Surgery – Diagnostic testing – Measuring anatomical characteristic or force applied to or...
Reexamination Certificate
1999-08-24
2001-04-24
Hindenburg, Max (Department: 3736)
Surgery
Diagnostic testing
Measuring anatomical characteristic or force applied to or...
C600S547000
Reexamination Certificate
active
06221031
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an improved process and device for locating the apex of a tooth.
More exactly, the invention provides a process and device for measuring in real time the distance between the distal end of an electrode inserted in the root canal of a tooth and the apex of said canal, this measurement being insensitive to anything other than the pulp, in said canal, of blood, pus, debris, water or antiseptics such as hydrogen peroxide, sodium chloride or sodium hypochlorite.
DESCRIPTION OF THE RELATED ART
The location of the apex or the apical constriction is important in the procedure of treating the dental canal because the success of the latter depends on the total removal of the pulp tissue.
To this end, the dentist uses a metallic endocanal rasp which slides in the root and, by its movement of rotation and back-and-forth movement, it scrapes the walls of the canal so as to depulp it and to descend more and more deeply into the root, and this without extending beyond the apical constriction, which can cause trouble for the patient and lead to an abscess.
It is therefore important to be able to locate precisely the apex of the root to be cleaned.
For this purpose, several processes have been used.
The process most used at present consists in inserting a rasp into the canal by successive approaches and monitoring with a succession of x-ray samples to place the rasp in position at the apex.
Then the dentist adjusts the abutment of the rasp against a cuspid scale to determine the depth of the canal.
This technique is inadequate and undesirable because of the dose of radiation to which the patient is subjected or because of curves in the canal or a lateral apex, which is a source of errors of reading and of analysis of the samples.
Another process (U.S. Pat. No. 5,049,069) based on the discovery that the measurement of electrical impedance between an electrode placed at the apex and a reference electrode placed in the mouth of the patient, gives a constant value no matter what the apex and no matter what the patient. 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 over several millimeters.
These processes, based on this discovery, are not reliable, because the measurement depends on variations of impedance at the level of the reference electrode disposed in the mouth of the patient.
They are adjusted for a measurement made in a sound pulp and they do not function in media such as hypochlorite, sodium chloride, blood, etc. because the impedance of the medium is modified.
Another more reliable process (French patent 93/13802) operates with canal media, known in advance, using measurements of impedance between an electrode such as a rasp inserted in the dental canal and two other reference electrodes connected to the lip of the patient, and permits eliminating errors due to variations of the reference contacts and hence to increase the reliability of the measurement. It can measure in blood or in very conductive media such as hypochloride, by creating a staged offset of origin of the resistivity of the medium.
Another process (U.S. Pat. Nos. 5,080,586 and 5,112,224) uses two impedance measurements at two different frequencies, for example 1 khz and 5 khz, between an electrode such as a rasp inserted in the root canal and an electrode abutting the oral mucosa, the impedances not having the same frequency response upon approaching the apex. There is carried out a substraction of the two measurements. This difference in approaching the apex will give the measurement. This process provides a manual or automatic zero reset of the output of the subtractor, by a button or a detection, when the rasp has been inserted in the canal, acting on a memorized offset of one of the inputs of the subtractor, and permits determining the movement of a zero reset at the output. A difference between the impedances having frequent respective frequency responses discloses at a specified value the position of the apical opening (FR 2.668.701-A1).
This process requires a calibration for each canal to be measured, which is hardly practical or is a source of errors in current usage.
Another process (U.S. Pat. No. 5,096,419) uses two impedance measurements at two different frequencies, for example 400 hz and 8 khz, between an electrode such as a rasp inserted in the root canal and an electrode abutting on the oral mucosa, the impedances having not the same response in frequency to the approach of the apex. There is carried out a ratio of the two measurements to eliminate the variation of the impedances due to the media in which the rasp is located in the canal.
This process gives errors when the medium becomes insulating such as hydrogen peroxide. Thus the responses of the two frequencies are no longer entirely ratiometric.
SUMMARY OF THE INVENTION
The present invention provides a different measurement process, without calibration, independent of the medium in the canal, and of high precision.
The present invention provides a process for locating the apex of a root canal of a tooth and/or for measuring the canal distance by means of the measurement of variations of time constants of the resistances/capacitances encountered, between an electrode such as a dental rasp inserted in the root canal, and a second electrode disposed for example on the buccal mucosa of the patient, characterized in that:
There is applied to the terminals of the electrodes a current or a given continuous voltage.
A square signal of predetermined frequency permits repetition of the measurements in real time, creating positive and negative alternation.
After amplification, the origin of the measurements is fixed at the level obtained at 0 &mgr;S.
There are thus carried out two time measurements of the alternation.
It will be noted on
FIGS. 5 and 6
, that one measurement (A) develops very little when the rasp is located between 5 mm and 1.5 mm, and revolves more in the region of the apex, whilst measurement (B) develops in a substantially linear manner.
A ratiometric computation of the measurements (A) and (B) is then carried out to eliminate the effect of perturbances such as the change of medium, the change of diameter of the rasps;
M
=
A
B
-
K1
or
M
=
K1
-
B
A
The squared measurements before computation of the ratio give a better linearity, thus the development of the signal to be measured is exponential.
The formulae operate for conductive media and very conductive media, they operate a bit less well in media that are hardly conductive, such as hydrogen peroxide.
To be less sensitive to the less conductive media:
There is carried out in time three measurements alternately. A measure (A) and a measure (B) carried out as before and a measure (C) as shown in
FIGS. 5 and 6
which develops in the portion between 5 mm and 0.5 mm and very little in the region of the apex.
There is carried out the computation
M
=
A
*
C
B
*
B
-
K1
or the calculation
M
=
K1
-
B
*
B
A
*
C
So as to attain a final result of the distance on the desired scale, the value M is multiplied by a suitable coefficient, which represents the distance comprised between the distal end of the rasp and the apex.
For the preceding radiometric computation, K1 is a known constant and permits obtaining location of the apex at a value located at zero voltage for example.
If a measurement is made with negative alternation, there is applied a current or a voltage of opposite direction. The resulting M will be inverted.
The measurements will be measurements of voltage at the terminals of the electrodes if the signal applied to the electrodes is a current.
The measurements will be measurements of current passing through the electrodes if the signal applied to the electrodes is a voltage.
The measurements are carried out with positive and/or negative alternation.
The present invention also provides a dev
Hindenburg Max
Young & Thompson
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