DE102006035681B4 - Method for determining the position of a measuring electrode introduced into a tooth root canal - Google Patents

Abstract

Method for determining the position of the tip of a measuring electrode introduced into a tooth root canal, in which the electrode is supplied with an electrical signal and the impedance between the electrode and a counter electrode fixed in or on the mouth is measured, in which a voltage jump function is applied between the two electrodes, characterized by forming the difference between the first voltage Ut1 detected at a time t1 and the second voltage Ut2 detected at a time t2.

Description

The invention relates to a method for determining the position of the tip of a measuring electrode inserted into a tooth root canal, in which the electrode is supplied with an electrical signal and the impedance between the electrode and a counter electrode fixed in or on the mouth is measured, wherein a voltage jump function between the two Electrodes is applied.

Such a method is known from DE 698 20 601 T2 The localization of the root of the tooth or root of the tooth is effected by a metallic file introduced into the root canal, with which the pulp is removed, whereby the dentist leading the file must not go beyond the root. It is therefore necessary to recognize that the file is approaching the root. For this purpose, the cited patent proposes to form the file as an electrode and to apply a jump voltage between it and a counter electrode applied in the patient's mouth via a resistor and then to measure the voltage course (ie the course of the current flowing between the electrodes). whereby a value corresponding to the impedance between the electrodes is determined.

In the cited patent, a first value is then acquired at a first time and a second value at a second time; an arithmetic circuit forms the quotient of both values.

From the EP 0 392 518 A1 It is known to apply the file with two different frequencies and to detect the difference of the impedances. Other known methods are in the US 5 080 586 A , of the DE 41 26 753 C2 and the US Pat. No. 6,845,265 B2 disclosed.

It has been found that these methods are subject to errors, in particular, a reliable change in the resulting value when approaching the root cause is not guaranteed.

The invention is therefore based on the object to propose a method that indicates the achievement of the root cause with greater accuracy.

According to the invention, this object is solved by the features of claim 1.

In this case, the electrodes are subjected to a voltage jump, the difference between a first voltage U t1 detected at a time t 1 and a second voltage U t2 detected at a time t 2 is understood, it being understood that instead of a voltage jump, a constant rising constant Power can be applied and the voltage function can be detected.

Preferably, the time t1 is 20 to 100 microseconds after the voltage jump and the time t2 40 to 200 microseconds after the voltage jump.

Particularly it is preferred that a control value is determined and a detected _t3 to a time t3, _t4 fourth voltage U by forming the difference between detected at a time t3 third voltage U and the measurement is rejected for failure to meet a minimum amount. The time t3 and the time t4 should be 1 ms to 4 ms after the start of the signal.

The invention will be explained below with reference to drawings. Showing:

1 the circuit structure for carrying out the method, and

2 the resulting voltage curve with the times t1, t2, t3 and t4.

In 1 the circuit layout is shown.

Via the resistors R1 and R2, a jump voltage of 50 mV is applied between the two electrodes, namely the file inserted into the tooth root canal and the counter electrode fixed in the mouth. An A / D converter in the microprocessor μC stores the voltage values U _t1 , U _t2 , U _t3 and U _t4 detected at the time t1, t2, t3 and t4 after the start of the step function and calculates the root channel length WL using the formula WL = U _t1 - U _t2 . Then the control value SAK (apparent apex control value) is rejected by means of the formula U _{t3 -U t4} and the determined value WL if the SAK value does not correspond to a minimum gradient.

Then a negative voltage jump of -50 mV is applied to discharge the electrodes, the next measuring cycle begins.

Claims (4)

Method for determining the position of the tip of a measuring electrode introduced into a tooth root canal, in which the electrode is supplied with an electrical signal and the impedance between the electrode and a counter electrode fixed in or on the mouth is measured, in which a voltage jump function is applied between the two electrodes, characterized by forming the difference between the detected at a time t1 the first voltage and the detected U _t1 to a time t2, second voltage U _t2. A method according to claim 1, characterized in that the time t1 20 to 100 microseconds after the beginning of the voltage jump and the time t2 40 to 200 microseconds after the beginning of the voltage jump. Method according to one of the preceding claims, characterized in that a control value is determined by forming the difference between the third voltage U _t3 detected at a time _t3 and the fourth voltage U _t4 detected at a time t4 and _discarding the measurement if a minimum amount is not reached , A method according to claim 3, characterized in that the time t3 and the time t4 is 1 ms to 4 ms after the beginning of the voltage jump.

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