U.S. patent number RE31,948 [Application Number 06/692,500] was granted by the patent office on 1985-07-16 for dental post and wrench therefor and method of restoring bulk to a tooth root therewith.
Invention is credited to Allan S. Deutsch, Barry L. Musikant.
United States Patent |
RE31,948 |
Deutsch , et al. |
July 16, 1985 |
**Please see images for:
( Certificate of Correction ) ** |
Dental post and wrench therefor and method of restoring bulk to a
tooth root therewith
Abstract
An improved unitary bulk restoring dental post having a stem of
substantially parallel threaded sides divided along its length into
separate legs for threaded insertion into a tooth root canal by a
wrench that applies a predetermined torque to the dental post to
thread it into the tooth root for crown restoration.
Inventors: |
Deutsch; Allan S. (New York,
NY), Musikant; Barry L. (New York, NY) |
Family
ID: |
26982973 |
Appl.
No.: |
06/692,500 |
Filed: |
January 18, 1985 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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321440 |
Nov 16, 1981 |
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Reissue of: |
568082 |
Jan 4, 1984 |
04480997 |
Nov 6, 1984 |
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Current U.S.
Class: |
433/221 |
Current CPC
Class: |
A61C
13/30 (20130101) |
Current International
Class: |
A61C
13/225 (20060101); A61C 13/30 (20060101); A61C
005/04 () |
Field of
Search: |
;433/225,221,174,175
;411/119,422 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Peshock; Robert
Attorney, Agent or Firm: Bauer & Amer
Parent Case Text
This application is a continuation-in-part of co-pending
application Ser. No. 321,440, filed Nov. 16, 1981 and now
abandoned.
Claims
What is claimed is:
1. A dental post for thread cutting insertion into a tooth root
comprising
a stem having a space defined therein dividing a lengthwise portion
of said stem into a plurality of relatively spaced legs,
self-tapping threads on said legs and stem to cut and form a thread
in the tooth root as said stem is threadedly inserted
thereinto,
said legs being movable relative to each other at said space during
the thread cutting insertion of said stem into the tooth root to
absorb the application of at least lateral fracturing forces to the
walls of the tooth root,
and said space including vent means extending from the insertion
end of said stem to at least beyond the tooth root to vent the
insertion end of said stem to the atmosphere to vent the build-up
of tooth fracturing forces from between said stem and tooth root
during the threading of said stem into the tooth root.
2. A dental post as in claim 1,
said space including a slot defined in and extending diametrically
through said stem. .[.3. A dental post as in claim 2,
said space including a groove coextensive with and forming a
vent
continuation of said slot..]. 4. A dental post as in claim 1,
anchor means unitary with said stem for anchoring a dental crown
thereto.
A dental post as in claim 1,
a body of greater width than said stem unitarily joined coextensive
with and between said stem and anchor means and having a
self-tapping thread
coextensive with said threads on said legs and stem. 6. A dental
post as in claim 5,
said body having a portion adjacent said stem and being rounded to
obviate fracture of the tooth during engagement with the same when
the stem and
body are threaded into the tooth root. 7. A tooth root as in claim
4,
said stem being enlarged along the length thereof between said legs
and
anchor means. 8. A dental post as in claim 4,
said self-tapping threads extending between an entry portion of
said stem
and said anchor means. 9. A dental post as in claim 4,
said anchor means extending in a direction opposite said stem and
having a plurality of relatively spaced means to which a dental
crown is cemented.
0. A dental post as in claim 1,
said walls of said stem being substantially parallel and of a
substantially
continuous diameter. 11. A dental post for use in a tooth root
canal comprising
a stem having a lengthwise extent for insertion into a tooth
root,
a space including a slot in a portion of the lengthwise extent of
said stem extending from the insertion end of said stem to form a
plurality of relatively spaced movable legs,
a tooth root cutting thread on said stem extending about and along
said legs to facilitate the thread cutting insertion of said
lengthwise extent into the tooth root by cutting the tooth root and
forming therein a thread corresponding to the cutting thread of
said stem during the threading insertion of said stem into the
tooth root,
said legs, moving relative to each other during the threading
insertion to absorb forces that result from the cutting and forming
of the threads in the tooth root to prevent the application of such
forces to otherwise fracture the tooth root,
and said space venting hydrostatic forces in the tooth root to the
atmosphere to avoid the application of such hydrostatic fracturing
forces
to the tooth. 12. A dental post as in claim 11,
said stem being substantially circular and of the same diameter
throughout
the insertion length thereof. 13. A dental post as in claim 11,
anchor means on the distal end of said dental post opposite said
stem for
anchoring a dental crown thereto. 14. A dental post as in claim
13,
an enlarged body on said stem between said stem and anchor means
and having a continuation of said cutting thread thereon. .[.15. A
dental post as in claim 11,
the insertion end of said legs being tapered to correspond to the
taper of the tooth root canal to provide for bulk support thereat
and at least a minimum of tooth thickness therebetween for
sufficient bulk and strength to resist fracture of the tooth
thereat..].
Description
This invention relates to an improved dental post for use in a
tooth root canal to restore bulk to the tooth root for crown
restoration.
Dental posts that were made in the past were generally of solid
unyielding construction. Dental posts exemplifying such
construction were made with tapered threaded surfaces as in the
U.S. Pat. No. 4,239,489 to Ellman. Other posts were made with
surfaces of continuous diameter substantially fully along their
lengths as exemplified by the U.S. Pat. Nos. 3,524,255 and
3,656,236 to Kurer and also U.S. Pat. No. 3,861,043 to Lieb. Some
dental posts even suggested a slot along the length of the side
thereof as in the U.S. Pat. No. 644,804 to Justi. The U.S. Pat. No.
838,296 to Best and the aforenoted patent to Ellman disclose hollow
posts. The U.S. Pat. No. 4,234,309 to Sellers exemplifies the
teaching of the combination of a wrench for use with a dental post,
while the Swiss Pat. No. 562,605 is substantially to the same
effect wherein the threads on the dental post stop short of the
leading end of the post where the greatest retentive force is
achieved. Simmons U.S. Pat. No. 1,524,409 teaches corrugated forked
members each of which is non-threadedly implanted in a separate
bifurcation of a dental root.
The teachings of the dental post of the prior art are that when the
post is threaded into the root canal of the tooth, the forces
applied by the thread of the post against the engaging walls of the
tooth exert outward expansive forces to the tooth root and that, at
times, cause the same to fracture. Fractured teeth are irreparable
and, therefore, it is important to prevent the fracture of the
tooth root during the threading application of the dental post
thereinto, and even during the subsequent use of the tooth after
the dental post and crown have been assembled to the root.
Dental posts of the type disclosed in the prior art have also
resulted in the fracture of the tooth root by reason of lateral
forces and stresses applied to the post during mastication.
Prior to the present invention, dental students and practicing
dentists and especially specialists in the art of endodontics as
well as teachers, professors, researchers and writers were taught
and continue to teach that a dental post must be rigid and
inflexible. Because of such teachings prior to the present
disclosure, it was believed that when a flexible or non-rigid
dental post was implanted in a tooth root canal, it would not
provide the required rigidity and support to the tooth that the
tooth needs to resist the stresses and forces to which it is
subjected.
The aforementioned problems of the prior art dental posts are
solved by the present invention. The present invention provides a
dental post that generates its own thread as it is threadedly
inserted into the tooth root canal and because its relatively
spaced threaded legs move radially to absorb the self-tapping
threading torque and other forces it prevents the application of
such forces and stresses to the walls of the tooth root so as to
permit the dental post to be threaded thereinto without fracture to
the tooth. While the dental post taps and is threaded into the
tooth, it is anchored by cement applied to the root canal so as to
prevent the occurrence of anti-rotational or unthreading forces
that might normally tend to cause the post to unthread from its
seat in the root of the tooth. Such anti-rotational or unthreading
forces are countered by the normal radial expansion and tangential
movement of the threaded legs of the dental post into tighter
frictional wedging engagement with the wall of the tooth root
canal. They are further prevented by the cement that anchors into
dentinal wall irregularities and in the slot between the legs.
Further, displacement and venting of the cement, debris, fluids and
build-up of hydrostatic forces from between the post and the root
canal is provided for.
The above description, as well as further objects, features and
advantages of the present invention, will be more fully appreciated
by reference to the following detailed description of a presently
preferred, but nonetheless illustrative, embodiment in accordance
with sthe present invention when taken in conjunction with the
accompanying drawings wherein:
FIG. 1 is an enlarged plan view of a dental post constructed
according to the invention;
FIG. 2 is a perspective view of a shock absorbing element for use
with the dental post of FIG. 1;
FIG. 3 is a perspective view of the dental post of FIG. 1 and shown
in combination with a torque wrench according to the invention;
FIG. 4 is an enlarged plan view of another embodiment of the dental
post;
FIG. 5 is a vertical cross section of FIG. 3 taken substantially
along lines 5--5 thereof;
FIG. 6 is an enlarged perspective view of another dental post;
.Iadd.and .Iaddend.
FIG. 7 is a smaller scale plan view of a dental post of the
invention threaded in a tooth root and crown thereon.[.;.]..
.[.FIG. 8 is an enlarged plan view of another dental post
constructed according to the invention;.].
.[.FIG. 9 is a view of the distal or anchoring end of FIG.
8;.].
.[.FIG. 10 is a cross section of FIG. 8 along lines 10--10;.].
.[.FIG. 11 is a cross section of FIG. 8 along lines 11--11;.].
.[.FIG. 12 is a cross section of FIG. 8 along lines 12--12;
and.].
.[.FIG. 13 is a plan view of the dental post of FIG. 8 threaded
fully into a tooth root..].
Referring now to FIGS. 1, 2 and 3 of the drawing, the dental post
there illustrated is generally identified by the numeral 10 and
comprises a stem 12 formed unitarily with a body 14 and a crown
anchoring means generally identified by numeral 16. The stem 12,
body 14 and crown anchoring means 16 all are integrally connected
together and formed as a unitary structure with a thread 18
provided on the stem and body. Hence, although the parts are
separately identified, none of them is intended to be normally
capable of separation from the other.
In the event the stem 12 is of an elongated length that is greater
than that of the length of the root canal into which the same is
adapted .[.to top a thread and.]. to be threadedly inserted, it may
be cut short .[.at its apical or insertion end.]. to the length of
the root canal by a dental diamond wheel. After pulp is removed
from the root canal 19 and the canal is obturated, it is reamed to
a diameter corresponding to that of the stem wall 12, but left
unthreaded.
The stem 12 is divided or separated into a desired plurality of
legs exemplified in the drawing by the two legs 20 and 22
relatively spaced by a through space or slot 24 that extends fully
along the length of the stem and therebeyond into the body 14 to
terminate in an enlarged curved opening 26. By providing the end of
the slot 24 with the curved termination 26, the same obviates the
possibility of fracture occurring at the closed end of the slot 24
when compressive forces are applied to the legs 20 and 22 in a
manner to be described.
Not only does the enlarged termination 26 of the slot 24 eliminate
the possibility of fracture of the dental post 10 at the end of the
slot, it also provides a means by which the legs 20 and 22 of the
stem of the post are permitted to flex and move relative to each
other so as to permit the same to collapse toward each other in a
radial direction and to skew arcuately and move tangentially
relative to each other. Thus, the connection between the legs 20
and 22 afforded at the surface surrounding the enlarged excavation
or termination end 26 of the slot functions as a spring-like joint
about which the legs flex and yield.
As will become apparent, the space of the slot 24 provides room
sufficient to permit the legs 20 and 22 to move radially and
tangentially toward and away from each other. It also serves to
permit the legs to absorb radial forces that are applied to the
legs when the same are threaded into the root canal 19 of the tooth
root 25. The ability of the legs to flex and move relatively
radially and tangentially toward and away from each other enables
them to create and form their own thread and to conform to the
irregularities of the thread 18 they generate in the root canal 19.
This movement permits the legs to absorb stresses and forces that
would otherwise be applied to the walls of the root canal 19 to
cause the tooth 25 to fracture in response thereto.
As will also become apparent, the lengthwise extent of the space or
slot 24 between the legs 20 and 22 terminates at a point 26 that is
within the body 14 and provides a unique advantage over the prior
art. The space of the slot 24 affords a vent for cement and dental
debris and releases hydraulic and pneumatic forces that normally
tend to build up beneath and about the dental post 10 as the same
cuts its own thread and is threaded with cement into the root canal
of the tooth. The space of the slot 24 that enables relative
movement of the legs, and being longer in length than the stem 12,
now effects a path of escape from the bottom of the root canal 19
of the tooth 25 and from beneath the leading or insertion end of
the step 12 upward to the surrounding atmosphere. The space 24
enables accumulation of the debris, air, fluids and gases therein
and to exhaust the same from the canal 19 without damage to the
tooth root.
The thread 18 of the stem 12 extends for the full length thereof
and for the full length of the larger widthwise dimensioned body
14. The body 14 may have its lower end 28 tapered or curved in the
manner as illustrated in FIG. 1 so as to permit the same to conform
substantially to the taper or curve of the complementary
countersunk tooth root 25 into which the stem and body are to be
threaded. Thus, when the stem 12 and body 14 are fully threaded
into the tooth root canal 19, the tapered or curved end 28 of the
body 14 will engage the inner countersunk surface of the tooth to
fit and seat conformingly thereagainst in a non-stressing manner.
The larger threaded body 14 fits snugly within the countersunk
coronal aspect to provide a full and larger wall-to-wall surface
retentive engagement therewith. This avoids the application of
lateral outward stressing forces against the engaged surface of the
tooth root 25 that might otherwise tend to fracture the tooth when
so engaged by prior art dental posts.
Although it has been found in practice that the conforming shape 28
of the body 14 avoids fracture of the tooth root when the same
engages therewith, it is within the contemplation of the invention
that an elasticized washer or seal 30 shown more clearly in FIG. 2
may be utilized with the dental post 10. The washer or seal 30 may
be made of any desired elastic or yieldable material, as silastic.
When the washer 30 is threaded upward along the threads 18 of the
stem 12, it stops in its abutment with the underside of the body 14
adjacent to the curved or tapered surface 28 thereof.
When the stem 12 and body 14 are threaded into the tooth root canal
19 to their full extent thereof, the washer 30 is compressed in its
engagement within the coronal aspect of the tooth root 25 to form
an air-tight seal between the tooth root and the surface 28 of the
body 14. When so engaged and compressed, it also functions as a
shock absorber to resiliently absorb the stresses and forces that
are otherwise applied during the threading of the tooth post 10
into the tooth root canal 25. After the post 10 is threadedly
implanted in the tooth root canal 19 and a crown 31 is built and
anchored about the root and about the anchoring portion 16 of the
dental post 10, the sealing washer 30 functions to absorb the
stresses and forces that are applied to the crown 31 and to the
tooth root 25 by way of the dental post 10 during mastication and
other grinding movements of the tooth.
The washer or seal 30 may be omitted from the dental post 10 in
certain instances when the seat and fit effected between the body
14 and the root 25 is deemed sufficient and adequate without it.
Under other conditions of use it may be desirable to include the
washer 30 to provide for the effective seal and force
absorption.
After the post 10 is securely threaded within the tooth root 25, it
provides sufficient restoration of bulk to the tooth root to enable
a crown to be restored to the tooth root about the anchoring means
16. The anchoring means hereshown is generally identified by the
numeral 16 that extends outward of the tooth root in a direction
opposite the threaded stem 12.
As illustrated in the drawing, the anchoring means 16 comprises a
series or plurality of truncated cones 32 each of which is
separated from the other along the length .Iadd.of the
.Iaddend.dental post 10 by integrally connected and unitarily
formed extensions or separators 34. Each of the truncated conical
elements 32 is provided with the larger diameter of its outer
tapered surface directed toward the stem end of the post that is
adapted to be threaded into the tooth root canal 19 or facing the
stem 12. This downward and outward direction of the tapered
surfaces of the cone elements 32 enhances the use of the post 10 in
a manner to be described. In the event the height of the anchoring
means 16 is greater than that required for crown restoration, the
same may be shortened in length simply by grinding away as many of
the trucated conical anchoring elements 32 and separators 34 that
are found to be excessive and unnecessary.
The threaded application and insertion of the stem 12 and body 14
into tooth root canal is accomplished in a self-tapping manner to
form the root canal thread 17, the sides of which are substantially
parallel and conform precisely to that of the self-tapping thread
18 and the outer sides of the stem 12 and body 14 of the dental
post 10. Dental cement is flooded into the root canal 19 and may
also be applied to the stem 12 and body 14 so as to be in intimate
contact with all the surfaces of the thread 18. Although the stem
is shown to be divided into a plurality of two legs, it is within
the scope of the invention that the stem may be divided into any
number of legs formed by similar venting spaces or separations 24
therebetween. After the cement is applied to the stem 12 and body,
the same is ready to be threadedly inserted into the tooth root
canal 19.
In accordance with prior known procedures, this has been done by
hand or with the use of a tool for rotating the dental post 10
downward along the threaded or unthreaded tooth root canal. It has
been found that the application of too great a torque to the dental
post 10 will tend to fracture the tooth if the same exceeds the
lateral strength of the tooth root or the resisting force the tooth
exerts against the stem 12 and the body 14 as the same is threaded
thereinto. Hence, it is within the contemplation of the present
invention that the dental post 10 be threadedly inserted into the
tooth root canal by means of a releasable torque wrench generally
identified by the numeral 40 illustrated in FIGS. 3 and 5. The
wrench 40 is capable of applying a threading torque to the post 10
that will be less than the fracture resisting strength of the tooth
root.
The torque wrench 40 comprises a manually rotatable driving handle
42, the interior of which is hollowed to form a chamber 44 as is
shown in FIG. 5. The lower end of the chamber terminates in a
closure wall 46 that has a centrally located opening 48 through
which a driven shaft 50 extends outwardly from the handle 42. The
driven shaft 50 has an enlarged head 52, the undersurface of which
provides a clutch or engaging surface that engages with the facing
engaging surface of the wall 46. The engaging surfaces of the head
52 and wall 46 function as clutch means to transmit the drive from
the drive head 42 to the driven shaft 50. The surfaces are
relatively smooth and, therefore, enable the surfaces to slip with
respect to each other when the same is desired and required.
The interior chamber 44 of the handle 42 is threaded as at 54 to
receive a threaded adjustment element in the form of a nut 56 that
may be conveniently provided with a screwdriver receiving slot 58
therein. Contained between the adjustment element 56 and the head
52 of the driven shaft 50 is a yieldable urging or force applying
means in the form of a spring 60. The spring 60 is trapped between
the adjustment element 56 and the head 52 and is variable in
tension by the adjustment of the element 56 within the chamber 44
of the driving housing 42.
The wrench interior may be closed against undesired tampering by
the application of a closure cap 62 applied to the thread 54. The
driven end of the shaft 50 may be provided with any convenient
engaging means to drive the dental post 10 during its threaded
rotation into the tooth root canal. For convenience of illustration
and understanding, the same is shown to have a very simple
screwdriver blade 64. The dental post 10 is provided at the top
thereof with a complementary engaging slot 66 to receive the blade
64. Those skilled in the art will recognize that other cooperating
engaging arrangements of structures may be provided to accomplish
the torque limiting teaching of the present invention. Prior to the
self-tapping threaded insertion of the dental post 10 into the
tooth root canal 19, the adjustment nut 56 of the torque wrench 40
is adjusted to compress the spring 60 to apply a predetermined
yieldable force against the head 52 of the driven shaft 50 to force
the same into surface-to-surface engagement with the wall 46. After
the torque wrench 40 is adjusted, the same is now ready for
use.
The stem 12 of the dental post is aligned with the tooth root canal
19. The initial rotation of the dental post 10 may be accomplished
by the fingers of the hand to set the dental post and its stem 12
into the canal 19. Thereafter, the dental post is more fully
self-tappingly threaded into the tooth root 25 by the use of the
torque wrench 40 by placing the blade 64 of the torque wrench into
engagement with the receiving slot 66 of the dental post 10 and
rotating the handle 42.
As the stem 12 and the body 14 thread themselves progressively into
the root canal 19 and form the thread 17, whatever fluids, debris,
gases or air trapped beneath the leading or insertion end of the
stem are accommodated or vented to the atmosphere during such
self-tapping insertion in a manner as previously discussed until
even the connection 26 is finally encompassed within the orifice
end of the canal 19. The spring-like connection formed between the
legs 20 and 22 permits the legs to flex inward radialy toward each
other conforming to and absorbing irregularities that may occur
during the engagement of the threads 18 with the root canal 19. In
this manner, whatever fracture producing forces that may occur
during such threaded engagement are now absorbed by the radially
inward yielding of the legs toward each other as afforded by the
slotted space 24 therebetween. The connection 26, having a memory,
acts in the nature of an outwardly urging spring, constantly causes
the threads 18 of the stem 12 and body 14 to move radially outward
into full contacting threaded engagement with the threads 17 they
form in the root canal 19. This assures that at all times the
fullest benefit of the threaded engagement between the two threads
17 and 18 is afforded.
When a sealing type washer 30 is utilized, as is illustrated in
FIG. 7, the same will be compressed between the exposed wall of the
tooth root and the body 14 to fully seal the space therebetween and
to provide a shock absorber thereat. When the sealing washer 30 is
omitted, the adjacent surface of the body 14 will come into full
surface-to-surface abutment and wall sealing engagement within
countersunk wall of the tooth root canal 19.
Although the dental cement previously applied to the stem 12 and
body 14 and its threads 18 is sufficient to retain the same in
cemented frictional engagement with the tooth root canal 19, when
the cement hardens, any tendency upon the part of the dental post
10 to reversely rotate outward of the tooth root 19 at a later time
is resisted by the radial outward spring-like force applied to the
legs 20 and 22 at the spring-like connection 26 therebetween. This
causes the sharp slotted edges of the legs to move tangentially
into wedging engagement with the wall of the root canal 19 to
resist reverse threading. Thus, the spring-like connection 26
affords a memory that tends to return the legs 20 and 22 into full
surface contact and anti-rotative engagement with the threads 17 of
the tooth root canal 19.
If during the threading of the stem 12 and body 14 into the root
canal 19 resisting forces occur that exceed that of the preset
force of the spring 60 in the torque wrench 40, the spring 60 will
permit relative slipping movement between the wall 46 of the handle
42 and the adjacent engaging surface of the head 52 of the driven
shaft 50. As a consequence, until such times as the resisting force
occurring between the threads 17 and 18 is removed or safely
reduced, it will not be possible to continue to thread the stem 12
and body 14 into the root canal 19 by the use of the torque wrench
40. Accordingly, rotation of the torque applied to the dental post
10 through the driven shaft 50 will terminate. No amount of
continued rotation of the handle 42 will cause the post 10 to
thread deeper into the root canal 19 until such time as the
fracture producing resisting forces exerted thereon are
removed.
From what has been disclosed, it will be clear that once the
adjustment of the element 56 in the torque wrench handle 42 is made
so that the spring 60 will not apply a predetermined frictional
engagement between the head of the driven shaft 50 and the surface
of the wall 46 of the handle 42 that will exceed the strength and
fracture resistance of the tooth, the tooth will not fracture
during use of the wrench 40. No amount of continued rotation of the
driving handle 42 will result in continued threaded engagement of
the stem into the tooth root 19 because the clutch surfaces will
slip and rotate relative to each other without transmitting drive
therebetween. Therefore, even though the stem 12 and body 14 are
capable of absorbing fracture producing stress forces applied
between it and the tooth root 19, the use of the torque wrench 40
provides further assurance that at no time during the use of the
same with the dental post 10 will the dental post exert a force on
the tooth root 25 that will exceed the strength of the tooth
root.
After the dental post 10 is applied to the tooth root 25 in the
manner as described, the same is now ready for the application of a
crown 68 to the tooth root 25 at the anchor means 16 of the dental
post 10. The crown 68 is constructed in the conventional manner to
provide a precise fit with the tooth root 25. It is provided with
the conventional hollow interior that is intended to be
circumpositioned about and over the anchoring means 16.
The crown 68 is shown schematically in FIG. 7. Its details of
construction may be changed and are not necessarily limited to
those here illustrated. Before the application of the crown 68 to
the anchoring means 16, a dental or composite cement is applied to
the interior thereof. Dental or composite cement may also be
applied about the exposed surfaces of the truncated conical
anchoring elements 32 and about the separators 34 and the body 14
of the dental post 10. The multi-truncated cone anchoring means 16
is unusually well adapted for use in restoring old or prior used
bridgework and crowns.
Previously it was noted that the narrow diameter ends of the
truncated cones 32 extend in a direction away from the stem 12 and
toward the interior opening of the crown 68, while the larger
diameter ends of the cones 32 extend downward toward the body 14
and the stem 12. The undersides of the larger diameters of each of
the anchoring cones 32 function as surfaces beneath which the
dental or composite cement flows and against which the same hardens
in engagement therewith. They are tapered in the manner as
illustrated and described to provide a natural flow of the dental
cement in a direction from along the narrower portions of the
truncated anchoring cones 32, along the enlarging surfaces and then
into the spaces afforded by the separators 34 between each of the
cone elements.
In practice, it has been found that when the dental cement is
compressed, it flows along the path of least resistance from the
narrower ends of the truncated anchoring cone elements 32 toward
the larger ends and then into the spaces afforded by the separators
3 therebetween. The initial application of the dental cement in
such spaces afforded by the separators 34 is even more fully
compressed upon and during the application of the crown 68 over the
whole of the anchoring means 16. The forces applied by the crown
cause the cement to flow into all of the spaces that exist beneath
the larger diameters of the truncated cones 32 so as to come into
full and cementing engagement therewith. This assures a proper
long-lasting connection and engagement between the crown 68 and the
anchoring means 16 and the elimination of air pockets within the
crown.
The embodiment of the dental post shown in FIG. 4 is generally
identified by the numeral 110. The 10's digits used in this
embodiment correlate with like elements of structure described with
respect to the embodiment 10 shown in FIGS. 1 and 3 and described
with respect thereto. Therefore, for convenience all numerals used
in connection with the description of the embodiment 110 of FIG. 4
will be identified in the 100 series.
FIG. 4 differs from that of the embodiment 10 previously described
in its omission of the two-tier body 14 therefrom. As distinguished
from the prior embodiment, the post 110 is unusually well adapted
for use with multi-rooted teeth in which two or more such posts 110
may be used. The embodiment 110 comprises a threaded substantially
parallel sided stem 112 whose thread 118 extends about each of the
plurality of legs 120 and 122. As in the embodiment 10, the legs
are divided and spaced from each other by a venting slot 124 that
extends for a substantial length of the stem and terminates
adjacent the end remote of the stem at the enlarged spring-like
memory returning connection 126.
In the embodiment 110, the lengthwise extent of the stem 112 is
such that its coronal end terminates at the orifice opening of the
root canal 19. In like manner, the spacing slot or vent 124
provides an adequate .Iadd.vent to the atmosphere from the leading
or insertion .Iaddend.end of the stem 112 during its self-tapping
insertion into the canal 19 until the connection 126 is finally
.[.closed.]..Iadd.enclosed .Iaddend.in the root canal.
The dental post 110 is of unitary construction and includes crown
anchoring means 116 that is constructed and functions in
essentially the same manner as the crown anchoring means 16 of the
embodiment 10 previously described. For this reason, a detailed
repetitious description of the same will be omitted.
To assure that the dental post 110 is properly self-tapped and
threaded into the tooth root canal 19 with the application of a
torque thereto that does not exceed the strength of the tooth 25,
the torque wrench 40 may be utilized in the manner as previously
described with respect to the embodiment 10. To enable the use of
the wrench 40, the embodiment 110 is provided with a complementary
screwdriver slot 166 that is adapted to receive the screwdriver
type blade 64.
It will be recognized by those who are skilled in the art that the
mere illustration and description of the complementary shaped blade
64 and slot 66 shall not constitute a limitation upon the scope of
the invention. Any other complementary engaging means may be used
to effect the self-tapping and threaded engagement of the dental
posts of the invention with the root canal 19 with a force that
will not exceed the strength of the tooth root 25.
Referring now to FIG. 6, the embodiment there illustrated
corresponds in many of the essential details to that of the
embodiment 10 described with respect to FIGS. 1 and 3. Hence, like
details of construction are identified with the same 10's digits,
with all of the numerals distinguishably numbered in the 200
series.
The similarity of the embodiment 210 with that of the embodiment 10
should at once become apparent. The stem 212 thereof terminates in
the body 214 and both are slotted at 224 to provide the plurality
of legs 220 and 222 that are separated and spaced for relative
yielding movement with respect to each other to absorb shock and
forces that might be applied to the self-tapping threads 218
thereof during the self-tapping threaded insertion and engagement
of the dental post 210 with the root canal 19.
As with the prior described embodiments, the embodiment 210 is of
unitary construction that includes a body 214 in which the defining
walls of the enlarged opening 226 function to retain the memory of
the separation of the plurality of legs 220 and 222. It also
provides accommodation for debris and for venting to the atmosphere
from the insertion end of the stem 212 during the threading of the
stem and body into the complementary countersunk coronal aspect of
the root 19. As illustrated in FIG. 6, the embodiment 210 may
utilize a silastic washer or seal .Iadd.230 .Iaddend.as described
with respect to the embodiment 10.
The embodiment 210 differs from that of the embodiment 10 in the
details of the anchoring means 216. The embodiment 210 is unusually
adapted for use with new crown restoration. For this reason, the
anchoring means 216 eliminates the plurality of relatively spaced
truncated cone anchoring elements 32 and combines it into a single
smooth-sided truncated cone 232. Its narrower end is spaced remote
from that of the stem 212 while its larger end faces in the
direction of its unitary connection with and extension of the body
214.
The use of the dental post 210 is accomplished substantially in the
same manner as previously described with respect to the prior
embodiments. With respect to the post 210, the anchoring element
232 is provided with a slot 266 that will receive the end 64 of the
driven shaft 50 of the torque wrench 40. The application and
threaded insertion of the stem 212 of the dental post 210 into the
threaded root canal 19 is accomplished in the same manner as
previously described for the use of the torque wrench 40.
The blade 64 is engaged in the slot 266 of the anchoring element
232 to rotate the same into the tooth root canal 19. If at any time
during such self-tapping threaded engagement forces are applied to
the legs of the stem 212 that exceed the force exerted by the
spring 60 in the torque wrench 40 as predeterminately set by the
adjustment of the adjustable nut 56 therein, the clutch surfaces
engaging between the wall 46 and the head 52 will slip and be
permitted movement relative to each other. This assures that at no
time will the application of torque to the dental post exceed the
strength of the tooth 25 nor will the same exert fracture producing
forces against the walls of the root canal 19 thereof.
As previously described, the legs 220 and 222 will flex and move
relative to each other independently in response to whatever forces
are exerted upon them during such self-tapping and threading
operation. This ability of the legs of the stem to yield in
response to the thread generating and threading forces enable the
same to function as a shock and force absorber that transfers such
forces to the stem legs for absorption thereby. In the absence of
such force absorber, the forces are exerted outwardly against the
new threaded wall of the tooth root canal 19 and will fracture the
tooth 25 if the forces exceed the tooth strength.
In each of the embodiments the plurality of legs are normally
spaced from each other by the slot formed between them. In each
case the legs will yield relative to each other in response to
forces applied to them to conform to irregularities encountered in
their self-threading movement along the tooth root canal 19.
In each instance, the spring biased connection afforded by the
walls surrounding the larger opening 26, 126 and 226 at the remote
end of the slot exerts a returning force on the legs to cause them
to tend to assume their normal parallel relationship. This outward
urging force exerted at the spring connection 26 causes the threads
18 of each of the dental posts into fuller and more complete
engaging relationship with the complementary surfaces of their
formed threads 17 of the tooth root canal 19. The spring action of
the legs uniformly allows them to absorb stress along their entire
lengths and the slotted portion of the body. This results in
greater cooperation and retention between the bulk restoring dental
post and their formed threads 17 of the tooth 25. This fuller and
greater extent of engagement also inhibits the anti-rotation or
possible accidental disassembly of the dental post from the tooth
root canal 19, while at the same time providing for complete shock
and force absorbing engagement therebetween.
.[.Referring to the dental post of FIGS. 8 to 13 inclusive the same
is generally identified by the numeral 310. As in the prior
described embodiments, the 10's digits here used will identify the
elements of structure used to identify like elements of each of the
prior described embodiments. For convenience, all numbers here used
will be in the 300 series..].
.[.The embodiment 310 of FIGS. 8 to 13 includes a body 314
coextensive and formed unitary with a stem 312 at its apical or
insertion end and with a crown anchoring means 316 at its opposite
or distal end. The stem 312 has an apical or leading end that is
tapered from the terminal end of the threads 318 that are formed on
each of the legs 320 and 322 produced by the space of the slot 324.
It will be seen that the full extent of each of the tapered entry
or apical ends 323 are free of threads but are angled to correspond
to that of the angle of the leading end of the tooth root canal
19..].
.[.The function of the unthreaded apical ends 323 will become
clearer as the description proceeds. However, at this point it is
noted that the same provide aligning means by which the thread
generating threads 318 are aligned with the root canal 19 when the
stem 312 is introduced into the root canal. They also function to
fit into and to fill and occupy substantially the full depth and
area of the previously drilled root canal 19. Because the angle of
the apical lead ends 323 correspond in angular relationship with
the taper produced in the root canal 19 by the drill used to
produce the root canal, the same will fill the end thereof
substantially fully below the threads 318. This provides a longer
post to root canal contact between the post 310 and the canal 19 to
add additional strength to the tooth 25 by providing a greater
length of stress absorption and distribution of forces..].
.[.The space of the slot 324 extends for a substantial length of
the stem 312 to assure the legs 320 and 322 thereof will be able to
move radially independently and tangentially relative to each other
to perform the described flexing and relative movements as the
self-tapping thread 318 generates the thread 317 in the tooth 25
during the threading of the past 310 thereinto. Although the space
of the slot 324 is shorter in the present embodiment 310 than in
the prior embodiments, the stem 312 and body 314 are provided with
at least a venting continuation and extension groove 327 of the
venting space 324. At least one or more venting spaces 324, 327 may
be provided on the stem 312. The vent spaces 324, 327 perform the
same venting function as was previously described with respect to
the venting spaces 24, 124 and 224 kof the prior described
embodiments since, as will be seen, the same extends
kuninterruptedly from the apical end of the stem 312 to at least
the distal end 326 of the body 314..].
.[.Hence, when the post 310 generates its own thread as it is
threaded into the root canal 319, the distal end 326 of the
combined vent 324, 327 always is exposed at the top of the root and
tooth 25. This assures that the cd cement, debris produced by the
cutting of the threads, fluids, air and other gases and pressure
building materials are vented and exhausted to the atmosphere from
the deepest apical end of the tooth root canal to prevent damage to
the tooth root. As in the prior described embodiments, the space
324, 327 vents from the root canal any possible build-up of
damaging hydrostatic pressure from beneath and about the apical end
323 of the post 310 as the post is self-tapped and threaded into
the root canal 19..].
.[.As in the prior described embodiments the anchoring means 316 is
provided to enable a crown to be mounted to the post 310. The
present anchoring means is of general cruciform shape with a
plurality of diametrically opposed anchoring lobes 332. Each of the
sets of anchoring lobes 332 are relatively axially and
longitudinally spaced from the other along the length of the
anchoring means 316 by separators or spacers 334. Those skilled in
the art will recognize that the selection of four lobes as is shown
in the drawing is but a matter of choice. Any other number of lobes
may be utilized. Four have been selected for illustration to permit
the use of a torque wrench to rotate the dental post
thereat..].
.[.The use and operation of the dental post 310 is essentially the
same as that previously described with respect to the prior
discussed embodiments. The benefits of the tapered apical leads 323
of the present embodiment may be readily utilized in the posts of
the prior embodiments by providing each of them with such apical
leads..].
.[.When in use, the present embodiment 310 provides a unique
advantage over prior art dental posts in that it takes into
consideration the need to assure the continued presence of a
sufficiently thick body of dentin between the outer wall of the
tooth and the post 310 that is threaded into the root canal 19. In
the use of prior art dental posts little, if any, concern was given
to the details of the dental post construction as to assure the
continued existence of a sufficiently thick tooth root wall capable
of resisting fracture of the tooth after the post tapped the same
and was threaded thereinto..].
.[.The present invention takes into account such problems of
fracture by arranging the details of structure of the dental post
310 to assure that there always exists at least a minimum tooth
wall thickness of not less than one mm. between the outer wall of
the tooth and the nearest adjacent detail of dental post structure.
To this end it will be seen from the illustration in FIG. 13 that
the space between the tooth root canal 19 and the outer wall of the
tooth 25 decreases toward the base of the tooth when the dental
post 310 is threaded into the tooth root canal 19. At that time the
tapered apical leading end 323 of the post 310 is closed to the
outer wall of the tooth than any other portion of the dental
post..].
.[.If, however, the space between the apical end of the post 310
and the outer wall of the tooth is less than one mm., there is not
sufficient wall thickness to sustain and resist those forces that
tend to fracture the tooth adjacent the nearest part of the dental
post. Therefore, to provide for such minimum tooth thickness and
still enable the dental post 310 to enter and be mounted as deep as
possible in a tooth so as to add strength to the tooth, the post is
tapered as at 323 with an angle corresponding substantially to that
of the leading end of the root canal as formed by the drill and tap
used to open the root canal and to thread the same. By so doing,
the deepest end 323 of the dental post 310 is always spaced at
least the distance of one mm. from the adjacent outer wall of the
tooth 25 as is illustrated in FIG. 13 by the double headed arrow
372..].
While there have been shown and described and pointed out the
fundamental novel features of the invention as applied to preferred
embodiments thereof, it will be understood that various omissions
and substitutions and changes in the form and details of the device
illustrated and in its operation may be made by those skilled in
the art without departing from the spirit of the invention. It is
the intention, therefore, to be limited only as indicated by the
scope of the claims appended hereto.
* * * * *