High-speed rotary endodontic file

Abstract

ENDODONTIC FILE FOR HIGH-SPEED ROTATION The invention relates to an endodontic file (1) equipped with a blade (14) having at least one cutting lip (13) which has: - a cutting face (Fs), delimited by the cutting lip (13) and configured to come against tissues to be removed from a root canal when the instrument is driven in a rotation in the direction (R); - a clearance face (Fd), delimited by the cutting lip (13), and opposite to the cutting face (Fs); - the cutting lip (13) having a negative cutting angle (c) and a clearance angle (a) greater than or equal to 0, measured in the direction (R). According to the invention: - a cutting angle (b) is between 95° and 150°, and a ratio between the surface area of ​​the blade (So) and the surface area of ​​a circumscribed circle (Se) of the blade is between 40% and 65%. Abstract figure: Fig. 2

Description

Title of the invention: High-speed rotating endodontic file FIELD OF INVENTION

[0001] The present invention relates to endodontics. STATE OF THE ART

[0002] During endodontic treatment, instrument breakage is one of the most frequent complications. The direct complications of this instrument breakage are clinical in nature.

[0003] To prevent canal breakage, it has been proposed to monitor the operating conditions of the canal instrument, particularly by means of torque limiters. Instrument dynamics designed to operate with such torque limiters generally involve rotational speeds below 500 rpm. US20190254774 describes such a system, in which the rotational speed is only 300 rpm.

[0004] Another complication of the treatment is failure to respect the canal geometry. The instrument may deviate from the canal's path, particularly if the canal has a curvature. The instrument then creates a bifurcation within the canal, which complicates the subsequent passage of other instruments, according to the treatment sequence.

[0005] The instrument may also machine the canal transversely and in an unbalanced manner, thus generating a "transport": the resulting shaping is not centered on the original trajectory of the canal. There is a risk that infected tissue may not have been sufficiently machined by the instrument, and that an infection may occur after treatment.

[0006] In order to obtain instruments that are resistant to breakage, are effective, and respect canal geometry, instrument manufacturers have tried multiple cross-section geometries of canal instruments, modifying in particular the cutting angles and the clearance angles of the cutting lips of such instruments.

[0007] Document EP0850600, on behalf of the Applicant, describes the use of different cutting and relief angles for an endodontic instrument. This document explains that the best cutting results are obtained with a positive cutting angle and a positive relief angle.

[0008] Documents FR3034648 and FR3034649, also in the name of the Applicant, illustrate different instrument geometries. Tests were carried out, in particular, with instruments having negative cutting angles, which yielded unsatisfactory results.

[0009] Document EP1716818 describes another type of instrument geometry, in which branches 22 thin out the limbs constituting the cross-section of the instrument, in order to give it significant flexibility. The efficiency of the resulting instrument is not optimal.

[0010] It is possible to further improve the cutting results of the instruments described in the prior art.

[0011] The invention therefore aims to propose a new instrument geometry as well as a new instrumental dynamic, allowing treatments to be carried out efficiently and safely. SUMMARY

[0012] The invention relates to an endodontic file configured to be driven in rotation around an axis and in a determined direction, in order to remove tissues from a root canal during a canal treatment; The endodontic file is equipped with a blade having at least one cutting edge, and the cutting edge having: - a cutting face, delimited by the cutting lip and configured to come against tissues to be removed from a root canal when the instrument is driven according to the rotation in the determined direction; - a draft face, delimited by the cutting lip, and opposite the cutting face; and in a section plane orthogonal to the axis: - the blade being inscribed in a circle whose center is placed on the axis, and tangent to the cutting lip at a point on the cutting lip which is furthest from the center; - the cutting edge presenting: - a negative cutting angle, for example between -15° and -75°, measured in the determined direction: - from a reference plane, orthogonal to the section plane and passing through the axis and the cutting lip, and - towards the cutting face; - a draft angle greater than or equal to 0, for example between 5° and 50°, measured in the determined direction: - from the side of the body, and - towards a conventional work surface, orthogonal to the section plane and the reference plane, and passing through the cutting edge

[0013] According to the invention, in the section plane: - a cutting angle, measured between the rake face and the clearance face, is between 95° and 150°, and - a ratio between the surface area of ​​the blade and the surface area of ​​the circumscribed circle is between 40% and 65%.

[0014] Surprisingly, the tests carried out showed that the files according to the invention, although having a negative cutting angle, provide very satisfactory cutting results, especially when the file is driven at a rotational speed greater than 2000 rpm, for example at 2500 rpm or even up to 4000 rpm and beyond.

[0015] Such rotation speeds are unusual in the sector concerned: canal shaping being carried out with a handpiece, and an instrument breakage being sudden, it is generally accepted that the rotation speeds of the instruments should not be too high in order to avoid an incorrect handling by the practitioner, in particular during canal preparation.

[0016] The instrument according to the invention is advantageous in that it allows for efficient treatments, without breakage, bifurcation, or transport, when driven at high speeds.

[0017] The cutting angle according to the invention provides a balanced cutting lip, in that it is neither fragile because it is too thin, nor imprecise because it is too thick.

[0018] The surface area ratio according to the invention makes it possible to obtain a compromise between a sufficiently flexible blade, which is necessary to tolerate the curvatures of the channel, and a blade that is nevertheless rigid enough to guarantee sufficient cutting efficiency.

[0019] In a first embodiment, the blade has several cutting edges, regularly distributed around the axis, and a first profile connects two successive cutting edges. The first profile has a curvature of radius greater than or equal to 0, preferably strictly greater than 0. Such a profile provides a convex cutting face between two successive edges. Preferably, the first profile has a single curvature, so that the first profile is an arc of a circle.

[0020] In this mode, better cutting results are obtained: - when the cutting angle is between -40° and -60°, preferably between -45° and -55°, and even more preferably between -48° and -53°; and / or - when the draft angle is between 30° and 50°, preferably between 34° and 43°, and even more preferably between 37° and 41°.

[0021] In a second embodiment, the blade has several cutting edges, regularly distributed around the axis, and a second profile connects two successive cutting edges. The second profile has at least two curves in opposite directions, and preferably only two curves in opposite directions. Such a profile provides an S-shaped cutting face between two successive edges.

[0022] In this mode, better cutting results are obtained: - when the cutting angle is between -20° and -30°, preferably between -21° and -26°, and even more preferably between -25° and -22°; and / or - when the draft angle is between 10° and 20°, and preferably between 12° and 16°.

[0023] The first and second embodiments provide excellent cutting results from 2500 rpm, and have been tested up to 4000 rpm.

[0024] In the first two embodiments, the cutting angle is between 95° and 110°, and preferably between 95° and 105°. Optimal cutting results are obtained when the cutting angle is between 98° and 103°.

[0025] A third embodiment of the invention relates to an instrument whose blade has several cutting edges, regularly distributed around the axis, and a third profile connects two successive cutting edges. The third profile has at least two curves in the same direction, that is to say, the third profile does not include curves in opposite directions, and does not correspond to an arc of a circle.

[0026] As with the first embodiment, the third profile provides a convex cutting face between two successive lips. However, the third profile makes it easier to adapt the values ​​of the cutting angle and the draft angle, relative to the surface ratio.

[0027] In this mode, better cutting results are obtained: - when the cutting angle is between -60° and -75°, and preferably between -65° and -70°; and / or - when the draft angle is between 12° and 25°, and preferably between 15° and 20°.

[0028] In the third embodiment, the cutting angle is between 130° and 150°, and preferably between 135° and 145°.

[0029] The third embodiment provides excellent cutting results from 2500 rpm, and has been tested up to 5500 rpm.

[0030] In order to simultaneously present a combination of the aforementioned technical characteristics, the blade has only two cutting lips.

[0031] The invention also relates to an endodontic system comprising a control unit programmed to drive a handpiece configured to rotate an endodontic file, - the endodontic file being equipped with a blade having at least one cutting lip with a negative cutting angle and a positive clearance angle, - The rotation should occur at a speed between 2000 rpm and 6000 rpm, preferably between 2500 rpm and 5000 rpm. Surprisingly and unexpectedly, such an endodontic system allows for effective endodontic treatments despite a negative cutting angle, while reducing the occurrence of breakage, bifurcation, and transport. Preferably, the file should have the aforementioned technical characteristics. BRIEF DESCRIPTION OF THE FIGURES

[0032] [Fig. 1] is a diagram of a first embodiment of an instrument endodontic according to the invention, illustrating the general structure of such an instrument.

[0033] [Fig.2] is a diagram illustrating a section of the first embodiment, illustrating more particularly the cutting, clearance, and cutting edges angles according to the invention.

[0034] [Fig.3] is a diagram illustrating a similar section of a second embodiment of the invention.

[0035] [Fig.4] is a diagram illustrating a similar section of a third mode of realization of the invention.

[0036] [Fig.5] is a diagram illustrating a section of a first comparative instrument, ne not corresponding to the invention.

[0037] [Fig.6] is a diagram illustrating a section of a second comparative instrument, ne not corresponding to the invention.

[0038] [Fig.7] is a table illustrating the evolution of the section of the second mode of execution, from a tip of the blade and towards a heel of the blade.

[0039] [Fig.8] is a diagram illustrating an endodontic system according to the invention. DETAILED DESCRIPTION

[0040] With reference to [Fig. 1], the present invention relates to an endodontic instrument (1), such as a file.

[0041] An endodontic instrument (1) comprises the following elements: - a handle (11) configured to manipulate the endodontic instrument (1), preferably by means of a motorized handpiece (2), and which constitutes a proximal end (1Op) of the endodontic instrument (1); - a heel (12), without cutting edges, and generally featuring grooves for positioning elastomeric stops which serve as length guides for the practitioner, - a blade (14), having at least one cutting lip (13) configured to remove tissue during use of the endodontic instrument (1) within a root canal to be treated, - a point (15) constituting a distal end (lOd) of the endodontic instrument (1).

[0042] An endodontic instrument (1) extends along an axis (a). Although the axis (a) may be curved, particularly in the case of preformed endodontic instruments (1), an endodontic instrument (1) is initially manufactured in a straight form. For the sake of simplicity, reference will be made only to a straight axis (a), although the technical features of the invention may apply to curved axes (a).

[0043] The blade (14) is inscribed within a base envelope (30) which is a shape of revolution centered on the axis (a). The base envelope (30) is frustoconical, having a circular base with a base diameter (00) and a taper (31). The base diameter (00) and the taper (31) are generally standard values ​​in the field of endodontics, for example: - base diameter (0O) is 0.2mm - the taper (31) is 6%.

[0044] Regarding length measurements, the tip (15) of the instrument serves as a reference point. For example, "D3" is a distance located 3 mm from the tip (15), and "D6" is a distance located 6 mm from the tip.

[0045] Figure 2 illustrates the cross-section of a first embodiment of the invention, obtained at a distance D3 and along a cross-sectional plane (Ps) orthogonal to the axis (a) of revolution. The endodontic instrument (1) comprises only two cutting edges (13), connected by a first profile (PI) having a single curvature.

[0046] The two cutting lips (13) are therefore connected by a convex profile, and the section of the instrument (1) resembles an eye.

[0047] The geometry of an endodontic instrument (1) is defined as follows: - The cutting face (Fs) is the front face of the instrument (1), with respect to the determined direction of rotation (R). The cutting face (Fs) is located by a plane orthogonal to the section plane (Ps), and tangent to the cutting face (Fs) at the level of the cutting lip (13). - The clearance face (Fd) is the rear face of the instrument, with respect to the direction of rotation (R). The clearance face (Fd) is located by a plane orthogonal to the section plane (Ps), and tangent to the clearance face (Fd) at the level of the cutting lip (13). - A reference plane (Pr), orthogonal to the section plane (Ps), connects the axis (a) of revolution to the cutting lip (13); - A conventional working plane (Pf), orthogonal to the reference plane (Pr) and to the section plane (Ps), passes through the cutting lip (13).

[0048] The angles are defined as follows: - the cutting angle (c) is measured from the reference plane (Pr) and in the direction of the cutting face (Fs), with respect to the determined direction of rotation (R): if the cutting face (Fs) is below the reference plane (Pr) according to the determined direction of rotation (R), then the cutting angle (c) is negative. - the draft angle (a) is measured from the draft face (Fd) and in the direction of the conventional working plane (Pf) according to the determined direction of rotation (R). - The cutting angle (b) is measured between the cutting face (Fs) and the clearance face (Fd). It is a solid angle and does not require a measurement direction.

[0049] According to the invention, the cutting angle (c) is strictly negative, and the clearance angle (a) is positive.

[0050] A negative cutting angle (c) does not allow the tissues to be cut, but only scraped. While prior art asserts the inferior performance of negative cutting angles, the Applicant has discovered, surprisingly and unexpectedly, that negative cutting angles (c) can prove to be effective if the endodontic instrument (1) is driven at a sufficient rotational speed, i.e., above 2000 rpm.

[0051] Furthermore, proper tissue removal with a negative cutting angle (c) is only achieved if the clearance angle (a) is positive, and preferably strictly greater than zero. A clearance angle (a) strictly greater than zero prevents the tissue from being crushed as it passes over the cutting lip (13), but rather ensures that the tissue is indeed detached for removal.

[0052] However, the Applicant has observed that not all endodontic files (1) with a negative cutting angle (c) and a positive clearance angle (a) provide the same results: for optimal cutting, the endodontic file (1) must have a balance between the flexibility needed to follow the curvatures of the root canal, and the rigidity expected to properly remove tissues.

[0053] An endodontic file (1) that is too rigid promotes bifurcations, transport and breakage, whereas an endodontic file (1) that is too flexible provides an inefficient cut, promotes untwisting, see also breakage.

[0054] Endodontic instruments are generally made of a hyper-elastic alloy, for example a nickel-titanium alloy known as "Nitinol" or "Niti". Heat treatment may be applied to the instruments to increase their lifespan.

[0055] But the predominant criterion for adapting the flexibility of the blade (14) and its cutting power is the geometry of the endodontic file (1).

[0056] Also, good cutting results were obtained with an endodontic file (1) having a cutting edge angle (b) between 95° and 110°, preferably between 95° and 105°, and even more preferably between 98° and 103° for the first and second embodiments, or between 125° and 155°, and preferably between 130° and 145° for the third embodiment. These cutting edge angle (b) values ​​give the cutting lip (13) adequate rigidity for removing tissue effectively, with a sufficient lifespan.

[0057] The cutting angle (c) is between -40° and -75° for the first and third embodiments, or between -20 and -26° for the second embodiment.

[0058] From these cutting angles (c) and in order to comply with the criterion of the cutting angle (b), the clearance angle (a) is between 30° and 50° for the first embodiment, or between 10° and 25° for the second and third embodiments.

[0059] Regarding the flexibility of the blade (14), it must be sufficiently thick to provide the necessary mechanical resistance, without being too rigid. It must also not fill the internal volume of the canal preparation, as this would hinder the removal of debris.

[0060] The geometry of the channel shaping corresponds to the basic envelope of the blade (14). In the section plane (Ps), the blade (14) is therefore inscribed in a circle (e) whose center is placed on the axis (a), and of radius such that the blade (14) is inscribed in the circle (e).

[0061] The good flexibility of the blade (14) is obtained when a ratio between a surface area of ​​the blade (So) and a surface area of ​​the circle (Se) is between 40% and 65%, i.e. ge [0,40,0,65}

[0062] Area measurements are carried out by any suitable means. Computer-aided design software generally includes area calculation tools. This is also the case for some drafting software.

[0063] In order to obtain such a surface ratio, it may be advantageous to provide a reduced pitch (P) for the winding of the cutting edges (13). The files according to the invention have at least 8 to 9 turns as illustrated in [Fig. 1], for a blade (14) approximately 15 mm long, and preferably up to 10 or 11 turns.

[0064] The pitch (P) is therefore on the order of 1 to 3 mm. Preferably the pitch (P) is variable, and increases from the tip (15) towards the heel (12).

[0065] For example, for an instrument reference: - the pitch (P) varies from 1 mm to 1.7 mm for size #14; - the pitch (P) varies from 1.2 mm to 2.4 mm for sizes #20, #30 and #45.

[0066] The pitch (P) can be variable along the endodontic file (1).

[0067] In the first embodiment, the blade (14) has several symmetries: - the first profile (PI) is identical to connect the first cutting lip (13) in the direction of the second cutting lip (13), and vice versa: the blade (14) therefore has a central symmetry with center (O). - the cutting angle (c) and the draft angle (a) are chosen so that the cutting face (Fs) and the draft face (Fd) are symmetrical with respect to the reference plane (Pr).

[0068] Such an endodontic file (1) is naturally adapted for use in reciprocity, that is to say according to an instrumental dynamic in which the rotation is carried out mainly in the determined direction (R), but with intermittent rotations in the opposite direction.

[0069] In this mode: - the cutting angle (c) is between -40° and -60° and preferably between -45° and -55°; - the draft angle (a) is between 30° and 50° and preferably between 34° and 43°; - therefore, the cutting angle (b) is between 95° and 110° and preferably between 95° and 105°.

[0070] The ratio between the surface area of ​​the blade (So) and the surface area of ​​the circle (Se) is between 43% and 53%, and preferably between 45% and 50%.

[0071] Figure 2 illustrates an instrument according to the first embodiment, whose values ​​are precisely: - cutting angle (c) of -51°; - draft angle (a) of 39°; - cutting angle (b) of 102°; - ratio of 48%.

[0072] With reference to [Fig.3], a second embodiment is defined by a second profile comprising two curves in opposite directions, giving an S-shape to the cutting face (Fs) and to the draft face (Fd).

[0073] The cutting angle (c) is between -15° and -35°, preferably between -20° and -30°, and even more preferably between -22° and -25°.

[0074] Starting from these values ​​of the cutting angle (c) and in order to respect the criterion of the cutting angle (b) which is between 95° and 110°, and preferably between 95° and 105°, the clearance angle (a) is between 10° and 20°, and preferably between 12° and 16°.

[0075] Such an endodontic file (1) is more suitable for continuous rotation uses, i.e. without reversing the direction of rotation.

[0076] Here again, the ratio between the surface area of ​​the blade (So) and the surface area of ​​the circle (Se) is between 40% and 65%. In this mode, the ratio is preferentially between 50% and 60%, and even more preferably between 52% and 58%.

[0077] Figure 3 illustrates an instrument according to the second embodiment, the values ​​of which are precisely: - cutting angle (c) of -24°; - draft angle (a) of 14°; - cutting angle (b) of 100°; - ratio of 55%.

[0078] With reference to [Fig. 4], a third embodiment is defined by a third profile comprising at least two curves in the same direction. The third profile is therefore not an arc of a circle.

[0079] In this third mode, the cutting angle is between -60° and -75°, and preferably between -65° and -70°, and / or the clearance angle is between 12° and 25°, and preferably between 15° and 20°, so that the cutting angle is between 130° and 150°, and preferably between 135° and 145°.

[0080] Like the first embodiment, such an endodontic file (1) is perfectly suited for use in alternating rotation, i.e. with reversal of the direction of rotation.

[0081] In this embodiment, the ratio between the surface area of ​​the blade (So) and the surface area of ​​the circle (Se) is between 52% and 65%, and preferably between 56% and 61%. Figure 4 illustrates an instrument according to the third embodiment, the values ​​of which are precisely: - cutting angle (c) of -67°; - draft angle (a) of 17°; - cutting angle (b) of 140°; - ratio of 58%.

[0082] By way of comparison, figures 5 and 6 illustrate two instruments sharing certain characteristics with the second embodiment, but not corresponding to the invention.

[0083] Fig. 5 illustrates a first comparative instrument, for which the cutting angle (b) is 161°.

[0084] Tests carried out by a practitioner indicate that the instrument is too rigid. This is partly due to the fact that the cutting edge angle (b) is too large. In particular, the ratio between the surface area of ​​the blade (So) and the surface area of ​​the circle (Se) is too high, so that the tool is too bulky and lacks sufficient flexibility to adapt to the trajectory of the root canal.

[0085] Fig. 6 illustrates a second comparative instrument, for which the cutting angle (b) is 92°.

[0086] During trials conducted by a practitioner, the instrument was found to produce little suction and provide good feel during canal shaping, which is advantageous. However, this instrument is not sufficiently torsionally resistant. This is due to the fact that the cutting edge angle (b) is too shallow. Consequently, the cross-section profile is too shallow, as the S-shape is too pronounced.

[0087] Figures 2 to 4 illustrate the instrument sections according to the invention, at a cutting plane located at D3. But the intrinsic taper (31) of an instrument endodontic (1) induces an evolution of the section of the blade (14), from the tip (15) to the heel (12).

[0088] With reference to [Fig.7], a table shows successive sections of an endodontic file (1) according to the second embodiment, at distances Db D3, D6, D9 and D12 relative to the tip (15).

[0089] The instrument in [Fig.7] differs from the instrument in [Fig.3] in that they do not have the same base diameter (0O), nor the same taper (31).

[0090] Firstly, it is observed that in certain embodiments, the endodontic file (1) is not symmetrical along the entire length of the blade (14): - a first cutting lip (13i) remains in contact with the circle (e), for each section of the endodontic file (1), - a second cutting lip (132) is in contact with the circle (e) on sections DI and D3, then is no longer in contact from section D6.

[0091] This asymmetry is obtained by piloting the trajectories of two grinding wheels machining the endodontic file (1) differently: one of the two grinding wheels makes a greater plunge, so that one of the sides of the endodontic file (1) is in retreat, which shifts the position of the second cutting lip (132).

[0092] This asymmetry increases the flexibility of the blade (14). This asymmetry also reduces the screwing sensation felt by the practitioner, particularly when the endodontic file (1) is driven at a high rotational speed, above 2000 rpm.

[0093] On the other hand, at the level of the tip (15), the section is preferably symmetrical so that the endodontic file (1) is balanced around the axis (a) during its rotation, which facilitates compliance with the canal trajectory: the creation of bifurcation is avoided.

[0094] This is why the section is symmetrical between the tip (15) and D4, and is asymmetrical only from D4 to the heel (12).

[0095] Of course, it is also possible to maintain the symmetry of the geometry all along the blade (14), from the tip (15) to the heel (12), as is the case for the first embodiment illustrated.

[0096] It is then observed, by comparing the different sections, that the cutting and clearance angles (a, c) are not constant along the blade (14).

[0097] During the manufacture of the blades (14), starting from a definition of the geometry at the level of the distal end (lOd), such as at D3, the grinding wheels follow an oblique trajectory towards the heel (12), while the endodontic file (1) is driven in rotation.

[0098] The oblique trajectory of the grinding wheels gives the endodontic file (1) the desired taper (31), while the combination of the movements of the grinding wheels and the rotation of the endodontic file (1) defines the pitch (P) of the winding of the cutting lips (13).

[0099] It follows that the resulting cutting and clearance angles are not constant. For example, the cutting angle (c) has a first value at DH, then a second value lower than the first value at D6, and then a third value greater than the first value at Di2.

[0100] The values ​​of cutting angle (c), clearance angle (a), tip angle (15) and ratio which are indicated above are those which the section presents at D3, which serves as a reference section for comparing endodontic files with each other.

[0101] Preferably, the endodontic file (1) has the indicated angle and ratio values ​​over the largest possible portion of the blade (14), for example up to Di2.

[0102] On the other hand, these values ​​do not concern a possible engagement portion of the endodontic file (1), which is located between the tip (15) and D2, and which is intended to facilitate the insertion of the endodontic file (1) into the canal in order to properly follow the canal trajectory.

[0103] The invention is applicable to instruments whose taper (31) is constant along the blade (14), as well as to instruments whose taper (31) is stepped.

[0104] The following instruments, corresponding to the invention, have been developed: - an endodontic file (1) 27.04 with stepped taper, i.e. an endodontic file (1): - whose base diameter (0O) is 0.27 mm, and - of stepped taper (31): - 4% of Do at D4, then - 3% from D4 to D8, then - 2% of D8 to Di 6; - an endodontic file (1) 20.04 with stepped taper, i.e. an endodontic file (1): - whose base diameter (0O) is 0.20 mm, and - of stepped taper (31) identical to that of the endodontic file (1) 27.04; - an endodontic file (1) 45.03 with stepped taper, i.e. an endodontic file (1): - whose base diameter (0O) is 0.45 mm, and - of stepped taper (31): - 3% of Do at D4, then - 2% from D4 to D8, then - 1% of D8 to Di2.

[0105] Such instruments make it possible to implement the following canal shaping protocol: a) use of an exploratory endodontic file, such as the one called by the anglicism "K file", in order to obtain the working length of the treatment (position of the apex), and to prepare the passage of the following instruments. b) canal shaping with an endodontic file (1) having a negative cutting angle and a positive clearance angle, preferably of type 27.04, and driven at a rotational speed between 2000 rpm and 5000 rpm, preferably between 2500 rpm and 3000 rpm.

[0106] It is noted that the endodontic files (1) according to the invention make it possible to avoid the use of a preparation file for canal shaping, such as those referred to by the anglicism "glide path".

[0107] The invention therefore makes it possible to carry out endodontic treatment more easily and economically, with only one instrument being necessary to perform the canal preparation.

[0108] It should be noted that although the three embodiments presented differ in the geometry of the section and in the value of the cutting angle (c), these three embodiments share the same technical characteristics and the same advantages with regard to the cutting angle (b), the surface area ratio, etc. Furthermore, some technical characteristics of the three embodiments presented are interchangeable. For example, the first embodiment may have a blade (14) with an asymmetrical cross-section.

[0109] Tests were carried out, at different rotation speeds, with an endodontic file (1) equipped with a blade (14) having two cutting lips (13) having a negative cutting angle (c) and a positive clearance angle (a).

[0110] The results are summarized in Table 1 below. [YES] [Table 1] Speed ​​(rpm) Instrument mechanical stability Cutting performance Canal trajectory adherence 1000 Instrument twisting in the first mm Need to slightly push the instrument Excellent trajectory adherence 1500 Instrument pitch lengthening in the first mm Need to slightly push the instrument Excellent trajectory adherence 2000 Instrument pitch lengthening in the first mm Need to slightly push the instrument Excellent trajectory adherence 2500 No twisting No need to push 1' instrument Excellent trajectory respect

[0112] First of all, it is observed that the use of a negative cutting angle (c) and a positive clearance angle (a) makes it possible to guarantee compliance with the canal trajectory, regardless of the rotation speed.

[0113] It is then observed that at an insufficient rotation speed, the cutting power of the endodontic file (1) is not sufficient, so that the practitioner feels a need to apply a certain force to the endodontic file (1) to make it progress within the canal.

[0114] On the other hand, when the rotation speed is sufficiently high, i.e. above 2000 rpm, for example at 2500 rpm, the cutting power of the endodontic file (1) is sufficient so that there is no need to apply a load on the endodontic file (1) in order to guarantee its progression within the canal.

[0115] Finally, we note: - that below a first threshold of rotation speed, the endodontic file (1) is ruined, by the untwisting of the helical cutting lips (13). - Between the first and second thresholds of rotational speed, the endodontic file (1) is degraded by an increase in the pitch (P) of the helical cutting edges (13). The increase in pitch (P) does not destroy the endodontic file (1), but it is nevertheless a defect. - beyond the second threshold of rotation speed, the endodontic file (1) is not degraded.

[0116] The degradation of the endodontic file (1) may be correlated with the efficiency of the cutting, since it is observed that the rotation speed of 2500 rpm provides both good cutting results and mechanical resistance of the endodontic file (1).

[0117] Thus, the invention also relates to the use of an endodontic file (1) equipped with a blade (14) having at least one cutting lip (13) having a negative cutting angle (c) and a positive clearance angle (a), the endodontic file (1) being driven in rotation at a speed between 2000 rpm and 5000 rpm, preferably between 2500 rpm and 3500 rpm.

[0118] It is indeed when an endodontic file (1) with a negative cutting angle (c) and a positive clearance angle (a) is driven in rotation at very high speed, above 2000 rpm, and preferably above 2500 rpm, that such an endodontic file (1) provides the best cutting and canal preparation results, while protecting the endodontic file (1) from mechanical damage such as untwisting.

[0119] Good shaping results were obtained at a speed of 2500 rpm, and even more preferably at 3000 rpm.

[0120] With reference to [Fig.8], the invention also relates to an endodontic system (3) configured for such use.

[0121] The endodontic system (3) includes a handpiece (2) equipped with a motor configured to drive the endodontic file (1) by means of a contra-angle (21), and a programming interface (22) allowing the entry of the operating parameters of the motor such as the speed of rotation, the direction of rotation, or a particular instrumental dynamic.

Claims

Demands

1. Endodontic file (1) configured to be driven in rotation about an axis (a) and in a determined direction (R), in order to remove tissue from a root canal during canal treatment; the endodontic file (1) being provided with a blade (14) having at least one cutting lip (13), the cutting lip (13) having, - a cutting face (Fs), delimited by the cutting lip (13) and configured to come against tissue to be removed from a root canal when the instrument is driven in a rotation in the determined direction (R); - a clearance face (Fd), delimited by the cutting lip (13), and opposite the cutting face (Fs); and in a section plane (Ps) orthogonal to the axis (a): - the blade (14) being inscribed in a circle (e) of center (0) placed on the axis (a), and tangent to the cutting lip (13) at a point of the cutting lip (13) which is furthest from the center (0);- the cutting lip (13) having: - a negative cutting angle (c), measured according to the determined direction (R): - from a reference plane (Pr), orthogonal to the section plane (Ps) and passing through the axis (a) and through the cutting lip (13), and - in the direction of the cutting face (Fs); - a clearance angle (a) greater than or equal to 0, measured in the determined direction (R): - from the clearance face (Fd), and - in the direction of a conventional working plane (Pf), orthogonal to the section plane (Ps) and to the reference plane (Pr), and passing through the cutting lip (13), characterized in that in the section plane (Ps): - a cutting angle (b), measured between the cutting face (Fs) and the clearance face (Fd), is between 95° and 150°, and - a ratio between a surface area of ​​the blade (So) and a surface area of ​​the circumscribed circle (Se) is between 40% and 65%.;

2. Endodontic file (1) according to claim 1, wherein the blade (14) has several cutting lips (13), regularly distributed around the axis (a), wherein a second profile (P2) connects two successive cutting lips (13), and the second profile (P2) presents at least two curvatures in opposite directions, and preferably only two curvatures in opposite directions.

3. Endodontic file (1) according to claim 2, wherein the cutting angle (c) is between -20° and -30° and preferably between -25° and -22°.

4. Endodontic file (1) according to any one of claims 2 or 3, wherein the clearance angle (d) is between 10° and 20°, and preferably between 12° and 16°.

5. Endodontic file (1) according to claim 1, wherein the blade (14) has several cutting lips (13), regularly distributed around the axis (a), and wherein a third profile (P3) connects two successive cutting lips (13), and the third profile (P3) has at least two curvatures in the same direction.

6. Endodontic file (1) according to claim 5, wherein the cutting angle (c) is between -60° and -75° and preferably between -65° and -70°.

7. Endodontic file (1) according to any one of claims 5 or 6, wherein the clearance angle (d) is between 12° and 25° and preferably between 15° and 20°.

8. Endodontic file (1) according to any one of claims 5 to 7, wherein the cutting edge angle (b) is between 130° and 150°, and preferably between 135° and 145°.

9. Endodontic file (1) according to any one of the preceding claims, wherein the blade has only two cutting lips (13).

10. Endodontic system comprising a control unit programmed to drive a handpiece (2) configured to rotate an endodontic file (1), - the endodontic file (1) being provided with a blade (14) having at least one cutting lip (13) having a negative cutting angle (c) and a positive clearance angle (a), - the rotation having a speed between 2000 rpm and 5000 rpm, preferably between 2500 rpm and 3500 rpm.