U.S. patent application number 12/174151 was filed with the patent office on 2008-11-13 for root apex position detection method.
Invention is credited to Masahiro Otsuka, Shigeru Shoji.
Application Number | 20080280261 12/174151 |
Document ID | / |
Family ID | 33549282 |
Filed Date | 2008-11-13 |
United States Patent
Application |
20080280261 |
Kind Code |
A1 |
Shoji; Shigeru ; et
al. |
November 13, 2008 |
ROOT APEX POSITION DETECTION METHOD
Abstract
Methods of detecting a root apex position of a root canal of a
test tooth, including applying a plurality of types of measurement
signals to one of the measurement electrode and the mouth
electrode; sequentially applying each of the plurality of types of
measurement signals to one of the measurement electrode and the
mouth electrode; sequentially detecting a plurality of electrical
characteristic values between the measurement electrode and the
mouth electrode based on each of the applied measurement signals
using a detection unit. The methods further include obtaining a
test tooth data group; comparing the test tooth data group with a
plurality of model tooth data groups; detecting whether one of the
plurality of model tooth data groups is in a predetermined
relationship with the test tooth data group; and displaying the
detected result.
Inventors: |
Shoji; Shigeru; (Miyagi-ken,
JP) ; Otsuka; Masahiro; (Kanagawa-ken, JP) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH LLP
Two Prudential Plaza, 180 North Stetson Avenue, Suite 2000
CHICAGO
IL
60601
US
|
Family ID: |
33549282 |
Appl. No.: |
12/174151 |
Filed: |
July 16, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11297993 |
Dec 9, 2005 |
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12174151 |
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PCT/JP2004/007046 |
May 18, 2004 |
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11297993 |
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Current U.S.
Class: |
433/215 |
Current CPC
Class: |
A61C 19/042 20130101;
A61C 19/04 20130101 |
Class at
Publication: |
433/215 |
International
Class: |
A61C 19/06 20060101
A61C019/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 11, 2003 |
JP |
2003-167008 |
Claims
1. A method of detecting a root apex position of a root canal of a
test tooth, wherein a measurement electrode is inserted into the
root canal, a mouth electrode is placed onto an intraoral surface,
and the measurement electrode is moved through the root canal
towards the root apex position, the method comprising: applying a
plurality of types of measurement signals to one of the measurement
electrode and the mouth electrode; sequentially applying each of
the plurality of types of measurement signals to one of the
measurement electrode and the mouth electrode; sequentially
detecting a plurality of electrical characteristic values between
the measurement electrode and the mouth electrode based on each of
the applied measurement signals using a detection unit; obtaining a
test tooth data group comprising the plurality of electrical
characteristic values sequentially detected by the detection unit;
comparing the test tooth data group with a plurality of model tooth
data groups, each of the model tooth data groups comprising
electrical characteristic values from between the measurement
electrode and the mouth electrode with respect to each of the
plurality of types of measurement signals obtained when a distal
end of a measurement electrode is placed at a root apex of a model
tooth, the model tooth including different model teeth for each
model tooth data group; detecting whether one of the plurality of
model tooth data groups is in a predetermined relationship with the
test tooth data group; and displaying the detected result.
2. The method of claim 1, wherein the plurality of types of
measurement signals differ from each other in at least one of
frequency, waveform, and peak value.
3. The method of claim 1, wherein the plurality of types of
measurement signals comprise two types of measurement signals, such
that the two types of measurement signals have voltages which
differ from each other in frequency.
4. The method of claim 1, wherein the electrical characteristic
value is at least one of an impedance value between the two
electrodes, a current value flowing between the two electrodes, a
voltage value between the two electrodes, and a phase difference
between the current value or voltage value between the two
electrodes and the measurement signal.
5. The method of claim 1, wherein the predetermined relationship
with the test tooth data group is at least one of a relationship in
which the test tooth data group coincides with any one of the
plurality of the model tooth data groups and a relationship in
which a difference between the test tooth data group and the model
tooth data group falls within a predetermined range.
6. The method of claim 1, wherein displaying the detected result is
used for at least one of displaying on, warning on, and controlling
a dental instrument.
7. The method of claim 1, wherein each of the plurality of model
tooth data groups is one of measured data based on an actual tooth,
theoretical data, simulation data, approximate data obtained by
calculation based on measured data, or a combination thereof.
8. The method of claim 1, further comprising root apex position
model data and predictive intra-root-canal-position-specific model
data, the root apex position model data comprising the plurality of
model tooth data groups and the predictive
intra-root-canal-position-specific model data comprising an
electrical characteristic value predicted in a state in which the
distal end of the measurement electrode is located at a position
before the root apex position, the method further comprising the
steps of: comparing a measured electrical characteristic value
sequentially detected by the detection unit with the root apex
position model data and the predictive
intra-root-canal-position-specific model data; detecting whether at
least one of the root apex position model data and the predictive
intra-root-canal-position-specific model data include data in a
predetermined relationship with the measured electrical
characteristic value; and outputting a detected result.
9. The method of claim 8, further comprising predicting an
electrical characteristic value at a position midway between an
intra-root-canal position indicated by the outputted, detected
result and the root apex position, wherein the predicted impedance
value is used as the intra-root-canal-position-specific model
data.
10. A method of detecting a root apex position of a test tooth and
a distance between a distal end of a measurement electrode and the
root apex position, wherein a measurement electrode is inserted
into the root canal, a mouth electrode is placed onto an intraoral
surface, and the measurement electrode is moved through the root
canal towards the root apex position, the method comprising:
applying a plurality of types of measurement signals to one of the
measurement electrode and the mouth electrode; sequentially
applying each of the plurality of types of measurement signals to
one of the measurement electrode and the mouth electrode;
sequentially detecting a plurality of electrical characteristic
values between the measurement electrode and the mouth electrode
with respect to each of the applied measurement signals using a
detection unit; obtaining a test tooth data group comprising the
plurality of electrical characteristic values sequentially detected
by the detection unit; comparing the test tooth data group with a
plurality of model tooth data groups, each of the model tooth data
groups comprising electrical characteristic values from between the
measurement electrode and the mouth electrode with respect to each
of the plurality of types of measurement signals obtained when a
distal end of a measurement electrode is located at each of a
plurality of predetermined positions in a model tooth, the model
tooth including different model teeth for each model tooth data
group; detecting whether one of the plurality of model tooth data
groups is in a predetermined relationship with the test tooth data
group; and displaying the detected result as a position
information.
11. The method of claim 10, further comprising displaying the
detected result using a display unit.
12. The method of claim 11, wherein the plurality of types of
measurement signals differ from each other in at least one of
frequency, waveform, and peak value.
13. The method of claim 11, wherein the plurality of types of
measurement signals comprise two types of measurement signals, the
two types of measurement signals having voltages which differ from
each other in frequency.
14. The method of claim 11, wherein the electrical characteristic
value is at least one of an impedance value between the two
electrodes, a current value flowing between the two electrodes, a
voltage value between the two electrodes, and a phase difference
between the current value or voltage value between the two
electrodes and the measurement signal.
15. The method of claim 11, wherein the predetermined relationship
with the test tooth data group is at least one of a relationship in
which the test tooth data group coincides with any one of the
plurality of model tooth data groups and a relationship in which a
difference between the test tooth data group and the model tooth
data group falls within a predetermined range.
16. The method of claim 11, wherein displaying the detected result
is used for at least one of displaying on, warning on, and
controlling a dental instrument.
17. The method of claim 11, wherein each of the plurality of model
tooth data groups is one of measured data based on an actual tooth,
theoretical data, simulation data, approximate data obtained by
calculation based on measured data, or a combination thereof.
18. The method of claim 11, further comprising
intra-root-canal-position-specific model data and predictive
intra-root-canal-position-specific model data, the
intra-root-canal-position-specific model data comprising the
plurality of model tooth data groups and the predictive
intra-root-canal-position-specific model data comprising an
electrical characteristic value predicted at a position midway
between a first predetermined position of a plurality of
predetermined positions and a second predetermined position, the
method further comprising the steps of: comparing a measured
electrical characteristic value sequentially detected by the
detection unit with the intra-root-canal-position-specific model
data and the predictive intra-root-canal-position-specific model
data; detecting whether at least one of the
intra-root-canal-position-specific model data and the predictive
intra-root-canal-position-specific model data include data in a
predetermined relationship with the measured electrical
characteristic value; and outputting a detected result.
19. The method of claim 18, further comprising predicting an
electrical characteristic value at a position midway between an
intra-root-canal position indicated by the outputted, detected
result and the next intra-root-canal position, wherein the
predicted electrical characteristic value is used as the
intra-root-canal-position-specific model data.
20. The method of claim 18, wherein the plurality of types of
measurement signals comprise two types of measurement signals, the
two types of measurement signals having voltages which differ from
each other in frequency.
21. The method of claim 18, wherein the electrical characteristic
value is at least one of an impedance value between the two
electrodes, a current value flowing between the two electrodes, a
voltage value between the two electrodes, and a phase difference
between the current value or voltage value between the two
electrodes and the measurement signal.
22. The method of claim 18, wherein the predetermined relationship
is at least one of a relationship in which the test tooth data
group coincides with any one of a plurality of model tooth data
groups in the intra-root-canal-position-specific model data and a
relationship in which a difference between the test tooth data
group and the model tooth data group falls within a predetermined
range.
23. The method of claim 18, wherein outputting the detected result
is used for at least one of displaying on, warning on, and
controlling a dental instrument.
24. The method of claim 18, wherein the root apex position model
data is one of measured data based on an actual tooth, theoretical
data, simulation data, approximate data obtained by calculation
based on measured data, or a combination thereof.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/297,993, filed Dec. 9, 2005, herein
incorporated by reference in its entirety, which is a continuation
application of International Patent Application No.
PCT/JP2004/007046, filed May 18, 2004, herein incorporated by
reference in its entirety, which was published under PCT Article
21(2) in Japanese.
[0002] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2003-167008,
filed Jun. 11, 2003, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to a root apex position
detection apparatus which is used to measure root canal length in
dental diagnosis and treatment.
[0005] 2. Description of the Related Art
[0006] When treating a tooth, a dentist sometimes needs to remove
the dental pulp and nerve in the root canal. In this case, the
dentist measures a distance between the tooth crown and the root
apex and removes the dental pulp and nerve in the root canal by an
amount corresponding to the distance or infected dentin or foreign
bodies in the root canal. For distance measurement, a root apex
position detection apparatus is used. In using the root apex
position apparatus, a mouth electrode is placed in oral cavity, and
a measurement electrode is inserted into the root canal. An AC
signal is then applied between the measurement electrode and the
mouth electrode, and the root apex position is detected in
accordance with the value of a signal (electrical characteristic
value) measured when the measurement electrode reaches the root
apex position.
[0007] By monitoring that the indicator of a display unit indicates
a predetermined position, the dentist knows that the measurement
electrode has reached the root apex.
[0008] It is important for treatment in the root apex to accurately
detect the root apex position of the tooth. If the root apex
position is not accurately detected, the above distance will
contain an error. If the dentist performs treatment trusting the
distance containing the error, the dental pulp and nerve or
infected dentin or foreign bodies may be left in the root canal, or
the dentist may damage the root apex during operation.
[0009] The state inside the root canal of the tooth to be treated
varies, case by case, from a dry state in which the interior of the
root canal is dry to a wet state in which the interior of the root
canal is filled with blood or the like. A conventional root canal
length measurement apparatus can accurately detect the root apex
position if the state inside the root canal of the tooth satisfies
predetermined conditions (thickness, shape (arcuation or
bifurcation), and the degree of dryness/wetness). If, however, the
state inside the root canal of the tooth does not satisfy the
specific conditions, the measured value contains an error.
[0010] A mark indicating the root apex position and marks adjacent
to the root apex position are formed on a scale mark on the display
of the conventional root apex position detection apparatus. If the
state inside the root canal satisfies the specific conditions as
described above, the scale mark can accurately indicate that the
measurement electrode is located at the root apex position.
However, the marks adjacent to the root apex position only indicate
that the measurement electrode is located around the root apex
position, but cannot indicate how far the measurement electrode is
away from the root apex position.
[0011] In addition, before measuring the root canal length with a
conventional root canal length measurement instrument, it is
necessary to match a position of a silicone stopper inserted in a
reamer or file to the root canal length by using a radiograph. Even
if a mark is made by the silicone stopper added to the reamer or
file or the silicone stopper added to the reamer or file which has
once determined the root canal length, the silicone stopper is
shifted, and an accurate length cannot be displayed in some cases.
When the mark is hidden behind the tooth and cannot be recognized
on a radiograph, the measurement operation must be stopped
halfway.
BRIEF SUMMARY OF THE INVENTION
[0012] It is an object of the invention of the present application
to solve at least one of the problems in the prior art described
above.
[0013] According to a first aspect of the invention of the present
application, there is provided a method of detecting a root apex
position of a root canal of a test tooth, wherein a measurement
electrode is inserted into the root canal, a mouth electrode is
placed onto an intraoral surface, and the measurement electrode is
moved through the root canal towards the root apex position. The
method includes applying a plurality of types of measurement
signals to one of the measurement electrode and the mouth
electrode; sequentially applying each of the plurality of types of
measurement signals to one of the measurement electrode and the
mouth electrode; sequentially detecting a plurality of electrical
characteristic values between the measurement electrode and the
mouth electrode based on each of the applied measurement signals
using a detection unit; obtaining a test tooth data group
comprising the plurality of electrical characteristic values
sequentially detected by the detection unit; comparing the test
tooth data group with a plurality of model tooth data groups, each
of the model tooth data groups comprising electrical characteristic
values from between the measurement electrode and the mouth
electrode with respect to each of the plurality of types of
measurement signals obtained when a distal end of a measurement
electrode is placed at a root apex of a model tooth, the model
tooth including different model teeth for each model tooth data
group; detecting whether one of the plurality of model tooth data
groups is in a predetermined relationship with the test tooth data
group; and displaying the detected result.
[0014] According to a second aspect of the invention of the present
application, there is provided a method of detecting a root apex
position of a test tooth and a distance between a distal end of a
measurement electrode and the root apex position, wherein a
measurement electrode is inserted into the root canal, a mouth
electrode is placed onto an intraoral surface, and the measurement
electrode is moved through the root canal towards the root apex
position. The method includes applying a plurality of types of
measurement signals to one of the measurement electrode and the
mouth electrode; sequentially applying each of the plurality of
types of measurement signals to one of the measurement electrode
and the mouth electrode; sequentially detecting a plurality of
electrical characteristic values between the measurement electrode
and the mouth electrode with respect to each of the applied
measurement signals using a detection unit; obtaining a test tooth
data group comprising the plurality of electrical characteristic
values sequentially detected by the detection unit; comparing the
test tooth data group with a plurality of model tooth data groups,
each of the model tooth data groups comprising electrical
characteristic values from between the measurement electrode and
the mouth electrode with respect to each of the plurality of types
of measurement signals obtained when a distal end of a measurement
electrode is located at each of a plurality of predetermined
positions in a model tooth, the model tooth including different
model teeth for each model tooth data group; detecting whether one
of the plurality of model tooth data groups is in a predetermined
relationship with the test tooth data group; and displaying the
detected result as a position information.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0015] FIG. 1 is a view showing one embodiment of a root apex
detection apparatus of the invention of the present
application;
[0016] FIG. 2 is a graph showing a relation between frequencies of
measurement signals applied to a measurement electrode at a root
apex position of each of a plurality of model teeth and measured
data of current values flowing between the measurement electrode
and a mouth electrode;
[0017] FIG. 3 is a cumulative plot of the current value flowing
between the measurement electrode and the mouth electrode with
respect to the measurement signals of 500 Hz and 2 kHz based on the
measured data in FIG. 2;
[0018] FIG. 4 is a cumulative plot of the current value flowing
between the measurement electrode and the mouth electrode with
respect to the measurement signals of 500 Hz, 2 kHz, and 4 kHz in
increasing order on the basis of the measured data in FIG. 2;
[0019] FIG. 5 is a view for explaining an apparatus according to
the fifth embodiment of the invention of the present
application;
[0020] FIG. 6 is a graph showing a relation between the frequencies
of measurement signals applied to the measurement electrode at a
position 1 mm before the root apex position of each of a plurality
of model teeth and the measured data of current value flowing
between the measurement electrode and the mouth electrode caused by
the measurement signals;
[0021] FIG. 7 is a graph showing a relation between the frequencies
of the measurement signals applied to the measurement electrode at
a position 3 mm before the root apex position of each of a
plurality of model teeth and the measured data of current values
flowing between the measurement electrode and the mouth electrode
caused by the measurement signals;
[0022] FIG. 8 is a graph showing electrical characteristic value
change patterns of a model tooth having an inverted conical root
canal; and
[0023] FIG. 9 is a graph showing electrical characteristic value
change patterns of a model tooth having a cylindrical root
canal.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The first embodiment of the present invention will be
described below with reference to the views of the accompanying
drawing.
[0025] Referring to FIG. 1, a power supply 1 outputs a plurality of
types of measurement signals Pn. The measurement signals Pn can be
signals of two different frequencies of, e.g., 500 Hz and 2 kHz.
The measurement signals Pn can be signals of three or more types of
frequencies. The measurement signals Pn can be signals which differ
from each other in at least one of frequency, waveform, or peak
value. According to the invention of the present application, it is
necessary to detect a plurality of types of electrical
characteristic values between a measurement electrode 10 and a
mouth electrode 11 on the basis of a plurality of types of
measurement signals Pn, and the types of the signals can be
selected on the basis of the principle of the invention of the
present application to be described below.
[0026] In addition, although the measurement signals Pn are applied
to the measurement electrode 10, the signals may be applied to the
mouth electrode 11.
[0027] For the sake of a more detailed description of this
embodiment, the embodiment will exemplify a case wherein signals of
two different frequencies, namely 500 Hz and 2 kHz, are used as the
measurement signals Pn, and the measurement signals are applied to
the measurement electrode. However, the invention of the present
application is not limited to this case.
[0028] The power supply 1 outputs the measurement signals of two
different frequencies, namely 500 Hz and 2 kHz.
[0029] A signal switching unit 2 sequentially supplies the
measurement signals of the two different frequencies, i.e., 500 Hz
and 2 kHz, output from the power supply 1 to the measurement
electrode under the control of a control unit 6. As the signal
switching unit 2, a switching unit such as a so-called multiplexer
or the like can be used.
[0030] A matching unit 3 is a portion which converts a signal from
the signal switching unit into a signal with a voltage level at
which the signal can be safely applied to the human body, and
prevents a measurement current from needlessly flowing in the human
body. The matching unit 3 adjusts the measurement signals Pn from
the power supply 1 to signals suitable for being supplied to the
measurement electrode 10. If, however, the measurement signals Pn
from the power supply are signals suitable for being applied to the
measurement electrode 10, the matching unit 3 can be omitted. In
this embodiment, the matching unit 3 adjusts the measurement
signals Pn of the two different frequencies, i.e., 500 Hz and 2
kHz, to a predetermined voltage value Vn.
[0031] An amplification unit 4 connected to the mouth electrode 11
amplifies a measured signal Qn output from the mouth electrode 11.
The measured signal Qn is a value associated with an electrical
characteristic value between the measurement electrode 10 and the
mouth electrode 11. The electrical characteristic value can be any
one of a current value In flowing between the two electrodes (to be
referred to as a "measured current value In" hereinafter), the
voltage value Vn between the two electrodes (to be referred to as
the "measured voltage value Vn" hereinafter), a phase difference
between the current value In and the measurement signal Pn, a phase
difference between the voltage value Vn and the measurement signal
Pn, and an impedance value Zn between the two electrodes (to be
referred to as an "intra-root-canal impedance value Zn"
hereinafter), or a combination of these tooth data groups.
[0032] These electrical characteristic values can also be obtained
from the measured signal Qn itself or by combining it with other
signal values.
[0033] An electrical characteristic value in the invention of the
present application is not limited to the measured current In. For
the sake of a more detailed description of this embodiment,
however, a case wherein the electrical characteristic value is the
measured current In will be described.
[0034] The amplification unit 4 converts the measured current In
into a voltage and amplifies the voltage, and a known amplifier can
be used.
[0035] A conversion unit 5 is a circuit which converts a measured
AC voltage Vn amplified by the amplification unit 4 into a DC
voltage Vdc which can be read and stored by the control unit.
[0036] The control unit 6 controls predetermined devices in a root
apex position detection apparatus 100 according to this
embodiment.
[0037] In this embodiment, a detection unit 25 comprises the power
supply 1, signal switching unit 2, matching unit 3, measurement
electrode 10, mouth electrode 11, amplification unit 4, conversion
unit 5, and control unit 6. The detection unit 25 can employ any
arrangement as long as it can detect electrical characteristics of
a tooth located between the measurement electrode and the mouth
electrode. The detection unit 25 applies each of the measurement
signals Pn of the two different frequencies, i.e., 500 Hz and 2
kHz, to the single measurement electrode 10, and detects two types
of electrical characteristic values between the measurement
electrode 10 and the mouth electrode 11 which are based on the
respective measurement signals.
[0038] In this embodiment, the control unit 6 controls
predetermined devices in the root apex position detection apparatus
100, and can also execute control to compare a plurality of model
tooth data groups of root apex position model data associated with
electrical characteristic values stored in a storage unit 9 with a
test tooth data group having electrical characteristic values of a
test tooth 24 to be treated which are detected by the detection
unit 25 so as to check whether or not there is any model tooth data
group which is in a predetermined relationship with the test tooth
data group.
[0039] The storage unit 9 stores the root apex position model data
associated with the electrical characteristic value In between the
measurement electrode 10 and the mouth electrode 11 while the
distal end of the measurement electrode 10 is located at a root
apex position 23' of a root canal 22' of a model tooth 24'. The
model teeth 24' are sample teeth which differ from each other in
root canal structure or the state inside the root canal (the degree
of wetness ranging from that in the dry state to that in the wet
state). This root apex position model data has a plurality of tooth
data groups comprising two types of electrical characteristic
values obtained when the measured signals Vn of the two different
frequencies, i.e., 500 Hz and 2 kHz, are applied to the model tooth
24'.
[0040] The respective groups can use measured data obtained from
different actual sample teeth as targets. The measured data of each
model tooth data group can be the electrical characteristic values
In between the measurement electrode 10 and the mouth electrode 11
which are obtained by applying the two types of measurement signals
Pn of 500 Hz and 2 kHz while the distal end of the measurement
electrode 10 is located at a root apex position 23 of the
predetermined model tooth 24'.
[0041] The measured data at this root apex position (physiological
root apex position) will be described in more detail with reference
to FIG. 2. Referring to FIG. 2, the ordinate represents the
(quantified) measured current In; and the abscissa, the frequency
of a measurement signal. FIG. 2 shows a relationship between the
measured current In and a frequency f in a state wherein the distal
end of the measurement electrode 10 is located at the root apex
position. One line represents data associated with one model tooth
24'. In this case, even one model tooth 24' having the same root
canal structure is considered as a different model tooth 24' if the
state inside the root canal (e.g., the degree of a dry state or wet
state or a change in thickness) is different.
[0042] This measured data was obtained by using Justy II (trade
name) available from Toei Electric Co., Ltd as a root apex position
detection apparatus upon partly modifying it. With this
modification, the frequencies of measurement signals of 500 Hz and
2,000 Hz could be set in the range of 250 to 8,000 Hz. The output
current of a detection output from the Justy II was supplied to a
detection resistor, and a voltage across the resistor was used as
measured data. Measurement targets were those from whom informed
concept was obtained.
[0043] FIG. 2 shows the measured data of the model teeth 24' in
about 30 cases. In FIG. 2, when perpendiculars are dropped at the
positions of frequencies of 500 Hz and 2 kHz, the model tooth data
group with the value of the intersection of each perpendicular and
measured data for each model tooth 24' can be obtained. Referring
to FIG. 2, the model tooth data groups of the values of the
intersections associated with the model teeth 24' in about 50 cases
can be obtained. Readings at 500 Hz indicate variation of about 70
to 280.
[0044] As described above, the ordinate data (electrical
characterized values) of the respective model teeth 24' do not
indicate any constant value. That is, it can be understood that the
respective teeth have unique electrical characteristic values.
[0045] Referring to FIG. 3, the model tooth data groups of the
values of the intersections associated with the model teeth 24' in
about 50 cases shown in FIG. 2 are rearranged in the order of the
measured data.
[0046] Referring to FIG. 3, the data indicated on the ordinate are
quantified values, the data marked with the crosses represent the
values of measured data at the measurement signal Pn of 2 kHz, and
the data marked with ".box-solid." represent the values of measured
data at the measurement signal Pn of 500 Hz. For each sample, data
corresponding to the two measurement signals form one model tooth
data group.
[0047] As is obvious from FIG. 3, about 50 model tooth data groups
which are obtained from the different model teeth 24' can be
obtained as root apex position model data to be stored in the
storage unit 9.
[0048] A comparison unit 12 compares the test tooth data groups of
the two types of electrical characteristic values In associated
with the test tooth 24 to be treated, which are detected by the
detection unit 25, with the values of the model tooth data groups
in the root apex position model data stored in the storage unit 9
to check whether or not the root apex position model data includes
any model tooth data group having a predetermined relationship with
the test tooth data group. The test result obtained by the
comparison unit 12 is sent as position information associated with
the position of the measurement electrode to a display unit 7. The
above-described "predetermined relationship" can be a relationship
in which the test tooth data group comprising the two types of
electrical characteristic values detected by the detection unit
coincides with any model tooth data group in the root apex position
model tooth data stored in the storage unit. Alternatively, the
above-predetermined relationship may be a relationship in which the
difference between the test tooth data group and the model tooth
data group falls within a predetermined range. This range can be
set to 5%.
[0049] The display unit 7 displays the output from the comparison
unit 12 as the detected result obtained by the root apex position
detection apparatus 100. That is, upon receiving information
indicating "coincidence" from the comparison unit 12, the display
unit 7 displays information indicating that the distal end of the
measurement electrode is located at the root apex position 23. Upon
receiving information indicating "incoincidence" from the
comparison unit 12, the display unit 7 displays information
indicating that the distal end of the measurement electrode is not
located at the root apex position 23.
[0050] As the display unit 7, any unit which can inform the dentist
of a root apex position, e.g., an analog meter, a digital meter, a
unit which produces a sound (e.g., a warning sound), a unit which
emits light (e.g., warning light), or a unit which produces
vibrations, can be used.
[0051] In the first embodiment, an output from the comparison unit
12 is sent to the display unit 7. The output from the comparison
unit 7 can also be used as an output for warning. In this case, the
output from the comparison unit 7 can be used to inform that the
distal end of the measurement electrode 10 is located at the root
apex position 23, by using sound, light, vibrations, or the like.
The output from the comparison unit 7 can be used to control a
dental instrument (e.g., an automatic root canal expanding
instrument with a dental electric engine).
[0052] An interface unit 8 is a circuit for supplying an output
from the comparison unit 12 to the automatic root canal expanding
tool with the dental electric engine. The automatic root canal
expanding instrument can mechanically execute root canal expanding
operation, instead of manual root canal expanding operation by the
dentist, by using a reamer and file which are rotated by the dental
electric engine controlled on the basis of data from the root canal
length measurement instrument.
[0053] The operation of the root apex position detection apparatus
according to the first embodiment of the invention of the present
application will be described.
[0054] (1) Root apex position model data associated with electrical
characteristic values between the measurement electrode and the
mouth electrode in a state wherein the distal end of the
measurement electrode 10 is located at the root apex position 23 of
the root canal is stored in the storage unit 9. This root apex
position model data is current values (electrical characteristic
values) flowing between the two electrodes when measurement signals
of the two different frequencies, i.e., 500 Hz and 2 kHz, are
applied to the measurement electrode 10 while the distal end of the
measurement electrode 10 is located at the root apex position 23'
of the root canal 22' of the model tooth 24'. It is preferable to
store model data about more model teeth 24'.
[0055] (2) The mouth electrode 11 is brought into contact with the
oral cavity having the test tooth 24, and the measurement electrode
10 is located at a measurement start position (e.g., a tooth crown
portion) in the root canal of the tooth.
[0056] (3) The measurement signals Pn of the two different
frequencies, i.e., 500 Hz and 2 kHz, are sequentially supplied from
the power supply 1 to the measurement electrode while the
measurement electrode 10 is moved toward the root apex position 23.
Alternatively, the supply of the measurement signals of the two
different frequencies, i.e., 500 Hz and 2 kHz, from the power
supply 1 to the two electrodes can be started before the
measurement electrode 10 starts to move toward the root apex
position 23.
[0057] (4) The signal switching unit 2 adjusts the supply timing of
each measurement signal Pn so as to sequentially supply the
measurement signals Pn of the two different frequencies, i.e., 500
Hz and 2 kHz, from the power supply 1 to the measurement
electrode.
[0058] (5) Two types of electrical characteristic values (current
values In in this case) between the two electrodes are output from
the mouth electrode 11 on the basis of the measurement signals Pn
of 500 Hz and 2 kHz sequentially supplied from the signal switching
unit 2 to the measurement electrode.
[0059] (6) Each of the current values In representing these two
types of electrical characteristic values is converted into a
voltage value and amplified by the amplification unit 4.
[0060] (7) Each of the two different amplified voltage values Vn is
converted into the DC voltage value Vdc by the conversion unit
5.
[0061] (8) The comparison unit 12 compares the test tooth data
group comprising the two different DC voltage values Vdc output
from the conversion unit 5 with a plurality of model tooth data
groups in the root apex position model data stored in the storage
unit 9 to check whether or not the test tooth data group comprising
the two different DC voltage values Vdc coincides with any one of
the plurality of model tooth data groups in the root apex position
model data.
[0062] (9) The test result obtained by the storage unit 9 is sent
to the display unit 7 and displayed on the display unit 7.
[0063] The second embodiment of the invention of the present
application will be described next. The second embodiment is the
same as the first embodiment in the mechanism of detecting a root
apex position. The second embodiment differs from the first
embodiment in that it detects a distance from a distal end of a
measurement electrode 10 to a root apex position 23 as well as the
root apex position.
[0064] The second measurement differs from the first embodiment in
the contents of data stored in a storage unit 9.
Intra-root-canal-position-specific model data are stored in the
storage unit 9.
[0065] It can be understood from the data shown in FIG. 2 that the
ordinate data at the root apex positions of a plurality of teeth do
not exhibit any constant value.
[0066] Likewise, it can be understood that the test tooth data
group of two types of electrical characteristic values with respect
to measurement signals of 500 Hz and 2 kHz at a predetermined
distance from the root apex position differs for each tooth and
does not exhibit any constant value.
[0067] Intra-root-canal-position-specific model data are data
(FIGS. 6, 7, and 2) associated with electrical characteristic
values Rn between the measurement electrode 10 and a mouth
electrode 11 at each distance from the measurement electrode 10 to
a root apex position 23' in the process of inserting the
measurement electrode 10 being inserted into a root canal 22' of a
model tooth 24' toward the root apex position 23'. That is, the
intra-root-canal-position-specific model data are the electric
characteristic values Rn between the two electrodes by the distance
from the measurement electrode 10 to the root apex position 23'.
More specifically, the intra-root-canal-position-specific model
data are the two types of electrical characteristic values Rn
obtained by applying measurement signals of 500 Hz and 2 kHz to the
measurement electrode 10 placed at each of a plurality of model
teeth 24'. The more the number of model teeth 24', the better.
[0068] The function of a comparison unit 12 is also different from
that in the first embodiment. The comparison unit 12 in the second
embodiment has the same comparing/checking function for detecting a
root apex position as that in the first embodiment. In addition to
the function, the comparison unit 12 in the second embodiment has a
second function of outputting a test result indicating how far a
distal end of the measurement electrode 10 is away from the root
apex position.
[0069] The second function will be described below. Referring to
FIG. 1, in the process of the distal end of the measurement
electrode 10 being inserted into the root canal 22', the power
supply 1 supplies measurement signals of 500 Hz and 2 kHz to the
measurement electrode 10. As a consequence, as the distal end of
the measurement electrode 10 is inserted into the root canal 22',
the electrical characteristic value Rn between the two electrodes
changes.
[0070] The comparison unit 12 compares this changing electrical
characteristic value (i.e., the two types of electrical
characteristic values Rn between the two electrodes with respect to
the measurement signals of 500 Hz and 2 kHz) with a plurality of
model tooth data groups in the intra-root-canal-position-specific
model data stored in the storage unit to detect a model tooth data
group which coincides with the changing electrical characteristic
value. The comparison unit 12 checks to which position on the model
tooth 24' this coincident model tooth data group corresponds, and
outputs the corresponding position information to a display unit 7.
The display on the display unit 7 allows the dentist to accurately
grasp how the measurement electrode 10 approaches the root apex
position 23.
[0071] As described above, generating the
intra-root-canal-position-specific model data of the model tooth
24' at 1-mm distance intervals from the root apex position in this
manner makes it possible to detect in a resolution of 1 mm how the
distal end of the measurement electrode 10 approaches the root apex
position 23'.
[0072] By improving the second embodiment, a state wherein the
distal end of the measurement electrode 10 approaches the root apex
position 23 can be detected more precisely. An example of this
improvement is that an intra-root-canal-position-specific model
data at least a point between point a1 and point a2 spaced apart by
1 mm is calculated by using an intra-root-canal-position-specific
model data at the point a1 and an
intra-root-canal-position-specific model data at the point a2 which
are stored in the storage unit 9. By using this calculated
approximate data as the above intra-root-canal-position-specific
model data, the position of the distal end of the measurement
electrode 10 can be detected more accurately.
[0073] The third embodiment will be described. As shown in FIG. 4,
the third embodiment uses three types of data. Referring to FIG. 4,
the data indicated on the ordinate are quantified values, the data
marked with the crosses represent the values of measured data with
a measurement signal Pn of 2 kHz, the data marked with
".box-solid." represent the values of measured data with the
measurement signal Pn of 500 Hz, and the data marked with
"quadrature." represent the values of measured data with the
measurement signal Pn of 4 kHz. An operation of the embodiment
using these three types of data is basically the same as in the
first and second embodiments described above.
[0074] The fourth embodiment will be described. In the first to
third embodiments, as root apex position model data, measured data
are used. In place of measured data in these embodiments, the third
embodiment uses one of theoretical data, simulation data, and
approximate data obtained by calculation based on measured data, or
data obtained by combining at least two or three of these data, as
a root apex position model data or an
intra-root-canal-position-specific model data. Where, simulation
data is data obtained by, for example, simulation based on tooth
models or computer software. Approximate data is data generated
from the viewpoint of complementing measured data. For example, in
FIG. 2, approximate data is data which satisfies the area without
any measured data between the lowest measured data and the measured
data immediately above the lowest data. This approximate data can
be approximately obtained by using the lowest measured data and the
measured data immediately above the lowest data in FIG. 2.
[0075] Theoretical data will be described. Based on the root canal
structures of various teeth and various intra-root-canal states,
the impedance in the root canal changes depending on the root canal
structure and the intra-root-canal state. In this case, the
intra-root-canal state is a state associated with the degree of
wetness from a dry state to a wet state. When the intra-root-canal
state of a model tooth 24' having a given root canal structure is
changed, the impedance in the root canal which changes can be
theoretically calculated.
[0076] A substance (e.g., blood) existing in the root canal can be
considered as a conductive liquid having a given resistance.
Therefore, intra-root-canal impedance values in various
intra-root-canal states associated with the tooth having the
corresponding root canal structure can be obtained by calculation
using the specific resistance of the liquid.
[0077] If the intra-root-canal impedance values in various
intra-root-canal states can be obtained, current values flowing in
the root canal, voltage values across the intra-root-canal
impedance values, and phase differences between the power supply
and the measured voltage values and current values can be obtained
by calculation or simulation. Electrical characteristic values of
the model tooth 24' which constitute a model tooth data group can
be theoretically obtained by using these values.
[0078] In the above calculation or simulation, a root canal having
a cylindrical shape with a constant root canal diameter is assumed
first. In this case, a resistance is proportional to the distance
from the root apex position. When the root canal has a conical
shape, the resistance exhibits a characteristic like a quadratic
curve as a function of the distance from the root apex
position.
[0079] The specific resistance of resistivity changes depending on
the environment in the root canal. The specific resistance in each
environment in the root canal and the root canal structure pattern
are stored in the storage unit. Root apex position model data or
intra-root-canal-position-specific model data can be calculated on
the basis of these data.
[0080] For example, intra-root-canal-position-specific model data
at each point before each root apex position is stored. It is
determined, on the basis of changes in the
intra-root-canal-position-specific model data, whether the data is
data of a characteristic corresponding to a constant root canal
diameter or data exhibiting a change in the diameter of the root
canal in a conical shape. It is predicted, on the basis of the
determined result, that the intra-root-canal-position-specific
model data will change along a specific curve to the next point.
The intra-root-canal-position-specific model data at that point is
then predicted on the basis of the prediction. A measured data at
the next point is compared with the predicted
intra-root-canal-position-specific model data, and their difference
is corrected to obtain the intra-root-canal-position-specific model
data, thereby minimizing the error.
[0081] The fifth embodiment will be described. The fifth embodiment
is associated with the above improvement of the second embodiment,
and is directed to detect more precisely how the distal end of a
measurement electrode 10 approaches a root apex position 23.
[0082] Referring to FIG. 5, the power supply 1 outputs a plurality
of types of measurement signals Pn. As the measurement signals Pn,
signals of two different frequencies, e.g., 500 Hz and 2 kHz, can
be used. The measurement signals Pn may be signals of three or more
different frequencies. The measurement signals Pn may be signals
which differ from each other in at least frequency, waveform, or
peak value. In the invention of the present application, it is
necessary to detect a plurality of types of electrical
characteristic values between a measurement electrode 10 and a
mouth electrode 11 on the basis of a plurality of types of
measurement signals Pn, and the types of these signals can be
selected on the basis of the principle of the invention of the
present application to be described below.
[0083] Although the measurement signal Pn is applied to the
measurement electrode 10, the signal may be applied to the mouth
electrode 11.
[0084] For the sake of a more detailed description of this
embodiment, this embodiment will exemplify a case wherein signals
of two different frequencies, namely 500 Hz and 2 kHz, are used as
the measurement signals Pn, and the measurement signals are applied
to the measurement electrode. However, the invention of the present
application is not limited to this case.
[0085] A power supply 1 outputs measurement signals of two
different frequencies, namely 500 Hz and 2 kHz.
[0086] A signal switching unit 2 sequentially supplies the
measurement signals of the two different frequencies, i.e., 500 Hz
and 2 kHz, output from the power supply 1 to the measurement
electrode under the control of a control unit 6. As the signal
switching unit 2, a switching unit such as a so-called multiplexer
or the like can be used.
[0087] A matching unit 3 is a portion which converts a signal from
the signal switching unit into a signal with a voltage level at
which the signal can be safely applied to the human body, and
prevents a measurement current from needlessly flowing in the human
body. The matching unit 3 adjusts the measurement signals Pn from
the power supply 1 to signals suitable for being supplied to the
measurement electrode 10. If, however, the measurement signals Pn
from the power supply are signals suitable for being applied to the
measurement electrode 10, the matching unit 3 can be omitted. In
this embodiment, the matching unit 3 adjusts the measurement
signals Pn of the two different frequencies, i.e., 500 Hz and 2
kHz, to a predetermined voltage value Vn.
[0088] An amplification unit 4 connected to the mouth electrode 11
amplifies a measured signal Qn output from the mouth electrode 11.
The measured signal Qn is a value associated with an electrical
characteristic value between the measurement electrode 10 and the
mouth electrode 11. The electrical characteristic value can be any
one of a current value In flowing between the two electrodes (to be
referred to as a "measured current value In" hereinafter), a
voltage value Vn between the two electrodes (to be referred to as
the "measured voltage value Vn" hereinafter), a phase difference
between the current value In and the measurement signal Pn, a phase
difference between the voltage value Vn and the measurement signal
Pn, and an impedance value Zn between the two electrodes (to be
referred to as an "intra-root-canal impedance Zn" hereinafter), or
a combination of these tooth data groups.
[0089] These electrical characteristic values can also be obtained
from the measured signal Qn itself or by combining it with other
signal values.
[0090] An electrical characteristic value in the invention of the
present application is not limited to the measured current In. For
the sake of a more detailed description of this embodiment,
however, a case wherein the electrical characteristic value is the
measured current In will be described.
[0091] The amplification unit 4 converts the measured current In
into a voltage and amplifies the voltage, and a known amplifier can
be used.
[0092] A conversion unit 5 is a circuit which converts the measured
AC voltage Vn amplified by the amplification unit 4 into a DC
voltage Vdc which can be read and stored by the control unit.
[0093] The control unit 6 controls predetermined devices in a root
apex position detection apparatus 100 according to the
embodiment.
[0094] Intra-root-canal-position-specific model data are stored in
a first storage unit 9. The intra-root-canal-position-specific
model data can be stored as it is or upon being converted into
mathematical expressions or graphs. In this case, the
intra-root-canal-position-specific model data are data having
electrical characteristic values between the measurement electrode
and the mouth electrode while the distal end of the measurement
electrode 10 is located at a plurality of predetermined positions
in a root canal 22' of a model tooth 24'. The larger the number of
model teeth 24', the better.
[0095] FIGS. 6 and 7 show the intra-root-canal-position-specific
model data associated with the model teeth 24' as in FIG. 2.
Referring to each graph, the ordinate represents the (quantified)
measured current In; and the abscissa, the frequency of a
measurement signal. FIG. 6 shows a relationship between the
measured current In and a frequency f in a state wherein the distal
end of the measurement electrode 10 is located 3 mm before the root
apex position. FIG. 7 shows a relationship between the measured
current In and the frequency f in a state wherein the distal end of
the measurement electrode 10 is located 1 mm before the root apex
position.
[0096] Referring to FIGS. 6 and 7, one line represents data
associated with one model tooth 24'. In this case, even one model
tooth 24' having the same root canal structure is considered as a
different model tooth 24' if the state inside the root canal (e.g.,
the degree of a dry state or wet state or a change in thickness)
differs.
[0097] This measured data was obtained by using Justy II (trade
name) available from Toei Electric Co., Ltd as a root apex position
detection apparatus upon partly modifying it. With this
modification, the frequencies of measurement signals of 500 Hz and
2,000 Hz could be set in the range of 250 to 8,000 Hz. The output
current of a detection output from the Justy II was supplied to a
detection resistor, and the voltage across the resistor was used as
measured data.
[0098] FIGS. 6 and 7 show the measured data of the model teeth 24'
in a plurality of cases. In FIGS. 6 and 7, when perpendiculars are
dropped at the positions of frequencies of 500 Hz and 2 kHz, the
model tooth data group with the value of the intersection of each
perpendicular and measured data for each model tooth 24' can be
obtained. Referring to FIGS. 6 and 7, the model tooth data groups
of the values of the intersections associated with the model teeth
24' in about 50 cases at the positions 3 mm and 1 mm before the
root apex can be obtained. The data indicated values at 500 Hz
indicate about 70 to 280 changes. These
intra-root-canal-position-specific model data are stored in the
first storage unit.
[0099] It can be understood from FIGS. 2, 6 and 7 that the ordinate
data (electrical characteristic values) of the model tooth 24' at
the root apex position and the positions 3 mm and 1 mm before the
root apex position do not exhibit constant values. That is, the
respective teeth have unique electrical characteristic values which
are different from each other.
[0100] The intra-root-canal-position-specific model data are data
associated with electrical characteristic values Rn between the
measurement electrode 10 and the mouth electrode 11 at each
distance from the measurement electrode 10 to a root apex position
23' in the process of the measurement electrode 10 being inserted
into the root canal 22' toward the root apex position 23'.
[0101] A comparison unit 12 in the fifth embodiment can have a
first function for detecting a root apex position the same as in
the first embodiment. In addition to this function, the fifth
embodiment can have a second function or/and third function of
outputting a test result (position information) indicating how far
the distal end of the measurement electrode 10 is away from the
root apex position.
[0102] The second function will be described below. The second
function is the same as the above second embodiment. That is, in
FIG. 5, in the process of the distal end of the measurement
electrode 10 being inserted into the root canal 22', the power
supply 1 alternately supplies measurement signals of 500 Hz and 2
kHz to the measurement electrode 10. As a consequence, as the
distal end of the measurement electrode 10 is inserted into the
root canal 22', the electrical characteristic value Rn between the
two electrodes changes.
[0103] The comparison unit 12 compares the changing electrical
characteristic value Rn with the plurality of the
intra-root-canal-position-specific model data stored in the first
storage unit to detect an intra-root-canal-position-specific model
data in a predetermined relationship. The comparison unit 12
detects to which position on the model tooth 24' the
intra-root-canal-position-specific model data in the predetermined
position corresponds, and outputs the detected result to a display
unit 7. Making a display unit 7 display the detected result allows
the dentist to accurately grasp how the measurement electrode 10
approaches the root apex position 23.
[0104] By generating the intra-root-canal-position-specific model
data of the model tooth 24' at 1-mm intervals from the root apex
position, the fifth embodiment can detect in a resolution of 1 mm
how the distal end of the measurement electrode 10 approaches the
root apex position 23'.
[0105] The third function will be described next. The third
function is to more precisely detect how the distal end of the
measurement electrode 10 approaches the root apex position 23. The
third function detects and displays that the distal end of the
measurement electrode is located at least one position anywhere
between positional in the root canal 22' of the model tooth 24' and
position a2 ahead of the point a1.
[0106] The third function can use an electrical characteristic
value change pattern of a test tooth. FIGS. 8 and 9 show examples
of electrical characteristic value change patterns of a test tooth.
For a model tooth 24' whose root canal 22' has an inverted conical
shape, FIG. 8 shows the change pattern of the electrical
characteristic value between the measurement electrode 10 and the
mouth electrode 11 as the measurement electrode having a diameter
of 0.2 mm is inserted from the root canal orifice into the root
canal 22' of the model tooth 24'.
[0107] Likewise, for a model tooth 24' whose root canal 22' has a
cylindrical shape, FIG. 9 shows the change pattern of the
electrical characteristic value between the measurement electrode
10 and mouth electrode 11 as the measurement electrode having a
diameter of 0.2 mm is inserted from the root canal orifice into the
root canal 22' of the model tooth 24'.
[0108] The third function will be described in a case wherein the
comparison unit 12 shown in FIG. 5 detects that the distal end of
the measurement electrode 10 has reached a position 3 mm before the
root apex, by detecting that the electrical characteristic value
between the mouth electrode 11 and the measurement electrode 10
inserted into a root canal 22 of a test tooth 24 coincides with one
of the intra-root-canal-position-specific model data shown in FIG.
6 on the basis of the second function.
[0109] The third function uses predictive data processed by a
prediction unit 14 shown in FIG. 5. That is, it is grasped, on the
basis of a change pattern obtained until the distal end of the
measurement electrode 10 reaches the position 3 mm before the root
apex, that the test tooth 24 has an inverted conical
intra-root-canal structure. Upon reception of this result, the
prediction unit 14 grasps, in the data shown in FIG. 8, that
detected data corresponding to each of the measurement signals of
500 Hz and 2 kHz which is obtained until the measurement electrode
reaches the position 1 mm before the root apex increases at the
same change rate as that of a predetermined inverted conical
pattern.
[0110] When the distal end of the measurement electrode 10 reaches
the position 3 mm before the root apex, the prediction unit 14
predicts an electrical characteristic value (i.e., detected data)
(to be respectively referred to as a "predicted electrical
characteristic value" and "predicted detected data" hereinafter)
when the distal end of the measurement electrode 10 reaches the
position 1 mm before the root apex, on the basis of a measured
electrical characteristic value (i.e., detected data) (to be
respectively referred to as a "measured electrical characteristic
value" and "measured detected data" hereinafter) and the increase
at the position 1 mm before the root apex which is graphed from
FIG. 8.
[0111] On the basis of these measured detected data and predicted
detected data, the comparison unit 12 predicts
intra-root-canal-position-specific model data at smaller intervals
between the position 3 mm from the root apex and the position 1 mm
before the root apex. This prediction can be executed by a method
of linearly approximating the interval between the position 3 mm
before the root apex and the position 1 mm before the root apex and
dividing the interval into a plurality of equal parts (e.g., 10 or
20 parts).
[0112] The predictive intra-root-canal-position-specific model data
predicted and fractionalized in this manner are stored in a second
storage unit. Although the second storage unit may be a storage
mechanism different from the first storage unit, the two storage
units may be realized by the same storage mechanism.
[0113] In the process of the distal end of the measurement
electrode 10 being inserted into the root canal 22 of the test
tooth 24, the power supply 1 supplies measurement signals of 500 Hz
and 2 kHz to the measurement electrode 10. As a result, as the
distal end of the measurement electrode 10 is inserted into the
root canal 22, the electrical characteristic value Rn between the
two electrodes changes.
[0114] The comparison unit 12 compares the changing electrical
characteristic values (i.e., the two types of measured electrical
characteristic values Rn with respect to the measurement signals of
500 Hz and 2 kHz) with the intra-root-canal-position-specific model
data stored in the first storage unit and the predictive
intra-root-canal-position-specific model data stored in the second
storage unit. When it is detected that an
intra-root-canal-position-specific model data stored in the first
and second storage units include data in a predetermined
relationship with the measurement electrical characteristic values,
the comparison unit 12 checks to which position in the root canal
the data in the predetermined relationship correspond, and outputs
the position as a positional information to the display unit 7.
Display on the display unit 7 then allows the dentist to precisely
grasp how the root apex position 23 approaches the root apex
position 23.
[0115] The fifth embodiment uses intra-root-canal-position-specific
model data at the positions 3 mm and 1 mm before the root apex.
However, the embodiment can use an
intra-root-canal-position-specific model data obtained at smaller
intervals (1-mm intervals).
[0116] By using predictive electrical characteristic values
predicted and fractionalized by the prediction unit in this manner,
the position of the distal end of the measurement electrode 10 can
be detected more precisely.
[0117] According to an embodiment of the invention of the present
application, a root apex position can be detected accurately.
[0118] According to an embodiment of the invention of the present
application, a root apex position can be measured more accurately
by reducing the influence of the state of the root canal.
[0119] According to an embodiment of the invention of the present
application, the distance of the distal end of the measurement
electrode from the root apex position can be measured
precisely.
[0120] According an embodiment of the invention of the present
application, the root canal can be enlarged accurately and
easily.
[0121] According to an embodiment of the invention of the present
application, the operation time for enlarging the root canal can be
shortened.
[0122] According to an embodiment of the invention of the present
application, it is not necessary to perform the operation of fixing
a silicone stopper to the measurement electrode, which is required
to finish the operation of the measurement electrode before the
root apex.
* * * * *