Dentistry – Apparatus – Broach
Reexamination Certificate
1999-01-05
2001-03-27
Manahan, Todd E. (Department: 3732)
Dentistry
Apparatus
Broach
Reexamination Certificate
active
06206695
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to improved endodontic cutting instruments and, in particular, to improved endodontic files or reamers with a modified taper for eliminating “step-back” and for obtaining a smooth interior surface root canal cavity.
BACKGROUND OF THE INVENTION
Endodontics, also known loosely as root canal therapy (RC) is a major part of dental treatment especially where saving an infected tooth is concerned. Endodontic instruments used to negotiate the canals inside the roots of teeth consist primarily of files and reamers. These instruments may be machine-driven, in which case a grasping end or shank is firmly grasped in a machine collet or chuck, such as in a rotary drill, a reciprocating filing machine or in an ultrasonic vibrating machine. Because of the sensitive nature of the root canal procedure and the small sizes of the cutting instruments, hand-held files and reamers are popular. Typically, hand-held files and reamers are provided with miniature or finger-size handles as a grasping end by which the dentist grasps the non-working end of the instrument for manipulation within the tooth nerve canal.
Files are elongated, round endodontic instruments designed for removing dentin from the inside of a tooth primarily with a vertical movement in the axial or elongated direction. Reamers are similarly elongated, rounded endodontic cutting instruments; however, they are designed primarily for enlarging or smoothing a hole in a tooth by the removal of dentin from the inside of the tooth primarily through rotation. Because of the difference in operation (i.e., an up-and-down movement, compared with rotational movement), files typically have a greater number of cutting edges and a higher twist angle and reamers have fewer cutting edges and a lower twist angle. Under the ISO standards, a file typically has four cutting edges formed as by twisting a small shaft having a square cross-section such that each of the four corner forms a cutting edge. The flat faces of the square form clearance flutes. A reamer is typically formed by twisting a triangular cross-sectional-shaped shaft such that it has three edges. The flat faces of the triangle form clearance flutes. The high twist angle of the files provides the cutting edge with a significant horizontal component relative to the up-and-down movement. The low angle of twist on a reamer provides the cutting edge with a significant vertical component for cutting by rotational movement. Many manufacturers have presented differently shaped cutting edges and flutes in order to provide different cutting characteristics.
U.S. Pat. No. 5,017,138 has, in its Background of the Invention, a summary of how endodontic instruments are standardized through the International Standard Organization (ISO). Basically, the shape, length, size and handle color of endodontic instruments are defined by ISO's Standard 3630.
FIG. 1
shows a prior art endodontic cutting instruments basically according to the current ISO standards.
Pursuant to Standard 3630, the diameter of the working tip of an endodontic file (or reamer) corresponds to the number that is used to identify the file. For instance, an ISO standard size 10 means that the working tip diameter, so called “D
1
” (as opposed to “D
2
” which is the shank, diameter further up the file), measures 0.10 mm. The next larger standard size file would be No. 15, indicating a working tip diameter of 0.15 mm at D
1
. The next larger standard size is 20, then 25, then 30, then 35 and so on, indicating 0.05 mm incremental size changes from one standard size to the next larger standard size until size 60 is reached. After size 60, then diameters at D
1
increase by 0.1 mm for each standard size increment so that the next standard size file greater than size 60 is size 70 with a diameter D
1
of 0.75 mm. Then, 80, 90, 100 and so on every 0.10 mm until size 150. However, apparently the largest size commonly available on the market is 140.
Other than the standardization of the working tip diameters and the standardization of incremental size difference between each diameter, the other noteworthy feature about the ISO standard is that it establishes an accepted international standard color scheme for the endodontic file and reamer handles. These colors are fixed and then correspond to the standard sizes of the tip diameters for the standardly tapered endodontic cutting instruments. Six basic colors are used, and accordingly to the ISO scheme, are repeated. The colors are: white, yellow, red, blue, green and black. Files outside of the standard range are sometimes available from various manufacturers, but there has been no accepted standard color scheme for differentiating the non-standard sizes from the standardized sizes or for differentiating the taper which is standard. Some manufacturers have developed their own unique colors, and some have merely printed different size measurements on the handles. Confusion has not been avoided.
Dentists and dental assistants can still depend on the fact that an ISO size 15 file will be white in color. This is also the file that most root canals are started with. When the dentist begins to negotiate the length of the root canal completely and reach the root tip with a size 15 file or reamer without blockage or binding, the next larger file, size 20 (which is yellow in color) is grasped or handed to the dentist by an assistant for removing additional material until the tip is reached. The process is repeated, step-wise, with the next larger size 25 (which is red). Then, the size 30 (which is blue), the size 35 (which is green) and followed by size 40 (which is black). The size differences and color-coding are set forth in Table I, below.
TABLE I
ISO STANDARD COLOR-CODE SYSTEM
Diameter of Instrument
Size
D
1
(mm)
D
2
(mm)
Color
10
0.10
0.42
Purple
15
0.15
0.47
White
20
0.20
0.52
Yellow
25
0.25
0.57
Red
30
0.30
0.62
Blue
35
0.35
0.67
Green
40
0.40
0.72
Black
45
0.45
0.77
White
50
0.50
0.82
Yellow
55
0.55
0.87
Red
60
0.60
0.92
Blue
70
0.70
1.02
Green
80
0.80
1.12
Black
90
0.90
1.22
White
100
1.00
1.32
Yellow
110
1.10
1.42
Red
120
1.20
1.52
Blue
130
1.30
1.62
Green
140
1.40
1.72
Black
150
1.50
1.82
White
The six colors are repeated again after size 40 (which is black) with ISO standard size 45 being white again. The standard size 50 is yellow, size 55 is red and size 60 is blue. As stated above, from standard size 15 to standard size 60, the standard incremental increase in working diameter is 0.05 mm. From size 60 to size 150, the standard incremental working diameter increase is 0.10 mm. The standard color scheme repeats sequentially for each next larger standard size. Since there is no standard size 65, size 70 is the next color in the sequence (i e., green), size 80 is black. Size 90 initiates the repetition of the sequence at white; then size 100 is yellow, size 110 is red, size 120 is blue, size 130 is green, through size 140 which is black. Size 150 is white, but is seldom used and is seldom commercially available. From size 15 to size 140, there are eighteen different standard endodontic instrument sizes for files and reamers under the ISO system. The color scheme of white-yellow-red-blue-green-black repeats three times.
If the dentist encounters a problem negotiating the root canal with a size 15 instrument, there are now three smaller ISO-recognized standard sizes—10, 8 and 6—with corresponding working tip diameters of 0.1 mm, 0.08 mm and the very fine 0.06 mm. They bear special ISO colors of purple, silver and pink, respectively.
This color scheme is taught to dental students from the beginning of their studies in endodontics. By the time the student graduates from dental school, he or she invariably has become very familiar with the scheme for standard sizes. If a white file is encountered, he or she immediately recognizes it as either a size 15, 45 or 90. A very large ISO file would be obvious. The size difference from one standard whole size to the next (i.e., 0.05 mm or 0.10 mm increas
Montgomery John W.
Wong Nelson J.
Manahan Todd #E.
Montgomery John W.
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