Dental anchor and a drill for use therewith

An anchoring pin for retention of a dental restoration onto a tooth stub, the pin including an upper retention portion on which a restoration is to be formed, a lower anchoring threaded portion self-threadable in a bore pre-drilled in the tooth stub and a stop collar interconnected between the retention portion and the anchoring portion. A stepped dental drill having two coaxial drill bits of different diameters is provided, which in addition to forming the bore makes a counterbore at the mount of the bore at the exposed excavated surface of the tooth. The counterbore receives the stop collar of the anchoring pin as the latter is driven into the tooth bore thereby preventing bottoming out of the pin so as to avoid concentrated stress at the tip of the pin and also providing distribution of stress as the wider collar abuts the bottom of the counterbore.

BACKGROUND OF THE INVENTION 
The present invention relates to a dental anchor or pin for aiding in the 
retention of a dental restoration and, more particularly to a dental 
anchor provided with means for reducing stress both upon a tooth stub in 
which it is inserted as well as reducing cracks in the restoration which 
is built up over the anchor. 
Dental anchors or pins for retaining dental restorations are well-known in 
the art of dentistry, particularly anchors or pins having threads thereon 
for securement in the tooth structure. The tooth stub is typically 
prepared by cutting it down and making a bore in the tooth stub, in which 
a dental post is inserted. Additional bores are formed in the tooth 
structure, into which pins or anchors are threaded. These pins have 
portions extended upwardly of the tooth surface for aiding in the 
retention of the dental restoration as well as avoiding rotation of the 
restoration on the tooth stub. Such anchoring pins are very small, i.e. in 
order of 0.03 inches in diameter and 0.2 inches in length. These pins are 
typically first loaded into a dental power tool or holder and inserted 
into prepared bores or channels made in the body of the tooth. Such bores 
or channels are formed in the body of the tooth by means of dental drills. 
Anchors or pins for anchoring and supporting a dental restoration are 
typically comprised of two portions, one of which is an anchoring portion 
threaded in the bore formed in the body of the tooth and another is a 
retention portion for embedding into the restoration. Typically the 
retention portion is coupled to a manipulating head extending from the 
retention portion and connected by at least one reduced diameter portion. 
In this way when the pin is threaded into the bore formed in the tooth the 
pin severs automatically upon bottoming out the lower end of the bore. The 
anchoring portion remains in the tooth with the retention portion 
extending upwardly from the tooth surface. 
Dental anchors or pins having a buttress-type thread has been disclosed in 
assignee's co-pending patent application Ser. No. 191,347. They have 
proven to have a most satisfactory retention capability inasmuch as 
buttress-type threads, particularly the reverse buttress-type threads 
described, provide improved holding power in the dentition and reduce the 
amount of dental damage during insertion. 
The aforementioned co-pending application discloses a dental anchor having 
a buttress-type thread, where the buttress-type thread includes a 
substantially planar lower surface facing toward the insertion end of the 
dental anchor, a beveled upper surface which tapers inwardly towards the 
retention portion of the dental anchor, and a sharp crest portion disposed 
between the planar lower surface and angled upper surface. A top member or 
collar is provided between the anchoring portion and the retention 
portion. The stop member limits the depth of insertion of the dental 
anchor into the bore. 
It should be appreciated, however, that even with highly efficient dental 
anchors or pins having buttress-type threads there is a continuous 
interest in further reducing or minimizing any stress on existing dentin, 
especially at the bottom or seat portion of the bore which receives the 
dental anchor. 
Accordingly, while the use of dental anchors having a buttress-type threads 
thereon has been proven quite useful in the dental art, further 
improvements in such dental anchors and means for anchoring the same in 
the tooth body are still of importance in order to yet further reduce any 
stress on dentin material and to facilitate anchoring or such pins. It is 
also of interest to facilitate insertion at surfaces of teeth which are 
inclined, curved or have any other non-planar exposed surfaces. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a dental anchor which 
avoids the aforementioned problems of prior art dental anchors. 
Another object of this invention is to provide a drill for making channels 
or bores receiving the dental anchors to substantially reduce stress on 
the dentin material of the tooth. 
Yet another object of the present invention is to facilitate preparation of 
the tooth stub for building thereon a dental restoration. 
It is a further object of the present invention to provide means for and a 
method of installing dental pins which would substantially minimize stress 
on the tooth stub as well as on the dental restoration to be built 
thereon. 
Briefly, the objects of the present invention are attained by a dental 
anchor for the retention of a superstructure on a tooth stub and 
insertable into a bore formed in the tooth stub. The dental anchor 
comprises an upper retention portion, on which the superstructure or a 
dental restoration is to be formed, an anchoring portion having a threaded 
portion thereon and being self-threadable into the bore in the tooth stub 
to secure therein the dental anchor, and a stop provided between the 
retention portion and the anchoring portion for limiting the depth of 
insertion of the dental anchor into the channel. The retention portion is 
of a smooth continuous configuration having no sharp corners thereby 
substantially reducing stress on the superstructure, avoiding the 
occurrence of cracks therein and providing a smooth distribution of the 
restoration material over the retention portion. 
In an embodiment, smoothly shaped undercuts are formed along the retention 
portion adjacent the anchoring portion. The restorative material is packed 
in these undercuts to provide improved retention onto the tooth stub. 
The objects of the invention are also attained by a stepped dental drill 
which not only drills the anchor receiving bore in the tooth stub but also 
forms a counterbore at the exposed excavated surface of the tooth. The 
drill is matched to the anchor so that the bore will be longer than the 
threaded portions of the anchor. When the dental anchor engaged in a 
holder is rotatably inserted into the bore the stop collar seats into the 
counterbore to stop further insertion of the anchor and prevent bottoming 
out of the anchor. The collar also serves to distribute the stress over a 
flat wide surface rather than concentrating stress on the bore edges 
having the threading. By making the collar wider than the crest of the 
threads, the collar will have a chance to sit on supported dentition which 
also distributes and reduces stress. 
In an embodiment, the drill is gripped in a holder so that its outer 
stepped portion axially extends a limited amount from the holder 
corresponding to the depth of the counterbore desired. Thus the holder 
forms a shoulder which constitutes a stop for drilling the channel with 
the counterbore into the tooth stub. 
The aforementioned objects, features and advantages of the invention will, 
in part, be pointed out with particularity, and will, in part, become 
obvious from the following more detailed description of the invention, 
taken in conjunction with the accompanying drawing, which form an integral 
part thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings in detail, FIG. 1 illustrates a dental anchor 
or pin 10 according to an embodiment of the present invention. Pin 10 
includes an upper manipulating portion 12 which is typically held in a 
shank portion as shown in FIG. 2 and described hereinbelow, for insertion 
into a manual driver or an automatic drill. The pin 10 includes a 
retention portion 14, an intermediate stop member 16 and a lower anchoring 
portion 18. The latter is inserted in a channel or bore formed in the body 
of the tooth stub to anchor the pin into the tooth body. The stop member 
16 is intended to limit the depth of insertion of pin 10 into the bore so 
that the retention portion 14 will extend upwardly from the exposed 
excavated surface of the tooth stub to form a retention means for a dental 
restoration formed on the tooth stub. The stop member 16 also serves to 
distribute stress, as will hereinafter be explained. 
The anchoring portion 18 is formed as an elongated cylindrical body 
provided with a thread, shown as a helical reverse buttress-type thread 20 
as is described in the aforementioned copending patent application. The 
buttress-type thread 20 has a substantially planar lower surface 22 which 
faces towards an insertion end 29 of the pin, and an angled or beveled 
upper surface 26 which tapers inwardly towards the retention portion 14 of 
pin 10. A knife-like cutting edge 28 is provided in the thread 20 between 
the planar surface. The threads on anchoring portion 18 are of a thread 
forming type which deform the dentin rather than cutting into the dentin. 
This also reduce stress on the tooth material as compared to 
thread-cutting pins. 
The buttress-type thread utilized in the dental anchor according to this 
invention is disclosed in detail in the aforementioned assignee's 
co-pending patent application. The buttress-type thread is of a reverse 
construction where the beveled surface 26 tapers inwardly towards the 
upper end of pin 10. In such a reverse construction, the force required to 
pull pin 10 out from the bore formed in the tooth is increased as compared 
to dental anchors known in the dental art since, in addition to a vertical 
force required for pulling out the pin an additional force normal to the 
plane of the buttress thread angle is required to pull out the pin. This 
substantially enhances the retention of the anchoring portion of the pin 
within the bore of the tooth over threads of other types. Distal end 24 of 
the anchoring portion 18 is chamfered at 30 and tapers inwardly towards the 
end surface of the anchoring portion 18. Anchoring portion 18 is integral 
with the substantially cylindrical stop member or collar 16. The external 
diameter of the collar is greater than the largest diameter of the thread 
crest 28. 
Retention portion 14 is an elongated barrel-like body having curved side 
walls tapering towards the collar 16 and merging at the upper end thereof 
into the substantially cylindrical manipulating portion 12. The angle 
.alpha. of tapering of the retention portion 14 downwards may vary between 
5.degree. and 10.degree.. A transition zone or undercut 32 helps retain the 
restorative material in place. The elongated body of the retention portion 
14 has no sharp corners or edges so that the whole retention portion of 
the pin 10, which receives thereon a dental restoration is extremely 
smooth. This significantly reduces stress in the restorative material 
thereby eliminating post curing (setting) cracks formed therein. Shaped 
undercut 32 permits packing of the restorative material to form a 
continuous band of restorative material under the upper part of the anchor 
to thereby help retain the dental restoration. The outer diameter of collar 
16 is greater than the major diameter of the threads by approximately 
10-15/1000". 
Cylindrical manipulating portion 12 terminates at a substantially 
frusto-conical end portion 36 which has a conical proximal end 38. A 
reduced diameter neck 34 forms a fracture groove between the manipulating 
portion 12 and the retention portion 14 to facilitate shearing of the 
anchor from the manipulating portion. The elongated cylindrical surface of 
the manipulating portion 12 constitutes guide means for the insertion of 
pin 10 in a standard shank driver 40 shown in FIG. 2. Shank driver 40 is 
provided with a standard locking arrangement 42 for insertion into a 
dental handpiece. In the alternative, shank 40 can also be connected to a 
manual drive tool. Shank driver 40 is used to drive the pin 10 into a bore 
formed in the tooth stub body. An indent 44 can be provided on the 
manipulating portion 12 of pin 10 to wedge the pin in the shank driver 40. 
Any other suitable means for firmly retaining pin 10 in the shank driver 40 
can be also used to allow pin 10 to be rotated and inserted in a 
corresponding bore in the tooth stub body. Pins 10 may be made of 
stainless steel, titanium or any other suitable material. 
FIGS. 3 and 4, illustrate a spiral drill 50 for producing bores or channels 
in the tooth body receiving the anchors previously described. Drill 50 is 
inserted in a shank driver 52 having an elongated cylindrical body 
provided at its proximate end with a standard coupling arrangement 54 for 
insertion into a dental handpiece. Drill 50 includes a substantially 
cylindrical guide portion 56 insertable and fixable in a cylindrical blind 
hole 58 formed in a drill receiving portion 60 of a reduced diameter front 
end 61 of the shank driver 52. The external cylindrical surface of the 
drill receiving portion 60 slightly tapers at 78 towards the distal end of 
the drill holder. 
As best shown in FIG. 4, a recess 62 formed in the upper surface of the 
guide portion 56 of the drill bit extends in the direction of the axis of 
the drill. An inwardly protruding elongated portion 64 formed on the inner 
surface limiting the blind hole 58 is snapped or keyed in recess 62 to 
firmly grip drill 50 in the shank driver 52. Two coaxial stepped drilling 
portions or bits 70 and 72 of different diameters are provided in drill 
50. Drill bit 72 of a greater diameter than that of drill bit portion 70 
is provided to produce a counterbore at the mouth of the main bore formed 
by the drill portion 70, as will be explained below. 
As shown in FIG. 3 guide portion 56 of the drill 50 is dimensioned so that 
it extends outwardly from the shank driver 52 to produce a protruding 
portion 76 of the larger diameter drill portion 72. The edge 78 of the 
shank forms a stop shoulder. This shoulder constitutes a stop for drilling 
and ensures a fixed length of the bore and a fixed depth of the 
counterbore. Holder portion 60 has its distal end curved at 78 to avoid 
sharp corners and prevent a striking effect on the exposed excavated 
surface of the tooth stub during the drilling process. 
The ratio between the length of the larger stepped drilling portion 72 and 
that of the main thinner drilling portion 70 amounts to 1:4 to 1:5 and, 
with drills 0.300 in. long the length of portion 72 is between 0.015 and 
0.20 in. 
Referring now to FIGS. 5 to 8, it is seen that the tooth to be prepared 
typically includes a dentin material 80, a pulp channel 90 and a layer of 
enamel 92. The stepped spiral drill 50 is urged into the dentin material 
of the tooth 80 to produce a plurality of channels and bores 82 extending 
into dentin 80 from an exposed excavated surface 84 from which decay was 
removed before drilling channels 82. The number of bores 82 varies with 
the area of exposed excavated surface 84 and the size of a dental 
restoration further to be built on the tooth. The diameter of the drill 
bit may be of a size depending on the pin size and tooth area. In one 
embodiment a diameter of 0.028 inches was used. As bore 82 is drilled by 
bit portion 70, the drill is further inserted into this bore until the 
enlarged drill bit portion 72 enters the dentin material at the proximal 
end or mouth of bore 82 and forms a counterbore 86. 
As mentioned hereinabove shoulder 78 formed by the drill shank driver 52 
limits the insertion of the enlarged portion 72 of the drill into the 
dentin material and thus the depth of the counterbore 86 substantially to 
the height of the collar 16 of the pin 10 which is to be received in the 
respective bore. After a desired number of bores 82 with counterbores 86 
have been produced, anchoring pins 10 are inserted into each of bores 82. 
It will be apparent that the diameter of the anchoring portions 18 of each 
pin is greater than the diameter "a" of the bore 82. Thus the anchoring 
portion 18 of each pin is tightly threaded into its respective bore 82 as 
the shank driver 40 which holds the manipulating portion 12 of the pin is 
rotated. As pin 10 is urged further into bore 82 collar 16 of pin 10 
enters the counterbore 86 and seats in the counterbore thus limiting any 
further extension of the pin end 24 into the distal blind end 96 of the 
bore. The counterbore 86 may extend by 1/1000 to 15/1000" below the 
surface 84 of the tooth. Upon insertion the pins shear at their reduced 
diameter portions and remain in place in the tooth stub. 
In conventional anchoring pins, the pins are introduced into respective 
bores formed in the tooth stub. The blind end of each bore has a mating 
angled configuration similar to the distal end of the anchoring portion of 
the pin and forms a seat therefor. As the pin is inserted, it continues 
till the pin bottoms out at the bottom of the bore where stress is exerted 
on the body of the tooth. The stress is concentrated. Such stress not only 
exists at the time of insertion but even during loading. 
In the present pin because collar 16 seats in the counterbore 86, it 
prevents the pin from bottoming out. This eliminates the stress at the 
lower end of the bore. Furthermore the collar distributes the stress over 
a much greater surface area than that of the distal end 24 of the pin. In 
addition, because the collar has a diameter greater than the crest of the 
threads, the collar sits on solid dentition that is not over a threaded 
undermined, edge, as shown at 95 in FIG. 7. Thus the stress is distributed 
in the region supported by solid dentition rather than in the region of the 
thread. The sizing of the drill with the mating size of the anchor is such 
that when the collar 16 is received in counterbore 86 a clearance of at 
least about one fourth of a mm remains between distal end 24 of the pin 
and the blind end 96. The collar and counterbore combination according to 
the present invention not only re-distributes stress on the tooth during 
the insertion of the pin but also significantly reduces stress during 
loading of the tooth. Collar 16 will constitute a positive stop preventing 
the threads from crushing. As the lower surface of collar 16 reaches the 
bottom of counterbore 86, shank holder 40 shears off at the reduced 
diameter section to enable pin 10 to be anchored in the bore. 
It will be also appreciated that due to the fact that the retention portion 
of pin 10 has no sharp corners and is anatomically shaped, stresses in the 
upper restorative material would also be reduced and post setting cracks 
in the amalgam or composite would be substantially prevent from the 
occurrence. 
It should be also noted that at inclined portions of the excavated surface 
84 the counterbore 86 produced in the tooth body 80 may be incomplete due 
to the tooth's anatomy as illustrated at the left-hand channel 82 of FIG. 
5. However, by making even a part of the counterbore, a flat bottom 
surface is produced on which the collar can sit. Thus, even though the 
tooth surface is uneven or inclined, nevertheless the pin will sit along a 
flat even surface of the counterbore and distribute the stress. Also, the 
collar 16 will sit within such counterbore and still, limit the further 
insertion of the pin into the bore. 
FIG. 8 shows a completed restoration with three pins 10 being employed and 
with the restorative material of choice 100 being secured over the pins. 
If necessary, a final outer cap 102 can be secured to the core. It should 
be appreciated that in some cases, a post could also be used with one or 
two of the pins and positioned in the tooth stub. 
It should be understood, of course, that the foregoing disclosure relates 
to only a preferred embodiment of the invention and that it is intended to 
cover all changes and modifications of the example of the invention herein 
chosen for the purpose of the disclosure, which modifications do not 
constitute departures from the spirit and scope of the invention.