Dentistry – Apparatus – Having motor or means to transmit motion from motor to tool
Reexamination Certificate
2000-08-24
2002-02-26
O'Connor, Cary E. (Department: 3732)
Dentistry
Apparatus
Having motor or means to transmit motion from motor to tool
Reexamination Certificate
active
06350125
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a handpiece for dental use, and more particularly, to a contra-angle dental handpiece to be used by a dental practitioner for cutting or drilling a root canal of a tooth.
BACKGROUND OF THE INVENTION
In forming a root canal of a tooth, dental cutting tools such as a dental reamer or a dental file is generally used. The dental reamer and/or dental file may be operated manually or with use of a handpiece with a drive mechanism. A dental reamer has a relatively gentle (large lead) spiral cutting edge which is rotated in a root canal for cutting a surrounding inner wall of the root canal. In contrast, a dental file has a spiral cutting edge having a lead smaller than that of the dental reamer for cutting the surrounding inner wall of the root canal. These are the basic ways in using the reamer and file, however, the reamer and file are also used by incorporating the back and forth movements as well as rotational movements at the same time.
Thus, a dental handpiece for operating such a dental reamer or file is sometimes capable of driving the reamer or file both the back and forth movements and rotational movements. This invention is directed to a contra-angle dental handpiece in which the handpiece has a shape which is bent about a right angle.
As is known in the art, a root canal is narrower toward a distal end and is also curved as a whole. Thus, it is practically impossible to visually monitor when cutting and forming the root canal until the distal end thereof, thus, involving cut-and-try like work. Further, when applying the rotational movement to the reamer or file, a continuous application of only one direction of rotation or repeated applications of both forward and reverse directions of rotation in the curved root canal tend to cause metal fatigue to the dental cutting tool (reamer or file) because of the continuous or alternate load. Furthermore, in this situation, torsional load applied to the dental cutting tool will be increased, which may break the cutting tool. To avoid the damage to the cutting tool, it is known in the art that there is a type of dental handpiece which is designed to drive the dental cutting tool both in a “rotary mode” to provide a rotational movement and a “reciprocating model” to provide a back and forth movement to the cutting tool.
FIG. 6
shows an example of conventional contra-angle dental handpiece proposed in Japanese Patent Laid-Open Publication No. 4-300534.
FIG. 6
is a cross sectional view showing essential components of the dental handpiece. As noted above, the dental handpiece in this example is able to apply both the rotational movement (rotary mode) and the back and forth movement (reciprocating mode) to the cutting tool (reamer or file).
The dental handpiece includes a frame
3
, a tool chucker
2
and a cap holder
4
. The tool chucker
2
for freely mounting a cutting tool
1
(such as reamer and file) therein is attached to the frame
3
in a manner rotational about an rotational axis a. The cap holder
4
is rotatable but is not removable from the frame
3
. The upper end of the cutting tool
1
has a hook which is latched by a projection of the cap holder
4
when the cap holder
4
is rotated in a small degree. Consequently, the cutting tool
1
is installed in the dental handpiece through the cap holder
4
and is moved in the direction of the rotational axis a in the reciprocating mode and is rotated about the rotational axis a in the rotary mode in response to the movement of the tool chucker
2
.
The handpiece of
FIG. 6
further includes an inner sleeve
5
and an outer sleeve
6
around the tool chucker
2
. The outer sleeve
6
is fitted to the tool chucker
2
through, for example, a pressed-in or screwed-in process and moves both in the rotary mode and reciprocating mode with the movements of the tool chucker
2
. The inner sleeve
5
is positioned between the tool chucker
2
and the outer sleeve
6
and independently rotates and moves back and forth.
The frame
3
of the handpiece is bent at about right angle where a crank shaft
7
is rotatably provided in a direction perpendicular to the cutting tool
1
(rotation axis a). The crank shaft
7
is driven by a drive mechanism such as a motor (not shown). The crank shaft
7
has, at its end, an eccentric shaft
8
and an eccentric ball
9
at the end of the eccentric shaft
8
.
The outer sleeve
6
has a guide groove
6
a
in which the eccentric shaft
8
of the crank shaft
7
is engaged. When the crank shaft
7
rotates, the eccentric shaft
8
rotates accordingly, thereby driving the outer sleeve
6
in the direction of the rotation axis a, although there is no rotation of the outer sleeve
6
. With the back and forth (reciprocating) movement of the outer sleeve
6
, the tool chucker
2
moves back and forth accordingly.
The surrounding wall of the inner sleeve
5
has a long hole
5
a
in the direction of the rotation axis a which is engaged with the ball
9
formed on the end of the crank shaft
7
. Thus, when the crank shaft
7
rotates, the ball
9
rotates accordingly, thereby rotating the inner sleeve
5
in the forward and reverse direction about the rotation axis a (rotary mode). However, the inner wall
5
is not driven by the ball
9
back and forth in the direction of the rotation axis a (reciprocating mode).
In the foregoing configuration of the handpiece of
FIG. 6
, by the rotation of the crank shaft
7
, the eccentric shaft
8
rotates accordingly, thereby driving the tool chucker
2
in the reciprocating mode and the rotary mode. Namely, in the reciprocating mode, the handpiece drives the tool chucker in the direction of the rotation axis a. In the rotary mode, the handpiece rotates the tool chucker
2
about the rotation axis a. In other words, the cutting tool
1
(reamer or file) moves back and forth in the direction of the rotation axis a while rotates about the rotation axis a in the forward and reverse direction at the same time.
The foregoing example of the conventional handpiece further includes a switch means so as to switch between the operation involving only the reciprocating mode (back and forth movement in the direction of axis a) driven by the eccentric shaft
8
and the other operation involving both the reciprocating mode and the rotary mode (forward and reverse rotation about the axis a) driven by the eccentric shaft
8
and the ball
9
. Such switching mechanism is unrelated to the point of the present invention, and thus, no further description is given here.
As in the foregoing, with use of the handpiece of
FIG. 6
, a root canal of a tooth can be effectively formed by the reciprocating mode and the rotary mode of the cutting tool
1
. As noted above, the reciprocating mode involves the back and forth movement of the cutting tool
1
in the axial direction of the axis a and the rotary mode involves the forward and reverse rotation of the cutting tool
1
, which is typically less than one rotation, i.e., 360°.
In the process of forming a root canal of a tooth, it is important to carefully operate the handpiece so that the cutting tool such as a reamer or file is driven in the reciprocating movement as well as the rotary movement. As shown in
FIG. 7
, in the cutting process of a curved root canal
10
, the cutting tool
1
is sent to a root opening
10
a
at the end of the root canal
10
and is rotated to cut the tissue in the area shown by the dotted line, thereby forming a seat at the root opening
10
a
. Under this situation, if the cutting tool
1
is driven by the continuous rotation in one direction at a high speed, or high speed repetition of the forward and reverse rotation, metal fatigue may be caused, which may damage the cutting tool
1
.
Further, in forming the root canal of the tooth, the debris generated by cutting the inner wall of the root canal must be effectively carried away to the outside. This is because the debris is full of germs causing inflammation and suppuration after the dental treatment if the debris is not sufficiently removed.
In the root canal tr
Mani, Inc.
Muramatsu & Associates
O'Connor Cary E.
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