JPH0473056A - Root point position detector - Google Patents

Abstract

PURPOSE:To dispense with complicated calibration while enabling accurate detection of a position of a root point by detecting the position of the root point depending on a deviation in phase or waveform between a voltage waveform and a current waveform. CONSTITUTION:Load current flowing between a measuring electrode 2 and a oral cavity electrode 3 is detected in the form of a voltage of a measuring electrode 2 and an equivalent circuit between both the electrodes 2 and 3 is considered as parallel circuit of a resistance and capacitor. So, when a measuring voltage waveform A is a sine wave, phase of load current waveforms B1 and B2 vary with a capacity of a capacitor though becoming the same sine waves. As a result, when a capacity component of an equivalent impedance increases as the tip 2a of the electrode 2 approaches near a root point, a deviation in phase of the load current waveform grows with respect to a waveform A and a current waveform C2 of a phase comparator circuit 6 becomes larger than the C1 according to a phase difference therebetween. Thus, display contents, for example, a deflection of a pointer of a display section 7 increases accordingly thereby indicating that the root point is reached by the deflection.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement of an apex position detection device in a root canal length measuring instrument used for dental diagnosis and treatment.

<Prior art> A device for measuring the root canal length by electrically detecting the position of the root apex is a device that measures the root canal length by electrically detecting the position of the root apex. A method that detects the resistance value of the electrode (for example, see Japanese Patent Publication No. 62-25381), or a method that detects the impedance between both electrodes (see, for example, Japanese Patent Publication No. 62-2817) is known. .

The former of the above publications detects that the resistance value decreases as the tip of the measurement electrode approaches the root apex, and the latter detects that the impedance value decreases as the tip of the measurement electrode approaches the root apex. Since the area between the measurement electrode and the oral cavity electrode is considered to be an equivalent circuit in which a resistor and a capacitor are connected in parallel, the latter is considered to be more suitable for the actual situation as a measurement principle. In particular, in the latter case, instead of simply detecting the impedance value, two different frequency signals are applied between the two electrodes and the impedance is detected for each signal.
The results are successively compared and it is detected from the state of change of the difference between the two that the electrode tip has reached the root apex.

<Problem to be solved by the invention> The former method described above simply detects the resistance value between both electrodes on the premise that the inside of the root canal is dry, so the inside of the root canal is a good conductor. If the inside of the root canal is moist, errors will occur, but it is actually difficult to perform measurements when the inside of the root canal is always dry. In addition, clinically, there are often medicinal solutions and blood in the root canal, and the equivalent resistance in the root canal decreases due to the influence of the medicinal solution, so an indication that the root apex has not been reached appears. There is a high possibility that under-display or measurement failure will occur. Furthermore, it is also influenced by external factors such as the diameter of the apical foramen and the thickness of the measuring electrode of the file drill, etc., so whether the change in resistance value is due to a change in the position of the file drill in the root canal or not. There was also the problem that it was difficult to distinguish between factors, and mislabeling was likely to occur.

On the other hand, although the latter method solves the above-mentioned problems, it requires applying two types of signals into the root canal at the same time and making judgments by successively comparing the detection results from these, which makes the circuit difficult. In addition, calibration is required each time a measurement is made to remove the influence of the condition inside the root canal, and especially in the case of multi-root canal teeth such as Tabe, calibration is required for each root, making the operation cumbersome. , there is a problem that efficiency of treatment is hindered.

FIG. 8 explains this calibration, with the horizontal axis representing the position of the electrode tip and the vertical axis representing the detected voltage corresponding to the impedance. Two types of frequencies f,,
The detected values for f, (where f,<f,) are generally larger for higher frequencies, and the rate of increase near the root apex is also large, and these values vary up and down depending on the condition inside the root canal. fluctuate.

Currently, the detected value in Sono's neck is ■. , Vl. , the detected value at the root apex position is V,, V, and the amount of change in each detected value due to a change in the electrode position is calculated as follows.1. If Δ■2, the difference in the amount of change Δ■2 - 8■ removes the influence of the condition inside the root canal,
It shows the relative change in impedance depending on frequency. That is, Δ■2−ΔV, = (V, −V
,. )-(V,-V,.)=(V2-V, )-(
V. - ■1°) is established, and the calibration corresponding to (■2° - ■1°) in the second term of the above equation is performed each time using the detected value at the son's neck. It is necessary to eliminate the influence of the conditions inside the pipe.

The present invention has focused on these points, and has been made with the object of providing an apex position detection device that does not require troublesome calibration and can accurately detect the apex position.

Means for Solving the Problems> In order to achieve the above object, the present invention includes a measurement signal output means for repeatedly applying a measurement voltage between a measurement electrode and an oral cavity electrode continuously or at predetermined intervals; Comparison means for comparing the waveform of the applied measurement voltage and the waveform of the load current flowing between both electrodes is provided, and when the tip of the measurement electrode reaches the vicinity of the root apex, the state of deviation between the voltage waveform and the current waveform is determined. The apex position is detected by detecting the change using a comparison means.

Further, the above-mentioned measured voltage is made into a repetitive waveform, and a phase shift between the measured voltage and the load current is detected by the comparison means.

Further, the measured voltage has a single waveform or a repetitive waveform, and the comparison means detects changes in the waveforms of the measured voltage and the load current.

Furthermore, at least two different transient phenomena caused by impedance including a capacitive component between the measurement electrode and the oral cavity electrode are used.
It is equipped with a measurement signal output means for repeatedly applying a measurement voltage consisting of a set of single-shot waveforms, and a comparison means for comparing the same set of waveforms of the load current flowing between both electrodes. The apex position is detected by detecting, by means of a comparison means, that a change occurs in the waveform of the load current of the same group when the load current reaches .

<Operation> When the capacitance component of the equivalent impedance increases, the phase of the current with respect to the voltage naturally changes. In addition, in the case of a single waveform, it is possible to understand it in terms of a transient phenomenon rather than the concept of phase, and as the capacitance component of the equivalent impedance increases, the transient phenomenon naturally changes, and the current waveform for a voltage of the same shape changes. Therefore, by focusing on phase or transient phenomena, it is possible to detect a phase shift or a change in waveform shape between a voltage waveform and a current waveform, and use a comparison method to detect changes in the state of the shift or change in waveform shape. By sensing this, the position of the root apex can be detected.

<Example> Next, this invention will be explained in detail.

Figures 1 and 2 show a first embodiment in which the measured voltage has a repetitive waveform and the phase shift of the load current is detected. Figure 1 is a block diagram, and Figure 2 is an explanatory diagram of the waveform. It is.

In Fig. 1, 1 is a tooth, 1a and 1b are its root canals and apices, 2 is a measuring electrode, 2a is its tip, 3 is an oral cavity electrode, 4 is a repetitive signal generation circuit, 5 is a current limiting resistor, and 6 is a In the phase comparison circuit, 7 is a display section.

The repetitive signal generating circuit 4 generates a repetitive signal of, for example, 1 kHz as a measuring voltage, and applies this to the measuring electrode 2 such as a reamer or file via a current limiting resistor 5. The load current flowing between the measurement electrode 2 and the oral cavity electrode 3 is detected in the form of the voltage of the measurement electrode 2, and this detection voltage and the measurement voltage are input to the phase comparator circuit 6. Phase comparison circuit 6
is configured to output a pulse voltage with a width corresponding to the phase difference between the two mold pressures, and the display section 7 uses an appropriate device such as a pointer type meter, a signal tone or intermittent tone generator, or an intermittent light emitter. and is driven according to the pulse width of the pulse signal output from the phase comparator circuit 6.

In FIG. 2, A is the measured voltage waveform output from the repetitive signal generation circuit 4, B is the detected load current waveform, and B8 and B are the measured voltage waveforms output from the repetitive signal generating circuit 4. This is the waveform when it is located nearby. Further, C is an output waveform of the phase comparison circuit 6, and C1 and C2 show waveforms when the tip 2a of the electrode 2 is located near the tooth neck and root apex, respectively. A, B, and C in FIG. 1 correspond to each of these signal waveforms.

Since the equivalent circuit between the picture electrodes 2 and 3 is considered to be a parallel circuit of a resistor and a capacitor, when the measured voltage waveform A is a sine wave as shown in the figure, the load current waveform B.

Even though B2 and B2 are the same sine wave, their phases differ depending on the capacitance of the capacitor. For this reason, electrode 2
When the tip 2a approaches the vicinity of the root apex and the capacitance component of the equivalent impedance increases, the phase shift of the load current waveform with respect to the waveform A increases, and the output waveform C2 of the phase comparison circuit 6 increases.
The pulse width of C1 becomes larger than that of C1 depending on the phase difference. Therefore, the content displayed on the display unit 7, for example, the deflection of the pointer increases accordingly, and the deflection indicates that the apex has been reached.

The above is an example in which the phase shift increases as one approaches the root apex, but FIGS. 3 and 4 show an example in which the phase shift becomes smaller. In this example, a compensating capacitor Cc is inserted between the resistor 5 and the measuring electrode 2 as shown in FIG.

Therefore, in the upper part of the root canal, the voltage of the measurement electrode 2 is not affected by the capacitance component in the root canal, and the phase advances due to the phase-advanced current caused by the capacitor Cc. However, as the root apex approaches, the capacitance component within the root canal increases and the current advances (the detected voltage of the measurement electrode 2 lags), and the phase shift becomes smaller.

Therefore, if the values of the capacitor Cc and the resistor 5 are appropriately selected, the position of the apex can be detected when the deviation becomes zero.

Next, a second embodiment will be described in which a deviation between the waveforms of the measured voltage and load current caused by a transient phenomenon is detected using a measured voltage having a single waveform with reference to FIGS. 5 and 6. FIG. 5 is a block diagram, and FIG. 6 is an explanatory diagram of waveforms.

In the figure, 11 is a single waveform generation circuit, 12 is a timing controller, 13 is a memory, 14 is a waveform comparison circuit,
15 is an A-D converter, and the others are the same as in FIG.

The single-shot waveform generating circuit 11 is configured to generate a triangular wave having an accurate slope and amplitude as a measurement voltage, such as the waveform shown in FIG. 6, and this triangular wave is applied to the measurement electrode 2 via a resistor 5. . The A-D converter 15 performs A-D conversion on the voltage generated at the measurement electrode 2 in response to the load current, that is, the load current waveform E, every predetermined unit time under the control of the timing controller 12, and It is configured to record the peak values of T1 to T. Also, memory 13
stores the peak values of the load current waveform obtained when the tip 2a of the electrode 2 reaches the root apex 1b at each time T1 to T as reference data, and the waveform comparison circuit 14 uses the reference data in the memory 13. and the load current waveform E obtained by the AD converter 15, and outputs a signal voltage according to the comparison result.

In other words, the load current waveform E1 when the tip 2a of the electrode 2 is located at the neck of the tooth, for example, has almost no capacitive component of the equivalent impedance, so it becomes a triangular wave that is equivalent to the measured voltage waveform, and there is a deviation in shape from the reference data. is large and the output of the waveform comparison circuit 14 is small. However, the tip 2a of the electrode 2
When the capacitance component of the equivalent impedance increases as the current approaches the root apex, the deviation of the load current waveform E2 from the reference data waveform becomes smaller due to the influence of the transient phenomenon, and the output of the waveform comparison circuit 14 increases. Therefore, on the display section 7, for example, the deflection of the pointer increases and the waveforms match, that is, the electrode 2
2 when the tip 2a has reached the root apex is displayed.

In this embodiment, the measured voltage has a single waveform, but even if the measured voltage has a repeated waveform, it can be detected by similar processing.

The invention of claim 4 is an extension of this method, in which the apex position is confirmed by the peak value and waveform shape of a single waveform, and FIG. 7 is an explanatory diagram of the waveform in this embodiment. Here, two triangular waveforms F and F' with different slopes and equal peak values are used as a set as the measurement voltage, and a waveform G corresponding to each triangular waveform F and F' is used as the load current.
, G' peak wave height values are detected and compared.

That is, when the tip 2a of the electrode 2 is located, for example, at the tooth neck, the equivalent impedance is almost only a resistance component, so there is no difference in the peak height value of the waveform G I IG' at that time. However, as the capacitive component becomes dominant near the apex, the transient phenomenon becomes different depending on the slope of the triangular waveform, so the waveforms differ in peak wave height values as shown in G, G,'. It becomes like this. Therefore, by using this phenomenon, the apex position can be detected in the same way as when using phase difference or waveform shape deviation.

Note that a set of two single-shot waveforms only needs to have different transient phenomena caused by capacitive impedance, and can be calculated by comparing the difference in waveform shape instead of comparing the peak wave height values as in the above example. It is also possible to detect the apex position.

<Effects of the Invention> As is clear from the explanation of the above embodiments, the present invention provides that when the tip of the measuring electrode reaches the vicinity of the root apex and the capacitance component of the equivalent impedance increases, the phase of the current with respect to the voltage and the transient phenomenon Based on a simple operating principle in which the current waveform changes, the apex position is detected based on the phase or waveform shift between the voltage and current waveforms.

Therefore, it is possible to always perform stable measurements regardless of the conditions inside the root canal, such as whether it is dry or wet, or whether there is a chemical solution or blood. There are no errors caused by external factors such as the thickness of the measurement electrode, and there is no need to perform troublesome calibration each time a measurement is made. Further, since the circuit configuration is simple, it is possible to reduce the size and reduce power consumption, and it becomes easy to obtain a device suitable for this type of device using a battery as a power source.

As described above, according to the present invention, various problems in the resistance detection method and impedance detection method described in the above-mentioned publication can be solved, and the root canal length measurement is simple in configuration, easy to operate, and clinically easy to use. It becomes possible to obtain a vessel.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of waveforms thereof, FIGS. 3 and 4 are block diagrams and explanatory diagrams of waveforms of a modified example of the embodiment, and FIG. 5 is an explanatory diagram of waveforms. is a block diagram of another embodiment, FIG. 6 is an explanatory diagram of its waveform, FIG. 7 is an explanatory diagram of the waveform of another embodiment of the invention, and FIG. 8 is an explanatory diagram of calibration in a conventional device. be. 1 Tooth, 1a Root canal, 1b Root apex, 2 Measuring electrode, 2a Tip, 3 Oral electrode, 4 Repetitive signal generation circuit, 5 Current limiting resistor , 6... Phase comparison circuit, 7... Display unit, 11... Single waveform generation circuit, 12... Timing controller, 13... Memo 1c, 14... Waveform comparison circuit, 15... A-D converter. Patent Applicant Morita Manufacturing Co., Ltd. Sub-Agent Patent Attorney Shino 1) Actual Figure 3 Figure 2 Figure 4 Figure Diagram Tooth neck 11 → Electrode position Apical diagram

Claims (4)

[Claims] (1) A device that detects the root apex position from changes in impedance between the measurement electrode and the oral cavity electrode, and measurement in which a measurement voltage is applied continuously or repeatedly at predetermined intervals between the measurement electrode and the oral cavity electrode. It is equipped with a signal output means and a comparison means for comparing the waveform of the applied measuring voltage and the waveform of the load current flowing between both electrodes, and when the tip of the measuring electrode reaches the vicinity of the root apex, the voltage waveform and the current waveform are compared. A root apex position detecting device, characterized in that the apex position is detected by detecting a change in the state of deviation of the root apex using a comparing means. (2) The apex position detection device according to claim 1, wherein the measured voltage has a repetitive waveform, and the comparison means detects a phase shift between the measured voltage and the load current. (3) The measured voltage is a single waveform or a repetitive waveform,
2. The root apex position detection device according to claim 1, wherein the comparison means detects changes in waveforms of the measured voltage and the load current. (4) A device for detecting the root apex position from a change in impedance between a measurement electrode and an oral electrode, the device comprising at least two different transient phenomena caused by impedance including a capacitive component between the measurement electrode and the oral cavity electrode. Equipped with a measurement signal output means for repeatedly applying a measurement voltage consisting of a set of single waveforms, and a comparison means for comparing the same set of waveforms of the load current flowing between both electrodes, the tip of the measurement electrode reaches near the root apex. A root apex position detection device, characterized in that the apex position is detected by detecting, by means of a comparison means, a change in the waveform of the load current of the same group.