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`
`0351
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`des brevets (11)
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`
`EUROPEAN PATENT APPLICATION
`
`(19)
`
`(12)
`
`EP 2 241 248 A2
`
`(43) Date of publication:
`20.10.2010 Bulletin 2010/42
`
`(51) Int Cl:
`AG61B 5/00 (2006.01)
`
`AG1B 1/24 (2006.01)
`
`(21) Application number: 10007060.6
`
`(22) Dateoffiling: 09.01.2009
`
`(84) Designated Contracting States:
`DE ES FI FR GB IT
`
`(30) Priority: 11.01.2008 US 972907
`
`(62) Document number(s)of the earlier application(s) in
`accordance with Art. 76 EPC:
`09000250.2 /2 078 493
`
`(71) Applicant: Carestream Health, Inc.
`Rochester, NY 14608-1733 (US)
`
`(72) Inventors:
`* Llang, Rongguang
`Penfield, New York 14526 (US)
`
`
`
`¢ Inglese, Jean-Mare
`77437 Bussy Saint Georges (FR)
`
`(74) Representative: Wagner, Karl H.
`Wagner & Geyer Partnerschaft
`Patent- und Rechtsanwalte
`Gewirzmihlstrasse 5
`80538 Munchen (DE)
`
`Remarks:
`This application wasfiled on 08 07 2010 asa
`divisional application to the application mentioned
`under INID code 62.
`
`(54)—_Intra-oral camera for diagnostic and cosmetic imaging
`
`ultraviolet illumination apparatus for fluorescence imag-
`(57)—An apparatus for obtaining images of a tooth
`comprises at least one image sensor disposed along an
`ine.
`In order to remove the specular reflection, one or
`optical axis to take polarized reflectance image and flu-
`more polarization elements are disposed along the opti-
`orescence image, at least one broadband illumination
`cal axis. A filteris disposed along the optical axis to block
`apparatus for reflectance imaging, and a narrow-band
`narrow-band ultraviolet light, and a switch for selecting
`one of the operation modes.
`
`150
`\
`
`
`
`FIG. 1
`
`Prinled by Jouve, 75001 PARIS (FR)
`
`0355
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`EP2241248A2
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`1
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`EP 2 241
`
`248 A2
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`2
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`Description
`
`FIELD OF THE INVENTION
`
`[0001] This invention generally relates tomethods and
`apparatus for dental imaging and more particularly re-
`lates to an intra-oral camera apparatus that includes ca-
`pabilities for caries detection as well as for shade match-
`ing.
`
`BACKGROUND OFTHE INVENTION
`
`[0002] Digitalimaging has been adapted to serve den-
`tistry for both diagnostic and cosmetic purposes. For ex-
`ample, there have been a number of dental imaging sys-
`tems developed for diagnosis of dental caries in its var-
`ious stages, capable of assisting in this diagnostic task
`without the use of x-rays or other ionizing radiation. One
`methed that has been commercialized employs fluores-
`cence, caused when teeth are illuminated with high in-
`tensity blue light. This technique, termed Light-Induced
`Fluorescence(LIF), operates on the principle that sound,
`healthy tooth tissue yields a higher intensity of fluores-
`cence under excitation from some wavelengths than
`does de-mineralized tooth tissue that has been damaged
`by caries infection. The strong correlation between min-
`eral loss and lossof fluorescencefor blue light excitation
`is then used to identify and assess carious areas of the
`tooth. A different relationship has been found for red light
`excitation, a region of the spectrum for which bacteria
`and bacterial by-products in carious regions absorb and
`fluoresce more pronouncedly than do healthy areas. Uti-
`lizing this behavior, U.S. Patent No. 4,290,433 entitled
`"Method and Apparatus for Detecting the Presence of
`Caries in Teeth Using Visible Luminescence" to Alfano
`discloses a method to detect caries by comparing the
`excited luminescence in two wavelengths. The use of
`fluorescenceeffects for caries detectianis also described
`in U.S. Patent No. 6,23- ,338 entitled "Method and Ap-
`paratus for the Detection of Carious Activity of a Carious
`Lesion in a Tooth" to de Josselin de Jong et al.
`[0003] Reflectance characteristics of visible light have
`also been usedfor oral caries diagnosis. For example,
`U.S. Patent No. 4,479,499 entitled "Methed and Appa-
`ratus for Detecting the Presenceof Caries in Teeth Using
`Visible Light" to Alfano describes a method to detect car-
`ies by comparing the intensity of the light scattered at
`twodifferentwavelengths. Commonly assigned U.S,Pat-
`ent Application Publication 2007/0099148, previously
`mentioned, describes an improved method for caries de-
`tection that combines both fluorescence and reflectance
`effects.
`[0004] Amongcommercialized products for diagnostic
`dental imaging using fluorescence behavior is the QLF
`Clinical System from Inspektor Research Systems BV,
`Amsterdam, The Netherlands, described in U.S. Patent
`6,231 338. Using a different approach, the Diagnodent
`Laser Caries Detection Aid fram KaVo Dental GmbH,
`
`Biberach, Germany, described in U.S. Patent 6,024,562,
`detects caries activity monitoring the intensityof fluores-
`cence of bacterial by-products under illumination from
`red light. Othercommercial products, such as the DIFOTI
`system from Electro-Optical Sciences, Irvington, NY, de-
`scribed in U.S. Patent 6,672,868, use transmission of
`light through the tooth structure for diagnostic imaging.
`[0005] Diagnostic imaging methods have been devel-
`oped for use with hand-held devices. For example, U.S.
`Patent Application Publication 2005/0003323, entitled
`"Diagnostic Imaging Apparatus” by Naoki Katsuda et al.
`describes a complex hand-held imaging apparatus suit-
`able for medical or dental applications, using fluores-
`cence and reflectance imaging. The’3323 Katsuda et al.
`disclosure shows an apparatusthat receivesthe reflec-
`tion light from the diagnostic object and/or the fluores-
`cence of the diagnostic object with different light irradia-
`tion. However, with such an approach, any unwanted
`specular reflection producesfalse positive results in re-
`flectance imaging. Moreover, with the various illumina-
`tion embodimentsdisclosed, the illumination directed to-
`ward a tooth or other diagnostic object is not uniform,
`since the light sourceis in close proximity te the diagnos-
`tic abject.
`[0006] Cosmetic dentistry has also taken advantage
`of digital imaging capability to some extent, primarily for
`shade-matching in tooth restoration or replacement.
`There have been numerous solutions proposed for pro-
`viding some form of automated shade matching to assist
`the dentist. A few examples are given In U.S. Patents
`No. 6,132,210 and6,305,933, both entitled "Tooth Shade
`Analyzer System and Methods” both to Lehmann; and
`in U.S. Patent Application Publication No. 2005/0074718
`entitled "Tooth Shade Scan System and Method"to Gra-
`ham et al. Apparatus solutions for cosmetic imaging are
`outlined, for example,
`in International Publication No.
`W02005/080929 entitled "Equipment and Method for
`Measuring Dental Shade”by Inglese and in U.S. Patent
`No. 4,881, 811 entitled "Remote Color Measurement De-
`vice" to O’Brien. Commercialized hand-held productsdi-
`rected te shade matching include the ShadeScan™sys-
`tem from Cynovad, Montreal, CA, described in Cynovad
`brochure 1019 of February 2002; and the Shade-Rite™
`Dental Vision System from X-Rite Inc., Grandville, MI,
`described in U.S. Patent 7,030,986. Notably, hand-held
`shade-matching systems are not designed for ease of
`access to any but the front teeth Conventional shade-
`matching techniques can match tooth color acceptably,
`but may not provide enough data for providing a substi-
`tute tooth that appears real and exhibits some amount
`of translucence. This is largely because conventional
`cosmetic imaging systems are directed primarily to color
`matching, but provide insufficient information on tooth
`translucency and surface texture. For cosmetic systems
`that measure translucency, little or no attention is paid
`to uniformity of illumination. This results in an uneven
`distribution of light and reduces the overall accuracy of
`the system for measuring tooth translucency.
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`3
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`EP 2 241 248 A2
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`4
`
`In spite of the growing range of imaging devices
`[0007]
`that is now available to -he dental practitioner for diag-
`nostic and cosmetic purposes, thereis still room for im-
`provement. Diagnostic imaging apparatus and shade-
`matching systemsarestill separate pieces of equipment,
`each system having its own requirements for system op-
`tics.
`|o a large extent, this is the result of their different
`functions, affecting numerous components from illumi-
`nation, light shaping, and imaging subsystems. For ex-
`ample, the illumination requirements for diagnostic im-
`aging, largely using fluorescenceeffects, differ signifi-
`cantly from those of cosmetic imaging, which largely em-
`ploys reflective light. Specular reflection can be undesir-
`able for both diagnostic and cosmetic imaging, but must
`ke compensatedin different ways for each type of imag-
`ing. Image sensing, the use of polarization and spectral
`content, and otherfeatures furtherdifferentiate diagnos-
`tic from cosmetic systems. Thus,
`it would be advanta-
`geousto provide anintra-oral camera that could be used
`for both diagnostic and cosmetic functions.
`
`SUMMARYOF THE INVENTION
`
`[0008] An object of the presentinvention is to provide
`improved apparatus and methods for dental imaging.
`With this object in mind, the present invention provides
`an apparatusfor obtaining an imageof atooth comprising
`at least one image sensordisposed along an optical axis;
`at least one broadband illumination apparatusfor reflect-
`ance imaging; a narrow-band ultravioletillumination ap-
`paratusfor fluorescence imaging; one or morepolariza-
`tion elements disposed along the optical axis to eliminate
`specularreflection; a filter disposed along the optical axis
`to block narrow-band ultraviolet light; and a switch for
`selecting one of the operation modesof reflectance and
`fluorescenceimaging.
`[0009] An embodiment of the method ofthe invention
`is useful for obtaining images of a tooth for cosmetic im-
`aging and comprisesstepsof directing light from the light
`source to tooth for obtaining a monochromatic image for
`translucency measurement, directing polarized visible
`light from one or morecolor light sources to the tooth for
`obtaining a polarized color reflectance image; calibrating
`the illumination uniformity and tooth shape; calculating a
`tooth shadefor tooth restoration according to the images
`obtained; displaying a simulated imageof the tooth using
`the calculated shade information; obtaining customer
`feedback on the displayed image; and sending or saving
`the tooth shade information.
`[0010] A feature of the present invention is that it uti-
`lizes a common optical system for both diagnostic and
`cosmetic imaging. An advantageof the present invention
`is that it provides a single imaging instrumentfor a range
`of dental applications.
`[0011] These and other objects, features, and advan-
`tages of the present invention will become apparent to
`those skilled in the art upon a reading of the following
`detailed description when taken in conjunction with the
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`drawings wherein there is shown and described anillus-
`trative embodiment of the invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0012] While the specification concludes with claims
`particularly pointing out and distinctly claimingthe subject
`matter of the present invention, it is believed that the in-
`vention will be better understood from the following de-
`scription when takenin conjunction with the accompany-
`ing drawings, wherein:
`
`Figure 1 is a schematic block diagram of an imaging
`apparatus for caries detection and shade matching
`according to one embodiment;
`Figure 2 is a schematic block diagram of an imaging
`probe for diagnostic and cosmetic imaging;
`Figures 3a to 3d show example schematic diagrams
`for different arrangements of components suitable
`for use as anillumination apparatus in embodiments
`of the present invention;
`Figure 4 is a schematic block diagram of an imaging
`probe configured for diagnostic imaging;
`Figure 5 shows,in a front view taken along line 5-5
`of Figure 4, one arrangementfor multiple illumination
`apparatus used in the embodiment shownin Figure
`4.
`Figure 6 showsan alternate embodimentof the im-
`aging probe that employs a fold mirror for improved
`accessto tooth surfaces:
`Figure 7 showsanotheralternate embodimentof the
`diagnostic mode optical path using a polarization
`beamsplitter;
`Figures 8a and 8b show twoconfigurations for a color
`sequential illumination method;
`Figures 9a and 9b show two embodimentsof an at-
`tachmentfor capture of transmittedlight;
`Figure 10 shows an arrangementof probe 100 with
`two sensors;
`Figure 11 shows an arrangementof probe 100 with
`three sensors;
`Figure 12 shows an arrangementof probe 100 with
`three sensing regions;
`Figure 13 shows a point-based method for measur-
`ing tooth translucency;
`Figure 14 is a logic flow diagram showing how the
`imaging apparatus of the present invention can be
`operatedin either diagnostic or cosmetic modes;
`Figure 15 is a logic flow diagram that shows how
`processor logic usesthe translucency and color data
`obtained in the process of Figure 14 to provide shade
`matching; and
`Figure 16 showsanalternative arrangementof light
`sources suitable for use in the apparatus of the in-
`vention.
`
`0357
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`

`5
`
`EP 2 241 248 A2
`
`6
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`[0013] The method and apparatus of the present in-
`vention combine both diagnostic and cosmetic functions
`to provide a versatile intra-oral imaging system for use
`by dental practitioners. As noted earlier in the back-
`ground section, there are significant ditterences in re-
`quirements between diagnostic and cosmetic imaging,
`including different light source and optical system re-
`quirements, appropriate compensation for specular re-
`flection, and different image processing. Moreover, cos-
`metic imaging itself is complex and can involve more than
`merely shade matching.
`In addition to matching color,
`accurate cosmetic imaging also requires that additional
`information on more subtle tooth features be obtained,
`including translucency, surface texture, gloss, and other
`characteristics.
`[0014] Commonly assigned U.S. Patent Application
`Publication No. 2007/0099148, previously mentioned
`and incorporated herein by reference, describes a diag-
`nostic imaging approach that combines both fluores-
`cence and reflectance effects in order to provide Fluo-
`rescence
`Imaging with Reflectance Enhancement
`(FIRE). Advantageously, FIRE detection can be accurate
`at an earlier stage of caries infection than has been ex-
`hibited using existing fluorescence approaches that
`measurefluorescence alone. The apparatus and meth-
`odsof the present invention further expand upon the use
`of FIRE imaging, as described in detail in the "9148 ap-
`plication,
`in order to provide the added advantages of
`cosmetic imaging when using a singleintra-oral camera.
`[0015] The schematic block diagram of Figure 1 shows
`basic components of an imaging apparatus 150 for both
`diagnostic and cosmetic intra-oral imaging in one em-
`bodiment. An imaging probe 100 is uscdto obtain images
`from atooth 20, either for diagnostic or cosmetic purpos-
`es. A control
`logic processor 140 communicates with
`probe 100to obtain the image data and providesthe proc-
`essed image on a display 142.
`[0016]
`Imaging apparatus 150 can operatein either of
`two modes: a diagnostic mode or a cosmetic imaging
`mode. Subsequent embodiments give examples show-
`ing how operationin either or both modes can be obtained
`using a suitable configuration of probe 100 and adapting
`the illumination, data collection, imaging processing, and
`data recording and display functions accordingly.
`[0017] The schematic diagram of Figure 2 shows an
`embodiment of imaging probe 100 that can be used for
`both diagnostic and cosmetic imaging purposes. Probe
`100 has a handle 32 andaprobe extension 40. A common
`optical axis O applies for both diagnostic and cosmetic
`image capture. Illumination for any type of imageis pro-
`vided from one or moreofillumination apparatus 12a,
`12b, 12c, or 12d, which include light sources and beam
`shaping optical elements. An optional attachment30 pro-
`videsillumination for translucency measurement. Probe
`100 also includes a mode switch 36 which is used to
`select either of the operating modes: diagnostic or cos-
`
`metic. Animaging assembly 34 contains the imaging sen-
`sor and its supporting optical components, as described
`subsequently.
`[0018]
`Each of illumination apparatus 12a-12d may
`have both light source and beam shaping optics. Each
`illumination apparatus could have its own light source,
`or a single light source could serve for multiple illumina-
`tion apparatus 12a-12d, provided with an appropriate
`spectral selection filter for each illumination apparatus,
`for example. The light source could be a solid-state light
`source, such as a light emitting diode (LED)or laser, or
`could be a broadband light source such as xenon arc
`lamp or other type of light source.
`[0019]
`Figures 3a to 3d show example schematic dia-
`grams for different arrangements of components that
`could be used for illumination apparatus 12a-12d in em-
`bodiments of the present invention. Each of these con-
`figurations has a light source 21. Beam-shaping optical
`elements 22, such as beam-shaping components 22a,
`22b, or 22c condition and shape the light for uniform il-
`lumination on the tooth surface.If the beam profile from
`the light source is uniform enoughforillumination on the
`tooth surface, nobeam shaping optics are needed. Beam
`shaping component 22a of Figure 3ais a diffuser. Beam
`shaping component 22b of Figure 3b is a spherical or
`aspherical optical element. Beam shaping component
`22c of Figure 3c is a light pipe. Figure 3d shows a con-
`figuration using a number of these different components
`in combination within an illumination apparatus. Other
`beam shaping components that are part of illumination
`apparatus 12a - 12d can include light guiding or light dis-
`tributing structures such as an opticalfiber or aliquid light
`guide, for example (not shown). The lightlevel is typically
`a few milliwatts in intensity, but can be moreorless, de-
`pending on the light shaping and sensing components
`used.
`Each illumination apparatus 12a -12d can be
`[0020]
`arranged in a number of ways, as shown in detail sub-
`sequently. Light source 21 for each illumination appara-
`tus emits light with appropriate wavelengths for each dif-
`ferent imaging mode. In one embodiment, for example,
`lightsource 21 inillumination apparatus 12a emits broad-
`band visible light (400nm - 700nm)for polarized reflect-
`ance imaging, or a combination from light sources with
`different spectrum, such as acombination of Red, Green
`and Bluelight emitting diodes (LEDs). Light source 21 in
`illumination apparatus 12b emits narrow bandultraviolet
`(UV)light (875nm - 425nm) to excite tooth fluorescence.
`Light source 21 inillumination apparatus 12c emits Near-
`Infrared (NIR) light for translucency measurement. Light
`source 21 in illumination apparatus 12d emits blue light
`or UV for tooth surface texture measurement. The light
`used in the illumination apparatus 12a can be also ob-
`tained from other sources, such as a daylight simulator.
`
`Diagnostic Imaging Mode
`
`foo21] The schematic diagrams of Figures 4 and 5
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`7
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`EP 2 241 248 A2
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`8
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`show probe 100 as configured for diagnostic imaging.
`Probe 100 has a handle 32 and a probe extension 40
`that is designedfor insertion into the mouth for both im-
`aging modes. Illumination apparatus 12a, with the coop-
`eration of polarizer 42a, which is placed in front of the
`illumination apparatus 12a, provides uniform polarized
`white light illumination on the tooth surfacefor polarized
`reflectance imaging. Illumination apparatus 12b directs
`UV light toward tooth 20 through a bandpassfilter 46 to
`excite fluorescencein the tooth. Bandpassfilter 46 is an
`option and is helpful for improving spectral purity of illu-
`mination from the light sourcein illumination apparatus
`12b.
`Light reflected from tooth 20 passes through a
`[0022]
`central opening among theillumination apparatus and
`through an analyzer 44. One or more lenses 66 then di-
`rect reflected light through a spectralfilter 56. Spectral
`filter 56 has a long pass that captures fluorescence data
`over a range of suitable wavelengths and blocks the ex-
`citation light from the light source. In order to obtain a
`true color reflectance image, the cut-off wavelength of
`the spectralfilter 56 is selected so that it can block the
`excitation light from illumination apparatus 126, but not
`block the blue portion of the light from illumination appa-
`ratus 12a. The fluorescence image that has been ob-
`tained from tooth 20 can havea relative broad spectral
`distribution in the visible range, with light emitted that is
`outside the wavelength range of the light used for exci-
`tation. The fluorescence emission is typically between
`about 450 nm and 600 nm, while generally peaking in
`the green region, roughly from around 510 nm to about
`550 nm. A sensor 68 obtains the fluorescence image,
`typically using the green color plane. However, other
`rangesof the visible spectrum could also be used in other
`embodiments. When taking fluorescence image, analyz-
`er 44 can be movedoutof the optical axis O if necessary
`to increase the fluorescence signal. Referring back to
`Figure 1, this image data can then be transmitted back
`to control logic processor 140 for processing and display.
`[0023]
`Still referring to Figures 4 and 5,polarized re-
`flectance image data is also obtained using many of the
`same components.Anillumination apparatus 12a directs
`visible light, such as a white light or other broadband light,
`through a polarizer 42a, and toward tooth 20. Analyzer
`44, whosetransmission axis is oriented orthogonally with
`respect to the transmission axis of polarizer 42, rejects
`light from specular reflection and transmits light used to
`form the reflectance image onto sensor 68.Filter 56 may
`be removed out of the optical axis O or replaced with
`another filter element as needed.
`[0024] Sensor 68 maybe any of a number of types of
`imaging sensing camponent, such as a complementary
`metal-oxide-semiconductor (CMOS) or charge-coupled
`device (CCD) sensor. Light sources usedin illumination
`apparatus 12a and 12b can belasersor other solid-state
`sources, such as combinations using one or morelight
`emitting diodes (LEDs). Alternately, abroadband source,
`such as a xenon lamp having a supporting color filter for
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`passing the desired wavelengths, could be used.
`[o025]
`Figure 5 shows one arrangementfor multiple
`illumination apparatus used in the embodiment shownin
`Figure 4. As Figure 4 showed, probe 100 has multiple
`illumination apparatus 12a, 12b, 12c, and 12d. Illumina-
`tion apparatus that have the same light spectrum are
`arranged to be symmetric to the optical axis of the imag-
`ing optics for a uniform illumination.
`[0026] The imaging optics, represented as lens 66 in
`Figure 4, could include any suitable arrangement of op-
`tical components, with possible configurations ranging
`from a single lens component to a multi-elementlens.
`Clear imaging of the tooth surface, which is not flat but
`can have areas that are both smoothly contoured and
`highly ridged, requires that imaging optics have sufficient
`depth offield. Preferably, for optimal resolution, the im-
`aging optics provides an imagesize that is suited to the
`aspect ratio of sensor 68.
`[0027] Camera controls are suitably adjusted for ob-
`taining eachtype of diagnostic image. For example, when
`capturingthe fluorescence image,itis necessary to make
`appropriate exposure adjustments for gain, shutter
`speed, andaperture, since this image may not be intense.
`When sensor 68 is a color sensor,color filtering can be
`performed by color filter arrays (CFA) on the camera im-
`age sensor. That is, a single exposure can capture both
`back-scattered reflectance and fluorescence images.In
`one embodiment, the reflectance image is captured in
`the blue color plane; simultaneously, the fluorescence
`image is captured in the green color plane.
`[0028]
`Image processing by imaging apparatus 150
`(Figure 1) combines the reflectance and fluorescence
`images in order to obtain a contrast-enhanced image
`showing caries regions, as is described in the '9148
`Wong et al. application. Various methods can be used
`for processing, combining, and displaying the images ob-
`tained.
`Figure 6 shows an alternate embodiment of
`[0029]
`probe 100 that employs a fold mirror 18 for improved
`access totooth 20 surfaces. This fold mirror is necessary
`in order to access the buccal surface of the molars and
`the occlusal and lingual surface of all teeth. Figure 7
`shows another alternate embodimentof the diagnostic
`mode optical path using a polarization beamsplitter 38.
`Anillumination apparatus 14 provideslight of one polar-
`ization directed through a beam shaping optical element
`14a from a light source 14b, whichis reflected from po-
`larization beamsplitter 38 and directed toward tooth 20.
`Beam shaping optical element 14a shapesthe light from
`an illumination apparatus 14 to provide uniform illumina-
`tion on the tooth surface. Reflected light of the opposite
`polarization state is then transmitted through polarization
`beamsplitter 38 toward sensor 68. This arrangementre-
`moves specularreflected light from other scattered light,
`so that the returned light includes a high proportion of
`reflectancelight from caries sites. Using the arrangement
`of Figure 7, illumination apparatus 14 can be selected
`from a number of configurations, such as a combination
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`of the light sources with different wavelengths ora single
`light source with spectrum selection filter. The light
`source 14b can also be outside of the handheld probe
`and the light delivered to the beam shaping optical ele-
`ment 14a through an optical fiber or other light guide such
`as a liquid light guide. One advantageof this embodiment
`is that illumination apparatus 14 can be easily changed
`to meetdifferent applica-ions. For example, illumination
`apparatus 14 can be changed to provide a daylight sim-
`ulator for dental shade matching in cosmetic imaging
`mode, as is described subsequently.
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`Cosmetic Imaging Mode
`
`[0030] When switched to cosmetic imaging mode,
`probe 100 operates under a different set of requirements.
`Inthis modethe illumination sources and optical path are
`suitably configuredfor the types of measurementthat are
`of particular interest for cosmetic imaging. This includes
`the following:
`
`(i) Color shade measurement;
`(ii) Translucency measurement; and
`(iii) Surface texture or gloss measurement.
`
`In embodiments of the current invention, color
`[0031]
`shade measurement can be obtained using a number of
`approaches.
`In one approach,illumination is provided
`from polarized Red (R), Green (G), and Blue (B) light
`sources, sequentially. The resulting R, G, B images are
`then captured in sequence. The tooth shade can be cal-
`culated from the RGB images that are obtained.
`In an
`alternate approach, a polarized whitelight source is used
`as sourceillumination. The color shade of the tooth is
`then calculated from data in RGB planesof the white light
`image.
`In one conventional method, unpolarized light
`[0032]
`is used in tooth shade measurement. One problem with
`unpolarized light illumination relates to specular reflec-
`tion. The light from specularreflection has the same spec-
`trum as the illumination light source and doesn’t contain
`colorinformation for the tooth. Additionally, very little sur-
`face informationis obtained when specularreflection pre-
`dominates and saturates the sensor.
`[0033]
`By using polarized light illumination and spec-
`ular reflection removal, embodiments of the present in-
`vention overcome this limitation and obtain scatteredlight
`fromthe enamel and dentin. This scatteredlight contains
`the true base color of the tooth.
`[0034] Referring to Figures 4 and 5, when probe 100
`of the present invention is used to measuretooth color,
`a broadband light sourcein illumination apparatus 12a
`is turned on. The broadbandlight from illumination ap-
`paratus 12a passes polarizer 42a andilluminates the
`tooth surface. Of all the light reflected backfrom the tooth,
`only the light having orthogonal polarization passes
`through analyzer 44 and reaches sensor 68. Tooth shade
`information is calculated from the R, G, and B plane data
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`of sensor 68.
`[0035] Because sensor andfilter performance are im-
`perfect, there is some amountof cross talk between each
`color plane when broadband illumination is used. An al-
`ternative solution fortooth color measurementisto obtain
`3 separate images sequentially, each image separately
`illuminated using light of red, green, and blue spectra
`separately. These images can then be combined to pro-
`duce more accurate tooth shade information. One dis-
`advantage of this methodis that it may require additional
`imageprocessingin ordertoalign the threedifferent color
`imagessince they are taken atdifferent time.
`[0036]
`Figures 8a and 8b showtwoconfigurations for
`a color sequentialillumination method. Thefirst config-
`uration of Figure 8a comprises three light sources 21
`such as red, green and blue LEDs, and one beam shap-
`ing optical element 22, which can be one of beam shaping
`elements 22a, 22b, or 22c, previously described or some
`combination of these elements. These threelight sources
`can be switchedeither simultaneously or sequentially in
`order to obtain each of the composite Red, Green, and
`Blue images separately. The second configuration of Fig-
`ure 3b comprises a broadband light source 21, spectrum
`selection filter 23 and beam shaping optical element 22.
`While using this configuration, the spectrum selection fil-
`ter 23 is rotated to changethe illumination spectrum in
`order to obtain Red, Green and Blue images. Lightsource
`21 and spectrum selection filter 23 of this embodiment
`can be built in or provided outside of probe 100. Illumi-
`nation from these color sources could be directed to
`probe 100 by optical fiber or liquid light guide. This type
`of arrangement allows a wide selection of light sources,
`without the constraints imposed by size and weightlim-
`itations for probe 100.
`[0037] The translucency of a tooth can be determined
`by measuring the reflectance light returned from the tooth
`or, alternately, the light transmitted through the tooth. The
`translucency can be used as a coordinate of the meas-
`urement point in one dimension of the shade space ded-
`icated to this pararneter.It can also be used for correction
`of at least one other coordinate of the measurementpoint
`in another dimension.
`[0038] To use the reflectancelight to deterrnine tooth
`translucency, specular reflection must be removed either
`by changing the illumination angle, or by using polarized
`light illumination. One advantage of embodiments of the
`present invention using polarized lightillumination re-
`lates to the light captured by the sensor and scattered in
`enamel and dentin. If unpolarized light is used, specular
`light reflected from the tooth surface and from the super-
`ficial layer of the enamel is much more pronouncedthan
`is the light returned from enamel and dentin. This can
`lead to inaccurate translucency data.
`[0039] Theoretically, with the uniform illumination and
`ideal enamel, the tooth is more translucent if the light
`level of the polarized light, reflected from the tooth sur-
`face, and captured by the sensor 68, is lower. However,
`there are several factors that can affect the light level of
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