Endodontic Post

FIG. 1 is an elevation view of a spirally grooved endodontic post of the present invention. A lower portion of a root canal is shown having the lower tip of the post received therein.

FIG. 2 is an elevation sectioned view of a multi-canaled tooth. The upper portion of the tooth has been broken off or removed.

FIG. 3 is a view of the tooth of FIG. 2 after the root canals have been endodontically prepared to form endodontic post spaces for receiving a post construction.

FIG. 4 illustrates the tooth of FIG. 3 after spirally grooved endodontic posts have been cemented in place within the prepared canals.

FIG. 5 illustrates the tooth of FIG. 4 after a tooth restoration has been mounted on the tooth and anchored by the spirally grooved endodontic post construction.

FIG. 6 is a partial elevation view of the upper end of the post of FIG. 1 taken along line 6--6 of FIG. 1.

FIG. 7 is a cross-sectional view of the post of FIG. 1, taken along line 7--7.

FIG. 8 is an elevation view of a graduated diameter, spirally grooved endodontic post of the present invention.

FIG. 9 is an elevation sectioned view of a single-canaled tooth illustrating the graduated diameter, spirally grooved endodontic post in place within a prepared endodontic canal with a tooth restoration anchored by the endodontic post.

FIG. 10 is an elevation view of a graduated diameter endodontic post of the present invention.

FIG. 11 is an elevation sectioned view of a single canaled tooth, illustrating the graduated diameter endodontic post in place within a prepared endodontic canal with a tooth restoration anchored by the endodontic post.

FIG. 12 is an elevation view of a graduated diameter endodontic drill of the present invention.

In FIG. 1, the endodontic post of the present invention is shown and generally designated by the numeral 10. The post 10 generally has an elongated cylindrical shape, and has a length 12 and a diameter 14.

A major portion 16 of the length 12 is cylindrical in shape, having a cylindrical outer surface 18. A spiral groove 20 is defined in the cylindrical outer surface 18. There is one and only one spiral groove 20 defined in the cylindrical outer surface 18. The groove 20 is set at a pitch angle 22 in a range of from about 35.degree. to about 55.degree.. Preferably, the pitch angle 22 is approximately 45.degree..

The groove 20 preferably has a smooth curvilinear cross section, and preferably is semi-circular in cross section. The semi-circular cross-section groove 20 preferably has a radius, and thus a depth within post 10, from about 5% to about 30% of the diameter 14 of the outer cylindrical surface 18 of the post 10. Preferably, the groove 20 has a depth in a range of from about 15% to about 20% of the diameter 14.

It will be appreciated by those skilled in the art that endodontic posts such as the post 10 are typically provided in several different diameters so that a suitable post can be selected to be relatively closely received within a prepared root canal of a human tooth. Typical diameters in which posts such as the post 10 are provided are 1.0 mm., 1.2 mm., 1.4 mm., and 1.6 mm. These posts typically have a length of less than 20 mm.

The post 10 illustrated in FIG. has been drawn approximately to scale to represent a 1.6 mm. diameter post, 20 mm. in length, having a groove of 0.3 mm. radius set at a pitch angle of 45.degree.. Thus, the groove 22 spirals around the post 10 approximately six times.

As is apparent in FIG. 1, with such a construction, an ungrooved area of the outer cylindrical surface 18 is substantially greater than a grooved area of the outer cylindrical surface 18. As is apparent in FIG. 7, any cross-section of the cylindrical portion 16 of post 10 comprises a circular periphery 23 interrupted at one location by groove 20. Since groove 20 is smooth in cross-section, there are no significant points of stress concentration created.

This substantial ungrooved area of outer cylindrical surface 18 provides an important function in addition to the fact that it provides a strong uninterrupted cross-sectional area. It also resists rotational motion of the tooth restoration 56 relative to the post 10 . This is particularly true as compared to the relative performance of a post like that of U.S. Pat. No. 4,268,253 to Gross et al. which has its entire outer surface grooved. When the tooth restoration 56 is subjected to chewing forces, those forces both push down on tooth restoration 56 and twist tooth restoration 56. When twisting forces are applied to a restoration mounted on a post like that of the Gross et al. '253 patent, the restoration tends to climb the incline of the external flutes of the post as it twists. This causes a repeated lifting force on the restoration and on the post relative to the cement which tends to break the bonds between the post and both the restoration and the cement. With the post 10 of the present invention, however, the ungrooved cylindrical surface 18 resists these twisting forces without creating a lifting force and thus provides a more secure bond between the post and both the restoration and the cement.

Post 10 has an axially outer end 24 on which is defined a wrench flat 26 which may be generally referred to as an engagement means 26 for engaging a tool, such as a wrench, for rotating the post 10 to thread the post 10 out of a prepared root canal.

An axially inner end 28 of the post 10 has a tapered and rounded tip means 30 defined thereon for minimizing stress concentrations at areas of engagement of the inner end 28 of post 10 with a tooth.

In FIG. 2, a human tooth 32 is shown. The tooth 32 illustrated is a molar tooth having two root canals 34 and 36 extending down into root portions 38 and 40 of the tooth.

An irregular upper surface 42 is shown where the tooth 32 has been broken off or cut away. Gum tissue 44 is illustrated adjacent the broken upper surface 42 of the tooth.

The root canal 34 extends downward from the upper surface 42 to an apical foramen or opening 46 in the lower end of the root 38. The root canal 36 is similarly formed.

Prior to placement of a tooth restoration or artificial crown on the tooth 32, the root canals 34 and 36 will typically be endodontically prepared in a manner well known to those skilled in the art through the use of endodontic files to enlarge the root canals 34 and 36 removing the pulp material therefrom and providing enlarged prepared root canals a portion of which can be referred to as endodontic post spaces 48 and 50 as illustrated in FIG. 3.

In FIG. 4, two of the posts 10 have been inserted in and cemented in place within the prepared post spaces 48 and 50.

As will be appreciated by those skilled in the art, cement may be placed within the post spaces 48 and 50 prior to insertion of the posts 10, or the posts 10 may be coated with cement prior to being inserted within the post spaces 48 and 50. Also, cement may be placed within the post spaces 48 and 50 and also coated on the posts 10 prior to insertion In any event, the posts 10 are inserted within the post spaces 48 and 50 and cemented in place therein.

It is significant to note that the posts 10 are generally not threaded into the post spaces 48 and 50. As best illustrated in the lower portion of FIG. cement 52 generally surrounds the post 10, and the post 10 is not actually tightly wedged or threaded into the post space 48. It is the cement 52 which binds the post 10 to the tooth 32, rather than a mechanical engagement of the post 10 with the tooth material 32 as is the case with many prior art threaded posts.

After the cement 52 has set, however, a spiral ridge 54 of cement is formed within the groove 20.

It is preferred that points of high stress concentration engagement of the post 10 with the post space 48 be avoided. It will be appreciated when one considers the relatively large forces which are applied to the tooth restoration 56 during the chewing of food and the like, that those forces are transmitted to a significant extent downward through the post 10 to the tooth structure 32. Sharp points of engagement between the post 10 and the tooth structure 32, particularly at the inner end 28 thereof can lead to fracturing of the tooth root.

By forming the inner end 28 of post 10 as a smooth tapered rounded tip 30, such stress concentrations are minimized.

The groove 20 of post construction 10 provides three separate important functions.

First, the groove 20 functions as a vent to vent cement and/or air from the post space 48 as the post 10 is inserted downward into the post space 48. This is particularly important when the post space 48 is filled with cement prior to insertion of the post 10.

A second function provided by the spiral groove 20 is that it aids in retention of the post 10 in place within the post space 48 by increasing the area of contact of the post 10 with the cement 52.

Finally, in the unlikely but possible event that it is necessary to remove the post 10 after the cement 52 has set, the post 10 can be readily removed by rotating it in a counterclockwise direction thus unthreading the groove 20 from the ridge 54 of cement.

It is because of this function of unthreading the post 10 to remove it from the tooth 32 that the engagement means 26 is provided on the outer end 24 of post 10. As previously noted, the post 10 is not generally threaded into place within the post space 48 but may simply be longitudinally inserted into the post space 48. It is, however, threaded out of the post space 48 after the cement 52 has set.

A curvilinear cross-section shape and particularly the semicircular cross-section shape previously described for groove 20 is preferred as compared to a square or triangular cross-section groove as it eliminates points of stress concentration within the post 10. This combined with the fact that only a single groove interrupts any cross section of the post 10, reduces the possibility of breakage of the post 10 when subjected to chewing forces.

FIG. 8 shows graduated diameter, spirally grooved endodontic post 60. Post 60 is characterized by overall length 62 and three decreasing diameters, primary diameter 64 extending over length 65, first decreased diameter 66 extending over length 67 and second decreased diameter 68 extending over length 69. Diameters 64, 66 and 68 allow post 60 to diminish in size as it passes into a prepared post space having complementarily graduated stages, which can coincide with natural root taper. While three graduated stages are shown in this preferred embodiment, posts having at least two graduated stages or any number of stages greater than two stages can be fabricated as needed for a particular endodontic post application. The prepared post space can be formed by sequentially drilling each graduation to the required depth with a corresponding diameter drill or can be drilled more precisely in a single step with a complementarily graduated drill of the present invention having at least two stages of decreasing diameter.

Primary stage 70, first decreased diameter stage 72 and second decreased diameter stage 74 are all cylindrical in shape and have cylindrical outer surfaces 75, 76 and 77, respectively. Graduated post 60 can have large, intermediate and small diameter stages where the stages have aspect ratios, which are defined as a stage length divided by a stage diameter, in the range 7.5 to 5.5, 1.5 to 3.5 and 2.5 to 3.5, respectively. These ratios are calculated from stage dimensions for different length posts given in Table I. Use of such parallel-sided graduations allows post 60 to taper while retaining superior resistance to extracting forces as a result of parallel surfaces between post 60 and a prepared post space wall as compared to a continuously graduated post whose surfaces are not everywhere parallel to the prepared post space wall. The graduated post design reduces post diameter as it enters a small region of the tooth root, thus reducing stress exerted thereon.

A spiral groove 78 is defined in cylindrical outer surfaces 75, 76 and 77. There is one and only one spiral groove 78 defined in each cylindrical outer surface 75, 76 and 77. Spiral groove 78 is set at pitch angle 80 to a longitudinal axis 82 of post 60. Pitch angle 80 is in a range of from about 35.degree. to about 5.degree.. Preferably, pitch angle 80 is approximately 45.degree..

Spiral groove 78 preferably has a smooth curvilinear cross-section, and preferably is semi-circular in cross-section. Semi-circular cross section groove 78 preferably has a radius, and thus a depth within post 60 from about 5% to about 30% of primary diameter 64. Preferably, groove 78 has a depth in a range of from about 15% to about 20% of primary diameter 64. Groove depth is substantially constant over all post graduations and may be slightly deeper at points where a transition occurs between graduated stages.

Post 60 can be provided in several different diameters to provide a post suitably dimensioned to be closely received within a prepared root canal. Typical post primary diameters 64 are 0.6 mm, 0.8 mm, 1.0 mm and 1.2 mm with overall lengths of respectively 10 mm, 12 mm, 15 mm and 18 mm. Typical graduated post design parameters are given in Table I. The design parameters listed in Table I provide examples of stage dimensions for posts having four different lengths. Post length and stage dimensions can be adjusted to fulfill particular post requirements.

Axially inner end 84 has a tapered and round tip means 86 to minimize stress concentration at areas of engagement of end 84 with a tooth.

FIG. 9 shows graduated, spirally grooved post 60 inserted into prepared, graduated post space 87 in dentine 88 prepared using a complementarily graduated drill shown in FIG. 12. The post space has at least two stages of decreasing diameter and is partially filled with gutta percha or other filler 90. Cement not shown which can be placed in the post space prior to post insertion or coated around the post prior to insertion generally surrounds post 60. Post 60 is neither tightly wedged in the post space nor does it mechanically engage tooth material. Cement bonds post 60 to dentine 88. Amalgam 92 and crown 94 surround post 60. Post 60 can optionally include an engagement means for post removal.

FIG. 10 shows graduated post 100 having overall length and three graduated diameters, primary diameter 112 extending over length 113, first graduation diameter 114 extending over length 115 and second graduation diameter 116 extending over length 117. Each graduation 118, 120 and 122 has a cylindrical outer surface 123, 124 and 125, respectively. Graduated post 100 is the same as post 60 shown in FIG. 8, except that post 100 has smooth, cylindrical outer surfaces 123, 124 and 125, without a spiral groove such as groove 78 of post 60.

FIG. 11 shows graduated post 100 inserted into graduated post space 129 prepared into dentine 130 and partially filled with filler 132. Post 100 is inserted into post space 129 using the same method as used for insertion of spirally grooved post 60.

FIG. 12 shows a graduated diameter endodontic drill 140. Drill 140 is characterized by an overall length 142 which is greater than or equal to the length of an endodontic post which can be placed in a post space prepared using drill 140. Drill 40 is further provided with three graduated diameters, primary diameter 144 extending over length 146, first graduation diameter 148 extending over length 150 and second graduation diameter 152 extending over length 154. Diameters 144, 148 and 152 allow drill 140 to drill a prepared post space having correspondingly graduated diameters and stages corresponding to those of a graduated endodontic post. Primary graduation 156, first graduation 158 and second graduation 160 are all cylindrical in shape. Endodontic drill 140 can have large, intermediate and small diameter stages. Endodontic drill 140 can be used to prepare a graduated post space having large, intermediate and small diameter stages complementarily shaped to an endodontic post which can be inserted into the prepared post space.

Endodontic drill 140 has engagement means 162 at one end which connects the drill to another tool such as a right-angled dental hand piece used to advance the drill within tooth material. Drill flutes 164 remove material as the drill advances to prepare a post space. The drill interior end 168 has rounded tip 170 and does not perform any cutting function.

Use of graduated endodontic drill 140 permits preparation of a graduated prepared post space in a single operation which produces a considerably more precisely shaped prepared post space than could be obtained using a series of conventional drills such as Gates-Glidden drills of varying diameters to sequentially drill multiple stages of a particular diameter to a particular depth.

Thus it is seen that the apparatus and method of the present invention readily achieve the ends and advantages mentioned as well as those inherent therein. While certain preferred embodiments of the invention have been illustrated and disclosed for purposes of the present disclosure, numerous changes in the arrangement and construction of parts and steps may be made by those skilled in the art which changes are encompassed within the scope and spirit of the present invention as defined by the appended claims.