WO2005070320A1

WO2005070320A1 - Self adjusting instrument

Info

Publication number: WO2005070320A1
Application number: PCT/IL2005/000086
Authority: WO
Inventors: Rephael Hof; Ehud Teperovich; Amir Meir Zilbershtain
Original assignee: Redent-Nova Ltd.
Priority date: 2004-01-26
Filing date: 2005-01-24
Publication date: 2005-08-04
Also published as: EP1849430A2; US20090130638A1; EP1849430A3; US20070054238A1; BRPI0507110A; IL160074A0; RU2373891C2; EP1708638A1; ES2309711T3; MXPA06008432A; DE602005018833D1; JP2007518513A; ATE395007T1; RU2006130741A; BRPI0507110B1; EP1708638B1; CN1917826A; CN1917826B; SG134329A1; DE602005006735D1

Abstract

The invention is an instrument for cleaning and/or shaping and/or widening a channel that exists in or through a solid object. The design of the instrument the superelastic and shape memory properties of the material from which it is made, allow the inner volume enclosed by the instrument, its outer contour, or both to change as a result of the forces exerted upon it while working, thereby shaping the instrument to the three-dimensional contour of the channel. A preferred embodiment of the instrument is an endodontic file for use in the cleaning, shaping, and widening stages of a root canal procedure.

Description

SELF ADJUSTING INSTRUMENT

Field of the Invention

The present invention is related to the field of tools. Specifically the present

invention relates to an instrument for cleaning and/or shaping and/or

widening a channel, existing in or through a solid object.

Background of the Invention

Publications and other reference materials referred to herein, including

references cited therein, are incorporated herein by reference in their

entirety and are numerically referenced in the following text and

respectively grouped in the appended Bibliography which immediately

precedes the claims.

There are many situations in which it is required to use an instrument for

cleaning out and/or shaping and/or widening a channel that exists in or

passes through a solid object. One of the best examples illustrative of the

problem and of the shortcomings of the prior art is from the field of dental

instruments, specifically root canal procedures. Root canal procedure is one

of the most demanding tasks for a dental surgeon. Root canal treatment consists of two stages: (a) shaping, cleaning, and widening of the root canal

and (b) obturation of the canal space. The first stage is aimed at removing

all tissue remnants, shaping the canal space and disinfecting it, while the

second stage is aimed at sealing the root canal and preventing its

recontamination. Failure to achieve either of those goals may result in

persistent apical periodontitis - associated with periapical bone resorption

and occasional or chronic suppuration.

In the simplest case, in which the canal is relatively straight and has a

relatively uniform circular cross-section, the work is carried out by starting

with a small diameter instrument (known as a dental file) and replacing it

with a series of increasingly larger diameter files until the desired final

diameter of the canal is attained. If the canal is not straight, using the

conventional stainless steel files will most probably result in a poor quality

of treatment. In cases in which the curvature is not too great, nickel

titanium alloy files are able to adapt themselves to the longitudinal

curvature of the canal; thus achieving better results; however existing

nickel-titanium alloy files cannot adapt themselves to changes in the shape

or diameter of the canal, therefore a series of files must be used to clean out

a canal as is the case with stainless steel files. Also the use of any type of

existing file in a canal having non uniform or non circular cross -section

results in a canal that is either not completely cleaned out or one having a circular cross-section, the uniform diameter of which is at least as large as

the maximum width of the original canal.

The anatomy of a tooth is shown in Fig. 1. Topographically tooth 1 is divided

into two sections. The crown 2, covered by enamel 4, is the visible part of the

tooth. The root 3 is below the gums and anchors the tooth in place in the jaw

bone. Within the dentin 6, which comprises the principal mass of the tooth,

is located the pulp chamber 5 and one or more root canals 7, both of which

are filled with pulp 8.

Figs. 2A to 2C illustrate the major steps of the root canal procedure. In the

first step (shown in Fig. 2A) part of the crown is removed and the pulp is

cleaned out of the pulp chamber. In the second step (Fig. 2B) the openings of

the root canals are widened. Then (Fig. 2C) the canal system is shaped,

cleaned, and widened, removing all pulp particles and infection. In a final

step (not shown in the figures) the clean and disinfected root canals are

obturated.

Endodontic failures are more common than the profession is willing to

acknowledge. The commonly quoted success rates are based mainly on

studies carried out in teaching institutes and/or by endodontists.

Nevertheless, surveys carried out on the general public indicate that in association with up to 58% of the endodontically treated teeth a periapical

lesion was evident (1).

This represents, most probably, a poor quality of treatment (1);

nevertheless, it may also represent a basic flaw in the common approach to

root canal treatment. Root canals are usually perceived as having a

gradually tapering diameter with a round cross section (Fig. 3A). This may

be true for many upper anterior teeth; however, it is far from reality in

many of the bicuspids and molars. In these teeth ribbon-like root canals,

with a flat cross section (Fig. 3B) are common (2). The flat dimension of

these canals is at the bucco-lingual plane, which is not seen on a radiograph,

and usually has its maximal width at 5 mm from the apex. This anatomy is

especially pronounced in the second upper bicuspids, in distal roots of lower

molars, as well as in many canines and lower incisors. Additionally, canals

with a tear-shaped cross section (Fig. 3C) are common in roots that have two

canals, such as the mesial roots of lower molars and those of upper first

bicuspids as well as in many of the mesio-buccal roots of upper molars. The

fact that all of these anatomical variations are not seen on a regular

periapical radiograph is one of the reasons for the common misconception

and presents a major obstacle in achieving the goal of high quality

endodontic treatment. The traditional, common, approach for cleaning, widening, and shaping root

canals utilizes hand files having round cross-sections and a standardized

cylindro-conic shape. Sequential use of files of increasing diameter, with

intermitted flushing with antiseptic solution, results in a canal in which a

cylindro-conic gutta-pecha cone may intimately be fitted in the apical part of

the canal and used as a "master cone". With the proper paste type sealer

and accessory cones they are expected to seal the apical part of the canal.

The common cleaning, widening, and shaping procedures are designed to

adapt the apical part of the root canals to the form of these standardized

master cones.

This common concept is based on the image of a root canal that has a round

cross section, which may gradually be enlarged by round files to the shape of

a standardized master cone. Although suitable for anterior teeth, when

applied in many posterior root canals, this approach may often lead to

failure. Cleaning, widening, and shaping a flat root canal with round files

will frequently leave a remaining buccal and/or lingual recesses along the

root canal filling, untouched and full of tissue remnants, bacteria, or both

(3,4). This will inevitably result in failure. Recent studies indicate that this

problem is much more common than previously appreciated (2, 3).

When using traditional hand-held stainless steel files some of these recesses

are inevitably only partially cleaned. In Fig. 4 is shown a set of stainless steel K- files. A great deal of experience is necessary to choose the proper

length and diameter as the canal is cleaned out from the top to the bottom.

When the root canal curves it is only possible to follow the curvature by

increasing the diameter of the canal. This problem is illustrated in Fig. 5A.

If the curvature of the canal becomes to great, generally near the apex of the

canal, then one of two undesirable situations arises. The first, shown in Fig.

5B, is that the process is terminated resulting in creation of a ledge in the

canal and debris in the untreated lower part of the canal. The second

alternative, shown in Fig. 5C, is that the procedure continues until

perforation of the tooth occurs, also resulting in a false canal or apex

enlargement. One other major difficulty encountered during root canal

treatment is shown in Fig. 5D; if one of the solid files breaks and can not be

removed, a not infrequent occurrence, then the root canal treatment fails

and the tooth is usually removed.

The hand-held stainless steel instruments are currently gradually being

replaced by nickel titanium rotary files. As in the case of K-files, current

leading nickel titanium rotary files are used as series of instruments with

gradually enlarging diameters but, unlike the stainless steel files, are able

to adapt longitudinally to the canal shape. Nickel titanium rotary files are

more efficient and allow the operator to complete a case in a somewhat

shorter time. Unfortunately, this efficiency has a price: the prepared canal is of a perfect round cross section and the cleaning of the recesses in flat and

tear-shaped canals is not done.

Recognition of the above problem has led some professional authorities to

consider a further enlargement of the apical part of the canals, to a diameter

that will include the flat remaining parts. The preparation of a root canal

by enlargement for root canals having round, flat, and tear-shaped cross-

sections is shown schematically in Figs. 6A, 6B, and 6C respectively. Such

enlargement could not be safely done in bent root canals with traditional

stainless steel instruments because of their rigidity (3). Rotary nickel

titanium files made it possible to enlarge bent canals in a mesial root of a

lower molar to accept a No. 45-50 gutta-percha master cone. Nevertheless,

this approach has two short comings: it may frequently lead to either

unwanted excessive local thinning of the remaining root canal wall (2) or to

the use of a single-cone root canal filling in the apical third of the canal.

The first may lead to a higher frequency of vertical root fractures, while the

second was discarded long ago for its inferior sealing abilities. Furthermore,

in many cases the diameter required to really include the recesses is so

large that it will cause a perforation of the canal wall (2) (see Fig. 6B and

Fig. 6C). The issue of cleaning, widening, shaping, and obturation of root canals with

non-round cross sections does not currently have an adequate, efficient

solution.

It is therefore a purpose of the current invention to provide an instrument

that is capable of changing its interior volume, contour, or both during use

in cleaning and/or shaping and/or widening a channel, existing in or through

a solid object, in order to shape itself to the channel's three-dimensional

contour.

It is another purpose of the current invention to provide an endodontic file

that is capable of cleaning and shaping and widening root canals having

circular and/or non-circular cross sections.

It is another purpose of the current invention to provide an endodontic file

whose contour varies during use thus allowing the use of a single file for an

entire root canal procedure.

It is yet another purpose of the current invention to provide an endodontic

instrument that is sufficiently flexible to allow it to adapt itself

longitudinally to the curvature of the root canal up to its apical end. It is still another purpose of the current invention to provide an endodontic

instrument through which antiseptic solution can continuously flow into the

root canal while working.

It is a further purpose of the current invention to provide an endodontic file

that has significantly greater endurance and strength than existing

instruments used to perform root canal treatments.

It is another further purpose of the current invention to provide an

endodontic file that requires significantly less time to perform root canal

treatments than existing instruments.

It is a still further purpose of the current invention to provide an endodontic

instrument that is significantly easier to use and has a significantly shorter

learning curve than existing instruments used to perform root canal

treatments.

Further purposes and advantages of this invention will appear as the

description proceeds.

Summary of the Invention

The present invention can be realized in many different embodiments and

has applications in many fields in which it is necessary to clean out and/or shape and/or widen a channel, existing in or through a solid object

Examples of such applications can be found, for example, in such widely

differing fields as drilling for oil, dental surgery, and material machining. In

order to best illustrate the many advantages of the instrument of the

invention over existing tools, a specific embodiment of the invention for use

in dental root canal treatment, one of the most demanding applications for

instruments of this type, has been chosen as an illustrative and non-limiting

example to be described herein.

The preferred embodiment of the endodontic instrument of the invention,

known herein as the SAF (self adjusting file) is a nickel titanium

instrument of a unique self adjusting design. The SAF has an original round

cross-section to which it always tries to return as a result of superelastic

properties that are given to it. Simultaneously this property combined with

its unique geometry gives it an extreme ability to adapt itself to the shape of

the canal walls. When inserted into a narrow canal it will have a contour

narrower than its original one, which will gradually increase with use, thus

allowing it to be used as a single instrument for the whole root canal

procedure. Moving the instrument of the invention in the root canal,

preferably by rotating the instrument but optionally by moving it back and

forth in a direction essentially parallel to the longitudinal axis of the canal

or by causing it to vibrate, will result in the removal of a layer from all inner

surfaces of the canal, to which it adapts itself, while gradually attempting to - li ¬

re turn to its original round shape. The instrument will thus perform an

ideal shaping, widening, and cleaning, without unwanted localized thinning

of the root wall.

The unique design of the instrument allows it to adapt itself both

longitudinally and in the cross section and thus follow the original three

dimensional shape of the root canal. Thus, a canal with a round cross

section will be enlarged as round, while a flat canal will be enlarged as a flat

canal of greater dimensions. Even the trickiest canals, those with a tear

shaped cross section, will essentially maintain their original shape. Further

the design of the instrument allows it to achieve different shapes and

dimensions along the length of the canal, thereby allowing effective cleaning

of the entire canal without excessive widening of the canal walls. The

method of the prior art to extensively enlarge root canals in order to include

in their diameter the flat or tear-shaped recesses is thus eliminated.

Due to the special open and/or hollow design, antiseptic solution can

continuously flow into the root canal while working, thus saving valuable

time and improving the debridement and disinfection procedures. The

constant flow also increases the efficiency of filing and prevents clogging the

canal with dentin-mud and debris. The structural design of the self adjusting file of the invention allows top

elasticity. In the extreme case of an instrument failure and breakage inside

the canal, specially designed extractors can be used to easily remove the

separated part of the SAF, no matter what the position or depth of the

broken-off part is in the root canal.

In a first aspect the present invention provides an instrument for cleaning

and/or shaping and/or widening a channel that exists in or through a solid

object. The instrument of the invention is characterized in that its inner

volume, contour, or both changes during use in order to shape it to the

three-dimensional contour of said channel. In particular the shape of the

perimeter of the instrument adjusts during use to conform to the perimeter

of the local cross section of the channel at each radial plane located along

the length of the instrument that is inserted into the channel.

The instrument of the present invention can be made from a superelastic

material and a material which either has or has been treated to give it

shape memory properties. In a preferred embodiment, the instrument of the

invention is made from a nickel titanium alloy.

Preferably a single instrument is inserted into the channel and used for the

entire procedure of cleaning and/or shaping and/or widening the channel

before being withdrawn. In some applications, more than one file is used to clean, and/or shape, and or widen the channel. If the instrument breaks

inside the channel, the broken piece can be withdrawn from without damage

to the object containing the channel.

In a preferred embodiment of the instrument of invention, its body is

comprised of one or more longitudinal elements and one or more

circumferential elements. The longitudinal and circumferential elements

can have a three-dimensional shape chosen from the group comprising:

blade shaped, polygonal prism shaped, rod shaped, curved shaped, and

round shaped elements. The cross-sectional shape of the longitudinal and

circumferential elements can be chosen from the group comprising:

polygonal, round, and curved shapes. The longitudinal elements and the

circumferential elements can be straight or curved. In a preferred

embodiment, the number of longitudinal elements is at least one and the

circumferential elements are distributed along the longitudinal axis of said

instrument. In another embodiment, the number of longitudinal elements is

at least one and the circumferential elements are distributed along the

longitudinal axis of the instrument. The circumferential elements in a given

radial plane define the local cross-sectional shape of the instrument.

In a preferred embodiment of the instrument of the invention, the

longitudinal and circumferential elements define the instrument's three-

dimensional shape. That shape being that of a body with an empty space surrounding the longitudinal axis and bounded radially by a wall having an

open lattice-like structure.

In preferred embodiments of the instrument of the invention, at least a part

of the outer surface of the instrument is constructed or modified in such a

way as to allow the instrument to remove material from the wall of the

channel when relative motion takes place between it and the wall. The

relative motion can be rotational, translational, vibrational, or a

combination of two or more of these types of motion. In one embodiment, at

least part of the outer surface of the instrument is coated with a coating of

an abrasive material, which can be for example, diamond powder, titanium

nitride, or tungsten carbide. In other embodiments, at least part of the outer

surface of the instrument of the invention is roughened, comprises

numerous small teeth, or comprises a cutting edge.

Preferably, fluid can flow into the channel and or debris resulting from the

cleaning and/or shaping and/or widening can be removed from the channel

while the instrument of the invention is inserted and working in the

channel. The fluid can flow and/or the debris can be removed via the interior

of the instrument and/or, in other embodiments via the space between the

wall of the channel and the outer surface of the instrument. In preferred embodiments of the instrument of the invention, a uniform

amount of material is removed from the wall of the channel, along the entire

insertion length of the instrument in the channel, during the procedure of

cleaning and/or shaping and/or widening the channel. In other

embodiments, the instrument can be constructed such that different

amounts of material are removed from the channel wall at different

locations along the insertion length of the instrument. The instrument of

the invention can be inserted into the channel such that it passes through

the entire length or only a portion of the entire length of the channel.

In preferred embodiments of the instrument of the invention, the cross-

sectional shape of the channel, along the entire insertion length of the

instrument, is essentially the same after the procedure of cleaning and/or

shaping and/or widening the channel as it was before the procedure.

Another embodiment of the instrument of the invention comprises a long

narrow balloon, which is inserted into the channel and then inflated.

Preferred embodiments of the instrument of the invention are endodontic

files. In this case, the channel is a root canal, and cleaning and/or shaping

and/or widening of the channel comprises the cleaning, shaping, and

widening stage of a root canal procedure. In another aspect, the present invention supplies a method of using the

instrument of the invention for cleaning and/or shaping and/or widening a

channel that exists in or through a solid object. The method comprises the

following steps:

- inserting the instrument into the channel; causing relative motion between the instrument and the wall of the channel; optionally, removing the debris resulting from the cleaning and or shaping and/or widening from the channel while the relative motion takes place; optionally, causing fluid to flow into the channel while the relative motion takes place; and

- removing the instrument from the channel when the cleaning and/or shaping and/or widening have been completed.

In the case in which the instrument of the invention is an endodontic file,

the method of cleaning, and/or shaping, and/or widening a root canal

comprises the following steps:

- inserting the file into the root canal; causing the file to move relative to the wall of the root canal;

- optionally, removing the debris resulting from the cleaning, shaping, and widening from the root canal while the file moves relative to the wall of the root canal; optionally, causing fluid to flow into the root canal while the file moves relative to the walls of the root canal; and

- removing the file from the root canal when the cleaning, shaping, and widening have been completed.

All the above and other characteristics and advantages of the invention will

be further understood through the following illustrative and non-limitative

description of preferred embodiments thereof, with reference to the

appended drawings.

Brief Description of the Drawings

- Fig. 1 shows the anatomy of a tooth;

- Figs. 2A to 2C illustrate the major steps of the root canal procedure;

- Figs. 3A to 3C show root canals having different cross sectional shapes;

- Fig. 4 shows a set of stainless steel K-files;

- Figs. 5 A to 5D show some of the problems encountered in using prior art files to perform root canal treatments;

- Figs. 6A to 6C show the stages, according to the prior art, in preparing root canals having different cross sectional shapes;

- Figs. 7A, 7B, and 7C are respectively perspective, front, and flattened-out, views of the instrument of the invention; - Figs. 8A and 8B show cross-sectional views of the instrument of the invention before being inserted into the root canal and inside a tear shaped canal respectively;

- Figs. 9A, 9B, and 9C show schematically the preparation of a root canal, using the self adjusting instrument of the invention, for root canals having round, flat, and tear-shaped cross-sections respectively;

- Fig. 10 shows how the instrument of the invention adapts its shape as it is inserted up to the apical end of the root canal; and

- Figs. 11A to 11F show cross-sections of examples of different embodiments of the instrument of the invention.

Detailed Description of Preferred Embodiments

In general, the channels to be widened and/or cleaned and/or shaped by the

instrument of the invention are relatively long and narrow. These channels

will be described hereinbelow in terms of a single 'longitudinal axis", which

is the line defined by the loci of the center points of the channel along its

length, and a multitude of "radial axes", wherein each such radial axis is

defined by a line originating at a point on the longitudinal axis and

perpendicular to the longitudinal axis at that point. Rotation of a given

radial axis around its origin defines the localized "radial plane". The

direction essentially parallel to the longitudinal direction will be known as

the "longitudinal direction" and the direction essentially parallel to one of

the radial axes will be known as the "radial direction". Because the instrument of the invention conforms to the shape of the canal similar

terminology will be used to describe the principal axes of the instrument.

The instrument of the invention can be inserted completely to the end of the

channel or only partially into the channel, in which case only part of the

channel will be widened and/or shaped and/or cleaned. The length of the

instrument that is inserted into the channel is known as the "insertion

length" which term also indicates the depth of the channel that is worked on

by the instrument.

As an illustrative, but non-limitative, example of the instrument of the

invention embodiments of an endodontic file for performing root canal

treatments will be described hereinbelow.

The preferred embodiment of the endodontic instrument of the invention,

known herein as the SAF (self adjusting file) is a rotary nickel titanium

instrument of a unique design. While current leading rotary files must be

used as series of instruments with gradually enlarging diameters, the SAF

is used as a single instrument for the whole procedure. When inserted into a

narrow canal, whose nominal diameter is less than its own nominal

diameter, the instrument is compressed, its superelastic property allowing it

to adapt itself to the cross-sectional shape of the walls of the canal in each

radial plane along the longitudinal axis of the canal. Rotating in the canal it removes tissue and debris from the canal and the canal wall. As the debris

is removed from the canal wall, the super elastic property of the SAF causes

it to gradually expand with time in the radial direction while continually

maintaining contact with the canal wall at every point. Thus material is

uniformly removed from the dentinal walls of the canal until the desired

nominal diameter is achieved.

A preferred embodiment of the SAF is shown respectively in perspective,

front, and flattened out, views in Figs. 7 A, 7B, and 7C. The SAF 10 is made

of a nickel titanium alloy (Nitinol) and originally is given a cylindrical

shape. The walls of the upper end, the neck 12, are solid and are gripped by

either the dental hand piece or are attached to a handle for manual use. The

main part of the body of the SAF is an open, lattice-like structure made up

of longitudinal elements 14, that run the length of the instrument from neck

to tip 16 and short circumferential elements 18 that connect adjacent

longitudinal elements. In the preferred embodiment shown in the figures,

there are four longitudinal elements and the circumferential elements, in

their undeformed state are arcs of a circle. In a radial plane containing

circumferential elements, the circumferential elements that lie in that plane

define the cross-sectional shape of the instrument in that plane. Both the

circumferential and longitudinal elements have a flat rectangular blade-like

cross section. After manufacture, the Nitinol cylinder is constrained in a mold and heat treated to give it its shape memory property while changing

its shape to cylindrical-conic.

The surfaces of the instrument of the invention that are in contact with the

walls of the canal are treated in some way to enable them to remove

material from the wall as the instrument rotates. One possible treatment is

to coat the surfaces with an abrasive material such as, for example,

diamond powder, titanium nitride, and tungsten carbide, that will remove

dentin from the canal wall by friction as the SAF is rotated, thus cleaning

out and enlarging the inside of the root canal. In other embodiments, the

surfaces in contact with the wall of the canal can be manufactured with

roughened surfaces comprising, for example numerous small teeth as in a

file or a rasp. Alternately, these surfaces can comprise a cutting edge

similar to the edge on a drill bit. In some embodiments of the instrument of

the invention, the surfaces in contact with the canal wall can be relatively

smooth and abrasive slurry can be introduced into the canal to be trapped

between the instrument and the wall.

The material scraped from the wall of the canal passes through the openings

in the lattice structure of the body of the SAF into the hollow interior from

which it can easily be removed by rinsing or suction without stopping

rotation of the instrument or withdrawing it from the root canal. In other

embodiments, the debris can also be removed via the space between the canal wall and the instrument. The design allows for fluids, such as

antiseptic or saline solution, to continuously flow into the root canal, either

through the center of the instrument or between the outer surface of the

instrument and the canal wall, while the instrument is working, thus saving

valuable time and improving the debridement and disinfection procedures.

The constant flow also increases the efficiency of filing and prevents

clogging the canal with dentin-mud and debris. Another advantage of the

hollow structure of the SAF is that, in the extreme case of instrument

failure and breakage inside the canal, the separated part of the instrument

of the invention can be easily and safely removed, using specially designed

extractors, no matter what the position of the broken piece of the

instrument in the root canal.

After part of the crown is removed and the pulp is cleaned out of the pulp

chamber, and a sufficient access to the canal is obtained the SAF is inserted

into the root canal. As the instrument is pushed into the canal, its

superelasticity allows it to be guided to the apical end of the root canal by

following the path of least resistance (through the pulp rather than the

much harder dentine). Prior art nickel titanium files can also adapt

themselves to the canal shape longitudinally but are unable to change their

volume and contour as can the SAF. Additionally the solid structure of the

prior art files makes them less flexible than the hollow lattice-like structure SAF. In Fig. 10 is shown the SAF adapting its shape as it is inserted up to

the apical end of the root canal.

The instrument is now moved relative to the walls of the root canal in order

to carry out the cleaning, widening, and shaping process. The motion can be

longitudinal, i.e. the instrument can be moved up and down in the canal;

rotational; vibrational, i.e. the instrument can be caused to vibrate by

connecting it to, for example, an ultrasound transducer; or a combination of

these motions. In the preferred embodiment of the invention the SAF is

rotated either manually or by means of a dental handpiece. As the

instrument rotates, the SAF's super elastic property keeps its elements

pressed against the root canal wall in all the radial planes along the length

of the instrument.

Figs. 8A and 8B show cross-sectional views of the instrument of the

invention outside of and inside a tear shaped root canal respectively. The

views in the cross-sections shown in Figs 8A and 8B are in radial planes

wherein each such radial plane is located at and contains a single set of

circumferential elements. Since the axis of the SAF essentially lies on the

longitudinal axis of the canal, each plane intersects the walls of the canal at

right angles. The perimeter of the SAF in each of these planes is made up of

eight segments - 14a to 14d, the longitudinal elements, and 18a to 18d, the

circumferential elements. The material and structure of the SAF have three properties that allow it to carry out the desired function. Firstly, the

superelasticity of the alloy makes the device constructed from it extremely

flexible, allowing it to be deformed to conform to the shape of the canal at

the position at which it is located. Secondly, the diameter of the original

cylindro-conic state of the instrument is greater than the diameter of the

canal. Therefore the stress created in the alloy by the deformation from

contact with the walls of the canal as the instrument is rotated and the

super elastic property causing the instrument to try to return to its original

cylindro-conic shape. The internal force exerted in attempting this return to

the original shape constantly pushes the elements of the device against the

inner wall of the canal. Thirdly each element made of the super elastic alloy

has the property of being able to stressed/strained up to 8% to 10% from it's

original shape, depending on the exact composition of the alloy, thus

allowing the internal volume of the SAF to increase with time and its

elements to remain in constant contact with the walls, even as material is

continually being removed from them. As the instrument rotates each of the

circumferential elements 18a to 18d changes in length and shape

independently from the others, thus the instrument is able to conform to the

local shape of the canal wall.

The fact that the circumference of the instrument is divided into four

elements, each of which can independently change shape imparts to the SAF

a degree of flexibility, an ability to adapt to the shape of the root canal, and the ability to expand in size that goes far beyond that of existing files. These

properties can be further increased by building the instrument with a

greater number of peripheral elements, however increased flexibility, etc.

will be gained at the expense of the strength of the device.

Thus, in the plane shown, as the instrument rotates, its cross- sectional

shape is constantly changing to conform to the shape of the canal wall and

the length of the circumference of the device in that plane is constantly

increasing as material is removed from the wall. This is to be compared to

the situation with existing files in which the shape of the canal is changed to

conform to the shape of the file and the files must constantly be replaced

with files of larger diameter in order to clean, widen, and shape the canal.

The description given hereinabove applies for each successive set of

circumferential elements located in different radial planes along the length

of the instrument. The adaptation to the local shape of the canal and

changes in contour and length of the circumferential elements that comprise

each successive set is essentially independent of its neighbors. This behavior

explains how the instrument of the invention can deal with the common

situation described hereinabove in which the canal narrows along much of

its length and then becomes wide near the apical tip before narrowing

again. Because the instrument is moved (rotated) as a single unit, the

amount of material removed from the canal wall, which mainly depends on how long the instrument is revolved, is essentially constant along the entire

length of the portion of the instrument that is inserted into the canal.

For almost all cases, the deviations of the diameter of the root canal from its

average diameter are such that the instrument of the invention can be

designed to allow use of a single instrument to clean out the whole length of

the canal. In the preferred embodiments of the invention, the outer surface

of the instrument is uniformly treated to enable removal of material from

the wall, in which case essentially the same amount of material will be

removed from the wall of the canal at each radial plane along its entire

length. However, the skilled person will know how the instrument can be

designed and treated to allow non-uniform removal of material at different

positions along the length of the canal, if this result is desired for specific

applications. Based on statistical information regarding the dimensions of

root canals from a large number of teeth, a single nominal width can be

determined for the instrument of the invention. It may be however, that it is

preferable to provide instruments having several different nominal

diameters, for example a small diameter for a narrow canal and a larger

diameter for wide canals. In any case, once the correct size instrument has

been selected, the entire cleaning, widening, and shaping procedure is then

carried out using only that instrument which, once inserted into the canal,

is only withdrawn at the end of the procedure. It is to be noted that in some

cases, the channel to be worked on by the instrument of the invention may have an exceptionally widely varying cross section, in which case more than

one instrument, having different nominal diameters, will have to be used to

shape, widen, and clean the entire channel.

The preparation of a root canal, using the self adjusting instrument of the

invention is shown schematically Figs. 9A, 9B, and 9C for root canals having

round, flat, and tear-shaped cross-sections respectively. The figures are a

series of images showing the stages of the cleaning, shaping, and widening

step in the procedure. The images range from the untreated root canal on

the left to the canal at the end of the procedure on the right. From the

figures, it can be seen that the rotating SAF removes a relatively uniform

layer from all inner surfaces of the canal wall and therefore the final shape

of the cleaned out canal (right image) is very close to that of the original

canal. The shaping and widening are done by removing a minimal amount

of the canal wall and therefore without causing localized thinning of the root

wall as is the case in the prior art (see Figs. 6B and 6C). Using the SAF to

clean out the root canal, the nominal diameter and shape of the canal at

each radial plane along its length is preserved. In other words the shaped

and cleaned canal does not have an essentially circular cross section having

a uniform cross-sectional area along its length as is the case with the prior

art. Shaping, widening, and cleaning the root canal with one instrument, while

flushing with a constant flow of antiseptic solution, may significantly cut

down treatment time. Additionally shaping and cleaning the root canal with

one instrument eliminates the necessity of the operator following complex

and tricky flow charts in order to accomplish a simple root canal treatment

procedure, as is demanded by current leading rotary file systems.

Heat-softened gutta-percha methods can be easily adapted for obturation of

the prepared root canal obtained with the instrument of the invention.

Many variations in the choice of materials and especially in the design of

the structure of the device are possible. For example, the device does not

have to be built from Nitinol but other types of material, such as, for

example, stainless steel, steel, plastic, nickel based alloys, and titanium

based alloys can be chosen. Instead of having circumferential and

longitudinal elements with a flat rectangular blade-like shape as described

hereinabove the elements can have, for example, polygonal prism, rod-like,

or curved shapes. Similarly, elements having polygonal (including

rectangular, square and triangular), round, and curved cross sections can be

used. The combination of original cylindrical shape of the instrument and

cylindrical-conic shape after heat treatment, which is most suitable for root

canal work, can be replaced by other shapes which might be more suitable

for specific applications. Additionally the structure of the instrument need not be the same as the preferred embodiment of the SAF described

hereinabove. Figs. llA to llF show cross-sections of some examples of

different embodiments of the instrument of the invention. The longitudinal

elements are designated by numeral 20 and the circumferential elements

21. Fig. 11A shows the SAF and Fig. 11B is a similar design except that, in

this embodiment, only the outer surfaces of the longitudinal elements are in

contact with the canal wall. Using the embodiment of Fig. 11B, the debris

can be removed upwards through the space between the canal wall and the

circumferential elements while fluid flows downwards through the center of

the device, or vice versa. The embodiment of Fig. 11C is triangular shaped.

The longitudinal elements can be round and covered with abrasive material

or teeth or they can be triangular shaped with the outward facing apex

acting as a cutting/scraping edge. The embodiment shown in Fig. 11D has a

single square longitudinal element with four blades attached to it. The

embodiments of Fig. HE and Fig. llF have a single longitudinal element

from which project radially a multitude of blade-like or wire-like elements.

The means of designing and manufacturing these and other embodiments of

the instrument of the invention, including providing the necessary

superelastic and shape memory properties is within the scope of the

knowledge of skilled persons and therefore will not be discussed in further

detail herein. In another embodiment, the instrument of the invention comprises a long

narrow balloon, which is inserted into the channel and then inflated. This

embodiment can be realized in several ways. For, example, an instrument

based on the design of the SAF can be built in which the circumferential

elements are removed and a balloon is mounted to the device along its

longitudinal axis and inside the longitudinal elements. The balloon is

attached to the device at the neck and to the distal ends of the longitudinal

elements. The instrument is inserted into the canal with the balloon

deflated. When in position, fluid is introduced into the interior of the balloon

using conventional techniques and the balloon expands pushing the

longitudinal elements against the walls of the channel. The outer surfaces of

the longitudinal elements are treated or shaped in some way to enable them

to remove material from the wall as the instrument is moved relative to the

walls of the channel. With embodiments comprising a balloon, the relative

motion is preferably translational, i.e. the instrument is alternately pushed

and pulled in the direction of the longitudinal axis of the channel.

In an alternate embodiment, the device can comprise a balloon only which is

coated with an abrasive material on its outer surface. To give the balloon

sufficient rigidity, a rod or wire is inserted into the interior of the balloon

and attached at the distal end. The balloon is inserted into the channel and

then inflated pressing the sides of the balloon against the walls of the

channel. The relative motion is preferably translational i.e. pushing and pulling the internal rod in the direction of the longitudinal axis of the

channel will cause the balloon to move relative to the wall cleaning,

shaping, and widening the channel. When the work is completed, the

balloon is deflated and withdrawn from the channel.

Although embodiments of the invention have been described by way of

illustration, it will be understood that the invention may be carried out with

many variations, modifications, and adaptations, without departing from its

spirit or exceeding the scope of the claims.

Bibliography

1. Saunders, WP, Saunders, EM, Sadiq, J, Cruickshank, E, Technical

standard of root canal treatment in an adult Scottish sub-population, Br

Dent J 182: 382-386, 1990.

2. Wu, M-K, R'oris, A, Borkis, D, Wesselink, PR, Prevalence and extent of

long oval canals in the apical third, Oral Surg Oral Med Oral Pathol 89:739-

743, 2000.

3. Tan, BT, Messer, H H, The quality of apical canal preparation using

hand and rotary instruments with specific criteria for enlargement based on

initial apical file size, J Endodon 28: 658-664, 2002.

4. Wu, M-K, Wesselink P R, A primary observation on the preparation and

obturation of oval canals, In. Endod J 34:137-141, 2001.

Claims

Claims 1. An instrument for cleaning and/or shaping and/or widening a channel that exists in or through a solid object; characterized in that the inner volume enclosed by said instrument, the outer contour of said instrument, or both change during use in order to shape said instrument to the three-dimensional contour of said channel.

2. An instrument according to claim 1, wherein the shape of the perimeter of said instrument adjusts during use to conform to the perimeter of the local cross section of the channel at each radial plane located along the length of said instrument that is inserted into said channel.

3. An instrument according to claim 1, wherein said instrument is made from a superelastic material.

4. An instrument according to claim 1, wherein said instrument is made from material having shape memory properties.

5. An instrument according to claim 4, wherein the material of which said instrument is treated to give it shape memory properties.

6. An instrument according to claim 3, wherein the superelastic material is a nickel titanium alloy.

7. An instrument according to claim 4, wherein the instrument having shape memory properties is made from a nickel titanium alloy.

8. An instrument according to claim 1, wherein a single instrument can be inserted in the channel and used for the entire procedure of cleaning and/or shaping and/or widening said channel before being withdrawn.

9. An instrument according to claim 1, wherein, if said instrument breaks inside the channel, the broken piece of said instrument can be withdrawn from said channel without damaging the solid object.

10. An instrument according to claim 1, wherein the body of said instrument is comprised of one or more longitudinal elements and one or more circumferential elements.

11. An instrument according to claim 10, wherein the longitudinal and circumferential elements have a three-dimensional shape chosen from the group comprising: - blade shaped;

- polygonal prism shaped;

- rod shaped; curved shaped; and

- round shaped.

12. An instrument according to claim 10, wherein the longitudinal and circumferential elements have a cross-sectional shape chosen from the group comprising:

- polygonal;

- round; curved; and

- blade-shaped.

13. An instrument according to claim 10, wherein the longitudinal elements have a shape selected from the group comprising: straight elements; and curved elements.

14. An instrument according to claim 10, wherein the circumferential elements have a shape selected from the group comprising: straight elements; and

- curved elements.

15. An instrument according to claim 10, wherein the number of longitudinal elements is at least one and the circumferential elements are distributed along the longitudinal axis of said instrument.

16. An instrument according to claim 10, wherein the longitudinal and circumferential elements define the three-dimensional shape of said instrument, such shape being an empty volume surrounding the longitudinal axis, said volume bounded radially by a wall having an open lattice-like structure.

17. An instrument according to claim 1, wherein at least a part of the outer surface of said instrument is constructed or modified in such a way as to allow said instrument to remove material from the wall of the channel when relative motion takes place between said outer surface and said wall.

18. An instrument according to claim 17, wherein at least part of the outer surface of said instrument is coated with a coating of an abrasive material.

19. An instrument according to claim 18, wherein the abrasive material is chosen from the group comprising: diamond powder; titanium nitride; and tungsten carbide.

20. An instrument according to claim 17, wherein at least part of the outer surface of said instrument is roughened.

21. An instrument according to claim 17, wherein at least part of the outer surface of said instrument comprises numerous small teeth.

22. An instrument according to claim 17, wherein at least part of the outer surface of said instrument comprises a cutting edge.

23. An instrument according to claim 17, wherein the relative motion is chosen from the group comprising:

- rotation; translation;

- vibration; and a combination of two or more of these motions.

24. An instrument according to claim 1, wherein debris resulting from the cleaning and/or shaping and/or widening can be removed from the channel while said instrument is inserted and working in said channel.

25. An instrument according to claim 24, wherein the debris is removed via the interior of said instrument.

26. An instrument according to claim 24, wherein the debris is removed via the space between the wall of the channel and the outer surface of said instrument.

27. An instrument according to claim 1, wherein fluid can flow into the channel while said instrument is inserted and working in said channel.

28. An instrument according to claim 27, wherein the fluid flows via the interior of said instrument.

29. An instrument according to claim 27, wherein the fluid flows via the space between the wall of the channel and the outer surface of said instrument.

30. An instrument according to claim 1, wherein, during the procedure of cleaning and/or shaping and/or widening the channel, a relatively uniform amount of material is removed from the wall of said channel along the entire insertion length of said instrument in said channel.

31. An instrument according to claim 1, wherein, during the procedure of cleaning and/or shaping and or widening the channel, a different amount of material is removed from the wall of said channel at different positions along the insertion length of said instrument in said channel

32. An instrument according to claim 1, wherein said instrument is inserted into the channel such that it passes through the entire length of said channel.

33. An instrument according to claim 1, wherein said instrument is inserted into the channel such that it passes through only a portion of the entire length of said channel.

34. An instrument according to claim 1, wherein, after the procedure of cleaning and/or shaping and/or widening the channel, the cross- sectional shape of said channel, along the entire insertion length of said instrument into said channel, is essentially the same as the cross-sectional shape before said procedure of cleaning and/or shaping and/or widening said channel.

35. An instrument according to claim 1, comprising a long narrow balloon, which is inserted into the channel and then inflated.

36. An instrument according to claim 1, wherein said instrument is an endodontic file, the channel is a root canal, and cleaning and/or shaping and/or widening of the channel comprises the cleaning, shaping, and widening stage of a root canal procedure.

37. A method of using the instrument of claim 1 for cleaning and/or shaping and/or widening a channel that exists in or through a solid object said method comprising the following steps:

- inserting said instrument into said channel;

- causing relative motion between said instrument and the wall of said channel;

- optionally, removing the debris resulting from said cleaning and/or shaping and or widening from said channel while said relative motion between said instrument and said wall of said channel takes place; - optionally, causing fluid to flow into said channel while said relative motion between said instrument and said wall of said channel takes place; and removing said instrument from said channel when said cleaning and or shaping and/or widening have been completed.

38. A method of using the endodontic file of claim 36 for cleaning, and/or shaping, and/or widening a root canal, said method comprising the following steps:

- inserting said file into said root canal; causing said file to move relative to the wall of said root canal;

- optionally, removing the debris resulting from said cleaning, shaping, and widening from said root canal while said file moves relative to said wall of said root canal; optionally, causing fluid to flow into said root canal while said file moves relative to said walls of said root canal; and

- removing said file from said root canal when said cleaning, shaping, and widening have been completed.

39. A method according to claim 37 or claim 38, wherein more than one file is used to clean, and or shape, and/or widen the channel.