U.S. patent application number 11/366059 was filed with the patent office on 2007-09-06 for endodontic files having variable helical angle flutes.
Invention is credited to William B. Johnson.
Application Number | 20070207438 11/366059 |
Document ID | / |
Family ID | 38093520 |
Filed Date | 2007-09-06 |
United States Patent
Application |
20070207438 |
Kind Code |
A1 |
Johnson; William B. |
September 6, 2007 |
ENDODONTIC FILES HAVING VARIABLE HELICAL ANGLE FLUTES
Abstract
A rotatable endodontic file for cleaning/shaping a tooth root
canal, comprising an elongated shaft having a proximal end portion,
a distal end and a tapered working portion having a rotational
axis, the working portion extending from the proximal portion to
the distal end, the external surface of the shaft working portion
having a plurality of at least two spiraled, spaced apart
continuous helical flutes, the flutes having therebetween an equal
number of spiraled, spaced apart flanges, each flange having in a
plane perpendicular the rotational axis an outer end surface
forming a continuous spiraled scraping/cutting edge extending the
length of the shaft working portion, the flutes having helical
angles relative to the rotational axis of between 10.degree. and
30.degree. and wherein the helical angles vary at selected
longitudinal locations.
Inventors: |
Johnson; William B.; (Tulsa,
OK) |
Correspondence
Address: |
GABLE & GOTWALS
100 WEST FIFTH STREET, 10TH FLOOR
TULSA
OK
74103
US
|
Family ID: |
38093520 |
Appl. No.: |
11/366059 |
Filed: |
March 2, 2006 |
Current U.S.
Class: |
433/102 |
Current CPC
Class: |
A61C 5/42 20170201 |
Class at
Publication: |
433/102 |
International
Class: |
A61C 5/02 20060101
A61C005/02 |
Claims
1. A rotatable endodontic file for cleaning/shaping a tooth root
canal, comprising: an elongated shaft having a proximal end
portion, a distal end and a tapered working portion having a
rotational axis, the working portion extending from said proximal
portion to said distal end; the external surface of said shaft
working portion having a plurality of at least two spiraled,
equally spaced apart continuous concaved helical flutes, the flutes
having therebetween an equal number of spiraled, spaced apart
flanges, each flange having in a plane perpendicular said
rotational axis an outer end surface forming a continuous spiraled
scraping/cutting edge extending the length of said shaft working
portion, said flutes each having a helical angle as measured
relative to said shaft rotational axis at each location along the
length of said shaft working portion and wherein there are at least
two different helical angles for each said flute and wherein the
helical angles are proportionally unrelated to locations or
diameters along the length of said working portion.
2. A set of rotatable endodontic files for cleaning/shaping a tooth
root canal, comprising: a plurality of files each having an
elongated shank having a proximal end portion, a distal end and a
tapered working portion of a selected angle of taper and having a
rotational axis extending from said proximal portion to said distal
end; the external surface of said shank working portion of each
file having a plurality of at least two equally spaced apart
continuous concaved helical flutes, the flutes having therebetween
an equal number of spiraled, spaced apart flanges, each flange
having in a plane perpendicular said rotational axis an outer end
surface forming a continuous spiraled scraping/cutting edge
extending the length of said shaft working portion, said flutes
each having a helical angle as measured relative to said shaft
rotational axis at each location along the length of said shaft
working portion and wherein there are at least two different
helical angles for each said flute, wherein the helical angles are
proportionally unrelated to locations or diameters along the length
of said working portion, and wherein each file in the set has
essentially the same helical angles at selected locations and
wherein each file in the set has a different diameter and/or
taper.
3. An endodontic file according to claim 1 wherein areas of said
shaft working portion having flutes with a helical angle that
produces increased threading action and reduced scraping action as
said shaft is rotated and areas of said shaft working portion
having flutes with a helical angle that produces decreased
threading action and improved scraping action as said shaft is
rotated.
4. An endodontic file according to claim 1 wherein a first area of
said shaft working portion adjacent said proximal end portion has
flutes with a selected helical angle and a second area of said
shaft working portion adjacent said distal end has flutes with a
second helical angle.
5. An endodontic file according to claim 1 wherein said outer end
surface of each of said flanges has in one area a positive
scraping/cutting edge and in another area a negative
scraping/cutting edge.
6. A rotatable endodontic file according to claim 1 wherein each
said flange outer end surface has a radius of curvature of the said
shaft working portion.
7. A set of rotatable endodontic files according to claim 2,
wherein at least one of said files in said set has a flange outer
end surface having a radius of curvature of said shaft working
portion.
Description
REFERENCE TO PENDING APPLICATIONS
[0001] This application is not based upon any pending domestic or
international patent applications.
REFERENCE TO MICROFICHE APPENDIX
[0002] This application is not referenced in any microfiche
appendix.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates generally to endodontic files
and more particular to root canal files or reamers used in the
cleaning of material present in the root canal of human teeth and
for enlarging and shaping the root canal so that it is prepared for
receiving filling material.
[0005] 2. Description of the Related Art
[0006] A great improvement in the dental profession in the last
half century has been in the field of endodontics, that is, the
treatment of abscessed teeth by treatment of the tooth root canal.
A relatively, but yet difficult dental procedure is that of
cleaning, shaping and filling the root canal of a patient's tooth.
In the performance of the root canal procedure typically a hole is
first drilled in the crown or the exposed portion of the tooth. The
hole drilled through the crown provided access to the interior of
the tooth and specifically access to the tooth root canal or root
canals. In order to treat the tooth, the canal or canals must be
thoroughly cleaned of pulpal material that, in the case of an
abscessed tooth, is typically infected. The technician or dental
practitioner must remove this pulpal material to alleviate the
infection. Next the technician or dental practitioner must clean
and shape the root canal so that it can be effectively filled with
a filler material, such as gutta percha.
[0007] Much work has been done on the instrumentation need for
effective treatment of root canals. Root canals are typically
treated with endodontic files. The term "file" as used in this
patent application means an elongated device insertable into a root
canal and that can be manipulated either manually or by machine, to
clean and shape the root canal. Thus a dental file serves two basic
purposes. First it serves to remove pulpal material from the
interior of the tooth. Second it serves to shape the tooth root
canal so that it can be more effectively filled. Thus, in addition
to the cleaning function, a typical dental file serves also as a
reamer, that is, a device to enlarge and shape the canal. In this
application, the term "file" is intended to mean a "reamer/file"
since it functions not only to clean a root canal of pulpal
material but also to shape or ream the root canal.
[0008] For background information relating to endodontic files of
the type that is the subject of this patent application, reference
may be had to the following issued United States patents and
publications: TABLE-US-00001 PATENT NUMBER INVENTOR(S) ISSUE DATE
TITLE 4,443,193 Roane Apr. 17, 1984 Endodontic Instrument 4,536,159
Roane Aug. 20, 1985 Endodontic Instrument 4,934,934 Arpaio, Jr. et
al. Jun. 19, 1990 Dental File/Reamer Instrument 5,380,200 Heath et
al. Jan. 10, 1995 Endodontic Instrument Of Predetermined
Flexibility 5,464,362 Heath et al. Nov. 7, 1995 Endodontic
Instrument 5,503,554 Schoeffel Apr. 2, 1196 Endodontic Files
5,658,145 Maillefer et al. Aug. 19, 1997 Set Of Instruments For
Boring Dental Radicular Canals And Method Therefor 5,676,541
Maillefer et al. Oct. 14, 1997 Set of Instruments Of Increasing
Dimension For The Boring Of Radicular Dental Canals 5,692,902 Aeby
Dec. 2, 1997 Set Of Instruments For The Boring Of Radicular Dental
Canals 5,873,719 Calas et al. Feb. 23, 1999 Dental Reamer 5,897,316
Buchanan Apr. 27, 1999 Endodontic Treatment System 5,921,775
Buchanan Jul. 13, 1999 Endodontic Treatment System 5,975,899 Badoz
et al. Nov. 2, 1999 Dental Reamer 6,012,921 Riitano Jan. 11, 2000
Endodontic Systems For The Anatomical, Sectional And Progressive
Corono-Apical Preparation Of Root Canals With Three Sets Of
Dedicated Instruments 6,074,209 Johnson Jun. 13, 2000 Reduced
Torque Endodontic File 6,217,335 Riitano et al. Apr. 17, 2001
Endodontic Systems And Methods For The Anatomicall, Sectional And
Progressive Corono-Apical Preparation Of Root Canals With Minimal
Apical Intrusion 6,267,592 Mays Jul. 31, 2001 Highly Flexible
Instrument For Dental Applications 6,312,261 Mays Nov. 6, 2001
Endodontic Obturator With Removable Carrier And Method Of Use
Thereof 6,315,558 Farzin-Nia et al. Nov. 13, 2001 Method Of
Manufacturing Superelastic Endodontic Files And Files Made
Therefrom 6,390,819 Riitano May 21, 2002 Endodontic Systems And
Methods For The Anatomical, Sectional And Progressive Corono-Apical
Preparation Of Root Canals With Dedicated Stainless Steel
Instruments And Dedicated Nickel/Titanium Instruments 6,419,488
McSpadden et al. Jul. 16, 2002 Endodontic Instrument Having A
Chisel Tip 6,514,076 Bleiweiss et al. Feb. 4, 2003 Precipitation
Hardenable Stainless Steel Endodontic Instruments And Methods For
Manufacturing And Using The Instruments 6,520,774 Mays Feb. 18,
2003 Highly Flexible Instrument For Medical Applications 6,644,972
Mays Nov. 11, 2003 Endodontic Obturator With Removable Carrier And
Method Of Use Thereof 6,746,245 Riitano et al. Jun. 8, 2004 Methods
For Cleaning And Shaping Asymmetrical Root Canals In An Anatomical
Fashion 2004/0121283 Mason Jun. 24, 2004 Precision Cast Dental
Instrument 2003/0077553 Brock Apr. 24, 2003 Endodontic Instrument
Having Notched Cutting Surfaces 2004/0058297 Danger Mar. 2, 2004
Root Canal Instrument 2004/0043357 Garman Mar. 4, 2004 Endodontic
Instrument 2004/0023186 McSpadden Feb. 5, 2004 Multi-Tapered
Endodontic File Re. 34,439 Heath Nov. 9, 1993 Dental Compactor
Instrument
BRIEF SUMMARY OF THE INVENTION
[0009] The invention herein relates to endodontic files having
variable helical angle flutes. The file of this invention is for
cleaning and/or shaping a root canal of a human tooth. The improved
file is in the form of an elongated shaft having a proximal end
portion, a distal end and a tapered working portion having a
rotational axis, the working portion extending from the proximal
portion to the distal end. The external surface of the shaft
working portion has a plurality of at least two spiraled, equally
spaced apart, continuous concave helical flutes. The spaced apart
flutes have a concave flute surfaces. The flute surfaces have
therebetween an equal number of spiraled, spaced apart, continuous
flanges. Each flange has, in a plane perpendicular the rotational
axis, an outer end surface forming a continuous spiral
scraping/cutting edge. The scraping/cutting edge extends the length
of the shaft working portion.
[0010] The flutes have helical angles relative to the rotational
axis. The angle of the helical flutes can vary between about
10.degree. and about 30.degree.. In preferred embodiments, the
helical angle can typically vary between 10.degree. and
20.degree..
[0011] The shaft working portion is typically tapered from a larger
diameter adjacent the proximal end portion to a small diameter
adjacent the distal end. In some files, the helical angle varies in
proportion to the cross-sectional diameter of the shaft working
portion.
[0012] In short, a typical endodontic file in use today has flutes
with consistent helical angles, the consistency being in one case
where the same helical angle exists from one end to the other of
the tapered working portion or in the case where the helical angle
varies in proportion to the diameter of the file. Further, the file
can have an outer end surface of each flange that in one area
provides a positive scraping/cutting edge and in another area a
negative scraping/cutting edge. An important aspect of the
invention herein is the provision wherein the helical angle of the
flute is selectably varied at selected areas along the length of
the file to thereby vary the characteristics of the file.
[0013] Most passive files have helical angles that are constant
from the tip to the top of the shaft. In the smaller sizes this
presents few problems. However, in sizes above 30 or 35 hundreds of
a millimeter tip diameter the surface area of the radial lands in
contact with the root canal sidewall is so great the file has a
tendency to self-thread or pull into the canal. By reducing the
helical angle the surface area of the radial lands in contact with
the root canal sidewall is reduced and slippage of the rotating
file occurs reducing the feed rate of the file into the canal.
[0014] In an additional embodiment, the invention is in the form of
a plurality of sets of endodontic files wherein all of the files in
each set have essentially the same helical angle and wherein
different sets have variable diameters and/or tapers.
[0015] A better understanding of the invention will be obtained
from the following detailed description of the preferred
embodiments and claims, taken in conjunction with the attached
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is an elevational external view of a typical
endodontic file. The file illustrated in this figure is for use in
a hand piece by which the endodontic file is mechanically rotated
and by which the file can be manipulated in the root canal of a
patient. Basically, endodontic files are of two types, that is,
manually manipulated and machine manipulated. FIG. 1 illustrates an
example of a machine manipulated file.
[0017] FIG. 2 is a cross-sectional view of the endodontic file of
FIG. 1 taken along the line 2-2 of FIG. 1. The cross-sectional view
is perpendicular the longitudinal/rotational axis of the file and
illustrates a geometry having essentially passive cutting/scraping
action.
[0018] FIG. 3 is a cross-sectional view as in FIG. 2 but showing an
alternate embodiment of the cross-sectional of the file providing
more aggressive cutting/scraping action.
[0019] FIG. 4 is another alternate embodiment of the
cross-sectional configuration of the endodontic file of FIG. 1
showing a cross-sectional arrangement that produces more aggressive
cutting/scraping action than that of FIG. 2 or FIG. 3.
[0020] FIG. 5 is an elevational view of an endodontic file having a
shank portion designed for rotational use in a hand piece as
employed by an endodontist and showing an alternate configuration
of the file working portion. In the embodiment of FIG. 5 a pair of
equally spaced apart continuous concaved helical flutes are formed
into the working portion, the helical flutes having a small,
approximately 10.degree. helical angle. FIG. 5 illustrates a file
primarily designed for scraping action within the root canal rather
than a coring or cutting action. The design of FIG. 5 is primarily
for shaping a root canal and has limited ability to remove material
from within the root canal.
[0021] FIG. 6 shows part of a shaft working portion of an
endodontic file and shows a plurality of helical flutes forming the
working surface and wherein the helical flutes have an angle of
30.degree.relative to a plane of the file longitudinal/rotational
axis.
[0022] FIG. 7 shows the exterior shape of the working portion of an
endodontic file as in FIG. 6 in which the working portion is
defined by equally spaced apart continuous concaved helical flutes,
the flutes having a helical angle of 24.degree. relative to a plane
of the longitudinal/ rotational axis of the file. FIGS. 6 and 7
illustrate the fact that files of the same diameter and same taper
can have different helical angles.
[0023] FIG. 8 shows the external surface of the working portion of
an endodontic file having a plurality of spiraled equally spaced
apart continuous concaved helical flutes, the flutes having
therebetween an equal number of spiraled, spaced apart continuous
flanges, and wherein the flanges have in one portion of the file
intermediate the file proximal end and distal end have an angle
relative to a plane of the longitudinal/rotational axis of
13.degree., and wherein another portion of the shaft working
portion adjacent the distal end has helical flutes and helical
flanges having a helical angle with respect to a plane of the file
longitudinal/rotational axis of 17.degree., illustrating the fact
that the helical angle can selectably vary along the length of the
file working portion.
[0024] FIG. 9, like FIG. 8, shows an external view of a portion of
the shaft working portion having a plurality of at least two spaced
spiraled continuous helical flutes with spiraled, spaced apart,
continuous flanges therebetween and wherein in the intermediate
portion of the length of the shaft working portion the flanges have
an angle with respect to a plane of the longitudinal/ rotational
axis of 17.degree.while the portion of the shaft working portion
adjacent the distal end provides spiral flanges having an angle
with respect to a plane of the longitudinal/rotational axis of
13.degree..
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] It is to be understood that the invention that is now to be
described is not limited in its application to the details of the
construction and arrangement of the parts illustrated in the
accompanying drawings. The invention is capable of other
embodiments and of being practiced or carried out in a variety of
ways. The phraseology and terminology employed herein are for
purposes of description and not limitation.
[0026] Elements illustrated in the drawings are identified by the
following numbers: TABLE-US-00002 10 Endodontic file 12 Chuck stem
14 Proximal end 16 Distal end 18 Shaft working portion 20
Longitudinal/rotational axis 22 flute 24 Flute surface 26 Flange 28
Flange end surface 30 Scraping/cutting edge 32 A-D Planar end
surfaces 34 A-B Scraping edges 36 A-F Helical angle
[0027] Referring to the drawings and first to FIG. 1, an endodontic
file is indicated generally by the numeral 10. The file includes a
chuck stem 12 that is at a proximal end 14 of the file. The distal
end 16 is of substantially reduced diameter compared to the
proximal end. Between proximal end 14 and distal end 16 is an
elongated shaft working portion generally indicated by the numeral
18.
[0028] Chuck stem 12 is typically integrally formed with the metal
file and is configured to be received in a chuck (not shown) of a
dental hand piece by which the file is rotated and by which the
file can be manipulated in and out of a root canal by an
endodontist. Chuck stem 12 can be replaced by a small plastic
handle portion configured for manual manipulation by an endodontic
practitioner. Whether a chuck stem or a handle portion is used is
irrelevant to the invention herein and the specific configuration
of chuck stem 12 is not part of the invention. Instead, an
important aspect of the present invention is the configuration of
the external surface of the file shaft working portion 18.
Exemplary cross-sectional configurations are illustrated in the
cross-sectional views of FIGS. 2, 3 and 4.
[0029] FIG. 2 is a cross-sectional view taken along the line 2-2 of
FIG. 1. The plane of this cross-sectional view is perpendicular to
a longitudinal axis 20 of the file working portion 18 which also is
the longitudinal axis of the chuck stem 12. This longitudinal axis
can also be termed a rotational axis as it is the axis about which
file working portion 18 is rotated when positioned within a tooth
root canal. Rotational axis 20 is seen in each of the
cross-sectional views.
[0030] Formed on the exterior surface of shaft working portion 18
are a plurality of at least two helical flutes 22. In the
illustrated arrangement there are three spaced apart helical flutes
22. These helical flutes are formed into the exterior surface of
the file working portion 18. Each helical flute has a flute surface
24. While three helical flutes 22 are illustrated, the file can be
manufactured with only two flutes or can be manufactured with more
than three flutes. As a practical consideration, however, the file
is typically made with two or three flutes with three flutes being
ideal. While four or more flutes could be employed, additional
flutes serve to increase the complexity of manufacture without
adding significantly to performance of the tool. Thus, for
practical purposes, the ideal file construction that incorporates
the principles of this invention will employ three flutes 22. These
flutes provide therebetween three helical flanges 26.
[0031] Each of the helical flanges 26 has, at the outer end
thereof, an end surface 28. Each end surface 28 contacts, in
cross-sectional views, opposed flute surfaces 24. A continuous
spiraled scraping/cutting edge 30 is formed at the outer end of
each end surface 28, that is, where each end surface 28 contacts an
opposed flute surface 24.
[0032] Each of the flange end surfaces 28 of FIG. 2 are arcuate,
that is, each is formed of an arc that has a radius of curvature
substantially equal to the basic radius of curvature of the shaft
working portion in the area where the cross-sectional view of FIG.
2 is taken except that the rotational axis is offset relative to
the longitudinal/rotational axis 20. In this way, each of the
flange end surfaces 28 provides a scraping/cutting edge 30. This
arrangement provides a small rake angle. That is, a tangent taken
of flange end surface 28 at the scraping/cutting edge 30 departs
only slightly from the tangent of the rotation of the shaft working
portion at the area where the cross-sectional view of FIG. 2 is
taken. In the embodiment of FIG. 2 each of the three flange end
surfaces 28 are the same.
[0033] FIG. 3 is an alternate embodiment of FIG. 1 having
essentially all of the same elements as indicated in FIG. 2 and
differs only in that in FIG. 3 there are two arcuate flange end
surfaces 28 each having a scraping/cutting edge 30, however, one of
the flange portions 26 does not terminate in an arcuate end
surface. Instead, in FIG. 3 flange 26A terminates in an outer end
surface defined by intersecting planes 32A and 32B so that a
scraping edge 34A is formed at the intersection of the planes 32A
and 32B.
[0034] In the illustrated embodiment of FIG. 3 spiral scraping edge
34A extends at a radius from the longitudinal/rotational axis 20
essentially equal to the radius of scraping/cutting edges 30 as
described with reference to FIG. 2. Scraping edge 34A has a
different kind of scraping action than scraping/cutting edges 30.
Typically, a file having the three spiraled cutting edges of FIG. 3
provide more aggressive, scraping cutting action than that of the
embodiment of FIG. 2.
[0035] FIG. 4 is an alternate embodiment of FIG. 3 differing only
in that flange 26B terminates at the outer end with planar end
surfaces 32C and 32D. The only significant difference between the
embodiment of FIG. 4 and that of FIG. 3 is that the planar end
surfaces 32C and 32D of FIG. 4 intersect at a sharper angle than
the end surfaces of 32A and 32B of FIG. 3. This forms a sharper
spiraled cutting edge 34B that provides a more aggressive
cutting/scraping edge and correspondingly a file having slightly
different scraping/cutting action.
[0036] FIG. 5 is an embodiment of the endodontic file 10 as shown
in FIG. 1 with a basic difference. That difference is a highly
reduced helical angle. As shown in dotted outline in FIG. 5, the
endodontic file has spiraled flutes 22 with spiraled flute surfaces
24 and with flanges 26 formed between the spiraled flutes. Each
flange having an outer end surface 28. The difference of FIG. 5 and
FIG. 1 is that in FIG. 5 the angle of the helical flange taken at a
cross-section relative to the longitudinal axis 20 is very small.
In the embodiment of FIG. 5 the angle of flange 26 with respect to
a plane of the longitudinal/rotational axis 20 is approximately
10.degree..
[0037] FIGS. 6 through 9 each show an elevational view of a shaft
working portion 18 of an endodontic file of the type shown in FIGS.
1 and 5. FIG. 6 illustrates the arrangement wherein the helical
file flange has an angle with respect to a plane of the file
longitudinal/rotational axis 20 of 30.degree.. The helical angle in
FIG. 5 of 10.degree. can be contrasted with the helical angle of
30.degree. in FIG. 6. While in FIG. 6 the helical angle 36B is
30.degree., in FIG. 7 the helical angle 36C is 24.degree.. Thus
FIGS. 5, 6 and 7 show that helical flutes and flanges can have
highly selectable angles relative to a plane of a file
longitudinal/rotational axis. The selected helical angle has a
dramatic impact on the operation of a file as used in performing an
endodontic procedure. Files having helical angles of 20.degree. and
greater tend to have a dramatic screwing action as they are rotated
in a root canal. That is, they tend to thread toward the apical end
of the root canal. On the other hand, files that have a small
helical angle, such as less than 20.degree., do not have a strong
screwing action but have a more pronounced scraping action. In
performing an endodontic procedure, there are advantages to both
screwing action and scraping action of a file. Scraping action
tends to dislodge pulpal material and inwardly protruding portions
of the root canal so as to clean and shape the root canal. However,
scraping action is deficient if no provision is made for removing
loosened material from within the root canal. That is, portions of
the root canal wall must not only be scraped loose but must be
removed. Screwing action of the file has a strong tendency to
remove the dislodged material from within a root canal. Thus in
selecting a helical angle for a file it is always a compromise
between achieving good scraping action and achieving good removal
action.
[0038] Further, the helical angle has a dramatic effect on the
possibility of the file breaking off within the tooth. That is, a
file that has a pronounced screwing action tends to thread deeper
towards the apical area of the tooth and to become more quickly and
easily stuck in a position within the tooth so that further
rotation can cause the file to be twisted into broken pieces.
Breaking a file in a root canal is always a serious matter. One of
the important concepts of this invention is that advantages can be
taken of the helical angle of the flanges so that the advantages of
both higher helical angles and lower helical angles can be combined
into a file.
[0039] FIG. 8 shows a portion of a shaft working portion, generally
indicated by the numeral 18. This view shows the portion of the
shaft that extends from approximately the lower half of the shaft
working portion terminating in distal end 16. Shaft working portion
18 has, as with the previously described embodiment, spaced apart
spiraled flutes 22 with flange portions 26 therebetween, each of
the flanges providing a scraping/cutting edge 30. The illustrated
working portion has a longitudinal/rotational axis 20. A unique
feature of FIG. 8 is the provision wherein the helical angle 36D of
one portion of the length of the file working portion is different
from the helical angle 36E of a portion adjacent distal end 16.
[0040] The arrangement of FIG. 8 gives an endodontic file unique
properties when being used to clean and shape a root canal. The
upward portion having a helical angle 36D of 13.degree.provides
improved scraping action whereas the portion having a helical angle
36E of 17.degree. adjacent distal end 16 has more threading action,
tending to draw the file deeper into the root canal.
[0041] FIG. 9 shows a section of a shaft working portion as in FIG.
8 with the file having essentially the same base diameter and taper
as FIG. 8 but wherein the portion adjacent distal end 16 has a
helical angle 36F of 13.degree., with the working portion of the
shaft farther displaced from distal end having a helical angle 36G
of 17.degree.. Thus, the arrangement of FIG. 9 provides a file
wherein the portion of the working surface adjacent distal end 16
has a small helical angle and thereby provides more scraping action
and less threading action as contrast with an intermediate portion
of the working surface that has a helical angle of
17.degree.providing increased threading action and reduced scraping
action.
[0042] FIGS. 8 and 9 are indicative of the way the invention can be
practiced by varying the helical angle along the length of a
working portion of an endodontic shaft to minimize breakage, that
is, to reduce the threading action of certain portions of the
length of the shaft and increasing scraping action so that maximum
effectiveness of the file can be achieved. In other words, the file
can be arranged to most effectively clean and at the same time
threadably remove debris from the interior of a root canal while
minimizing the chance that the file will be subjected to increased
torque resistance that could result in the file being twisted in
two and leaving a portion of the file within the root canal.
[0043] While the invention has been described with a certain degree
of particularity, it is manifest that many changes may be made in
the details of construction and the arrangement of components
without departing from the spirit and scope of this disclosure. It
is understood that the invention is not limited to the embodiments
set forth herein for purposes of exemplification, but is to be
limited only by the scope of the attached claim or claims,
including the full range of equivalency to which each element
thereof is entitled.
* * * * *