(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2006/0223032 A1
`(43) Pub. Date:
`Oct. 5, 2006
`Fried et al.
`
`US 20060223O32A1
`
`(54) NEAR-INFRARED TRANSILLUMINATION
`FOR THE IMAGING OF EARLY DENTAL
`DECAY
`
`(76) Inventors: Daniel Fried, San Francisco, CA (US);
`Robert Jones, San Francisco, CA (US)
`Correspondence Address:
`JOHN P. O'BANION
`OBANON & RITCHEY LLP
`4OO CAPTOL MALL SUTE 15SO
`SACRAMENTO, CA 95814 (US)
`(21) Appl. No.:
`11/347,637
`
`(22) Filed:
`
`Feb. 3, 2006
`Related U.S. Application Data
`(63) Continuation of application No. PCT/US04/25872,
`filed on Aug. 6, 2004.
`(60) Provisional application No. 60/493.569, filed on Aug.
`8, 2003.
`
`Publication Classification
`
`(51) Int. Cl.
`(2006.01)
`A6IC 5/00
`(2006.01)
`A6B 5/17
`(52) U.S. Cl. ............................ 433/215; 433/114; 433/29:
`6OO/590
`
`(57)
`
`ABSTRACT
`
`A method for detecting tooth decay and other tooth anoma
`lies wherein a tooth is transilluminated with a near-infrared
`light source preferably in the range from approximately
`795-nm to approximately 1600-nm, more preferably in the
`range from approximately 830-nm to approximately 1550
`nm, more preferably in the range from approximately 1285
`nm to approximately 1335-mm, and more preferably at a
`wavelength of approximately 1310-nm, and the light passing
`through the tooth is imaged for determining an area of decay
`in the tooth. The light source is a fiber-optic bundle coupled
`to a halogen lamp or more preferably a Superluminescent
`diode, and the imaging device is preferably a CCD camera
`or a focal plane array (FPA).
`
`30-N
`
`46
`
`44
`
`36 50
`
`f
`
`
`
`--"
`I o-
`-
`w
`e.
`-- -------
`50-' u v
`
`w
`Fiber-Bundle
`or SLD
`
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`Patent Application Publication Oct. 5, 2006 Sheet 1 of 9
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`US 2006/0223032 A1
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`
`
`180
`
`160
`
`140
`
`120
`
`100
`
`80
`60
`
`40
`
`20
`
`18
`
`Enamel
`
`(ty-six westww.
`600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600
`Wavelength (nm)
`FIG. 1
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`Patent Application Publication Oct. 5, 2006 Sheet 2 of 9
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`US 2006/022.3032A1
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`
`
`Position near-infrared
`light source adjacent
`to tooth
`
`Transilluminate tooth
`with near-infrared light
`
`Detect intensity of light
`passing through tooth at a
`plurality of spatial
`positions and generate image
`
`Evaluate intensity gradients
`in image for defined boundary
`or edges indicating decay
`in sound tooth enamel
`
`FIG. 2
`
`
`
`32
`
`Fiber-Bundle
`or SLD
`
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`Patent Application Publication Oct. 5, 2006 Sheet 3 of 9
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`US 2006/022.3032 A1
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`60
`
`N 66
`
`64-N
`
`H----- - J
`
`-----
`
`.
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`62
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`Patent Application Publication Oct. 5, 2006 Sheet 4 of 9
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`US 2006/022.3032 A1
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`80
`
`F.G. 5A
`
`
`
`FIG. 5B
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`Patent Application Publication Oct. 5, 2006 Sheet 5 of 9
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`US 2006/0223032 A1
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`FIG. 5C
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`Patent Application Publication Oct. 5, 2006 Sheet 6 of 9
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`US 2006/022.3032 A1
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`FIG. 6B
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`Patent Application Publication Oct. 5, 2006 Sheet 7 of 9
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`US 2006/022.3032 A1
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`FIG. 6C
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`F.G. 6D
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`Patent Application Publication Oct. 5, 2006 Sheet 8 of 9
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`US 2006/022.3032 A1
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`FIG. 6E
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`Patent Application Publication Oct. 5, 2006 Sheet 9 of 9
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`US 2006/022.3032A1
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`0.8
`
`0.6
`
`E
`O
`O O.4
`9.
`()
`O)
`- 0.2
`
`O.O
`
`
`
`2
`
`5
`4
`3
`Sample Thickness (mm)
`FIG. 7
`
`6
`
`7
`
`FIG. 8
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`Oct. 5, 2006
`
`NEAR-INFRARED TRANSILLUMINATION FOR
`THE MAGING OF EARLY DENTAL DECAY
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`0001. This application claims priority from, and is a 35
`U.S.C. S 111(a) continuation of, co-pending PCT interna
`tional application serial number PCT/US2004/025872, filed
`on Aug. 6, 2004, which designates the U.S., incorporated
`herein by reference in its entirety, which claims priority from
`U.S. provisional application Ser. No. 60/493,569, filed on
`Aug. 8, 2003, the entirety of which is herein incorporated by
`reference.
`0002 This application is related to PCT International
`Publication Numbers WO 2005/013843 A2 and WO 2005/
`0.13843 A3, each of which is incorporated herein by refer
`ence in its entirety.
`
`INCORPORATION-BY-REFERENCE OF
`MATERIAL SUBMITTED ON A COMPACT
`DISC
`
`0003) Not Applicable
`
`STATEMENT REGARDING FEDERALLY
`SPONSORED RESEARCH OR DEVELOPMENT
`0004. This invention was made with Government support
`under Grant No. 1-RO1 DE 14698 and Grant No. T32
`DE07306-07 awarded by NIH/NICDR. The Government
`has certain rights in this invention.
`
`BACKGROUND OF THE INVENTION
`0005 1. Field of the Invention
`0006. This invention pertains generally to detection of
`dental caries by transillumination of a tooth, and more
`particularly to transillumination at wavelengths that are not
`Subject to scattering by Sound tooth enamel and identifica
`tion of dental caries in interproximal sites between teeth.
`0007 2. Incorporation by Reference of Publications
`0008. The following publications are incorporated by
`reference herein in their entirety:
`0009 J. D. B. Featherstone and D. Young, “The need for
`new caries detection methods.” Lasers in Dentistry V. San
`Jose, Calif., Proc. SPIE 3593, 134-140 (1999).
`0010) J. Peltola and J. Wolf, “Fiber optics transillumina
`tion in caries diagnosis.” Proc Finn Dent Soc, 77, 240-244
`(1981).
`0011 J. Barenie, G. Leske, and L. W. Ripa, “The use of
`fiber optic transillumination for the detection of proximal
`caries.” Oral Surg, 36, 891-897 (1973).
`0012 R. D. Holt and M. R. Azeevedo, “Fiber optic
`transillumination and radiographs in diagnosis of approxi
`mal caries in primary teeth.’ Community Dent Health, 6.
`239-247 (1989).
`0013 C. M. Mitropoulis, “The use of fiber optic transil
`lumination in the diagnosis of posterior approximal caries in
`clinical trials.” Caries Res, 19, 379-384, (1985).
`0014) A. Peers, F. J. Hill, C. M. Mitropoulos, and P. J.
`Holloway, “Validity and reproducibility of clinical exami
`
`nation, fibre-optic transillumination, and bite-wing radiol
`ogy for the diagnosis of Small approximal carious lesions.”
`Caries Res., 27, 307-311 (1993).
`0.015 C. M. Pine, “Fiber-Optic Transillumination (FOTI)
`in Caries Diagnosis,” in Early Detection of Dental Caries,
`G. S. Stookey, ed., (Indiana Press, Indianapolis, Ind. 1996).
`0016 J. Vaarkamp, J. J. t. Bosch, E. H. Verdonschot, and
`E. M. Bronkhorst, “The real performance of bitewing radi
`ography and fiber-optic transillumination for approximal
`caries diagnosis,” J Dent Res, 79, 1747-1751 (2000).
`0017 A. Schneiderman, M. Elbaum, T. Schultz, S. Keem,
`M. Greenebaum, and J. Driller, "Assessment of Dental
`caries with Digital Imaging Fiber-Optic Transillumination
`(DIFOTI): In vitro Study.” Caries Res., 31, 103-110 (1997).
`0018 D. Fried, J. D. B. Featherstone, R. E. Glena, and W.
`Seka, “The nature of light scattering in dental enamel and
`dentin at visible and near-IR wavelengths. Appl. Optics, 34,
`1278-1285 (1995).
`0.019
`R. Jones and D. Fried, “Attenuation of 1310 and
`1550-nm laser light through dental enamel,” in Lasers in
`Dentistry VIII, San Jose, Proc. SPIE 4610, 187-190 (June
`2002).
`0020 G. M. Hale and M. R. Querry, “Optical constants of
`water in the 200-nm to 200-um wavelength region. Appl.
`Optics, 12, 555-563 (1973).
`0021 D. Spitzer and J.J. ten Bosch, “The absorption and
`scattering of light in bovine and human dental enamel.”
`Calcif. Tiss. Res., 17, 129-137 (1975).
`0022. S. Keem and M. Elbaum, “Wavelet representations
`for monitoring changes in teeth imaged with digital imaging
`fiber-optic transillumination.” IEEE Trans MedImaging, 16,
`653-63 (1997).
`0023. 3. Incorporation by Reference of Patents
`0024. The following U.S. patents which describe transil
`lumination techniques and devices are incorporated by ref
`erence herein in their entirety:
`0025 U.S. Pat. No. 6,341,957
`0026 U.S. Pat. No. 6,243,601
`0027 U.S. Pat. No. 6,201,880
`0028 4. Description of Related Art
`0029. During the past century, the nature of dental decay
`or dental caries has changed dramatically due to the addition
`of fluoride to the drinking water, the widespread use of
`fluoride dentifrices and rinses, and improved dental hygiene.
`Despite these advances, however, dental decay continues to
`be the leading cause of tooth loss in the United States. By
`age 17, 80% of children have experienced at least one cavity.
`In addition, two-thirds of adults in the age range of 35 to 44
`have lost at least one permanent tooth to caries. Older adults
`suffer tooth loss due to the problem of root caries.
`0030 Today, almost all new decay occurs in the occlusal
`pits and fissures of the posterior dentition and the interproxi
`mal contact sites between teeth. These early carious lesions
`are often obscured or “hidden' in the complex and convo
`luted topography of the pits and fissures or are concealed by
`debris that frequently accumulates in those regions of the
`
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`posterior teeth. Such decay, particularly in the early stages,
`is difficult to detect using the dentist’s existing armamen
`tarium of dental X-rays and the dental explorer (a metal
`mechanical probe). Therefore, new imaging technologies are
`needed for the early detection of such lesions.
`0031 Moreover, the treatment for early dental decay or
`caries is shifting away from aggressive cavity preparations
`that attempt to completely remove demineralized tooth
`structure toward non-Surgical or minimally invasive restor
`ative techniques. In non-Surgical therapy, a clinician pre
`scribes antibacterial rinses, fluoride treatments, and dietary
`changes in attempt to naturally remineralize the decay
`before it becomes irreversible. The success of this type of
`therapy is contingent on early caries detection and also
`requires imaging modalities that can safely and accurately
`monitor the Success of Such treatment. Conventional X-rays
`do not precisely measure the lesion depth of early dental
`decay, and due to ionizing radiation exposure are not indi
`cated for regular monitoring. These constraints and limita
`tions are the impetus for investigating optical imaging
`systems that could detect early dental decay, while providing
`the biologically compatible wavelengths that facilitate fre
`quent Screening.
`0032. Before the advent of X-rays, dentists used light for
`the detection of caries lesions. In the past 30 years, the
`development of high intensity fiber-optic illumination
`Sources has resurrected this method for caries detection.
`Previous groups pursuing visible light transillumination,
`have used or proposed more advanced imaging techniques
`like temporal or coherence gating and Sophisticated image
`processing algorithms to enhance the imaging and detection
`of dental decay.
`0033 Fiber-optic transillumination (FOTI) is one tech
`nology being developed for the detection of interproximal
`lesions. One digital-based system, DIFOTITM (Digital
`Imaging Fiber-Optic Transillumination) from Electro-Opti
`cal Sciences, Inc., that utilizes visible light, has recently
`received FDA approval. During FOTI a carious lesion
`appears dark upon transillumination because of decreased
`transmission due to increased scattering and absorption by
`the lesion. However, the strong light scattering of Sound
`dental enamel at visible wavelengths, 400-nm to 700-nm,
`inhibits imaging through the tooth.
`
`BRIEF SUMMARY OF THE INVENTION
`0034. The present invention is directed to the detection,
`diagnosis, and imaging of carious dental tissue. The inven
`tion resolves changes in the state of mineralization of dental
`hard tissues with sufficient depth resolution to be useful for
`the clinical diagnosis and longitudinal monitoring of lesion
`progression. One aspect of the invention is to provide system
`and method for the detection, diagnosis, and imaging of
`early caries lesions and/or for the monitoring of lesion
`progression. Another aspect of the invention is to provide a
`near-infrared transillumination system and method for the
`detection and imaging of early interproximal caries lesions.
`A further aspect of the invention is to provide a near-infrared
`transillumination system and method for the detection of
`cracks and imaging the areas around composite restorations.
`0035) In one mode, near-IR light at 1310-nm is used for
`the detection and imaging of interproximal caries lesions
`where a high contrast between sound enamel and simulated
`
`lesions is exhibited. In addition, occlusal lesions, root caries,
`secondary decay around composite restorations, and cracks
`and defects in the tooth enamel can be seen.
`0036). In accordance with one aspect of the invention, a
`method for detecting tooth anomalies comprises transillu
`minating a tooth with light having a wavelength in the range
`from approximately 795-nm to approximately 1600-nm, and
`the step of imaging light passing through said tooth for
`determining an anomaly or area of decay in said tooth. In
`accordance with other aspects of the present invention, a
`tooth is transilluminated with near-infrared light at a wave
`length more preferably in the range from approximately
`830-nm to approximately 1550-nm, more preferably in the
`range from approximately 1285-mm to approximately 1335
`nm, and more preferably at a wavelength of approximately
`1310-nm.
`0037. In another mode, the light is filtered to remove
`extraneous light. The light may be polarized with one or
`more polarizing filters to remove light not passing through
`said tooth. The polarizing filters are preferably crossed
`high-extinction polarizing filters. The method may also
`comprise filtering said light with a bandpass filter to remove
`light outside a specified bandwidth.
`0038 Generally, transilluminating a tooth comprises
`directing light from a near-infrared light source at a surface
`of said tooth. The light source may be a fiber-optic bundle
`coupled to a halogen lamp, a Superluminescent laser diode,
`or similar IR source.
`0039. In one mode of the invention, the light source may
`be manipulated behind the tooth to direct said light at a
`lingual surface of the tooth. Alternatively, the light source
`may be manipulated in front of said tooth to direct said light
`at a facial surface of the tooth.
`0040. In one embodiment, the step of imaging light
`passing through the tooth comprises detecting intensity of
`light passing through the tooth at a plurality of spatial
`positions, developing a spatial profile of the detected light
`intensity, using the spatial intensity profile to identify an area
`in said tooth exhibiting intensity gradients, designating said
`area of said tooth exhibiting intensity gradients as an area of
`tooth decay. In another embodiment, detected light intensity
`is compared over at least a portion of said spatial positions
`for determining an area of decay in said tooth and an area of
`the tooth exhibiting a lower detected light intensity than an
`at least partially surrounding area is designated as an area of
`tooth decay.
`0041. In one aspect of the invention, the step of detecting
`the intensity of light passing through said tooth comprises
`directing a first detector at an aspect of the tooth, such as a
`facial aspect of the tooth, an occlusal aspect of the tooth, an
`opposite aspect of the tooth from the light Source, or the
`same aspect of the tooth as the light source.
`0042. According to another embodiment of the invention,
`a second detector a second detector may at a different aspect
`of the tooth than the first detector. For example, the second
`detector may be directed at an occlusal aspect of the tooth
`while the first detector is directed at a facial aspect of the
`tooth. The detector may comprise a focal plane array,
`near-infrared CCD camera, or the like.
`0043. The method may be used to determine anomalies
`Such as an area of decay, a crack, a composite restoration,
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`and dental caries in an occlusal site or interproximal contact
`site between said tooth and an adjacent tooth of said tooth.
`0044 According to another aspect of the invention, a
`system for detecting tooth decay comprises a near-infrared
`light Source emitting light having a wavelength in the range
`from approximately 785-nm to approximately 1600-nm
`wherein the light source is configured to transilluminate a
`tooth, and means for imaging light passing through said
`tooth and determining an area of decay in said tooth. In
`accordance with other aspects of the present invention, a
`light source has a wavelength more preferably in the range
`from approximately 830-nm to approximately 1550-nm,
`more preferably in the range from approximately 1285-mm
`to approximately 1335-mm, and more preferably at a wave
`length of approximately 1310-nm. In one mode, the light
`Source comprises a polarized light Source. In another mode,
`the light source comprises an unpolarized light Source. In
`one embodiment, the light source comprises a fiber-optic
`bundle coupled to a halogen lamp. In another embodiment,
`the light source comprises a Superluminescent diode (SLD).
`In still another embodiment, the imaging means comprises
`a CCD camera. In another embodiment, the imaging means
`comprises a focal plane array (FPA).
`0045 According to yet another aspect of the invention, a
`system for detecting a tooth anomaly comprises a near
`infrared light Source having a wavelength in the range from
`approximately 795-nm to approximately 1600-nm, wherein
`the light source is configured to transilluminate a tooth. The
`system further includes an imaging device configured to
`detect intensity of light from said light source passing
`through said tooth, whereby an anomaly in said tooth can be
`determined from intensity of light detected by said imaging
`device.
`Further aspects of the invention will be brought out
`0046.
`in the following portions of the specification, wherein the
`detailed description is for the purpose of fully disclosing
`preferred embodiments of the invention without placing
`limitations thereon.
`
`BRIEF DESCRIPTION OF THE SEVERAL
`VIEWS OF THE DRAWING(S)
`0047. The invention will be more fully understood by
`reference to the following drawings which are for illustrative
`purposes only:
`0.048
`FIG. 1 is graph comparing the attenuation coeffi
`cient of dental enamel and water as a function of wave
`length.
`0049 FIG. 2 is a flowchart of an embodiment of a
`method for detecting dental caries by near-infrared transil
`lumination according to the present invention.
`0050 FIG. 3 is a schematic diagram of a system for
`Near-Infrared Transillumination of whole teeth and tooth
`sections according to the present invention.
`0051
`FIG. 4 is a schematic diagram of another system
`for Near-Infrared Transillumination of whole teeth and tooth
`sections according to the present invention using two light
`SOUCS.
`0.052 FIGS.5A-5D are views of a tooth with a simulated
`lesion. FIG. 5A is a side view of a 3-mm thick tooth section
`with a simulated lesion. FIG. 5B illustrates that the lesion
`
`cannot be seen using transillumination with visible light and
`a CCD camera. FIG. 5C illustrates that the lesion is clearly
`visible under NIR. FIG.5D is an x-ray of the section using
`D-speed film indicates the small contrast difference between
`the simulated lesion and Sound enamel.
`0053 FIGS. 6A-6F are NIR transillumination images of
`tooth sections with simulated lesions are shown for sample
`thicknesses of 2-mm, 3-mm, 4-mm, 5-mm, 6-mm and 6.75
`mm, respectively. The corresponding spatial line profiles are
`shown on the inset in the lower right of each image, and the
`measured lesion contrast is shown in the lower left. The left
`axis represents the pixel intensity ranging from 0 to 4096,
`and the bottom axis the pixel position through the lesion.
`0054 FIG. 7 is a graph showing the mean ts.d lesion
`contrast plotted versus thickness of plano-parallel enamel
`samples, n=5.
`0.055 FIG. 8 is an NIR image of a whole tooth sample.
`A natural carious lesion and a composite restoration are seen
`on the left and right, respectively. The tooth is slightly
`rotated to present different viewing angles. A crack is also
`visible in the center of the tooth.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`0056 Referring more specifically to the drawings, for
`illustrative purposes the present invention is embodied in the
`system(s) and method(s) generally shown in FIG. 2 through
`FIG. 8. It will be appreciated that the apparatus may vary as
`to configuration and as to details of the parts, and that the
`method may vary as to the specific steps and sequence,
`without departing from the basic concepts as disclosed
`herein.
`0057. A principal limiting factor of light in the visible
`wavelength range from approximately 400-nm to 700-nm
`being transmitted through a tooth is light scattering in Sound
`enamel and dentin. The present invention overcomes that
`limiting factor by employing near-infrared (NIR) for tran
`sillumination of a tooth. The magnitude of light scattering in
`dental enamel decreases as 1/7, where is the wavelength,
`due to the size of the principal scatterers in the enamel. The
`attenuation coefficients of dental enamel measured at 1310
`nm and 1550-nm were 3.1 cm and 3.8 cm, respectively.
`As shown in FIG. 1, the magnitude of Scattering at those
`wavelengths is more than a factor of 30 times lower than in
`the visible range. This translates to a mean free path of 3.2
`mm for 1310-nm photons, indicating that enamel is trans
`parent in the near-infrared (NIR). At longer wavelengths
`past 1550-nm, the attenuation coefficient is not expected to
`decrease any further due to the increasing absorption coef
`ficient of water, 12% by volume, in dental enamel.
`0058 As indicated above, at shorter wavelengths the
`light is Subject to scattering. On the other hand, at longer
`wavelengths, absorption of water in the tissue increases and
`thereby reduces the penetration of infrared light.
`0059) Note also that, during the caries process,
`micropores are formed in the lesion due to partial dissolution
`of the individual mineral crystals. Such small pores can
`behave as Scattering centers Smaller than the wavelength of
`the light. Accordingly, there can be an increase in both the
`magnitude of light scattering and the contribution of large
`angle scattering to the scattering phase function in caries
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`lesions due to the increased microporosity. Changes in the
`optical constants and scattering phase function of enamel
`and dentin result in more rapid depolarization of incident
`polarized light. Accordingly, polarized light (e.g., via linear
`or circular polarization) will provide a greater image con
`tract than unpolarized light and can be exploited to aid in the
`near-infrared optical detection of carious lesions.
`0060. The present invention is particularly useful in
`detecting occlusal caries (biting Surfaces) and interproximal
`caries or lesions located at interproximal contact sites
`between adjacent teeth. The present invention is also useful
`in detecting other anomalies such as root caries, cracks, and
`imaging around composite restorations.
`0061
`Referring to FIG. 2, an exemplary method for
`detecting tooth anomalies such as dental decay or caries
`according to the invention is illustrated. First, a near-infrared
`light source is positioned adjacent to a tooth to be examined,
`as shown at block 20. Next, the tooth is transilluminated
`with the near-infrared light, as shown at block 22. The
`wavelength of the light is preferably in the range from
`approximately 795-nm to approximately 1600-nm, more
`preferably in the range from approximately 830-nm to
`approximately 1550-nm, more preferably in the range from
`approximately 1285-nm to approximately 1335-mm, and
`more preferably at a wavelength of approximately 1310-nm.
`Use of near-infrared light in these ranges provides deeper
`depth resolution and improved contrast between sound and
`carious enamel as compared to light at other wavelengths.
`0062 Once the tooth is transilluminated, the intensity of
`the light passing through the tooth at a plurality of spatial
`positions is detected, thereby forming an image of the tooth
`structure, as shown at block 24. The detected light intensity
`over at least a portion of the spatial positions is then
`compared so that an area of tooth decay can be identified, as
`shown at block 26. This is preferably accomplished by
`developing a spatial profile so that intensity gradients can be
`seen. An area of the tooth that exhibits a lower detected light
`intensity than an at least partially Surrounding area is indica
`tive of an area of tooth decay. While contrast alone can be
`used as an indicator of tooth decay, more preferably the
`existence of a defined boundary or edge between areas
`exhibiting intensity gradients is a more accurate indicator. It
`will be appreciated, of course, that a dentist or trained
`clinician will review and evaluate the images to distinguish
`lesions from, for example, areas containing fillings, com
`posite restorations, or other non-dental caries areas that
`effect intensity gradients in the image. Note that the incident
`light is preferably linearly polarized and, preferably, only
`light in the orthogonal polarization state is measured.
`0063 An exemplary NIR imaging device 30 is shown
`schematically in FIG. 3. Light 50 is emitted from a light
`source 32, through polarizer 38 and aperture 34 toward tooth
`or series of teeth 36. Light source 32 preferably comprises
`a broadband light source. Such as fiber-optic bundle coupled
`to a halogen lamp, or a Superluminescent laser diode (SLD).
`It was found that the speckle of conventional narrow band
`width diode lasers such as a 50-mW 1310-nm source, Model
`QLD-1300-50 (Qphotonics Inc., Chesapeake, Va.) interfered
`significantly with image resolution and were not optimal for
`the present invention.
`0064 Crossed near-IR polarizers, 38, 40 are used to
`remove light that directly illuminated the array without
`
`passing through the tooth. In a clinical situation, the light
`passing between the teeth will saturate the image preventing
`detection. Dental enamel is birefringent and, therefore, the
`polarization state of the light passing through the tooth may
`be altered to reduce extinction. Polarization gating using
`crossed high extinction polarizers 38, 40 removes extrane
`ous light that does not pass through the tooth and exploits the
`native birefringence of the tooth enamel to rotate the plane
`of polarization so that only light that passes through the
`tooth is measured. Caries lesions depolarize light which
`provides better image contrast between Sound and carious
`tissue
`0065 Light passing through tooth 36 and polarizer 40 is
`further filtered with bandpass filter 42 to remove all light
`outside the spectral region of interest.
`0066. The light is then focused with lens 44 and picked
`up with detector 46 to acquire images of tooth or teeth 36.
`In a preferred embodiment, detector 46 comprises a near
`infrared (NIR) InGaAs focal plane array (FPA).
`0067. The illuminating light intensity of light source 32,
`the diameter of aperture 34, and the distance of the light
`source to tooth 36, may all be adjusted to obtain the
`maximum contrast between the lesion and the Surrounding
`enamel without saturation of the InGaAs FPA around the
`lesion area.
`0068 Alternatively, detector 46 may comprise a CCD
`camera with the IR filter 42 and a 70-nm bandpass filter
`centered at approximately 830-nm. Alternatively, the band
`pass filter may be removed. Imaging with a near-IR CCD
`camera is less expensive with an InGaAs detector, but does
`not perform as well as an InGaAs detector. As another
`alternative, transillumination can also be conducted using a
`CCD camera with a near-infrared phosphor in the range of
`approximately 1000-nm to approximately 1600-nm.
`0069. In yet another alternative embodiment, image qual
`ity may be improved by utilizing biocompatible index
`matching fluids and gels and/or solid materials of high
`refractive index to reduce reflection, total internal reflection,
`and refraction at the tooth entrance and exit Surfaces. Such
`materials would be placed on the end of the illumination
`source 32 and/or the detector 46 and would make physical
`contact with the tooth surface
`0070) Now referring to FIG. 4, an alternative embodi
`ment of NIR imaging device 60 is shown schematically for
`imaging tooth 36. This device 60 may be used for the
`near-IR imaging of occlusal and pit and fissure lesions by
`placing light source 62 on the facial aspect 68 or lingual
`aspect 70 of the tooth and placing a second imaging source
`66 above the occlusal surface 72 of the tooth 36 in addition
`to the first imaging source 68 either the facial or lingual
`aspects, 68, 70. Detection of light 50 along different axes
`may be achieved with a combination of prisms, mirrors or
`optical fiber components. For example, the imaging fiber
`optic bundle 62 could be fitted with a 900 prism (not shown)
`and connected to a near-IR imaging camera. Alternatively,
`the light source may also be placed in any combination of
`these viewing angles, including having the light source and
`imager on the same aspect of the tooth.
`
`Page 14
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`OMNI 2024 - IPR20-00209
`
`

`

`US 2006/0223O32 A1
`
`Oct. 5, 2006
`
`EXAMPLE 1.
`
`Sample Preparation
`0071. Thirty plano-parallel sections of enamel of various
`thicknesses (2-mm, 3-mm, 4-mm, 5-mm, 6-mm, and 6.75
`mm) were prepared from non-carious human teeth. These
`sections were stored in a moist environment to preserve
`tissue hydration with 0.1% thymol added to prevent bacte
`rial growth. Uniform scattering phantoms simulating dental
`decay were produced midway through each section by
`drilling 1-mm diameterx 1.2-mm deep cavities in the proxi
`mal region of each sample and filling the cavities with
`hydroxyapatite paste. A thin layer of unfilled composite
`resin was applied to the outside of the filled cavity to seal the
`hydroxyapatite within the prepared tooth cavity.
`
`NIR Imaging
`0072 Both a 150-watt halogen lamp, VisarTM (Den-Mat,
`Santa Maria, Calif.), and a 1310-nm superluminescent diode
`(SLD) with an output power of 3.5 mW and a bandwidth of
`25-30 nm, Model QSDM-1300-5 (Qphotonics Inc., Chesa
`peake, Va.) were separately used as the illumination source.
`0073 Model K46-252 (Edmund Scientific, Barrington,
`N.J.) crossed near-IR polarizers were used to remove light
`that directly illuminated the array without passing through
`the tooth. A 50-nm bandpass filter centered at 1310-nm
`Model BP-1300-090B (Spectrogon US, Parsippany, N.J.)
`was used to remove all light outside the spectral region of
`interest.
`0074. A near-infrared (NIR) InGaAs focal plane array
`(FPA) having a resolution of 318x252 pixels was used to
`acquire all of the images. The particular FPA used was an
`Alpha NIRTM (Indigo Systems, Goleta, Calif.) with an
`InfinimiteTM lens (Infinity, Boulder, Colo.).
`0075. The acquired 12-bit digital images were analyzed
`using IRVistaTM software (Indigo Systems, Goleta, Calif.).
`0.076 The illuminating light intensity, source to sample
`distance, and the aperture diameter were adjusted for each
`sample to obtain the maximum contrast between the lesion
`and the Surrounding enamel.
`0077 Although the 3.5-mWSLD source provided similar
`image quality to the halogen lamp source, all the images
`illustrated herein were acquired using the fiber-optic illumi
`nator. Due to the natural tooth contours, the sides near the
`simulated lesions in the tooth sections were masked with
`putty to ensure that light traveled the full width of the
`sample. This masking is not applicable in a clinical situation
`and was not necessary to acquire images of whole teeth.
`0078. In addition, good images of teeth were obtained
`using the 3.5 mW SLD operating at 1310-nm. This is
`important because this illumination source is very compact
`and can be easily placed in the oral cavity. Furthermore, the
`SLD is much more compact than the illumination Source
`used for DiFOTI and can be integrated into a small dental
`explorer and manipulated behind the teeth for collection of
`images using the camera.
`
`Visible and X-ray Imaging
`0079 A tooth section of minimal sample thickness,
`3-mm, was chosen for comparison of the NIR transillumi
`
`nation system with conventional visible light FOTI and
`