U.S. patent application number 11/943303 was filed with the patent office on 2008-06-05 for surgical bur with anti-chatter flute geometry.
Invention is credited to Denis O'Donoghue, Denis F. O'Sullivan.
Application Number | 20080132929 11/943303 |
Document ID | / |
Family ID | 39476755 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080132929 |
Kind Code |
A1 |
O'Sullivan; Denis F. ; et
al. |
June 5, 2008 |
SURGICAL BUR WITH ANTI-CHATTER FLUTE GEOMETRY
Abstract
A surgical bur (20) including a shaft with a bur head. A number
of flutes are formed on the bur head. Each flute has a cutting edge
(54). The flutes are formed so that some of the flutes having
cutting edges emerge from the bur head at locations relatively
close to the distal end tip of the head. Still other flutes are
formed so as to have cutting edges that start, extend proximally
rearward, from locations that are, spaced proximal from the distal
end tip.
Inventors: |
O'Sullivan; Denis F.;
(County Cork, IE) ; O'Donoghue; Denis; (County
Kerry, IE) |
Correspondence
Address: |
INTEL. PROP./ RND;STRYKER CORPORATION
4100 EAST MILHAM AVE.
KALMAZOO
MI
49001-6197
US
|
Family ID: |
39476755 |
Appl. No.: |
11/943303 |
Filed: |
November 20, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/IB2006/002118 |
Jul 17, 2006 |
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11943303 |
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60700384 |
Jul 19, 2005 |
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60866735 |
Nov 21, 2006 |
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Current U.S.
Class: |
606/170 |
Current CPC
Class: |
A61B 17/32002 20130101;
A61B 17/1615 20130101; A61B 17/1673 20130101 |
Class at
Publication: |
606/170 |
International
Class: |
A61B 17/32 20060101
A61B017/32 |
Claims
1. A surgical bur comprising: an elongated shaft having opposed
proximal and distal ends; a coupling feature associated with the
proximal end of the shaft, the coupling featured shaped to engage a
drive unit of a surgical handpiece so that the handpiece can rotate
the shaft; a bur head attached to the distal end of the shaft, the
bur head having: a body with a distal end tip; a first set of
flutes, each said flute having a cutting edge and said first set of
flutes emerging from said flute head body so that the cutting edge
of said first set of flutes emerge from said bur head so as to have
cutting edges that start at a first location proximal from the bur
head distal end tip; and a second set of flutes, each said flute
having a cutting edge, wherein said second set of flutes emerge
from said flute body and are interleaved with the flutes of said
first set of flutes and said second set of flutes are interleaved
with said first flutes end and are shaped to have cutting edges
that start at a second location proximal from the bur head distal
end tip, the second location being proximally spaced from the first
location.
2. The surgical bur of claim 1, wherein: each said flute is formed
with a rake surface and a clearance surface that meets to form the
cutting edge of said flute; each said flute of said second set of
flutes is formed to have chamfered surfaces that extends proximally
from said bur head distal end tip between the flute rake surface
and the clearance surface so that the cutting edge of the said
flute does not extend forward of the chamfer surface.
3. The surgical bur of claim 1, wherein the bur head is constructed
so that the flutes forming the first and second set of flutes
alternate with each other around the circumference of the bur
head.
4. The surgical bur of claim 1 wherein: the flutes forming the
first and second flutes are shaped so that the cutting edges
thereof have a common proximal end terminus along the length of the
bur head.
5. The surgical bur of claim 1 wherein the bur head body is formed
to have a third set of flutes that have cutting edges wherein said
third set of flutes are shaped so that the cutting edges of said
flutes start at a third location proximal from the bur head, the
third location being proximally spaced from the second
location.
6. The surgical bur of claim 1, wherein the first set of flutes are
arranged symmetrically around the bur head and the second set of
flutes are arranged symmetrically around the bur head.
7. The surgical bur of claim 1, wherein the bur head has shape
selected from one of the following: acorn style; spherical; barrel;
egg; pear; and drum.
8. A surgical bur, said bur van elongated shaft having opposed
proximal and distal ends; a coupling feature associated with the
proximal end of the shaft, the coupling featured shaped to engage a
drive unit of a surgical handpiece so that the handpiece can rotate
the shaft; a bur head attached to the distal end of the shaft, the
bur head having: a body with a distal end tip; and a plurality of
flutes that emerge from said body at locations proximal to the
distal end tip, wherein each said flute has a rake surface and a
clearance surface that meet to define a cutting edge wherein: there
is a first set of flutes each flute of said first set of flute
emerging from said bur head so as to have cutting edges that start
at a first location proximal from the bur head distal end tip; and
there is a second set of flutes, said first and second set flutes
being interleaved with each other around said bur head, each flute
of said second set of flutes also having a chamfer surface that
extends proximally from the bur head distal end tip over the rake
and clearance surfaces of said flute so that the flute cutting
edges originate at the chamfer surface so that the cutting edges of
the second set of flutes start at a second location proximal from
the bur head distal end tip, the second location being spaced
proximally relative to the first location.
9. The surgical bur of claim 8, wherein said first set of flutes
comprises a single pair of flutes that are symmetrically to each
other around the bur head distal end tip.
10. The surgical bur of claim 8, wherein: said first set of flutes
comprises a single pair of flutes that are symmetrically to each
other around the bur head distal end tip so that said first set
flutes are separated by an arcuate space; and in the arcuate space
between each said flute of the said first pair of flutes there is
at least one flute of the second set of flutes; and between each
said flute of the first pair of flutes and the adjacent flute of
the second pair of flutes there is a flute from a third set of
flutes, each flute of said third set of flutes having a chamfer
surface that extends over the rake and clearance surfaces of said
flute so that the flute cutting edges originate at the chamfer
surface so that the cutting edges of the third set of flutes start
at a third location proximal from the bur head distal end tip, the
second location being spaced proximally relative to the first
location.
11. A surgical bur comprising: an elongated shaft having opposed
proximal and distal ends; a coupling feature associated with the
proximal end of the shaft, the coupling featured shaped to engage a
drive unit of a surgical handpiece so that the handpiece can rotate
the shaft; a bur head attached to the distal end of the shaft, the
bur head having a body and a distal end and a plurality of
arcuately spaced apart flutes that emerge from the body, each flute
having a cutting edge wherein the bur head is formed so that the
there is a first pitch angle between a first pair of adjacent
flutes and a second pitch angle between a second pair of adjacent
flutes (176, 178)
12. The surgical bur of claim 11, wherein the bur head is formed so
that pitch angles between adjacent pairs of flutes is different.
Description
RELATIONSHIP TO EARLIER FILED APPLICATION
[0001] This application is a continuation of PCT App. No.
PCT/IB2006/002118, filed 17 Jul. 2006 which claims priority from
U.S. Pat. App. No. 60/700,384 filed 19 Jul. 2005. This application
also claims priority from U.S. Pat. App. No. 60/866,735 filed 21
Nov. 2006.
BACKGROUND OF THE INVENTION
[0002] This invention is generally related to surgical burs. More
particularly, this invention is related to a surgical bur with a
bur head geometry that substantially reduces chatter when the bur
is applied to a surgical site.
BACKGROUND OF THE INVENTION
[0003] A tool used to perform a surgical procedure is the bur. A
bur generally consists of a head formed from rigid material,
typically metal, shaped to have a number of flutes. The flutes are
formed to define tissue cutting edges. A shaft extends rearwardly
from the head. The free end of the shaft has a feature that
facilitates locking the shaft to a powered handpiece. The actuation
of the handpiece results in the rotation of the bur. During a
surgical procedure, the bur head is placed against a surgical site
where a section of tissue is to be removed. The rotating cutting
edges excise tissue away from the surgical site. Burs of various
shapes and sizes are used in procedures such as orthopedic surgery,
neuro and spinal surgery, ear noise and throat surgery and in other
surgical procedures in which a sub-procedure is to selectively
remove a section of tissue.
[0004] Burs work well for the purposes for which they are designed.
Nevertheless, a problem associated with some burs is chatter.
Chatter is the back and forth vibration of a bur head against the
surface to which the bur head is applied. Chatter occurs as a
result of bur's individual cutting edges repeatedly being forced
against the tissue against which the bur head is applied.
Generally, there three reasons a bur may start to chatter.
[0005] One reason a bur starts to chatter is because it receives an
input of energy due to a process known as regeneration of waviness.
This process is due to the fact that when a cutting edge passes
across a section of tissue, it leaves a specific wavy (essentially
sinusoidal) profile along the surface of the tissue. If two
adjacent cutting edges cut in phase, the second cutting edge
excises tissue along a surface profile identical to that along
which in was excised by the first flute. In practice, due to the
invariable movements of the bur head and the tissue, this does not
happen. When any two successive cutting edges pass over the same
tissue section, the second flute cutting edge removes tissue on a
path that does not overlap the tissue wave excised by the first
cutting edge. Consequently, the debris chips cut by the second
cutting edge have variable thickness. This means, during the
process in which the second cutting edge excises the chip from the
tissue, the cutting edge and its flute are subjected to variable
forces. Over time, the repetitive exposure of the bur flutes to
these variable forces causes the bur to undergo forced
vibration.
[0006] A second reason a bur may chatter is that it is rotated at
its resonant frequency. If this occurs, the repetitive force
against the flutes self-excites the bur to move back and forth
through a continually increasing range of motion.
[0007] The third reason a bur may chatter is due to the depth of
the cut in the tissue against which the bur head is applied. If a
bur head is pressed against the tissue so as to make only a
relatively shallow cut, the overall time any two adjacent flutes
are exposed to the tissue being cut is relatively low. The time in
which the two adjacent flutes, as well as the spatial gap between
the flutes, are exposed to the open environment is relatively high.
During these relatively long time periods, tissue cut from bur and
entrained in this gap is able to be discharged away from the bur
head. This gap is then relatively debris-free the next time it
rotates against the in-place tissue. Additional newly excised
tissue fills this gap. However, if the bur head is pressed against
the tissue to make a deep cut, the time in which the spatial gap
between any two flutes is located against the in-place tissue
increases. The time this gap is exposed to the open environment
drops. Consequently, there may not be enough time for tissue
entrained in this gap to be discharged. These gaps between the
flutes clog. If this occurs, during the next time period in which
the gap is rotated against the in-place. It is believed that that
build up of chips between the flutes and their cutting edges clogs
the bur head. This clogging, in turn, it is believed causes a
forced vibration and the resultant chatter.
SUMMARY OF THIS INVENTION
[0008] This invention is directed to the design of a new and useful
surgical bur. The bur of this invention is provided with cutting
edges positioned to reduce, if not eliminate, chatter that occurs
during the use of the bur.
[0009] The bur of this invention has plural sets of flutes. Each
flute defines a cutting edge, an edge that removes tissue from the
surgical site to which the bur is applied. The flutes in a first
set of flutes are shaped to have cutting edges that emerge from the
body of the bur head at a first position relative to the distal end
tip of bur head. Often, but not always, these cutting edges emerge
from the distal end tip. The flutes in the second set of flutes are
shaped to have cutting edges that emerge from the bur head body at
a second position spaced proximally from the first position.
[0010] In some versions of the invention, the distal ends of the
second set of flutes are chamfered. As a result of the chamfers,
the cutting edges of the flutes start at positions proximal to the
distal ends of the flutes.
[0011] In some versions of the invention, the bur head is formed so
that the second set of flutes emerges from the bur head at
locations proximal to the locations from which the first set
emerges.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention is pointed out with particularity in the
claims. The above and further features of this invention may be
better understood by reference to the following detailed
description taken in conjunction with the accompanying drawings in
which:
[0013] FIG. 1 is a side view of a basic surgical bur constructed in
accordance with this invention;
[0014] FIG. 1A is a side view of an the surgical bur of this
invention illustrating an alternative geometric feature for
coupling the shaft to a surgical handpiece;
[0015] FIGS. 2 and 2A are enlarged side views of a bur head shaped
in accordance with this invention;
[0016] FIG. 3 is a front view, looking proximally rearward, of the
bur head of FIG. 2;
[0017] FIG. 4 is a cross sectional view of the bur head of FIG. 2
taken along line 4-4 of FIG. 2A;
[0018] FIG. 5 is a cross sectional view of the bur head of FIG. 2
taken along line 5-5 of FIG. 2A; and
[0019] FIG. 6 is a cross sectional view of the bur head of FIG. 2
taken along line 6-6 of FIG. 2A;
[0020] FIGS. 7 and 7A are side views of an alternative bur head
constructed in accordance with this invention;
[0021] FIG. 8 is a front view, looking proximally rearward, of the
bur head of FIG. 7;
[0022] FIG. 9 is a cross sectional view of the bur head of FIG. 7
taken along line 9-9 of FIG. 7A;
[0023] FIG. 10 is a cross sectional view of the bur head of FIG. 7
taken along line 10-10 of FIG. 7A;
[0024] FIG. 11 is a cross sectional view of the bur head of FIG. 7
taken along line 11-11 of FIG. 7A;
[0025] FIG. 12 is a side view of a second alternative bur head
constructed in accordance with this invention;
[0026] FIG. 13 is a cross section view of the bur head of FIG. 12
taken along line 13-13;
[0027] FIG. 14 is a cross section view of the bur head of FIG. 12
taken along line 14-14;
[0028] FIG. 15 is a cross section view of the bur head of FIG. 12
taken along line 15-15;
[0029] FIG. 16 is a front view, looking proximally rearward of a
third alternative bur constructed in accordance with this
invention;
[0030] FIG. 17 is a cross sectional depiction of an alternative bur
constructed in accordance with this invention.
[0031] FIG. 18 is an isometric view of an alternative bur of this
invention.
[0032] FIG. 19 is a front view of the bur head of FIG. 18 showing
respective flute chamfers and cutting edges;
[0033] FIG. 20 is a side view of the bur head of FIG. 18 shaped in
accordance with this invention;
[0034] FIG. 21 is a side view of the bur head of FIG. 18, rotated
along the axis of the bur;
[0035] FIG. 22 is a cross sectional view of the bur head of FIG.
18;
[0036] FIG. 23 is a side view of a bur head shaped in accordance
with this invention, rotated along the axis of the bur, showing the
pitch angles of the chamfer surfaces; and,
[0037] FIG. 24 is a side view of a bur head shaped in accordance
with this invention showing the pitch angles of the chamfer
surfaces.
DETAILED DESCRIPTION
[0038] FIG. 1 illustrates a surgical bur 20 constructed in
accordance with this invention. Bur 20 has a head 22 that forms the
distal end of the bur. ("Distal" it shall be understood, means
towards the surgical site to which the bur is applied. "Proximal"
means away from the surgical site.) Bur head 22 has a distal end
tip 23 that is the most forward portion of the bur 20. A shaft 24
extends proximally rearward from the bur head 22.
[0039] The proximal end of the shaft 24 is provided with coupling
features 26. The coupling features 26 are geometric features that
facilitate the removable engagement of the shaft 24 to a coupling
assembly integral with the rotating shaft of a powered surgical
tool with which bur 20 is used (tool not illustrated.) The
illustrated coupling features 26 are a set of planar faces recessed
relative to the outer diameter of the shaft 24. One such geometry
is described and illustrated in U.S. Pat. No. 5,888,200, issued 30
Mar. 1999, Multi-Purpose Surgical Tool System, the contents of
which is incorporated herein by reference. An alternative geometry
for coupling features 26 in the form of linearly aligned opposed
concave surfaces is illustrated in U.S. Pat. No. 6,562,055, issued
13 May 2003, Cutting Attachment For A Surgical Handpiece Designed
To Be Selectively Coupled To The Handpiece, the contents of which
is incorporated herein by reference. It should be appreciated that
these two geometries of coupling features are exemplary, not
limiting. In alternative versions of the invention, these coupling
features may for example, be threading. Alternatively, as depicted
in FIG. 1A, tabs 27 that project outwardly from the outer surface
of shaft 24 may function as the coupling features. The exact
geometry of the coupling feature is not relevant to the structure
of this invention.
[0040] Bur head 22, as seen best in FIGS. 2, 2A and 3, is formed
with a number of arcuately spaced flutes 30-44. Each flute 30-44,
as seen by the cross sectional view of flute 30 in FIG. 6, is
formed by a rake surface 50 and a clearance surface 52. Rake
surface 50 extends approximately radially from the longitudinal
axis of the center core of the bur head 22. In the Figures, the
outer perimeter of the center core is generally represented by
dashed circle 48. It should be understood that, as the outer
diameter of the bur changes along the length of the bur, the outer
diameter of the center core changes. Each clearance surface 52
extends generally tangentially from the outer perimeter of the bur
head center core. More specifically, each clearance surface 52
extends approximately tangentially away from the base of the rake
surface 50 of the flute adjacent the flute formed by the clearance
surface. Thus, the clearance surface 52 of flute 30 extends from
the position along the perimeter of the bur head core from which
rake surface 50 of flute 32 extends.
[0041] The rake surface 50 and clearance surface 52 that form an
individual flute meet to forming a cutting edge 54. The bur cutting
edges 54 are the edges of the bur head 22 that perform the cutting
when the bur 20 is applied to a surgical surface.
[0042] As seen best by FIG. 3, bur head 22 of this invention,
flutes 30, 34, 38 and 42 are formed so that their rake and
clearance surfaces 50 and 52, respectively, meet to form cutting
edges 54 that start at a location relatively close to the distal
end tip 23 of the bur head. Flutes 32, 36, 40 and 44 are formed so
that, at the distal ends of the flutes, chamfer surfaces 56, angled
from the rake surfaces 50, extend between the rake surfaces 50
inwardly towards and to the clearance surfaces 52. Flutes 32, 36,
40 and 44 thus have chamfer edges 58 that are the edge surfaces
along the interfaces between the clearance surfaces 54 and chamfer
adjacent chamfer surfaces 56. As seen by FIGS. 2, 4, 5 and 6,
chamfer surfaces 56 are formed on flutes 32, 36, 40 and 44 to end
at the points along the flutes where the flutes have the largest
outer diameter relative to the longitudinal center axis of the bur
20.
[0043] Bur head 22 may be formed by first shaping the head to
provide eight (8) identical flutes that extend the full length of
the head from the distal end tip to the shaft. Then portions of
flutes 32, 36, 40 and 44 are selectively removed to form chamfer
surfaces 52. Grinding, electro-discharge machining or laser cutting
or other machining methods may be employed to excise the material
from flutes 32, 36, 40 and 44 to form chamfer surfaces 56.
[0044] Owing to the presence of the chamfer surfaces 56, at any
location along the longitudinal axis of the bur head where some
flutes have cutting edges 54 and other flutes chamfer edges 58, the
chamfer edges 58 are closer to this axis than cutting edges 54.
Thus, chamfer edges 58 do not cut the tissue against which the bur
head 22 is applied.
[0045] When a surgeon applies a bur 20 to a surgical site, often
the section of the bur adjacent the distal end tip 23 is the
section of the bur head 22 that is pressed against the tissue to be
excised. It is at this time the above-described geometry of the bur
of this invention becomes advantageous. There are a reduced number
of cutting edges 54 at the distal end tip 23. It is believed this
reduces the extent to which forces generated as a result of
regeneration of waviness excite the bur into chatter vibration.
Moreover, since there are a reduced number of cutting edges 56 at
the most distal section of the bur head 22, the interstitial gap
between cutting edges is wider than it would be otherwise. The
relatively large size of these gaps minimizes the extent to which
excised tissue is trapped in these spaces. This reduces the extent
to which tissue entrained in the inter-flute gaps imposes addition
vibration-causing force on the bur head 22.
[0046] The reduction of the number of cutting edges also reduces
the tooth passing frequency at the distal tip of the bur 20. This
is the frequency at the cutting edges 54 press against the tissue
being excised. This frequency, TPF, is calculated according to the
formula:
TPF=[RPM.times.No. of CE]/60
Here, RPM is the revolutions per minute of the bur 20. Variable CE
is the number of bur head 22 cutting edges at the position along
the bur head at which the bur head is being applied to the tissue
to be excised. With bur head 22 of this invention, since there are
fewer cutting edges at the distal end of the bur head 22 than at
more proximal locations, the tooth passing frequency at the distal
end locations is less than the tooth passing frequency at the more
proximal locations along the length of the bur head.
[0047] This reduction in distal end tooth passing frequency further
reduces the chatter of bur 20 of this invention. This is because a
further means of reducing chatter is to operate the bur at a speed
so that the tooth passing frequency as closely as possible matches
the chatter frequency. This frequency matching assists in the
nulling of bur chatter vibration. By reducing the number of flute
cutting edges 54 at the distal end of the bur head 22, it is more
likely that when, this end of the bur head is pressed against
tissue, the tooth passing frequency will more closely approximate
the chatter vibration frequency.
[0048] Bur head 22 of bur 20 has what is referred to as an acorn
style head. As depicted by FIGS. 7, 7A and 8-11, this invention may
be incorporated into bur heads having alternative shapes.
Specifically, bur 70 of this version of the invention has what is
referred to as a round or spherical head 72. As seen by reference
to FIG. 8, bur head 72 has flutes 74-88. Each of the flutes 74-88
originate at the distal end tip 90 of bur head 72.
[0049] Each flute 74-88, as best seen in FIG. 11, is formed with
both a rake surface 94 and a clearance surface 96. Flutes 74, 78,
82 and 86 are formed to have cutting edges 98 that, like the flutes
themselves, originate at the distal end tip 90 of the bur head.
[0050] Flutes 76, 80, 84 and 88 are formed with chamfer surfaces
102, best seen in FIGS. 8, 9 and 10, that start adjacent bur head
distal end tip 90. Flutes 76, 80, 84 and 88 thus are formed with
chamfer edges 104 where each clearance surface 96 meets the
associated flute chamfer surface 102. Chamfer surfaces 102 are
formed on flutes 76, 80, 84 and 88 so that chamfer edges 104
terminate and cutting edges 98 begin at the point where the bur
head has its largest outer diameter.
[0051] FIGS. 12-15 illustrate another bur 110 constructed in
accordance with this invention. Bur 110 has a spherical bur head
112. Bur head 112 is shaped to have ten (10) flutes 114-132 best
seen in FIG. 15. Each flute 114-132 has a rake surface 134 and a
clearance surface 136. The rake and clearance surfaces 132 and 134,
respectively, of each flute 114-130 meet to form a cutting edge 138
that extends along the length of the flute.
[0052] Bur head 112 of this invention is formed so that the flutes
originate from the core of the bur head, represented by dashed
circles 139 at different positions along the length of the bur
head. FIG. 13, for example, illustrates the flutes present at a
position adjacent distal end tip 140 of bur head 112. It can be
seen here that only flutes 114, 118, 122, 126 and 130 have emerged
from the core of bur head 112. Thus, clearance surface 136 of flute
130 emerges from the base of rake surface 134.
[0053] Extending proximally along the bur head 112, away from the
distal end tip 140, flutes 116, 120, 124, 128 and 132 start to
emerge from the core of bur head 112 as seen in FIG. 14. Initially
the rake surfaces 134 of flutes 116, 120, 124, 128 and 132 are
shorter in length than the length of rake surfaces 134 of flutes
114, 118, 122, 126 and 130. Thus, the cutting edges 138 of flutes
116, 120, 124, 128 and 132 are spaced inwardly of the cutting edges
of flutes 114, 118, 122, 126 and 130. Consequently, at the bur head
position of line 14-14 of FIG. 7A, cutting edges 138 of flutes 116,
120, 124, 128 and 132 do not contribute to the cutting of the
tissue to which the bur 110 is applied.
[0054] As seen by FIGS. 12 and 15, at the position along the length
of the bur head 112 where the head is of largest diameter, flutes
116, 120, 124, 128 and 132 are fully emerged from the head core.
All flutes 114-132 are of equal height relative too the perimeter
of the bur head core. Thus the cutting edges 138 all contact, and
therefore cut, the tissue against which this section of the bur is
placed.
[0055] This version of the invention may be constructed by first
forming bur head 112 so that all the flutes extend the full length
of the bur head. Then material is removed from flutes 116, 120,
124, 128 and 132 so that the flutes emerge from the bur head core
at a position proximal to the distal end tip 140. The means used to
form chamfer surfaces 56 are employed to similarly shape flutes
116, 120, 124, 128 and 132.
[0056] FIG. 16 represents an alternative version of the invention
of FIGS. 1-6. In this version of the invention bur head 22a is
formed with flutes 30a-44a. Flutes 30a, 34a, 38a and 42a are not
formed with chamfered surfaces. Flutes 32a and 40a are formed with
chamfered surfaces 140. Flutes 36a and 44a are formed with
chamfered surfaces 142. Flutes 32a and 40a are formed so that
chamfered surfaces 140 extend a first distance proximally rearward
along the length of bur head 22a. Flutes 36a and 44a are formed so
that chamfered surfaces 142 extend a second distance proximally
rearward along the length of the bur head 22a. This second distance
is greater than the first distance chamfered surfaces 140 extend.
Thus, bur head 22a of this embodiment of the invention is
constructed to have a first set of cutting edges 146, where the
clearance and rake surfaces of flutes 30a, 34a, 38a and 42a meet,
which emerge from the core of the bur head at a first location
along the length of the bur head. A second set cutting edges 148,
where the clearance surfaces and chamfered surfaces 140 of flutes
32a and 40a meet, emerges from the core of the bur head at a second
location along the length. A third set of cutting edges 150, where
the clearance surfaces and chamfered surfaces of flutes 36a and 44a
meet, emerges at a third location along the length of the bur head.
This third location is, relative to the distal end tip, spaced
further away than the second location.
[0057] FIG. 18 illustrates another surgical bur 160 constructed in
accordance with this invention. Bur 160 has a head 162 with a
distal end tip 163. As seen in FIGS. 18 and 19, bur head 162 is
formed with a number of arcuately spaced flutes 170-184. Each flute
170-184, as seen by the front view of flute 170 in FIG. 3, is
formed by a rake surface 190 and a clearance surface 192 (FIG. 22).
Rake surface 190 extends approximately radially from the
longitudinal axis of the center core of the bur head 162. It should
be understood that, as the outer diameter of the bur changes along
the length of the bur, the outer diameter of the center core
changes. Each clearance surface 192 extends generally tangentially
from the outer perimeter of the bur head center core. More
specifically, each clearance surface 192 extends approximately
tangentially away from the base of the rake surface 190 of the
flute adjacent the flute formed by the clearance surface. Thus, the
clearance surface 192 of flute 170 extends from the position along
the perimeter of the bur head core from which rake surface 190 of
flute 172 extends.
[0058] The rake surface 190 and clearance surface 192 that form an
individual flute meet to form a cutting edge 194. The bur cutting
edges 194 are the edges of the bur head 162 that perform the
cutting when the bur 160 is applied to a surgical surface.
[0059] As seen best in FIGS. 19-21, bur head 162 of this invention,
first set of two flutes, flutes 170 and 178, are formed so that
their rake and clearance surfaces 190 and 192, respectively, meet
to form cutting edges 194 at a location that starts relatively
close to the burr head distal end tip 163. More specifically, the
area on the surface of the bur immediately around tip 163 can be
considered to be a land that is fluteless. Flutes 179 and 178,
including their cutting edges 194, emerge from this land. Flutes
170 and 178 are also symmetrical to one another, 180.degree.
apart.
[0060] Within each arcuate section of the bur head between flutes
170 and 178 there are plural additional flutes. In one section
there are flutes 172, 174 and 176. The second arcuate section
contains flutes 180, 182 and 184. These intermediate sets of flutes
172-176 and 180-184 are formed with chamfers surfaces. These
chamfer surfaces effectively "cut-off" the cutting edges of flutes
172-36 and 180-184 so that their cutting edges 194 emerge from the
bur head at locations spaced from the distal end tip of the bur
creating flute cutting edge progression.
[0061] There is a common chamfer surface, surface 196 over each set
of flutes 172-176 and 180-186. Each of the chamfer surfaces 196
forms the common distal end face of one of the intermediate flute
sets, flute set 172-176 and flute set 180-186. Each chamfer surface
196 starts at the distal at the perimeter of the land at the distal
end tip of the bur head. Chamfer surfaces 196, relative to the
cutting edges 194 of flutes 170 and 178 are angled closer to the
proximal end of the bur shaft. Thus, the presence of chamfer
surfaces 196 means that the cutting edges of flutes 172-176 and
180-186 emerge from the bur head at distances that are spaced
proximal to the distal end tip of the bur head.
[0062] Symmetrically opposed flutes 176 and 184 each have a chamfer
surface 200. Each chamfer surface 200 emerges from adjacent the
distal end tip of the bur head. Thus each chamfer surface 200 forms
an edge with an adjacent chamfer surface 196. Each chamfer surface
200 also abuts the distal end rake surface 190 of one of the flutes
170 or 178. Each chamfer surface 200 has an angle from the
longitudinal axis of the bur shaft than the angle of the adjacent
chamfer surface 196.
[0063] Each flute 176 and 184 is formed with a second chamfer
surface, chamfer surface 202. Each chamfer surface 202 extends
distally rearward from the point where the abutting chamfer
surfaces 196 and 200 move apart from each other. Thus, each chamfer
surface 202 extends between the rake and clearance surfaces 190 and
192, respectively, of the associated flute 176 or 184.
[0064] Each chamfer surface 202 extends proximally rearward along
the bur head further than the associated chamfer surface 196. Owing
to the presence of chamfer surfaces 202, the cutting edges 194 of
flutes 176 and 184 emerge from the bur head at position proximal to
those where cutting edges 194 of flutes 174 and 182 emerge.
[0065] Each flute 172 and 180 is formed with its own chamfer
surface 204. Each chamfer surface 204 starts at a point a short
distance proximally rearward from the distal end tip of the bur
head, at the perimeter of the land. Each chamfer surface 204
extends between the rake and clearance surfaces 190 and 192,
respectively, of the associated flute 172 or 180. The distal
portion of each chamfer surface 204 intersects the adjacent chamfer
surface 196.
[0066] Each chamfer surface 204 extends rearward along the
associated flute 172 or 180 a distance approximately equal to the
distance along which chamfer surfaces 202 extend. (These distances
being from the distal end tip of the bur head.) Thus, owing to the
presence of chamfer surfaces 204, cutting edges 194 of flutes 172
and 180 emerge from the bur head at the approximately the same
position at which the cutting edges 194 of flutes 176 and 184
emerge. Here "position" is understood to be a location along the
longitudinal axis of the bur head 162 relative to the distal end
tip.
[0067] Each chamfer surface 196, 200, 202, and 204 is defined by at
least two chamfer edges.
[0068] Chamfer surfaces 196 each have two chamfer edges 210 and
212. Starting at the most proximal location of each chamfer surface
196, cutting edge chamfer edge 210 starts at the distal end of the
cutting edge 194 of flute 174 or 182 and extends generally linearly
and distally forward. Chamfer edge 210 then arcuately curves to
intersect, or abut, the respective chamfer surface 204 present on
flute 172 or 180. Also starting at the distal end of the cutting
edge of flute 174 or 182 is the chamfer edge 212. Distally forward
of this point, edge 212 curves away from edge 210. Edge 210 curves
until the edge 210 becomes the boundary between chamfer surface 196
and the adjacent chamfer surface 202. From this intersection of
surface 192 and 202, edge 212 curves inwardly toward the distal end
tip 163. The section of edge 212 intersects the point where
surfaces 196, 200 and 202 meet. Distally forward of this point,
edge forms the boundary between surfaces 196 and 200.
[0069] Each chamfer surface 200 is defined by two additional edges
chamfer edges 214 and 216. Chamfer edge 214 extends from the from
the point surfaces 196, 200 and 202 intersect to the point where
surfaces 192 of flute 176 or 184 and surfaces 200 and 202
intersect. Chamfer edge 214 is generally linear in shape. Chamfer
edge 216 forms the outer boundary of chamfer surface 200. Extends
from the intersection of surface 192 of the flute 176 or 184 and
surfaces 200 and 202 to the rake surface of the adjacent flute 178
or 170. Edge 216 is generally linear.
[0070] Two additional chamfer edges are present on the perimeter of
each chamfer surface 202; a chamfer edge 218 and 220. Chamfer edge
202 starts where the clearance surface 192 of flute 174 or 182 and
the adjacent chamfer surfaces 196 and 202 meet. From this point,
chamfer edge 202 extends generally linearly to the distal end of
the cutting edge of the associated with flute 176 or 184. Chamfer
edge 220 starts at the proximal end terminus of chamfer edge 216.
Chamfer edge 216 initially angles away from edge 218. Edge 218 then
curves to and terminates at the point the cutting edge 194 and
chamfer edge 218 meet.
[0071] Lastly, the chamfer surface 204 includes two chamfer edges
222 and 224. Chamfer edge 222 extends proximally from the distal
end tip land to the cutting edge of the associated flute 172 or
180. Edge 222 is generally linear. Chamfer edge 222 starts at the
intersection of the clearance surface 192 of the flute 172 or 180
and the adjacent chamfer surfaces 196 and 202. Initially, chamfer
edge 224 angles away from edge 222. Edge 224 then curves toward
edge 202. Chamfer edge 224 then terminates at the point cutting
edge 194 and chamfer edge 202 meet.
[0072] The chamfer edge geometry of each chamfer surface 196, 200,
202, and 204 is not limited to the described version of the
invention. It is purely a product of machining and chamfer surface
size whether or not chamfer edges are shared or intersect one
another. It is within the scope of the present invention to have
chamfer surfaces that share fewer edges. Alternatively, one chamfer
surface could extend radially around the entire surface of the bur
head 162 in a fashion where small chamfer surfaces extend proximal
to the large circumferential chamfer surface.
[0073] Yet another unique variable to the disclosed invention
relates to the particular angles of each chamfer surface 196, 200,
202, and 204 relative to the longitudinal center axis of the bur
head 162. For the most part, each chamfer surface is not perfectly
flat and is arcuate in nature. Therefore, extending a line
tangentially to each chamfer surface yields an approximate
particular angle relative to the distal end tip 163. It is to be
noted, that though chamfer surface 196 looks flat, it is indeed
curved. The radius of chamfer surface 196 is so large in nature
that when such a small portion of the radius is looked at, the
surface visually looks flat. As can be seen in FIG. 24, both
chamfer surfaces 202 and 204 have the same angles relative to the
longitudinal center axis, LCA, of bur head 162. Thus, .alpha.1
equals .alpha.4. Tangent line T1 extends tangentially from the
chamfer surface 202 intersecting the longitudinal center axis LCA
to create angle .alpha.1 therebetween. Likewise, tangent line T4
extends tangentially from the surface of chamfer surface 204
intersecting the longitudinal center axis LCA to create angle
.alpha.2 therebetween. Since .alpha.1 equals .alpha.4, the chamfer
surfaces 202 and 204 have the same angle, or pitch, on bur head
162.
[0074] FIG. 23 shows the relationship between .alpha.1, .alpha.2,
.alpha.3, .alpha.4, and .alpha.5; though it does not show .alpha.4,
it has already been shown that .alpha.1 is equivalent to .alpha.4.
Like FIG. 23, each chamfer surface 196, 200, and 202 has a
respective line T3, T2 and T1, respectively, that corresponds to
the approximate chamfer pitch or cutting edge pitch. Each
tangential line T1, T2, and T3 intersects the longitudinal center
axis LCA creating an angle .alpha.1, .alpha.2 and .alpha.3,
respectively, therebetween. It can be seen that .alpha.1 is greater
than .alpha.2, which is greater than .alpha.3; which in turn is
greater than .alpha.5. Since the obtuse angle between the lines T1,
T2 and T3 and longitudinal center axis lines were used, the
relationship between angles and chamfer pitch or cutting edge pitch
are inversed in relationship to the longitudinal center axis line
LCA. Following the corollary relationship between angles, chamfer
surface 202 has less of a pitch in relationship to the longitudinal
center axis of the bur head 162 than chamfer surface 200, which in
turn has less of a pitch than chamfer surface 196. The pitch of the
cutting edges of flutes 170 and 178 are represented by the line T5
and angle .alpha.5. Angle .alpha.5 has the greatest pitch at the
distal end tip 163 as compared to the pitches of each chamfer
surface 196, 200, 202, and 204.
[0075] As seen in FIG. 22, proximal from the distal end tip 163,
where all the cutting edges 194 are present, bur head 162 is formed
so that the cutting edges 164 are equangularly spaced apart.
[0076] Bur head 162 may be formed by first shaping the head to
provide eight (8) identical flutes that extend the full length of
the head from the distal end tip to the shaft. Then, portions of
flutes 174 and 182 are selectively removed to form chamfer surfaces
196. Similarly, portions of flutes 172, 176, 180, and 184 are
selectively removed to form chamfer surfaces 198. Grinding,
electro-discharge machining or laser cutting or other machining
methods may be employed to excise the material from flutes 172-36
and 180-184 to form their respective chamfer surfaces 196.
[0077] Alternatively formed, the bur head 162 may be formed by
casting the bur head and grinding down the desired edges to form a
cutting edge. By casting the bur head, the chamfer surfaces do not
need to be grinded down due to the design of the cast.
[0078] When a surgeon applies a bur 160 to a surgical site, often
the section of the bur adjacent the distal end tip 163 is the
section of the bur head 162 that is pressed against the tissue to
be excised. It is at this time the above-described geometry of the
bur of this invention becomes advantageous. There are a reduced
number of cutting edges 194 at the distal end tip 163, two that are
symmetrical to one another in the preferred embodiment of an eight
flute bur. This reduces the extent to which forces generated as a
result of regeneration of waviness excite the bur into chatter
vibration. Moreover, since there is a reduced number of cutting
edges 194 at the most distal section of the bur head 162, the
interstitial gap between cutting edges 194 is wider than it would
be otherwise. The relatively large size of these gaps minimizes the
extent to which excised tissue is trapped in these spaces. This
reduces the extent to which tissue entrained in the inter-flute
gaps imposes addition vibration-causing force on the bur head
162.
[0079] Since there are only two flutes 170 and 178 present at the
location immediately proximal to the distal end tip 163, the tooth
passing frequency at this location is very low. This further
increases the likelihood that the low frequency tooth passing will
matches and the chatter frequency and therefore cancels the
chatter.
[0080] It should be recognized that the foregoing are particular
embodiments of the invention. Other versions of the invention may
have features different from what has been described. For example,
in the disclosed version of the invention, the flutes with the
short length cutting edges are alternate with the flutes having the
longer length cutting edges. This feature of the invention need not
be incorporated in all versions of the invention. Thus, in some
versions of the invention a bur head may be arranged so that two or
more long length cutting edges are followed by one or more flutes
with shorter length cutting edges.
[0081] Similarly, in some burs of this invention, each pair of
adjacent flutes with long length cutting edges may be separated by
two or more flutes with shorter length cutting edges. In regard to
these versions of the invention, there may be some applications
wherein flutes with shorter length cutting edges are adjacent, one
flute may formed to have a cutting edge of a first length and a
adjacent short length flute formed to have a cutting edge of a
second length. Thus, a bur head may be constructed to have, in
sequence: a flute with a cutting edge that extends from the distal
end tip of the head; a flute with chamfer surface 140; and a flute
with chamfer surface 142.
[0082] Further, there is no requirement that the bur heads of this
invention be constructed so that the different length cutting
surfaces are symmetrically arranged around the outer perimeter of
the bur head. For example a bur head with eight (8) cutting edges
may be constructed so that where the individual cutting edges are
all present, the edges are spaced 45.degree. apart. In this version
of the invention, the first, second, fourth, sixth and seventh
flutes are constructed so as to have cutting edges that start
adjacent the bur head distal end tip. The third, fifth and eighth
flutes are constructed to have cutting edges that start at a
position spaced proximally to where the first set of flutes
start.
[0083] In the above version of the invention it may be provide the
bur shaft with a feature that offsets the asymmetric structure of
the bur head. Such feature may include one or more tabs or fingers
that are extend outwardly from the body of the shaft. These tabs
are asymmetrically positioned to offset the asymmetrical loading.
Alternatively, this feature may comprise one or more pins embedded
in the shaft that are flush with the shaft. These pins are of
different density than the material forming the bur shaft and are
again asymmetrically positioned to offset the asymmetric
loading.
[0084] FIG. 17 illustrates in cross section an alternative bur head
240 of this invention. Bur head 240 is shaped to have a number of
arcuately spaced apart flutes 242-256. In this version of the
invention flutes 242-256 may extend the complete length of the bur
head 240, from the distal end tip to where the proximal end is
joined to the shaft.
[0085] Bur head 240 is further formed so that around the
circumference of the head, the flutes 242-256 are not equangularly
spaced apart; the pitch angles between the adjacent flute pairs are
different. For example, in the illustrated version of the invention
flutes 242-256 and 248-250 are spaced apart angle
.phi..sub.1=38.degree.. Adjacent flutes 242-244 and 250-252 are
spaced apart angle .phi..sub.2=43.degree.. Adjacent flutes 244-246
and 252-254 are spaced apart angle .phi..sub.3=52.degree.. Adjacent
flutes 246-248 and 254-256 are spaced apart angle
.phi..sub.4=47.degree..
[0086] When the bur having this head geometry is employed, the
between two adjacent pairs of flutes, for example between adjacent
flutes 244-246 and 246-248, the time between when each flute in the
pair strikes the tissue is different. Thus in the above example the
time between when flute 246 strikes the bone after it is first
struck by flute 244 is less than the time between when flute 248
strikes the bone after it is initially struck by flute 246. This
variable periodicity between flute strikes is believed to reduce
the extent the bur is forced into chatter-causing vibration.
[0087] This feature of the invention may or may not be incorporated
into the versions of the invention with variable length cutting
edges. Also, the bur head of this invention may be constructed so
that not all adjacent pairs of the flutes have pitch angles that
vary from each other. Thus, for example with a bur having eight
flutes, there may be a first pitch angle between 6 of the adjacent
flute pairs and a second pitch angle between two of the adjacent
flute pairs
[0088] It should likewise be appreciated that the disclosed basic
bur head shapes are exemplary, not limiting. In alternative
versions of the invention, the bur heads may have alternative
shapes including barrel head, conical, egg, pear or drum shaped.
Thus, there in some versions of the invention, the distal end tips
of the bur heads may have profiles different than the curved convex
profile of the illustrated embodiments.
[0089] Likewise, there is no requirement that, in all versions of
the invention, the shorter length cutting edges emerge at the
location where the bur heads reach there maximum diameter. The
shorting length cutting edges are fully emerged at positions along
the bur head distal to where the bur head has its largest
diameter.
[0090] Also, in some versions of the invention, the flutes with the
shorter length cutting edges may have shorter length cutting edges
by virtue of the cutting edges terminating at a position along the
bur head spaced distally from the locations along which other
cutting edges terminate. Some versions of the invention may be
constructed so that, between flutes with cutting edges that extend
the full length of the bur head, there are flutes with cutting
edges that start a position proximal to the bur head distal end tip
and terminate at a position distal to the proximal terminus of the
bur head.
[0091] Further while two means of shaping the bur to provide
cutting edges of different lengths are shown, it other versions of
this invention may have different flute arrangements and flute
shapes to provide the same structural features. Also, flutes of
different shapes may be provided on a single bur. Thus, a single
bur may have: a first set of flutes that are relatively long and
shaped with relatively long cutting edges; a second set of flutes
that are also relatively long and shaped with chamfered surfaces to
have short cutting edges; and a third set of one or more flutes
that are relatively short in length.
[0092] The various features of the different versions of the bur of
this can be combined as appropriate. Thus the bur of FIG. 18, with
only two flutes that fully emerge from the distal end tip may be
combined with the bur having variable pitches between flutes of
FIG. 17.
[0093] It is likewise understood that the shaft structure is not
limited to what has been disclosed. The bur of this invention may
have a tubular shaft. In these versions of the invention the shaft
typically has an opening immediately proximal to the bur head. The
opening functions as a port through which irrigating fluid is
discharged or a suction is drawn. In these versions of the
invention, the coupling feature of the bur is often a hub attached
to the proximal open end of the shaft. The hub has both geometric
features that facilitate the coupling of the bur to a drive
handpiece and a port to establish fluid communication to a suction
device or from a source of irrigating fluid.
[0094] Thus, it is an object of the appended claims to cover all
such variations and modifications that come within the true spirit
and scope of this invention.
* * * * *