TITLE

APPARATUS FOR TESTING THE EFFECTIVENESS OF ENDODONTIC TOOLS

DESCRIPTION

Field of the invention The present invention relates to dentistry and, in particular, it refers to an apparatus for testing dental tools effectiveness, in particular the effectiveness of metal rotating endodontic tools, such as the so-called "files" that are made of Ni-Ti alloys.

Background of the invention In the dental practice, a wide variety of tools is used to perform endodontic, orthodontic and conservative dental treatments.

In particular, an endodontic operation provides removing pulp tissue that is inflamed or affected due to deep caries and to related bacterial contamination, or to a trauma. An acute or chronic inflammation may diffuse from a dental root apex to a surrounding bone and cause lesions such as abscesses, or granulomas, which can be detected by radiographic methods.

The operation provides removing both crown and root pulp tissue and replacing it with a permanent gutta-percha and root canal cement, after suitable root canal preparation. In the last years, new endodontic practices have increasingly spread ensuring a canal cleaning that is better and faster root than traditional techniques. The new endodontic techniques are based upon novel tools that can effectively work even in case of extremely unfavourable operating conditions. An example of such tools, are the endodontic files as shown in Figs, from

1 to 3.

In particular, a common endodontic file 10 comprises working portion 15, which is similar to small drill bit, and a manoeuvre portion 16 which is adapted to engage with an endodontic tool 500 (Fig. 2), or to be handled by a specialist. File 10 comprises, furthermore, a stop element 18, usually a plastic resin ring, which is longitudinally movable with respect to file 10. In particular, stop element 18 is prearranged in a predetermined position by the dentist,

according to the tooth that must undergo the endodontic operation. In practice, portion 15 is put into a canal 81 of a tooth 80 during the endodontic operation; by rotating inside the canal at a high rotation speed the file expels the dental pulp (Fig. 3). The files can be a steel one, or it can be made of an equiatomic Nickel-

Titanium alloy.

The former files have a stiffness that is proportional to the tool size, which tends therefore to keep its initial shape when inserted into a curved canal, and exerts straightening forces on the canal itself. These forces are particularly strong at the junction between the tip and the cutting edges of the file, and cause canal transports, aberrations and perforations, which leads to a final root canal cross sectional shape that is more difficult to fill, to not tooled endodontic regions and to root structure damages.

In use, the files are subjected to a high cyclic fatigue and torsional stress that may damage or even break the tool. For each turn within the curved canal, the tool is subjected to a pull/compression stress cycle. In fact, the portion that remains out of the curvature is subjected to tensile stress, whereas the portion that is inside the canal is subjected to compressive stress. Obviously the higher the curvature degree, the stronger the stress and, by a given canal curvature, larger and therefore stiffer tools are subjected to higher stress. Therefore, in the clinical practice, larger tools are not necessarily to be considered safer tools, in particular if they engage important coronal curvatures where they receive a considerable stress.

Furthermore, an important role is played by crystalline phase changes, that may be caused by high stress and temperature changes, because the tool is most likely to break during crystals modifications. Sudden rotation speed changes break the metal matrix cohesion, which causes the formation and the propagation of cracks.

It is therefore essential to provide a motor that is adapted to keep the material in its martensitic phase, applying a limited stress by a fixed speed. Furthermore, it is important to start rotation before inserting the tool into the canal, and to move it axially to distribute the stress along it. An extremely unfavourable condition occurs when an attempt is made to start again file rotation after the file has become blocked within the root canal.

Another variable that must be taken into account is the torsion load to which the tool is subjected, which depends both on how handling the tool by an operator and on the tool shape. The tool shape must be adapted to avoid stress concentration at the cutting edges. Owing to above-mentioned reasons, endodontic treatments are commonly performed by means of files that are made of "NITINOL" , which is a Nickel (Ni) and Titanium (Ti) alloy. The elastic modulus of this material is very low, hence it has outstanding hyperelastic properties. Therefore, during endodontic treatment the NITINOL endodontic files exert lower forces on the side surface of the canal than the steel files, and the straightening action is less strong.

However, despite the increased flexibility, also Ni-Ti tools may break during operation. This is essentially caused by repeated fatigue cycles to which they undergo. It is not unusual that that a file breaks during an endodontic operation, and remains trapped in the tooth canal of the patient with subsequent harm for the patient, risk of recurring infections that may be even more dangerous than the original disease. A portion of file that has been left inside the root canal is often difficult, or even impossible to extract, due to the tortuous shape of the canal and of the resilient force that is exerted by the portion against the walls of the canal.

Moreover, besides the break of the file, that may be caused by torsion overloads and yield point trespassing, a file has in any case a limited fatigue life, due to continuous bending and torsion cycles. Fatigue break does not depend only upon the number to times the file is used, but also it depends upon curvature radius and angle of the canals that are treated with it, as well as it depends upon the tool diameter and rotation speed. In the case of steel tools, an immediate stress evaluation is easier, because on the tool surface clear helical plastic deformation creases appear when the yeals limit has been trespassed. This may be observed even in the case of NiTi tools, but the progressive effects of fatigue on NiTi alloy is often hidden, due to its capacity of restoring original shape.

Therefore, the decision of disposing of a tool after it has been used a certain number of times, to prevent it from breaking, is based on the number of canals that have been treated, on their resistance and curvature, and on the

time that they have remained inside the canals, and therefore such decision is difficult to take.

Normally, file manufacturers indicate an average number of treatments after which the tool should be replaced, i.e. a safety limit of the risk which is fulfilled if this prefixed number is not trespassed.

However, in the case of very narrow-curved canals it might be necessary to dispose of the file after one use.

It is therefore desirable to provide a device that can make measurements on the file and establish whether the file must be disposed of or it can be re- used further.

In CA1336012 an electronic device is described for fine adjustment of transducers controlling circuits, in particular circuits for controlling ultrasonic pulse transducers used in dental tools. The electronic device modifies the value of the main parameters of the transducer circuit responsive to current operative conditions such that a maximum effectiveness of the transducer is achieved both at minimum load conditions and at high load conditions. However, this device is neither useful nor adaptable for checking the fatigue weakening rate to which an endodontic file may have been subjected.

In WO9801736 a device is described for measuring the resilience of an object at a test area. The device comprises a source of oscillations, a means for transmitting the oscillations generated from the source of the oscillations to the test area and a means for measuring the damping of the oscillations caused by the test area, wherein the oscillations occur parallel to the test area.

The main object of the device is to detect a caries in a tooth of a patient. Neither this device is therefore adapted to check the fatigue weakening which an endodontic file may have been subjected to.

Summary of the invention

It is therefore a feature of the present invention to provide a method for testing the effectiveness of an endodontic tool that is adapted to carry out a non-destructive testing.

It is also a feature of the present invention to provide a method for testing the effectiveness of an endodontic tool that is quick and easy to carry out.

These and other features are accomplished with one exemplary apparatus for testing the effectiveness of a dental tool, said endodontic tool

having an elongated shape, in particular a dental hyperelastic mechanical tool, such as a file, a reamer and the like, comprising: a support means for supporting said endodontic tool, said endodontic tool having an elongated shape; - a vibration means for applying vibrations at a predetermined frequency to a first point of said endodontic tool, said vibrations propagating through the elongated shape of said endodontic tool; a measuring means for measuring at a second point said vibrations that have propagated through said endodontic tool, said measuring means suitable for generating a respective propagation signal; a processing means for processing said propagation signal and for generating a corresponding tool integrity signal.

In particular, the endodontic tool may comprise a working portion that is adapted to carry out an endodontic action in the root canal of a patient's tooth, and a manoeuvre portion. At the manoeuvre portion a determined action is applied for causing a predetermined movement of the working portion. More in detail, the predetermined movement is transmitted to the working portion through the manoeuvre portion. Even more in detail, the manoeuvre portion can be handled by a specialist, or coupled to a dental handpiece. In the latter case, the endodontic tool is an rotary tool for the dental handpiece, said dental handpiece adapted to transmit a rotational movement to said rotary tool. More precisely, the rotary tool has a first end that, in use, engages with said dental handpiece and another end that is adapted to carry out an endodontic action in a patient. In particular, the vibration means and/or the measuring means may comprise a contact end that is adapted to be arranged next to the tool.

Advantageously, said support means comprises a housing for the tool. In particular, the housing and the tool comprise respective surfaces that can be reciprocally engaged. In particular, the first point may be chosen proximate or adjacent to an end of the endodontic tool, and the second point may be chosen proximate or adjacent to the opposite end of the tool.

In an exemplary embodiment of the invention, the first point may be chosen proximate or adjacent to an end of the working portion of the

endodontic tool, and the second point proximate or adjacent to the opposite end of the working portion.

Advantageously, the vibration means and the measuring means are arranged at a prefixed portion that has a length d which is less than the overall length L of the endodontic tool, said processing means generating a corresponding local tool integrity signal. More precisely, in this case the first point and the second point are arranged adjacent to the end of the prefixed portion of the endodontic tool.

In particular, the vibration means and the measuring means may be arranged at a plurality of adjacent portions of the endodontic tool, each portion of said plurality having a prefixed length //, for each portion said processing means generating a corresponding local tool integrity signal.

Advantageously, the overall length ∑// of said plurality of portions corresponds to the overall length L of the endodontic tool. In an exemplary embodiment of the invention, the vibration means and the measuring means are arranged at opposite sides with respect to the tool.

Advantageously, the vibration means and/or the measuring means are arranged longitudinally movable with respect to the tool.

Advantageously, the vibration means and/or the measuring means are integral to the support means.

In particular, at least one means among the vibration means and the measuring means may be housed in a respective recess that is made in the support means.

Advantageously, the recess in which the measuring means and/or the vibration means are housed communicates with said housing of said support means in which said endodontic tool is arranged. This way, it is easy to bring the measuring means and/or the vibration means into contact with said tool.

Advantageously, the support means comprises a first and a second portion that can move towards/away from each other between a rest position, in which the arrangement of said endodontic tool is allowed between them, and a locking position, in which said endodontic tool is gripped between said them.

In particular, the support means may comprise a first housing for the tool to be examined and a second housing for a reference sample tool. In this

case, the processing means compare propagation signals measured on said endodontic tool with a propagation signal measured on said reference sample tool.

In particular, the vibration means may comprise an ultrasonic pulse emitter that is adapted to convert an electric signal into a vibration.

Advantageously, the measuring means may be selected from the group comprised of: an ultrasonic pulse receiver, for example a piezoelectric sensor that is adapted to convert the vibration into an electric signal, - an optical sensor.

In an exemplary embodiment, the receiver and the emitter can be integrated in an ultrasonic pulse transducer.

In particular, the ultrasonic pulse emitter can be selected from the group comprised of: - a piezoelectric transducer; a magnetostrictive transducer.

Advantageously, the processing means comprises a means for measuring the impedance, in particular the acoustic impedance. In particular, the measuring means for measuring the acoustic impedance are adapted to measure an acoustic impedance variation, for example a variation that is caused by the presence of cracks, inclusions, and the like, in the endodontic tool.

Brief description of the drawings

The invention will be now shown with the following description of an exemplary embodiment thereof, exemplifying but not limitative, with reference to the attached drawings in which: figure 1 shows a top plan view of a prior art endodontic file that can be analysed by the apparatus, according to the invention, for testing the effectiveness of endodontic tools; - figure 2 shows a front view of the file of Fig. 1 during a prior art endodontic operation; figure 3 diagrammatically shows a configuration of the file in a curved root canal that I subject to the endodontic operation of Fig. 2; figures from 4A to 10 show diagrammatically some possible

exemplary embodiments of the apparatus, according to the invention.

Description of preferred exemplary embodiments With reference to Fig. 4A, an exemplary embodiment is shown of an apparatus 1 , according to the invention, for measuring the integrity degree, and therefore the effectiveness, of an endodontic tool 10, in particular of an endodontic tool that is made of a hyperelastic material such as a Ni-Ti alloy. Apparatus 1 comprises a support 50 on which tool 10 is arranged for carrying out the effectiveness test.

As shown, for example, in Fig. 4A, support 50 may comprise a first and a second portion 50a and 50b that can move towards/away from each other between a rest position, in which the arrangement of tool 10 is allowed between the first and the second portion (shown by dashed lines) and a locking position, in which tool 10 is gripped between the first and the second portion. In an exemplary embodiment of the invention, support 50 may comprise a single fixed part which has a housing 55 whose surface 58 is suitably shaped to allow an engagement with a surface 18 of a coupling portion 16 (Fig. 4B). In both cases, as shown in Fig. 4A and 4B, tool 10 is cantilevered at support 50. Apparatus 1 comprises, furthermore, a means 150 for applying vibrations at a predetermined frequency at a point P1 of the tested tool and a measuring means 250 for measuring the vibrations that reach a point P2 after propagating through distance d between P1 and P2. Measuring means 250 for measuring the vibrations at point P2 may comprise an optical sensor 251 that is suitable for measuring the oscillations caused at a free end 11 and for sending a corresponding signal to a control unit 200. Control unit 200 analyses the received signal and generates a corresponding propagation signal responsive to the integrity degree of endodontic tool 10. Vibration means 150 comprises, for instance, an ultrasonic pulse generator 251 (Fig. 4A). Control unit 200 may be adapted to measure the effectiveness degree of endodontic file 10 by measuring the vibrations that travels along file 10 without substantial modification. Therefore, the test is carried out by measuring the amount of vibrations that propagate along the whole endodontic tool 10

without dispersions due to imperfections, or structural irregularities, which could cause the break of the tool itself during an endodontic operation.

Furthermore, a monitor may be provided, such as an oscilloscope, for displaying the position of any defects that may be present in file 10. The endodontic tool may be, for instance, a file 10 for endodontic treatments that comprises a working portion 15, which is shaped similarly to a small drill bit, that is adapted to carry out an endodontic action in a patient, and a manoeuvre portion 16 that is adapted to be handled by a specialist, or to be coupled with a dental handpiece 500 that transmits a determined movement to tool 10, in particular a rotational movement.

As shown in Fig. 4B, vibration means 150, for applying the vibrations to file 10, may comprise a source 100 of ultrasonic pulses that is operatively connected to an ultrasonic pulse emitter 20 that is brought into contact with file 10 to be tested, at a point P1 , in order to apply the high frequency vibrations, also called starting echo, that is generated by source 100. Furthermore, measuring means 250 may comprise an ultrasonic pulse receiver 25 that is arranged against or proximate to file 10, in order to measure the vibrations, also called return echo, which reaches a point P2 that is arranged at a distance I from P1. More precisely, the distance d may correspond to the length L of tool 10 (Fig. 9), or may coincide with the length I of working portion 15 (Fig. 1 ), or may be less than length L, and even less than length I (Fig. 10). In the latter case, vibration means 20 and measuring means 25 may be arranged at a plurality of adjacent portions 13 of endodontic tool 10. For each portion 13 of endodontic tool 10, the processing means generate, in such case, a corresponding local-integrity signal of the endodontic tool. Therefore, if the above described step is repeated n times, at least one partial integrity datum may be obtained, in addition to the local integrity datum. In particular, if the overall length ∑(li) of tested portions 13 corresponds to overall length L of endodontic tool 10, an overall integrity datum may be obtained. In the example of Fig. 1 , emitter 20 is arranged against or proximate to file 10 at a free end 11 of working portion 15, whereas receiver 25 is arranged against or proximate to file 10 at the other end 12 of working portion 15.

In the example of Fig. 5, emitter 20 and receiver 25 are arranged at opposite sides with respect to file 10 to be tested and are arranged

longitudinally movable with respect to it. In particular, emitter 20 and receiver 25 are slidingly mounted on respective guides 120a and 120b, that are substantially parallel to file 10, such that a scanning step can be performed to identify a possible damaged region of the tool. In the exemplary embodiment shown in Fig. 6A, file 10 is arranged on a support 50 that is adapted to keep it vertical, as shown in the detail of Fig. 6B; in this case, support 50 comprises, furthermore, an opening 53 through which emitter 20 is housed in housing 55, in order to transmit the vibrations at end 16 of file 10. In an exemplary embodiment, not shown in the figures, emitter 20 can be housed through opening 53, in a recess that is separated from housing 55. In this case, emitter 20 is not arranged next to tool 10.

According to an exemplary embodiment shown in Fig. 7 the emitter and the ultrasonic pulse receiver can be integrated in an ultrasonic pulse transducer 300, for example a piezoelectric transducer. Ultrasonic pulse transducer 300 is provided integral to a carriage 115 that is slidingly mounted on a guide 110 that is substantially parallel to file 10 to be tested, in order to cause the transducer 300 to longitudinally run along at least one portion of file 10.

In further exemplary embodiments shown in Fig. 8 and 9, apparatus 1 comprises a support 50 that has a housing 55 in which file 10 to be tested is arranged and a second housing 55' in which a reference sample 10' is arranged.

More in detail, in the exemplary embodiment of Fig. 8, housings 55 and 55' are separate from each other and two emitters 20 and 20' are arranged in contact with file 10 and with sample 10', respectively, at free end 11 and 11 '. Instead, receivers 25 and 25' are arranged in contact with file 10 and 10', respectively, at end 12 and 12' of working portions 15 and 15'.

Alternatively, as shown in Fig. 9, housings 55 and 55' of support 50 can communicate with each other and provide a portion 55" at which a single emitter 20 may be arranged that transmits the vibrations to both files 10 and 10', at respective portions 16 and 16'. The vibrations are subsequently detected at free end 11 and 11' of file 10 and of sample file 10' by means of respective detectors 25 and 25'.

In both cases of Figs. 8 and 9, control unit 200 compares the signal that

is associated to the return echo that is detected at file 10 to be tested, with the return echo that is detected at reference sample 10', and calculates a corresponding integrity degree of tested file 10, with respect to sample model 10'. Furthermore, the exemplary embodiment of Fig. 9, by using a single emitter 20 for applying the vibrations both to file 10 and to sample file 10' avoids any measurement error that may derive from the use of two distinct emitters.

The foregoing description of specific embodiments will so fully reveal the invention according to the conceptual point of view, such that others, by applying current knowledge, will be able, to modify and/or adapt for various applications such embodiments without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiments. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.