DEVICE FOR MEASURING MECHANICAL AND THERMAL LOADS ON A ROTATING INSTRUMENT

Description

[0001] The present invention relates to the field of medical technology and can be applied to endodontic handpieces with rotating surgical instruments. The device according to the invention enables the thermal and / or mechanical loads of rotating instruments to be determined in real time using impedance measurement methods.

[0002] In dentistry, endodontic or root canal treatment is usually performed to preserve a diseased and bacterially infected tooth in the long term. During root canal treatment, the damaged tooth is opened, and the root canal is then enlarged and prepared using a root canal file. This treatment uses rotating root canal files made of shape memory alloys (SMA), generally nickel-titanium alloys. Due to the natural curvature of the root canals, frictional moments occur that exert torsional loads on the file. This can lead to undesirable instrument jamming in the root canal during treatment. Friction occurs during the treatment, leading to a rise in temperature in the file. This can cause a phase transition in the nickel-titanium instruments, resulting in plastic deformation and an increased risk of file breakage.In particular, cyclic fatigue is characterized by the rotation of the instrument, which leads to bending stress, local hardening, embrittlement of the material, and fatigue. These fatigue phenomena are not visible externally.

[0003] There are devices that display or calculate the probability of material fatigue. For example, EP 1400217 A1 discloses a method and device for measuring the fatigue of dental instruments. The number of cycles performed by the dental instrument is measured and compared with a target value. From this, an estimate of the probability of instrument breakage is derived and displayed. The probability calculation is influenced by the type of endodontic instrument and the curvature of the root canal. The measurement is performed, among other things, via the number of cycles of rotation of a motor that rotates the dental instrument. For this purpose, the current or power of the motor is measured.The number of rotation cycles of the endodontic instrument is recorded throughout its lifetime and compared with a corresponding target fracture risk value, which indicates the probability of fracture of the dental instrument.

[0004] EP 1937180 B1 relates to a method and device for monitoring and identifying a medical instrument. The device comprises an electronic tag (commonly referred to as a TAG) integrated into the handle of the instrument. The tag communicates via radio frequency with the software of a motor that drives the instrument via a read / write interface module. The data transmitted by the motor is evaluated in the TAG, with the drive motor software controlling the drive motor according to the cyclic fatigue of the dental instrument and, if necessary, stopping the motor and emitting an acoustic or optical signal if the cyclic fatigue is exceeded and the use of the instrument poses a risk to the patient.

[0005] EP 2215981 A1 describes a surgical power tool having an actuation assembly comprising a force sensor and a switch. The force sensor is provided to detect an actuation force applied by the user, and the switch is transferred from a first switching state to a second switching state by the actuation force. A combined evaluation of the force sensor signal and the switching state enables, for example, a plausibility check to increase the functional reliability of the power tool.

[0006] Approaches based on impedance measurement are used, for example, in dental treatment to determine the penetration depth of root canal files. During rotation of the dental instrument, an impedance measurement is taken, thereby determining the apical (lower) opening of the root canal.

[0007] For example, US 6520773 B1 discloses an endodontic file comprising an electrically conductive shaft with a lower cutting section at its distal end and an electrically non-conductive handle with an electrically conductive head at the proximal end of the shaft. The handle is located between the head and the distal end. The electrically conductive head serves for electrical connection to an instrument for measuring the internal cavity of the tooth.

[0008] A dental drilling system with electrical impedance measurement, disclosed in WO 2018165390 A1, indicates when a drill of the drilling system approaches the cortical-cancellous bone or the bone-soft tissue interfaces. The drilling system includes a dental drill handle with a cannula bearing electrically coupled to a drill, the drill having an electrically insulated portion and an exposed portion. The cannula bearing is coupled to an electrical impedance spectroscopy sensor device configured to measure the impedance between the cannula bearing of the dental drill handpiece and a base plate, and a processing system distinguishes when the drill of the drilling system approaches the cortical bone, the cancellous bone, or the bone-soft tissue interfaces.

[0009] Likewise, DE 10303964 A1 (US 2006 / 241628 A1) discloses a medical drilling device for drilling human or animal tissue, comprising a drill with a drilling electrode and a counter electrode. Both electrodes are charged by a resistance meter, and the electrical resistance of the tissue, preferably the impedance, between the drill and the counter electrode is measured. A monitoring device provides the surgeon with information about the type of tissue and the drilling depth. A similar approach is also pursued in US 2014 / 094808 A1.

[0010] The prior art also describes various patents that indicate the temperature of a rotating surgical instrument. For example, US 6786897 B2 relates to a temperature indicator element for attachment to a powered surgical instrument to provide a visual indication of the temperature of at least a portion of the surgical instrument. The thermochromic element provides a visual indication of the temperature of a portion of the instrument when the temperature exceeds a predetermined value.

[0011] EP 2524666 B1 discloses a medical, in particular dental, handpiece with a temperature measuring device for contactless measurement of the temperature of the handpiece or a part of the handpiece by detecting electromagnetic radiation, in particular thermal radiation. Alternatively, an electrical temperature measuring device can be used.

[0012] A portable power tool disclosed in GB 2438877 A comprises a motor configured to drive a cutting tool. Said cutting tool has a sensor for detecting an environmental characteristic (e.g., temperature). This sensor can communicate wirelessly with a controller to control the power tool in response to the detected parameter when certain thresholds are exceeded.

[0013] Similarly, JP H0347249 A aims to prevent overheating of a holding part for a surgical instrument by generating a voltage between two ends of a temperature measuring element, converting it into a digital signal, and inputting it as temperature information into a control circuit. If a certain temperature threshold is exceeded, either an alarm signal is issued or the power supply to a motor driving the surgical instrument is stopped.

[0014] US 5516285 A discloses a surgical drill with a temperature sensor for detecting and measuring the temperature at the drill tip. A method for measuring the temperature of the drill tip in a patient's bone is also disclosed.

[0015] US 2009 259244 discloses a power supply device for outputting power to a surgical instrument comprising a temperature detection section for detecting a temperature of the surgical instrument and an abnormality detection section for detecting an abnormality of the surgical instrument based on the detected temperature.

[0016] WO 2018 165390 discloses a dental drilling system with electrical impedance measurement which indicates when a part of the drilling system approaches the cortical-cancellous interface or the bone-soft tissue interface. Description of the invention

[0017] The invention is intended to contribute to reducing or preventing the risk of breakage and / or damage to rotating instruments and the surrounding materials. To this end, the object of the invention is to enable monitoring of mechanical and / or thermal loads on rotating, particularly modular, instruments using an impedance measurement method. The loads to be monitored can be thermally, chemically, or physically induced material changes.

[0018] The problem is solved with the features of the main claim, with the subclaims describing further embodiments.

[0019] The device according to the invention for measuring mechanical and thermal loads on a rotating medical instrument comprises an endodontic handpiece with the rotating medical instrument at the distal end of the handpiece. According to the invention, an impedance unit is electrically connected to the rotating medical instrument via an electrical contact to the medical instrument and to a counter electrode.

[0020] In one embodiment, the impedance unit is an impedance-based measuring, evaluation and control unit (iMAR unit) with an integrated frequency generator and a measuring unit.

[0021] In another version, the impedance unit is integrated into the handpiece. However, the impedance unit can also be located outside the handpiece.

[0022] In another embodiment, the rotating medical instrument is a root canal instrument, preferably a root canal file or a drill.

[0023] In another design, the electrical contact is a sliding contact or a sliding contact.

[0024] In a further embodiment, the counter electrode has a larger surface area than the surface of the rotating instrument.

[0025] In a further embodiment, the counter electrode is arranged on the patient or on the treatment device or on the practitioner.

[0026] The solution to this problem is achieved through real-time impedance measurement and its evaluation by integrated electronics. One example is reducing the risk of breakage and jamming of root canal files due to excessive thermal and / or mechanical stress, enabling optimized treatment of, for example, dental diseases.

[0027] By directly coupling the rotating drive with the impedance measurement technology, the torque applied to the rotating instrument and / or the speed of rotation is reduced in the event of imminent overheating and / or excessive bending and / or material changes in order to avoid breakage.

[0028] A system that performs real-time measurements of the thermal and / or mechanical loads on rotating instruments using impedance measurement techniques does not currently exist. In particular, there are currently no systems that enable real-time impedance measurements during instrument rotation.

[0029] Current rotating systems pose a risk of instrument or tool breakage due to heat buildup or jamming. Integrated impedance measurement technology makes it possible to shut down or reduce the rotation of the rotating instrument according to predefined criteria. Until now, such stress in rotating instruments could not be determined directly during treatment.

[0030] The invention can reduce the problem of file or tool breakage due to excessive thermal stress and / or bending of the rotating instrument, in particular root canal files or drills.

[0031] One application, for example, is the integration of electronics for impedance measurement into the handpiece of a root canal file drive. Furthermore, in dental drills, the electrical contact of the rotating instrument can be made in the drill head in a similar way to the root canal file, although this is not covered by the claimed invention. This makes it possible to measure impedance not only during root canal treatment, but also during drilling processes, for example in dentistry and orthopedic surgery, and thereby draw conclusions about the thermal state of the file or drill. In the event of excessive heating, the torque and / or the speed of rotation are then reduced in order to prevent instrument breakage and tissue damage due to excessive thermal stress. Implementation of the invention

[0032] The invention is explained using an exemplary embodiment. Figure 1 shows a device according to the invention for measuring mechanical and thermal loads on a rotating medical instrument in a first embodiment, and Figure 2 shows a further embodiment of the device according to the invention.

[0033] The Figure 1 The first embodiment shown relates to a device for measuring and regulating mechanical and thermal loads on a rotating, in particular medical, instrument. The device comprises an endodontic handpiece 1, an impedance unit 5, which in this embodiment is integrated into the handpiece 1, and a counter electrode 7. The impedance unit 5 is an impedance-based measurement, evaluation, and control unit (iMAR unit).

[0034] The distal end of the handpiece 1 is connected to the rotating instrument 2, e.g., a root canal instrument, in particular a root canal file or a drill. An electrical contact 3, for example, a sliding contact, connects the rotating instrument 2 to the impedance unit 5 via an electrical line 4. The contact 3 to the electrically conductive parts can be made, for example, via two sliding contacts, both of which are arranged either in a ring shape or in a different shape on the shaft of the rotating instrument 2 and are insulated from one another, or the contact 3 can be made in another way. Due to this exemplary arrangement, the contact 3 is in electrical contact with the handpiece 1 during the rotary movement of the rotating instrument 2.

[0035] The impedance unit 5, in turn, is connected to the counter electrode 7 via another electrical line 6. The counter electrode 7 is attached to the patient, the treatment device, or the practitioner themselves. The shape of the counter electrode 7 is undefined. However, the surface area of ​​the counter electrode 7 must be larger than the surface area of ​​the rotating instrument 2.

[0036] Figure 2 shows a further embodiment of the device according to the invention with an endodontic handpiece 1, an externally arranged impedance unit 5 and a counter electrode 7. The electrical contact 3 to the rotating instrument 2 (here again, for example, a root canal file), the arrangement of the counter electrode 7 and the electrical lines 4 and 6 are according to the Figure 1 provided.

[0037] The impedance unit 5 is both in Figure 1 as well as in Figure 2directly coupled to the rotating drive of the rotating instrument 2 via the electrical contact 3. This enables the impedance to be measured and evaluated in real time during the treatment process. The impedance used to evaluate the condition of the rotating instrument 2 is the internal impedance of the rotating instrument 2 itself and not the impedance of the environment. The impedance unit 5, as an impedance-based measuring, evaluation, and control unit, contains an integrated electronic circuit with an integrated frequency generator and measuring unit that processes the recorded data and regulates it at previously defined limit values ​​for changes in the internal impedance during thermal and / or mechanical stress on the rotating instrument 2.The limit values ​​result from the real-time evaluation of the measured impedance spectra of the internal impedance of the rotating instrument 2 and define the shutdown criteria for excessive mechanical and / or thermal stress on the rotating instrument 2. Likewise, the phase transition in the instrument material can be determined depending on its temperature, which represents an additional improvement of the analysis method.

[0038] For example, the thermally induced phase transition of the SMA (shape memory alloy) material is determined within a small frequency window based on a characteristic shift in the internal impedance of the rotating instrument 2. Impedance changes in other frequency ranges and / or the entire spectrum are also used to interpret other load-relevant parameters. For example, the impedance gradient within a defined frequency range is evaluated in real time, and the corresponding states of the rotating instrument 2 are determined based on the gradient. Furthermore, using RCL equivalent circuits consisting of resistors (R), capacitors (C), and coils (L), theoretical curves can be created, which are compared with the measured curves. Relevant parameters can be calculated using the measured impedances.If previously defined target criteria for thermal stress and / or excessive deformation are exceeded, the rotating instrument 2 is shut down or the applied torque and / or rotation speed are reduced. This can specifically prevent instrument overheating and / or bending and / or material changes with the resulting risk of breakage or jamming.

[0039] When using a rotating instrument 2, which is modularly attached to a handpiece 1, the force is transmitted by means of positive or non-positive engagement. This makes it only possible to establish electrical contact with the rotating instrument 2 to a limited extent. In this case, contact is established via electrical (sliding) contacts, which can be used to measure impedance with or without rotation of the rotating instrument 2. This contact can be permanent or temporary.

[0040] The impedance measurement is limited to essential measurement points in order to increase measurement efficiency and reduce the power consumption of the required electronics. The measurement points are within the frequency range of the impedance measurement. In addition to measurement points, measurement ranges can also be used, meaning a spectrum is measured over a narrow frequency range, and these values ​​are used for evaluation. The corresponding equivalent circuit depends on the specific application. Different equivalent circuits are used for evaluation for different purposes. Reference symbol

[0041] 1Handpiece 2Root canal file 3Electrical contact 4Electrical cable 5Impedance unit 6Electrical cable 7Counter electrode

Claims

1. Device for measuring mechanical and thermal loads on a rotating medical instrument (2), the device comprising an endodontic handpiece (1) with the rotating medical instrument (2) at the distal end of the handpiece (1), with an impedance unit (5) being electrically connected to the rotating medical instrument (2) via an electrical contact (3) to the medical instrument (2) and electrically connected to a counter electrode (7).

2. Device according to Claim 1, characterized in that the impedance unit (5) is an impedance-based measurement, evaluation and control unit (iMAR unit) having an integrated frequency generator and a measuring unit.

3. Device according to Claim 1 or 2, characterized in that the impedance unit (5) is integrated in the handpiece (1).

4. Device according to Claim 1, characterized in that the rotating medical instrument (2) is a root canal instrument, preferably a root canal file or a dental drill.

5. Device according to Claim 1, characterized in that the electrical contact (3) is a sliding contact or a sliding-action contact.

6. Device according to Claim 1, characterized in that the counter electrode (7) has a larger surface than the surface of the rotating instrument (2).

7. Device according to Claim 1 or 6, characterized in that the counter electrode (7) is arrangeable on the patient or on the treatment equipment or on the practitioner.