JP2008197080A - Caries detection method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tooth decay detection method and device for detecting an early tooth decay with sensitivity, accuracy, and safety. <P>SOLUTION: A terahertz spectroscope capable of frequency sweeping or a terahertz analyzer generating only a specific wavelength is applied to a decayed tooth diagnosis to detect a tooth decay mainly from crystallinity evaluation or from crystal defects caused by changes in the composition. Nondestructive, noninvasive, and quantitative diagnosis is realized through evaluation by using the reflection intensity characteristic, in particular, of the tooth surface. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for detecting caries in the field of dentistry or dental research. In particular, the present invention relates to a technique for spectroscopically measuring the crystallinity of a tooth material for the early detection of early caries and the effect of preventive treatment.

  Although early caries can be detected by X-rays, it is difficult to diagnose very small areas at the very initial stage, and there is a risk of exposure, so many actually rely on dentist inspection. This is the current situation. However, it cannot be said that a sufficient diagnosis result can be obtained by visual observation, and there is a demand for a quantitative diagnosis method that is more reliable, safe for the human body, and quantitative.

  As a more quantitative method, for example, QLF (quantitative light) described in Non-Patent Document 1 (Stookey, GK, et al. Dental careers diagnosis, Dent Clin North Am., 43; 665-77, 1999.). Fluorescence) method. In this method, blue to ultraviolet excitation light is irradiated to detect visible or infrared fluorescence from the vicinity of the boundary between enamel and dentin. It utilizes the phenomenon that the fluorescence intensity of the caries site is weaker than the fluorescence intensity from the healthy site. However, since it is fluorescent light having a wavelength of about visible light, it is difficult to obtain sufficient intensity as compared with disturbance light, and it is difficult to increase detection sensitivity.

  Further, for example, in Patent Document 1 (Japanese Patent Application No. 2002-326431), dental caries is quantitatively evaluated based on the amount of scattered light, such as Raman scattering, induced by laser light to be absorbed by the tooth structure. A method is described. However, in general, in order to induce a nonlinear optical effect, a powerful laser beam is required, and it is unavoidable that there is a risk in actual clinical use particularly in dentistry for the head.

  The present invention provides a caries detection method and apparatus for detecting initial caries with high sensitivity and accuracy.

  It is known that information reflecting crystallinity can be obtained in a spectral spectrum in a terahertz region where a natural vibration frequency such as a molecule constituting a living body exists (Non-Patent Document 2 Jun-ichi Nishizawa, Ken Suto, Tetsuo). Sasaki, Tadao Tanabe, Takenori Tanno, Yutaka Oyama, Fumikazu Sato, 'GaP Raman Terahertz high accuracy spectrometer and its application to detect organic and inorganic crystalline defects', Proceedings of the Japan Academy Ser.B82 (9), 2006, 53-358), and generally are used in the identification and compositional analysis of the material was measured.

On the other hand, for example, a terahertz signal generator that generates coherent terahertz waves using a phonon-polariton of a semiconductor GaP crystal has been developed. A high-accuracy terahertz spectrometer (GaP terahertz spectrometer) with a frequency accuracy of 500 MHz has been realized (for example, Non-Patent Document 3 J. Nishizawa, T. Sasaki, K. Suto, T. Tanabe, T. Yoshida, T. et al.). Kimura, K. Saito, 'Frequency-tunable terhertz-wave generation from GaPusing Cr: forsterite lasers', INTERNATIONAL JOURNAL OF I FRARED AND MILLIMETER WAVES 27 (6): 779-789 JUN 2006).
Such a frequency-swept terahertz spectrometer, or a terahertz analyzer that generates only a specific wavelength adapted to the measurement object, is applied to dental diagnosis, and its crystallinity is mainly evaluated by crystallinity evaluation or composition change. Caries are detected from the deterioration of the so-called crystal defects. In particular, non-destructive and non-invasive quantitative diagnosis is realized by evaluating using the reflection intensity characteristic of the tooth surface.

  In the treatment of teeth, the crystallinity, or so-called nano-order scale evaluation, makes it possible to detect caries and caries at the very initial stage, as well as to detect the effect of fluorination, which is effective in preventing caries. In addition, by adopting reflection measurement and fiber optical system, a highly reliable diagnosis is possible with easy operation. Furthermore, terahertz waves do not affect the human body even if they are considered from their energy, so that safe diagnosis can be performed.

  The outermost surface of the tooth is called enamel and consists almost entirely of hydroxyapatite crystals. Tooth decay begins when the balance between the two chemical reactions that occur regularly on the surface of the enamel, “remineralization” and “decalcification” is lost, and demineralization predominates and the enamel begins to melt.

  That is, the initial caries is the detachment of atoms from the crystal, in other words, the introduction of crystal defects.

  On the other hand, terahertz spectroscopy has shown that defects in organic and inorganic molecules can be detected. If the frequency of interatomic vibration, intermolecular vibration, or lattice vibration exists in the terahertz band, highly sensitive quantitative evaluation is possible. It becomes.

  FIG. 1 shows absorption spectra measured for a hydroxyapatite crystal and fluoroapatite crystal standard powder reagent using a GaP terahertz spectrometer. The sample measured at this time is obtained by grinding an appropriate amount of powder into polyethylene powder having low absorption in the terahertz region, mixing the powder, and compacting it into a pellet. Grinding is essential to prevent the terahertz waves from being scattered, and the particle size is adjusted to be approximately 5 microns or less.

  Hydroxyapatite has characteristic absorption at 2.9 THz and 5.7 THz. Fluoroapatite has characteristic absorption at 1.4 THz, 2.8 THz, 3.1 THz, 5.5 THz and 6.0 THz.

  Further, FIG. 1 also shows a terahertz absorption spectrum of white shark teeth which were pulverized in the same procedure as described above, mixed with polyethylene powder at an appropriate concentration, compacted and molded into a pellet. This spectrum shows characteristics very similar to hydroxyapatite crystals, and qualitatively shows that the tooth of a tooth is made of hydroxyapatite. In order to handle it more quantitatively, it is necessary to perform peak separation and evaluate each absorption intensity and half width. Here, white shark teeth were used for the convenience of the experiment, but human teeth are also made of the same hydroxyapatite, so that they can be applied without problems.

  It is said that when the enamel surface is fluorinated to form a fluoroapatite crystal, it can be used for the prevention of dental caries because it does not become caries. Since the absorption peak of fluoroapatite is very different from that of hydroxyapatite, it can be distinguished from spectral measurements. In other words, this technique can be used to evaluate the effect of fluorination on preventing dental caries. It is also said that calcium hydrogen phosphate dihydrate is present as an intermediate during remineralization. The spectrum of calcium hydrogen phosphate dihydrate is also shown in Fig. 1, but characteristic absorption lines are seen at 3.9 THz, 5.2 THz, and 5.9 THz, and remineralization is also applied to the evaluation. it can.

  Incidentally, hydroxyapatite is polycrystalline in the enamel of teeth, and one crystal is elongated as a particle size of 200 to 2000 nm × 10 to 80 nm, and these crystals are strongly oriented. For such objects, polarization spectroscopy in which the polarization direction of the incident terahertz wave is strictly controlled is effective.

  In the method of Example 1, it is necessary to remove or cut a tooth in order to measure a tooth, which is not non-invasive and difficult to use for diagnosis. Non-invasive diagnosis can be realized by performing terahertz reflection spectroscopy measurement.

で表される。この周波数依存性を調べることが、テラヘルツ反射分光測定である。When electromagnetic waves are perpendicularly incident on a material with refractive index n ₁ and extinction coefficient k ₁ placed in air, the reflectance is

It is represented by Examining this frequency dependence is terahertz reflection spectroscopy measurement.

と表されるので、屈折率変化が反射の変化として現れることになる。屈折率の異常分散は物質に固有のものであるので、屈折率の周波数依存性から物質を特定することができる。例えば、テラヘルツ帯における反射分光測定法は、特許公開２００５−１７２７７４「反射光学特性によって物性を測定する装置および測定方法」において示されている。If n1 >> k1,

Therefore, a change in refractive index appears as a change in reflection. Since the anomalous refractive index dispersion is specific to a substance, the substance can be specified from the frequency dependence of the refractive index. For example, a reflection spectroscopic measurement method in the terahertz band is shown in Patent Publication 2005-172774 “Apparatus and measurement method for measuring physical properties by reflection optical characteristics”.

  FIG. 2 shows an example of a reflection terahertz spectroscopy measurement system. A terahertz wave 1 emitted from the GaP terahertz signal generator is divided into two by a beam splitter 2, and the reflected wave is guided to a reference terahertz detector 6. The other transmitted wave is condensed by the parabolic mirror 3 and guided to the measurement sample 5 by the mirror 4. At this time, the incident angle is controlled to be constant. The reflected wave from the measurement sample 5 is guided to the measurement terahertz detector 7 by a mirror. By adopting a double beam method using two detectors for reference and measurement, measurement in which the intensity change of the light source is corrected is realized.

  FIG. 3 shows a reflected terahertz spectrum for the white shark's teeth measured using this measurement system. Corresponding to the tooth absorption frequency of 2.9 THz shown in FIG. 1, there is a frequency dispersion in which the reflectance is greatly reduced at this frequency. It can be seen that the terahertz wave reflectivity of the tooth surface is dominated by the frequency dependency of the refractive index, and it is shown that the spectroscopic evaluation of the tooth surface material can be performed by reflection spectroscopy. Here, white shark teeth were used for the convenience of the experiment, but human teeth are also made of the same hydroxyapatite, so that they can be applied without problems.

  This measurement does not require complicated pre-processing or complicated calculation processing of measurement results, and is extremely easy to measure and does not take time. In terahertz absorption measurement, treatments such as tooth surface drying, humidification, application of a reflection film or antireflection film, freezing, and polishing may be included in order to improve sensitivity or improve measurement accuracy. . Further, the terahertz spectroscopy measurement system is not limited to the GaP terahertz spectroscopy device, and a far infrared FTIR measurement device, a terahertz time domain spectroscopy (THz-TDS) device, or the like may be used. Furthermore, if the frequency is selected in advance, a semiconductor high-frequency oscillator such as a TUNNETT diode, an IMPATT diode, or a GUNN diode, a vacuum tube high-frequency oscillator such as a BWO (Backward Oscillator), or a quantum cascade laser may be used. A narrow element may be used as the light source.

  Terahertz waves belong to so-called far infrared rays and have low energy, so they are safe for the human body unless a special high intensity is obtained. Therefore, it can be used for medical diagnosis with peace of mind.

  In order to obtain a terahertz reflection or absorption spectrum at an arbitrary position, for example, a terahertz wave 11 can be guided by a hollow fiber 12 as shown in FIG. In this case, the reflected wave 15 on the surface of the measurement sample 13 may be guided directly to the detector 14, may be collected by a parabolic mirror 16, an integrating sphere 17, or the like, or again the hollow fiber 12 or the like. May be guided to the detector 14. The terahertz wave irradiating unit may collect light with a lens, a convex mirror, a parabolic mirror, an antenna, or the like, or may shape the beam shape as necessary. By reducing the beam shape, minute caries can be detected, and even very early caries can be detected. If this spot is scanned spatially, a terahertz reflection spectrum mapping of the tooth surface can be obtained, which corresponds to mapping of caries. Instead of the hollow fiber, a photonic fiber that guides the terahertz wave with a periodic structure may be used.

  In addition, the terahertz light source at this time is not limited to the GaP terahertz oscillation device, and a white light such as a high-pressure mercury lamp or an ultrashort pulse laser may be used. Furthermore, an element having a relatively narrow frequency sweep range may be used, such as a semiconductor high-frequency oscillator such as a TUNNETT diode, an IMPATT diode, or a GUNN diode, a vacuum tube high-frequency oscillator such as a BWO (Backward Oscillator), or a quantum cascade laser.

  Terahertz absorption spectra of hydroxyapatite, fluoroapatite standard reagent, and white shark tooth powder samples   Example of terahertz reflection spectroscopy measurement system   Reflected terahertz spectroscopic spectra of white shark teeth   Terahertz reflection measuring device using waveguide

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Terahertz wave 2 ... Beam splitter 3 ... Parabolic mirror 4 ... Mirror 5 ... Measurement sample 6 ... Reference terahertz detector 7 ... Terahertz detector 11 for measurement 11 ... Terahertz wave 12 ... Hollow waveguide 13 ... Tooth surface 14 ... Terahertz detector 15 ... reflective terahertz wave 16 ... parabolic mirror 17 ... integral sphere

Claims (4)

  With regard to measurement using terahertz waves, terahertz wave frequency sweeping that can limit the range, or a terahertz wave designating at least one arbitrary single frequency, and a human or animal tooth surface Apparatus and method for examining the progress of dental caries such as detection or prevention of dental caries from at least reflected wave intensity of terahertz waves irradiated to In claim 1, at least one or a combination of 2.9 THz, 5.7 THz absorption lines of hydroxyapatite, or a ratio between a plurality of absorptions,
2.8 THz, 3.2 THz, 5.6 THz, 6.0 THz absorption lines of fluorinated apatite, or a combination between absorptions,
Using at least one of a combination of 3.9 THz, 5.2 THz, 5.9 THz absorption lines of calcium hydrogen phosphate dihydrate, or a ratio between a plurality of absorptions, A measuring apparatus and method characterized by examining the progress of caries such as detection or caries prevention effect.   3. The measuring apparatus and method according to claim 1, wherein the physical property to be evaluated is a tooth composition or a crystal defect.     5. The measuring apparatus and method according to claim 1, wherein the terahertz wave to be irradiated is guided by a fiber and the reflected wave is detected.

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