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`(19)
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`des hrevets (11)
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`
`EUROPEAN PATENT APPLICATION
`
`EP 2 241 248 A2
`
`(43) Date of publication:
`20.10.2010 Bulletin 2010/42
`
`(51) Int Cl.:
`A613 momma”
`
`A61B 1/24 (200601)
`
`(21) Application number: 10007060.6
`
`(22) Date of filing: 091012009
`
`(84) Designated Contracting States:
`DE ES FI FR GB IT
`
`(30) Priority: 11.01.2008 US 972907
`
`(62) Document number(s) ofthe earlier application(s) in
`accordance with Art. 76 EPC;
`090002502 /2 078 493
`
`(71) Applicant: Carestream Health, Inc.
`Rochester, NY 14608—1733 (US)
`
`(72) Inventors:
`0 Llang, Rongguang
`Penfield, New York 14526 (US)
`
`0 lnglese, Jean-Marc
`77437 Bussy Saint Georges (FR)
`
`(74) Representative: Wagner, Karl H.
`Wagner & Geyer Partnerschaft
`Patent- und Rechtsanwalte
`Gewiirzmiihlstrasse 5
`80538 Miinchen (DE)
`
`Remarks:
`This application was filed on 08 O7 201 O as a
`divisional application to the application mentioned
`under INID code 62.
`
`
`
`(54)
`
`Intra-oral camera for diagnostic and cosmetic imaging
`
`An apparatus for obtaining images of a tooth
`(57)
`comprises at least one image sensor disposed along an
`optical axis to take polarized reflectance image and flu-
`orescence image, at least one broadband illumination
`apparatus for reflectance imaging, and a narrow—band
`
`ultraviolet illumination apparatus forfluorescence imag-
`ine.
`In order to remove the specular reflection, one or
`more polarization elements are disposed along the opti-
`cal axis. Afilteris disposed along the optical axis to block
`narrow—band ultraviolet light, and a switch for selecting
`one of the operation modes.
`
`150
`
`‘1
`
`
`
`FIG. 1
`
`Piiiited by Juuve, 75001 PARlS (FR)
`
`0355
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`EP2241248A2
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`

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`1
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`EP 2 241 248 A2
`
`2
`
`Description
`
`FIELD OF THE INVENTION
`
`[0001] This invention generally relates to methods and
`apparatus for dental imaging and more particularly re—
`lates to an intra-oral camera apparatus that includes ca—
`pabilities forcaries detection as well asfor shade match-
`ing.
`
`BACKGROUND OF THE INVENTION
`
`[0002] Digital imaging 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
`method 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 thatsound,
`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 loss of fluorescence for 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 pro nouncedly 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
`fluorescence effects forcaries detection is also described
`in U.S. Patent No. 623‘ ,338 entitled "Method and Ape
`paratus for the Detection of Carious Activity of a Carious
`Lesion in aTooth" to de Josselin de Jong et ai.
`[0003] Reflectance characteristics ofvisible light have
`also been used for oral caries diagnosis. For example,
`U.S. Patent No. 4,479,499 entitled "Method and Appa-
`ratus for Detectingthe Presence of Caries in Teeth Using
`Visible Light" to Alfano describes a method to detect car-
`ies by comparing the intensity of the light scattered at
`two differentwavelengths. 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] Among commercialized 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 from KaVo Dental GmbH,
`
`Biberach, Germany, described in U.S. Patent6,024,562,
`detects caries activity monitoring the intensity of fluores—
`cence of bacterial by-products under illumination from
`red light. Othercommercial products, such as the DiFOTl
`systemfrom Electro-Optical Sciences, lrvington, 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 apparatus that receives the 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 produces false positive results in re-
`flectance imaging. Moreover, with the various illumina-
`tion embodiments disclosed, the illumination directed to-
`ward a tooth or other diagnostic object is not uniform,
`since the light source is in close proximity to the diagnos-
`tic object.
`[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 and 6,305,933, both entitled "Tooth Shade
`Analyzer System and Methods” both to Lehmann; and
`in U.S. PatentApplication Publication No. 200510074718
`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 lnglese and in U.S. Patent
`No. 4,581, 81 1 entitled "Remote Color Measurement Dee
`vice" to O’Brien. Commercialized hand-held products di-
`rected to shade matching include the ShadeScan'"I sys-
`tem from Cyn ovad, Montreal, CA, described in Cynovad
`brochure 1019 of February 2002; and the Shade-Rite1M
`Dental Vision System from X-Ftite lnc., 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
`
`EP 2 241 248 A2
`
`4
`
`In spite of the growing range of imaging devices
`[0007]
`that is now available to the dental practitioner for diag—
`nostic and cosmetic purposes, there is still room for im-
`provement. Diagnostic imaging apparatus and shade—
`matching systems are still separate pieces of equipment,
`each system having its own requirements for system op—
`tics.
`lo a large extent, this is the result oftheir different
`functions, affecting numerous components from illumi-
`nation, light shaping, and imaging subsystems. For ex—
`ample, the illumination requirements for diagnostic ime
`aging, largely using fluorescence effects, 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
`be compensated in different ways for each type of imag-
`ing. Image sensing, the use of polarization and spectral
`content, and otherfeatures further differentiate diagnos-
`tic from cosmetic systems. Thus,
`it would be advanta—
`geous to provide an intra—oral camera that could be used
`for both diagnostic and cosmetic functions.
`
`SUMMARY OF THE INVENTION
`
`[0008] An object of the present invention is to provide
`improved apparatus and methods for dental imaging.
`With this object in mind, the present invention provides
`an apparatus forobtaining an image of atooth comprising
`at least one image sensor disposed along an optical axis;
`at least one broadband illumination apparatus for reflect—
`ance imaging; a narrow—band ultraviolet illumination ap—
`paratus for fluorescence imaging; one or more polariza—
`tion elements disposed along the optical axis to eliminate
`specular reflection; afilter disposed alongthe optical axis
`to block narrow-band ultraviolet light; and a switch for
`selecting one of the operation modes of reflectance and
`fluorescence imaging.
`[0009] An embodiment of the method ofthe invention
`is useful for obtaining images of a tooth for cosmetic im—
`aging and comprises steps of directing lightfrom the light
`source to tooth for obtaining a monochromatic image for
`translucency measurement; directing polarized visible
`light from one or more color light sources to the tooth for
`obtaining a polarized color reflectance image; calibrating
`the illumination uniformity andtooth shape; calculating a
`tooth shadefortooth restoration accordingto the images
`obtained; displaying a simulated image of 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 advantage ofthe present invention
`is that it provides a single imaging instrument for 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 an illus-
`trative embodiment of the invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0012] While the specification concludes with claims
`particularlypointing out and distinctlyclaimingthe subject
`matter of the present invention, it is believed that the in-
`vention will be better understood from the following de—
`scription when taken in conjunction with the accompanye
`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 an illumination 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 Figure4, one arrangementfor multiple illumination
`apparatus used in the embodiment shown in Figure
`4.
`Figure 6 shows an alternate embodiment ofthe im-
`aging probe that employs a fold mirrorfor improved
`access to tooth su rfaces;
`Figure 7 shows another alternate embodiment of the
`diagnostic mode optical path using a polarization
`beamsplitter;
`Figures 8a and 8b showtwo oonfigurationsfor a color
`sequential illumination method;
`Figures 9a and 9b show two embodiments of an at-
`tachment for capture of transmitted light;
`Figure 10 shows an arrangement of probe 100 with
`two sensors;
`Figure 11 shows an arrangement of probe 100 with
`three sensors;
`Figure 12 shows an arrangement of 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
`operated in either diagnostic or cosmetic modes;
`Figure 15 is a logic flow diagram that shows how
`processor logic uses the transluce ncy and color data
`obtained in the process of Figure 1 4to provide shade
`matching; and
`Figure 16 shows an alternative arrangement of 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 cosmeticfunctions
`to provide a versatile intra-oral imaging system for use
`by dental practitioners. As noted earlier in the back—
`ground section, there are significant differences in re—
`quirements between diagnostic and cosmetic imaging,
`including different light source and optical system re—
`quirements, appropriate compensation for specular ref
`flectlon, and different image processing. Moreover, cos-
`meticimaging itself is complex and can involve morethan
`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. 200710099148, 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
`measure fluorescence alone. The apparatus and meth—
`ods of 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 single intra-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 prooessor 140 communicates with
`probe 1 OOto obtain the image data and providesthe proc—
`essed image on a display 142.
`[0016]
`Imaging apparatus 150 can operate in either of
`two modes: a diagnostic mode or a cosmetic imaging
`mode. Subsequent embodiments give examples show-
`Ing how operation in either orboth 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 and aprobe extension 40. A common
`optical axis 0 applies for both diagnostic and cosmetic
`image capture. Illumination for any type of image is pro-
`vided from one or more of illumination apparatus 12a,
`12b, 12c, or 12d, which include light sources and beam
`shaping optical elements. An optional attachment 30 pro-
`vides illumination fortranslucency measurement. Probe
`100 also includes a mode switch 36 which is used to
`select either of the operating modes: diagnostic or cos-
`
`metic.Animaging assembly34containstheimagingsen-
`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 solidestate light
`source, such as a light emitting diode (LED) or laser, or
`could be a broadband light source such as xenon arc
`lamp or othertype 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 unifon'n enough for illumination on the
`tooth surface, no beam shaping optics are needed. Beam
`shaping component 22a of Figure 3a is 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 optical fiberora liquid light
`guide, forexample (not shown). The light level is typically
`a few milliwatts in intensity, but can be more or less, 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-
`seq uently. 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 in illumination apparatus i2aemits broad-
`band visible light (400nm — 700nm) for polarized reflect—
`ance imaging, or a combination from light sources with
`different spectrum, such as a combination of Red, Green
`and Blue light emitting diodes (LEDs). Light source 21 in
`illumination apparatus 12b emits narrow band ultraviolet
`(UV) light (375nm - 425nm) to excite tooth fluorescence.
`Light source 21 in illumination apparatus 12cemits Near-
`lnfrared (NIR) lightfortranslucency 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
`
`[0021] The schematic diagrams of Figures 4 and 5
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`0358
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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 designed for 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 123, provides uniform polarized
`white light illumination on the tooth surface for polarized
`reflectance imaging. Illumination apparatus 12b directs
`UV light toward tooth 20 through a bandpass filter 46 to
`excite fluorescence in the tooth. Bandpass filter 46 is an
`option and is helpful for improving spectral purity of illu-
`mination from the light source in illumination apparatus
`12b.
`Light reflected from tooth 20 passes through a
`[0022]
`central opening among the illumination apparatus and
`through an analyzer 44. One or more lenses 66 then di—
`rect reflected light through a spectral filter 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 orderto obtain a
`true color reflectance image, the cut-off wavelength of
`the spectral filter 56 is selected so that it can block the
`excitation light from illumination apparatus 12b, but not
`blockthe blue portion of the light from illumination appa—
`ratus 12a. The fluorescence image that has been ob-
`tained from tooth 20 can have a 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
`ranges ofthe visible spectrum could also be used in other
`embodiments. Whentaking fluorescence image, analyze
`er 44 can be moved out of the optical axis 0 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 forprocessing and display.
`[0023]
`Still referring to Figures 4 and 5, polarized re-
`flectance image data is also obtained using many of the
`same components. An illumination apparatus 12a directs
`visible light, such as awhlte light or other broadband light,
`through a polarizer 42a, and toward tooth 20. Analyzer
`44, whose transmission axis is oriented orthogonallywith
`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 0 or replaced with
`anotherfilter element as needed.
`[0024] Sensor 68 may be any of a number of types of
`imaging sensing component, such as a complementary
`metal-oxide-semiconductor (CMOS) or charge-coupled
`device (CCD) sensor. Light sources used in illumination
`apparatus 12a and 12b can be lasers or other solid-state
`sources, such as combinations using one or more light
`emitting diodes (LEDs). Alternately, a broadband source,
`such as a xenon lamp having a supporting colorfilter for
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`passing the desired wavelengths, could be used.
`[0025]
`Figure 5 shows one arrangement for multiple
`illumination apparatus used in the embodiment shown in
`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-element lens.
`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 of field. Preferably, for optimal resolution, the im—
`aging optics provides an image size that is suited to the
`aspect ratio of sensor 68.
`[0027] Camera controls are suitably adjusted for ob-
`tainingeachtype of diagnosticimage. Forexample, when
`capturingthefluorescence image, itis necessaryto make
`appropriate exposure adjustments for gain, shutter
`speed, and aperture,sincethisimage may notbeintense.
`When sensor 68 is a color sensor, color filtering can be
`performed by colorfilter 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
`forprocessing, combining, and displayingthe 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 embodiment of the diagnostic
`mode optical path using a polarization beamsplitter 38.
`An illumination apparatus 14 provides light of one polar-
`ization directedthrough a beam shaping optical element
`14a from a light source 14b, which is reflected from po—
`larization beamsplitter 38 and directed toward tooth 20.
`Beam shaping optical element 14a shapes the lightfrom
`an illumination apparatus 14 to provide uniform illumina-
`tion on the tooth surface. Reflected light of the opposite
`polarization state is thentransmitted through polarization
`beamsplitter 38 toward sensor 68. This arrangement re-
`moves specular reflected lightfrom other scattered light,
`so that the returned light includes a high proportion of
`reflectance light from caries sites. Usingthe arrangement
`of Figure 7, illumination apparatus 14 can be selected
`from a number of configurations, such as a combination
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`EP 2 241 248 A2
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`of the light sources with differentwavelengths 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—
`ment14athrough an opticalfiberor otherlight guide such
`as a liquid light guide. One advantage of this embodiment
`is that illumination apparatus 14 can be easily changed
`to meet different applications. 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.
`
`Cosmetic Imaging Mode
`
`[0030] When switched to cosmetic imaging mode,
`probe 100 operates under a different set of requirements.
`In this mode the illumination sources and optical path are
`suitably configured forthetypes 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 measurementcan 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 white light source is used
`as source illumination. The color shade of the tooth is
`then calculatedfrom data in RGB planes ofthe 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 reflece
`tion. The lightfrom specular reflection has the same spec-
`trum as the illumination light source and doesn’t contain
`colorinformation forthe tooth. Additionally, very little sur-
`face information is obtained when specular reflection pre—
`dominates and saturates the sensor.
`[0033]
`By using polarized light illumination and spec-
`ular reflection removal, embodiments of the present in-
`vention overcomethis limitation and obtain scattered light
`fromthe enamel and dentin. This scattered light 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 measure tooth color,
`a broadband light source in illumination apparatus 12a
`is turned on. The broadband light from illumination ap-
`paratus 12a passes polarizer 42a and illuminates the
`tooth surface. Of all the light reflected backfromthetooth,
`only the light having orthogonal polarization passes
`through analyzer44 and reaches sensor 68. Tooth shade
`information is calculatedfrom the R, G, and B plane data
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`of sensor 68.
`[0035] Because sensor and filter performance are im—
`perfect, there is some amount of cross talk between each
`color plane when broadband illumination is used. An al—
`te rnatlve solutionfortooth color measurementis to 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 ot this method is that it may require additional
`image processing in orderto alignthethree different color
`images since they are taken at different time.
`[0036]
`Figures 8a and 8b show two configurations for
`a color sequential illumination method. The first config—
`uration of Figure Ba comprises three light sources 21
`such as red, green and blue LEDs, and one beam shap—
`ing optical element 22, which can be one ofbeam shaping
`elements 22a, 22b, or22c, previously described orsome
`combination ofthese elements. Thesethree lightsources
`can be switched either 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 change the illumination spectrum in
`orderto 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 weight lim-
`itations for probe 100.
`[0037] The translucency of atooth can be determined
`by measuring the reflectance light returned fromthetooth
`or, alternately, the lighttransmittedthroughthe tooth. The
`translucency can be used as a coordinate of the meas—
`urement point in one dimension of the shade space dede
`icatedto this parameter. It can also be usedforcorrection
`of at least one othercoordinate ofthe measurement point
`in another dimension.
`[0038] To use the reflectance light to determine 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 light illumination re—
`lates to the light captured bythe sensor and scattered in
`enamel and dentin. If unpolarized light is used, specular
`light reflectedfrom the tooth surface and from the super-
`ficial layer of the enamel is much more pronounced than
`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 mo