CA2246292A1 - Toothbrush - Google Patents

Abstract

A device for the detection of plaque on teeth or dentures situated in a conductive fluid, particularly during the course of a cleaning operation, the device having at least one electrode (9) provided with external insulation and having a conductive tip (8) which can be placed onto the surface of a tooth (5), a counter-electrode (13) having an electrical connection to the fluid (17), a power source (12) being connected to the electrode (9) and counterelectrode (13), a measuring device (18) being located between the power source (12) and electrode (9) or counter-electrode (13), the measuring device determining the electrical impedance between the electrode (9) and counterelectrode (13), and an evaluation device (19) and/or indicator device (20) which processes and/or indicates the values measured.

Description

Toothbrush The invention relates to a device for the detection of plaque on teeth or dentures which are in a conductive fluid, particularly during the course of a cleaning operation, and to a method that is used for said detection.
Plaque is one of the principal causes for the formation of caries and other diseases of the teeth and oral cavity as it promotes the settlement of harmful bacteria and makes available the carbohydrates required by such bacteria as food. For this reason the principal aim of oral hygiene is to remove dental plaque as completely as 10 possible. Monitoring of the cleaning operation is extremely difficult as the layers of plaque are virtually invisible and are consequently difficult to see, particularly if a person tries to check his own mouth by means of a mirror. With dentures too, thorough monitoring of cleaning is required as layers of plaque can also form ontheir surface and provide bacteria that cause infl~mm~tion with a suitable habitat.
15 To establish whether there is any residual plaque after cleaning it is known to use colouring agents, for example in the form of chewable tablets, which are deposited to a significantly greater extent on plaque than on teeth free of plaque. However, even after thorough cleaning there is still intense residual coloration of the entire oral cavity, which naturally does not find favour with the user. Such monitoring20 therefore takes place sporadically at best. A fur~her factor to be considered is that many people do not wish to ingest a colouring agent for health or psychological reasons. Moreover, the areas of the teeth which are particularly difficult to clean and hence susceptible to plaque are to be found in the buccal space - an area requiring considerable effort by someone to check hirnself even when the layers of 25 plaque are intensely coloured. Thus cle~nlin~ss is generally only checked in the area of the front teeth, while the m~ lly more important buccal area escapes anycontrol. Moreover prior art methods require the check to be carried out after the teeth have been cleaned, and therefore this is frequently not done owing to lack of time or convenience.
Some methods of detecting dental defects including dental plaque are known, for example US-A-5382163 and WO-A-920667 disclose an apparatus for detecting - 1 - 9 ~

dental plaque based on lllmin~scence of dental plaque after exciting it with light.
FR-A-2642282 discloses a device to elimin~te dental plaque and calculus after exciting the surface with an electric current emitted by a special toothbrush; US-A-4537573 discloses a detector for diagnosing dental caries which measures the 5 electrical resistance between the teeth and buccal mucous membrane.
Against this backdrop the invention has set itself to overcome the problem of developing a device and a method for detecting dental plaque which in a simple manner permit detection even in poorly accessible areas of the mouth, w'nich enable colouring agents to be dispensed with and which can also be used during the 10 cleaning operation.
This problem is solved in accordance with the invention by the provision of a device for the detection of plaque on teeth or dentures which are situated in a conductive fluid, particularly during the course of a cleaning operation, characterised in that:
tne device has at least one electrode provided with external insulation and having a conductive tip which can be placed onto the surface of a tooth, a counter-electrode is present which has an electrical connection to the fluid, a power source is connected to the electrode and counter-electrode, a measuring device is located between the power source and electrode or 20 counter-electrode which determines the electrical impedance between the electrode and counter-electrode and an evaluation and/or inllieator device processes and/or indicates the electrical impedance values measured.
The invention is based on the Knowledge that the electrical impedance of 25 different materials in the human mouth varies considerably. Teeth, which consist predominantly of crystalline material, have a very high impedance which generally is in excess of 30 kQ. The same applies to dentures made of plastic or ceramic material, whereas the impedance of amalgam fillings is negligible. In the human mouth the teeth are situated in saliva, which is present as a film over the teeth, 30 gums, tongue etc. and other parts of the mouth cavity. The impedance of saliva and the gums, which are coated with saliva and permeated by blood-filled capillary A~ J'~

vessels, is in the region of around 100 Q, which is equivalent to physiological saline. A layer of plaque can unambiguously be differentiated from all these materials owing to its electrical impedance~ which is between a few and around 10 Q depending on the thickness of the layer.
A device for the detection of dental plaque is theretore proposed which is based on the principle of measurement of electrical impedance. To this end an externally insulated electrode with a conductive tip or contact area is required which can be placed onto the surface of a tooth. The extent of the projecting conductible area above the surrounding insulation is expediently less than the thickness of the 10 layer of plaque to be detecte(:l. A counter-electrode is also necessary, this produces an electrical connection to a fluid in which the tooth is situated, generally the saliva of the oral cavity. A power source connected to the electrode and counter-electrode produces a closed circuit via the fluid, and a device for measuring electrical impedance, i.e. the size of the current flow at a given voltage, is inserted into this 15 circuit. Although direct current operation with a battery as the power source is generally preferred, an alternating current circuit is also conceivable for measuring the irnpedance. The measured values obtained in this way are processed and/or indicated by an evaluation and/or indicator device.
If an electrode comes into contact with a clean tooth whose surface is wet 20 with saliva or a comparable fluid, the current flow is primarily through the low-ohm layer of fluid while the tooth may normally be regarded as an insulator owing to its high impedance. Thus, in the case of a clean tooth, the low electrical impedance of the saliva is measured. If, however, the conductive area of the electrode dips into a layer of plaque, the direct contact with the fluid is interrupted. In this case the 25 higher irnpedance of the layer of plaque must additionally be overcome, and therefore a marked increase in the measured value is recorded. The size of the increase consequently not only inrlirates the presence or absence of a layer of plaque but also its thickness.
Should the device be used primarily by lay people for chec~ing their daily 30 dental care routine, it is expedient - to simplify operation - to use as simple an indicator device as possible, for example light diodes or an acoustic signal ~ ~ r ~: . r ~- ~

tr~n.srnitter which are switched on at an impedance value indicating the presence or absence of layers of plaque. Also conceivable is use of the device as a dental diagnostic device, with the measured values either being indicated directly or being tr~nSmittec~ to an electronic computing device as evaluation unit, which processes 5 the impedance values and as a consequence indicates the presence of plaque.
In a similar way the device can also be used for checking possible layers of plaque on dentures or dental prostheses, where there is a similar impedance situation. If checking takes place outside the oral cavity, attention must be paid to the fact that a fluid is used whose impedance differs suff1ciently from that of a layer 10 of plaque. This is generally the case, however, with the majority of conventional fluids for cleaning dental prostheses.
The principal advantage of the proposed detection device is that it enables dental plaque to be checked simply even in areas that are difficult to inspect, if at all. Checks can also be made during a cleaning operation as an impaired view due15 to cleaning agent has no effect on the measured values. The use of colouring or chemical substances is rendered entirely superfluous, and therefore there is no possibility of allergic reactions. Simplicity of use and total reachability of the oral cavity constitute a significant advance in the detection of dental plaque.
In an advantageous development of the invention the electrode is a filarnent 20 made of elastic, in~ul~ting rnaterial, preferably a plastic, which has a core made of flexible, conductive material. Unlike rigid constructions, such an electrode effectively prevents possible injury in the oral cavity and can easily be produced by ~let~rlling lengths from a continuous filament. Although a metal wire is also conceivable as a core, a core made from carbon, particularly in the form of a 25 carbon fibre, is preferred as it is chemically very resistant and toxicologically safe and rules out any possibility of damage to the surface of the tooth.
Particular advantages are offered by the proposed detection device if it is used to check for dental plaque, i.e. cle~nlinloss, during a cleaning operation. For this purpose it is proposed that the electrode be mounted on a cleaning device for 30 teeth or dentures. In this way the indicator device can be restricted to a signal as to h.~

whether plaque can still be detected, i.e. whether the cleaning operation is at an end or should be continued.
The proposed detection device may expediently be inserted in particular into a m~n11~11y or electrically operated toothbrush, with the power supply, measuring device, indicator and/or evaluation device being advantageously located in the handle. In this case filaments are preferably used as electrodes, replacing one,several or all the traditional filaments of the toothbrush. The counter-electrodes too may be in the form of filaments.
Filaments of toothbrushes bend in an uncontrollable manner under strain and 10 with increasing wear and tear. If the deformed filaments serve as electrodes, false readings may occur in the future resulting in the measuring device becoming completely unusable. Since it is primarily the filaments in the marginal areas of the brush head which are affected by such deformation, the electrodes may be fitted only in specific areas of the brush head, preferably in its centre. It can also be lS advantageous, however, to fit electrodes in the front part of the brush head, i.e.
furthest from the handle, as the marginal areas of the oral cavity can also be reached easily in this way. Moreover a smaller number of filaments serving as electrodesresults in lower cost, as they are more expensive to produce than conventional filaments and contact between them is required.
If the device for detectin~ dental plaque is fitted to a motor-operated cleaning device, particularly an electric toothbrush, it is possible to dispense with an in~lie~tor device. The evaluation device may be arranged to control actuation of the c!e~nin~ device and such a construction can be arranged to end the cleaning operation ~tom~tically if no more plaque is detected.
It frequently proves advantageous if electrode and counter-electrode are of the same design, for example if they are both filaments. Both may also form a single component or be directly conn~ctPd to one another mech~nic~11y. Examples are a filament having two conductive cores, one serving as electrode and the other as counter-electrode, or electrodes inserted into openings of a conductive plate30 con.~ti~lting the counter-electrode and optionally partly encompassing the shaft of the electrode.

~ r ~ . ~r In all cases it is possible to assign neighbouring electrodes and counter-electrodes in pairs~ in rows or in groups, i.e. to provide for several discrete power circuits. Even the cormection in series of several electrodes and counter-electrodes has occasionally proved expedient.
If the detection device, for example on a toothbrush, is used for checking the cleaning operation in the mouth of the user, a fully or sectionally conductive handle may also be used as counter-electrode. The circuit in this case is closed via the hand, arm and body of the user and via the saliva in his mouth. This very simpledesign of counter-electrode considerably facilitates manufacture. Further 10 advantages can be achieved with regard to production if all the electrodes are connected in parallel and are linked by a conductor, e.g a conductive plate or foil, in the head of the toothbrush.
The purpose of the evaluation device is primarily to process the measured impedance values in such a way that the user is given a readily interpretable 15 reading. It is therefore n~cess~ry to suitably calibrate the device to the individual conditions and impedance values in the user's mouth and to isolate any interference Assemblies suitable for this task are in particular counting and/or integrating and/or differentiating and/or delay elements and/or threshold switches. By means of a differentiating element it can be established whether changes in the conflllcr~n~e of 20 the tooth surface are occurring during the cleaning operation or whether a limit value is being approached, i.e. the cleaning operation is complete. Using an integrating element it is possible to make a comparison with changes that occurred previously. Furthermore, counting and integrating elements are suitable for establishing how large overall the areas are which have uniform impedance, in 25 particular a layer of plaque. Threshold switches permit the singling out of obviously erroneous measurements which may occur for example if the electrode islifted off the surface of the tooth or there is a short-circuit via a metallic filling.
One or more delay elements in the evaluation unit ensures that only these changes in impe~nl~e are recorded whose duration is within predetermined limits.30 If the detection device is used in conjunction with a cleaning device where the cleaning operation proceeds in a cyclic maMer, the tirne constant of the delay C702~0 .
element is preferably aligned to the period length of the cleaning operation. If for example an electrical toothbrush is used, the period length corresponds to the duration of oscillation of a brush head. Even during manual cleaning of the teeth there occur typical period lengths which may be taken into account with a delay element.
Examples are the period when a brush head is lifted from one set of teeth and placed on another set, or periods in which the filament tips glide without contact over the interdental spaces. The duration of the time constant of the delay element does not necessarily have to coincide with the period lengths, but multiples 10 or fractions of the period length may prove to be expedient time constants.
Particularly for diagnostic purposes it is advantageous to record the size and local distribution of plaque-coated areas. For this it is proposed that several electrodes at a known distance apart are present which are cormected individually or in groups with measuring devices assigned to them. It is also conceivable to use a 15 single measuring device and to connect the electrodes successively to it in the manner of multiplex procedure.
In a suitable process for using the proposed device, if the teeth or dentures are not already in the saliva of the oral cavity, they may be introduced into a conductive fluid. A electrical connection is made between the fluid and the counter-20 electrode. After the electrode has been placed onto the surface of the tooth the power source causes a flow of electrical current, thus allowing the electrical impedance to be measured. It can be determined from the size of the impedance measured whether the tip of the electrode is on a clean dental surface or in a layer of plaque.
In a further development of the process the electrode is moved along the surface of the teeth during measurement, for example during a cleaning operation, when it is mounted on a toothbrush. This ensures that layers of plaque on the surface of the teeth are detected not only at certain points but also over a wide area.
To obtain a low-interference signal there is preferably constant electrical 30 contact between the electrode and surface of the teeth, i.e. complete interruption of the current flow is avoided. Therefore a fluid is advantageous which is in the forrn of a foam and largely fills the oral cavity of the subject. This can be achieved by adding a foam-forming surfactant to the fluid, as for example is contained in commercial toothpastes. If the device is used during normal cleaning of the teeth, such a contact-improving foam is normally formed during the cleaning operation.
Further particulars, features and advantages of the invention can be gathered from the following part of the description in which embodiments of the inventionwill be explained in greater detail of the basis of a non-limiting example illustrated by the accompanying drawings, which show:
Figure 1. Cross-section through a toothbrush with the device in accordance 10 with the invention for detecting plaque.
Figures 2 - 4. Cross-sections through alternative arrangements of electrodes andcounter-electrodes .
Figures 5-6. Overhead view of various designs of the brush head.
Figure 1 shows a cross-section through a toothbrush (1) which has a handle 15 (2) and a brush head (3) and which is provided with a device in accordance with the invention for detecting layers of plaque (4) on the surface of teeth to be cleaned (5).
For this purpose, instead of traditional bristles the toothbrush (I) has filaments (6) made from an inc~ tinP material which are provided with a conductive core (7).
The core (7) is freely accessible at the tip (8) of the filament (6), resulting in the 20 formation of an electrode (9) which at its other end makes contact with a printed circuit board (10) in the brush head. Leads (11 ) connect the electrode (9) via a power source (12) to a counter-electrode (13) which is formed by a m~t~llic layer (14) on the surface of the handle (2) of the toothbrush (1). If the user of the toothbrush grips the handle (2) with his hand (15) and places the toothbrush (1) with 25 the filaments (6) onto his teeth (5), a closed circuit is formed, as in~icate~ by the broken line (16), via his arm, body and the saliva in his mouth as the conductive fluid (17). A measuring device (18) serves to record the flow of current, or electrical impedance, in the circuit.
The principle of measurement is based on the fact that the fluid (17) of the 30 saliva has a comparatively low electrical impedance, while that of the tooth (5) is considerably greater and the layer of plaque has a impedance value somewhere in-C-~tET

between. It can thus be determined from the size of the current flow whether thetips (8) of the electrodes (9) in the fluid (17), on a clean dental surface or in a layer of plaque (4). A evaluation device (19), preferably a microchip, processes the values recorded by the measuring device (18) and controls an indicator device (20) 5 which in(liç~t~os by means of light diodes (21) whether the cleaning operation has ended, in other words, whether the layer of plaque (4) has been removed. The evaluation device (19) is also used to take into account erroneous measurements, for example when the toothbrush (1) is lifted off the tooth (5), and for identification of measured values to which the presence or absence of plaque (4) can be assigned. It 10 goes without saying that it is possible in a similar way also to provide an electric toothbrush with a device for detecting dental plaque.
The printed circuit board (10) means there are various possibilities for contact between the electrodes (9) which, for example, are connected to a measuring device (18) individually or in groups, the connection of several 15 electrodes (9) in series also being possible. Further advantageous embodiments of the device are shown in Figures 2 to 4 where the counter-electrode too (13) is located in the brush head (3). To simplify the drawings only the arrangement formeasuring impedance has been shown in each case.
In Figure 2 both the electrodes (9) and the counter-electrodes (13) are 20 filaments (6) with a conductive core (7), in other words they are of similar design.
This considerably extends the possibilities for contact between them, for exarnple, the depicted series connection of all electrodes (9) and counter-electrodes (13) is conceivable.
Figure 3 shows a toothbrush (1) with a counter-electrode (13) in the form of 25 a conductive plate on a brush head (3) into openings on which the electrodes (9) are inserted. For good. uniform contact, adequate wetting of the brush head (3) by the fluid (17) is required in this case, and this can be achieved by the forrnation of foam using a commercial toothpaste.
Figure 4 shows the electrode (9) and counter-electrode (13) provided in a 30 corr~mon filament (6) which is provided with two cores (7).

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Particularly in the marginal areas of the toothbrush there is always a danger that the filaments (6) will bend outwards, resulting in false measurements. To reduce this problem the filaments (6) may be located only in specific areas (22) of the brush head while traditional filaments (23) are used in the rem~ining areas.5 Figures S and 6 show two such embodiments. ln addition, considerable cost savings can be achieved in this way as only a small number of the more expensivefilaments (6) are required and have to make contact.
The end result is a device for detecting layers of plaque which even during a cleaning operation permits cle~nlinPss to be checked in a careful, simple manner10 and in a way that covers all regions of the teeth.

- 10 - ~S.~ ,r ~

Claims (18)

Claims:

1. Device for the detection of plaque on teeth or dentures which are situated in a conductive fluid, particularly during the course of a cleaning operation, characterised in that the device has at least one electrode (9) proved with external insulation and having a conductive tip (8) which can be placed onto the surface of a tooth (5),a counter-electrode (13) is present which has an electrical connection to the fluid (17), a power source (12) is connected to the electrode (9) and counter-electrode (13), a measuring device (18) is located between the power source (12) and electrode (9) or counter-electrode (13) which determines the electrical impedance between the electrode (9) and counter-electrode (13), and an evaluation (19) and/or indicator device (20) processes and/or indicates the electrical impedance values measured.

2. Device according to claim 1, characterised in the electrode (9) is a filament (6) made from an elastic insulating material with a core (7) made from a flexible conductive material.

3. Device according to claim 2, characterised in that the core (7) comprises carbon.

4. Device according to any one of the preceding claims, characterised in that the electrode (9) is mounted on a cleaning device for teeth (5) or dentures.

5. Device according to claim 4, characterised in that the cleaning device is a manual or electric toothbrush (1) with a brush head (3).

6. Device according to claim 5, characterised in that the power source (12), measuring device (18), evaluation (19) and/or indicator device (20) are located in a handle (2) of the toothbrush.

7. Device according to claim 5 or 6, characterised in that one or more filament.(6, 23) of the toothbrush (1) are electrodes (9) or counter-electrodes (13).

8. Device according to claim 7, characterised in that the electrodes (9) are located in specific areas (22), preferably in the centre of the brush head (3).

9. Device according to any one of claims 4 to 8, characterised in that the evaluation device (19) controls actuation of a motor-operated cleaning device.

10. Device according to any one of the preceding claims, characterised in that the electrode (9) and the counter-electrode (13) are of the same design.

11. Device according to any one of the preceding claims, characterised in that the electrode (9) and counter-electrode (13) form a single component or are mounted side by side.

12. Device according to any one of claims 1 to 9. characterised in that the device has an at least partially conductive handle (2) forming the counter-electrode (13).

13. Device according to any one of the preceding claims, characterised in that the evaluation device (19) comprises an threshold switch and/or a counting and/or integrating and/or differentiating and/or delay element.

14. Device according to claim 13, characterised in that the time constant of thedelay element is aligned to the period length of cyclic cleaning operations.

15. Device according to any one of the preceding claims, characterised in that several electrodes (9) are present, each of which is connected to a measuring device assigned to it (18) or is connectable successively to a common measuring device (18).

16. Method of detecting plaque on teeth or dentures, which are situated in a conducting fluid, using a device according to any one of the preceding claims, characterised by the following steps:
- production of an electrical connection between the counter-electrode (13) and fluid (17), - placing of the electrode (9) onto the surface of the tooth (5) or dentures, - measurement of the electrical impedance, - evaluation of the values measured.

17. Method according to claim 16, characterised in that the electrode (9) is moved along the surface of the teeth (5) or dentures during measurement.

18. Method according to claim 16 or 17, characterised in that the fluid (17) is a foam.