GB2112683A - A dental post and wrench therefor - Google Patents

Abstract

A dental post 10 having a stem 12 of substantially parallel threaded sides divided along its length into separate relatively movable legs 20, 22 for threaded insertion into a tooth root canal by a wrench 40 that applies a predetermined torque to the dental post to thread it into the tooth root for crown restoration. <IMAGE>

Description

SPECIFICATION A dental post s wrench therefor s method of restoring bulk to a tooth root therewith 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, and to a torque wrench for use in combination therewith.

In the past dental posts were made of solid unyielding construction. Some such dental posts were made with tapered threaded surfaces as exemplified by the United States patent to Ellman No. 4,239,489. Others were made with elongated surfaces of continuous diameter substantially fully along their lengths as exemplified by the United States patents to Kurer Nos. 3,524,255 and 3,656,236 and also to Lieb No. 3,861,043. Some dental posts even suggested a slot along the length of the side thereof as in the United States patent to Justi No. 644,804. The United States patent to Best No. 838,296 and the aforenoted patent to Ellman disclose hollow posts. The United States patent to Sellers No.

4,234,309 exemplifies the teaching of the combination of a wrench for use with a dental post, while the Swiss patent 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.

In each of the exemplary prior art teachings noted above, the nature of the dental post is such that when it 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.

The aforementioned problems of the prior art dental posts are sought to be solved by the present invention. The present invention provides a dental post that is capable of being threadedly inserted into the tooth root canal by a wrench preset to apply a predetermined torque to the dental post to prevent the application of undue 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 is inserted into the tooth, it is anchored by cementing so as to prevent anti-rotational forces that might normally tend to cause the post to unthread from its seat in the root of the tooth. These anti-rotational forces are aided by the normal expansion of the threaded legs of the dental post into tighter frictional engagement with the threads of the tooth root canal.They are further aided by the cement that anchors into dentinal wall irregularities and in the slot between the legs.

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 the present invention when taken in conjunction with the accompanying drawings wherein:: Figure 1 is an enlarged plan view of a dental post constructed according to the invention; Figure 2 is a perspective view of a shock absorbing element for use with the dental post of Fig. 1; Figure 3 is a perspective view of the dental post of Fig. 1 and shown in combination with a torque wrench according to the invention; Figure 4 is an enlarged plan view of another embodiment of the dental post; Figure 5 is a vertical cross section of Fig. 3 taken substantially along lines 5-5 thereof; Figure 6 is an enlarged perspective view of another dental post; and Figure 7 is a smaller scale plan view of a dental post of the invention threaded in a tooth root and crown thereon.

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 1 2 formed unitarily with a body 1 4 and a crown anchoring means generally identified by numeral 1 6. The stem 12, body 1 4 and crown anchoring means 1 6 all are integrally connected together and formed as a unitary structure. 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 1 2 is of an elongated length that is greater than that of the length of the root canal into which the same is adapted to be threadedly inserted, it may be cut short to the length of the root canal by a dental diamond wheel. After pulp is removed from the root canal 1 9 and the canal is obturated it is reamed to a diameter corresponding to that of the stem wall 1 2.

The stem 1 2 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 slot 24 that extends fully along the length of the stem and therebeyond into the body 1 4 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. 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 slot 24 provides room sufficient to permit the legs 20 and 22 to move radially toward and away from each other. It also serves to absorb radial forces that are applied to the legs when the same are threaded into the root canal 1 9 of a tooth 25. The ability of the legs to flex and move relatively toward and away from each other enables them to conform to the irregularities of the thread 1 7 of the root canal. This movement permits the legs to absorb stresses and forces that would otherwise be applied to the walls of the root canal 1 9 to cause the tooth 25 to fracture in response thereto.

As will also become apparent, the lengthwise extent of the slot 24 between the legs 20 and 22 terminates at a point 26 that is within the body 1 4 and provides a unique advantage over the prior art. The space of the slot 24 affords a vent for dental debris and that releases hydraulic and pneumatic forces that normally tend to build up beneath the dental post 10 as the same is threaded with cement into the root canal of the tooth. 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 1 9 of the tooth 25 and from beneath the leading or insertion end of the stem 1 2 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 1 9 without damage to the tooth root.

The thread 1 8 of the stem 1 2 extends for the full length thereof and for the full length of the larger widthwise dimensioned body 14.

It 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 1 2 and body 1 4 are fully threaded into the tooth root canal 19, the tapered or curved end 28 of the body 1 4 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 rententive 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 1 0.

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 1 8 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 1 9 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 1 9 and a crown 31 is built and anchored about the root and about the anchoring portion 1 6 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 1 6. The anchoring means here-shown is generally identified by the numeral 1 6 that extends outward of the tooth root in a direction opposite the threaded stem 12.

As illustrated in the drawing, the anchoring means 1 6 comprises a series or plurality of truncated cones 32 each of which are separated from the other along the length of the 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 1 9 or facing the stem 1 2.

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 1 6 is greater than that required for crown restoration, the same may be shortened in length simply by grinding away as many of the truncated conical anchoring elements 32 and separators 34 that are found to be excessive and unnecessary.

The threaded application and insertion of the stem 1 2 and body 1 4 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 1 8 and the outer sides of the stem 1 2 and body 1 4 of the dental post 1 0. Dental cement is flooded into the root canal 1 9 and may also be applied to the stem 1 2 and body 1 4 so as to be in intimate contact with all the surfaces of the thread 1 8. 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 1 2 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 1 2 and body 1 4 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 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 1 2 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 1 2 into the canal 1 9.

Thereafter, the dental post is more fully selftappingly 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 1 2 and body 1 4 thread themselves progressively into the root canal 1 9 and form the thread 17, whatever fluids, debris, gases or air trapped beneath the leading or insertion end of the stem are accommo dated or vented to the atmosphere during such self-tapping insertion in a manner as previously discussed until even the connection 26 is finally encompassed with the orifice end of the canal 1 9. The spring-like connection formed between the legs 20 and 22 permits the legs to flex inward radially toward each other conforming to and absorbing irregularities that may occur during the engagement of the threads 18 with the root canal 1 9.

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 1 8 of the stem 1 2 and body 1 4 to move radially outward into full contacting threaded engagement with the threads 1 7 they form in the root canal 1 9. This assures that at all times the fullest benefit of the threaded engagement between the two threads 1 7 and 1 8 is afforded.

When a sealing type washer 30 is utilized, as is illustrated in Fig. 8, the same will be compressed between the exposed wall of the tooth root and the body 1 4 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 1 9.

Although the dental cement previously applied to the stem 1 2 and body 1 4 and its threads 1 8 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 1 9 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. 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 1 2 and body 14 into the root canal 1 9 resisting forces occur that exceed that of the present 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 time as the resisting force occurring between the threads 1 7 and 1 8 is removed or safely reduced, it will not be possible to continue to thread the stem 1 2 and body 14 into the root canal 1 9 by the use of the torque wrench 42. Accordingly, rotation of and 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 1 9 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 1 9 because the clutch surfaces will slip and rotate relative to each other without transmitting drive therebetween.

Therefore, even though the stem 1 2 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 1 6 of the dental post 1 0. 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 multitruncated cone anchoring means 1 6 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 1 2. 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 34 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 1 6 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 1 4 therefrom. As distinguished from the prior embodiment, the post 110 is unusually well adapted for use with multirooted teeth in which two or more such posts 110 may be used. The embodiment 110 comprises a threaded substantially parallel sided stem 11 2 whose thread 11 8 extends about each of the plurality of legs 1 20 and 122. As in the embodiment 10, the legs are divided and spaced from each other by a venting slot 1 24 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 1 26.

In the embodiment 110, the lengthwise extent of the stem 11 2 is such that its coronal end terminates at the orifice opening of the root canal 1 9. In like manner the spacing slot or vent 1 24 provides an adequate vent to the atmosphere from the leading or insertion end of the stem 11 2 during its self-tapping insertion into the canal 1 9 until the connection 1 26 is finally enclosed in the root canal.

The dental post 110 is of unitary construction and includes crown anchoring means 11 6 that is constructed and functions in essentially the same manner as the crown anchoring means 1 6 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 threaded into the tooth canal 1 9 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 1 0. To enable the use of the wrench 40, the embodiment 110 is provided with a complementary screwdriver slot 1 66 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 threaded engagement of the dental posts of the invention with the root canal 1 9 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 21 2 thereof terminates in the body 214 and both are slotted at 224 to provide the plurality of legs 220 and 222 that are separated for relative yielding movement with respect to each other to absorb shock and forces that might be applied to the threads 218 thereof during the selftapping 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 1 26 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 1 9. As illustrated in Fig. 6, the embodiment 210 may utilize a silastic washer or seal 230 as described with respect to the embodiment 1 0.

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 21 2 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 1 9 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 64 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 torwue 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 1 9 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 threading operation. This ability of the legs of the stem to yield in response to the threading forces enables 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 selfthreading movement along the tooth root canal 19.

In each instance the spring biased connection afforded by the walls surrounding the larger opening 26, 1 26 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 1 8 of each of the dental posts into fuller and more complete engaging relationship with the complementary surfaces of their formed threads 1 7 of the tooth root canal 1 9. 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 1 7 of the tooth 25. This fuller and greater extent of engagement also inhibits the antirotation 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.

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 (25)

1. In a dental post for insertion into a tooth root canal, a stem for threaded insertion into a tooth root canal and having substantially parallel threaded sides extending from the insertion end of said stem for at least the full length of said stem to be threadedly inserted into the tooth root canal, a slot in said stem extending from said insertion end for a substantial length thereof to form said slotted stem into a plurality of elongated threaded legs each of which has a space therebetween defined by said slot to permit said legs to move relative to each other to absorb fracture producing forces that are applied to the same during the threaded insertion of said stem into a tooth root canal, and means unitary with said stem for anchoring a dental crown thereto.

2. In a dental post as in Claim 1, said anchoring means being formed as a unitary part of said post and extending in a direction opposite from said insertion end of said stem and including a plurality of relatively spaced truncated conical elements decreasing in dia meter in the direction away from said stem.

3. In a dental post as in Claim 1, a threaded body interposed between and unitary with said stem and anchoring means and having a greater width than that of said stem.

4. In a dental post as in Claim 3, said body adjacent said stem being rounded to obviate fracture of the tooth during engage ment therewith when said stem and body are inserted thereinto.

5. In a dental post as in Claim 3, force absorbing means between said body and stem compressible between said body and the tooth root when said stem and body are threaded thereinto to absorb forces applied therebetween.

6. In a dental post as in Claim 3, said slot extending beyond said stem and into said body terminating therein in an enlarged curved opening that obviates fracture of said body at the ends of said slot and enhances the relative movement of said legs.

7. In a dental post as in Claim 3, said anchoring means being a truncated coneshaped extension of and larger than said body opposite said stem.

8. In a dental post as in Claim 1, said anchoring means being relatively spaced truncated cone-shapes.

9. A dental post for engagement with a tooth root canal comprising a stem having substantially parallel sides and being threaded along said sides for a length of the stem at least to be threaded fully into a root canal, said stem being relatively spaced and divided into a plurality of legs each unitarily connected together at their ends remote from the leading end of said thread of said stem for spring-like compressive movement relative to each other, each of said legs having a portion of said thread such that when said stem is threaded into the root canal said legs will spring inward toward each other into said space to absorb forces that tend to fracture the tooth root while said spring connection urges said legs into threaded engagement with the root canal to restrain said stem from accidental unthreading therefrom, and anchoring means connected with said stem to anchor a dental crown thereto.

10. A dental post as in Claim 9, said space between each of said plurality of legs extending from the leading end of the threaded stem and therebeyond to provide a vent therefrom to the atmosphere to prevent the build-up of forces in the tooth root canal at said leading end of said stem.

11. A dental post as in Claim 9 in combination with a wrench therefor comprising a manually rotatable handle, a shaft rotatable by and relative to said handle, said shaft and handle having surfaces in engagement with each other for rotation of said shaft in accordance with the manual rotation of said handle, means applying a force urging said surfaces into engagement with each other for conjoint rotation and yieldable to permit the same to rotate relative to each other when a force applied to said shaft resisting its rotation exceeds the applied force of said urging means.

and means on said shaft and said dental post releasably engageable to threadedly rotate said stem into said tooth root canal.

12. A dental post and wrench as in Claim 11, and means adjustable on said handle to vary the applied force of said urging means such that said surfaces rotate relative to each other when the force applied to said stem during its threaded insertion into the tooth root canal exceeds said adjusted applied force.

1 3. A dental post and wrench as in Claim 11, a body between said stem and anchoring means, said thread along said stem being selftapping and extending along said body.

1 4. A combined dental post for threaded insertion into a tooth root canal and torque wrench therefor, said dental post having an end for threaded insertion into a tooth root canal and anchor means forming a unitary part of said dental post for anchoring a dental crown thereto, said dental post having an elongated outer substantially parallel sided surface threaded therealong and being divided into a plurality of legs spaced from and movable relative to each other at said leading end and connected together remote from said leading end for said relative movement, and said wrench comprising a post driving shaft and a rotatable handle each of which has surfaces yieldingly biased into driving engagement with the other to rotate said shaft in response to the rotation of said handle, spring means in said handle to yieldingly bias said surfaces into said driving engagement, and cooperating means on said anchor means and post driving shaft to enable the driving application of the rotative torque of said handle to said dental post and to release said driving torque of said handle to said dental post when a resisting threading force applied to said dental post exceeds the driving torque of said handle.

1 5. A combined dental post and torque wrench as in Claim 14, said cooperating means on said anchor and post driving shaft including interengaging means.

16. A torque wrench for releasably driving a dental post comprising a manually rotatable handle having driving means, a driven shaft having driven means, means yieldingly urging said driving and driven means into engagement to cause said shaft to rotate with said handle and yieldable in response to a resistance supplied to said shaft greater than the force of said urging means to cause said urging means to yield to enable slipping between said driving and driven means during continued rotation of said handle, and means on said driven shaft for connec tion with a dental post to rotate the same in response to the rotation of said handle.

1 7. A torque wrench as in Claim 16, said driving and driven means being relatively smooth surfaces.

18. A torque wrench as in Claim 17, said handle having a chamber in which a defining wall has an opening through which said driven shaft extends outward therefrom, and said driving means of said handle is formed by a wall of said chamber.

1 9. A torque wrench as in Claim 18, said urging means being a spring within said chamber and biasing said driving and driven means into engagement with each other.

20. A torque wrench as in Claim 19, and means on said handle adjustable to vary the biasing force of said spring to predeterminately control the torque at which said driving and driven means will slip and rotate relative to each other.

21. In the method of restoring bulk to the root canal of a tooth root comprising a thread, threading into the root canal a dental post having threaded substantially straight sided outer walls with spaces therebetween to enable the walls to move relative to each other to absorb fracture producing forces on said tooth root while the dental post is threaded into the root canal, venting the tooth root canal to the atmosphere at the spaces between the walls to prevent the build-up of forces in the tooth root canal, leaving a portion of the dental post exposed beyond the tooth root canal as a means to anchor to the tooth root, and cementing the threaded walls of the dental post to the tooth root canal.

22. In the method as in Claim 21, tapping the tooth root canal with the thread of the dental post.

23. The method as in Claim 22, threading the dental post into the tooth root canal by a releasable torque wrench applying a predetermined rotative force thereto.

24. The method as in Claim 23, setting the torque wrench to a predetermined torque to be applied to the dental post, terminating the application of rotative force to the dental post by the torque wrench when the resisting forces at the threads of the tooth root canal and the walls of the dental post exceed the predetermined torque at which the wrench is set.

25. The method as in Claim 21, anchoring a dental crown and the like to the exposed portion of the dental post.