Endodontic instrument having a continuous engagement profile

Abstract

The invention relates to an endodontic instrument (1) extending along an axis (a) and comprising an engagement portion (20) connecting a tip (15) to a blade (14), and having a geometry designed to facilitate the endodontic instrument (1) in following the canal trajectory; - in a plane containing the axis (a), the engagement portion (20) having an engagement profile (21) defined, within an orthonormal coordinate system, by: - an abscissa (x) measured from the tip (15) towards the root (11), and - an ordinate (y) which is dependent on the abscissa (x); - the ordinate (y) being smaller on the tip (15) side than the ordinate on the blade (14) side, characterised in that the engagement profile (21) is continuous; and - an increase in the ordinate (y) strictly decreases from the tip (15) towards the blade (14).

Description

TITLE OF THE INVENTION: ENDODONTIC INSTRUMENT WITH CONTINUOUS ENGAGEMENT PROFILE FIELD OF INVENTION

[0001] The present invention relates to the field of endodontics and more particularly to that of canal instruments. STATE OF THE ART

[0002] During endodontic treatment, one difficulty lies in respecting the trajectory of the root canal, which generally has one or more curves.

[0003] During the progression of an endodontic instrument within a canal, at the level of a bend, it may happen that the instrument does not follow the curved trajectory, and creates a deviation within the dentin of the root of the tooth.

[0004] This deviation in trajectory complicates the smooth progress of the treatment.

[0005] Referring to Figure 1, US patent US5104316 describes an endodontic instrument having, at its distal end, an engagement portion (20) comprising a hemispherical tip (15) followed by a cylindrical portion. This engagement portion (20) is designed to prevent deviation of the instrument during its progression within the canal.

[0006] This engagement portion (20) exhibits an excessive increase in the diameter of the endodontic instrument, from the tip (15) towards a blade (14) of the instrument, relative to the length of the engagement portion: the hemispherical, or rounded, shape of the tip (15) results in an excessively rapid increase in diameter. Conversely, the cylindrical portion, with its constant diameter, does not provide any real assistance in centering the endodontic instrument within the canal. The cylindrical portion unnecessarily lengthens the engagement portion (20).

[0007] With reference to Figure 2, document FR3121620 describes an engagement portion (20) comprising a conical tip (15). The advantage of this portion The short length of engagement (20) is a significant drawback. However, the operation of this portion of engagement (20) can be improved.

[0008] With reference to Figure 3, document WO2014 / 139039 describes an engagement portion (20) comprising a hemispherical tip (15), and a transition towards the blade (14). The transition has an inflection (16), at which there is a break in the slope of a profile of the engagement portion.

[0009] The engagement component of this instrument can still be improved.

[0010] Therefore, there is a need to improve the engagement portions of canal instruments such as endodontic files. SUMMARY

[0011] The invention therefore aims to solve the problem of deviations when using an endodontic instrument during the treatment of a root canal, by proposing an improved engagement portion.

[0012] To this end, an endodontic instrument has been developed extending along an axis, and comprising, from a proximal end to a distal end: - a handle configured for manipulating the endodontic instrument, preferably using a motorized handpiece, - a heel, without cutting edges, - a blade, having at least one cutting lip configured to remove tissue when using the endodontic instrument within a root canal to be treated, - a tip forming the distal end of the endodontic instrument, - the endodontic instrument further comprising an engagement portion connecting the tip to the blade, and having a geometry configured to facilitate the following of the canal trajectory by the endodontic instrument, - in a plane containing the axis, the engagement portion presenting an engagement profile defined, within an orthonormal coordinate system, by: - an abscissa measured from the toe towards the heel, and - an ordinate that depends on the abscissa; - the ordinate being lower on the side of the tip, compared to the ordinate on the side of the blade.

[0013] According to the invention, the engagement profile is continuous, that is to say that the engagement profile is devoid of break points in the slope of the engagement profile; and an increase in the ordinate is strictly decreasing from the tip to the blade.

[0014] In this way, the engagement profile shows a progressive increase in its cross-section, in a plane orthogonal to the axis, which allows for better adherence to the trajectory of the root canal.

[0015] The absence of discontinuities within the profile prevents deviations. Indeed, breaks in slope within the profile result in points or edges on the surface of the engaged portion. These points or edges can catch on the tissues within the root canal, particularly the dentin, and generate deviations. The continuous profile avoids these problems.

[0016] Moreover, the absence of discontinuities, particularly in the form of concave geometries, avoids areas of stress concentration that are conducive to instrument breakage during canal treatment.

[0017] The constant growth of the ordinate avoids areas of weakness in the committed portion.

[0018] The strictly decreasing increase in the ordinate means that the cross-section of the instrument grows progressively smaller from the tip towards the blade. This results in an oblong, ogive-shaped engagement portion, which has proven very effective in following the root canal without generating deviations or obstructions.

[0019] Since the increase in the ordinate is distributed over the entire length of the engagement portion, the instrument blade is not unnecessarily shortened for a given instrument length.

[0020] The engagement portion according to the invention therefore allows for easier use of the file, while respecting the trajectory of the root canal.

[0021] In a preferred embodiment, the ordinate is a function of the abscissa, and the function is elliptic and / or parabolic and / or logarithmic and / or polynomial. These functions allow for the creation of a profile with the aforementioned characteristics, while also being easy to draw using computer-aided design software.

[0022] In order that there is no discontinuity at the level of an envelope of the instrument when it is rotated, the engagement profile is tangent with a truncated conical envelope defining the basic geometry of the endodontic instrument.

[0023] To ensure that the instrument cannot grind the dentin and create a deviation, the engagement portion includes a first inactive part, without cutting lips, on the tip side.

[0024] In this case, the first inactive part has a length between 0.03 mm and 0.25 mm to provide sufficient length for the first inactive part to play a pilot tip role.

[0025] For the same purpose, the engagement portion includes a second inactive part, in which a passive lip presents: - a draft angle of zero, or less than 5°, preferably less than 3°; and / or - a cutting angle between -80° and -30°, and preferably between -60° and -45°.

[0026] Still with the aim of avoiding machining of the dentin, in order to respect the canal trajectory, at the level of a median plane of the engagement portion (20), the passive lip presents a heeling section extending over a groping angle between 25° and 100°, and the groping angle is preferably more than 30°, and even more preferably more than 35°.

[0027] Advantageously, the engagement portion has a length between 0.2 mm and 1.5 mm, measured from the tip towards the blade. Such a length is a good compromise between: - the length of the instrument dedicated to the pilot tip, and - the remaining length for the blade.

[0028] To ensure a gradual increase in instrument cross-section and facilitate instrument insertion while respecting the canal trajectory, over the first one-eighth of the engagement profile length, the ratio between the variation in the ordered F divided by one-eighth of the engagement portion length should be between 0.2 and 0.9, preferably between 0.4 and 0.9, and even more preferably between 0.45 and 0.7. Higher ratios result in excessively steep profile slopes, causing the instrument to bind at canal bends. Conversely, lower ratios result in excessively sharp engagement portions, leading to instrument deviations at bends.

[0029] The increase in the ordinate, more gradual than with a hemispherical tip or an arc-shaped profile, facilitates the insertion of the instrument into the canal. BRIEF DESCRIPTION OF THE FIGURES

[0030] [Fig.1] is a diagram of an engagement portion of a canal instrument of the anterior art, showing a hemispherical tip and a cylindrical portion.

[0031] [Fig.2] is a diagram of a portion of engagement of a canal instrument of the anterior art, featuring a conical tip.

[0032] [Fig.3] is a diagram of a portion of engagement of a canal instrument of the anterior art, exhibiting a stepped taper.

[0033] [Fig.4] is a general diagram representing an instrument according to the invention.

[0034] [Fig.5] is a diagram detailing a portion of the instrument engagement of figure 4.

[0035] [Fig.6] is a diagram illustrating a section of an initial inactive part of the engagement portion of the instrument in Figure 4.

[0036] [Fig.7] is a diagram illustrating a section of a second passive part of the engagement portion of the instrument in Figure 4.

[0037] [Fig.8] is a diagram illustrating minimum and maximum variations of the ordinate of an engagement profile according to the invention, the ordinate at the tip being non-zero.

[0038] [Fig.9] is a diagram illustrating minimum and maximum variations of the ordinate of an engagement profile according to the invention, the ordinate at the tip being zero. DETAILED DESCRIPTION

[0039] With reference to figure 4, the present invention relates to an endodontic instrument (1), for example an endodontic file.

[0040] 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, and which constitutes a proximal end (1Op) of the endodontic instrument (1); - a heel (12), without cutting edges (13), 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).

[0041] An endodontic instrument (1) extends along an axis (a). Although the axis (a) may be curvilinear, particularly in the case of preformed endodontic instruments (1), an endodontic instrument (1) is prefabricated in a straight form.

[0042] The blade (14) is inscribed within a basic envelope (30) which is a shape of revolution centered on the axis (a). The basic envelope (30) is frustoconical, having a circular base with a base diameter (32) and a taper (31). The base diameter (32) and the taper (31) are generally standard values ​​in the field of endodontics, for example: - base diameter (32) is 0.2mm - the taper (31) is 6%.

[0043] The taper (31) can vary along the blade (14). In the context of the present invention, we are interested in the taper (31) at the distal level of the instrument (1), at the level of an engagement portion (20) which connects the tip (15) to the blade (14).

[0044] For the sake of simplicity, the following will not be referred to in the rest of this document: - than to a straight axis (a), although the invention can also be applied to a non-straight axis (a); - than to a blade (14) having a constant taper (31), although the invention can also be applied to a variable taper (31).

[0045] With reference to figure 5, the endodontic instrument (1) according to the invention has an engagement portion (20) connecting the tip (15) to the blade (14), and which is configured to facilitate the following of the canal trajectory by the endodontic instrument (1).

[0046] According to the invention, the engagement portion (20) has a continuous engagement profile (21), and a progressive increase in a section of the engagement portion (20), the section being orthogonal to the axis (a).

[0047] By defining an orthonormal coordinate system (O, x, y) centered on the tip (15), and whose x-axis coincides with the axis (a) of the instrument (1) at the level of the tip (15), then the y-coordinate of the engagement profile (21) is strictly increasing from the tip (15) and in the direction of the blade (14).

[0048] The slope of the engagement profile (21) is strictly decreasing from the tip (15) towards the blade (14), so that in a plane orthogonal to the axis (a), a section of the engagement portion (20) grows less and less from the tip (15) towards the blade (14).

[0049] The actual envelope of the engagement portion (20), when the instrument is rotated, therefore has a geometry of the type of an ogive.

[0050] This continuous and progressive increase in the section of the engagement portion (20) guarantees its effectiveness.

[0051] It is recalled that the endodontic instrument (1) has one or more cutting lips (13) which are generally helical which are inscribed, when the endodontic instrument (1) is in rotation around the axis (a), within a basic envelope.

[0052] The engagement profile (21) corresponds, at the distal end (lOd), to a reduction in the dimensions of the endodontic instrument (1), so that the engagement portion (20) is inscribed within a real envelope which is: - contained in the basic envelope; - defined by the engagement profile (21).

[0053] Thus, at the level of the engagement portion (20), the cutting lips (13) are clipped so as to be inscribed, when the endodontic instrument (1) is rotating around the axis (a), in a real envelope defined by the engagement profile (21).

[0054] At the tip (15), the engagement portion (20) may have a non-zero tip diameter (Dp), for example of the order of 0.05mm, so that the endodontic instrument (1) has a flat at the tip (15).

[0055] This flat surface facilitates the manufacture of the endodontic instrument (1). Its diameter being small, i.e. less than 0.1mm, this flat surface does not hinder the following of the canal trajectory.

[0056] In some embodiments, this flat is absent, so that the tip diameter (Dp) is zero.

[0057] At the distal end (lOd) of the endodontic instrument (1), the cutting edges (13) join the engagement portion (20). Depending on the engagement profile (21), the engagement portion (20) may have different sub-portions.

[0058] A first inactive portion (22) is located on the side of the tip (15). This first inactive portion (22) is devoid of cutting lips (13).

[0059] With reference to figure 6, a section of the first inactive portion (22) is therefore circular.

[0060] The absence of cutting lips (13)s at the level of the first inactive portion (22) prevents the endodontic instrument (1) from generating a stop or a deviation when the root canal has a curvature.

[0061] The first inactive portion (22) has a length between 0.1 mm and 0.25 mm, measured from the tip (15) and towards the blade (14).

[0062] Since the cutting lips (13) are generally helical while the engagement profile (21) is in a plane containing the axis (a), the cutting lips (13) can be modified at the distal level of the endodontic instrument (1).

[0063] For example, in the embodiment illustrated in Figure 5, the engagement portion (20) includes a second inactive portion (23), at which the cutting edge of the cutting lip (13) has been trimmed, so that the second inactive portion (23) has inactive lips (24). This trimming can be achieved using a grinding wheel.

[0064] An inactive lip (24) is not configured to remove tissue from the root canal.

[0065] With reference to figure 7, we see a section of the second inactive portion (23), illustrating the geometry of the inactive lips (24).

[0066] The illustrated embodiment has two inactive lips (24), but the number of lips is not a feature of the invention which could for example work with three lips.

[0067] For a given direction of rotation (R), the inactive lip (24) has a leading edge (25), and preferably a trailing edge (26).

[0068] At the level of the attack edge (25), a cutting angle (y) is less than 0°, that is to say that its measurement, from a center of rotation of the endodontic instrument (1), located on the axis (a), and in the direction of the attack edge (25), is opposite to the direction of rotation (R) of the endodontic instrument (1).

[0069] It is known that a negative cutting angle (y) hinders tissue removal within the root canal. Indeed, better tissue removal results are obtained with positive cutting angles, which tend to excavate the tissues.

[0070] Some endodontic instruments (1) nevertheless have negative cutting angles (y), however their value is generally small, on the order of -5°, see - 10°.

[0071] Indeed, a negative cutting angle (y) produces an endodontic instrument geometry (1) which tends to slide over the tissues, but without removing them from the canal.

[0072] A negative cutting angle (y) of significant value, for example less than - 30°, provides an initial guarantee that no tissue will be removed from the canal: the endodontic instrument (1) therefore cannot grind the dentin and cause a deviation. Maintaining the canal trajectory is facilitated.

[0073] The cutting angles (y) of the passive lips (24) according to the invention have values ​​less than -30°, and preferably less than -50°.

[0074] In addition, the inactive lip (24) has a draft angle (a) strictly less than 5°, preferably less than 3°, and even more preferably a zero draft angle (a).

[0075] A shallow taper angle (a) hinders the removal of tissue that might otherwise detach from the inner wall of the root canal under the action of the endodontic instrument (1). A shallow taper angle (a) therefore provides a second guarantee that tissue will not be removed from the canal: the endodontic instrument (1) cannot grind the dentin and cause deviation. Maintaining the canal path is thus facilitated.

[0076] In the embodiment illustrated in Figure 5, the clearance angle (a) is zero, so that the inactive lip (24) has a leading edge (25) and a trailing edge (26). The endodontic instrument (1) is therefore in contact with an internal wall of the root canal over an angular portion extending from the leading edge (25) to the trailing edge (26).

[0077] We also speak of heeling, the chamfered face of the endodontic instrument (1) being in contact with the root canal being treated.

[0078] The endodontic instrument (1) is positioned at an angular section extending from the leading edge (25) to the trailing edge (26) to form a shim section. The presence of a shim section (27) is an extreme case of zero taper angle (a), which further aims to respect the canal path by avoiding tissue removal.

[0079] The extent of the heeling section (27) varies along the engagement portion (20). Measured at half the length of the engagement portion (20), the heeling section (27) can extend over a groping angle (ô) between 25° and 100°, and the groping angle (ô) is preferably greater than 30°, and even more preferably greater than 35°.

[0080] In the embodiment illustrated in figure 7, the angle of trial and error (ô) is 38°.

[0081] In one embodiment, the engagement profile (21) is a function of the elliptic, parabolic, logarithmic, or polynomial type. The engagement profile (21) may also comprise several segments, each being a function of one of the aforementioned types.

[0082] In the example illustrated in Figure 5, the engagement profile (21) is a portion of an ellipse, that is, the function is of type b for se differentiate from an arc of a circle.

[0083] More specifically, the example shown is a file of type 30.04, that is to say a file with a base diameter of 0.3mm and a taper of 4%, and the values ​​used for the equation are as follows: - a=0.36mm; - b=2.4mm.

[0084] In order to obtain a tip diameter (Dp) of 0.05mm, the center of the ellipse is shifted towards the tip (15) of the endodontic instrument (1), so that the length between the tip (15) and the center of the ellipse is only 1.188mm.

[0085] Other values ​​for the minor axis (a) and major axis (b) can be chosen according to the following parameters: - base diameter (32); - taper (31); - number of cutting lips (13); - geometry of the cutting lips (13), for example its cutting angles (y) and draft angles (a).

[0086] An elliptical profile provides an excellent compromise between the progressive increase in the cross-section of the endodontic instrument (1) and its length devoted to the engagement portion (20).

[0087] Since tissues must be removed from the canal up to an apex of the canal, it is indeed important not to lengthen the engagement portion (20) excessively, at the risk of compromising the canal preparation performance of the endodontic instrument (1).

[0088] Engagement portion lengths (20) between 0.2 mm and 1.5 mm, measured from the tip (15) and towards the blade (14), allow a satisfactory compromise to be obtained.

[0089] On the exemplified 30.04 file, the engagement portion (20) measures 0.69 mm in length. Other files may have an engagement portion (20) of 0.28 mm, 0.4 mm, or even 0.7 mm.

[0090] The engagement profile (21) and the length of the engagement portion (20) can also be adapted according to the parameters of the endodontic instrument (1), namely its base diameter (32), its taper (31), the number of cutting lips (13) and their geometry.

[0091] On the other hand, in order that the increase in the section of the engagement portion (20) is not too abrupt, nor too small, it is necessary that at the level of the distal end (lOd) of the endodontic instrument (1), the ordinate (y) of the engagement profile (21) does not grow too rapidly.

[0092] In practice, over the first eighth of the engagement portion (20), the slope of the engagement profile (21) must be between 0.2 and 0.9. That is to say, the ordinate (y) must satisfy the criterion 0.2; y(0) + ~ ' 0.9], The being the length of the engagement portion (20), measured from the tip (15) and in the direction of the blade (14).

[0093] With reference to figures 8 and 9, engagement profiles (21) respecting this slope range are illustrated.

[0094] In Figure 8, the tip diameter (Dp) is non-zero, so that y(0) = — . The

[0095] For the value of abscissa — , the ordinate (y) must therefore be: 8 z • zi Dp Le - greater than or equal to a — + — ■ 0.2 ; and - less than or equal to 0.9.

[0096] A first engagement profile (211) is close to the minimum profile The possible scenario: for x = — , its ordinate (y) is close to the lower bound of a preferred range [0.4; 0.9] of the profile slope.

[0097] A second engagement profile (2H) is close to the maximum conceivable profile: For x = —, its ordinate (y) is close to the upper bound.

[0098] The following criteria can be taken into account when choosing the slope: - If the instrument is small, for example with a base diameter (32) of 0.2 mm, then the slope is generally lower. Suitable slope values ​​can be between 0.2 and 0.6. Conversely, for larger instruments, for example with a base diameter (32) of 0.4 mm, the slope is generally higher. Suitable slope values ​​can be between 0.45 and 0.9. - Furthermore, the slope is adjusted according to the presence or absence of a flat section at the tip (15). If the tip diameter (Dp) is non-zero, then the profile slope is shallower, because the difference between the tip diameter (Dp) and the base diameter (32) is reduced. Conversely, if the tip diameter (Dp) is zero, then the slope is steeper.

[0099] In figure 9, the tip diameter (Dp) is zero, so y(0) = 0. The

[0100] For the value of abscissa — , the ordinate (y) must therefore be: 8 - greater than or equal to 0.2; and The - less than or equal to — ■ 0.9.

[0101] Similarly, two engagement profiles (21i, 2U) are shown in Figure 8, which are close to the minimum and maximum profiles that can be considered.

[0102] When the tip diameter (Dp) is zero, the preferred range of [0.4; 0.9] will be used for the slope value.

[0103] As illustrated in Figures 5, 8 and 9, another feature that can help to respect the canal trajectory is that the engagement profile (21) is tangent to the base envelope (30) of the endodontic instrument (1), at the junction between the engagement portion (20) and the blade (14).

[0104] This tangency prevents, at this point on the endodontic instrument (1) as well, any break in slope that could create a sharp edge or point on the instrument (1). Such a sharp edge or point could become embedded in the dentin and cause the endodontic instrument (1) to generate a stop or a deviation.

[0105] Finally, the technical characteristics of the various embodiments and variants mentioned above can be combined, in whole or in part. Thus, the endodontic instrument (1) can be adapted in terms of cost, functionality, and performance.

Claims

DEMANDS 1. Endodontic instrument (1) extending along an axis (a), and comprising, from a proximal end (lOp) to a distal end (lOd): - a handle (11) configured for manipulating the endodontic instrument (1), preferably by means of a motorized handpiece, - a heel (12), without cutting edges (13), - 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 the distal end (lOd) of the endodontic instrument (1), - the endodontic instrument (1) further comprising an engagement portion (20) connecting the tip (15) to the blade (14), and having a geometry configured to facilitate the following of the canal trajectory by the endodontic instrument (1), - in a plane containing the axis (a), the engagement portion (20) presenting an engagement profile (21) defined, within an orthonormal coordinate system, by: - an abscissa (x) measured from the toe (15) towards the heel (11), and - an ordinate (y) depending on the abscissa (x); - the ordinate (y) being lower on the tip side (15), compared to the ordinate on the blade side (14), characterized in that the engagement profile (21) is continuous; and - an increase in the ordinate (y) is strictly decreasing from the tip (15) towards the blade (14).

2. Endodontic instrument (1) according to claim 1, wherein the ordinate (y) is a function of the abscissa (x), and the function is elliptic and / or parabolic and / or logarithmic and / or polynomial.

3. Endodontic instrument (1) according to any one of the preceding claims, wherein the engagement profile (21) is tangent with a frustoconical envelope (30) of the endodontic instrument (1).

4. Endodontic instrument (1) according to any one of the preceding claims, wherein the engagement portion (20) comprises a first inactive part (22), devoid of cutting lips, on the tip side (15).

5. Endodontic instrument (1) according to claim 4, wherein the first inactive part (22) has a length between 0.1 mm and 0.25 mm.

6. Endodontic instrument (1) according to claim 4 or 5, wherein the engagement portion (20) comprises a second inactive part (23), in which a passive lip (24) has a clearance angle of zero, or less than 5°, and preferably less than 3°.

7. Endodontic instrument (1) according to claim 6, wherein the passive lip (24) has a cutting angle between -80° and -30°, and preferably between -60° and -45°.

8. Endodontic instrument (1) according to claim 6 or 7, wherein, at the level of a median plane of the engagement portion (20), the passive lip (24) has a heeling section (27) extending over a heeling angle (ô) between 25° and 100°, and the heeling angle (ô) is preferably more than 30°, and even more preferably more than 35°.

9. Endodontic instrument (1) according to any one of the preceding claims, wherein the engagement portion (20) has a length between 0.2 mm and 1.5 mm, measured from the tip and in the direction of the blade.

10. Endodontic instrument (1) according to any one of the preceding claims, wherein, over a first eighth of the engagement profile length, a ratio between a variation of the ordinate (y) divided by one eighth of the engagement portion length (20) is between 0.2 and 0.9, preferably between 0.4 and 0.9, and even more preferably between 0.45 and 0.7.

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