Dental product combining a reamer tool and anchor post

There is provided a combination dental tool for forming a bore in a tooth stub and which can then be used for the anchoring of a dental prosthesis to the stub. The combination tool is formed having a first cutting end portion and an opposite, and second, holder end portion, to be held by a dental handpiece. The holder portion is formed adjacent a crown anchor portion and the holder portion can be removed after the bore is formed. Preferably, the crown anchor portion is formed of a softer material which can be readily formed to the desired shape for the prosthesis. The cutting portion preferably has alternating sections of larger and smaller diameter and has laterally facing cutting surfaces to form undercut portions along the bore to aid in firmer seating of the anchor post.

BACKGROUND OF THE INVENTION 
The present invention relates to a combination product which combines the 
utility of a tool and a prosthesis support post for use in dentistry, and 
more particularly to a product which first can be used as a dental tool 
which provides for the drilling of a bore hole and for the forming of 
lateral undercuts along the interior longitudinal surface of the bore hole 
into a tooth canal, and which can be rotated by a dental handpiece 
associated with a dental drill, and at least a portion thereof can then be 
maintained within its own drill-hole as an anchor, or support, post for a 
dental prosthesis. 
It is well known in the dental field to provide a drill tool bit for 
forming a bore hole through the root canal of a tooth. It is also common 
to grind away the upper surface of the tooth, using a dental grinding tool 
to provide space for a dental prosthesis to be anchored to the tooth via 
an anchor post extending into and cemented within the bored out root 
canal. Such dental anchors are generally cemented into the bore hole and 
in some cases the anchors are provided with undulating lateral surfaces to 
further assist in securing the anchor to the cement. It has been found, 
however, that the security of the dental prosthesis may be compromised by 
a failure of the cement holding the anchor in the bore, as well as by the 
difficulty of seating the prosthesis around a projecting portion of the 
anchor and onto the top of the tooth. Further problems can be created by 
the use of an improperly matched anchor post for the reamer diameter, 
especially where a passive anchor post is desirable. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a dental 
tool which combines the effectiveness of a bore drill, or reamer, and an 
undercutting routing tool, and can act as the prosthesis anchor post, to 
provide improved accuracy of fit and for the security of the cemented 
anchor within the tooth. It is a further object of the present invention 
to optimally provide on the tool a counterboring portion to enlarge the 
outer end of the bore. It is a further object of the present invention to 
provide all of these effects by a single tool, which can then be reformed 
into the anchor post, thus permitting not only efficiency in the number of 
tools required, but also simplifying the problem of maintaining the 
accuracy of fit and the integrity of, and desired mutual relationships 
between, the bore hole and the cemented anchor post in the bore hole. 
These and other objects are achieved in accordance with the present 
invention wherein the combination dental device includes a first holder 
end portion designed to be receivable in a dental tool holder, such that 
the dental tool holder can rotate the dental tool; a second drilling, or 
reaming, end portion tapering longitudinally endwardly to a minimum 
effective diameter at the second end and providing an axially facing 
cutting surface for forming a bore of sufficient diameter in a tooth of a 
patient, upon rotation of the tool, to receive an anchor post; a drill 
shank portion extending from the drilling end portion towards the holder 
portion and preferably including at least two alternating longitudinally 
extending shank sections, the first drill shank section having laterally 
facing cutting surfaces and a relatively larger effective diameter, and 
the second drill shank section having a smaller effective diameter and a 
non-cutting surface such that the application of laterally directed force 
to the tool while the tool is being rotated within the bore of the tooth 
provides for the routing out of notches, or undercut surfaces, along the 
interior of the bore in the direction of the laterally directed force. The 
drilling end of this tool is intended to include means for forming a hole 
by drilling, as well as reaming means to enlarge the tooth root canal. 
There is further preferably provided, at a portion intermediate the drill 
shank portion and the first holder end, a divergent counterbore drilling 
section capable of forming an enlarged bore diameter at the outer end of a 
bore hole in a tooth, and a planar grinding surface. 
The first holder end portion of the tool is designed to be removably 
secured to a conventional dental handpiece so as to be rotatably driven 
from the handpiece. The tool is to be secured into the handpiece such that 
it will maintain its position upon the application of longitudinal force 
exerted toward the second drilling end of the tool and upon the exertion 
of lateral force while the tool is being rotated as described in the 
above-identified copending application. 
Immediately adjacent to the maximum diameter end of the counterbore, and 
extending towards the holder end, is a prosthesis core support portion 
which preferably has a maximum diameter at least about equal to the 
maximum effective diameter of the counterbore. 
In one embodiment, where the prosthesis core support portion diameter is 
not significantly larger than the maximum effective diameter of the 
counterbore, a prosthesis core can be built up around the core support 
portion, which may have to be shortened by removing the holder end, if 
necessary. In another embodiment, the maximum core support diameter is 
significantly larger than the counterbore and an e.g., all metal core 
unitary with the anchor post can be prepared by working and shaping the 
core support portion by known means. In this latter situation, the axially 
facing surface of the core support portion is a planar grinding surface 
for cutting down and levelling the tooth surface and surrounding the 
counterbore to support the prosthesis. 
The core anchor section preferably tapers inwardly towards the holder end 
and can be rippled, or scored, to present undercuts to improve adhesion of 
the core anchor section to composite or cement material forming a core for 
the immediate support of a crown, or prosthesis, above the tooth stub. If 
the core anchor section has a diameter sufficient to form a unitary core, 
the undercuts are to be added after the section has been cut and shaped to 
accept the crown prosthesis. 
After the bore hole is reamed, and routed out to form the undercuts, the 
reamer is replaced into its self-drilled hole, and cemented into place as 
an anchor post. The holder end extends above the bore, and serves as a 
useful handle for manipulating the anchor post until the post is cemented 
in place. 
Any pre-formed undercuts in the core anchor section are to be limited in 
depth so as not to reduce the structural strength of the reamer such that 
it would not be able to withstand the stress of boring. After the drilling 
end is cemented into the bore hole, the portion protruding above the bore 
hole can be trimmed and cut to the desired size using a conventional edge 
grinder disk, for example, and undercuts can be added. 
The combination dental tool and post of the present invention is to be used 
with a conventional dental tool handpiece as providing support and driving 
power for the device. The size and shape of the holder end is thus 
necessarily limited by the requirements of conventional handpieces. 
As used in the process of this invention, the drill point, or reamer, is 
placed at the exposed root canal opening of a tooth. The tooth has been 
reduced to approximately the desired height above the gum line by removing 
broken or decayed dental material. The combined tool post is held by a 
conventional dental handpiece and the power applied to rotate the tool at 
low speeds in a conventional manner, pressing downwardly against the tooth 
to bore out a hole of the desired depth. This procedure is especially 
useful for preparing a tooth for the placing of a crown on an anterior 
mandibular or maxillary tooth. 
It is well known in the dental field to select a drill, or reamer, of a 
proper length and diameter to obtain the desired size bore hole. For the 
present invention, however, the length of the drill shank is preferably 
carefully calibrated with the desired depth of the bore, as the drill 
shank is preferably inserted substantially completely into the bore hole, 
such that the counterbore portion of the tool forms a funnel-shaped 
enlargement of the entrance to the bore hole, by reaming out a 
counterbore, and the planar grinding surface, if present, can grind to a 
level plane the surface of the tooth. In addition, the core post shank 
should extend above the top surface of the tooth to form the central 
support for the prosthesis core. The enlarged counterbore is preferably 
provided at the zone of greatest stress, at the interface of the ground 
down tooth and the crown. 
After a hole is bored out to the desired depth, using the preferred tool of 
the present invention, the tool is withdrawn a short distance above the 
bottomed out position, and lateral pressure exerted by the tool on the 
sides of the bore, preferably alternately and only in the facial and 
lingual directions. In this manner, the enlarged first shank sections rout 
out laterally undercut notches at the spaced positions of such first 
sections along the bore, in the preferred lingual and facial directions. 
It is noted that the tool preferably does not widen the cross-section 
around the entire circumference of the inner bore in the tooth, but only 
elongates those portions contacted by the cutting surfaces of the first 
sections of the drill shank portion in the direction in which lateral 
pressure is exerted. 
The combination tool/post is withdrawn from the bore hole and disconnected 
from the handpiece. The drill shank is then inserted back into the bore, 
leaving the core post shank extending beyond the tooth. Cement is packed 
into the bore hole with the post in the conventional manner, but 
surrounding the anchor post, and extending into the bore hole undercuts, 
securing the post in the bore hole; the holder end portion is then usually 
cut off from the anchored post at the desired length. The core anchor 
section, if large enough, can be shaped and cut to the proper size to 
serve as a unitary core for a crown. The security of the cemented seal is 
improved by the interaction between the routed out undercuts in the bore 
and the varying diameter along the drill shank.

Referring to the drawings, a combination reamer tool and post, indicated by 
the numeral 125 is shown having a reaming, or drilling, first pointed end 
127, a drill shank portion, indicated by the numeral 128, comprising a 
plurality of cutting and routing sections 129, separated by a plurality of 
relatively smaller diameter shank stop sections 130. Located immediately 
adjacent the innermost stop section 130 is the divergent counterbore 
section 132. Immediately adjacent the maximum diameter of the counterbore 
section 132, and extending axially towards the holder end 122 is a 
cylindrical core post shank section 123, and immediately adjacent thereto, 
and tapering inwardly towards the holder portion 122, is the rippled or 
undercut core anchor section, generally indicated by the numeral 124. A 
holder end portion 122 extends outwardly from the core anchor post section 
124. 
The outer section of the holder end portion 122 is of conventional design 
suitable for being secured to conventional dental handpieces, and can be 
adapted for whichever dental handpiece is to be used. 
The cross-sections of the cutting portions 132, 129, 127 are preferably 
substantially square. The cross-section of the core post shank 123 is 
round as can be the cross-sections of the smaller diameter intermediate 
shank stop sections 130; these latter sections are herein shown as square 
in the drawings. 
The cutting portions of the tool 128 of FIG. 1, include the lower drilling 
end 127, the counterbore portion 132, and the larger routing shank 
sections 129. The smaller diameter shank stop sections 130 do not include 
a lateral cutting surface, such as are present on the routing shank 
sections 129. The various cutting surfaces and the drilling point end 127 
can be coated with a hard, fine granular substance, such as diamond dust. 
The cross-sectional views of FIGS. 6 and 7 show that both the routing 
sections 129 and the intermediate, smaller diameter shank stop sections 
130, are substantially square in cross-section. 
Both of the embodiments depicted in the drawings are provided with 
laterally cutting routing sections 129, having an outer surface forming a 
substantially continuous curve in an axial direction, between two smaller 
diameter intermediate stop sections 130. The curved cutting surfaces of 
the routing sections 129 can be also optionally coated with hard, fine 
granular material, such as diamond dust, if desired. 
The combination tool and post 125 can alternatively be formed having 
cross-sections of various other regular polygons, as desired, the apices 
of the polygons in the routing sections 129, drill point 127, and 
counterbore 132, providing the cutting edges. Included within the scope of 
such polygonal cross-sections are shapes having at least one curved side, 
such as so-called half-round or quarter-round shapes. Preferably, the 
polygons have no more than six sides. When the term "diameter" is used for 
such polygonal cross-sections, it refers to the "effective diameter", 
i.e., the diameter of a bore hole cut by such sections rotating about a 
single axis. 
The core post shank 123 is substantially circular in cross-section, being 
substantially cylindrical in overall shape. The core anchor section 124 is 
substantially a truncated pyramid in overall shape, having substantially 
square cross-sections, with the apices rotated about 45.degree. relative 
to the apices of the drill shank section 128. The undercut portions 114, 
have a substantially reduced diameter, providing for more secure adhesion 
to the core composite cement. 
If desired, the combination device of the present invention can be 
fabricated with marked segments, or score lines, indicating units of 
length. For example, the segments on the anchor core section, or the 
individual drill routing sections, can be formed to a specific length, 
e.g., 1 mm. This permits readily cutting or grinding the drill or reamer 
to the desired length by merely counting segments. 
The initial reaming out of the tooth root canal is carried out not only by 
the end drilling portion 127 but by the leading routing ring section 129. 
Referring to FIG. 8, and to FIG. 9, wherein the combination tool of the 
present invention is located within a bored hole, the tool 125, is 
operatively supported and held by a conventional handpiece, generally 
indicated by the numeral 50. The handpiece is of a conventional type, 
which can provide support and carry the driving power to the tool 125 to 
cause it to rotate. The handpiece 50 can securely hold and mechanically 
drive the tool 125, while being subjected to longitudinal forces exerted 
axially into the tooth, during a reaming out operation, or while being 
subjected to force applied laterally, and against the lateral interior 
surfaces of the bore, during a routing operation. Such hand pieces are 
well-known, and can, e.g., be air- or motor-driven, or directly gear 
driven, by straight or right angle dental rotary devices. 
Referring to FIG. 14, a combination tool is shown, generally indicated by 
the numeral 225, wherein the anchor core section 224 is substantially 
larger than that of the counterbore 232. A planar grinding surface 252 is 
formed defining the edge of anchor core 224 and extending annularly about 
the counterbore maximum diameter. The drill shank 228 is substantially 
similar to that of the first embodiment of FIG. 1, and all of the cutting 
surfaces 227, 229, 232 and the grinding surface 252 can be formed of 
similar hard materials and coated with the hard granular material, such as 
diamond dust. 
In carrying out the procedure in accordance with the present invention, 
after the bore is fully formed in the tooth, as shown by FIG. 9, including 
an enlarged counterbore at the top surface of the tooth, the tool 128 is 
lifted above its bottommost position, as shown in FIG. 10, such that the 
counterbore 13 is above the top surface of the tooth. Lateral pressure is 
exerted from the handpiece 50 through the tool 125 and against the inside 
of the tooth bore, while the tool 125 is continuously rotated at the 
desired speed. Such pressure is preferably exerted successively in the 
lingual and facial directions, such that the grinding rings 129 are forced 
against the sides of the bore, routing out undercut surfaces, or notches, 
along the surface of the bore in those directions. The pressure is exerted 
first in one of the preferred directions and then in the other of the 
lingual and facial directions. 
The router portions 129 are preferably approximately 25% larger in diameter 
than the second, lesser diameter stop sections 130, such that upon fully 
routing out the undercut notches, the notches have a major elliptical 
diameter approximately 50% greater than the original bore hole diameter. 
The maximum diameter of the counterbore 132 is preferably at least 50% 
larger than that of the router sections 129, and the diameter of the 
planar grinding surface 252 is at least about 50% larger again. 
A fully reamed and routed out reduced tooth T, from which the reamer has 
been withdrawn, is shown in FIG. 11. The reamer 125 is removed from the 
handpiece 50, and the portion comprising the counterbore 132, the drill 
shank 128 and drill tip 127 is reinserted into the reamed and routed out 
tooth bore, as the anchor post base, as shown in FIG. 13, and cemented in 
place. 
The anchor post base 128 is inserted into the prepared bore hole, with 
cement to secure the anchor in place. The inherently accurate size 
relationship between the bore hole and the anchor post diameters, permits 
this anchor post 128 to be readily used as a so-called "passive" anchor, 
where the post need not be screwed in place into the bore hole. The post 
128 merely drops passively, or is gently pushed, into the bore. As shown 
in FIGS. 13 and 15, the larger diameter router sections 129, 229 are not 
juxtaposed with the routed out, undercut tooth bore sections (B). In this 
manner, the cement has been found to more securely hold the anchor post in 
place. 
Extending outwardly from the tooth bore is the core anchor post, which 
comprises the cylindrical core post shank 123 and the convergent anchor 
127 section 124, and the holder end 122, which anchors a tooth prosthesis, 
P. If necessary, the protruding holder end 122 is cut down to the desired 
length beyond the surface of the bore hole, and to the desired shape, and 
then cemented integrally with a core to support the desired crown 
prosthesis. 
In FIG. 15 there is depicted a crowned tooth prepared with a unitary anchor 
post and crown core 228, 224, made of an integral piece of material; the 
anchor core section 224 is shaped and sized (from its original shape shown 
in dashed lines) to the core size shown in the drawing, by well known 
dental fabricating means. This unitary core can directly retain and secure 
that crown prosthesis by being cemented to the crown directly. 
The present invention not only reduces the number of individual items the 
dentist must keep in stock and sterilize for use, but also avoids the 
problem of a misfit between the anchor post base and the bore hole. 
Although the particular shape of the core anchor post 121 shown, is not a 
necessary feature of this invention, the combination of the cylindrical 
core post shank 123 and the undercut tapered pyramidal core anchor section 
124, provides an especially secure, core anchor post beneath a composite 
core. 
The particular shape of the drill cutting segments 132, 128, 127 of this 
combination dental product is also not critical to the invention. For 
example, any of the drill shank embodiments described in the 
above-identified co-pending application can be used with this invention, 
and can be used as the anchor post base. A straight, constant diameter, 
drill shank can be provided, if desired. 
It is understood that the core anchor section 124 and the core post shank 
117, or the unitary core 224, need not be made of the same material as the 
rest of the combination product, i.e., the holder end 122 and drill shank 
128 (which is inserted into the tooth bore). For example, titanium alloy, 
or other hard and tough material, such as stainless steel, is the material 
of choice for the drill shank 128, i.e., that portion of a prosthesis 
anchor to be inserted into the tooth bore. The core anchor portions 117, 
124, or unitary core 224, however, can be formed of the same metal or of a 
softer, more easily shaped material, such as a ceramic dental material, a 
polymer composite, or a ceramic/metal or polymer/metal laminate, or 
another metal, for example. The undercut core anchor section 124, or the 
unitary core section 224, should, however, have sufficient torsional 
strength to withstand the stress of rotary drilling. All of these anchor 
post materials, as well as other materials well-known to the art, can be 
formed as a unit with the drill shank and counterbore portion by 
well-known means, such as welding, soldering, or casting or molding 
together.