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.

Description

This application is a continuation-in-part of co-pending application Ser. No. 321,440, filed Nov. 16, 1981 and now abandoned.

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; to top a thread andvent to the atmosphere from the leading or insertion 230

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.

Claims

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.