CA1161120A

CA1161120A - Method and apparatus for detecting the presence of caries in teeth using visible luminescence

Info

Publication number: CA1161120A
Application number: CA000358694A
Authority: CA
Inventors: Robert R. Alfano
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-08-20
Filing date: 1980-08-20
Publication date: 1984-01-24
Also published as: DE3031249C2; NL8004712A; JPS5640137A; FR2463608B1; GB2058343B; US4290433A; FR2463608A1; DE3031249A1; GB2058343A

Abstract

METHOD AND APPARATUS FOR DETECTING THE PRESENCE OF CARIES
IN TEETH USING VISIBLE LUMINESCENCE

ABSTRACT OF THE DISCLOSURE
A method an apparatus for detecting the presence of caries in human teeth using visible luminescence. A region to be examined is excited with a beam of monochromatic light.
The intensity of the visible light emitted from the region is measured at two predetermined wavelengths, one where the intensity dependence on the spectra is about the same for caries and noncaries and the other where the relative intensity increases significantly in the presence of caries. A signal corresponding to the difference in the two intensities is obtained and then displayed. By first determining the magnitude of the difference signal at a nondecayed region, any increases in the magnitude as other regions are probed indicate the presence of caries.
The invention is based on the discovery that the visible luminescence spectra for decayed and nondecayed regions of a human tooth are substantially different and that the differences are such that visible luminescence from teeth can be used to detect the presence of caries.

Description

B~CKGE~OU~ID OF '['IIF lNVEN'L'LON
The present :invention relates to a method arld apparatus for detectiny the presence of caries in -teeth and rnore particularly, to a me-~hod and apparatus for detecting the presence of caries in the tee-th of a person usiny visible luminescence.
Dental caries or tooth decay is a very common and well known type of disease which, if not properly treated, results in a breakdown of the hard structures of the teeth. The progress of the tooth decay is gradual, starting slowing from -the outside at the enamel and then progressing more rapidly in the dentin. It is believed that dental caries are caused prim~rily by the action of acid-producing bacteria or certain carbohydrates, principally sugar. If detected, dental decay can be treated by removing the decayed area and filling the resulting cavity with silver amalgam or other inert cavity material. If untreated, dental caries can cause the eventual destruction of the tooth as well as infection of abscess oE
the jawbone.
In the past, dental caries has been detected by two techniques, one by visual inspection and the other through the use of X-rays.
The problem with visual inspection is that it is not always possible to detect the presence of caries by simply looking at the teeth, especially if the caries is very sma]l or in a very early stage or in an area where it cannot be easily seen. On the other hand, although X-rays have proven to be a very effective manner for detecting the presence of caries and other problems or disorders in the teeth and/or dm~ - 2 -gums, the potentialLy harmE1l1 e~Efects of suhjecting people to x-rays radiation has become a matter of great concern over the last several years. In particular, the quantitive relationship between low-dose exposure to X-rays and possible harmful effects, such as cancer, is not clearly known.
In view of the possible dangerous effects of ~~rays, it would appear that a definite need exists for a new technique for detecting the presence of caries and specifically for a technique which can either eliminate or substantially reduce the necessity of X-ray examinations.
Experiments have been conducted in the past which reveal that teeth luminesce when excited by light. In an article by R.L. Hartles and A.G. Leaver appearing in the 1954 Biochemistry Journal, pp. 632-638, the results of certain experiments performed to determine the luminescent properties of teeth when exposed to ultraviolet radiation are discussed at length. Other known articles dealing with the luminescent properties of teeth when exposed to ultraviolet radiation are an article by K.G. Hoerman and ~.A. Mancewicz appearing in the 1964 Oral Biology Journal, Volume 9, pp. 517-534 and an article by K.G. Hoerman and S.A. Mancewicz appearing in the 1964 Oral Biology Journal, Volume 9, pp. 535-544.
In U.S. Patent 2,437,916 to W.F. Greenwald there is described a technique for examining living tissue which involves illuminating the tissue with a beam of light and then measuring the intensity of the reflected light at certain wavelength ranges using a phototube and different colored filters.
In U.S. Patent 3,674,008 to C.C. ~ohnson there is described an instrument which quantitatively measures optical density of a transilluminated body portion. Irhe instrument dm: ' comprises a controllab1e, rel~lt:iv~ly low-freqllerlcy oscilla-tor generating pulses which are applled to a ligh-t source through a first expand and delay circui-t. A light-conducting source -to one side of the body portion and a sirnilar means optically couples another side of the body portion to a light detector.
Alternatively, the light source and detector may be placed directly on the body portion. After compensation for ambient light, the output of the detector is coupled to a simple and hold circuit which is triggered by the controllable oscillator through a second expand and delay circuit. The stored signal in the sample~and hold circuit is proportional to transmittance and is converted to a visual indication of optical density by a calibrated display means. Methods of using the instrument in diagnosis are discussed, as are further applications to spectrophotometric determinations.
In U.S. Patent 3,963,019 to R.S. Quandt there is described a method and apparatus for detecting changes in body chemistry, for example, glycemia, in which a beam of light is projected into and through the aqueous humor of the patientls eye An analyzer positioned to detect the beam on its exit from the patient's eye compares the effect the aqueous humor has on said beam against a norm. An excess or deficiency of glucose present in the aqueous humor produces a corresponding positive or negative variation in the exiting beam and thereby indicates a hyper or hypo glycemia condition in the body chemistry of the patent being tested.
In U.S. Patent ~,029,085 to D.P. DeWitt et al there is described a method for determining the bilirubin concentration dm~

in the blood sc~rum of a person frorn rneasurerrleJIt of tile spectral reflec-tance of ~.he skin. The d.;sclosed method detec-ts the severity of jaundice, a common neonatal condition, and enables.
determination of the type of treatrnent regimen needed to prevent the bilirubin level from becoming sufficiently hiyh to cause kernic-terus which can result in brain damaye. The method includes measuring the reflectance of the skin within a predetermined frequency spectrum, and more particularly, at a number of specific wavelengths in the visible portion of the spectrum.
In Medical and Biological engineering, Volume 6, No. 4, August 1968, pp. 409, 413, there is described a technique for tissue identification during needle puncture by reflection spectrophotometry.

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SUMMA~Y OF Tf_E INVENY'LON
It is a Eeature of this inven-tion to provide a new and improved technique for detecting the presence of caries in teeth.
Another feature of this invention is to provide a technique for detecting the presence of caries in the teeth which does not involve the use of X-rays.
It is another Eeature of this invention to provide a - technique for detecting the presence of caries in teeth which does not require the use of X-ray sensitive plates or film.
It is a preferred feature of this invention to provide a technique for detecting the presence of caries in teeth that does not involve the use of other potentially harmful radiation, such as ultraviolet radiation.
It is a feature of one embodiment of this invention I to provide a technique for detecting the presence of caries in teeth which is suitable~for use with a recording medium such as conventional photoaraphic film.
It is a feature of another émbodiment of this invention to provide a technique for detecting the presence of caries in teeth using visible light as an exciting source and visible luminescence to probe for caries.
This invention provides a technique for detecting the presence of caries in the teeth of a person which is reliable, inexpensive, and easy to use.
The present invention is based on the discovery that the visible luminescence spectra from caries and nondecayed regions of a tooth are substantially different, and in dm~ 6 -.~

particular, tha-t in certain regions of th~ visible spectrum the intensity of the luminescence for caries and nondecayed teeth is about the same while in other regions of the visible spectrum the relative intensity increases substantially in the presence of caries. The present invention is also based on the further discoveries that the emission from amalgam and metals is weaker than the emission from caries in the region ..where the emission increases in the presence of caries and that the relative intensity change of the spectrum from ` 10 adaptic is less than the relative intensity change for noncarious regions in.the red portion of the spectrum. Finally, it has been discovered that the visible luminescence can be achieved using visible light as the excitation source.
The method for detecting the presence of caries according to the teachings of this invention and based on the above noted discoveries involves illuminating a region to be examined with a beam of light that is at least substantially monochromatic, measuring the intensity of the visible luminescent radiation at a wavelength where the intensity dependence of the spectrum is about the same for caries and noncaries and at a wavelength where the intensit.y dependence of the spectrum changes a measurable amount in the presence of caries and then determining if caries is present in accordance with these measurements.
In another aspect,the method for detecting the presence of caries in the teeth of a person comprises exciting a region of the teeth to be examined with a beam of substantially monochromatic light, the beam oE monochromatic dm~ 7 .~ ' light having a wavelength ~1, measuring the intensity of the light emitted from the region at a wavélength ~3, and determining if caries is present in accordance with the intensity of the light emitted at the wavelength ~3, wherein ~3 is a wavelength where the intensity of emitted light decreases in the presence of caries and ~1 is a wavelength `
which will produce emission from teeth at a wavelength ~3.
The apparatus for detectlng the presence of caries according to the teachings of -this invention and based on the above noted discoveries includes source means for generating a beam of monochromatic light having a wavelength ~1, means for directing light from the monochromatic source onto a region of teeth to be examined and receiving the light emitted therefrom, means for measuring-the intensity of the emitted light at a wavelength ~2 and a wavelength ~3, and means for generating a signal related to ~2 and ~3, where ~2 is a wavelength where the intensity is about the same for caries and noncaries, ~3 iS a wavelength where the intensity changes in the presence of caries and ~1 is a wavelength that will produce emitted light when illuminating teeth at wavelengths ~2 and ~ 3 .
The foregoing and other objects and advantages will appear from the description to follow. In the description, reference is made to the accompanying drawing which forms a part thereof, and in which is shown by way of illustration a specific embodiment for practicing the invention. This embodiment will be described in sufficient detail to enable those skilled in the art to practice the invention, and it dm~ 8 -V
is to be understood that other embodiments may be wtilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawlngs illustrate a complete embodiment of the invention according to the best mode so far devised for the practical application of the principles thereof, and in which:
Fig. 1 is a graphical illustration of emission spectra measurements made on a known noncarious region of a human tooth excited with blue light at a wavelength of 410~5 nm;
Fig. 2 is a graphical illustration of the emission spectra measurements made on the same tooth as in Fig. 1 with the same light but at a known carious region; -Fig. 3 is a graphical illustration of the difference of the spectra in Fig. 1 and the spectra in Fig. 2;
E'igs.4 and 5 are graphical illustrations similar to Figs. 1 and 2 respectively but for a different tooth;
Figs. 6 and 7 are graphical illustrations similar to Fig. 3 for the tooth used in Figs. 1 and 4, respectively, but with a light source of 350 nm rather than 410 nm; and Fig. 8 is a simplified diagram of an embodiment of the apparatus of the invention.

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DETI~Ir,ED DESCRIPTIO~I
The present invention is directea to a method and appara-tus for detecting the presence of caries in the teeth of a person using vlsible luminescence.
Referring now -to the drawings, there is shown in Figure l a graph of emissi,on spectrum measurements made on an extracted human tooth Tl excited by blue light at a wavelength of 410 + 5 nm on a region,'known to be noncarious and in Figure

2 a graph of emission spectrum measurements made on the same tooth by the same light over a region known to have caries.
Luminescent radiation from the tooth was collected into a SPEX ~ - meter scanning spectrometer blazed at 500 nm, second order. An RCA 7265 (S~20) photomultiplier located at the exit of the spectrometer measured the intensity at different wave-lengths. The output of the photomultiplier was connected to a lock-in-recorder to display the spectrum. The emission spectra were uncorrected for the spectral response of the system. The intensities from both regions were comparable in magnitude, however, the spectra were normalized to unity at the intensity maximum. The emission spectra from the region containing caries (Fig. 2) contained no more than a 25% contribution from the surrounding region. The intensity variations of the teeth examined for caries and noncaries were typically in an order of magnitude of each other.
The difference spectra between the nondecayed and the decayed regions is illustrated in Figure 3.
The salient features of the data displayed in Figures 1~3 are that the caries spectra are shifted to the red by about 200 A and have more intensity in the longer wavelength ~'~ dm:' - lO -reyion than the spectra obtairted frorn a non-cariouS reyion.
The largest difference between the spectra from caries and noncaries occurs in the region bet:ween 540 and 650 nm. wi-th the larges-t difEerence occuriny at 620 nm. On the other, in the region between around 450 and 500 nm. the difference is ex-tremely small and about constant. Furtherrnore, when the spectrum for caries is divided by -the spectrurn fox noncaries, the relative intensity chanye in the red por-tion of the spectrum ti.e. 540 to 650 nm) is about two to four times larger than the intensity chanye in the blue portion of the spectrum (i.e. 420 to 500 nm).
Graphs of the visible emission spectrum measurements for another tooth T2 over a known noncarious region and a known carious region using the same equipment as above, but being corrected for the spectral response of the detection system are illustrated in Figures 4 and 5 respec-tively.
Graphs of the difference spectra for teeth Tl and T~
obtained using the same equipment as used to obtain the graphs in Figures 1-3, but with a light source of 350 nm. inskead of 410 nm are illustrated in Figures 6 and 7 respectively.
As can be seen, in each case the intensity over a carious region is substantially greater than the intensity over a noncarious region in the red region of the spectrum and in each instance there is an area in the blue region of the spectrum where the difference in decayed and nondecayed regions is minimal.
Referring now to Figure 8 there is illustrated an apparatus for detecting the presence of caries in the teeth of a person according to the teachings of this invention.
The apparatus includes a source 11 of white light, such as a tungsten-halogen filament lamp, and a narrow band fil-ter 13.

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~lternative:Ly, source :Ll may coMpri~C~e a laselr. L,ig~lt source ]1 has power coup]ed to i-t fror[l a con~entional power supp]y (not shown). Narrow band filter 13 has a bandwidth of less than about 30 nm and preferably less -than about 10 nrn and is designed to pass light a-t a wavelength ~1.
Light from source 11 that is passed by Eilter 13 is passed through a chopper 14 which removes any ambient light present and is then fed into an input leg 15 of a fiber optic probe 17. The light entering fiber optic probe 17 emerges at the probing end 19 and impinges on a tooth Ts enters probing end 19 and is conducted out oE fiber optic probe 17 through output legs 21 and 23 which are located at the same end as input leg 15.
Fiber optic probe 17 is made up basically of a bundle of optlcal fibers. The diameter of the bundle is preferably about ~ to 3 mm. The fibers within the bundle are preferably randomly arranged to reduce any geometrical collection effects.
Fiber optic probe 17 may,include a lens or lens system (not shown) at -the probing end 19 so that non-contact probing may be achieved, facilitating examination of areas between teeth or other areas not easily reachable by direct contact~probing.
Light emerging from output leg 21 is passed through a narrow,band filter 25 having a bandwidth of less than about 10 nm and designed to pass light at a wavelength ~2, in the visible spectrum where the intensity is cons-tant for carie-s and non-caries, and impinges on a photodetector 27. Light emerging from output leg 23 is passed through a narrow band fil-ter 29 having a bandwidth of less than about 10 nm and designed to pass light at a wavelength ~3, in the visible spectrum where the intensity increases in the presence of caries, and impinges on a photodetector 31.

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, The value o:E ~2 clepends~ at l.east partially, on the value of ~1- For example, i~ ~1 ls ~10 nm, then ~2 may be 450 nm. The value of ~3 iS also, a~ least parti~lly, dependent on ~1. Thus, if ~1 is ~10 nm then ~3 may be around 610 nm. The value of ~1 i.s any wavelength that will cause teeth to luminesce in -the visible spectrum at a wavelength ~2 where the intensity is constant for caries and noncaries and at a wavelength ~3 where the intensity increases measurably in the presence of caries. Wavelength ~1 is preferably in the visible ra-ther than ultraviolet region to avold the potential hazards of exposure to ultraviolet radiation. Photodetectors 27 and 31 are conventional photodetectors having minimum sensitivity in the regions of interest, namely at wavelengths ~2 and ~3 respectively.
Photodetectors 27 and 31 each produce an electrical signal output whose magnitude Sl and S2 respectively, is proportional to the intensity of the incident light. The electrical output signals from photodetectors 25 and 29 are each fed into an electronic circuit 33, such as a differential lock-in amplifier, which is turned to the frequency and phase of the chopper and which produces an electrical output signal whose magnitude S3 is equal to the differences between the two output si~nals S1 and S2. Alternatively, electronic circuit 33 may be a differential amplifier tuned to the frequency of the chopper 14. Furthermore, chopper 14 maybe eliminated, if the ambient light around the region being probed i.s not in the area of spectral in-terest.
The output of electronic circuit 33 is connec-ted to a display 35 which may be in the form of a digital or analog meter or alight or buæzer which is activated when difference signal S3 exceeds a predetermined threshold. Display 35 may be mounted directly on fiber optic probe 17.

dm: - 13 -Light source 1l, narrow band f;llers 13, 2S and 2~ and photodetec-tors 27 and 31 are a]l situated in a light-tl~ht compartmented housing 37.
In detec-ting the presence of caries in accordance with the invention, the probe signals S1 and S2 are firs-t dekermined for a known non-carious region. Any changes in the difference between signals Sl and S2 will indicate that caries are present.
In practice, the probe signals Sl and S2 received from a known nondecayed region are preferably balanced to zero (i.e. Sl ~ S2 adjusted to zero) so that any increase in S2 1 will produce an unbalanced condition or a voltage signal S3 having a magnitude greater than zero. This allows the threshold value for an indicator light or buzzer to be zero. The signals Sl and S2 can be adjusted to zero by any known means such as by adjusting the base voltages of the photodetec-tors or adding the necessary circuitry to permit adjustment of electronic circuit 31.
Instead of taking the difference between signals S
and S2, the ratio of signals S1 and S2 may be used to determine the relative change of the spectra. This may be achieved using any conventional type of dividing circuit.
The reiative magnitudes of probe signals Sl and S2 actually obtained from a nondecayed area of a human tooth, from amalgam, from adaptic and from a decayed portion of the same tootn when ~1 is 410 nm, ~2 is 460 nm and ~3 is 600 nm, are shown in the following table. In the table, the probe signals Sl and S2 for the non-decayed regionof the tooth were balanced and the same value by adjusting the base voltages of the photodetectors and the values of probe signals Sl and S2 for the amalgam, for the adaptic and for the decayed region are values after such adjustments.

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;~able l Tooth Amalgam Aclaptic Tooth Non-Decayed Area Decayed Area Sl - 200 MV Sl = 2 MV Sl - 200 MV Sl - 100 MV
S2 200 MV S2 = 1 MV S2 - 190 MV S2 - 200 MV

As can be seenj once the probe signal Sl and S2 are balanced at a nondecayed area, the difference between Sl and S2 (i.e. Sl - S2) is about 1 MV for amalgam, about ~ 10 MV
- for adaptic and about - 100 MV for a decayed area. Thus, a decayed area can be clearly distinguished from a nondecayed area, from amalgam and for adaptic. It has been found that with a balance accuracy of l~, caries of about 100 microns can be separated from nondecayed regions with a signal to noise ratio of greater than one. It has also been found that caries 0,01 cm2 in size between teeth can be detected from the scattered light of a 1 cm2 surface.
In another embodiment of the invention, the presence of caries can be detected by exciting a region of the teeth to be examined with a beam of substantially monochromatic light, forming an image of the light emitted from the region at a wavelength where the intensity decreases in the presence of caries and then recording the image on a suitable recording medium.
As can be appreciated, the invention does not involve the use of X-ray radiation and does not require the use of radiation sensitive plates. Furthermore, since the indication of caries is based on the difference between dm~ 15 -V
signals Sl and S2 and not merely the intens:Lty of signal S2 any changes in the ligh-t emitted from a reyion under test, such as may be caused by increasing or decreasing the distance from the probe to the region under test, will not produce a change in the difference. Also, since the excitation radiation is visible light, the tooth or region thereof being illuminated can be easily observed.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for detecting the presence of caries in the teeth of a person comprising:
(a) exciting a region of the teeth to be examined with a beam of light that is at least substantially monochromatic (b) measuring the intensity of the visible luminescence emitted from the region at two predetermined wavelengths, one where the relative intensity dependence of the spectra is about the same for caries and non-decayed regions and the other where the intensity changes measurably in the presence of caries, and (c) determining if caries is present in accordance with said measurements.

2. The method of claim 1 and wherein determining if caries is present comprises determining the difference in intensities at the two wavelengths in a noncarious region and then detecting increases in the difference as other regions are excited.

3. The method of claim 1 and wherein determining if caries is present includes producing a signal corresponding to the difference between the intensities at the two wavelengths and then displaying said signal.

4. The method of claim 1 and wherein determining if caries is present comprises producing a signal proportional to the difference between the intensity at the wavelength where the relative intensity dependence of the spectrum is about the same for caries and noncaries and the intensity at the wavelength where the intensities increase in the presence of caries.

5. The method of claim 4 and wherein the beam of light is visible light and has a bandwidth of about no more than 30 nm.

6. The method of claim 5 and wherein the visible light is between about 400 nm and 700 nm.

7. The method of claim 6 and wherein one of said wave-lengths at which the intensity is measured is between 440 and 470 nm and the other wavelength at which the intensity is measured is between 560 and 640 nm.

8. The method of claim 1 and wherein determining if caries is present comprises determining the ratio of the intensities at the two wavelengths in a noncarious region and the detecting increases in the ratio as other regions are excited.

9. The method of claim 1 and wherein the beam of exciting light has a wavelength between 350 and 600 nm.

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10. A method for determining the presence of caries in the teeth of a person comprising:
(a) exciting a region of the teeth to be examined with a beam of monochromatic light at a wavelength .lambda.l, (b) measuring the intensity of the visible luminescence emitted from the region at a wavelength .lambda.2 and at a wavelength .lambda.3, (c) producing a signal corresponding to the intensity at wavelength .lambda.3 less the intensity at wavelength .lambda.2, (d) displaying said signal, and (e) determining if caries is present in accordance with said signal, wherein .lambda.2 is a wavelength where the relative intensity dependence of the spectra is about the same for caries and noncaries, .lambda.3 is a wavelength where the intensity increases in the presence of caries and Al is a wavelength that will produce emission from teeth at .lambda.2 and .lambda.3

11. A method for detecting the presence of caries in the teeth of a person comprising:
(a) exciting a known noncarious region of the teeth with a beam of monochromatic light, (b) measuring the intensity of the emission at a wavelength where the relative intensity dependence of the spectra is about the same for caries and noncaries and at a wavelength where the intensity increases in the presence of caries, (c) displaying a signal corresponding to the dm:

differences in the two intensities and then (d) detecting increases in said signal as other regions of the teeth are excited.

12. A method for detecting the presence of caries in a region of teeth of a person comprising:
(a) exciting the region with light, (b) measuring the intensity of the visible luminesce from the region at a wavelength where the relative intensity dependence of the spectra is about the same for caries and non-caries and at a wavelength where the intensity increases in the presence of caries, and (c) determining if caries is present on the basis of the difference in intensities at the two wavelengths.

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13. Apparatus for use in detecting the presence of caries in the teeth of a person comprising:
(a) means for illuminating a region to be examined with a beam of monochromatic light, the wavelength of the beam of monochromatic light being one which will produce emission from the region at a wavelength where the intensity is about the same for caries and noncaries and at a wave-length where the intensity increases in the presence of caries, (b) means for measuring the intensity of the light emitted from said region on illumination by said illuminating means at a wavelength where the relative intensity dependence of the spectra is about the same for caries and noncaries and at a wavelength where the intensity increases in the presence of caries and producing an electrical signal whose output corresponds to the intensity at each wavelength (c) means producing an electrical signal correspond-ing to the difference in said two electrical signals, and (d) means for displaying said difference electrical signal.

14. Apparatus for detecting the presence of caries in the teeth of a person comprising:
(a) a source of visible monochromatic light for illuminating a region at a wavelength which will produce emission at a wavelength where the intensity is about the same for caries and noncaries and at a wavelength where the intensity changes in the presence of caries, dm:

(b) a pair of photodetector means for measuring the intensity of light emitted from said region at two different wavelengths, one of said wavelengths being a wavelength where the intensity is about the same for caries and noncaries and the other wavelength being a wavelength where the intensity changes in the presence of caries, both of said wavelengths being different from the wavelength of the source, (c) means for directing light to said region from the source and transmitting said emitted light from said region to said photodetector means, (d) means coupled to the photodetector means for producing a signal corresponding to the difference in the output signals from the two photodetector means, and (e) means for displaying said difference signal.

15. The apparatus of claim 14 and wherein the means for directing the light to the region and transmitting light from the region comprises a fiber optic probe.

16. The apparatus of claim 15 and wherein each photo-detector means comprises a photodetector and a narrow band filter disposed in front of said photodetector.

17. The apparatus of claim 15 and wherein said light is mounted on said probe..

18. The apparatus of claim 15 and wherein said source of monochromatic light comprises a source of white light and a narrow band filter.

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19. The apparatus of claim 14 and wherein said display is a buzzer.

20. The apparatus of claim 14 and wherein said display is a light.

21. The apparatus of claim 14 and wherein said display is a meter.

22. The apparatus of claim 14 and wherein said source of monochromatic light is a laser.

23. The apparatus of claim 14 and wherein said mono-chromatic light source is at a wavelength .lambda.1 and the photodetector means includes means for passing light at wavelength .lambda.2 and .lambda.3 wherein .lambda.2 is a wavelength where the intensity is about the same for caries and noncaries, .lambda.3 is a wavelength where the intensity changes in the presence of caries and .lambda.1 is a wavelength that will produce emission on teeth at .lambda.2 and .lambda.3.

24. The apparatus of claim 23 and wherein .lambda.1 = around 410?5 nm, .lambda.2 = between around 450 and 500 nm and = between around 540 and 620 nm.

25. A method for detecting the presence of caries in the teeth of a person comprising:

(a) exciting a region of the teeth to be examined with a beam of light that is at least substantially mono-chromatic at a wavelength .lambda.1, dm:

(b) forming an image of the light emitted from the region at a wavelength .lambda.3 where the intensity decreases in the presence of caries, and (c) recording the image on a recording medium.

26. A method for detecting the presence of caries in the teeth of a person comprising:
a) exciting a region of the teeth to be examined with a beam of substantially monochromatic light, said beam of monochromatic light having a wavelength .lambda.1, (b) measuring the intensity of the light emitted from the region at a wavelength A 3, and (c) determining if caries is present in accordance with the intensity of the light emitted at the wavelength .lambda.3 wherein .lambda.3 is a wavelength where the intensity of emitted light decreases in the presence of caries and .lambda.1 is a wave-length which will produce emission from teeth at a wavelength .lambda.3

27. The method of claim 26 and wherein Al is a wavelength in the visible frequency range of the light spectrum.

28. Apparatus for use in detecting the presence of caries in the teeth of a person comprising:
(a) source means for generating a beam of monochromatic light having a wavelength Al, (b) means for directing light from said monochromatic source onto a region of teeth to be examined and receiving the light emitted therefrom, dm: 23 (c) means for measuring the intensity of the emitted light at a wavelength .lambda.2 and a wavelength .lambda.3, and (d) means for generating a signal related to .lambda.2 and .lambda.3 where .lambda.2 is a wavelength where the intensity is about the same for caries and noncaries .lambda.3 is a wavelength where the intensity changes in the presence of caries and is a wavelength that will produce emitted light when illuminating teeth at wavelengths .lambda.2 and .lambda.3.

29. A method for detecting the presence of caries in the teeth of a person comprising:
radiating a region of the tooth to be examined with light;
selecting a first wavelength in the near neighbor-hood of the wavelength having the largest intensity of light from the tooth in noncarious regions;
selecting a second wavelength to maximize the difference in the intensity difference of the light from caries and noncarious regions at said first wavelength and the intensity difference of the light from caries and noncarious regions at said second wavelength;
producing first and second signals corresponding to the intensity of -the light from the tooth at firs-t and second wavelengths, respectively;
setting the difference in the value of said first and second signals at said first wavelength for a noncarious region to be substantially zero;
producing a third signal corresponding to the difference between said first and second signal;

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determining the standard value of said third signal in a known noncarious region;
detecting the presence of caries in other regions by said third signal changing from said standard value in a predetermined manner.