FIELD OF THE INVENTION This invention relates, in general to an oral treatment to kill

Porphyromonias gingivalis bacteria and, in particular, to the use of a nonthermal gaseous plasma to treat halitosis, to a method of breath freshening, to a device for use in treating halitosis, and to a kit for use in treating halitosis, the use, the method, the device and the kit being able to perform the function of killing at least some of the Porphyromonias gingivalis bacteria in the oral cavity of a human being (or animal).

BACKGROUND OF THE INVENTION The Porphyromonias gingivalis {P. gingivalis) bacterium is an anaerobic bacterium which plays a key role in the development of halitosis. This bacterium is able to break down certain sulphur-containing peptides or proteins into a complex mixture of molecular volatile compounds including H ₂ S, CH ₃ SH and certain volatile fatty acids. The bacterium also gives rise to the dental condition, gingivitis, which is common in the adult population and which, if left untreated, may give rise to periodontal disease, a disease which not only prejudices the dental health of sufferers, but can be life threatening in the case of people who have chronic heart disease or diabetes. It is therefore important to reduce and preferably eliminate the population of P.gingivalis bacteria in the oral cavity of a person who is suffering from halitosis or bad breath.

The most effective day-to-day treatments for halitosis involve the use of a mouthwash which contains an antibacterial agent. Preferred mouthwashes are generally considered to be those that contain chlorhexadine, typically at a level in the order of 0.2% by weight. See, for example, "Microbiology and treatment of Halitosis", Loesche et al, Periodontology, 2000, Vol. 28, 2002, pp 256 to 279.

However, in practice, such mouthwashes rarely provide a complete solution to the problems posed by the presence of significant colonies of the P.gingivalis bacterium in the oral cavity of a person seeking to treat bad breath or halitosis.

It is therefore an aim of the invention to provide an alternative or additional treatment means.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided the use of a non-thermal gaseous plasma to treat halitosis in vivo by killing at least part of a population of Porphyromonas gingivalis bacteria in the oral cavity of a or mammal.

According to a second aspect of the present invention there is provided a method of treating halitosis in vivo comprising introducing into the oral cavity of a human (or mammal) suffering from halitosis a flow of a non-thermal gaseous plasma at a temperature acceptable for oral administration of the non-thermal gaseous plasma and for a time sufficient for the non-thermal gaseous plasma to kill at least a part of any population of Porphyromonas gingivalis bacteria in said oral cavity.

According to a third aspect of the present invention there is provided a method of freshening breath comprising introducing into the oral cavity of a human (or mammal) a flow of non-thermal gaseous plasma at a temperature suitable for oral administration and for a time sufficient for the non-thermal gaseous plasma to kill at least some of any Porphyromonas gingivalis bacteria present in the oral cavity. According to a fourth aspect of the present invention there is provided a device for treating halitosis comprising a generator of a non-thermal plasma and an applicator communicating with the generator, the oral applicator comprising a member which has a configuration such that it may be

positioned over the tongue and direct non-thermal plasma having a

temperature suitable for oral administration at the back of the tongue, whereby, in use, the non-thermal plasma is able to kill at least a part of any population of Porphyromonas gingivalis bacteria present.

According to a fifth aspect of the present invention there is provided a kit for treating halitosis comprising a generator of a non-thermal plasma and an oral applicator communicating or able to be placed in communication with the generator, and a set of instructions for using the generator and applicator to treat halitosis by killing at least a part of a population of Porphyromonas gingivalis that is present in the oral cavity of the or mammal to be treated.

The use, methods, device and kit according to the invention all exploit the discovery that a non-thermal gaseous plasma has a bactericidal effect on the Porphyromonas gingivalis bacterium.

It is believed that a non-thermal gaseous plasma may have bactericidal effects on other anaerobic bacteria that may contribute to halitosis, for example, Fusobacterium nucleatum, Treponena denticola, Prevotella intermedia, B forsythus, and Eubacterium. Those bacteria are all found in the oral cavities of human beings and can all produce appreciable quantities of CH ₃ SH and H ₂ S, from methionine, cysteine or serum proteins.

The term 'non-thermal gaseous plasma' as used herein includes with in its scope a non-thermal gaseous plasma that has partially or totally decayed or collapsed but still contains active species in the form of radicals or excited atoms or molecules. The excited atoms are able to react with ambient air to form single oxygen atoms and hydroxyl radicals.

The non-thermal plasma may comprise or consist of a noble gas or a mixture of noble gases. Helium may readily be converted into a non-thermal gaseous plasma, Its fugacity may assist in the treatment of halitosis or in breath freshening. A non-thermal plasma of helium consists of a mixture of helium ions, electrons, and excited states of the helium ions, electrons, and excited states of the helium atom. It is believed that on encountering air, the non-thermal helium plasma will react with the components of air to form a number of different species including single oxygen atoms and hydroxyl radicals (if the air is moist) to which we believe the bactericidal properties of the non-thermal plasma may be attributable. A gaseous non-thermal plasma of, say, argon has a similar effect to that of helium, but requires more energy for its formation. The initial non-thermal plasma contains ions, electrons, and excited atoms or molecules. Each of these species has a given half-life. The non-thermal plasma will itself decay as ions and electrons recombine. In the use, methods and device according to the invention, the non-thermal plasma may have collapsed by the time of its contact with halitosis-causing bacteria. Even if in a collapsed state, the non-thermal plasma is believed to have bactericidal properties, through entrainment of air gases which react with residual excited atoms or molecules to form free radicals.

Because a non-thermal plasma of noble gas will react readily with ambient air, there is no need to include any oxygen or other component in the gas from which the non-thermal plasma is generated. Indeed, the inclusion of, say, 5% by volume of oxygen may increase the energy required to form a non-thermal plasma and may result in the formation of undesirably high concentrations of ozone. In general, therefore, it is permissible to minimise the presence of oxygen impurity in the noble gas, although some oxygen impurity may be difficult to avoid. The non-thermal plasma preferably enters the cavity at a temperature in the range of 10 to 40°C. Higher temperatures may be used provided no thermal damage to the oral cavity or the gums or teeth is caused. In general, a temperature in the range of 25 to 35°C is ideal, as at such temperatures the non-thermal plasma will not cause any unpleasant sensations in the oral cavity. In general, a non-thermal plasma is not able to be produced below the ambient temperature except if cooling is applied to the gaseous plasma during or after its generation. The non-thermal plasma is preferably directed at those locations in the oral cavity which are prone to colonisation by the Porphyromonas gingivalis bacterium. These locations include interdental spaces and the back of the tongue. Even short treatment times are believed to be beneficial, provided the treatment is regularly repeated. For example, a person may include the methods according to the invention as part of their normal dental hygiene, and perform this at least twice a day. Each anti-bacterial treatment may last from 30 seconds to 300 seconds, but can be shorter. In the time allotted to the treatment, a flow of the non thermal plasma can be directed at the interdental spaces and the back of the tongue. The treatment can be combined with tongue scraping and can be performed in sequence with gargling with a mouthwash, particularly an anti-bacterial mouthwash, and/or cleaning teeth using a toothbrush and toothpaste.

In the device according to the invention, the generator preferably includes at least one electrode and forms part of a handset. The handset preferably contains in addition to a plasma generator, a capsule containing under pressure a gas able to be converted into a non-thermal plasma. The handset preferably also includes a source of electrical energy, typically a rechargeable battery (or a plurality of such batteries), and signal generator means for converting electrical energy from said source into a pulsed signal which when applied to the electrode or electrodes of the plasma generator is able to convert gas passing from the capsule through the generator into a non-thermal plasma. The handset may include a suitable switch or switches for initiating a flow of gas from the capsule to the plasma generator and for initiating a flow of electrical energy to the signal generation means. The handset containing the plasma generator, the source of electrical energy, the signal generation means and the gas capsule preferably has a size and weight such that it can be both held and operated by a user by hand, the flow of non-thermal plasma being directed at a region for treatment within the oral cavity of a user.

Alternatively, the source of electrical energy, the signal generation means, a gas supply such as a cylinder and the plasma generator may all be discrete units separate from one another.

A sensor may be provided for sensing the flow of gas released from the gas capsule. Preferably the said switch is arranged to allow activation of the signal generation means only if the flow of gas is above a predetermined mass or volume flow rate.

The said oral applicator may include physical tongue scraping means.

The said oral applicator preferably has at least one and preferably a plurality of outlets for plasma, the outlets adapted to impart to the non-thermal plasma a component of velocity in the direction from the back to the front of the tongue.

The kit according to the present invention may include a plurality of interchangeable oral applicators. Such applicators may comprise firstly, a lower hollow gum shield having orifices for directing non-thermal plasma at the user's lower teeth, secondly an upper hollow gum shield having orifices for directing non-thermal plasma at the user's upper teeth, thirdly a hollow needle or hollow pick for directing non-thermal plasma interdentally, and fourthly a member adapted to be inserted in the oral cavity over the tongue and to direct non-thermal plasma from the back to the front of the tongue.

BRIEF DESCRIPTION OF THE DRAWINGS

The users, methods, device and kit according to the present invention will now be described, by way of example, with reference to the

accompanying drawings, in which:

Figure 1 is a schematic block diagram of equipment for use in generating a non-thermal plasma which may be used in the methods according to the invention;

Figures 2 to 4 are schematic diagrams of a handheld plasma generator according to the invention;

Figure 5 is a schematic diagram of an applicator for use in conjunction with the apparatus shown in Figure 1 or Figure 2, the applicator being adapted to apply a non-thermal plasma to the user's tongue;

Figure 6 is a schematic diagram of an alternative applicator to that shown in Figure 5, and

Figure 7 is a sectional side elevation of a gas capsule for use in the handheld plasma generator shown in Figures 2 to 4;and

Figure 8 is a schematic diagram illustrating the engagement of an applicator with the housing or handpiece of a plasma generator as shown in any one of Figures 2 to 4.

The drawings are not to scale. DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Figure 1 shows the apparatus used in the experiments to be described below. This apparatus comprised a gas supply unit 102, an electrical signal generating unit or means 104, and a handheld plasma generator unit 106.

The gas supply 102 consisted essentially of a small (one litre water capacity) cylinder 110 containing compressed helium under a pressure of 200 bar. The cylinder 110 was fitted with a valve 112 of a kind containing an integral pressure regulator which reduced the pressure of gas drawn from the cylinder 110 to 8 bar gauge. The valve 112 communicated with a heavy duty flexible hose 114 providing a path for the flow of helium gas from the cylinder 110 to the plasma generator unit 106. The hose 114 had disposed therealong a flow control valve 116 to enable the rate of flow of helium to the plasma generator unit 106 to be adjusted, and a pressure regulator 118 which was set to deliver helium to the plasma generator 106 at a pressure of 0.5 bar gauge (1.5 bar absolute). The signal generation unit 104 was essentially a device for converting a 12V DC signal into a 6kV AC plasma driving signal for generating the nonthermal plasma. In addition, the unit 104 provided a microcontroller for controlling the gas supply to the plasma generator unit 106. The signal generator 104 comprised a 12V rechargeable battery 120 associated with a main on/off switch 124 for powering up a logic circuit 122. The logic circuit 122 was, as shall be described below, used to ensure that the plasma generator would operate only in certain circumstances. The battery 120 also had associated with it a monitor 126 for displaying a low battery power condition. Depression of the switch 124 caused the logic circuit 122 to initiate operation of a low voltage signal generator 128 able to generate a pulsed low voltage AC signal from a DC voltage source and to transmit the signal to a high voltage signal generator 130. The signal generator 130 was able to produce a pulsed AC signal of 6KV, the pulses being produced on a 15% duty cycle, i.e. for 85% of its operating time the generator means 130 produced no signal. The voltage and frequency of the signal produced by the signal generator 130 was controlled by means of voltage/frequency control circuits 132. The arrangement was such that the signals would be produced by the generator 130 only if the main switch 124 was on and the logic circuit 122 indicated that the gas was flowing to the plasma generator unit 106.

The handheld plasma unit 106 had an on-off switch 140 which when in its "on" position, caused a signal from the logic circuit 122 to activate a solenoid valve 150, as shall be described below. The arrangement was such that the plasma generator was operated only when the switch 140 was in its "on" position. The unit 106 had a gas inlet 142 connectable to the hose 114. The gas inlet 142 led to a passage 144 leading to a plasma generator cell 146. The cell 146 had a pair of spaced apart electrodes (not shown), both acting through quartz dielectrics (not shown). The high voltage signal from the signal generator 130 was applied across the electrodes of the cell 146. The arrangement was, however, that no such voltage was applied until a predetermined time after a flow sensor 148 in the passage 144 transmitted a signal to the logic circuit 122, the circuit 122 enabling the high voltage signal to be generated by the generator 130 only after a predetermined time delay. Operation of the switch 140 to place it in its "on" position enabled the logic circuit 122 in the unit 104 to send a signal to open a solenoid valve 150 at the inlet to the plasma generator cell 146. Opening of a solenoid valve 150 caused helium to be admitted to the plasma cell 146, the helium flowing therethrough to an applicator 152. The unit 106 was held in an operator's hand so as to direct the non-thermal helium plasma at a chosen target.

In operation the helium cylinder 110 contained helium of 99.9999% purity. The apparatus shown in Figure 1 was used to conduct the following experiment.

Porphyromonas gingivalis bacteria were grown under anaerobic conditions on fastidious anaerobe agar (FAA) plates for 3 to 5 days. They were then suspended in phosphate buffered saline (PBS) solution to gain an optical density (OD) reading of 0.6 at 600nm. The resulting culture was transferred in aliquots of 1 ml per well into a six well plate. The plate was subjected to treatment with a non-thermal helium plasma at approximately 25°C for varying amounts of time. Results at zero, 30 and 300 seconds are given below. A non-treated control sample was included. To measure the effect of the non-thermal helium plasma on the bacteria, the samples were plated out using a WASP 2 spiral plater. The places were incubated anaerobically for three days and the colonies counted, from which a calculation of the number of Colony Forming Units (CFUs) in each culture at the time of transfer to the Wasp plates was made using the Wasp calculation system.

Results

Time/s No. of CFUs/m ¹

0 (control) 4.0 x 10 ⁸

30 3.6 x 10 ⁸

300 1 .6 x 10 ⁸

The results demonstrate a distinct bactericidal effect of the helium nonthermal plasma on the P. gingivalis bacteria.

It is believed that an improved experimental protocol would be able to achieve improved results. It was noted during the experiments that the jet or plume of nonthermal helium plasma discharged from the apparatus almost instantaneously developed a blue colour indicating that the non-thermal plasma was

interacting with the surrounding atmosphere, the blue colour being indicative of emissions from the nitrogen ions. It is believed that the plume of nonthermal plasma induces gas molecules into it from the surrounding

atmosphere to produce bactericidal species including but not limited to hydroxyl radicals. For home use, it is desirable to substitute for the apparatus shown in

Figure 1 , a wholly hand held device as shown in Figures 2 to 4.

Referring to Figures 2 and 4, a device 210 is shown for generating a non-thermal plasma which may be a flow of gas plasma in the form of a gas plasma plume or jet emitted from the device. The flow of gas plasma is generated and emitted from the device generally at atmospheric pressure. The device comprises a gas capsule, or pressure vessel, 212 for holding a gas or mixture of gases 214 under pressure and forming a flow of gas through a plasma generator 216 to an applicator 218 when released from the capsule. Gas released from the gas capsule is energised in the plasma generator to form a gas plasma.

The device further comprises a source 220 of electrical energy and gas plasma energising (signal generating) means 222 electrically connected to the source 220 of electrical energy for energising gas 214 in the plasma generator 216 to form a gas plasma. The applicator 218 directs flow of plasma from the plasma generator 216 to an opening 226 in the applicator and the plasma may issue from the opening 226 in the form of a plume.

A handpiece (or housing) 228 houses the gas capsule 212, plasma generator 216, source of electrical energy 220, and plasma energising means 222. The device is sized and of a weight such it can be held and operated by a user by hand and the plasma 224 readily directed by a user into their oral cavity. In this regard, the device 210 is operable without the requirement for its connection by a gas line to an external gas supply. Such a prior art arrangement can be inconvenient. The self-contained arrangement of the device 210 allows easy use in a domestic environment, for instance, in a bathroom. The device 210 may receive power from the source without the requirement for electrical cabling connecting the device to a mains supply. However, typically electrical cabling is less of an impediment to use in the domestic environment than a gas line, as cabling is usually flexible and lightweight, although in device 210 electrical cabling is not required when the device is in use.

In order that the device is suitable to be held and operated by hand, it should not exceed an upper size or an upper weight. It will also be appreciated that treatment of a region within the oral cavity using the device may require intricate and fine movements which are possible if the device is hand-held only if it is relatively light. In one example, the device is

approximately the size and mass of a typical electric tooth brush. Other known hand-held and operated devices in other fields, which are referred to herein to aid understanding of the size and mass of the device 210, are for example, aerosol cans. The upper size of handpiece 228, or the device as a whole, may be approximately 30cm in length by 5cm in breadth. The upper limit of the breadth is determined by the ability of a hand to hold the device. Otherwise the device becomes uncomfortable to hold and use. The upper limit of the length is determined by the ability of a user to use the device without it becoming unwieldy and it will also be appreciated that because the device is used to treat the oral cavity, the device will normally be less than an arm's length and preferably in the region of about 20 cm or less. Preferably, the handpiece 228 is contoured to so that it can be held comfortably in the palm of the hand. The mass of the housing, or device as a whole, is preferably less than one kilogram. ln an alternative arrangement (not shown), the capsule containing compressed gas is located externally of the housing 228 and docks therewith. In such an arrangement, the device can be held by the capsule rather than the housing 228.

The components of device 210 will now be described in more detail, giving modifications and alternatives where relevant. A control indicated generally at 230 is provided for selectively releasing gas from the gas capsule for forming the flow of gas. As shown in this example, the control comprises a valve 232 which when open allows the flow of gas through a conduit from the gas capsule 214 to the plasma chamber 216, and when closed resists flow. The control 230 comprises a mechanical push switch 234 which can be operated by a user for controlling the valve 232. Alternatively, other user activation means can be provided to operate the valve, such as a mechanical slide switch or an electronic switch which can be closed for example to open a solenoid valve. Still further, the user activation means may be adapted such that flow can be activated from the gas capsule in response to first user input and deactivated in response to a second user input.

The valve 232 may be any suitable means for opening and closing flow between the gas capsule and the plasma generator. Further, the valve may be variable for adjusting the flow between fully open and fully closed, for example a butterfly valve.

The handpiece 228 comprises means 236 for locating the gas capsule 212 in the housing so that the gas capsule is operable to release gas for forming the gas flow. The locating means 236 may be adapted such that the gas capsule 212 can be removed from the housing 228, for example when the gas contained therein is depleted or low so that a replacement gas capsule which is full can be located in the housing. In this regard, the locating means 236 may comprise a chamber shaped for receiving the gas capsule and a closure member (not shown) for closing the chamber when the gas capsule 212 is located in the chamber. In another example, the gas capsule may be push-fitted or screw-fitted into the chamber.

The handpiece may comprise a formation or other gas release mechanism operable to release gas from the gas capsule when the locating means locates the gas capsule in the chamber. The gas capsule may comprise a pressure release valve biased to prevent the release of gas from the pressure vessel. The gas release mechanism operates on the pressure release valve against the bias so as to release gas from the capsule.

One example of the gas release mechanism and pressure release valve is shown in Figure 7. The gas capsule 212 cooperates with a member 238 having an outlet to afford communication between the gas capsule 212 and the plasma generator 2 6, the member 238 forming part of the locating means 236. The gas capsule 212 comprises a valve 240 at the head 242 of the capsule. In this example, an outer surface of the head 242 is threaded for engaging with a complementary threaded surface of the member 238 so as to locate the pressure vessel in position. The valve 240 comprises a sliding member 244 received for sliding movement in the neck of the pressure vessel and biased by a biasing means, which in this example is a spring 246, into a closed position. When the pressure vessel is located in the housing, a formation, or protrusion, 248 engages the sliding member 244, pushing it into the vessel and opening the valve to allow gas flow from the vessel. The valve 240 has sufficient sealing strength to retain gas in the pressure vessel at the maximum pressure of the vessel, for example, 80 bar. The valve may, for example, be a Schrader valve.

Although a separate valve 232 is shown in Figure 2 for selectively allowing flow of gas to the plasma generator 216 in addition to the pressure release valve 240, in an alternative arrangement, as shown in Figure 3, the separate valve 232 can be omitted such that gas is released from the capsule 212 solely by the pressure release valve 240, the gas flowing into an expansion chamber 215 via an orifice plate 213. The separate filler valve 252 shown in Figure 2 is also omitted from the device shown in Figure 3.

Referring again to Figure 2, the mass or volume flow rate of gas entering the plasma chamber 216 may be regulated so as to control the generation of plasma. For instance, the rate of flow controls the residence time of gas in the plasma chamber. Accordingly, the device 210 may comprise a flow regulator 250 for regulating the flow of gas between the gas capsule and the plasma generator. Additionally or alternatively, a flow regulator can be located to regulate the flow of gas and plasma from the plasma generator. The flow regulator may be a variable flow control valve arranged in a feed back loop with a flow sensor. As an alternative to a flow regulator, a pressure regulator may be provided for regulating the pressure of gas in the plasma generator. Preferably, the flow regulator is operable to achieve constant flow of gas to the plasma generator throughout a pressure range of gas in the gas capsule that is, a relatively high pressure when the capsule is full and a relatively low pressure when the capsule becomes empty.

The gas capsule may contain a sufficient amount of gas for generating a plasma plume or jet for at least two minutes.

The amount of gas which can be contained in the pressure vessel, or gas capsule, is limited by the design of the pressure vessel and overall weight and size of the device. In this latter regard, a relatively heavy pressure vessel may be capable of storing large quantities of gas, however, such a heavy vessel is not suitable for the device 210 as it would render the device incapable of being held and operated by hand. It has been found that a suitable gas capsule is adapted to contain the equivalent of approximately four litres of gas at atmospheric pressure stored at a pressure of at least 80 bar. The gas capsule may, for example, have an internal volume sufficient to contain between5ml to 100ml of water. The gas capsule may be generally cylindrical and less than 100mm in length and 35mm in diameter. In the example shown in Figure 7, the gas capsule is approximately 100 mm in length and 35 mm in diameter. The vessel may be made from aluminium or stainless steel, or mild steel or any other suitable robust material.

As shown in Figure 2 and described in more detail below, the device 210 comprises a filler valve 252 for allowing gas from a gas supply to re-fill or recharge the gas capsule 212. The filler valve 252 is, in normal use, closed to prevent evacuation of gas from the gas capsule and can be opened when it is desired to recharge the vessel. The valve 252 may be similar to the arrangement shown in Figure 2 in that a recharging unit engages with the valve 252 to open the valve and allow the recharging of gas. Additionally, the gas capsule may be formed integrally with the housing 228 and re-filled when empty. Alternatively the gas capsule 212 can be withdrawn from the device 210 and inserted into a recharging unit 334 by the user. The recharging unit may include electrical recharging circuits 336 connectable to a mains electricity supply and a gas supply 338 adapted to recharge the gas capsule 312. In another alternative, an empty gas capsule is simply replaced by a full one.

The plasma energising means 222 comprises two electrodes 254, 256 for generating an electric field in the plasma generator 216. In certain configurations a single electrode may be provided and more than two electrodes may be provided for example with two electrodes receiving a driving signal and one electrode being earthed. A signal generator 258 generates an electrical signal for driving, or energising, the electrodes. At least one, and preferably both or all of the electrodes are dielectric barrier discharge electrodes insulated from gas in the plasma chamber by a dielectric to prevent excessive heating of the plasma caused by continuous or prolonged arcing. Suitable dielectric materials are ceramic, plastics or glass. Insulating the or each electrode reduces the duration of arcing in the plasma chamber when an electric current flows from one electrode through the plasma or gas to the other electrode or each of the other electrodes.

The electrodes 254, 256 are spaced apart one from another in order to generate an electric field that occupies most of the plasma chamber. In this way, it is possible to increase the formation of plasma since gas in all portions of the plasma chamber interacts with the electric field.

One of the electrodes 254 and 256 is formed around a periphery of the plasma generator. If the plasma generator is formed from a dielectric the electrode may be embedded in the structure of the wall of the plasma generator or on the outer surface of the wall. If the plasma generator is formed from an electrical conductor, the wall of the plasma generator itself may act as an electrode.

It has been found that plasma generation is promoted if one of the electrodes 254 and 256 is formed by a probe extending into the plasma generate The probe is tapered at an end portion thereof to form a point for increasing the generation of plasma in said plasma generator. In this regard, the density of electric field is increased particularly in the region of the plasma generator proximate the point of the probe. The probe may be electrically insulated along its length with a dielectric.

The plasma energising means 222 may operate in any of one or more plasma energising modes for example AC, DC, pulsed, and can be

capacitively coupled or inductively coupled to the plasma chamber.

In one arrangement, the signal generator 258 may be configured to generate an AC signal output at 1 kV and 30 to 80 kHz for driving the electrodes 254, 256. This range is greater than 20 kHz so that the signal generator is not typically audible to people during use. Use at less than 20kHz may produce audible hissing.

In the AC example, the plasma energising means 222 comprises an amplifier for amplifying the output from the signal generator for driving the electrodes. A suitable matching circuit may be provided for matching impedance of the load and the source.

A suitable pulsed DC signal for plasma generation may typically need a battery 220 for example, one that generates 12V. The signal generator 258 may through a number of components and circuits (not individually shown) convert the electrical current from a 12V battery into a pulsed output voltage in the range 4 to 6kV at a frequency of 2-10 kHz which is suitable for generation of a non-thermal plasma. Such circuits and components are well known in the fields of electronics and electrical engineering and need not be described in full detail herein. Essentially circuits of a kind used with xenon flashlamps can be used to enable the battery to charge a capacitor up to, say, 320V. A transformer can be used to set up the voltage and enable voltage pulses in the desired range of 4 to 6kV to be generated. In order to produce clear, well defined pulses it is desirable to keep the number of turns and inductance of the windings of the transformer to low levels and to have modest step-up ratios. This approach helps keep the unwanted parasitic elements of leakage inductance and stray winding capacitance to a minimum, both of which contribute to pulse distortion.

Because a pulse transformer has low primary winding inductance, the magnetising current that generates the working magnetic flux in the core is substantial, leading to significant stored magnetic energy in the transformer during the pulse generation. For an efficient design, this magnetic energy is recovered at the end of the pulse and temporarily held in another form

(usually as a charge on a capacitor) ready to generate the next pulse. ln any case, the magnetic flux in the core must be returned to zero before the next pulse is generated otherwise the flux builds up with

successive pulses until the core saturates, at which point the transformer stops working and acts as a short circuit to the drive electronics.

A common method of magnetic energy recovery in switched-node power supply transformers, which may be used in this case, is through the use of a so-called "flyback" winding. This is usually identical to the primary winding and both wound on the core at the same time (a bipolar winding) in order to ensure a high level of magnetic coupling between the two. The flyback winding connects between ground and the reservoir capacitor of the DC supply via a blocking diode.

During pulse generation a fixed voltage is applied to the primary winding and current ramps up building up magnetic flux in the core - this induces an equal and opposite voltage across the flyback winding (but no current flows due to the blocking diode). Interruption of the primary current at the end of the pulse forces the magnetic field to start collapsing which reverses the induced voltage across the flyback winding and causes current to flow back into the supply capacitor. The flux and current ramp down smoothly to zero ready for the next pulse.

Another suitable transformer configuration is a push-pull design in which two identical bifilar wound primary windings are alternately connected to the DC power supply. The phasing of the windings is such that magnetic flux in the core is generated with opposing directions which each is alternately driven.

A push-pull design also allows stored magnetic energy to be recovered and returned to the supply capacitor in a very similar fashion to the flyback approach, where the blocking diode now becomes an active transistor switch. The same transformer design may be used for either approach. Although the push-pull design requires additional switching transistor and control, it allows the possibility of doubling the change in magnetic flux within the limits of the core by using both positive and negative flux

excursions. The flyback design outlined above only allows unipolar flux excursions.

For a given flux ramp rate, the push-pull design has the capability to produce a continuous pulse with twice the duration of a flyback version using the same transformer.

Referring again to Figure 2, a control is operably connected to the plasma energising means 222 for controlling energisation of the electrodes. In this example the control comprises an electrical switch 270 which when closed allows energisation of the electrodes 254, 256. The switch 270 is manually operable by a user using the previously referenced button switch 234 (which also activates valve 232). Alternatively, a separate user input device may be used to operate switch 270. The use of the same user input device for controlling the flow of gas into the plasma chamber and the energisation of the electrodes 254, 256 is desirable because preferably gas flow and energisation of the electrodes occurs at the same time or there may be a predetermined time delay between gas flow and energisation. Further, it is preferable that energisation of the electrodes does not occur unless gas flow exceeds a predetermined minimum required flow. Accordingly, the controls may be integrated and comprise flow valve 232 for allowing the flow of gas and switch 270 for allowing energisation of the electrodes. If desired, a sensor (not shown) may be provided for sensing the flow of gas released from the pressure vessel 212. The switch 270 allows energisation of the

electrodes only if the flow of gas is above a predetermined mass or volume flow rate or has been established for a chosen period of time. The source 220 of electrical energy may be one or more batteries and preferably the batteries are rechargeable. In this case, the housing 228 may comprise an electrical socket for receiving a plug connected to a mains power source and a recharging circuit 282 for recharging the batteries. Alternatively, the device comprises means for example primary windings in a recharging unit and secondary windings in the device connected to the batteries for inductively coupling the batteries to a recharging unit for recharging.

The handpiece 228 comprises an enclosure 284 for locating the batteries in the housing and electrical terminals (not shown) which connect to the batteries when they are located in the enclosure for supplying energy to the plasma energising means 222.

In order to permit a free range of movement of the device by a user, it is preferable that the source of electrical energy is not connected to a mains or other supply during use. It will also be appreciated that as the device may be used in a wet environment for instance a bathroom it is advantageous to avoid cabling. Further, some bathrooms do not have an electrical socket. However, the device 210 may be connected by an electrical cable to a socket during use. In this case, the source 220 of electrical energy may comprise a transformer and the housing comprises a socket for receiving a plug connected to an electrical power supply. The transformer is adapted to supply energy in a form suitable for the plasma energising means 222. The plug and transformer may be adapted for connection to the energy supply of a vehicle, for example by inserting the plug into a socket of a cigar lighter of the vehicle and delivering suitable power to the plasma energising means.

Referring again to Figure 2, the device 10 may comprise a display 330 for displaying a value representative of a condition of the device, for example, one or more of the gas content of the gas capsule 122, the amount of charge remaining in the source of electrical energy 220, or a temperature of the plasma plume emitted from the applicator. The display may be a graphical LCD. Additionally, or alternatively, means 332 may be provided for alerting a user when a condition of the device, such as gas content of the pressure vessel, charge in the source of electrical energy, or temperature of the plasma plume decreases or increases beyond a predetermined amount. The alerting means 332 may comprise means for generating a sound which is audible to user or a warning light, such as an LED, prompting the user to recharge or replace the gas capsule or the source or to remove the device from the treatment region to avoid harm. The devices shown in Figures 2 to 4 have an applicator 218 for applying the non-thermal plasma generated in the plasma generator 216. A particularly suitable form of applicator 218 for the treatment of halitosis, or for breath freshening is shown in Figure 5. In general, the applicator 218 may have a number of different configurations; alternatively there may be a plurality of interchangeable applicators of different configurations. The configuration of the or each applicator is such as to facilitate the application of the active species contained in the plasma to a region or regions of the oral cavity where anaerobic bacteria tend to proliferate. One of those regions is the back of the throat. The applicator can therefore take the form of an elongate probe which is able to direct the plasma at the back of the throat.

Referring to Figure 5, the applicator 218 shown therein has a proximal end 502 which is adapted to be releasably attached to the outlet from the plasma generator 216 (see Figure 2) and a distal end 504. The applicator 218 has a hollow tube 506 at its proximal end 502. The tube 506 terminates in a hollow plate 508. Orifices 5 0 are formed in the distal end portion of the plate 508. The orifices face downwards, as shown, and are made obliquely so that gas ejected therefrom has a component of velocity in the direction from back to front of the tongue. In use the applicator 218 is intended to be inserted plate-first into the oral cavity. When correctly positioned the orifices 510 direct non-thermal gaseous plasma typically at a temperature in the range 20 to 40°C at the human or animal tongue in the oral cavity. The orifices 510 are arranged so that the plasma gas has a component of velocity towards the opening of the oral cavity as it leaves the orifices 510, but is also able to make contact with the back of the human or animal tongue so as to impact upon any colonies of P. gingivalis at the back thereof and have a bactericidal effect upon the colonies.

If desired, the distal end of the plate 508 may carry a tongue-scraper

512. If desired the tube 506 may be formed at its proximal end with an adaptor 514 which shall be described below.

Alternative forms of applicator 218 may be used. For example, referring to Figure 6, an applicator 60 comprising hollow gum shields, 600 and 602, both formed with gas orifices 604 as shown in Figure 6. This applicator may be used to treat the gum area of the oral cavity.

Another alternative form of applicator 218 is shown in Figure 4. In this example, the applicator 218 takes the form of a hollow needle with a single outlet orifice at its distal end. This applicator may be used to treat teeth interdentally. Another feature of the device shown in Figure 4 is that the device is provided with evacuation means comprising an exhaust duct 316 in the applicator 218 communicating with pumping means 318 in the device, the pumping means 318 being adapted to be driven by a motor 320 which may be arranged such that it can be actuated by the push button 234.

Each of the above described applicators may have an adaptor 514 provided at its proximal end, as shown in Figure 5. Referring now to Figure 8, the adaptor 514 is configured to engage with a complementary connecting portion 602 at an end of the handpiece 228 for fixing the applicator 218 to the handpiece 228. The adaptor 514 comprises a plurality of formations, or keys, 610 which are received in a respective plurality of recesses, or key holes, 612 in the connecting portion 602. Once received in the recesses, the applicator and handpiece are relatively rotated to lock the applicator in place.

The adaptor 514 and connecting portion 602 are configured to allow activation of one or more functions of the device when connected and to prevent activation of functions when not connected. Similarly, the connection of one applicator to the housing may allow activation of one set of functions whilst the connection of another applicator to the handpiece may activate another set of functions. The connection of applicator 218 to the handpiece 228 is, referring again to Figure 2, configured to allow activation of the plasma energising means 222 and of gas flow to plasma chamber 216 when user input device 234 is operated. Without such connection, operation of the user input device cannot activate these functions.

As schematically shown in Figure 8, the adaptor 514 and the

connection portion 602 may comprise complementary electrical contacts which are closed to allow activation of certain, selected, functions. The adaptor 514 is rotatable in connecting portion 602 to lock the applicator to the handpiece. When locked, electrical contacts 614 on the adaptor 514 contact electrical contacts 616 on the connecting portion 102 thereby closing respective electronic switches allowing activation of the gas flow by valve 32 and, activation of the plasma energising means by switch 70.

An oral care kit for the treatment of halitosis or for breath freshening comprising any of the devices shown in Figures 2 to 4, with one or more applicators as shown in Figure 5, Figure 6, Figure 8 or Figure 4, together with other items such as one or more bottles of mouthwash, and suitable instructions for use, may be provided in accordance with the invention.