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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is in the field of denture retention. More
specifically, the present invention is directed to a connector-support
structure which with or without magnets anchors overdentures to implant
fixtures which are themselves embedded within the jaw bone or tooth root
of a person, and cushions the bone or tooth root from masticatory force
loads generated by the dentures.
2. Brief Description of the Prior Art
Implant fixtures embedded in the jaw bone or in the tooth root, and
connectors removably mounted to the implant fixtures, to provide support
for complete and partial dentures are known in the prior art. The
dentures, which include one or more false teeth, are affixed, usually in a
removable manner, to the connectors. There is a relatively large number of
United States and foreign patent disclosures, articles and publications
which describe various ways for affixing the overlying dentures to the
underlying implant fixtures.
More specifically, the following United States and foreign patents,
articles and publications describe various structures wherein magnets are
employed to attach the removable dentures to the bone- or tooth root
embedded implants: U.S. Pat. Nos. 4,508,507, 4,431,419, 4,626,213,
4,209,905, 4,184,252, 4,214,366, Australian Provisional Patent
Specification titled "Magnet Structure" by A. R. Gillings, French Patent
Nos. 73.12280 and 75 12748, German Published Patent Application No.
2201415, an article titled "Retentive characteristics of different
magnetic systems for dental applications" by Ron Highton et al. in THE
JOURNAL OF PROSTHETIC DENTISTRY Volume 56 pp 104-106, Jul. 1986, an
article titled "A magnetic attachment for overdentures" by H. Sasaki et
al. in THE JOURNAL OF PROSTHETIC DENTISTRY Volume 51 pp 450-455 (1984), a
publication titled "THE USE OF RARE EARTH MAGNETIC ASSEMBLIES FOR
RETENTION OF DENTAL PROSTHETICS" by T. R. Jackson and a publication titled
"MAGNETIC RETENTION UNITS FOR OVERLAY DENTURES" BY B. R. D. Gillings.
U.S. Pat. No. 3,787,975, describes a bone or root canal embedded implant
which utilizes a mechanical device, including a socket and a matching
ball, for removably attaching the denture to the anchor. A device of
related construction, well known in the art under the trade name ZEST of
Zest Anchors Inc. of San Diego, Calif., uses a bone or tooth root embedded
implant fixture, a connector having a transmucosal cuff including an
interior socket, and a keeper member having a ball which fits into the
socket, for retaining dentures in the patient's mouth. The keeper member
utilizes a strong permanent magnet in the denture to hold the denture.
Other references related to dental prostheses or tissue integrated
prostheses include U.S. Pat. Nos. 4,261,350, 4,330,891, British Patent
Specification No. 1291 470 and the article titled "BIOPHYSIKALISCHER
BEITRAG ZUR PROBLEMATIK STARR ABGESTUTZTER FREIENDPROTHESEN" by H. Rehm at
al., DZZ 17 1962 pp 963-975.
It has been recognized in the prior art, that mastication (chewing)
subjects a person's teeth, underlying tooth roots, tissue and bone
structure to significant forces. Normal, healthy teeth and tissue
structure are capable of resiliently yielding under the masticatory
forces, and accommodate and absorb these forces without harmful effect.
For artificial teeth, and for the underlying implanted fixtures and bone
structure, the masticatory forces, however, present a significant problem,
and often cause patient discomfort and deterioration of the fixation of
the implant fixture in the bone or in the tooth root.
The following articles, publications discuss the nature and magnitude of
masticatory forces and their effect on dental prostheses:
"Tissue-Integrated Prosthesis" by Branemark/Zarb/Albrektsson (Quintessence
Books) pages 123-128; "The Bar Joint Denture" by E. Dolder and G. T.
Durrer (Quintessence Books) 1978, pages 95-102; "Precision Work for
Partial dentures" by A. Steiger et al. pages 143-145. The last mentioned
publication discloses that a healthy human tooth has a resiliency of
approximately 0.1 mm in its socket, and that healthy mucous tissue
provides a resiliency of approximately 4 to 20 times greater than the
resiliency of the tooth in the socket. Conventional rigid prosthetic
dental structures, on the other hand, provide virtually zero resiliency.
In fact, and in sharp contrast with the resiliency of natural healthy
teeth, there have only been ineffectual attempts in the prior art to
provide a limited degree of freedom of motion and force absorbing
capability to dental prosthetic structures.
For example, the prior art device known in the art under the ZEST name
employs a socket and ball type attachment of the dentures to the
underlying implant fixture. By its nature, the socket and ball joint
provides a slight degree of freedom of motion and a slight degree of
vertical resiliency.
A publication titled "Stress Absorbing Elements in Implants" prepared by
Core-Vent Corporation of Encino, Calif., discusses stress absorption in
dental prostheses by using plastic screws in the "anchoring" structures,
and by the use of intermediate plastic (polyoxymethylene, DELRIN)
connector plates such as employed by an IMZ dental implant system and
distributed by Interpore International of Irvine, Calif. This publication
actually expresses doubt regarding the practical utility of these prior
art attempts to provide resiliency to dental prostheses.
In light of the foregoing, there is a need in the prior art for connectors
or anchors for dental prostheses, which have significant ability to absorb
masticatory forces, and provide a desirable freedom of motion to the
prostheses. The present invention satisfies this need.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an anchoring or
connecting structure for dental prostheses which absorbs a significant
portion of the masticatory forces normally transmitted from the dentures
to the underlying bone or tooth root.
It is another object of the present invention to provide an anchoring or
connecting structure for dental prostheses which allows limited but
substantially universal motion of the denture relative to the implant
fixture anchoring it to the underlying bone or tooth root.
It is still another and more specific object of the present invention to
provide a connector structure anchoring a denture to an underlying implant
fixture, which absorbs a significant portion of the masticatory forces
transmitted by the denture, and which allows limited but substantially
universal motion of the denture relative to the underlying implant
fixture.
It is yet another and more specific object of the present invention to
provide a shock-absorbing connector structure for anchoring dentures to an
underlying implant fixture, which can be utilized in conjunction with
state of the art implant fixtures.
The foregoing and other objects and advantages are attained by a dental
support structure having a first member which is attached to the jaw bone
or tooth root through an implant fixture embedded in the bone or tooth
root, and a second, keeper member to which a denture is attached. The
second keeper member is removably mounted to the first member. A
resilient, elastic member, such as an O ring, is disposed between the
first member and the second, keeper member to permit limited but
substantially universal motion of the keeper member relative to the first
member, and to absorb forces transmitted by the denture through the keeper
member towards the underlying bone or root structure.
The objects and features of the present invention are set forth in the
appended claims. The present invention may be best understood by reference
to the following description, taken in connection with the accompanying
drawings wherein like numerals indicate like parts.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a first preferred embodiment of a dental
connector of the present invention;
FIG. 2 is an exploded perspective view of the first preferred embodiment;
FIG. 3 is a cross-sectional view of the first preferred embodiment, the
cross-section being taken on lines 3,3 of FIG. 1;
FIG. 4 is a partial cross-sectional view showing the top of a keeper
member, and an interfacing magnet disposed in a denture mountable to the
keeper member, in accordance with a second preferred embodiment of the
present invention;
FIG. 5 is a partial cross-sectional view showing the top of a keeper
member, and an interfacing magnet disposed in a denture mountable to the
keeper member, in accordance with a third preferred embodiment of the
present invention;
FIG. 6 is a partial cross-sectional view showing the top of a keeper
member, and an interfacing magnet disposed in a denture mountable to the
keeper member, in accordance with a fourth preferred embodiment of the
present invention;
FIG. 7 is a cross-sectional view of the first preferred embodiment, the
view showing a resilient O ring member in a compressed state;
FIG. 8 is another cross-sectional view of the first preferred embodiment,
the view showing rocking motion of a keeper member relative to a first,
transmucosal cuff member;
FIG. 9 is a cross-sectional view of a fifth preferred embodiment;
FIG. 10 is a schematic view of the first preferred embodiment carrying a
denture;
FIG. 11 is schematic view of a sixth preferred embodiment, carrying a
denture;
FIG. 12 is a partially exploded perspective view of a seventh preferred
embodiment, and
FIG. 13 is a schematic view of the seventh preferred embodiment, caring a
denture.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following specification taken in conjunction with the drawings sets
forth the preferred embodiment of the present invention. The embodiments
of the invention disclosed herein are the best modes contemplated by the
inventor for carrying out his invention in a commercial environment,
although it should be understood that various modifications can be
accomplished within the parameters of the present invention.
Referring now to the drawing Figures, and particularly to FIGS. 1 through
3, a first preferred embodiment 20 of the dental support structure of the
present invention is disclosed. It should be noted at the outset of the
present description that all of the herein described preferred embodiments
of the dental support structures of the present invention are adapted to
be affixed to implant fixtures of the type which are well known in the
state-of-the art. As is known, such state-of-the-art implant fixtures
usually comprise a titanium body embedded into the jaw bone or into tooth
root of a person. The implant fixtures usually include an internal
threaded opening into which the herein described dental support
structures, or connectors, are mounted. Because the implant fixtures are
state-of-the-art they are shown in the appended drawing Figures only
schematically, for example as item 22 on FIGS. 10-13. Furthermore, as it
known in the art, implant fixtures are implanted into the bone, or tooth
root in a surgical procedure, after which there is a substantial time
period, up to approximately one year, during which a healing process
occurs. It is during this healing process that the implant fixture becomes
embedded and accepted in the bone or tooth root.
Referring again primarily to FIGS. 1-3, the dental support structure or
connector 20, includes a first member 24 which has a downwardly protruding
substantially cylindrical threaded post 26. The threaded post 26 is
utilized to mount the connector 20 to the implant fixture 22. The first
member 24 is called, in accordance with usual practice in the art, a
transmucosal cuff, and this terminology is used henceforth in the present
description. The manner of affixing the transmucosal cuff 24 to the
implant fixture 22 is not critical, instead of a threaded connection the
transmucosal cuff 24 can also be cemented into the implant fixture 22.
The transmucosal cuff 24 includes an internal threaded opening 28. The
threaded opening 28 receives a screw 30 which mounts a second or keeper
member 32 to the transmucosal cuff 24. It will be readily understood by
those skilled in the art that the transmucosal cuff 24 must be made of a
material which is well adapted for implantation into the oral cavity.
Titanium metal, and certain titanium alloys, which per se are well known
in the art, are best suited for this purpose. Accordingly, the preferred
embodiments of the transmucosal cuff 24 of the present invention are made
from titanium or an alloy of titanium.
The keeper member 32 is also shown on FIGS. 1-3. It has a substantially
cylindrical configuration, a hollow interior 34 and a hole or opening 36
in the bottom. A titanium screw 30 fits into the interior 34 of the keeper
member 32, passes through the hole 36 and attaches the keeper member 32 to
the transmucosal cuff 24. Instead of titanium the screw 30 can be made
from other biocompatible materials, however titanium or titanium
containing alloys are preferred.
The keeper member 32 of the first preferred embodiment is made from a
material which comprises a magnetic alloy. Nobel magnetic alloy, such as
cobalt palladium or CM 572 (made by Cendres & Metaux, S.A. Switzerland) is
well suited, and is presently preferred for this purpose. The nobel metals
reduce the possibility of stress and stress corrosion, crevis corrosion,
fretting corrosion, galvanic corrosion, pitting and corrosion fatigue. See
Chapter 1 "Corrosive Response of the Interface Tissue To . . . (certain)
Alloys" in a book entitled "The Dental Implant" by McKenney, Jr. and
Lemons in American Academy of Implant Prosthodonics, copyright 1985
I.S.B.N. 0-88416-491-8.
Although certain improvements are described below in this connection, the
magnetic properties of the keeper member 32 can be utilized, substantially
in accordance with the state of the art to removably attach a denture 38
by means of a permanent magnet to the keeper member 32, as is shown on
FIG. 10. In order to removably mount the denture 38 to the keeper member
32, the denture 38 includes a permanent magnet 39 disposed with open or
closed field magnetic polarity to the magnetic alloy keeper member 32, so
that the keeper 32 strongly attracts the magnet 39 embedded in the
overdenture.
A cap or cover 40 preferably also made of the same magnetic material, such
as Nobel magnetic alloy CM 572, is press fitted into the keeper member 32,
so as to close the opening 34 when the keeper member 32 is assembled to
the transmucosal cuff 24. In an alternative embodiment of the invention,
shown on FIG. 6, the cap or cover 40 has a male threaded shoulder 42 which
is mounted into matchingly threaded opening 28 of the keeper member 32. In
this embodiment, the cap 40 includes a slot 44 to accept a screw driver
(not shown) for assembly and disassembly and for the acceptance of the
Shiner magnetic system (see U.S. Pat. No. 4,626,213).
Returning now again to the description of the first preferred embodiment,
an important novel feature of the dental connector of the present
invention is a resilient, elastic member 46 which is disposed between the
adjoining, interfacing surfaces of the transmucosal cuff 24 and the keeper
member 32. The resilient, elastic member 46, configured substantially as
an O ring, performs important functions in the present invention.
First, the resilient member 46 acts as a shock or energy absorber, to
dampen forces which are generated during mastication, and which are
transmitted from the denture 38, through the keeper member 32 to the
transmucosal cuff 24 and thence to the underlying bone or tooth root. As
it is mentioned in the introductory section of the present application for
patent, substantial forces (100 lbs and greater) are generated during
normal mastication. Whereas normal healthy teeth, gum and bone tissue are
capable of resiliently absorbing these forces, prior art rigid dentures do
not absorb them, with adverse consequences to the patient.
The resilient member or O ring of the herein described preferred embodiment
is preferably made of silicone rubber. It can be made from other resilient
plastic materials, the requirements in this connection are merely that the
material must be compatible with implantation into the oral cavity, and
must provide such resiliency that approximately 0 to 0.4 mm compression of
the O ring occurs during normal masticatory load forces, so that the
keeper member 32 moves within a range of approximately 0 to 0.4 mm
relative to the transmucosal cuff 24.
The screw 30 controls the height of the keeper 32 with respect to the cuff
24. The length of the screw 30 may also vary to provide an additional
selected range of motion. The resiliency of the O-ring 46 may also be
varied for controlling the range of movement in combination with or
independently of the length of the screw 30.
A second function of the O-ring 46 is to permit universal "rocking" motion
of keeper member 32 relative to the transmucosal cuff 24. In other words,
the O-ring 46 functions to permit limited, but universal motion of the
keeper member 32 relative to the transmucosal cuff 24. Simple up-and-down
motion of keeper member 32 while compressing the O ring 46 is illustrated
on FIG. 7 of the appended drawings, whereas "rocking" universal motion is
illustrated on FIG. 8. The herein described preferred embodiments of the
O-ring has a substantially flattened exterior wall 48, so as not to be
pinched as is shown on the drawings.
It is emphasized in connection with the above-noted functions of the
resilient member, O ring 46 in the dental connector structure of the
invention, that these functions and the herein described structure is
significantly different from the functions and structure described in U.S.
Pat. No. 4,204,321. In that prior art patent, an elastomeric O ring is
used in a dental post to apply retentive force and secure a denture to the
post.
In order to disassemble the dental connector of the present invention, the
cap or cover 40 must be first removed to gain access to the screw 30. In
the first preferred embodiment, this can be accomplished by the dentist or
oral surgeon (not shown) strongly pushing down on the keeper member 32
until the head of the screw 30 pushes against and lifts off the
press-fitted cap 40 or the cap may be unscrewed as per FIG. 6. FIG. 7
illustrates the the O ring 46 in a compressed position, and the screw head
approaching the position wherein the cover 40 is about to be touched and
lifted off from the keeper member 32.
It should be understood in connection with the present invention, that the
resiliency of the resilient member 46 may be adjusted to fit particular
requirements of a patient. Furthermore, as it was mentioned above, it
takes substantial time after surgical implantation for the implant
fixtures 22 to become accepted in the underlying bone or tooth root, and
therefore for these fixtures to reach their maximum load bearing capacity.
See the article in CDA Journal, October 1987 by W. Eugene Roberts, D.D.S.,
Ph.D et al. entitled "Bone Physiology and Metabolism". The article
emphasizes the need for stress reduction during the maturation phase of
the healing bone. In light of the foregoing, it is often desirable after
implantive surgery to increase the load only gradually over a period of
several months on the implanted fixtures 22. This can be accomplished in
accordance with the present invention by either gradually changing, after
implantive surgery, the resiliency of the O rings 46, or by using
different lengths of the screw 30 to restrict the compressive travel of
the O ring so as not to exceed a desired load force on the O ring.
The exploded view of FIG. 2 illustrates grooves or recesses 50 disposed in
the respective surfaces of the transmucosal cuff 24 and the keeper member
32, which provide a gland for the O ring 46.
The manner in which the denture 38 is mounted to the keeper member 32 is
not critical for the purposes of the present invention. Although magnetic
mounting, which can be accomplished in accordance with the
state-of-the-art, is preferred, mechanical mounting of the denture 38 to
the keeper member 32 is also possible while practicing the present
invention.
FIGS. 4, and 5 illustrate alternative embodiments with respect to the
manner of magnetically mounting the denture 38 to the keeper member 32. In
the embodiments shown in FIGS. 4 and 5, the cap 40 has convex or concave
curvature respectively, and a permanent magnet 39 of the denture 38 has a
curvature complementary to the curvature of the cap 40.
FIG. 11 illustrates still another embodiment, wherein the denture is
mounted by magnetic means to the keeper member 32, and wherein the second
magnet 39 of the denture 38 has a skirt 52. The skirt 52 surrounds the
upper portion of the keeper member 32 to prevent or limit lateral movement
of the denture 38 on the keeper 32. A small clearance 53 is provided
between the skirt 52 and the top of the keeper 32 to allow the denture to
be readily fitted to the keeper member 32.
The downwardly extending skirt 52 must provide a skirt clearance to the
keeper assembly (32 to 40) to allow insertion of the overdenture. The
downwardly extending skirt 52 can be a part of the original magnet housing
39 or a retrofit to existing magnet housings.
FIG. 9 illustrates yet another embodiment of the dental connector of the
present invention. In this embodiment the keeper member 32 is not made of
a magnetic alloy. Rather it is made from a suitable gold alloy, such as
CERAMICOR. In this embodiment the denture 38 is mounted to the keeper 32
by mechanical means, such as casting a portion (not shown) of the denture
38 about the keeper 32. An annular recess 54 shown on FIG. 9 in the side
wall of the cylindrical keeper 32 of this embodiment serves to locate
during assembly and increase the strength with which the casting (not
shown) around the keeper 32 adheres to the keeper 32.
The embodiment shown on FIG. 9 illustrates yet another novel feature of the
invention. In this embodiment the surface of the head 56 of the screw 30
is curved, opposite to the curvature of the interior surface 58 of the
keeper member 32 so as to minimize the contact area between the screw 30
and adjoining curved surface 58 of the keeper member 32. The just
described configuration facilitates the universal joint type action of the
O ring 46, in permitting facile movement of the keeper member 32 relative
to the transmucosal cuff 24.
Referring back to FIGS. 1-3 and 7 and 8 which illustrate the first
preferred embodiment, the interior surface 58 of the keeper member 32 is
curved in the same manner as in the embodiment illustrated in FIG. 9.
Although the adjoining surface of the screw head 56 is flat in this
embodiment, still, only a relatively small contact area (theoretically
only a contact line) exists between the screw 30 and the keeper member 32.
This is an advantage, because the contact is between two different metals
(the screw 30 is titanium, the keeper member 32 is a magnetic alloy), so
that minimal contact is desirable to minimize possible corrosion of these
components.
The fact that the transmucosal cuff 24 and the keeper member 32 are
separated from one another by the resilient member 46 in accordance with
the invention, is a further advantage over prior art, in that the
separation of these components further avoids undesirable corrosion when
these two parts are made from different metals.
In alternative embodiments (not shown) the surface of the screw head 56
used in magnetic keeper members 32 also has a curvature of the opposite
kind of the curvature of the interior surface 58 of keeper member 32. This
further minimizes contact between the titanium screw and the magnetic
metal keeper 32, and thereby further minimizes corrosion.
Referring now to FIGS. 12 and 13, yet another preferred embodiment 60 of
the dental connector or support structure of the present invention is
shown. This embodiment is designed to be analogous to the dental connector
commonly known in the art under the ZEST mark, and is capable of being
mounted into the same type of implant fixture 22 as a ZEST connector.
The embodiment 60 includes a transmucosal cuff 24 having a cavity 28 which
forms a socket 62 for a ball type end 64 of a post 65 of a matching keeper
member 32. The ball type end 64 includes mechanically extended retainer
balls 66. A portion 68 of the post 65 is conical, and there is a
cylindrical portion 70 above the conical portion 68. An annular recess 72
is disposed in the cylindrical portion 70 to serve as a gland for the
resilient O ring member 46. A top part 74 of the keeper member 32 accepts
a strong permanent magnet to attach a denture (not shown on FIGS. 12 and
13), in the manner well known in the art. An undersurface 76 of the
magnetic top part 74 of the keeper 32 is also curved to form a gland to
accommodate the O ring 46. The function and purpose of the resilient O
ring member 46 in this embodiment is substantially the same as in the
other above-described embodiments with the ability to control the
resiliency by changing the O-rings.
Several modifications of the above-described invention may become readily
apparent to those skilled in the art in light of the disclosure.
Therefore, the scope of the present invention should be interpreted solely
from the following claims, as such claims are r | | |
