EP0727969A1

EP0727969A1 - Method and device for localizing the apex of a tooth

Info

Publication number: EP0727969A1
Application number: EP95901475A
Authority: EP
Inventors: Roger Heraud
Original assignee: Xelyx
Current assignee: Xelyx
Priority date: 1993-11-09
Filing date: 1994-11-09
Publication date: 1996-08-28
Also published as: AU1070095A; FR2712170B1; WO1995013032A1; FR2712170A1

Abstract

Method of localizing the apex (4) of a root canal (3) of a tooth (1), using electrodes, with a measuring electrode (A) being inserted in the root canal (3) and a reference electrode (B) being placed in the mouth (5). The invention is characterized in that a second reference electrode (C) is placed in the mouth (5) and in that three impedance measurements (X, Y, Z) are effected between electrodes (A and B), (A and C) and (B and C) respectively. Based on the relation X + Y - Z = 2R, where R is the impedance of the fraction of the root canal (3) between the measuring electrode (A) and the apex (4), the impedance of the root canal (3) being a linear function of the length an evaluation, or determination, and display is effected of the distance separating, on each measurement of the set of values (X, Y, Z), said measuring electrode (A) from the apex (4), the operation then being repeated in a cyclic or non-cyclic manner.

Description

METHOD AND DEVICE FOR LOCATING THE APEX OF A TOOTH

The present invention relates to a method and a device for locating the apex of a tooth. More specifically, the invention aims to propose a method and a device for real-time measurement of the distance separating the end of a so-called measurement electrode, inserted into a root canal of a tooth, from the apex of said channel.

The apex, also called cemento-dentinal junction or apical constriction, is the point where the nerve and other blood vessels enter the root canal of the tooth.

Dentists are sometimes required to devitalize a tooth by cleaning and sealing the root canals of the teeth. The cleaning of the canal consists in removing all the pulp tissues from the canal until the apex of the latter.

For this purpose, they use an endo-canal file which they slide into the roots and, by rotational and / or back and forth movements, they scrape the walls of the canals in order to pulp them.

During this cleaning work, they descend deeper and deeper into the root, until reaching the apex. To avoid any risk of abscess, it is necessary to clean the canal up to the apex of the latter. On the other hand, the dentist must above all not cross this apex with the file, because 0 it risks causing inconvenience to the patient and in particular causing an abscess. It is therefore important to be able to precisely locate the apex of the root to be cleaned.

Several methods are used for this purpose.

Among these methods, a method is commonly used which consists in inserting a file into each root of the tooth, and in performing a canal x-ray. This radiography carried out, the dentist adjusts the stop of his file from the picture obtained. This technique requires a lot of know-how on the part of the dentist and has above all the drawback of subjecting the patient to significant X-ray radiation, all the more important since, depending on the morphology of the tooth, a single photograph does not allow not always obtain the desired measurement and a second shot, taken from a different angle, is then necessary.

Another drawback lies in the duration of the intervention, since it is necessary to wait for the development of the image (s) before continuing to clean the canal. In addition, the cost of using radiography devices is also a drawback of such a method.

This is why other methods have been proposed in order to locate the apex of the root to be cleaned.

Among these methods, mention may be made of that described in document US Pat. No. 5,049,069. This method is based on the discovery that the measurement of the electrical conductance between an electrode placed at the apex and an electrode placed in the mouth, for example in contact with the lips, gives an impedance value which is constant whatever the measuring apices in the mouth and whatever the patients. Also, it has been established that between the apex and a point along the root canal, the impedance was proportional to the distance between said point and the apex.

Thus, the method proposed in the document US consists in carrying out a measurement of conductance or the like between two electrodes, one of which, called measurement, is inserted in the root canal, and the other electrode, called reference, is positioned in the mouth, and to determine from this measurement the distance between the end of the reference electrode and the apex.

However, these methods are not reliable, since the measurement depends on variations in impedance at the level of the reference electrode placed in the patient's mouth. For example, the presence or not of saliva on the reference electrode significantly disturbs the measurement carried out. We cannot therefore rely in all cases on the results obtained by this process.

The object of the present invention is to provide a method of locating the apex of a tooth by means of electrodes, which makes it possible to overcome the abovementioned measurement defects.

To this end, the subject of the invention is a method of locating the apex (4) of a root canal (3) of a tooth (1), by means of electrodes, one of which, known as a measurement (A ), is inserted into the root canal (3) and another, called the reference channel (B), is placed in the mouth (5), characterized in that a second reference electrode (C) placed in the mouth is used (5), and in that: three impedance measurements (X, Y, Z) are carried out respectively between the electrodes (A) and (B), (A) and (C), (B) and (C) ; and - from the relationship X + Y - Z = 2R, where R is the impedance of the fraction of the root canal (3) between the measurement electrode (A) and the apex (4), we evaluate or determine and display, the impedance of the root canal (3) being a linear function of the length, the distance separating, at each measurement of the trio of values (X, Y, Z), said measurement electrode (A) from l apex (4), the operation then being repeated cyclically or not.

The use of the two reference electrodes makes it possible to dispense with measurement errors due to the variations of impedance at the level of these electrodes. Indeed, in this process with three electrodes, the variations of the two measurement points of the two reference electrodes are automatically compensated for by the calculation carried out, so as to give a result independent of random factors such as the presence or not of saliva on the reference electrodes.

According to one embodiment of the method, the operator repeats the process of carrying out the three measurements and of determining the position of the measurement electrode, in particular an endo-canal file, relative to the apex, as much as often as desired as it moves the file through the root canal. According to an implementation variant, the measurement-determination process is automatically repeated cyclically so that the operator is constantly informed, without having to intervene, on the situation of the measurement file relative to the apex. This allows, in particular, to completely clean the root canal by constantly checking that the apex is not exceeded.

The invention also relates to a device for implementing the method, characterized in that it consists of: a measuring electrode (A) capable of being inserted into the root canal (3) of a tooth ( 1); two reference electrodes (B, C) capable of being placed in or on the mouth (5) of the patient; means for measuring the impedance between any two of said electrodes (A, B, C); - means connected to said measurement means, for evaluating or determining from said impedance measurements the distance between the measurement electrode (A) and the apex (4); and means (31) for displaying said distance thus evaluated or determined. According to a particular embodiment of the device, means are provided for automatically repeating cyclically the process of measurement, determination and display of said distance separating the measurement electrode and the apex.

Other characteristics or advantages will emerge from the description which follows of an embodiment of the device for implementing the method in accordance with the present invention, description given by way of example only, with reference to the appended drawings in which:

Figure 1 is a sectional view of a tooth in line with a root canal; - Figure 2 is a diagram of an embodiment of a device for implementing the method of the present invention; Figure 3 is a diagram showing part of a variant of the embodiment shown in Figure 2. In Figure 1, there is shown in section a tooth 1 housed in the maxillary bone 2. The tooth 1 has a root canal 3 ending in an apex 4. The reference numeral 5 generally designates the surrounding tissues. An endo-canal file 6, provided with an adjustable stop 7, is shown directly above the channel 3. A flexible electrical conductor 8 is connected to the file 6 by means of pliers 9. Two hooks 10, 1 1 are shown schematically on either side of the tooth 1, in contact with the surrounding tissues 5, generally the mouth. Each hook 10, 11 is connected to a flexible electrical conductor, respectively 12, 13.

The conductors 8, 12, 13 are connected to the measuring device 45 of the invention, a diagram of an embodiment of which is illustrated in FIG. 2.

In this FIG. 2, the file 6 forms a first electrode, called the measurement electrode A. The hooks 10, 1 1 respectively form the first reference electrode B and the second reference electrode C.

The three electrodes A, B, C are switched using a sequencer 14, connected by three links 15, 16, 17 to the controls of three switches 18, 19, 20 which successively switch the electrodes A and B two by two , B and C, A and C. The outputs of the three switches 18, 19, 20 are connected to a meter 21 and to a generator 22. The output of the meter 21 is connected to the inputs of three memories 23, 24, 25, these memories being respectively synchronized by the sequencer 14 by means of three links 26, 27, 28. The role of the sequencer 14 is, on the one hand, to control the succession of the three measurements between the electrodes A, B and C and, on the other hand, to repeat this measurement process automatically and cyclically.

These three memories 23, 24, 25 are connected to a computer 29 whose output is connected to a constant adder 30. The constant adder 30 is connected by a second input to a constant memory 30a. The output of the constant adder 30 is connected to a display 31 and to comparators 32, 33, 34, 35, comparing the measurement with different predetermined values in memories 36, 37, 38, 39 and actuating one or several indicator lights 40, 41 and / or audible noisers 42 and / or other external outputs or appropriate devices 43.

In the device shown, the generator 22 generates a measurement current, alternating for example with a frequency of 2500 hertz, and the meter 21 is adapted to impedance measurements.

Figure 3 is a variant 45 'of the device shown in Figure 2, in which the impedance measurements are carried out simultaneously. For this purpose, the electrodes A and B are connected to a measuring device 21 ', the electrodes B and C are connected to a measuring device 21 ", and the electrodes A and C are connected to a measuring device 21" " . The output of each device 21 ', 21 ", 21'" is connected to the computer 29 of FIG. 2 and the circuit at the output of the computer 29 is identical to that of FIG. 2.

The devices 21 ', 21 ", 21'" are advantageously controlled so as to automatically and cyclically repeat the three measurements between the electrodes A, B and C and of course the subsequent calculation and display operations.

The principle of the device is as follows. It is explained with reference to device 45 in FIG. 2, but the principle of device 45 'in FIG. 3 is similar and will therefore not be explained again. First of all, by means of the hooks 10, 11, the reference electrodes B and C are placed in the patient's mouth, for example at the corners of the lips. Then, by means of the clamp 9, the file 6 is connected to the measuring electrode A.

The measurements are carried out three by three. Namely, the impedance between the measurement electrode A and the reference electrode B is measured on the one hand, between the electrode A and the reference electrode C on the other hand and, finally, between the electrodes B and C.

X denotes the impedance measurement obtained between A and B, Y that obtained between A and C, and Z that obtained between B and C. These three measurements are obtained by switching the electrodes A, B,

C by means of the sequencer 14, for example at a frequency of 15 hertz, and of the three switches 18, 19, 20 connected to the meter 21 whose signal output is delivered to memories 23, 24, 25 synchronized with switches 18, 19, 20 using the sequencer 14.

Thus measurement X is stored in memory 23, measurement Y in memory 25, and measurement Z in memory 24. The computer 29 adds the values measured between A and B as well as between A and C and subtracts the value measured between B and C, that is M = X + Y - Z = 2R, where R is the impedance between the apex and the end of the measuring electrode A. It should be noted that the impedance of the desmodont is negligible compared to the other impedances involved, in particular compared to R.

This calculation makes it possible to overcome measurement errors originating from possible variations in impedance which may occur at the right of the reference electrodes B and C and originating in particular from the quality of the physical contact and from the modification of the local resistivity of the medium. The value M obtained is divided by two, then converted into distance from the known law of proportionality between the distance between the apex and a point of the root canal and the impedance between them.

These operations are carried out by the computer 29 which thus outputs a value, in an appropriate unit, for example the millimeter, of the instantaneous distance between the end of the file-electrode A and the apex 4.

The output signal from the computer 29 is sent directly to the display 31, or indirectly as illustrated in FIG. 2, by means of a constant adder 30. The device 30 may be used to introduce an offset of origin in distance measurement, for example to obtain zero at a determined value.

By comparing the calculated distance value with reference or threshold values supplied by suitable devices 36, 37, 38, 39, for example manual, adjustable potentiometers, the respective comparators 32, 33, 34, 35 activate the indicator lights 40, 41 and / or the sound buzzers 42 and / or the external outputs 43. It is thus possible to visually and / or acoustically control the step-by-step approximation of the file 6 with respect to the apex 4, each corresponding step at one of the thresholds. One of the visualization and / or sound signaling devices (40 to 42) can be assigned to signaling that the apex 4 has been exceeded, the end of the file-electrode A then being in the desmodont.

The measurement frequency, approximately 15 times per second in the example above, is sufficient for the indications on the display 31 to correspond to the effective distance between the measurement file A and the apex 4, at l of each measurement. By measurement is meant taking into account the three relative measurements between the electrodes A, B and C.

It should be noted that the use of a second reference electrode and the method of determining M-j makes it possible to overcome measurement errors due to said reference electrodes.

Once the end of the file 6 is at the level of the apex 4, the operator can position the stop 7 in order to take the measurement of the useful cleaning depth. He can then continue cleaning this root without using the device of the invention, or continue to use it in order to check at any time that the file does not exceed the apex 4.

Instead of the automatic cyclic measurement device illustrated in FIG. 2, it is possible to produce a simplified device operating piecemeal, that is to say performing the simple series of three relative measurements between the electrodes A, B, C, the process being repeated at the request and under the control of the operator whenever the latter so desires.

Furthermore, if there is an appearance in the blood channel and / or use of sodium hypochlorite or any other liquid capable of modifying the resistivity of the medium, the measurement carried out by the measurement electrode A will change. To overcome this, one can provide on the computer 29 a multi-position switch with manual control allowing the operator to introduce into the computer a new reference for compensating for the change in resistivity brought by blood, hypochlorite or any other liquid. . It is also possible to provide, when the operator observes a drift in the measurement, the insertion, by the operator himself, of a series compensation impedance, symbolized by dotted lines at 44 in FIG. 2, between the measuring electrode A and switches 18, 20 for measuring X and Y, in order to hold account for the variation in impedance resulting from the presence of one of these conductive liquids.

Of course, the invention is not limited to the embodiment described and shown, but on the contrary covers all variants, in particular with regard to the voltage and the frequencies used, the number of indicator lights 40, 41 and / or audible sounders 42 and / or external outputs 43.

It should be noted that the device described performs measurements in alternating current, but that it could also operate in direct current, the impedances measured being resistances.

Claims

1. Method for locating the apex (4) of a root canal (3) of a tooth (1), by means of electrodes, one of which, known as a measurement (A), is inserted into the root canal ( 3) and another, known as a reference (B), is placed in the mouth (5), characterized in that a second reference electrode (C) placed in the mouth (5) is used, and in that: three impedance measurements are made (X, Y, Z) respectively between the electrodes (A) and (B), (A) and (C), (B) and (C); and from the relation X + Y - Z = 2R, where R is the impedance of the fraction of the root canal (3) between the measuring electrode (A) and the apex (4), we evaluate or determine and we display, the impedance of the root canal (3) being a linear function of the length, the distance separating, with each measurement of the trio of values (X, Y, Z), said measurement electrode (A) of the apex (4), the operation then being repeated cyclically or not.

2. Method according to claim 1, characterized in that the distance separating the measurement electrode (A) and the apex (4) is measured and displayed (31) in an appropriate measurement scale.

3. Method according to claim 1, characterized in that the distance separating the measurement electrode (A) and the apex (4) is identified in a scale of predetermined value.

4. Device for implementing the method according to any one of claims 1 to 3, characterized in that it consists of: a measuring electrode (A) capable of being inserted in the root canal (3 ) a tooth (1); - two reference electrodes (B, C) which can preferably be placed in or on the mouth (5) of the patient; means for measuring the impedance between any two of said electrodes (A, B, C); means connected to said measurement means, for evaluating or determining from said impedance measurements the distance between the measurement electrode (A) and the apex (4); and means (31) for displaying said distance thus evaluated or determined.

5. Device according to claim 4, characterized in that it further comprises means connected to said measurement and determination means and automatically and cyclically repeating the measurement process, determination and display of said distance between the measurement electrode (A ) and the apex (4).

6. Device according to claim 4 or 5, characterized in that said measuring means consist of three independent circuits (21 ', 21 ", 21"') each assigned to one of the three combinations per pair of electrodes (A , B, C).

7. Device according to claim 5, characterized in that said measuring means consist of a single measuring device (21) connected to said electrodes by three switches (18, 19, 20) switched by a sequencer (14), said device (21) being connected via three memories (23,24,25) to a computing device (29), said memories being connected to the sequencer (14).

8. Device according to claim 6 or 7, characterized in that it comprises, in parallel with the display means (31), means (32, 33, 34, 36, 37, 38) delivering a light signal ( 40, 41) and / or sound (42) informing that the signal intended for said display means (31) has reached predetermined thresholds.

9. Device according to any one of claims 4 to 8, characterized in that the impedance measurements are carried out with direct or alternating current.

10. Device according to any one of claims 4 to 9, characterized in that the measurement electrode (A) is an endo-canal file

(6).