Apparatus for undercutting a tooth

A dental tool is disclosed having a hollow cylindrical body portion, with an enlarged angular ring at one end, said ring having an abrasive coating thereon. The size and configuration of the enlarged annular ring allows the tool to be used to undercut the tooth surfaces in various ways, thereby allowing new methods in the securing of dental prostheses to existing teeth or to the jaw itself, or to the augmentation, or grafting, of bone material to reinforce a tooth, including (a) the creation of an undercut groove at the base of a prepared tooth into which a gasket can be positioned to form a seal with the dental prosthesis (b) the drilling of an annular or cylindrical cavity with an undercut portion in a tooth or jaw bone into which a shaped insert can be securely mounted, which insert can act as a mounting for a dental prosthesis, and (c) harvesting a core or plug of bone material from a jaw bone, crushing the harvested bone and implanting said harvested bone around a tooth situated in the same jaw as the crushed bone was harvested, as a bone augmentation procedure to strengthen said tooth.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a tool to be used in dentistry and the use 
of this tool in new methods for the enplacement of dental prostheses. More 
particularly, the present invention relates to a tool which allows 
excavation or undercutting of a tooth or jaw bone in different 
configurations and depths, which may be used to (a) form an indentation 
around the base of a prepared tooth into which a gasket can be inserted to 
seal a veneer, crown or jacket in place on the tooth, (b) form either an 
annular or cylindrical hole in a tooth or jaw to receive an insert upon 
which a crown or artificial tooth can be mounted, or (c) obtain a plug of 
bone material, which harvested bone material can be crushed to granular 
particles and placed around the base of a tooth as a bone augmentation and 
strengthening procedure. 
2. State of the Art 
It is conventional practice in dentistry to apply a veneer prosthesis to a 
tooth which has been damaged either as a result of trauma or disease, i.e. 
caries. Generally, the surface enamel of the tooth is partially removed by 
grinding to form a relatively even surface, a mold is taken of the tooth 
and the surrounding portion of the mouth to form a prosthesis, which is 
then adhesively secured to the previously ground down surface. 
Such a veneer is generally not subject to the extreme structural stress to 
which the facing transverse surfaces of teeth are subject, but rather, is 
applied to a vertical, buccal or labial surface. The veneer is intended 
primarily for cosmetic purposes, but also to protect the remaining enamel 
of the tooth from further damage caused by chemical or bacterial action. 
Great care must be taken to insure that the veneer is securely applied to 
the tooth substrata so as to not only be cosmetically satisfactory, but 
also insure against stress during chewing. Dentists must carefully place 
the veneer against the surface, and by eye insure that it has been 
properly placed 
In teeth which have received more extensive damage, major portions of the 
tooth's surface may be replaced by a crown. Normally the surface is 
prepared to a desired shape which will help retain the crown. A mold is 
then made of the remaining prepared tooth in order to shape the portion of 
the crown which will be in contact with the tooth. The resulting crown is 
thereafter mounted on the prepared tooth. Various tools have been 
developed to shape the tooth, such as seen in U.S. Pat. No. 2,250,058 
issued Apr. 8, 1940 to Brooks, or U.S. Pat. No. 4,473,354 issued Sept. 25, 
1984 to Rigaud. Additionally, a post may be mounted in the tooth or in the 
underlaying jaw as an aid to holding a crown or artificial tooth in place. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a new tool which will 
allow the dentist to use improved procedures for the attachment of 
veneers, jackets or crowns to teeth, or the implanting of artificial teeth 
or crowns directly into the jaw. This tool and related procedures will 
improve the efficiency of prior art procedures to accomplish similar 
purposes, and to strengthen the bonding and stability of such veneers, 
jackets, crowns and artificial teeth (hereinafter collectively referred to 
as "dental prosthesis") mounted by use of such tool and procedures. It is 
yet a further object of the present invention to provide a new, improved 
tool for more efficiently preparing the tooth or jaw for applications of a 
dental prosthesis, and for so securing the dental prosthesis to its 
supporting substrata. Yet a further object of the invention is to provide 
a tool and procedure for augmenting bone around a weakened natural tooth 
where the surrounding bone has withered by obtaining and crushing a plug 
of bone material and implanting said crushed bone around said tooth. 
These and other objects are achieved in accordance with the present 
invention through the employment of the tool of the present invention. The 
tool has an elongated shank portion, one end of the shank portion being 
designed to be conventionally secured to a driving member, such as a 
dentist's drill handpiece, for causing rotation of the tool. The remainder 
of the tool is in the form of a hollow shaft. At the end of the shaft 
farthest from the shank, there is an enlarged annular ring having a larger 
outer diameter and a smaller inner diameter than the hollow portion of the 
shaft. 
A cutting surface, such as an abrasive coating, is secured to at least the 
outermost circumferential surface of said enlarged annular ring. When the 
tool is to be used to make an annular or cylindrical hole in a tooth or 
jaw or to obtain a cylindrical plug of bone, the bottom of the enlarged 
annular ring (i.e. the transverse surface farthest from the shank) and the 
innermost circumferential surface must also be coated with abrasive 
material. When so used, the hollow shaft can have a device to limit the 
depth of penetration of the tool into the tooth or bone, such as a depth 
limiting surface mounted in the hollow shaft with a means for accurately 
varying the perpendicular distance between the depth limiting surface and 
the bottom surface of the enlarged annular ring. 
Since the tool is designed to work in or on a tooth, the outer diameter of 
the annular ring should be substantially less than that of a tooth and 
would normally be on the order of 3 mm to 4 mm. The enlarged outer 
diameter of the annular ring in comparison with that of the hollow shaft 
limits engagement of the tool with the tooth to the surface of the annular 
ring, thereby reducing the heat generated through friction. The tool may 
be hollow throughout to allow liquid or air cooling of the drilling 
operation and for chip and ground tooth displacement and removal during 
drilling. As a further aid in removal of ground material, the hollow shaft 
may have one or more openings which allow communication and passage of 
material between the interior of the hollow shaft and the space between 
the outer diameter of the hollow shaft and the wall of the hole in the 
tooth or jaw formed by the cutting surfaces of the tool. 
The size and configuration of the enlarged annular ring allows the tool to 
be used to undercut the tooth surfaces in various ways, thereby allowing 
new methods in the securing of dental prostheses to existing teeth or to 
the jaw itself, or to the augmentation, or grafting, of bone material to 
reinforce a tooth, including (a) the creation of an undercut groove at the 
base of a prepared tooth into which a gasket can be positioned to form a 
seal with the dental prosthesis; (b) the drilling of an annular or 
cylindrical cavity with an undercut portion in a tooth or jaw bone into 
which a shaped insert can be securely mounted, which insert can act as a 
mounting for a dental prosthesis; and (c) harvesting a core or plug of 
bone material from a jaw bone, crushing the harvested bone and implanting 
said harvested bone around a tooth situated in the same jaw as the crushed 
bone was harvested, as a bone augmentation procedure to strengthen the 
support for said tooth.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
FIGS. 1-6 show the dental tool 10 of the present invention. The tool 10 has 
an elongated shank portion 11 of conventional construction to be secured 
to a rotational driving means, such as a latch or friction grip type 
handpiece on a dentist's drill. The remainder of the tool 10 primarily 
consists of a shaft 12 of smaller diameter than shank 11. The shank 11 and 
the shaft 12 are connected by a beveled section 13. 
The portion of the shaft 12 farthest from the shank 11 has a cavity 18 
therein. At the end of the shaft 12 farthest from the shank 11, there is 
an enlarged annular ring 14 which define the opening into cavity 18. The 
outer diameter of the annular ring 14 has a larger diameter than the outer 
diameter of shaft 12. Equally, the inner diameter Of the annular ring 14 
is less than the inner diameter of the hollow portion of the shaft 12. 
Since the tool is designed to work in or on a tooth, the outer diameter of 
the annular ring 14 is substantially less than that of a tooth. Typically, 
the diameter of the shaft 12 is on the order of 3.5 mm and the difference 
between the outer diameter of the annular member and its inner diameter is 
1.2 mm. 
The outer circumferential surface of the annular ring can form a beveled 
surface around the axis of the tool, or a curved surface around the tool 
axis, or a stepped surface. 
The cutting surface of the tool 10 is in the form of an abrasive coating 
secured to the outer circumferential surface 15, the inner circumferential 
surface 16, and the bottom 17 of annular ring It may be formed by any 
conventional abrasive coating for dental drill bits and the like. 
The radial distance between the outer diameter of the annular member 14 and 
the outer diameter of the shaft 12 is greater than the radial distance 
between the inner diameter of the hollow portion of shaft 12 and the inner 
diameter of the annular member 14. Among other things, this assures that 
when the tool 10 is used to an undercut an annular or cylindrical hole in 
the surface of a tooth or jaw, a space will remain between the outer 
surface of the hollow shaft 12 above the enlarged annular member 14 and 
the excavate wall of the tooth or jaw, as will be more fully discussed 
below. The clearance between the outer surface of the annular ring 14 to 
the Outer surface immediate adjacent portion of shaft 12 acts to limit the 
heat generated from frictional engagement of the tool 10 with a tooth or 
jaw bone to the immediate area of the annular ring 14. The enlarged size 
of the annular ring 14 also aids in dissipating any such heat generated. 
While the annular member 14 and, in particular, its outer wall 15 have 
been shown as cylindrical, the annular ring may take other forms, such as 
having a beveled, stepped, or curved outer surface 15. 
As seen in FIG. 2, the hollow portion 18 of shaft 12 does not extend the 
entire length of the shaft 12. The tool 10, however, may have a hollow 
passage throughout to allow passage of a stream of liquid or air for 
cooling of the drilling operation and/or for bone chip and ground tooth 
displacement and removal. 
To allow the passage of ground tooth or bone away from the drilling 
surface, the hollow shaft 12 may have one or more openings 19 
communicating with the interior hollow portion 18 of shaft 11. As seen in 
FIGS. 1 and 3, in the preferred embodiment, four such openings 19 are 
spaced equally around the circumference of the shaft 12. The openings 19 
allow communication and passage of material between the interior cavity 18 
of shaft 12 and the space between the outer diameter of the shaft 12 and 
the walls of the hole being excavated by the tool. The openings 19 also 
allow for insertion of a tool (not shown) for removal of any solid 
cylindrical material trapped in the hollow portion 18 of shaft 12. 
The openings 19 may have calibrations 20 aligned therewith to allow a 
visual determination of the depth of a hole excavated by the tool 10. 
Alternatively, to control the depth of excavation, a plug having a screw 
thread which would co-act with a thread in cavity 18 or other limiting 
device (not shown) may be positioned in cavity 18. The calibrations 20 may 
be used in conjunction with openings 19 to position the plug or other 
limiting device within cavity 18, providing a depth limiting surface which 
would prevent further drilling of the tooth. Openings 19 could also aid in 
the removal of the plug or other limiting device. 
The size and configuration of the enlarged annular ring 14 allows the drill 
to be used to undercut a tooth's surface in various ways. For example, the 
tool 10 can be used to form the undercut groove 26 in a tooth 24 prepared 
to receive a dental prosthesis 28. A gasket 29 can be mounted in the 
undercut groove 24 to form a seal between the dental prosthesis 28 and the 
prepared tooth 24. 
As seen in FIGS. 7 and 8, to prepare a tooth to receive a dental 
prosthesis, at least a portion of the enamel 21 is removed in any 
conventional manner to form a prepared core 22. This results in the 
prepared core 22 having a shoulder 25 adjacent the gum 23 at or slightly 
below the gum line 27. 
As shown in FIG. 9, the tool 10 of the present invention is used in 
connection with an already prepared tooth 24 which has had the outer 
enamel removed. The tool 10 is rotated by a dentist drill (not shown). It 
is moved around the shoulder 25 of prepared tooth 24 while being pressed 
against the shoulder 25 of the prepared tooth 24. The outer 
circumferential surface 15 of the enlarged annular ring 14 acts to form an 
undercut indentation or channel 26 around the entire circumference of the 
tooth 24 at or underneath the gumline 27. Since the abrading action is 
radial rather than axial, if the instrument 10 is to be used only for this 
purpose, it is unnecessary for abrasive coating to be placed on the bottom 
surface 17 of the tool 10. 
The tool 10, however, may be used to not only form channel 26 in the 
prepared tooth 24, but to further shape the shoulder 25 of the tooth 24 by 
means of the abrasive bottom surface 17. As seen in FIGS. 13 through 16, 
simultaneously with the formation of the undercut 26, the shoulder 25 of 
the already prepared tooth 24 can be further shaped, i.e. flattened and 
otherwise worked, by the abrasive bottom surface 17 of the annular member 
14, to better prepare the tooth 44 to receive a dental prosthesis 28. 
As is seen in FIGS. 17 through 19, the channel 26 is used to further lock 
dental prosthesis 28 against the tooth core 24 and to form a seal between 
the dental prosthesis 28 and the core 24. As noted above, the prepared 
tooth 24 is undercut to form channel 26 around the base 25 of the tooth at 
or below the gum line 27. A gasket 29 shaped to tightly fit the channel 26 
is set in channel 26. The gasket 29 may be made from any conventional 
dental gasket material. In order to insure the positive interlocking of 
the dental prosthesis 28 with the prepared core 24, the gasket may itself 
be undercut at 30. The dental prosthesis 28 would have a corresponding 
projection 31 to interlock with the cutaway portion 30 of gasket 29. 
Alternatively, a projection on the dental prosthesis 28 may directly mate 
and interlock with channel 26 (not shown). 
As seen in FIG. 18, if a more positive interlock is desired between the 
dental prosthesis 28 and the core 24, after the tool 10 has been used to 
form a channel 26 as seen in FIG. 17, the tool 10 may be turned so that 
surface 15 is positioned against shoulder 25 at right angle to its former 
position in forming groove 26. The tool 10 is then moved radially toward 
the tooth root and around the tooth core 24 to extend groove 26 further 
into the tooth core 24. The undercut portion 30 of gasket 29 and the 
extended portion 31 are correspondingly shaped to fit together and to fit 
the extended groove 26. This forms an even more positive interlock between 
the dental prosthesis 28 and the prepared tooth core 24. 
As seen in FIG. 19, a gasket 29 without an undercut can be mounted in the 
groove 26 in tooth 24. The gasket is shaped to completely fill the channel 
26, and mate with the corresponding portion of dental prosthesis 28, 
sealing the interface between the dental prosthesis 28 and tooth core 24. 
Tool 10 may also be used to drill an annular hole in the surface of the 
tooth for positively holding an insert 32 in position in the tooth. Such 
insert 32 can act as a post for holding a dental prosthesis (not shown) in 
position on a tooth. As seen in FIGS. 20 through 23, the insert 23 is 
generally cylindrical in shape with a cylindrical body portion 35 having 
an extended cavity 38 therein. Body 35 has a cylindrical top 33, which is 
enlarged in comparison with body 35, having a larger diameter. The top 33 
has an opening 34 along its central axis. The opening 34 communicates with 
cavity 38 in the body portion 35. As an aid to adhering the insert 32 to a 
dental prosthesis (not shown), the top 33 of the insert 32 is knurled. The 
hollow body 35 of the insert 32 has two slots 36 diametrically opposite 
each other. Slots 36 allow the bottom of the insert 32 to be pressed 
together to allow insertion in a confined space. At the bottom of the body 
35 is a flange 37 for interaction with the an undercut portion 45 of the 
hole 44 in which the insert 33 is to be mounted. The insert may be made of 
any suitable plastic or metal. 
FIGS. 24 through 31 show the use of tool 10 in forming an annular hole 44 
in a tooth 40 for holding insert 32 in place and the process for bonding 
insert 32 to the tooth 40 As seen in FIG. 24, tool 10 is positioned above 
the tooth 40 at the location in which the insert is to be mounted. The 
tool 10 is moved axially against the surface of the tooth 40, to drill an 
annular shaft or hole 44 into tooth 40. During this drilling operation, 
the removed tooth material can flow between of the hollow portion 18 of 
shaft 12 and the space 41 between the outer wall of the shaft 12 and the 
walls of the cavity 44 through openings 19 thereby facilitating the 
removal of such material for the drill site. 
As previously discussed, the depth of drilling may be controlled visually 
through the markings 20 on the side of the tool 10, or through a use of a 
plug (not shown) or other depth limiting device positioned in hollow 
section 18 of shaft 12. After the desired depth is reached, the tool is 
moved radially to form an enlarged annular opening 45 at the bottom of the 
hole 44. The interior walls of the hollow portion 18 of shaft 12 and there 
interaction with the core 44a of the tooth material left after drilling of 
the annular hole 44 controls the size of annular opening 45. Since, as 
noted previously, the radial distance between the outer diameter of the 
annular member 14 and the outer diameter of the shaft 12 is greater than 
the radial distance between the inner diameter of the hollow portion of 
shaft 12 and the inner diameter of the annular member 14, the space 41 is 
always maintained between at least one surface of shaft 12 and the cavity 
wall 44 during the radial movement of tool 10 and the geometry of 
subsequent annular opening 45 is set. 
After formulation of enlarged annular opening 45, the tool 10 is removed 
from hole 44. Hole 44 is then filled to overflowing with a conventional 
bonding agent. 
Central portion 35 of insert 32 approximately the dimension and shape of 
shaft 12. The outer diameter flange 37 is approximately the same as that 
of enlarged cavity 45. Accordingly, when as seen in FIG. 30 the insert 32 
is forced into the filled hole 44, the sides of insert 32 will be forced 
to flex at slots 36 in order to enter hole 44. When fully inserted flange 
37 will snap into enlarged opening 45 thereby positively interlocking the 
insert 32 with the tooth 40 The excess bonding agent passes through 
opening 34 in the top 33 of insert 32 which excess is then removed. After 
the bonding agent has fixed, the insert 32 may be used as a mounting post 
for a dental prosthesis (not shown). 
Alternatively, tool 10 can be used to form an essentially cylindrical 
opening in a tooth 40. FIGS. 32 through 35 show as cylindrical insert 45 
for use with such a cylindrical opening. It has a solid top 46, with a 
knurled outer surface 47 to aid bonding of the insert to a dental 
prosthesis (not shown). The main body of the insert 45 is a substantially 
solid cylindrical element 48 with a slot 49 therein to allow deflection of 
the insert 32 during insertion in a tooth. In addition, there is a small 
cylindrical cavity 50 at the bottom of the body 48. Flange 51 at the base 
of the body 48 is for interconnection with an enlarged opening 45 made by 
tool 10 in the base of the receiving hole 44. 
FIGS. 36 through 42 show the use of tool 10 to make a cylindrical opening 
44 in tooth 40 for insertion of said insert 45 and the method for such 
insertion into the cavity 44. As discussed in connection with the making 
of an annular cavity, tool 10 is moved axially into the tooth body 40, 
creating an annular hole 44. As shown in FIG. 38, the tool 10 is then 
moved radially to make an enlarged annular chamber 45 at the bottom of 
hole 44 and then removed. As a result, there is left a core 52 in the 
tooth having a narrow portion 53 and an extended portion 54. As shown in 
FIG. 40, this core may be broken off at the narrow portion 53 and removed, 
leaving a cavity 55 formed from the hole 44, enlarged portion 45, and a 
space previously occupied by the extended core portion 54. The insert 45 
is then forced into resulting hole 55. The diameter of the central portion 
48 of insert 45 is the same, or slightly less than the diameter of the 
upper portion of hole 55. Accordingly, flange 51 would not normally fit in 
hole 55. Because of the slot 49, however, the insert 45 will be internally 
deflected sufficiently to allow the insert 45 to be positioned in 
cylindrical hole 55, and pressed axially until the flange 51, snaps into 
the portion of hole 55 formed from the enlarged section 45. This would by 
itself hold the insert 45 rigidly in place. Of course a cement may be used 
to further lock insert 45 in place. 
Tool 10 may also be used to excavate a cavity 71 in a jaw bone 70 for 
holding an insert 60 upon which a dental prosthesis may be mounted. FIG. 
43 through 46 show an insert 60 for mounting such dental prosthesis in a 
jaw bone 70. The insert 60 is basically cylindrical in configuration, 
having a wider cylindrical top 61 with a central opening 62 therein and a 
cylindrical body portion 63. The external surface of at least part of 
central body portion 63 is threaded. The opening 62 in the top 61 of the 
insert 60 is the entrance to a threaded cavity which proceeds 
approximately half way down the insert body 63, formed in a solid upper 
portion 65 of such insert 60 Below said solid portion 65, the insert 60 
has a hollow cavity 66 having slots or openings 67 therein. These slots or 
openings 67 are to allow regenerated bone to grow into the insert 60, 
thereby further fixing and holding the insert 60 in place in a jaw bone. 
As seen in FIGS. 47 through 54, tool 10 is moved axially against the jaw 70 
to drill an annular passage 71 into the jaw. The tool 10 is the removed 
part way up the shaft to a portion corresponding to where the top 66A of 
cavity 66 of insert 60 would be positioned when insert 60 was fitted in 
the jaw 70. The tool 10 is moved radially to form an enlarged annular 
chamber 72, and then removed from the jaw 70. After tool 10 is removed, 
there is left an annular hole 71 having an enlarged portion 72 with a 
corresponding central core of bone material 77 with a reduced portion 
corresponding to enlarged section 72. The core 77 is then broken at said 
reduced portion 72A and removed, leaving a combined chamber 76 with the 
remaining central core of bone 77 therein. The insert 60 is then 
installed, by screwing it into the hole 71 in jaw 70. Dental prosthesis 78 
is then installed in insert 60. Due to the holes 67 in insert 60 the jaw 
70 is allowed to regenerate into cavity 66 and further fix the insert 60 
in the jaw 70. 
The tool 10 can also be used to obtain material for use to help regenerate 
bone structure around a tooth. As seen in FIGS. 55 through 59, a core 82 
of bone material is obtained by use of tool 10. As done in other 
application of tool 10, tool 10 is used to make an annular hole 80 in jaw 
bone 70, which is enlarged at its lower end 81 by radial movement of the 
tool 10. A core 82 of bone tissue can thus be removed as in other 
applications of the tool 10. As seen in FIG. 60, the bone tissue is then 
be crushed to form relatively course bone particles 83. These particles 83 
are then positioned around the bone of a tooth 84 between the tooth 84 and 
the surrounding withered bone 85 below the gum 86. This will aid 
regeneration of the withered bone 85 around the tooth. 
The embodiment of the present invention herein described and disclosed is 
presented merely as an example of the invention. Other embodiments coming 
within the scope of the present invention will be readily suggest 
themselves to those skilled in the art, and shall be deemed to come within 
the scope of the appended claims.