JPH0464354A - Root point detecto - Google Patents

Abstract

PURPOSE:To detect a position of a root point accurately eliminating complicated calibration by detecting a change in ratio of impedance values within a root tube as a tip of a measuring electrode gets near the root point to decrease an equivalent impedance. CONSTITUTION:An output is applied to a measuring electrode 2 through a buffer 14. A load current is detected in the form of a voltage with a resistance 5, rectified with a waveform rectifier circuit 16 to shape a waveform thereof and then, converted to a digital data with an A/D converter 17. An arithmetic circuit 18 is so arranged to compute a ratio between a data by a measuring signal with a frequency (f) and a data by a measuring signal with the frequency 5f sequentially latching the data. The results of the computation are sent to a display section 19. Generally larger between detection values attributed to the two frequencies (f) and (5f) is the one with the higher frequency, an increas ing rate thereof is higher near the root point and hence, the ratio thereof increases as a tip 2a of the electrode 2 approaches the root point. For example, a deflection of a pointer indicates that the tip 2a of the electrode 2 reaches the root point.

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 affected by external factors such as the diameter of the apical foramen and the thickness of the measuring electrode of the file, reamer, etc., so whether the change in resistance value is due to a change in the position of the file or reamer in the root canal or external factors. There was also the problem that it was difficult to distinguish between the two, and mislabeling was likely to occur.

On the other hand, with the latter method, the above-mentioned problems are almost solved, but calibration is required each time measurements are taken to remove the influence of the conditions inside the root canal, especially when using multiple root canals such as prints. In the case of teeth, there is a problem in that calibration is required for each root, making the operation cumbersome and hindering the efficiency of treatment.

FIG. 4 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.

Now, the detected value at the tooth neck is Vl. , 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 expressed as Δ■1. Assuming Δv2, the difference in the amount of change Δ■, -Δ■1 removes the influence of the condition inside the root canal,
It shows the relative change in impedance depending on frequency. That is, Δ■, -ΔV, = (V,
-V. )−(V, −V□.)=(V, −V,
)−(V, .−■, .) holds true, and the second term of the above equation (v2゜−■,
. ) It is necessary to perform calibration each time to compensate for the bias amount corresponding to the amount of bias corresponding to the root canal, and to remove the influence of the condition inside the root canal. This has been done, for example, by manipulating adjustment resistors to adjust the offset of the device.

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-mentioned object, the present invention includes a signal output means for applying measurement signals of different frequencies between the measurement electrode and the oral cavity electrode, and a signal output means for applying measurement signals of different frequencies between the measurement electrode and the oral cavity electrode, and and a relative ratio detection means for calculating the ratio of the obtained intra-root canal impedance values, and when the tip of the measurement electrode reaches near the root apex, the equivalent impedance decreases and the ratio of the above-mentioned intra-root canal impedance values changes. The position of the root apex is detected by detecting the

<Operation (Explanation of Principle)> The operation and principle of this invention will be explained with reference to FIG. (a) of the figure shows the configuration of the measurement circuit, and (b) shows its equivalent circuit.

In the figure, 1 is a tooth, 1a and 1b are its root canal and root apex, 2 is a measurement electrode, 2a is its tip, 3 is an oral cavity electrode, and 4
5 is a measurement voltage generating circuit, and 5 is a load current detection resistor. The inside of the root canal, that is, between the measurement electrode 2 and the oral cavity electrode 3, can be regarded as an equivalent circuit in which a resistor and a capacitor are connected in parallel.The measurement voltage is V, the resistance value of the detection resistor 5 is R1, and the capacitance of the equivalent capacitor is Let kR be the value of C1 equivalent resistance. however,
k is a coefficient. The characteristic points here are as follows.

(a) Since C is very small in the II neck and k is very large compared to that in the root apex, kR is also large.

(b) The value of C increases exponentially and kR decreases as one approaches the root apex.

(C) Near the root apex, approximately (:, = 50nF, kR =
It becomes about 6.5Ω. Hereinafter, C at this time will be referred to as C0.

(d) The coefficient is determined by the environment in the root canal, such as the presence of medicinal solutions and blood; it is small when a good conductive liquid is dripped, and large when it is dry, so this acts as an error factor. do. Note that k also changes depending on the position within the root canal.

Now, let the voltage applied to the equivalent circuit of the root canal be Vt, and the load current be i, where ω = 2πf, f is the distance to the frequency V = i - R + Vt, the vertical axis is the voltage Vt, and the solid line When I was a big boy,
The broken line shows the change in the voltage Vt when the value is small. Near the root apex, there is a large difference in voltage Vt between the solid line and the broken line, indicating that it cannot be used as a detected value.

Here, 2 adopted in the latter described in the above-mentioned publication
The method of detecting the difference in impedance values corresponding to different types of frequency signals involves finding the Vt of the above equation 0 at different frequencies and calculating the difference. That is, for example, when using angular frequencies of ω and 5ω, the VtO value fluctuates as follows, and cannot be used as a detected value as it is. Figure 2 explains this relationship, and the horizontal axis is the root apex 1b of the tip 2a of the measuring electrode 2.■ In order to eliminate the echo, it is necessary to calibrate each root. It becomes.

On the other hand, in the present invention, the ratio of impedance values at two types of frequencies is determined, and the influence of k is reduced using the following equation (2).

In other words, ωC6R becomes smaller by the division process for k=1 to 10, and calibration for each root becomes unnecessary.

For example, in formula 0, C=100nF, R=10, Ω,
When =1 to 10 are substituted into f=1 as a ratio, the following table is obtained. As shown in this table, even if k changes, it is hardly affected, and by taking the ratio of impedance values at two types of frequencies, the influence of the condition inside the root canal is automatically eliminated. This eliminates the need for calibration for each root, which was required with the method of calculating the difference in impedance values, and enables accurate measurement regardless of the condition inside the root canal.

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

In the block diagram of FIG. 3, 11 is an oscillator that outputs a measurement signal of frequency f, 12 is an oscillator that outputs a measurement signal of frequency 5f, 13 is an analog multiplexer, and 14
1 is a buffer, 15 is a timing controller, 16 is a waveform shaping circuit, 17 is an A-D converter, 18 is an arithmetic circuit, 1
Reference numeral 9 is a display section, and the other parts are the same as in FIG. 1.

The timing controller 15 controls the timing of the operation of each circuit, and under this control, the analog multiplexer 13 changes the output of each oscillator 11, 12 to l, for example.
It is switched every O0m5ec, and its output is applied to the measurement electrode 2 via the buffer 14. The load current is detected in the form of voltage by the resistor 5, rectified by the waveform shaping circuit 16 to shape the waveform, and then converted to digital data by the AD converter 17. The arithmetic circuit 18 is configured to sequentially calculate the ratio between the data of the measurement signal of frequency f and the data of the measurement signal of frequency 5f while latching this data, and the calculation result is sent to the display section 19. For the display section 19, an appropriate device such as a pointer type meter, a signal tone or intermittent tone generator, or an intermittent light emitter is used.

With the above configuration and operation, the calculation results are displayed on the display unit 19, but the detected values at the two types of frequencies f and 5f are generally larger for the higher frequency, and the increase rate near the root apex is also higher. Since the ratio increases as the tip 2a of the electrode 2 approaches the root apex, the fact that the tip 2a of the electrode 2 has reached the root apex is indicated by, for example, the deflection of the pointer.

In addition, in this embodiment, the circuit after multiplexer 13 is configured in one system, so even if a malfunction occurs due to deterioration of some parts, the effect can be canceled by the division process to obtain the ratio. will be done. Therefore, there is an advantage that the stability of the device is improved and accurate measurements can continue to be made even if there is some aging of the circuit components.

<Effects of the Invention> As is clear from the above description, the present invention applies measurement signals of different frequencies between the measurement electrode and the oral cavity electrode, and calculates the intraroot canal impedance value obtained corresponding to each measurement signal. The apex position is detected by calculating the ratio and detecting a change in the ratio.

By taking the ratio of detected values in this way, it is possible to determine the conditions inside the root canal, such as whether the root canal is dry or moist, the presence of conductive fluids such as medicine or blood, and the apical pore. The influence of external factors such as the diameter of the electrode and the thickness of the measurement electrode is automatically eliminated, eliminating the need for troublesome calibration every time a measurement is made. It is also possible to automatically eliminate the effects of deterioration of component parts. Furthermore, since the influence of hum and other noises caused by AC power can be reduced, applications such as incorporating it into a scaler and enlarging root canals become easy. Therefore, it is possible to obtain a root canal length measuring instrument that is easy to operate, has high measurement accuracy, and is easy to use clinically, without the problems of the resistance detection method or impedance detection method described in the above-mentioned publication. be.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are diagrams showing a measurement circuit and its equivalent circuit for detailed explanation of the present invention, Figure 2 is an explanatory diagram of detection results, and Figure 3 is a block diagram of one embodiment. Figure, 4th
The figure is an explanatory diagram of calibration in a conventional device. l...Sonoga, 1a...root canal, 1b...root apex, 2.
...Measuring electrode, 2a... Tip, 3... Oral electrode, 4
...Measurement voltage generation circuit, 5...Load current detection resistor,
11.12... Oscillator, 13... Analog multiplexer, 15... Timing controller, 18.
...Arithmetic circuit, 19...Display section. Patent applicant Morita Seisakusho Co., Ltd. Multiple agents Patent attorney Shino 1) Actual diagram

Claims (1)

[Claims] (1) A device for detecting the root apex position from a change in impedance between a measurement electrode and an oral cavity electrode, comprising a signal output means for applying measurement signals of different frequencies between the measurement electrode and the oral cavity electrode, and each measurement and a relative ratio detection means for calculating the ratio of the intra-root canal impedance values obtained in response to the signals, and when the tip of the measuring electrode reaches the vicinity of the root apex, the equivalent impedance decreases, and the above-mentioned intra-root canal impedance value decreases. A root apex position detection device characterized by detecting a root apex position by detecting a change in the ratio.