[0001] This invention relates to an apparatus and method for magnetically stimulating nerves within a tooth, and more particularly but not exclusively for testing vitality of pulp tissue within a tooth.

BACKGROUND

[0002] Human teeth are a hard mineralized shell (the Dentine and Enamel) surrounding a "pulp" of blood vessels and nerves. The dentine, though hard, is a living tissue containing extensions ("processes") of odontoblast cells whose nuclei sit at the edge of the pulp. Dentine is a very tough tissue because it is a nanoscale mix of proteins (e.g. collagen) and hard minerals (e.g. hydroxylapatite), and the mix is actively maintained by the cells.

[0003] However, it is well known that teeth decay and this decay needs to be treated. Many people during their lifetime will experience one or more teeth that have deep decay and become painful and/or sensitive. When treating a decayed tooth, it is crucially important to know whether the pulp within the tooth is dead or alive (i.e. its vitality), because the treatment is very different in the two cases. If the pulp is dead a root canal procedure may be necessary in which the pulp chamber is opened, then cleaned out and filled with rubber. Once the pulp has been removed, the tooth is effectively dead and no new dentine will be produced within the tooth and this results in the tooth becoming gradually more brittle over time. For this reason, the tooth is often capped as part of the root canal procedure in order to protect it from fracturing.

[0004] On the other hand, a tooth in which the pulp is alive is generally treated by crowns and fillings, and care is taken not to open the pulp cavity. The prognosis for a live tooth, in which nutrients can continue to be delivered to the pulp via blood vessels and in which new dentine can continue to be produced to maintain the internal structure of the tooth, is generally much better than for a tooth which has undergone a root canal procedure. Thus, it is important to reliably detect the vitality of the pulp in a tooth undergoing treatment in order to allow a live tooth to be preserved if at all possible.

[0005] Currently, the most reliable method for diagnosing that a tooth is dead uses X-ray images obtained weeks or months after the tooth dies. Once a tooth dies it will at some point be colonized by bacteria, and the bacterial infection will lead to the formation of an abscess under the tooth. This abscess is visible on an X-ray, providing a clear indication that the pulp in the tooth is no longer alive. However, this is a very slow diagnostic and does not in itself allow the vitality of the pulp to be determined, relying on the detection of secondary effects caused by an infection in the pulp cavity of a dead tooth. The formation of an abscess under the tooth will generally result in a significant amount of pain being experienced by the patient before a clear diagnosis can be achieved from an X-ray of the tooth. Furthermore, the tooth itself may be put at increased risk by the undetected presence of the bacterial infection prior to the formation of an abscess, and the delay in diagnosing the pulp vitality may allow such an infection to spread beyond the dead tooth. For these reasons, waiting until an abscess has been formed in order to diagnose the vitality of the pulp is not satisfactory. Furthermore, it is generally preferable to limit the number of X-ray images taken both on cost grounds, and also in order to limit a patient's exposure to ionizing radiation.

[0006] Electronic pulp testers have been developed in an attempt to allow pulp vitality to be determined more easily and without waiting for an abscess to be formed underneath the tooth. These electronic pulp testers work by passing a current from an electrode into the tooth in an attempt to stimulate nerves within the pulp chamber of the tooth. The magnitude of the current required to cause a sensation in the tooth is measured and used to diagnose the vitality of the tooth pulp. If the tooth is alive, the magnitude of the current needed to cause a sensation should be low as nerves in the pulp are stimulated; however, if the tooth is dead, more current should be needed as the first available nerves are below the tooth and the current is spread over a larger area. [0007] Unfortunately, in clinical practice, it is common for teeth needing to be tested to have previously been treated and therefore to comprise large fillings. Such fillings may be insulators, or metallic, or metallic in an insulating bed, and will therefore substantially change the path of the current flow. Because the shape of the filling is not precisely known, and especially if the filling and/or the tooth around it may be damaged in unknown ways, the amount of current that flows through the pulp chamber is unpredictable. The variation in current flow through teeth is so large that readings for live teeth can overlap readings for dead teeth, and thus in practice it has been found that the technique cannot give a reliable answer.

[0008] Other techniques have been used for example applying cold to a tooth and waiting for a reaction from the patient, but such tests may be subjective, awkward to apply to the tooth, and may still be unreliable when applied to a tooth with fillings.

[0009] In Endodontics: Part 2 diagnosis and treatment planning {Br Dent J, 197(5):231 -238, Sept. 2004, doi:10.1038/sj.bdj.481 1612) P. Carrotte said of currently available techniques that "Most of the diagnostic tests used to assess the state of the pulp and periapical tissues are relatively crude and unreliable. No single test, however positive the result, is sufficient to make a firm diagnosis of reversible or irreversible pulpitis". [0010] Thus, at present there is no reliable method to test whether a tooth is dead or alive.

[0011] Transcranial Magentic Stimulation (TMS) is a common experimental technique in Experimental Psychology. By applying a rapidly changing magnetic field to the head of a subject, TMS uses electromagnetic induction to induce an electric current in parts of the subject's brain, which results in neural activity. Typically, the region of the brain which is stimulated can be targeted to within a few centimeters.

[0012] TMS is known to have a number of side effects on the patient, including causing discomfort or pain from the stimulation of the scalp and associated nerves and muscles on the overlying skin. [0013] It is an aim of embodiments of the present invention to at least partly mitigate the above-mentioned problems associated with the prior art.

[0014] It is an aim of certain embodiments of the present invention to provide an apparatus for determining the vitality of pulp within a tooth independent of the presence of any fillings in the tooth.

BRIEF SUMMARY OF THE DISCLOSURE

[0015] According to a first aspect of the invention, there is provided an apparatus for magnetically stimulating pulp within a tooth, the apparatus comprising a magnetic core, and stimulation means for causing a changing magnetic field to be generated in the magnetic core, and wherein the apparatus is configured to apply the generated changing magnetic field to the tooth.

[0016] The stimulation means may comprise a coil magnetically coupled to the magnetic core, and may further comprise an LC resonator circuit.

[0017] The magnetic core may comprise a 'c'-shaped magnetic core, wherein the 'c'-shaped magnetic core may include a gap configured to receive a tooth to be stimulated. Alternatively, the magnetic core may comprise a rod shaped magnetic core.

[0018] The apparatus may be contained within an electrically isolating material.

[0019] According to some embodiments, the stimulation means may comprise a permanent magnet arranged to be swept past the magnetic core. The permanent magnet may be coupled to a rotor arranged to sweep the magnet past the magnetic core upon rotation of the rotor. A plurality of permanent magnets may be distributed around the circumference of the rotor.

[0020] The magnetic core may comprise a laminated soft iron core. Alternatively, the magnetic core may comprise a ferrite core. [0021] According to embodiments, the maximum amplitude of the changing magnetic field may be greater than 0.5T. According to further embodiments, the maximum amplitude of the changing magnetic field may be greater than 1.5T.

[0022] According to a further aspect of the invention, there is provided a system comprising an apparatus as described above, the system may further comprise a capacitor coupled to the coil, and control circuitry configured to precharge the capacitor and to initiate discharge of the capacitor into the coil.

[0023] The control circuitry may be configured to cause a series of magnetic pulses to be generated in the magnetic core by repeatedly charging and discharging the capacitor into the coil. Each magnetic pulse in the series of magnetic pulses may have a greater or smaller magnitude than a preceding magnetic pulse.

[0024] The system may further comprise a hand held switch, and the control circuitry be configured to stop generation of any further pulses upon activation of the hand held switch.

[0025] According to a further aspect of the invention, there is provided a method of testing vitality of pulp within a tooth, the method comprising applying a changing magnetic field to the tooth to thereby induce an electric current within the pulp, and determining if a sensation is felt in the tooth in response to the changing magnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 shows a high level representation of a magnetic stimulation device according to embodiments of the invention;

Figure 2 illustrates a simulated magnetic flux density in a 'C'-shaped magnetic core according to embodiments of the invention;

Figure 3 illustrates a magnetic stimulation device according to embodiments of the invention;

Figure 4 shows a schematic representation of a system for testing pulp vitality including a magnetic stimulation device; and

Figure 5A and 5B illustrate side and front views respectively of a mechanically operated magnetic stimulation device according to embodiments of the invention.

DETAILED DESCRIPTION [0027] Embodiments of the present invention provide a Magnetic Dental stimulator that can be used to magnetically stimulate dental pulp, and in particular nerves within the pulp, contained within a tooth to allow vitality of the pulp to be determined.

[0028] Figure 1 provides a high level representation of a magnetic stimulation device 10 according to embodiments of the invention. The device 10 illustrated in figure 1 comprises a magnetic core 12, and an excitation coil 14 wound around the magnetic core 12. The magnetic core 12 comprises a 'C'-shaped core with a gap 18, the gap being of a suitable size to contain a tooth 16 to be tested. In the described example, the magnetic core 12 may be made of laminated soft iron or ferrite, although it will be recognized that any of a range of 'soft' magnetic materials could be used.

[0029] In operation, the device is placed in the mouth of a patient such that a tooth 16 to be tested is located within the gap of the magnetic core 12. An oscillating current is then applied to the coil 14 such that an AC magnetic field is generated within the magnetic core. For example a capacitor can be discharged into coil 14 to generate a large electric current in the coil which in turn produces the magnetic pulse. Due to the location of the tooth 16 within the gap 18, the magnetic field is applied to the tooth 16. Typically, the duration of the magnetic pulse is in the order of 1 ms and the maximum magnitude of the magnetic pulse may be a number of tesla leading to a very high rate of change of magnetic field in the order of kilotesla per second.

[0030] According to Faraday's Law of induction, the changing magnetic field passing through the dental pulp of the tooth 16 will generate an electrical field in the pulp. If the pulp within the tested tooth 16 is alive, the electrical fields generated within the pulp may stimulate the nerves within the pulp, leading to a sensation that can be felt by the patient. However, if the pulp is dead, no nerves will be stimulated by the generated electrical field, and no sensation will be reported by the patient. Thus, the magnetic stimulator device 10 can be used to determine vitality of pulp within a tooth.

[0031] In practice, an operator may gradually increase the magnitude of the applied magnetic pulse until some sensation is reported by the subject, and then compare the applied dB/dt value against values for known live or dead teeth in order to determine the status of the tested tooth.

[0032] As will be appreciated from this disclosure, operation of the above described magnetic stimulation device relies on the usually undesirable side effects of applying a changing magnetic field to the human body, as discussed above in relation to transcranial magnetic stimulation. In particular, the changing magnetic field is applied to the tooth in order to cause a sensation, which may be experienced as pain or discomfort, as sometimes results in the scalp of a subject when TMS is applied.

[0033] However, in contrast to TMS the magnetic pulse applied by the magnetic stimulation device 10 is targeted to a much smaller region, i.e. limited to the size of the tooth or less so that only one tooth is stimulated at one time. This targeting is achieved by the use of the magnetic core to guide the applied magnetic field, along with the ability to bring the device into close proximity with a region to be stimulated which is not possible in TMS. Furthermore, the magnetic stimulation device of the present invention may produce a higher rate of change of magnetic field than TMS devices in order generate a sufficiently large potential across the nerve cells being targeted, which are typically smaller than those cells targeted by TMS.

[0034] The materials traditionally used to form fillings in teeth are substantially non-magnetic, and as such, the applied magnetic field will not be significantly affected by the presence of fillings in the tooth. Similarly, while the magnetic pulse may generate a force on conductive filings present in the tooth, this force is not of a sufficient magnitude that it could lead to loosening of fillings which would be undesirable. Finite element simulations of the effects of a magnetic pulse on fillings show that while some eddy currents may be induced in conductive fillings, the magnitude of the eddy currents remain relatively small and will have limited effects on the testing process.

[0035] According to embodiments of the invention, the magnetic core 12 may be formed of laminated soft-iron or ferrite, or other suitable magnetic material. As the magnetic stimulation device 10 is to be placed into a subjects mouth during testing in order to bring the device into close proximity with a tooth to be tested, the device may be sealed against liquid, for example by impregnation with epoxy resin in order to electrically isolate the device from the subject.

[0036] Figure 2 illustrates a finite element analysis of surface magnetic flux density in a magnetic core 12 during operation of a magnetic stimulation device 10 according to embodiments of the invention. In particular, Figure 2 illustrates that a magnetic field strength of 1 .5T can be generated in a gap of 5mm of an ordinary C-core magnet using laminated soft- iron. In the example simulation, a 1 ms pulse was achieved using a simple RLC circuit (for example using a Capacitance of 2mF, a peak voltage of 30V and a peak current of 100A). Such a 1 ms pulse results in a dB/dt passing through the tooth pulp that is comparable to values applied in TMS.

[0037] For embodiments implemented using a ferrite core the maximum magnetic field strength that can be generated is reduced, for example the maximum magnetic field strength may be limited to around 0.5T. However, other aspects of the described apparatus remain the same as for the soft iron cored embodiment. [0038] As can be seen in Figure 2, the maximum magnetic field strength within the gap 18 is tightly restricted to a small, focused, region. Outside this focused region of maximum magnetic field strength, the magnetic field strength is seen to rapidly fall to a low level.

[0039] In order to stimulate nerves, it is generally necessary to exceed a certain threshold level of electrical field strength applied to the nerve cells. As the induced electrical field strength depends on the magnitude of the rate of change of the magnetic field, the induced electrical field within the tooth will also be concentrated within the focused region containing the maximum magnetic field strength. Thus, unless very high magnetic fields are applied to the tooth 16, nerves within the pulp will only be stimulated if they are within the focused region. This allows embodiments of the invention to limit stimulation of nerves to within a small region of the tooth. According to some embodiments, by arranging for the focused region to pass through different parts of the same tooth, it is possible to test vitality of tooth pulp within different roots of the same tooth, and to thereby map vitality of pulp in different regions of a tooth. [0040] While in the above example, a field strength of 1 .5T was generated having a duration of 1 ms, the invention is not limited to these values. Rather, as discussed above the maximum field strength of the magnetic pulse may be increased as subsequent pulses are applied to a tooth. Furthermore, different teeth having different sizes and configurations, the maximum magnitude of the magnetic pulse may be controlled according to the type of tooth being tested.

[0041] Figure 3 illustrates an alternative arrangement of the magnetic stimulation device 30 in accordance with embodiments of the invention. In the embodiment of Figure 3, the magnetic core 32 is rod, or 'pen', shaped having a coil 34 wound around the magnetic core 32. An end 36 of the magnetic core is tapered and provides an application end to be applied to a tooth to be tested.

[0042] In operation, the tapered end 36 of the magnetic stimulation device 30 is held against a tooth and a magnetic field is generated as described above with reference to the magnetic stimulation device of Figure 1. The 'pen like' embodiment shown in Figure 3 is easier to handle for the operator when testing teeth, and may be more comfortable for the subject of the test.

[0043] Figure 4 illustrates a system including a magnetic stimulation device as described above, along with control circuitry 40 for controlling testing of one or more teeth using the stimulation device. The control circuitry controls the application of voltage and current to the coil 34, and thereby controls the generation of one or more magnetic pulses to be applied to a tooth during testing. In the example system of Figure 4, the control circuitry 40 include a capacitor 44, a precharging circuit 42 for precharging the capacitor to a selected level, and discharge control circuit 46 for triggering discharge of the capacitor through the coil 34 of the magnetic stimulation device 30 to thereby generate the magnetic pulse.

[0044] According to some embodiments, once a test has been initiated, a series of magnetic pulses may be generated with each subsequent pulse increasing in magnitude until a sensation is reported by the test subject. A hand held switch may be provided, coupled to the control circuitry, and arranged to be held by the test subject during testing to allow the subject to signal when a sensation is felt in the tooth being tested.

[0045] Alternatively, a suitable capacitor may be integrated into the magnetic stimulation device to reduce the distance between the capacitor and the coil 14. Such an arrangement allows for a shorter conduction path between the capacitor and the coil which may help to reduce electrical losses in the system.

[0046] While in the above discussion, the magnetic stimulation device has been described as applying magnetic pulses to the target tooth, according to other embodiments other wave forms, for example sinusoidal, square wave, or sawtooth patterns, could be used. Alternatively, stimulation of the tooth may be performed using a sequence of magnetic impulses with each pulse in the sequence having equal or different magnitudes. According to some embodiments a sequence of pulses or a wave forms may be applied having a frequency of between 10 Hz and 10 kHz.

[0047] Figure 5A and 5B illustrate a further embodiment of the invention which employs one or more permanent magnets to generate a changing magnetic field in a magnetic core 52, and hence does not require a power supply to generate the magnetic field for testing pulp vitality of a tooth. Rather, the change in magnetic field is achieved by introducing and removing the permanent magnet from the magnetic circuit.

[0048] Figure 5A shows a side view of the mechanically operated embodiment in which a soft iron magnetic 'core' 52 has a first end which is configured to be held in proximity to a tooth 16 to be tested. A permanent magnet 54 is attached to a rotor, or disc, 56 which can be rotated such that the permanent magnet is swept past a second end of the magnetic core 52 on each rotation of the rotor 56. The movement of the permanent magnet past the magnetic core 52 generates a changing magnetic field in the magnetic core 52 which is then applied to the tooth 16. The permanent magnet may, for example, be a magnet made of neodymium iron boron (NdFeB).

[0049] In use, the rotor 56 is rotated at a high frequency, for example using an electric motor, leading to a rapidly changing magnetic field being generated in the magnetic core 52 and thereby applied to the tooth 16. In some embodiments, multiple permanent magnets may be carried on the rotor 56, distributed at equal distances from each around the circumference of the rotor, thereby reducing the frequency at which the rotor 56 must be rotated to generate a changing magnetic field of a certain frequency. Alternatively, the multiple permanent magnets may be distributed around the circumference at different distances from each other to generate a desired pattern of changing magnetic fields in the magnetic core 52.

[0050] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0051] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0052] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.