JPS6220183Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a root canal length measuring device that measures the root canal length by inserting a probe into the root canal of a tooth and detecting an impedance value according to the insertion depth.

When it is necessary to know the root canal length when treating a tooth, one electrode is brought into contact with, for example, the oral mucosa, and the probe serving as the other electrode is inserted into the root canal of the tooth. It is well known that the root canal length is measured by detecting the impedance between the two electrodes, and a low frequency oscillator is generally used as the source of the measurement current flowing between the two electrodes. Conventionally, this type of root canal length measurement device uses a dry cell battery as a power source to avoid the influence of 60 (50) Hz noise from commercial power sources, and various devices for dental diagnosis use electric power lines as a power source. However, there are cases where only the root canal length measurement device uses dry batteries.
This means that when trying to configure a system that collectively processes data from various dental diagnostic devices,
When exchanging data between the root canal length measuring device and other devices, power supply isolation problems and power consumption problems arise. Furthermore, while the system operates on commercial power, having to switch the power source to dry cell batteries when measuring root canal length is not desirable from the operational standpoint of the entire system, and malfunctions due to voltage drop in the dry cell batteries may occur. There was also the problem of easy forgetfulness.

In order to solve the problems caused by devices using dry batteries, the present inventors have devised a root canal length measuring device that uses commercial power and have already filed an application. Its contents are as follows.

Of course, this is a device that operates without any problems with commercial power supply, and the oscillation frequency of the oscillation stage is set sufficiently higher than the frequency of the commercial power supply, the output impedance is set low, and the probe It is characterized by sending the obtained signal output to the detection section via a bandpass filter, and as shown in Fig. 1, it includes a power supply section 2 that converts the commercial power supply 1 to direct current, and a low frequency output for the measurement current. An oscillation stage 3 that oscillates, a differential amplification stage 5 that amplifies the signal output generated across the resistor 4, a bandpass filter 6, and a detection stage 7.
The ground-side electrode 8 is brought into contact with an appropriate location on the oral mucosa, the probe 9 is inserted into the root canal of the tooth, and a measurement current is passed through the human body. Then, by utilizing the fact that the current changes depending on the insertion depth of the probe 9 into the root canal and the voltage across the resistor 4 changes accordingly, this voltage is amplified by the differential amplifier 5 to insert the probe into the root canal. The length of the root canal is measured by reading with a meter 10 that the tip of the probe 9 has reached the root apex and measuring the insertion length of the probe 9 at that time.

Here, the oscillation stage 3 operates at a sufficiently high frequency o (for example o
= 1000Hz), and the output side A
The output impedance at the point is set to a sufficiently low value (for example, several tens of ohms). At point B of the probe 9, 60 (50) Hz is applied to the human body by induction from an electric light line.
noise is generated, and this noise increases the resistance of the human body.
Assuming that the resistor 4 is 10MΩ and that noise enters point B from 100V AC through the human body, the resistor 4 is 5Ω.
Then, the noise voltage is 100V/10MΩ×5KΩ=
The voltage is 50 mV, which is approximately the same level as the signal level (several mV to several tens of mV) that is to be measured. This noise is superimposed on the original signal,
Although it is amplified by the differential amplifier 5, the characteristics of the bandpass filter 6 are set to have a narrow passband centered at o as shown in FIG.
Noise at a frequency sufficiently lower than o is attenuated by the bandpass filter 6, and only the original signal at the frequency o is sent to the detection stage 7, so that the meter 10 has high accuracy unaffected by noise.

By the way, in the circuit shown in FIG. 1, the measurement current flowing through the tooth is set to be small so as not to cause pain to the patient, so the alternating current voltage applied to the tooth is also small. Therefore, it is easily affected by 60 (50) Hz noise, and this problem could be solved by making the oscillation frequency sufficiently higher than that of the commercial power supply as described above. However, when this circuit was actually operated, it was found that a low applied voltage caused the effects of temperature changes, ie, voltage fluctuations and instability of the frequency output level. This is oscillation stage 3
This is particularly noticeable when using a sine wave oscillator such as a CR oscillator, in which the peak voltage value changes and frequency stability cannot be obtained.

This invention was made with the aim of eliminating such inconveniences, and the oscillation stage that supplies the measurement current is composed of a crystal or ceramic resonator that converts the DC voltage of the commercial power supply into a rectangular pulse output, and its oscillation output. A C-MOS counter that divides the AC frequency into a measurement frequency that is sufficiently higher than the commercial power supply frequency, a buffer circuit that converts this divided output into an exchange signal, and an attenuator that attenuates this AC signal into a weak voltage that is applied to the probe tip. It is characterized by having been configured.

A preferred embodiment of this invention will be described below with reference to FIGS. 3 and 4. In this figure, the same components as in FIG. 1 are denoted by the same reference numerals.

In the oscillation stage 11, X ₁ is a crystal oscillator or ceramic oscillator with good frequency accuracy and temperature characteristics, and the oscillation circuit 12 is formed by this X ₁ , amplifier IC ₁ , resistors R ₁ , R ₂ , and capacitors C ₁ , C ₂ . configured. The oscillation frequency of this _crystal resonator or ceramic resonator
It is led to IC ₂ and converted to a frequency of 1KHz as shown in the circuit shown in Figure 1. This C-MOS frequency divider IC ₂ has a characteristic that the output voltage level is stable, and the stability of the amplitude of the oscillation output for measurement with respect to temperature is achieved. This 1KHz
Since the oscillation output is not centered on OV, it is sent to a puffer circuit 13 including an operational amplifier OP ₁ , resistors R ₃ and R ₄ , and a capacitor C ₃ , and the average value is converted to AC at OV. This output is divided by resistors _R5 and _R6 that make up the attenuator, and the AC voltage applied to the probe 9 is adjusted to an appropriate value for measurement (several mV to several tens of mV).
mV), and then sent to the probe 9 through a resistor _R7 . At this time, the resistance R ₆ is set to a small value (for example, about 10Ω). This is clear from the explanation of FIG. Also, capacitor _C4 is for DC cut.

It is clear that the differential amplification stage 14 amplifies the voltage generated across the resistor _R7 by differential operation, but the resistor is used especially for gain adjustment.
R ₈ is provided with a resistor R ₉ for CMR adjustment.

The bandpass filter 15 needs to be stable against temperature changes because the measurement involves the amplitude of the detection signal. In an active filter using operational amplifiers OP ₂ to _{OP 4} like this circuit,
The temperature characteristics are mostly determined by the temperature characteristics of C and R, and since C and R inevitably change with temperature, a circuit configuration is desired that reduces the change in the characteristics of the entire filter (element sensitivity) in response to these changes. Here, a biquad circuit with low element sensitivity is used, and a polystyrene capacitor and metal film resistor are used.

The half-wave rectifier stage 16 performs half-wave rectification by means of an ideal diode using an operational amplifier _OP5 .

The low-pass filter 17 is not necessary when the measured value is indicated by the meter 10 as shown in FIG. 1, but when the measured output is passed through an A/D converter for digital conversion and processing, Since this is inconvenient, this circuit is connected in this embodiment.

Therefore, the 250KHz rectangular wave pulse created by the oscillation circuit 12 is reduced to 1KHz by the C-MOS frequency divider IC ₂ , and converted into an AC signal by the puffer circuit 13, and the attenuator resistors R ₅ and R ₆ After the voltage is attenuated to a small voltage of several mV to several tens of mV, it is sent to the probe 9. The current changes depending on the insertion depth of the probe 9 into the root canal, and the differential amplifier 14 extracts and amplifies the change in voltage across the resistor _R7 that follows this, and then the bandpass filter 15 The narrow pass band centered around 1KHz attenuates noise at frequencies sufficiently lower than 1KHz (commercial power supply frequency), and only the original 1KHz signal is passed through the half-wave rectifier stage 1.
After converting it to direct current in step 6, it passes through a low-pass filter 17.

In this way, in the oscillation stage 11, the oscillation output is obtained by the crystal resonator or ceramic resonator _X1 with excellent frequency accuracy and temperature characteristics, and the frequency is divided by the C-MOS frequency divider _IC2 with stable amplitude. Since the oscillation output is obtained, accurate root canal length measurement can be performed by eliminating voltage fluctuations and frequency instability caused by temperature changes. This can be improved by synergistically with the biquad configuration, suppressing temperature changes in gain and increasing measurement accuracy. Furthermore, since the alternating current voltage applied to the probe 9 is low, ranging from several mV to several tens of mV, there is almost no electrical stimulation and a high level of safety can be achieved.

As is clear from the detailed explanation above, when using the present invention, the oscillation frequency is The drawbacks of the prior application mentioned above, which adopted a configuration that makes the frequency sufficiently higher than the commercial power supply frequency, are that the applied voltage is low, so the voltage fluctuates due to temperature changes, and the output level of the frequency This prevents instability and allows accurate root canal length measurement at all times, and the gain of the bandpass filter
Measurement accuracy can be improved by synergistic frequency characteristics.

Furthermore, since the alternating current voltage applied to the probe can be made weak by using an attenuator, there is almost no electrical stimulation to the patient, resulting in practical effects such as ensuring the safety of measurements.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a root canal length measurement device previously filed by the applicant of this invention, Figure 2 is a characteristic diagram of a bandpass filter, Figure 3 is a block diagram of this invention, and Figure 4 is its details. This is a circuit diagram. Explanation of symbols, 8... Ground side electrode, 9... Probe, 11... Oscillation stage, 13... Puff circuit,
X ₁ ……Crystal resonator or ceramic resonator,
IC ₂ ... C-MOS counter (frequency divider), R ₅ , R ₆ ...
...Attenuator.

Claims (1)

[Scope of utility model registration request] a power supply section that converts commercial current into direct current, an oscillation stage that supplies a measurement current between an electrode that is in contact with the oral mucosa, etc., and a probe serving as the other electrode that is inserted into the root canal of the tooth; The probe is equipped with a differential amplification stage for amplifying the signal output obtained from the probe, a bandpass filter having a characteristic of adapting the signal output to the oscillation frequency, and a detection stage, and the probe is inserted into the root canal of the tooth. In a root canal length measurement device that measures the root canal length by detecting an impedance value between the two electrodes according to the insertion depth of the root canal, the oscillation stage converts a voltage obtained by converting a commercial power source into a DC voltage into a rectangular pulse output. A crystal or ceramic resonator and a C that divides its oscillation output into a measurement frequency that is sufficiently higher than the commercial power supply frequency.
- A root canal length measuring device comprising a MOS frequency divider, a puffer circuit that converts the frequency-divided output into alternating current, and an attenuator that attenuates this alternating current to a weak voltage applied to a probe.