Tooth structure measuring device and tooth structure measuring method

Abstract

To provide a tooth structure measurement device and a tooth structure measurement method capable of grasping an index which indicates a thickness of a dentin layer using a terahertz pulse wave.SOLUTION: A wave reception part 120 receives a first reflection wave RW1 reflected on a first interface 221 and a second reflection wave RW2 reflected on a second interface 222 of a terahertz pulse wave which entered an object tooth 200. A reflection interval measurement part 131 measures a first reflection interval which is a time difference between time when the first reflection wave RW1 is received and time when the second reflection wave RW2 is received. A user designated on a designation part 133, to which layer the second dentin layer 212 corresponds, out of a plurality of kinds of propagation speed known dentin layers for which a propagation speed of a terahertz wave is known in advance. A calculation part 135 calculates an index which indicates a thickness of the second dentin layer 212, using the known propagation speed of the terahertz pulse wave on the propagation speed known dentin layer which is designated as the layer corresponding to the second dentin layer 212, and the first reflection interval.SELECTED DRAWING: Figure 7

Description

Technical Field

[0007]

[0001] The present invention relates to a dental structure measuring device and a dental structure measuring method.

Background Art

[0002] As disclosed in Patent Document 1, it has been proposed to use pulsed terahertz waves (hereinafter referred to as terahertz pulse waves) for measuring the structure of teeth. In this specification, the terahertz wave refers to an electromagnetic wave having a frequency of 10 GHz or more and 300 THz or less.

[0003] Patent Document 1 discloses a step of receiving, respectively, a reflected wave from the interface between the enamel layer (hereinafter referred to as the enamel layer) and air and a reflected wave from the interface between the enamel layer and the dentin layer (hereinafter referred to as the dentin layer) of the terahertz pulse wave incident on the tooth, and calculating the intensity ratio of the mutual reflected waves.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] There are cases where it is desired to grasp the thicknesses of various layers (hereinafter collectively referred to as dental layers) that make up the tooth, such as the enamel layer and the dentin layer.

[0006] An object of the present invention is to provide a dental structure measuring device and a dental structure measuring method capable of grasping an index representing the thickness of a dental layer using terahertz pulse waves.

Means for Solving the Problems

[0007] The dental structure measuring device according to the present invention is A radiating unit that emits terahertz pulse waves toward the target tooth to be measured, A wave receiving unit that receives a first reflected wave, which is the interface between the first tooth structure layer and the second tooth structure layer located outside the first tooth structure layer of the target tooth, and a second reflected wave, which is the interface between the first tooth structure layer and the second tooth structure layer located outside the first tooth structure layer of the target tooth, respectively. A reflection interval measuring unit measures the first reflection interval, which is the time difference between the time the first reflected wave is received and the time the second reflected wave is received. A designation unit for the user to specify which of the multiple types of tooth layers with known propagation speeds that constitute a tooth, the terahertz pulse wave propagation speed of which has been measured in advance, corresponds to the second tooth layer, A calculation unit calculates an index representing the thickness of the second tooth layer using the known propagation velocity of the terahertz pulse wave in the tooth layer with a known propagation velocity designated as the second tooth layer, and the first reflection interval. It is equipped with.

[0008] The wave receiving unit also receives the third reflected wave, which is the terahertz pulse wave incident on the target tooth and reflected at the third interface located on the surface of the third tooth layer located outside the second tooth layer in the target tooth. The reflection interval measuring unit also measures the second reflection interval, which is the time difference between the time the second reflected wave was received and the time the third reflected wave was received. The designation part also designates which of the multiple types of tooth layers with known propagation speeds the third tooth layer corresponds to. The calculation unit may also calculate an index representing the thickness of the third tooth layer using the known propagation velocity of the terahertz pulse wave in the tooth layer with a known propagation velocity designated as the third tooth layer, and the second reflection interval.

[0009] The multiple types of tooth structure layers with known propagation speeds that are options for designating in the aforementioned designation section may include dentin and demineralized dentin layers that are more demineralized than the dentin layer.

[0010] The multiple types of tooth structure layers with known propagation speeds that are selected as options when specifying in the designated section may include an enamel layer and a demineralized enamel layer that is more demineralized than the enamel layer.

[0011] The first tooth structure layer may also be the pulp layer.

[0012] The tooth structure measurement method according to the present invention is A radiation step in which terahertz pulse waves are emitted toward the target tooth to be measured, A wave receiving step that receives a first reflected wave of the terahertz pulse wave incident on the target tooth, which is reflected at the first interface, which is the interface between the first tooth structure layer and the second tooth structure layer located outside the first tooth structure layer in the target tooth, and a second reflected wave that is reflected at the second interface located on the surface of the second tooth structure layer of the target tooth. A reflection interval measurement step, which measures the first reflection interval, which is the time difference between the time the first reflected wave is received and the time the second reflected wave is received. A designation step to specify which of the multiple types of tooth layers with known propagation speeds that constitute a tooth, the tooth layer in which the propagation speed of the terahertz pulse wave has been determined in advance by measurement, corresponds to the second tooth layer. A calculation step of calculating an index representing the thickness of the second tooth layer using the known propagation velocity of the terahertz pulse wave in the tooth layer with a known propagation velocity designated as the second tooth layer, and the first reflection interval, Includes.

[0013] In the wave receiving step, the third reflected wave, which is reflected at the third interface located on the surface of the third tooth structure layer located outside the second tooth structure layer in the target tooth, is also received from the terahertz pulse wave incident on the target tooth. In the reflection interval measurement step, the second reflection interval, which is the time difference between the time the second reflected wave was received and the time the third reflected wave was received, is also measured. In the specifying step, it is also specified which of the plurality of propagation speed-known dentin layers the third dentin layer corresponds to. In the calculating step, an index representing the thickness of the third dentin layer may also be calculated using the known propagation speed of the terahertz pulse wave in the propagation speed-known dentin layer specified as corresponding to the third dentin layer and the second reflection interval.

[0014] The plurality of propagation speed-known dentin layers as options in the specifying step may include a dentin layer and a demineralized dentin layer demineralized more than the dentin layer.

[0015] The plurality of propagation speed-known dentin layers as options in the specifying step may include an enamel layer and a demineralized enamel layer demineralized more than the enamel layer.

[0016] The first dentin layer may be a pulp layer.

Advantages of the Invention

[0017] According to the present invention, an index representing the thickness of the second dentin layer can be grasped using a terahertz pulse wave.

Brief Description of the Drawings

[0018] [Figure 1] Conceptual diagram showing the configuration of the propagation speed measurement device used in the first basic experiment. [Figure 2] Diagram showing the specifications of the terahertz non-destructive inspection device used in the first basic experiment. [Figure 3] Graph showing the dependence of the propagation speed of the terahertz pulse wave on the thickness of the first to sixth samples used in the first basic experiment. [Figure 4] Diagram showing the median, maximum value, and minimum value of the propagation speed of the terahertz pulse wave in the first to sixth samples used in the first basic experiment. [Figure 5]Graphs showing the waveforms of the reflected waves from the interface between the sixth sample and the mirror, and the reflected waves from the interface between the sixth sample and water, as used in the second basic experiment. [Figure 6] A graph showing the dependence of the reflected wave intensity on the thickness of the sixth sample used in the second basic experiment. [Figure 7] A conceptual diagram showing the function of the tooth structure measuring device according to the first embodiment. [Figure 8] A conceptual diagram showing the waveforms of the first to third reflected waves according to the first embodiment. [Figure 9] A conceptual diagram showing the configuration of the measurement unit according to the first embodiment. [Modes for carrying out the invention]

[0019] Before describing the embodiments, the following explains the fundamental considerations.

[0020] [First Basic Experiment] In dental research and treatment, it is sometimes necessary to determine the thickness of the dentin layer that makes up a tooth. The inventors of this invention have conceived a method for determining the thickness of any given dentin layer using the propagation speed of terahertz pulse waves in that dentin layer and the time required for the terahertz pulse waves to propagate through that dentin layer.

[0021] However, this method assumes that the propagation speed of terahertz pulse waves in the tooth structure layer does not depend on the thickness of that layer, and this assumption is not necessarily self-evident. Therefore, with the aim of confirming that the propagation speed of terahertz pulse waves does not depend on the thickness of the tooth structure layer, the following experiment was conducted.

[0022] Figure 1 shows the configuration of the propagation velocity measurement device used in this experiment. Sample 14 uses a thin plate-like slice of tooth structure, or a thin plate-like body made of a material that simulates tooth structure. The radiator 11 emits terahertz pulse waves toward the surface of sample 14.

[0023] A portion of the terahertz pulse wave incident on sample 14 is reflected by the surface of sample 14 and incident on receiver 12. The incident angle θ of the terahertz pulse wave on the surface of sample 14 was set to 10°.

[0024] Furthermore, some of the terahertz pulse waves incident on sample 14 enter the interior of sample 14, are reflected by the surface of mirror 13 which is in close contact with the back surface of sample 14, and are incident on the same receiver 12. The mirror 13 is made of aluminum.

[0025] Figure 2 shows the specifications of the terahertz non-destructive testing equipment (manufactured by Advantest Corporation, product model number: TAS7500TS) used as the radiator 11 and receiver 12. The center wavelength of the terahertz pulse wave emitted from the radiator 11 is 1550 nm, the pulse width is 50 fs or less, and the output intensity is 20 mW or more. The time resolution of the receiver 12 is 2 fs.

[0026] Returning to Figure 1, we continue the explanation. We measure the time difference (hereinafter referred to as the reflection interval) t between the time when the reflected wave reflected from the surface of sample 14 reaches receiver 12 and the time when the reflected wave reflected from mirror 13 on the back of sample 14 reaches receiver 12.

[0027] When the thickness d of sample 14 is known in advance, the propagation velocity v of the terahertz pulse wave in sample 14 can be approximately written as follows. v≒2d·cosθ / t≒2d / t (a)

[0028] Using the above relation (a), the propagation velocity v of terahertz pulse waves in various samples 14 with known thickness d was determined by measuring the reflection interval t. Specifically, the following six types of samples 14 with known thickness were prepared.

[0029] (1) First sample: Healthy human dentin (also referred to as "Dentin" in Figures 3 and 4, which will be referenced later), (2) Second sample: Healthy bovine dentin (also referred to as “Bovine Dentin” in Figures 3 and 4, which will be referenced later), (3) Third sample: Demineralized bovine dentin (also referred to as “Bovine Dentin (decalcification)” in Figures 3 and 4, which will be referenced later), (4) Fourth sample: A healthy enamel layer of a cow (also referred to as "Bovine enamel" in Figures 3 and 4, which will be referenced later). (5) Sample 5: A natural single crystal of hydroxyapatite (also referred to as "NSC" in Figures 3 and 4, which will be referenced later). (6) Sample 6: Hydroxyl apatite powder compressed by hot isostatic pressing (also referred to as "HIP" in Figures 3 and 4, which will be referenced later).

[0030] The third sample, consisting of demineralized bovine dentin, simulates carious dentin. Demineralization was performed by immersing healthy bovine dentin in a chelating agent, specifically a 5% sodium edetate (EDTA) solution, for seven days.

[0031] Furthermore, the fifth sample, which consists of natural single crystals of hydroxyapatite, and the sixth sample, which consists of hydroxyapatite powder that has been pressure-molded using a hot isostatic press method, both simulate the enamel layer.

[0032] For each of the first to sixth samples, samples of various known thicknesses d were prepared, and the propagation velocity v of the terahertz pulse wave was determined using equation (a) above.

[0033] Figure 3 shows the dependence of the propagation velocity of terahertz pulse waves on the thickness of sample 14 for each of the six samples designated as sample 14, from sample 1 to sample 6. The horizontal axis represents the thickness of sample 14, and the vertical axis represents the propagation velocity of terahertz pulse waves in that sample 14.

[0034] As shown in Figure 3, the distribution of the plots shows a generally flat trend in all six samples from the first to the sixth. From this, it was confirmed that the propagation speed of the terahertz pulse wave (hereinafter also simply referred to as propagation speed) does not depend on the thickness of the sample 14 in all six samples from the first to the sixth.

[0035] Furthermore, as shown in Figure 3, it appears that each of the six samples, from the first to the sixth, has its own unique propagation velocity. To quantitatively confirm this, the median, maximum, and minimum propagation velocities for each of the six samples were examined.

[0036] Figure 4 shows the results. Focusing on the median, it can be seen that each of the 1st to 6th samples has its own unique propagation velocity. In Figure 4, "Number" refers to the n number of each of the 1st to 6th samples.

[0037] In detail, the median propagation velocities are similar between the first and second samples, suggesting that the dentin layer has its own unique propagation velocities. Furthermore, the median propagation velocities are similar between the fourth through sixth samples, suggesting that the enamel layer also has its own unique propagation velocities. The propagation velocities in the dentin layer and the enamel layer are clearly different.

[0038] Furthermore, the median propagation velocity in the third sample is clearly different from the median propagation velocities in the first and second samples. This indicates that carious dentin has its own unique propagation velocity, distinct from that of healthy dentin. Although Figure 4 shows the median as a statistical value, the same conclusion can be drawn using the mean value.

[0039] As explained above, the first basic experiment confirmed that the propagation speed in the tooth structure layer does not depend on the thickness of that tooth structure layer. Furthermore, it was found that each tooth structure layer with a different material has its own unique propagation speed.

[0040] Therefore, if the propagation speed of a terahertz pulse wave in a certain tooth structure layer is measured in advance, the thickness of a tooth structure layer of the same quality but of unknown thickness (hereinafter referred to as the "target tooth structure layer") can be easily estimated. In other words, by measuring the time required for the terahertz pulse wave to propagate through the target tooth structure layer (hereinafter referred to as the "propagation time"), the thickness of that target tooth structure layer can be determined by multiplying the propagation time by the known propagation speed.

[0041] In this case, it is preferable to measure the propagation speed for various tooth layers in advance and prepare data that associates the propagation speed with each tooth layer. By doing so, the propagation speed in the target tooth layer can be determined by obtaining the propagation speed associated with a tooth layer of the same quality from that data. In this way, the thickness of any target tooth layer can be accurately and easily determined.

[0042] [Second Basic Experiment] As shown in Figure 1, in the first basic experiment, the mirror 13 was placed in close contact with the sample 14. The interface between the sample 14 and the mirror 13 simulates, for example, the interface between a demineralized enamel layer (hereinafter referred to as the demineralized enamel layer) and a healthy enamel layer, the interface between the enamel layer and the dentin heteroplasm, and the interface between a demineralized dentin layer (hereinafter referred to as the demineralized dentin layer) and a healthy dentin layer.

[0043] However, the tooth structure also includes a pulp cavity (hereinafter referred to as the pulp layer) filled with dental pulp. Unlike other tooth structures, the pulp contains a large amount of water. Furthermore, terahertz pulse waves are absorbed by water. For this reason, it is not always obvious whether reflected terahertz pulse waves can be obtained at the interface located on the surface of the pulp layer.

[0044] Therefore, in order to confirm that reflected terahertz pulse waves can be obtained even at interfaces located on the surface of the dental pulp layer, the following experiment was conducted.

[0045] Two configurations were prepared: one in which mirror 13 was placed on the back surface of the aforementioned sixth sample, and another in which water simulating dental pulp was placed on the back surface of the same sixth sample. Then, terahertz pulse waves were emitted toward the surface of the sixth sample in each configuration, and the reflected waves from each configuration were received.

[0046] Figure 5 shows the measured waveforms of the received reflected waves. The upper graph shows the reflected wave when mirror 13 is placed on the back of sample 6. The lower graph shows the reflected wave when water is placed on the back of sample 6. In both graphs, the vertical axis represents amplitude and the horizontal axis represents time.

[0047] In the upper graph, wave packet RA1 represents the reflected wave from the surface of sample 6. Wave packet RA2 represents the reflected wave from the interface between sample 6 (thickness 0.553 mm) and mirror 13. Wave packet RA3 represents the reflected wave from the interface between sample 6 (thickness 0.984 mm) and mirror 13.

[0048] In the lower graph, wave packet RB1 represents the reflected wave from the surface of sample 6. Wave packet RB2 represents the reflected wave from the interface between sample 6 (thickness 0.553 mm) and water. Wave packet RB3 represents the reflected wave from the interface between sample 6 (thickness 0.984 mm) and water.

[0049] As shown in the graph below, it was confirmed that reflected terahertz pulse waves could indeed be obtained from the interface between the sixth sample and water. Since water simulates dental pulp, it can be said that reflected terahertz pulse waves can also be obtained at interfaces located on the surface of the dental pulp layer.

[0050] Figure 6 shows the dependence of the reflected wave intensity on the thickness of the sixth sample. The vertical axis represents intensity, and the horizontal axis represents the thickness of the sixth sample. Graph RA shows the reflected wave intensity when mirror 13 is placed on the back surface of the sixth sample. Graph RB shows the reflected wave intensity when water is placed on the back surface of the sixth sample.

[0051] As can be seen from the fact that graph RB is positioned below graph RA, the intensity of the reflected wave decreases when water is placed on the back of sample 6 compared to when mirror 13 is placed on the back of sample 6. This is due to the absorption of the terahertz pulse wave by the water. However, as graph RB shows, a reflected terahertz pulse wave is indeed obtained even when water is placed on the back of sample 6.

[0052] Incidentally, if the intensity of the reflected wave is too low, it becomes difficult to distinguish it from noise. Based on the radiation intensity of the terahertz pulse wave used in this experiment, the limit for the thickness of the sixth sample in which the intensity of the reflected wave could be distinguished from noise was approximately 1.8 mm.

[0053] In other words, even under conditions where the pulp layer is located behind the tooth structure, a tooth structure with a sufficient thickness of approximately 1.8 mm can be measured. This value of 1.8 mm was determined as the intersection point of an extrapolation curve that fits the plot representing the measured results and a straight line representing the typical noise intensity.

[0054] However, the greater the radiation intensity of the terahertz pulse wave used, the more strongly a reflected wave with a strength discernible from noise can be obtained even from thick tooth layers. The appropriate radiation intensity of the terahertz pulse wave to use is a matter to be appropriately designed by a person skilled in the art depending on the situation.

[0055] [Embodiment] Based on the results of the first and second basic experiments described above, the tooth structure measuring device according to the embodiment will now be described.

[0056] Referring to Figure 7, we will first describe the structure of the main part of the tooth 200 to be measured (hereinafter referred to as the target tooth). The target tooth 200 has at least a first tooth structure layer 211, a second tooth structure layer 212 located outside the first tooth structure layer 211, and a third tooth structure layer 213 located outside the second tooth structure layer 212. Here, "outer side" means the side closer to the surface of the target tooth 200. In the following, the side closer to the pulp will be referred to as the "inner side."

[0057] Specifically, in this embodiment, the first tooth structure layer 211 is the pulp layer. The second tooth structure layer 212 is a healthy dentin layer. The third tooth structure layer 213 is a demineralized dentin layer. However, the combinations of the first to third tooth structure layers 211 to 213 are not limited to these.

[0058] In the following, the interface located on the surface of the first tooth structure layer 211, i.e., the interface between the first tooth structure layer 211 and the second tooth structure layer 212, will be referred to as the first interface 221. The interface located on the surface of the second tooth structure layer 212, i.e., the interface between the second tooth structure layer 212 and the third tooth structure layer 213, will be referred to as the second interface 222. The interface located on the surface of the third tooth structure layer 213, i.e., the interface between the third tooth structure layer 213 and air, will be referred to as the third interface 223.

[0059] Next, the configuration of the tooth structure measuring device 100 according to this embodiment will be described. The tooth structure measuring device 100 includes a radiation unit 110 that emits terahertz pulse waves toward the target tooth 200. The emitted terahertz pulse waves are incident on the target tooth 200.

[0060] Furthermore, the tooth structure measuring device 100 includes a wave receiving unit 120 that receives the reflected waves from the target tooth 200 of the terahertz pulse wave incident on the target tooth 200. Specifically, the wave receiving unit 120 receives the reflected wave RW1 (hereinafter referred to as the first reflected wave) reflected at the first interface 221, the reflected wave RW2 (hereinafter referred to as the second reflected wave) reflected at the second interface 222, and the reflected wave RW3 (hereinafter referred to as the third reflected wave) reflected at the third interface, respectively, of the terahertz pulse wave incident on the target tooth 200.

[0061] Furthermore, the tooth structure measuring device 100 includes a measuring main unit 130 that estimates the thickness of the second tooth structure layer 212 and the third tooth structure layer 213 using the results of the reflected waves received by the wave receiving unit 120. The measuring main unit 130 has a reflection interval measuring unit 131 that measures the time difference between the arrival of the first reflected wave RW1 to the third reflected wave RW3 at the wave receiving unit 120.

[0062] Referring to Figure 8, the operation of the reflection interval measurement unit 131 will be explained in detail. Figure 8 shows the time-domain waveforms of the first reflected wave RW1 to the third reflected wave RW3. Wave packet R1 represents the first reflected wave RW1. Wave packet R2 represents the second reflected wave RW2. Wave packet R3 represents the third reflected wave RW3.

[0063] First, the wave packet R3 of the third reflected wave RW3, reflected at the third interface 223 located on the surface of the target tooth 200, arrives at the receiving unit 120. Next, the wave packet R2 of the second reflected wave RW2, reflected at the second interface 222 located inside the third interface 223, arrives at the receiving unit 120. Then, the wave packet R1 of the first reflected wave RW1, reflected at the first interface 221 located inside the second interface 222, arrives at the receiving unit 120. Such a time-domain waveform is obtained at the receiving unit 120.

[0064] The reflection interval measuring unit 131 measures the time difference (hereinafter referred to as the first reflection interval) T1 between the time when the receiving unit 120 receives the wave packet R1 of the first reflected wave RW1 and the time when the receiving unit 120 receives the wave packet R2 of the second reflected wave RW2. The reflection interval measuring unit 131 also measures the time difference (hereinafter referred to as the second reflection interval) T2 between the time when the receiving unit 120 receives the wave packet R2 of the second reflected wave RW2 and the time when the receiving unit 120 receives the wave packet R3 of the third reflected wave RW3.

[0065] Returning to Figure 7, the explanation continues. The measurement unit 130 according to this embodiment stores data (hereinafter referred to as tooth layer-specific propagation velocity data) 132 that associates the propagation velocity of terahertz pulse waves in each of the multiple types of tooth layers constituting the tooth, for which the propagation velocity of terahertz pulse waves has been previously measured and is known (hereinafter referred to as tooth layer-specific propagation velocity data).

[0066] Specifically, the tooth structure layer propagation velocity data 132 associates the previously measured terahertz pulse wave propagation velocities with each of the tooth structure layers for which propagation velocity is known, including at least healthy dentin, demineralized dentin, healthy enamel, and demineralized enamel.

[0067] Furthermore, the measurement main unit 130 includes a designation unit 133 operated by the user, and a propagation speed setting unit 134 that determines the propagation speed of terahertz pulse waves in the second tooth layer 212 and the third tooth layer 213 based on the operation of the designation unit 133.

[0068] First, the propagation speed setting unit 134 presents to the user, via the designation unit 133, several types of tooth layers with known propagation speeds included in the tooth layer-specific propagation speed data 132, as options for tooth layers whose thickness can be estimated.

[0069] Next, the user specifies, through the designation unit 133, which of the multiple types of tooth layers with known propagation speeds presented as options each of the second tooth layer 212 and the third tooth layer 213 whose thickness is to be estimated in the target tooth 200 corresponds to. Specifically, in this embodiment, the user specifies, through the designation unit 133, that the second tooth layer 212 is a healthy dentin layer and the third tooth layer 213 is a demineralized dentin layer.

[0070] The propagation speed setting unit 134 then obtains the known propagation speed associated with the healthy dentin layer, which is a known propagation speed tooth layer designated as the second tooth layer 212, from the tooth layer-specific propagation speed data 132. The propagation speed setting unit 134 then sets the obtained propagation speed as the propagation speed in the second tooth layer 212.

[0071] Similarly, the propagation speed setting unit 134 obtains the known propagation speed associated with the demineralized dentin layer, which is a tooth structure layer with a known propagation speed designated as the third tooth structure layer 213, from the tooth structure layer-specific propagation speed data 132. The propagation speed setting unit 134 then sets the obtained propagation speed as the propagation speed in the third tooth structure layer 213.

[0072] Furthermore, the measuring main unit 130 has a calculation unit 135 that calculates an index representing the thickness of the second tooth structure layer 212 and an index representing the thickness of the third tooth structure layer 213.

[0073] The calculation unit 135 uses the known propagation speed of the terahertz pulse wave in the second tooth layer 212, which is determined by the propagation speed setting unit 134 based on the user's specifications as described above, and the first reflection interval T1 measured by the reflection interval measurement unit 131, to calculate an index representing the thickness of the second tooth layer 212.

[0074] Specifically, in this embodiment, the “index representing the thickness of the second tooth structure layer 212” is an approximate value of the thickness of the second tooth structure layer 212. From the previously described relation (a), the thickness d of the second tooth structure layer 212 is approximated by the following equation, where v is the known propagation speed of the terahertz pulse wave in the second tooth structure layer 212. d≒v·T1 / (2cosθ)≒v·T1 / 2 ···(b)

[0075] Similarly, the calculation unit 135 uses the known propagation speed of the terahertz pulse wave in the third tooth layer 213, determined by the propagation speed setting unit 134 based on the user's specification, and the aforementioned second reflection interval T2 measured by the reflection interval measurement unit 131, to calculate an index representing the thickness of the third tooth layer 213, specifically an approximate value of the thickness of the third tooth layer 213.

[0076] Furthermore, the measurement unit 130 has an output unit 136 that outputs the calculation results of the calculation unit 135. In this embodiment, the output unit 136 outputs an index representing the thickness of the second tooth layer 212 and the third tooth layer 213 as the calculation result of the calculation unit 135, by display.

[0077] Figure 9 shows the hardware configuration of the measurement unit 130 described above. The measurement unit 130 includes an input device 130b for the user to perform the aforementioned specifications and other input operations, and a display device 130c that displays the aforementioned selections and the calculation results of the calculation unit 135.

[0078] The input device 130b and the display device 130c constitute a graphical user interface. This graphical user interface enables the designation unit 133 and output unit 136 shown in Figure 7.

[0079] Furthermore, the measurement unit 130 is equipped with a storage device 130d that pre-stores tooth structure layer propagation velocity data 132, as shown in Figure 7. The storage device 130d also stores a tooth structure measurement program 130e that defines the procedure for calculating an index representing the thickness of the second tooth structure layer 212 and the third tooth structure layer 213.

[0080] Furthermore, the measurement main unit 130 includes a processor 130a that executes the tooth structure measurement program 130e. When the processor 130a executes the tooth structure measurement program 130e, the functions of the reflection interval measurement unit 131, the designation unit 133, the propagation speed setting unit 134, the calculation unit 135, and the output unit 136 shown in Figure 7 are realized.

[0081] As described above, the tooth structure measuring device 100 according to this embodiment provides the following advantages.

[0082] (I) Using terahertz pulse waves, an index representing the thickness of the second tooth structure layer 212 and an index representing the thickness of the third tooth structure layer 213 can be determined. Specifically, the user can know the approximate thickness of the second tooth structure layer 212 and the approximate thickness of the third tooth structure layer 213.

[0083] (II) The tooth structure measuring device 100 is pre-prepared with propagation velocity data 132 for each tooth structure layer, so the user only needs to specify which tooth structure layer with known propagation velocity corresponds to the second tooth structure layer 212 and the third tooth structure layer 213. Based on this specification, the specific propagation velocity corresponding to the second tooth structure layer 212 and the third tooth structure layer 213 is used. Specifically, different propagation velocities are used for healthy dentin and demineralized dentin. As a result, an index representing the thickness of the second tooth structure layer 212 and an index representing the thickness of the third tooth structure layer 213 can be accurately calculated.

[0084] (III) Despite the first tooth structure layer 211 being a pulp layer containing a large amount of moisture, the first reflected wave RW1 of the terahertz pulse wave can also be obtained from the first interface 221. Therefore, it is possible to determine the thickness of the tooth structure layer adjacent to the pulp layer. Specifically, the user can quantitatively determine the remaining amount of the second tooth structure layer 212, which is a healthy dentin layer adjacent to the pulp layer, using an index that represents the thickness of the second tooth structure layer 212.

[0085] Therefore, when the tooth structure measuring device 100 according to this embodiment is used, for example, in dental treatment, the dentist, as the user, can quantitatively grasp the amount of healthy dentin remaining adjacent to the pulp layer, and thus make an appropriate and prompt decision on whether to perform pulpectomy (removal of the pulp) or preserve the pulp.

[0086] Furthermore, dentists, as users, can quantitatively determine the thickness of the third dentin layer 213, which is a demineralized dentin layer adjacent to the healthy dentin layer, using this as an indicator of the third dentin layer 213's thickness. Therefore, when preserving the dental pulp, it is possible to remove the third dentin layer 213, which is a demineralized dentin layer, without excess or deficiency.

[0087] (IV) Unlike X-rays, terahertz pulse waves pose virtually no risk of radiation exposure. Therefore, when the tooth structure measuring device 100 according to this embodiment is used, for example, in dental treatment, the dentist, as the user, can measure the structure of the patient's target tooth 200 in real time and as many times as needed, while the patient remains seated in the dental chair.

[0088] The embodiments have been described above. The following modifications are also possible.

[0089] In the above embodiment, an approximate value of the thickness of the second tooth structure layer 212 was adopted as an index representing the thickness of the second tooth structure layer 212. However, the index representing the thickness of the second tooth structure layer 212 is not limited to this. The index representing the thickness of the second tooth structure layer 212 may be the thickness of the second tooth structure layer 212 or a physical quantity that depends on the thickness of the second tooth structure layer 212. The same applies to the index representing the thickness of the third tooth structure layer 213.

[0090] In the above embodiment, it was assumed that the first tooth structure layer 211 is the pulp layer, the second tooth structure layer 212 is a healthy dentin layer, and the third tooth structure layer 213 is a demineralized dentin layer. However, the combinations of the first to third tooth structure layers 211 to 213 are not limited to these. For example, the first tooth structure layer 211 may be a healthy dentin layer, the second tooth structure layer 212 may be a healthy enamel layer or a demineralized dentin layer, and the third tooth structure layer 213 may be a demineralized enamel layer.

[0091] In the above embodiment, a configuration for determining an index representing the thickness of two tooth layers, the second tooth layer 212 and the third tooth layer 213, was illustrated. However, the number of tooth layers to be included in the calculation of the index is not particularly limited. An index representing the thickness of only one tooth layer may be determined, or an index representing the thickness of three or more tooth layers may be determined.

[0092] The tooth structure measurement program 130e shown in Figure 9 can also be installed on existing smartphones, tablets, or other computers to enable the functionality of the measurement unit 130 on those computers. The tooth structure measurement program 130e can be distributed via a communication line or by storing it on a non-temporary recording medium. [Explanation of Symbols]

[0093] 11...Radioactive device, 12...Receiver, 13... Miller, 14... Sample, 100... Tooth structure measuring device, 110... Radiation section, 120…receiving section, 130... Measuring unit, 130a... Processor, 130b... Input device, 130c...Display device, 130d...Memory device, 130e... Tooth structure measurement program, 131...Reflection interval measurement unit, 132...Propagation velocity data by tooth structure layer, 133...designated section, 134...Propagation speed setting unit, 135...Calculation unit, 136...Output section, 200...Target teeth, 211...First tooth structure layer, 212...Second tooth structure layer, 213...Third tooth structure layer, 221...first interface, 222...second interface, 223...Third interface, RA, RB... graph, R1,R2,R3,RA1,RA2,RA3,RB1,RB2,RB3...Wave packet, RW1...first reflected wave, RW2…Second reflected wave, RW3…Third reflected wave.

Claims

1. A radiating unit that emits terahertz pulse waves toward the target tooth to be measured, A wave receiving unit that receives a first reflected wave, which is the interface between the first tooth structure layer and the second tooth structure layer located outside the first tooth structure layer of the target tooth, and a second reflected wave, which is the interface between the first tooth structure layer and the second tooth structure layer located outside the first tooth structure layer of the target tooth, respectively. A reflection interval measuring unit measures the first reflection interval, which is the time difference between the time the first reflected wave is received and the time the second reflected wave is received. A designation unit for the user to specify which of the multiple types of tooth layers with known propagation speeds that constitute a tooth, the terahertz pulse wave propagation speed of which has been measured and is known in advance, corresponds to the second tooth layer, A calculation unit calculates an index representing the thickness of the second tooth layer using the known propagation velocity of the terahertz pulse wave in the tooth layer with a known propagation velocity designated as the second tooth layer, and the first reflection interval. A tooth structure measuring device equipped with the following features.

2. The wave receiving unit also receives a third reflected wave, which is a terahertz pulse wave incident on the target tooth and reflected at a third interface located on the surface of the third tooth layer located outside the second tooth layer of the target tooth. The reflection interval measuring unit also measures the second reflection interval, which is the time difference between the time the second reflected wave was received and the time the third reflected wave was received. The designation part also designates which of the multiple types of tooth layers with known propagation speeds the third tooth layer corresponds to. The calculation unit also calculates an index representing the thickness of the third tooth layer using the known propagation velocity of the terahertz pulse wave in the tooth layer with a known propagation velocity designated as the third tooth layer, and the second reflection interval. The tooth structure measuring device according to claim 1.

3. The multiple types of tooth structure layers with known propagation speeds that are options for designation in the aforementioned designation section include dentin and demineralized dentin layers that are more demineralized than the dentin layer. The tooth structure measuring device according to claim 1 or 2.

4. The multiple types of tooth structures with known propagation speeds that are options for designating in the aforementioned designation section include an enamel layer and a demineralized enamel layer that is more demineralized than the enamel layer. The tooth structure measuring device according to claim 1 or 2.

5. The first tooth structure layer is the pulp layer. The tooth structure measuring device according to claim 1 or 2.

6. A radiation step in which terahertz pulse waves are emitted toward the target tooth to be measured, A wave receiving step in which the terahertz pulse wave incident on the target tooth is received by receiving a first reflected wave reflected at a first interface, which is the interface between a first tooth structure layer and a second tooth structure layer located outside the first tooth structure layer in the target tooth, and a second reflected wave reflected at a second interface located on the surface of the second tooth structure layer of the target tooth. A reflection interval measurement step, which measures the first reflection interval, which is the time difference between the time the first reflected wave is received and the time the second reflected wave is received. A designation step to specify which of the multiple types of tooth layers with known propagation speeds that constitute a tooth, the tooth layer in which the propagation speed of the terahertz pulse wave is known in advance by measurement, corresponds to the second tooth layer. A calculation step of calculating an index representing the thickness of the second tooth layer using the known propagation velocity of the terahertz pulse wave in the tooth layer with a known propagation velocity designated as the second tooth layer, and the first reflection interval, A method for measuring tooth structure, including the above.

7. In the wave receiving step, the third reflected wave, which is reflected at the third interface located on the surface of the third tooth structure layer located outside the second tooth structure layer in the target tooth, is also received from the terahertz pulse wave incident on the target tooth. In the reflection interval measurement step, the second reflection interval, which is the time difference between the time the second reflected wave was received and the time the third reflected wave was received, is also measured. In the aforementioned designation step, it is also specified which of the multiple types of tooth layers with known propagation speeds the third tooth layer corresponds to, In the calculation step described above, an index representing the thickness of the third tooth layer is also calculated using the known propagation velocity of the terahertz pulse wave in the tooth layer with a known propagation velocity designated as the third tooth layer, and the second reflection interval. The tooth structure measurement method according to claim 6.

8. The multiple types of tooth structure layers with known propagation speeds that are options for specifying in the aforementioned designation step include dentin and demineralized dentin layers that are more demineralized than the dentin layer. The method for measuring tooth structure according to claim 6 or 7.

9. The multiple types of tooth structure layers with known propagation speeds that are selected as options in the aforementioned designation step include an enamel layer and a demineralized enamel layer that is more demineralized than the enamel layer. The method for measuring tooth structure according to claim 6 or 7.

10. The first tooth structure layer is the pulp layer. The method for measuring tooth structure according to claim 6 or 7.

Images