion
of the post stem~ Only the terminal ridge 34z must be
forced into such a socket 38, and when the stem 22 is
forced into the socket so that the terminal ridge is
positioned closely adjacent to the deep end 39 of the
socket 3~, the remaining ridges 34 are in firm surface
contact with the siclewall of the socket but do not
deform the bone. Damage to the alveolar bone 32
~21736i.7
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resulting fro~ forcin~ the post into the alveolar bone,
therefore, is limited to a re~ion adjacent to the deep
end 39 of the socket.
~s a means to prevent rotation of t~he implanted
dental implant 20 within the socket 38, it is preferred
that at least a portion of the implant stem 22 have a
non-circular cross section. Ilerein, the lower end of
the stem is made non-circular in cross section by the
inclusion of vertical rows of fins 48 which extend
between adjacent rid~es 3~. In the preferred
embodiment, three rows of fins 48 are provided spaced
120 from each other so that one of the rows of fins 4~
is likely to be implanted generally perpendicular to the
line of teeth as shown in FIG. 3, whereby this row of
fins will approximate a vertical plate in either the
buccal or the lin~ual direction upon implantation,
increasing anti-rotational stabilization. The fins 48
also serve to increase the overall strength and
stability of the implant 20. Although adaitional rows
of fins could be provided, such additional fins would
reduce the volume of recess provided by the ~rooves.
The illustrated fins ~8, as best secn in FIGUR~
2, have slightly concave outer surfaces 49; however, the
depth of these surfaces relative to the cone ~4 is
substantially less than the depths of the corresponding
~rooves 36, i.e., typically less ~han about one-third of
the depth of the grooves, whereby sufficient growth of
tissue occurs inward of the outer fin surfaces ~9 to
prevent implant rotation.
Preferably, no fins are provided along the
first groove 36' below the neck 24 so that uppermost
ridge 3~b to which fins ~8 are associated will be
implanted at least about 2 mm. below the upper surface
50 of the alveolar bone 32. Fven if si~nificant
recision of bone and gin~iva takes place over time, the
patient will still be able to clean around the smooth
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groove 36' above the rows of fins 4~.
The implant 20 is formed as a unitary structure
from a strong biocompatible material, such as certain
metals or ceramics or fine grained, high density
5 graphites. Suitable metals include titanium, tantalum
and chromium-cobalt alloys, such as those 501cl under the
trademarl~ Vitallium. ~ suitable graphite material is
sold under the traclemarl~ Poco Graphite. A suitable
ceramic material is aluminum oxide. Typically, ceramic
10 implants are used for the more cosmetically important
implants, such as those used to support artificial
incisors.
To render the implant 20 fully biocompatible,
it is preferred that an isotropic carbon coating 51
15 (FIG.2) is applied to at least those surfaces of the
implant which contact body tissues. The carbon coating
for the graphite structure 51 may be pyrolytically-
deposited carbon, such as that sold under the trademark
Pyrolite, the carbon coating for the metal and ceramic
20 structures may be vapor-deposited carbon, such as that
sold under the trademark Biolite. These carbon coatings
are not recognized as foreign by the body and do not
provolce rejective reactions. The layer of carbon 51 is
thick enough to be impervious to liquids, but not so
25 thick that it is likely to crack, and the carbon coating
is typically, between about 0.1 and about 1.0 micron
thicX for the Biolite coating and about 0.5mm thick for
the Pyrolite coating. The Bacon ~nistropy Factor is
about 1.3 or lower, and the density is at lcast 1.5
30 g/cc. In addition to rendering the implants
biocompatible, such a carbon coating 51 may have a
porous surface whereby there is some ingrowth of tissue
fibrils into the carbon surface.
For implants 20 which support artificial
35 molars, it is generally most convenient to provide a
J uniform carbon coating 51 on the entire implant 20
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including the head 26. Where a ceramic implant is
provided for supportin~ a more visible artificial tooth,
in the case of the vapor deposited coatings it is
preferred that the carbon coating not be applied to the
head 26 so that the coating does not produce a "shadow"
in the artificial tooth.
Carbon coating 51 applied to the post 22 i5
unpolished so that the applied porous coatin~ will
promote the ingrowth of tissue fibrils. If the head '6
is coated, the surface of the carbon coatin~ is
unpolished to promote good bondin~ of an adhesive used
to apply the dental appliance 2~. On the other hand,
the surface on the nec]~ 2~ is preferably polished so as
to be non-irritating to the gingiva 25 through which the
neck passes.
Rapid and accurate prepara~ion of a tapered
socket 38 i5 accomplished, in accordance with the
invention, in a two drilling operations using first a
pilot and then a tapered drill bit ~6, such as that
shown in FIGUR~ ~. ~ drill bit ~6 is provided for each
size implant 20 having the exact taper of the implant
20; tha~ is, the edges 47 of the drill bit lie along the
contour of the right circular cone 44 to which the
non-terminal ridges 34 of the implant 20 are mutually
tan~ential. With the patient anesthesized and
immobili7ed, the gingiva 25 is cut to expose the
alveolar bone 32, and the socket 3~ is drilled into the
alveolar bone with the implant-Matched bit ~6 to a depth
appropriate for the length of the post 22.
~fter debris is washed from the socket 3~, the
socket is checked for size with a metal try-in device
having an insertion portion 50 in the shape of a
truncated cone (matched to the shape of the implant and
drill bit) and a handle portion 52. If the try-in
device 48 fits loosely, the socket 3~ may have to be
redrilled with a slightly lar~er bit 46 and a slightly
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g
larger implant 20 used. ~lost times, however, the final
drillin~ provides a suitable socket 38, the limitea
arilling incurring far less bone burning and trauma than
the severe drillings which are frequently used to
provide non-cylinclrical tapered osteotomies. The
tapered drill bit 56 is adapted for relatively slow
speed drilling, i.e., less than about ~00 revolutions
per minute, minimizing drill burn damage to bone tissue.
necause the socket 38 is in the shape of the
cone 4~ to which the non-terminal ridges 3~ are
tangential and because the terminal ridge 34z ex~ends
radially outward beyond this cone, the insert 20 does
not slide freely to the full depth of the soc]~et.
Ilowever, the matched tapers of the post 22 and soclcet 38
allow the post to slide a substantial distance inward
before the terminal ridge 34z encounters resistance to
further insertion from the side of the socket.
Full insertion of the implant 20 is effected by
forcing it the remaining distance into the socXet 38.
This may be accomplished ~lith thumb pressure by the
dental surgeon, the terminal ridge 3~z being forced into
the porous alveolar bone 32. Pressing the terminal
ridge into the bone tissue locks the implant into the
socket, the terminal ridge 34z slightly deforming the
alveolar bone so that the implant migllt only be
extracted with difficulty using pliers. At the same
time, the remaining ridges 3~ are brought into firm
surface contact with the remainder of the socket 38,
thereby fully immobilizing the implant 20. I1ith the
3~ implant 20 in firm surface contact with the tapered
socket 38 in several locations, i.e., along each ridge
34, the implant is not driven further into the alveolar
bone by the stresses of mastication. Accordingly, very
soon after implantation, the dental appliance 28 may be
secured to the head 26 permitting the implant 20 to be
used for mastication.
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A typical molar implant 20 will now be
described in ~reater detail. The implant 20 is formed
of a graphite substrate having a uniform pyrolytic
carbon coatin~ 0.5 mm thick. The total height Oc the
implant is 20 mm., the head 26 comprising about 4 mm. of
this height and the neck 24 another 2 mm. The post 22
has six ridges 34, the peaks of each spaced about 2 mm.
apart. The radius of curvature of the ridges 34 at
their peaks is about 0.75 mm whereas the radius of
curvature of the ~rooves 36 at their clepths is about
0.5 mm. The longitudinal distance (1/2l~J1 plus
1/2W2) from the peaks of the ridges 3~ to the depths
of the grooves 36 is about 1.~5 mm. The non-terminal
ridges 34 are tangential to the contour of a right
circular cone 44 having a side that an~les 10 relative
to its axis. The uppermost ridge 34a has a peak
diameter D2 of 5 mm. and the ridge 34y adjacent to the
terminal ridge 34z has a peak diameter D2 of 3.8 mm.
With this taper, the terminal ridge 34z would have a
peak diameter of about 3.6 mm if it were to be
tangential to the cone 44 to which the other ridges are
tangential; however, it has a peak diameter D2 of 3.7
mm. or about 0.1 mm. greater than it t~ould have if it
were tangential ~o the right circular cone.
To insert the implant 20, the gingiva 25 around
the region of tooth extraction is cut to expose the
alveolar bone 32, and a socket 38 is drilled into the
alveolar bone generally following the line of the root
of the extracted molar. The socket 38 is formed to a
depth of 14 mm. using a drill bit 46 precisely matched
in taper to that of the implant 20. ~fter examining the
socket 3~ with a try-in device 48, the implant 20 is
inserted as far as it will go freely, i.e., to a depth
of about 11 mm. Downward pressure on the head 26 forces
the implant 2 mm. further into the socket 38 leaving
about 1 mm of free space therebelot~, the terminal ridge
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34z being forced into the alveolar bone tissue and
slightly deforming the alveolar bone at the deep end 39
of the soc~et. Full insertion of the implant 20 brings
the remaining rid~es 3~ into firm surface contact wi~h
the side wall of the socket 3~3 fully and immediately
immobilizing the implant 20.
The ~in~iva 25 is then sutured to fit closely
around the neck 2~. After a period of about 5 to 20
days, fixation is sufficient to permit the application
of a dental appliance 2~ in the form of an artificial
crown or bridge to the head 26 of the implant, and at
this time, the patient has full use of the implant for
mastication.
Illustrated in FIGUR~ 7 is an alternative
embodiment of an implant 20', which may be used for
replacement of an incisor. The post stem 22' is th-lnner
and considerably shorter than the post stem of the molar
implant 20, and the head 26' is also considerably
thinner. The post 22' has only four ridges 34' (a
terminal 342' and three non-terminal ridges). The
implant 20' is formed of aluminum oxide, and the nec~
24' and post 22' are coated with a .5 micron layer of
vapor-deposited carbon 51', while the head 26' is left
uncoated.
~hile the invention has been described in terms
of certain preferred embodiments, modifications obvious
to one with ordinary skill in the art may be made
without departing from the scope of the invention. For
example, the ridges may be provided by cutting grooves
into a smooth outer surface leaving rid~es that have
flat rather than rounded surfaces. The invention is
intended to include implants having posts with uneven
outer surfaces otherwise configured, providing that the
radial extremities of the surface lie along the contour
of a right circular cone except in a terminal portion
where the radial extremities extend radially outward of
the contour of the right circular cone.
