Endodontic Needle Assembly

Abstract

A needle assembly for an endodontic device and a method for forming an endodontic needle are disclosed. The needle assembly includes a connector that detachably couples the needle assembly to a handpiece, a body portion extending from the connector and providing a fluid conduit, and a polymeric needle extending axially from a proximal end of the body portion to a distal tip. The tip has at least one opening, and the needle includes a lumen extending therethrough that defines a fluid passageway from the body's fluid conduit to the at least one opening. The needle may be conical. The method may include providing a cylindrical preform having a first length and a first diameter and molding the cylindrical preform into a conical needle that tapers inwardly along its length.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to an endodontic needle assembly and a method of forming an endodontic needle assembly. The present invention also relates to dental devices and methods, particularly endodontic devices and methods for endodontic debridement, cleaning, and / or disinfection. [Background technology]

[0002] Root canal therapy is used to save teeth when severe infection occurs. A typical root canal therapy procedure involves the following steps: (i) opening the cavity to access the pulp and root canals; (ii) enlargement with mechanical instruments and files; (iii) chemical irrigation (using a syringe) with sodium hypochlorite (bleach, NaOCl), EDTA, and / or other chemicals, usually repeated several times; (iv) optional activation of the NaOCl / chemicals with an ultrasonic cleaning device; and (iv) obturating (or filling) the root canal and closing the tooth. Such a multi-step procedure is very laborious and can take approximately 60 minutes or more to complete.

[0003] Some of the common problems dentists face when performing root canal treatment include one or more of the following: the considerable time and effort required to dilate the canal; the risk of weakening the tooth structure by filing the canal; the risk of the file breaking inside the root canal and becoming impossible to retrieve; the risk of bacteria in the smallest canals not being detected or reaching the canal with irrigants if they are not removed to avoid reinfection through the small canals; the occurrence and / or detection of vapor lock inside the canal (when air is trapped and cannot escape and pass through the fluid above, preventing the irrigant from disinfecting the apical third of the canal); the risk of NaOCl being forced beyond the apex into the soft and hard tissues; and / or blood ingress from outside the tooth.

[0004] Several systems are commercially available that aim to improve root canal cleaning and address or mitigate at least some of the above-mentioned problems. These systems aim to enhance the hydrodynamic action of irrigants to improve cleaning, debridement, and / or disinfection. While many root canal activation systems claim to generate "cavitation" to ensure efficient root canal disinfection, the applicant has discovered that this is not sufficient in practice. For example, in many systems, the cavitation generated is limited and appears to be non-inertial cavitation, where bubbles in the fluid simply oscillate in size and / or shape. Non-inertial cavitation does not result in the bubble collapse that causes the powerful shock waves seen in inertial cavitation. Furthermore, the applicant has discovered that many existing solutions are unable to generate cavitation within the narrow (less than 500 μm, or even less than 100 μm) canal segments of teeth, which are necessary for effective cleaning, debridement, and / or disinfection. A further drawback of existing systems is that due to their limited effectiveness or large size, they require the use of NaOCl or other agents to irrigate narrow root canals or small adjacent volumes, which can result in leakage of NaOCl from the apical opening into, for example, the sinuses, potentially posing a risk to the patient.

[0005] Accordingly, applicant has proposed an improved endodontic treatment device and method in co-pending International Patent Application PCT / EP2022 / 061638, the contents of which are incorporated herein by reference. This co-pending application discloses a system and method that ensures that inertial cavitation occurs within the root canal by providing a system with sufficient length and an outer diameter small enough to enter at least the coronal portion of the root canal (as opposed to many prior art devices in which a needle is simply inserted into the pulp chamber). The method and system utilizes relatively low system pressure and fluid backflow to create a cloud of inertial cavitation within the irrigation fluid within a confined space.

[0006] Applicant recognized that, while the systems and methods of PCT / EP2022 / 061638 are highly advantageous, currently available needles limit the ability to provide commercially attractive embodiments. For example, when selecting needle size, a compromise must be made between larger needle diameters (which cannot enter the smallest root canal areas or uninstrumented root canals) and smaller needles, which may require higher operating pressures to induce cavitation. While such pressures may be significantly lower than those of prior art systems, any need to increase the operating pressure directly impacts system cost (e.g., by requiring more expensive, higher-pressure-rated pumps) and thus becomes commercially unviable. Furthermore, because all needles used in embodiments are small (e.g., 30-34 G according to the Birmingham gauge system), care must be taken to ensure that the selected needles have sufficient pressure resistance for safe and effective operation.

[0007] Accordingly, embodiments of the present invention aim to provide further improvements and advantages to endodontic treatment methods and devices. In particular, some embodiments aim to provide a needle assembly that is suitable for and / or specifically optimized for endodontic treatment devices and methods. Summary of the Invention

[0008] According to a first aspect of the present invention, there is provided a needle assembly for an endodontic treatment device. The needle assembly includes a connector for removably coupling the needle assembly to a handpiece, a body portion extending from the connector and providing a fluid conduit, and a polymeric needle extending axially from the proximal end of the body portion to a distal tip. The tip has at least one opening, and the needle includes a lumen extending therethrough that defines a fluid passageway from the body's fluid conduit to the at least one opening. The distal tip has an outer diameter of 300 μm or less and a wall thickness of less than 50 μm (e.g., 10-50 μm, particularly 20-40 μm). The needle may be formed from a material (e.g., a polymer) having a tensile modulus of less than 10 GPa. The needle may be formed from a material having an ultimate tensile strength of at least 15 MPa. The needle may have a length of at least 20 mm.

[0009] Advantageously, needles of embodiments are formed from a polymer. The use of a polymer has the advantage of providing a flexible needle during use, and also generally provides high ductility (e.g., compared to the metals used in many conventional needles). Applicant has discovered that the ductility of polymers allows for the formation of particularly small, thin-walled needle tips during the needle manufacturing process (e.g., by using a drawing process, as described below).

[0010] It is understood that ultimate tensile elongation is a general indicator of ductility (e.g., it can be measured using established ISO or ASTM procedures). In embodiments, the needle can be formed from a polymer having an ultimate tensile elongation of at least 5%. In some embodiments, the needle can be formed from a polymer having an ultimate tensile elongation of at least 50% (e.g., 100% or more).

[0011] It is also understood that the needles of the embodiments are formed from a material having a higher tensile modulus than many polymeric materials. Applicant has determined that such a relatively high tensile modulus allows the needle tip to be small enough (and the wall diameter thin enough) to withstand the pressure required to generate an inertial cavitation cloud in front of the needle tip during an endodontic irrigation procedure within a root canal. It has been found that the combination of wall thickness and tensile modulus results in a needle that is stiff enough to insert into a root canal, can withstand the necessary pressure, and is flexible enough to be inserted into a curved root canal. In contrast, prior art needles are typically made from steel and are insufficiently flexible to reach the curved portions of a root canal.

[0012] In some embodiments, the needle is formed from a material having a tensile modulus of 1.5 GPa to 10 GPa. For example, the tensile modulus can be greater than 2 GPa. For example, the tensile modulus can be less than 7.5 GPa, such as less than 5 GPa. In some embodiments, the needle is formed from a material having an ultimate tensile strength of 40 MPa to 150 MPa. For example, the ultimate tensile strength can be greater than 50 MPa. For example, the tensile modulus can be less than 100 MPa. For example, the ultimate tensile strength can be 60 to 80 MPa.

[0013] The needle may have a tapered shape. The outer diameter of the needle portion may converge toward the distal end. The needle may, for example, be generally conical or frustoconical. It has been found that conical needles may generate cavitation at lower pressures and / or lower pressure differentials between the device and the tip compared to conventional cylindrical needle shapes. Applicant has also discovered that conical needles are less likely to get caught in the uneven wall structure of the root canal because the tip of the needle tends to be located in the center of the root canal.

[0014] Conical needles also allow for a significantly reduced tip diameter, allowing the tip to be placed in complex or narrow shapes and vessels. The outer diameter of the tip can be, for example, less than 50% of the diameter of the proximal end of the needle. In some embodiments, the outer diameter of the tip is 10-30% of the diameter of the proximal end of the needle. In embodiments, the diameter of the conical needle tip is less than that of a 32G needle (e.g., less than 320 μm), and in some embodiments, less than that of a 33G needle (e.g., less than 200 μm). The diameter of the proximal end of the conical needle (at least 20 mm from the tip) is at least 500 μm, e.g., at least 700 μm in some embodiments. In some embodiments, the rate of change of diameter can vary along the length of the needle. For example, the change in diameter can be less than 0.02 mm / mm at the distal end of the needle and up to 0.05 mm / mm at the proximal end.

[0015] Applicant has surprisingly discovered that current commercially available needle manufacturing methods are incapable of producing conical needles with extremely small tip diameters (e.g., commercially available injection-molded plastic cleaning tools have cannulae with tip sizes of 30G, formed from polymers that cannot withstand the pressures required to induce cavitation). In embodiments, the needle includes a needle formed in a two-step process. The needle is first manufactured in a cylindrical shape (e.g., by injection molding or extruding tubing) and then formed into a conical shape (e.g., by extrusion or stretching). Applicant has discovered that this two-step process results in a highly effective needle for use in endodontic treatment. It is understood that the two-step process may also include additional manufacturing steps, such as a finishing process applied to the conical needle or an initial step of creating multiple cylindrical sections of the required length from a larger tubing section. The cylindrical needle may be a non-extruded needle, such as an injection-molded needle. The cylindrical needle may be polycarbonate. The cylindrical needle may be a biocompatible polymer. In other embodiments, the needles may be any one of polyethylene, polypropylene, polyurethane, polyvinyl chloride, polysulfone, polymethyl methacrylate, polystyrene, polyamide, and other polymers that meet the mechanical properties, which may also be combined into copolymers, blends, or composites.

[0016] Applicant has discovered that the high flexibility of needles according to embodiments is advantageous. For example, needles according to embodiments can bend / flex laterally within the canal. For example, needles according to embodiments can access curved and / or uninstrumented portions of the root canal. This allows needles according to embodiments to access the entire root canal, where existing needles can only access the upper portion. Applicant has recognized that it is advantageous to have a needle with a tip that can flex under a relatively low load. Thus, in embodiments, the lateral deflection of a needle for a given tip load can be an important criterion for determining whether a needle can be easily inserted into a minimally instrumented root canal. Those skilled in the art will understand that the lateral tip deflection of a needle can be easily determined by fixing the proximal end of the needle (e.g., Applicant has found that a point 20 mm from the tip is useful for measurement), applying a load to the tip (or near the tip), and measuring the resulting lateral deflection.

[0017] Accordingly, Applicant has recognized that embodiment needle assemblies may have a tip that can deflect laterally by more than 2 mm when a tip load is 0.01 N. In particular, the tip can deflect laterally by more than 4 mm (e.g., 5 mm or more) under a tip load of 0.01 N. Additionally or alternatively, the tip can deflect laterally by more than 8 mm under a load of 0.05 N (e.g., the tip can deflect at least 10 mm). Tip deflection may be measured perpendicular to the axis of the undeflected needle. Tip deflection under load may be measured with the proximal end of the needle fixed (e.g., the needle can be fixed axially 20 mm from the tip).

[0018] The needles of embodiments may include an axially oriented main outlet at the tip. The axially oriented outlet allows the flow from the needle to generate a cloud of inertial cavitation in front of the needle tip (in stark contrast to prior art arrangements that may include an impact surface that blocks axial flow from the tip). In some embodiments, the needle may additionally or alternatively include at least one side vent in the needle wall between the proximal end of the body portion and the distal tip. The one or more side vents may direct at least a portion of the flow from the needle directly to the wall of the root canal. It is understood that in various embodiments, side vented needles can be used with or without an axially oriented main outlet.

[0019] According to a further aspect of the present invention, there is provided a method of forming an endodontic needle, the method comprising: providing a cylindrical preform having a first length and a first diameter; and shaping the cylindrical preform into a conical needle that tapers inwardly along its length, the conical needle having a length greater than the first length and a tip diameter less than the first diameter.

[0020] The preform can be provided by injection molding or extrusion. The formation of the conical needle can be done by extrusion or stretch molding.

[0021] In an embodiment, the method further includes forming a needle assembly, the needle assembly including a body and a needle according to an embodiment. The method may include molding the needle assembly using a cylindrical preform.

[0022] The method includes molding a needle assembly, the assembly including a body portion and a cylindrical preform, and molding the cylindrical preform into a conical shape that tapers inwardly along its length to form a tip having an outer diameter of 300 μm or less (e.g., 200 μm or less).

[0023] The method may further include the preliminary step of forming the cylindrical needle, for example by injection molding or extrusion of the cylindrical needle. The cylindrical needle may be formed, for example, from polycarbonate.

[0024] The step of stretching / pulling the cylindrical needle into a conical shape that tapers inward along its length can also elongate the needle to a length of at least 20 mm. It will be appreciated that forming a conical needle allows the final needle length and diameter to be tailored to specific requirements.

[0025] The step of molding the needle assembly may include providing a needle and molding a body portion to secure the needle to the integrated needle assembly. For example, the body portion may be secured to the needle by overmolding. Molding of the needle assembly to secure the needle can be performed before stretching / pulling the cylindrical needle into a conical shape. In other embodiments, the needle may be attached to the body portion by bonding, gluing, interlocking, or laser welding. Alternatively, the conical needle may be glued to the body, which may be a plastic or metal needle or hub.

[0026] Advantageously, methods according to embodiments can reduce the number of parts and manufacturing steps in forming a needle assembly. Additionally, the methods allow the needle assembly to be specifically shaped (e.g., with a special angled portion) for accessing a root canal. Embodiments also advantageously provide a pressure-resistant needle assembly with securely sealed sub-components.

[0027] While the needle assemblies of embodiments are specifically designed for use with endodontic debridement, irrigation, and disinfection devices (of the type disclosed in Applicant's co-pending PCT / EP2022 / 061638), those skilled in the art will appreciate that the improved access provided by the needles to narrow root canal regions may also be useful in other root canal procedures. For example, needles according to embodiments may be used to inject / place materials, such as filling materials, into root canals. In such procedures, the needle assemblies of embodiments may enable syringe injection of high-viscosity materials into areas where manual injection is not possible (e.g., due to excessive pressure). Furthermore, needles according to embodiments may be used for manual irrigation of root canals, where they are connected to a syringe and used to deliver irrigation fluids. In such procedures, the needle assemblies of embodiments may perform better due to their increased flexibility and conical shape. Further applications include, for example, treatment of dental caries infections or other dental or medical procedures requiring the delivery of disinfectant or fluid agents (e.g., periodontitis, dental implant cleaning, wound disinfection, etc.).

[0028] According to another aspect of the present invention, there is provided an endodontic treatment apparatus comprising: a source of irrigation fluid; a pump for delivering irrigation fluid under pressure from the source; and a handpiece in fluid communication with the pump, the handpiece comprising a needle assembly having a needle extending from a proximal rear end of the handpiece to a distal forward tip thereof, the needle having an opening at the tip for delivering fluid received from the pump into a dental cavity, the needle having a length from its rear end to its tip of at least 20 mm, an outer diameter of no more than 200 μm, and a wall thickness of less than 50 μm (e.g., between 40 μm and 20 μm), such that the tip of the needle is positionable within a portion of a root canal;

[0029] A pump delivers irrigant at a delivery pressure below 80 bar and above a threshold cavitation pressure, and the flow of irrigant through the needle creates a cloud of inertial cavitation in the irrigation fluid in the root canal in front of the tip of the needle.

[0030] Once the needle is placed in the root canal (in a manner that causes reflux), the specific pressure required to generate the inertial cavitation cloud can be selected based on the specific needle and root canal geometry. Such threshold pressures can be determined, for example, for various needle sizes.

[0031] The delivery pressure can be selected to provide a minimum exit velocity of the irrigant at the tip of the needle of at least 20 m / s (e.g., at least 30 m / s; particularly, the velocity can be 20-60 m / s, e.g., 30-50 m / s; in certain embodiments, the threshold cavitation point can be approximately 38 m / s). The flow rate of the irrigant through the needle is less than 175 ml / min (e.g., less than 50 ml / min, e.g., 10-50 ml / min, e.g., 20-40 ml / min; in certain embodiments, the flow rate at the minimum threshold cavitation point can be approximately 30 ml / min). In contrast, prior art systems have been proposed that use irrigant flows of as much as 50 ml / s (3000 ml / min), which poses a much higher risk of causing pain or damaging apical structures compared to embodiments of the present invention.

[0032] Because embodiments of the present invention utilize the hydrodynamic effects of the cavitation cloud to provide debridement and / or disinfection, the use of chemical disinfectants such as NaOCl for debridement, irrigation, and / or disinfection may not be necessary. Therefore, embodiments of the present invention may advantageously use water or saline as the irrigation fluid. Saline, particularly saline (e.g., 0.9% NaCl), is generally well tolerated by the body even when pushed beyond the apex and is less likely to cause significant pain, discomfort, or serious adverse events, such as "hypochlorite accidents," to patients than chemical disinfectants such as NaOCl.

[0033] In embodiments, the size of the cavitation cloud extends up to 0.5 mm, 1 mm, 3 mm, 5 mm, 7 mm, 10 mm, 15 mm, or 20 mm from the distal end of the needle, and its location and size are adapted by altering the needle size, outflow rate, and / or flow rate.

[0034] The cleaning fluid, e.g., saline, may contain one or more additives. For example, the cleaning fluid may further contain a disinfectant or antibacterial agent. These include, for example, alcohol, chlorine, iodine, or active oxygen-based disinfectants, or quaternary ammonium compounds (QACs), which are commonly used to disinfect skin, surfaces, or devices. Such agents may be in liquid, dissolved, or suspended state within the cleaning fluid, e.g., in the form of nanoparticles. The disinfectant or antibacterial agent may enhance the germicidal effect of the cleaning fluid. The cleaning fluid may be a low-surface tension liquid so that cavitation occurs more easily at lower pressures and / or temperatures. For example, ethanol, which is also a disinfectant, may be used as a low-surface tension liquid. Because such low-viscosity fluids may be selected as cleaning fluids, the viscosity of the liquid is also a variable in the cavitation state of the cleaning fluid. A low-surface tension and / or low-viscosity fluid may be a cleaning fluid selected with such properties, or it may be a cleaning fluid containing additives that reduce these properties. The cleaning fluid may also contain a dye, for example, to improve the detectability of the fluid or to stain soft tissue or bacterial biofilms.

[0035] The cleaning material may also be selected or tailored to enhance its abrasive effect, for example, the density of the cleaning material may be increased and / or the cleaning fluid may further include abrasive particles (e.g., solid particles suspended in the fluid).

[0036] The device may include a regulator for controlling the delivery pressure, which may allow the operator to adjust the delivery pressure to account for different tooth or root canal geometries, for example.

[0037] In embodiments, the device may further include a heater for controlling the temperature of the irrigant. The heater may be provided as part of the supply (either to bulk heat the irrigant or to heat the irrigant before delivery by the pump). Alternatively, the heater may be provided as part of the handpiece to heat the irrigant as it flows through the handpiece. The phase boundary of the irrigant is dependent on both temperature and pressure, and increasing the temperature of the irrigant for a given temperature provides more favorable conditions for cavitation. For example, the temperature may be increased to above 20°C. The temperature of the irrigant may also be selected to avoid any pain response, so the temperature may be below 60°C (or below 50°C).

[0038] In some embodiments, the device may further comprise a pulse generator for pulsing the flow of irrigation fluid, which may be, for example, a single piston pump, a controllable pressure relief valve between the pump and the needle, or an on / off valve between the pump and the needle.

[0039] Unless otherwise specified, each of the recited integers can be used in combination with any other integer, as will be understood by those skilled in the art. Furthermore, while all aspects of the present invention preferably "comprise" the features recited in connection with that aspect, it is specifically contemplated that it may "consist" or "consist essentially of" the features outlined in the claims. Furthermore, unless otherwise defined herein, all terms are intended to be given their meanings as commonly understood in the art.

[0040] Furthermore, in the discussion of the present invention, unless otherwise stated, the disclosure of alternative values ​​at the upper or lower limits of an acceptable range of a parameter should be construed as an implicit statement that each intermediate value of said parameter between the lower and upper alternatives is itself also disclosed as a possible value of the parameter.

[0041] Additionally, unless otherwise specified, all numerical values ​​set forth in this application should be understood as modified by the term "about."

[0042] The invention has been described above but extends to any inventive combination of the features set out above or in the following description or drawings. [Brief explanation of the drawings]

[0043] Embodiments of the present invention may be carried out in various ways and embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] 1 shows a schematic diagram of an apparatus according to one embodiment of the present invention. [Figure 2] FIG. 2 shows a detail of the schematic diagram of FIG. 1 showing the position of the needle within the tooth. [Figure 3] 3(A), 3(B), 3(C) and 3(D) illustrate the operating principles behind embodiments of the present invention. [Figure 4] FIG. 1 is a schematic diagram of a needle assembly according to one embodiment of the present invention. [Figure 5] 1 is a flowchart illustrating a method of forming a needle assembly according to an embodiment. [Figure 6] 1A and 1B show example steps for forming a needle assembly according to an embodiment. [Figure 7] 1 is a graph showing the pressure required to induce inertial cavitation for various needles. [Figure 8] 1 is a graph showing the deflection of various endodontic needles under load. DETAILED DESCRIPTION OF THE INVENTION

[0044] Detailed Description of the Embodiments It should be noted that the terms proximal and distal are used herein for convenience to refer to the device in its typical orientation during use. It is therefore understood that proximal may generally be used to refer to a surface, component, or direction that is closer to the operator's hand during use, and distal may generally be used to refer to a surface, component, or direction that is distal to the operator's hand (and thus proximal to the root canal). Similarly, anterior is understood to be used in reference to a direction away from the proximal end toward the distal end (and posterior is understood to be the opposite direction). However, it will be understood that such references are not intended to be limiting, and the device may be in any orientation during use.

[0045] An endodontic irrigation device 1 is shown schematically in FIG. 1. The device comprises a base unit 10 including a reservoir 12 that contains a source of irrigation fluid and a pump 14 that pumps irrigation fluid under pressure from the source through a flexible conduit 16. The base unit 10 may include a pressure sensor for monitoring and controlling the pressure, an overpressure relief valve, and a waste water container. The base unit 10 may also include a user interface 18 (which may be in any convenient format) that allows an operator to adjust operating parameters such as the pressure output of the pump 14.

[0046] The handpiece 20 is connected to the distal end of the flexible conduit 16, for example, by a conventional detachable connector, so that the handpiece 20 is in fluid communication with the base unit 10 and can receive irrigation fluid from the source 12 via the pump 14. The handpiece 20 includes a grip portion 22 at its proximal end and a head 24 connected to the grip portion 22 via a neck 23. The head 24 typically extends to a needle 30, which may be replaceably mounted within the head 24. As used herein, the term "needle" broadly refers to a thin, elongated conduit having a bore therethrough (the needle's "lumen") extending from the proximal end, where it receives a fluid supply during use, to an opening at the distal end through which the fluid is delivered during use. As best seen in FIG. 2 , the needle extends axially from the proximal end 33 to the distal tip 34 and has a length 1. A lumen 32 extends through the length of the needle 30 and provides a passage for irrigation agent. The tip of the needle 34 terminates in a forward-facing axial opening, allowing the irrigant to exit the lumen in a forward axial flow.

[0047] In use, the needle 30 is inserted into the tooth 100 through a cavity 110 (formed by any convenient method, e.g., by drilling) that provides access to the pulp chamber 120. According to an embodiment of the present invention, the needle has a length measured in direction l of at least 5 mm and an outer diameter measured in direction d of no more than 300 μm, such that the needle tip 34 can be positioned within a portion of the root canal 130. With the needle positioned in this manner, applicant surprisingly discovered that delivering an irrigant in a manner that generates an inertial cavitation cloud in front of the needle tip 34 can provide effective debridement and / or disinfection without the need for an NaOCl-based irrigant. In contrast, many prior art systems use needles that are too short to reach the root canal itself (instead simply positioning the tip within the cavity 100 or pulp chamber 120) and / or that are too large in diameter to enter the root canal.

[0048] Furthermore, embodiments of the present invention allow root canal treatment to be performed without the need for mechanical filing (at least in all but the most difficult cases—e.g., elderly patients with calcified and narrowed canals), thereby requiring only initial access to the root canal prior to using the inventive device. To provide such an inertial cavitation cloud, Applicant has discovered that the needle's inner diameter (i.e., lumen diameter) and delivery pressure (depending on the geometry of the particular tooth-needle combination) must be selected to exceed a threshold cavitation pressure, such that the flow of irrigant through the needle creates an inertial cavitation cloud within the irrigation fluid in the root canal ahead of the needle tip. For example, the lumen diameter may be at least 25 μm, e.g., at least 50 μm. Without understanding this effect, it might be natural to select a needle with too small an inner diameter (e.g., less than 50 μm to ensure a reliable fit in the root canal), but Applicant has recognized that such a needle introduces significant frictional losses, meaning that even very high delivery pressures will not provide a flow exiting the needle that generates effective cavitation. In contrast, in embodiments of the present invention, cavitation provides powerful debridement, disinfection, and / or removal of debris or bacteria due to the well-known erosive effect of the cavitation cloud resulting from shock waves caused by rapidly collapsing vapor bubbles within the fluid.

[0049] As shown in the 16,000 fps high-speed photograph in Figure 3(A), a glass micropipette (e.g., with an inner diameter of 1.2, 0.6, or 0.29 mm) can be used to simulate a root canal. When an appropriately sized needle 330 is inserted into the canal 350 and flow is provided at a pressure above the cavitation threshold, a clear cavitation cloud 360 forms downstream of the needle. The flow within the canal 350 is shown schematically in Figure 3(B). Importantly, the size of the needle (800 μm or less at 20 mm from the tip) ensures that fluid flow within the canal (or indeed the root canal) includes both inflow from the needle and outflow between the canal wall and the outside of the needle.

[0050] Cavitation occurs under the right conditions, where a liquid rapidly changes to a gas across a phase boundary. Without being bound by any particular theory, the applicant recognized that selecting a needle capable of generating reverse flow within a root canal, as shown in Figure 3(C), creates a strong shear layer effect between the inward and outward flow. This shear layer increases vortices within the flow, significantly increasing the occurrence of cavitation. The resulting conditions mean that very strong vortices can be generated at the interface between the inflow and outflow flows within the root canal. Within the vortex, the (dynamic) pressure drops significantly. This pressure drop makes cavitation more favorable (the onset point approaches the phase boundary). As a result of this effect, cavitation clouds can be generated within passages such as root canals under flow conditions (pressure, velocity, and flow rate) that would not cause cavitation in an open environment. Increasing the velocity at which the liquid exits the needle also helps increase the vortex, and for a given channel, there is a minimum nozzle exit velocity below which cavitation does not occur. If the needle's inner diameter is not excessively narrow, the delivery pressure can be used to control the needle exit velocity.

[0051] To test the performance of the device according to the embodiment, tests were conducted on a transparent plastic tooth (RepliDens Mandibular Molar, Transparent Type 03.2.1, Medicem GmbH, Weinfelden, Switzerland) with a realistic root canal structure filled with colored gelatin used to simulate the internal structure of the tooth. Various devices were tested, and the amount of gelatin removed before and after irrigation was measured using image analysis and pixel counting. The device according to one embodiment used a needle with a length of 20 mm and a gauge of 30G (corresponding to an inner diameter of 0.16 mm and an outer diameter of 0.31 mm). The delivery pressure was set to 60 bar. The irrigant was saline, and the needle was placed and moved up and down the canal for 180 seconds. Results from multiple root canal systems were compared based on the amount of gelatin before and after irrigation, and the percentage of material removed was determined. The same tests were performed using commercially available ultrasonic and laser-based irrigant activation systems. For the ultrasonic (EDDY, VDW GmbH, Munich, Germany), a vibrating tip was inserted into each canal and activated for 120 seconds. For the laser system (LiteTouch Er:YAG Laser, Orcos Medical AG, Küssnacht, Switzerland), a plastic pulp chamber was filled with water, the laser tip was placed in it, and activated for 120 seconds. The results, shown in Table 1 below, demonstrate that embodiments of the present invention significantly improved debridement of uninstrumented teeth (our invention) over commercially available systems: an ultrasonic system (no instrumentation / file), a laser system (no instrumentation / file), and instrumented mechanical filing (ProTaper, Dentsply, Vallée, Switzerland) followed by syringe irrigation. Experiments have shown that conventional ultrasonic and laser activation systems cannot adequately remove material from the interior of the canal. Therefore, they can only be used for activation and are not suitable for treating uninstrumented root canals (e.g., which may be defined as root canals dilated only with an ISO 10 flat file) and do not reduce the need for mechanical filing. For ultrasonic systems, the narrow root canal prevents the tip from vibrating side to side, resulting in damped vibrations. It was observed that with the laser system, gelatin did not come out of the root canal because sufficient flow was not generated.A combination of mechanical sanding and irrigation with a water-filled syringe performed better than the other methods, but was less effective and significantly slower than embodiments of the present invention. [Table 1]

[0052] Importantly, applicant also compared conditions between open-ended and closed / confined regions (where the root is closed). This showed unexpected results, demonstrating the importance of the shape of the tooth tube and needle on cavitation. It is believed that previous systems failed to consider this as a factor, which may reflect why such systems fail to provide truly effective cavitation.

[0053] To demonstrate this effect, experiments were performed using a 60 bar delivery pressure connected to needles of various shapes, diameters, and lengths. Water exiting the needles was discharged into either (i) a water bath, (ii) an open-ended glass micropipette, or (iii) a glass micropipette with one end completely sealed. The needles tested included standard gauge needles. The threshold pressure was recorded as the point at which a stable cloud of cavitation was first visible. The upstream pressure threshold for generating developed cavitation was generally much lower in closed-ended narrow tubes compared to open water baths. Experimental data confirmed that 20 mm or 15 mm 30 Gauge (needle gauge) needles generated cavitation only in micropipettes, not in open baths, and that higher pressures were required to generate cavitation in open baths. All other needle sizes, including 10 mm or 5 mm 30 Gauge needles, generated cavitation in open water. However, their use in micropipettes reduces the required upstream pressure by 15 to 40 bar. An exception was found for 25G needles and 0.6 mm tubing (Table 2; closed-end micropipette d = 0.6 mm, 25G) - in this case, the needle itself blocked backflow, and therefore the cavitation threshold increased after closing the end of the micropipette (because the outer diameter of the needle was very close to the inner diameter of the pipette tubing). Therefore, Applicant was able to confirm that backflow in the flow channel is necessary to efficiently induce cavitation. [Table 2]

[0054] The volumetric flow rate through a needle is highly dependent on the upstream pressure and needle diameter. Therefore, if lower pressure is required to generate cavitation, the flow volume decreases. This is actually advantageous because lowering the flow rate and / or pressure reduces the risk of a high flow rate causing the jet to cause undesired damage to the tooth. Experiments have shown that the maximum flow rate occurs with a needle with a maximum diameter of 25G and the minimum flow rate occurs with a needle with a minimum diameter of 34G. The lowest pressure threshold for cavitation occurred with a 25G needle with a length of 10 mm—72 ml / min at 6 bar. These results indicate that the cavitation threshold is significantly lowered within narrow, closed-end canals. Therefore, embodiments of the present invention can generate effective cavitation at lower flow rates and lower upstream pressures. Such flow offers the significant benefits of reduced pressure at the apex of the root canal and lower flow rate, both of which minimize the risk of apical extrusion.

[0055] Therefore, the results confirmed that the needle characteristics (diameter, length, etc.) have a significant impact on the threshold cavitation pressure. Furthermore, the experiments confirmed that the effect of backflowing fluid is very important - increasing the relative velocity and vortex formation, thereby significantly reducing the pressure required for cavitation onset.

[0056] The effect of needle length on cavitation threshold is straightforward: longer needles increase the pressure required for cavitation, which is thought to be consistent with the fact that shorter needles provide less flow resistance. However, in practical embodiments, this generally means that the choice of needle length is a compromise between increasing the threshold pressure and the length required to position the tip sufficiently within the root canal to deliver cavitation and effectively debride the canal.

[0057] Some embodiments of the present invention may include a heater 15 to raise the temperature of the irrigant (thereby bringing the irrigant closer to the phase boundary at a given pressure, further favoring cavitation). The heater 15 may be included as part of the base unit 10 or may be integrated into the handpiece. In some embodiments, the pump 14 or the base unit may include a pressure regulator.

[0058] In addition to, or as an alternative to, the user interface 18, the handpiece 20 may include controls such as switches on the handpiece (or associated with the handpiece, e.g., on a foot pedal). For example, a trigger may be provided to activate flow through the system.

[0059] Because embodiments of the present invention allow for the use of simple cleaning agents such as water or saline, it can be appreciated that embodiments can provide a variety of options during use. For example, the cleaning agent can be a low surface tension liquid or a high viscosity liquid. The cleaning agent can also include additives such as abrasive particles.

[0060] In some embodiments, the device may include a canal sensing system. For example, to ensure that fluid does not pass through the apex, embodiments may include an apex locator to measure the distance to the apex and assist the dentist in manipulating the device.

[0061] While the primary purpose of the endodontic irrigation device of the embodiments may be root canal treatment, it can also be appreciated that the debridement and / or disinfection effects of the cavitational flow can be applied to other uses within dental practice. For example, the device can be used to remove plaque from the outer or subgingival surfaces of teeth. Embodiments can also be used to perforate dental tissue (dentin, enamel) or cut soft tissue. The device can also be utilized to find an entrance to a root canal.

[0062] The applicant has recognized that commercially available needles present disadvantages to the use of the above-described method and device. In particular, because needle dimensions are directly related to the system pressure required for inertial cavitation, selecting a needle size requires a compromise between larger needle diameters that cannot penetrate the smallest root canal regions and smaller needles that may require higher operating pressures to induce cavitation. Importantly, the operating pressure required for a system can directly impact operational and equipment costs, such as the need for more expensive, higher-rated equipment, such as pumps. Therefore, providing a system that effectively operates at the lowest possible pressures offers both clinical and commercial advantages.

[0063] Figure 4 shows a needle assembly 400 according to an embodiment of the present invention. The needle assembly 400 is a single, integrated part that may be provided, for example, as a disposable, sterile consumable item, for use with the cleaning device 1 of Figure 1. The needle assembly 400 includes a connector 410, a body portion 420, and a needle 430.

[0064] The connector 410 is located at the proximal end of the needle assembly and is configured to removably couple to a corresponding coupling portion on the handpiece 20. It is understood that the connector 410 can be of any convenient type, for example, an existing standardized type to enable interconnection with existing equipment and / or provide a familiar operation for the user. One particularly suitable connector may be, for example, a Bal Seal (RTM) connector, which may include a spring-loaded retention device (e.g., a connector of the type disclosed in U.S. Patent No. 8,167,285 B2). The body portion of the needle assembly 420 extends forward from the coupling and defines a fluid conduit 422 that, in use, carries irrigant from the handpiece 20 to the needle 430. In the illustrated embodiment, a flange 425 is provided around the exterior central portion of the body 425 and may be configured, for example, to provide a stop or tactile feature for use in connecting the needle assembly 400 to the handpiece 20.

[0065] The needle 430 extends forward from the distal end of the needle assembly. The proximal end of the needle 433 is in fluid communication with the body fluid conduit 422. The distal end of the needle 430 terminates in a tip 434. The axial length of the needle from the proximal end 433 to the tip 434 is at least 20 mm. For ease of use, the axis of the needle 430 is angled relative to the axis of the body portion 420. Applicant has found that providing the needle 430 at an angle of 30 to 90 degrees, e.g., approximately 60 degrees, relative to the body portion 420 is beneficial in allowing a clinician to guide the tip 434 of the needle 430 into the root canal during use. In some embodiments, the needle may include an additional angled or curved portion, e.g., having a gooseneck shape, to aid in tip positioning during the procedure. The tip 434 is provided with an axially oriented opening for ejecting a primary flow of irrigant in the direction indicated by arrow A. Optionally, at least one side vent may be provided proximal (but rearward) of tip 434 to provide additional side flow that can be directed toward the side wall of the adjacent portion of the tube, as shown by arrow S.

[0066] The needle 430 is formed from a polycarbonate material (e.g., Macrolon 3258). The needle 430 is first injection molded as a cylindrical needle before being formed into a conical shape (described further below). Table 3 below shows the dimensions of a typical needle (labeled "Needle X" for ease of reference) made according to an embodiment. As shown in the table comparison, the outer diameter of the tip 434 of Needle X is less than 200 μm, which is thinner than a 33G needle, but the diameter of the proximal end 433 is greater than 750 μm. The thickness of the needle tip 434 is 40 μm, while the embodiment detailed in Table 3 has a wall thickness of 34 μm. The polycarbonate needle of the embodiment has been found to have significantly improved flexibility compared to metal needles while being able to withstand the required operating pressures that prohibit the use of many thermoplastic materials. The combination of the flexibility of the needles of the embodiments and the small tip diameter allows the tip to be placed in narrow root canals (e.g., those less than 300 μm) without the use of instruments, especially for root canals with high curvatures (e.g., greater than 30°) that are inaccessible with conventional needles. [Table 3]

[0067] A method of manufacturing a needle assembly 400 according to an embodiment is shown schematically in Figure 5. In step 510, an injection molded cylindrical needle preform (made of polycarbonate) is provided. The needle preform can be formed as a single cylindrical needle or as a section cut from a larger extruded or molded cylindrical tube.

[0068] The next step in the process (shown in step 520) involves forming the cylindrical needle preform into a conical needle of the required length and diameter. This second step is performed in a drawing process (also called a stretching process), which lengthens the needle as it is shaped. By forming the needle directly from the preform, the needle does not need to be glued or otherwise secured in place. This reduces manufacturing steps and provides a sturdy needle that can withstand the required pressure despite its thin wall thickness and small tip diameter. Alternatively, the conically extruded preform can be drawn into the shape of a cylindrical needle and then glued to a body or plastic / metal needle or hub that can be injection molded.

[0069] In some embodiments, an integrated needle assembly including a cylindrical needle preform can be first formed prior to the step of drawing the needle into its conical shape. For example, in some embodiments (shown in FIG. 6 and described below), the cylindrical preform may first be integrally molded with the body of the needle assembly (e.g., in an injection molding process). In other embodiments, the needle preform can be placed in a mold and the needle body can be overmolded using an injection molding process to form an integrated needle assembly including both the needle preform and the body. In alternative embodiments, the needle preform can also be bonded to the molded needle body (although it will be understood that this typically requires more manufacturing steps). After forming the integrated needle assembly, the next step in the process is to shape the cylindrical preform into a conical needle of the required length and diameter. This second step is performed in a drawing process that lengthens the needle as it is being formed. Forming the needle directly from the integrated needle assembly may eliminate the need to glue or otherwise secure the needle. This reduces manufacturing steps and provides a robust needle that can withstand the required pressure despite its thin wall thickness and small tip diameter.

[0070] An example of a needle assembly 400' including a body 420' and a needle preform 440' is shown in Figure 6A. In this example, the body 420' and the needle preform 440' (which is substantially cylindrical) are a single, integral, injection-molded part. Figure 6B shows the same example needle assembly 400' after the needle preform has been pulled to form a conical needle 430' of the required length and diameter.

[0071] Figure 7 shows tests performed on the conical needle of the present invention compared with conventional needles of 25G, 30G, and 31G gauge. To simulate the endodontic treatment method of the present invention, the needles were tested in a free water bath and with decreasing-sized micropipettes (1.2 mm, 0.6 mm, and 0.29 mm diameter) that simulate different sizes of dental canals. For each needle and environment, the threshold pressure required to induce cavitation in the irrigant stream in front of the needle tip was measured. The results clearly demonstrated that the conical needle of the present invention significantly reduced the threshold pressure required for cavitation, especially in closed canals (e.g., less than 20 bar for medium-sized micropipettes compared to 50 or 60 bar for existing needles). The conical needle of the present invention was the only needle capable of generating cavitation with the smallest micropipette (0.29 mm diameter).

[0072] Further testing was conducted to quantify the root canal penetration ability of needles according to embodiments compared to commercially available needles of the prior art. The needles according to embodiments (referred to as "Needle Y" for ease of reference) were tested alongside standard metal endodontic needles of sizes 30G and 31G (both Transcodent brand needles manufactured by Sulzer Mixpac, Germany) and flexible "Irriflex" needles (available from Produit Dentaires SA, Switzerland). For the purposes of this testing, standard clear resin endodontic training blocks with a single curved root canal were used. A 0.02 taper 15-30 2A block training block, commercially available from Dentsply Sirona, was used for the testing. The blocks were filed with an ISO 15 file (0.02 taper) and an ISO 20 file (0.02 taper) to form two different sizes of canals.

[0073] Each needle was inserted into two training blocks to its maximum penetration depth. This maximum penetration depth was then measured using an end stop and an endoscopic ruler. The maximum working length of each root canal was also measured using an ISO 10 hand file so that it could be compared with the penetration depth of each needle. The results are shown in Tables 4 and 5 below. [Table 4] [Table 5]

[0074] From this data, it can be seen that needle Y according to embodiments was the only needle capable of reaching the full working length of either ISO 15 or ISO 20 tubing. The penetration depth of needles according to embodiments significantly exceeded that of both conventional needles and "flexible" prior art needles. Needles according to embodiments were the only needles capable of reaching the full working length of tubing with minimal instrumentation (i.e., tubing that may be defined, for example, as tubing expanded only with an ISO 20 or ISO 15 hand file).

[0075] A key feature of the needles according to the embodiments, believed to contribute to their enhanced vascular penetration, is the high flexibility (particularly transverse flexibility relative to the needle axis) provided by the needle design and manufacture. To quantify flexibility, Applicant tested a series of needles alongside the needle according to the embodiments (designated "Needle Z"). The same set of needles as in the penetration test were tested: 30G and 31G Transcodent brand needles, flexible "Irriflex" needles, and needles according to the embodiments.

[0076] Each needle was clamped horizontally (in a desk vice) in a cantilever manner at a point 20 mm from the tip of the needle. A load point was marked 1 mm from the tip of the needle where a point load was applied. Each needle was then deflected under a series of loads (1 g, 2 g, 3 g, 5 g, 10 g, and 20 g, corresponding to loads of 0.01 N, 0.02 N, 0.03 N, 0.05 N, 0.10 N, and 0.20 N, respectively). The deflected position of the needle tip under each load was recorded. From the recorded position, the deflection in the vertical axis (i.e., perpendicular to the initial axis of the needle) was recorded in millimeters. The results for each needle are shown in Table 6 below and graphically in Figure 8. [Table 6]

[0077] It is particularly noteworthy that the tip of a needle according to one embodiment of the present invention deflects 5 mm with a load of only 0.01 N. In contrast, all other needles, including conventional "flexible" needles, change by more than 1 mm at most under this load. Furthermore, it takes at least five times more force to bend any other needle by the same 5 mm. It is clear that the needles of the embodiment are more flexible than any of the prior art needles, regardless of the applied load. The difference in flexibility between the needles of the embodiment and the prior art needles is particularly noticeable at low loads. While the deflection behavior of the metal needles (30 G and 31 G) is close to linear, Needle Z exhibits logarithmic behavior. Applicant has recognized that this is particularly beneficial for endodontic needles and for accessing highly curved root canals.

[0078] In use, this proves to provide a needle that bends more easily to follow the curves of the treated root canal with minimal instrumentation. This increased flexibility, particularly at the distal end of the needle according to embodiments, allows the needle to follow tightly curved canals where other needles would become stuck.

[0079] It will further be appreciated that the conical shape combined with the flexible material significantly reduces the risk of the needle tip getting stuck in the porous dentin wall (i.e., compared to a conical metal needle).

[0080] Although the invention has been described with reference to preferred embodiments, it will be appreciated that various changes or modifications can be made thereto without departing from the scope of the invention as defined in the appended claims.

Claims

1. 1. A needle assembly for an endodontic device, the needle assembly comprising: a connector for removably coupling the needle assembly to a handpiece; a body portion extending from the connector to provide a fluid conduit; a needle extending axially from the proximal end of the body portion to the distal tip, the distal tip has at least one opening, the needle having a lumen extending therethrough that defines a fluid passageway from the fluid conduit of the body to the at least one opening; the distal tip has an outer diameter of 300 μm or less and a wall thickness of less than 50 μm; A needle assembly wherein the needle is formed from a material having a tensile modulus of at least 1 GPa.

2. The needle assembly of claim 1 , wherein the needle is formed from a material having an ultimate tensile strength of 15 to 150 MPa.

3. The needle assembly of claim 1 or 2, wherein the needle has a tapered shape in which the outer diameter of the needle portion converges toward the distal tip.

4. The needle assembly of claim 3 , wherein the needle has a frustoconical shape.

5. 5. The needle assembly of claim 3, wherein the outer diameter of the distal tip is less than 50% of the diameter of the proximal end of the needle, and preferably the outer diameter of the distal tip is 10-30% of the diameter of the proximal end of the needle.

6. The needle assembly of any one of claims 3 to 5, wherein the needle comprises a conically shaped cylindrical needle.

7. 7. The needle assembly of any one of claims 1 to 6, wherein the needle assembly comprises a needle having flexibility such that a tip of the needle deflects laterally by more than 2 mm at a tip load of 0.01 N, and additionally or alternatively by more than 8 mm at a tip load of 0.05 N.

8. The needle assembly of any one of claims 1 to 7, wherein the needle is formed from polycarbonate.

9. The needle assembly of any one of claims 1 to 8, further comprising at least one side vent hole in a wall of the needle between the proximal end of the body portion and the distal tip.

10. 1. An endodontic device, comprising: a source of cleaning fluid; a pump for pumping cleaning fluid from said source under pressure; the handpiece comprising a needle assembly in fluid communication with the pump and including a needle extending from a proximal rear end of the handpiece to a forward tip distal to the handpiece, the opening in the tip delivering fluid received from the pump into the tooth cavity; the needle has a length extending from its posterior end to its tip end of at least 20 mm, an outer diameter of no more than 200 μm, and a wall thickness of less than 40 μm, so that the tip end of the needle can be positioned within a portion of the root canal; 1. An endodontic treatment device wherein the pump delivers irrigant at a delivery pressure below 80 bar and above a threshold cavitation pressure, such that the flow of irrigant through the needle creates an inertial cavitation cloud in the irrigation fluid in the root canal in front of the tip of the needle.

11. 1. A method of forming an endodontic needle, said method comprising: Providing a cylindrical preform having a first length and a first diameter; forming the cylindrical preform into a conical needle that tapers inwardly along its length, the conical needle having a length greater than the first length and a tip diameter less than the first diameter.

12. The method of claim 11 , wherein the preform is provided by injection molding.

13. 13. The method of claim 11 or 12, wherein forming the conical needle comprises extruding or stretching the cylindrical preform.

14. 14. A method of forming an endodontic needle assembly comprising a body and a needle according to the method of claim 11, 12 or 13, the method comprising: molding a body portion; and attaching the conical needle to the body portion.

15. 15. The method of claim 14, wherein attaching the conical needle to the body portion comprises attaching a proximal end of the cylindrical preform to the body portion prior to forming into a conical needle.

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