Endodontic instruments improving conformance to the geometry of tooth root canals

Abstract

The present disclosure relates to an endodontic instrument (100) made from a shape memory alloy and having a mechanism portion (110). The mechanism portion (110) has a substantially linear mechanism profile comprising a distal segment (120) and an intermediate segment (130). The intermediate segment (130) comprises a first bend (131) having a first peak (A1) and a second bend (132) having a second apex (A2) greater than the first peak (A1). The distal envelope (125) of the distal segment (120) forms a distal taper angle (β) with respect to the longitudinal axis (101). The intermediate envelope (135) of the intermediate segment (130), tangent to the first peak (A1) and the second peak (A2), forms a medial angle (β) with respect to the longitudinal axis (101), and the distal angle (α) is less than the medial angle (β).

Description

[Technical Field]

[0001] The present invention relates to the field of endodontics, and in particular to improved endodontic instruments for operating within tooth root canals, dental pulp, and surrounding areas, and more particularly to endodontic instruments that better conform to the geometry of a tooth's root canal and allow for better removal of foreign material from the root canal. [Background technology]

[0002] Cleaning and shaping the root canal of a tooth for the purpose of receiving a filling material is usually performed with endodontic instruments that have a cutting section, or so-called mechanism, whose purpose is to prepare, shape, and clean the inner walls of the root canal in preparation for receiving the therapeutic material, and subsequently the filling material, to block any oxygen that may allow bacteria to grow in the tooth, especially near the root.

[0003] The mechanism of an endodontic instrument typically has a generally cylindrical or conical envelope with a geometric shape symmetrical along the axial direction of the file, with one or more cutting edges spiraling along the mechanism. The endodontic instrument can be configured to "graze" the root canal wall to cut into a cavity without modifying the natural shape of the root canal by following its path. However, recent studies have shown that excessive cavity removal is not recommended due to the weakening of the tooth as a result of this procedure.

[0004] Root canal morphology varies significantly from patient to patient. The longitudinal root canal profile often has an irregular elliptical cross section along its length and may contain one or more narrow bends.

[0005] Modern endodontic instruments have a linear geometry and may have a certain flexibility that allows them to adapt to a certain extent to the longitudinal profile of the root canal, but when this flexibility introduces bending and cross-sectional changes, such flexibility does not guarantee effective cleaning of the entire wall.

[0006] Furthermore, the envelope for the space brushed by a standard endodontic instrument driven by rotation about an axis is approximately cylindrical or conical due to the axially symmetrical geometry of the instrument. As a result, the walls of a root canal with an elliptical cross section cannot be brushed with a single endodontic instrument, but requires a series of endodontic instruments with different diameters. Therefore, practitioners are forced to change endodontic instruments during the medical procedure, starting with small diameters and then gradually increasing in diameter. This is not only cumbersome, but also does not guarantee effective cleaning of the walls without damaging the canal.

[0007] Therefore, there is a need for an endodontic instrument that meets the requirements of practitioners, i.e., an endodontic instrument that is flexible enough to follow the profile of the root canal, contacts uneven and irregular areas of the root canal wall, and has a geometry that allows it to brush the root canal wall, such as to remove internal biofilm, without cutting into recesses.

[0008] From a material standpoint, endodontic instruments are generally made from medical-grade metals, including stainless steel and various machinable alloys. Most modern endodontic instruments are made from shape-memory alloys, such as nickel-titanium alloys, including "Nitinol" or "NiTi." Endodontic instruments made from nickel and titanium exhibit superior flexibility and torsional properties compared to stainless steel instruments.

[0009] International Publication No. WO 2016 / 004541 discloses an endodontic instrument for cleaning a root canal that conforms to the root canal's natural geometry. The endodontic instrument includes a mechanical sector made of a shape memory alloy having a transition temperature. Below the transition temperature, the shape memory alloy can be deformed, but when heated above the transition temperature, it returns to its pre-deformed ("memorized") shape. The mechanical sector includes a free end section intended to engage the root canal and a second active segment. Below the transition temperature, the second active segment is substantially straight, and above the transition temperature, the second active segment has a curved shape configured to contact and brush the surface of the root canal wall. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2016 / 004541 [Patent Document 2] International Publication No. 2021 / 240387 [Patent Document 3] U.S. Patent No. 9,931,179 [Non-patent literature]

[0011] [Non-Patent Document 1] International Standard ISO 3630-1, Third Edition 2019 08 (Section 4) Summary of the Invention

[0012] The present disclosure relates to an endodontic instrument for irrigating a root canal. The endodontic instrument has a mechanism portion made of a shape memory alloy and intended to engage in the root canal. The mechanism portion generally extends along a longitudinal axis between a tip and a shaft. The mechanism portion has a mechanism profile including a tip segment that is substantially linear with respect to the longitudinal axis and an intermediate segment that extends between the tip segment and the shaft. The intermediate segment has a first bend with a first peak relative to the longitudinal axis and a second bend with a second peak relative to the longitudinal axis that is greater than the first peak. The tip envelope of the tip segment forms a tip taper angle with respect to the longitudinal axis, and the intermediate envelope of the intermediate segment tangent to the first and second peaks forms an intermediate angle with respect to the longitudinal axis, the tip angle being less than the intermediate angle.

[0013] The mechanism of the endodontic instrument allows the endodontic instrument to better conform to the geometry of the root canal of the tooth, allowing for increased removal of debris from the root canal. The mechanism of the endodontic instrument can be easily introduced into the root canal.

[0014] Exemplary embodiments of the invention are disclosed in the description and illustrated by the drawings. [Brief explanation of the drawings]

[0015] [Figure 1] 1 shows an endodontic instrument with a mechanism portion according to an embodiment. [Figure 2] 1 illustrates a mechanism portion with a mechanism profile, according to an embodiment. [Figure 3] 1 shows a graph reporting the transition temperature of a Nitinol alloy containing 56% nickel and about 44% titanium by weight. DETAILED DESCRIPTION OF THE INVENTION

[0016] FIG. 1 shows an endodontic instrument 100 for cleaning a root canal, according to one embodiment. The endodontic instrument 100 comprises a mechanism portion 110 extending generally along a longitudinal axis 101 between a tip 103 and a shaft 104 of the endodontic instrument 100. The mechanism portion 110 is intended to engage a root canal to be treated. The endodontic instrument 100 further comprises a shank 105, which is fixed to the shaft 104 and is intended to be mounted on a rotating support, causing the endodontic instrument 100 to rotate about its longitudinal axis 101. Instead of a shank, the endodontic instrument 100 may include a handle 105, for example, for manually rotating the endodontic instrument 100.

[0017] 2 shows a mechanism portion according to one embodiment. The mechanism profile of mechanism portion 110 includes a tip segment 120 that is substantially linear with respect to longitudinal axis 101 and an intermediate segment 130 that extends between tip segment 120 and shaft 104. Tip segment 120 and intermediate segment 130 are disposed continuously from tip 103 to shaft 104.

[0018] Tip segment 120 may have a tapered section from intermediate segment 130 toward tip 103. As shown in FIG. 2, tip envelope 125 of tip segment 120 forms a tip taper angle α with respect to longitudinal axis 101.

[0019] The intermediate segment 130 is comprised of a first bend 131 and a second bend 132. The first bend 131 has a first peak A1 relative to the longitudinal axis 101, and the second bend 132 has a second peak A2 relative to the longitudinal axis 101. The first peak A1 and the second peak A2 correspond to the maximum amplitudes of the first bend 131 and the second bend 132, respectively, i.e., correspond to the maximum distances of the first bend 131 and the second bend 132 relative to the longitudinal axis 101.

[0020] In a possible configuration, the first bend 131 bends along the same plane as the second bend 132, but also bends in the opposite direction.

[0021] The first peak A1 and the second peak A2 are located at a first distance D1 and a second distance D2, respectively, from the tip 103 (toward the shaft 104). The first peak A1 is smaller than the second peak A2, such that the intermediate segment 130 has a tapered shape from the shaft 104 toward the tip 103. As shown in FIG. 2, an intermediate envelope 135 of the intermediate segment 130, which is tangent to the first peak A1 and the second peak A2, forms an intermediate angle β with respect to the longitudinal axis 101.

[0022] In some embodiments, the tip taper angle α is less than the intermediate taper angle β. A smaller tip taper angle α corresponds to the tapering of narrow endodontic instruments typically used in the early stages (entering the root canal). A larger intermediate taper angle β of the intermediate envelope 135 corresponds to the tapering of wider endodontic instruments used in the final stage or stages of a root canal procedure.

[0023] Endodontic instrument 100 can be considered a non-uniform taper instrument (or a Type 4 non-standard instrument according to International Standard ISO 3630-1, third edition 2019 08 (section 4)). Endodontic instrument 100 can also be considered a Type K reamer according to the aforementioned International Standard (section 8).

[0024] The mechanism 110 with the intermediate envelope 135 can act as a whip, which can brush the root canal walls and remove soft material that may be lining the surface. The function of the mechanism 110 is to clean the surface of the root canal walls regardless of the root canal geometry. The shape of the mechanism 110 allows for better removal of foreign material from the root canal.

[0025] The effective taper, ie, the tip taper angle α and the intermediate taper angle β, may be constant or may vary along the length of the mechanism portion 110.

[0026] In one embodiment, the tip taper angle α can be 0° to 7°, and the intermediate taper angle β can be 4° to 30°.

[0027] In one embodiment, the length of the tip segment 120 is about 2 mm to 5 mm.

[0028] The ratio of the first distance D1 to the length of the mechanism portion 110 is 0.18 to 0.45.

[0029] The ratio of the second distance D2 to the length of the mechanism portion 110 is 0.3 to 0.65.

[0030] For example, for a K-type endodontic instrument having a 16 mm long mechanism portion 110, the tip segment 120 may have a length of 3 to 5 mm. The first distance D1 may be 3 mm to 7 mm. The second distance D2 may be 5 mm to 10 mm.

[0031] In a preferred configuration, the tip segment 120 of the endodontic instrument 100 is coaxial with the longitudinal axis 101. Preferably, the mechanism portion 110 is also coaxial with the longitudinal axis 101.

[0032] The endodontic instrument 100 preferably includes cutting edges 20 along the mechanism 110. The cutting edges 20 are intended to cut material along the walls of the root canal. The cutting edges 20 may be helical cutting edges, such as those of traditional helical endodontic instruments, or other cutting edges known in the art. Alternatively, the cutting edges 20 may be beveled sections extending along a portion of the length of a polygonal, unfluted rod. In certain embodiments, the cutting edges 20 are alternating or selectively patterned based on the profile of the unique mechanism 110 of the endodontic instrument 100.

[0033] In some embodiments, the tip segment 120 can terminate at the tip 103 with a tip 121 that does not include a cutting edge. The tip 121 can be rounded. As described in the applicant's international patent application WO 2021 / 240387, the tip can include an angled cutting area configured to function to guide and cut an endodontic instrument into a root canal.

[0034] The endodontic instrument 100 can be made from a shape memory alloy that has a transition temperature below which the mechanism portion 110 of the endodontic instrument 100 is malleable and can deform plastically. Above the transition temperature, the mechanism portion 110 returns to its memorized shape and behaves elastically.

[0035] The mechanism profile of mechanism portion 110 can be obtained during manufacturing of endodontic instrument 100. More specifically, a molding or forming operation can be performed on mechanism portion 110 of endodontic instrument 100 to achieve a molded shape that matches the mechanism profile. During molding, mechanism portion 110 is heated to a heating temperature, for example, 400°C to 600°C, to memorize the molded shape.

[0036] In a preferred embodiment, the shape memory alloy of the endodontic instrument 100 may have a transition temperature close to the body temperature. For example, the transition temperature may be approximately 30°C to 36°C. When the endodontic instrument 100 is introduced into the root canal, the temperature of the endodontic instrument 100 is close to room temperature if it is below the transition temperature. Once placed in the root canal, the mechanism portion 110 is heated to a temperature close to the body temperature but above the transition temperature of the shape memory alloy. The mechanism portion 110 acquires a mechanism profile that adapts to the root canal manipulation. Depending on the shape memory alloy, the mechanism portion 110 may be elastic above the transition temperature or plastically deformable below the transition temperature.

[0037] In one embodiment, the endodontic instrument 100 is made from a nitinol alloy (e.g., typically about 56% nickel and about 44% titanium by weight). Nitinol alloys are in the R-phase below a transition temperature and in the austenite phase above the transition temperature. In the R-phase, the nitinol alloy is malleable and can be temporarily plastically deformed into a desired shape. The endodontic instrument 100 can also have excellent elasticity, achieved through alloy selection and specific processing, specifically heat treatment. FIG. 3 shows a graph reporting the transition temperatures of a nitinol alloy containing 56% nickel and about 44% titanium by weight. The nitinol alloy has a first transition temperature at which it transitions from the martensite phase to the R-phase and a second transition temperature at which it transitions from the R-phase to the austenite phase. The first transition temperature is about −60°C.

[0038] In one embodiment, the endodontic instrument 100 can be formed by heat treating the Nitinol alloy to a transition temperature between 15°C and 45°C. The endodontic instrument 100 can further be formed by memorizing a mechanism profile for the mechanism portion 110, i.e., a profile comprising a straight distal segment 120, and the distal segment 120 and intermediate segment 130 comprising a first bend 131 and a second bend 132. Such a method for forming the endodontic instrument 100 is described by the assignee of the present invention in U.S. Pat. No. 9,931,179. Following such a formation method, the mechanism portion 110 adopts the mechanism profile when the endodontic instrument 100 transitions from the martensite phase to the austenite phase, i.e., when the temperature is above the transition temperature of the Nitinol alloy. [Explanation of symbols]

[0039] 100 Endodontic Instruments 101 Vertical axis of the instrument 103 Tip 104 Shaft 105 Shank, handle 110 Mechanical part 110 Work Section 120 Tip Segment 121 Tip 125 Tip Envelope 130 Middle Segment 131 First Bend 132 Second Bend 135 Intermediate Envelope 20 Cut surface α Tip taper angle β Intermediate taper angle A1 First Peak A2 Second Peak D1 First distance D2 Second distance

Claims

1. An endodontic instrument (100) for cleaning a root canal of a tooth, comprising: The endodontic instrument (100) has a mechanism portion (110) made from a shape memory alloy and intended to engage in the root canal, the mechanism portion (110) extending generally along a longitudinal axis (101) between a tip (103) and a shaft (104); The mechanism portion (110) has a mechanism profile including a tip segment (120) that is substantially linear with respect to the longitudinal axis (101) and an intermediate segment (130) that extends between the tip segment (120) and the shaft (104); the intermediate segment (130) comprises a first curvature (131) having a first peak (A1) relative to the longitudinal axis (101) and a second curvature (132) having a second peak (A2) relative to the longitudinal axis (101) that is greater than the first peak (A1); An endodontic treatment instrument (100) wherein a tip envelope (125) of the tip segment (120) forms a tip taper angle (α) with respect to the longitudinal axis (101), and an intermediate envelope (135) of the intermediate segment (130) tangent to the first peak (A1) and the second peak (A2) forms an intermediate angle (β) with respect to the longitudinal axis (101), and the tip angle (α) is less than the intermediate angle (β).

2. The endodontic instrument of claim 1, wherein the tip segment has a length of 2 to 5 mm.

3. An endodontic instrument according to claim 1 or 2, wherein the first distance (D1) of the first peak (A1) from the tip (103) is between 5 mm and 8 mm.

4. An endodontic instrument according to any one of claims 1 to 3, wherein the second distance (D2) of the second peak (A2) from the tip (103) is between 5 mm and 12 mm.

5. The endodontic treatment instrument according to any one of claims 1 to 4, wherein the tip taper angle (α) is 0% to 7%.

6. An endodontic instrument according to any one of claims 1 to 5, wherein the intermediate taper angle (β) is between 4% and 30%.

7. An endodontic instrument according to any one of claims 1 to 6, wherein the tip segment (120) is coaxial with the longitudinal axis (101).

8. An endodontic instrument according to any one of the preceding claims, wherein the mechanism part (110) is coaxial with the longitudinal axis (101).

9. An endodontic instrument according to any one of claims 1 to 8, wherein the first bend (131) bends along the same plane as the second bend (132), but also in the opposite direction.

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