WO2015082300A1

WO2015082300A1 - Device for dental use for discriminating the color of teeth

Info

Publication number: WO2015082300A1
Application number: PCT/EP2014/075805
Authority: WO
Inventors: Jordi PEREZ CASAS; Angelo Putignano; Walter DEVOTO
Original assignee: Style Idea Factory Sociedad Limitada
Priority date: 2013-12-05
Filing date: 2014-11-27
Publication date: 2015-06-11
Also published as: EP3105558A1; TW201521686A; AR098632A1; HK1232285A1

Abstract

A device (1) for dental use for discriminating the color of teeth, comprises: a cellular phone (2) with a digital camera (20) comprising a lens (21) and a light source (22) acting as flash, a case (3), a spacer (7) mounted on the case (3) in correspondence of the lens (21) and the light source (22), a first polarization filter (4) and a second polarization filter (5) disposed inside the spacer (7), respectively on said lens (21) and on said light source (22), a calibration label (8) disposed in the spacer (7), a database (100) containing a plurality of digital sample images that univocally define sample colors, and a comparison software (101 ) to compare the digital image of the tooth taken with the device (1) with said sample images of the database (100) to discriminate the color of the photographed tooth.

Description

Device for dental use for discriminating the color of teeth

The present patent for industrial invention relates to a device for dental use for discriminating the color of teeth.

One of the main problems in the replacement of teeth or part of their structure is represented by the color correspondence between the original tooth and the replacement. Color determination is extremely important for the dentist in order to obtain a natural look of the replacement. Therefore it is important to know the color of the existing tooth in order that the replacement can be associated precisely.

In the dental field empirical subjective methods are used in the dental field, which are based on standardized color scales created by companies that produce the reconstruction materials. A color scale that is popular with the majority of operators is the Vita™ scale, which comprises sixteen different shades. Other less popular scales include guides provided by Bioform™ and SR-Vivadent™.

However, these scales are used in a rudimentary way. The guide is a plastic or metal plate with a plurality of color samples shaped as a tooth, for example a front tooth. In general, in order to assess the dental color of a patient, the dentist removes one of the color sample from the guide and places it close to the patient's tooth so that the dentist can perceive the most accurate correspondence possible. After determining the color of the tooth, the information will be used in the following procedure. Obviously, such a method is random because it depends on the subjectivity of the dentist in making a visual assessment.

In the adhesive or reconstructive odontology, for instance, the composite materials that are used for restoration are already specified with the name of the range in the color scale, for example, one of the sixteen colors of the Vita™ scale. More particularly, if restoration is necessary, the color of the patient's tooth must be determined and perfectly perceived by the dentist or correctly informed to the laboratory in charge of making the reconstruction.

The procedure used to select the material for a specific tooth color implies some difficulties in the assessment and the production of the correct color match. If, for example, the dentist wants to make a restoration with shade A3 of the VITA™ range, the materials are stratified on a model or directly in the tooth to be restored. Restoration is made with layers in order to obtain transparency as well as a natural look. Each layer has a specific color and intensity. In order to generate shade A3, the technician or the dentist must follow a recipe given by the manufacturer or self-manufactured that requires a different shade at every layer-

The color correspondence process can be additionally complicated if the dentist is not skilled in determining such information. For this reason, dentists often send their patients directly to a laboratory for a technician to determine the color information. Alternatively, dentists sometimes ask the technician to go and take the tooth color in the dental office. In both cases the risk is to create an additional level of subjective uncertainty in determining the patient's dental color. Therefore there is a need for additional improvement in this field.

The communication of the color information between the dentist and the laboratory is extremely important. Mistakes are often made during the communication, thus resulting in a product that is not of the same color as the patient.

In some cases dentists use color scales that are not common in the market, thus giving the technician very subjective information and the responsibility of converting this information in a standard shade of the Vita™ scale (given the fact that composite materials and ceramics are often made from the Vita ™ color scale). This can result in an improper color correspondence.

The situation is additionally complicated when commercial color scales are considered, with reference to color standardization for application in dentistry. The differences between companies and materials can be considerable and, therefore, the nomenclature may not work, and in the worst case, it can be misleading and confusing.

The subjective color correspondence is evidently affected by many factors, such as the environment, the operator's skill, the perception, the color scale used and the different materials used to make the color scale. It is logical that objective color assessment methods must be used (for instance, spectrophotometer, and colorimeter).

Objective color assessment methods are known, which use complicated expensive instruments, such as spectrophotometers and colorimeters. However, generally speaking, intraoral spectrophotometers and colorimeters are extremely sensitive to light variations and require frequent calibration. Consequently, color measurements are often inaccurate.

The use of digital images for tooth color assessment has become popular in recent years. A large majority of dentists uses intraoral video cameras, video systems, reflex photo cameras, compact photo cameras and smartphones to obtain digital dental images for communication with the laboratory.

However, the lack of standardization of digital images is a real problem. For examples, images tend to be different even if they are taken with the same camera and by the same operator. Therefore digital images often fail in giving reliable numerical values and this determines the subjectivity of the "digital imaging" method.

It would be desirable to have a standardized digital photography in which all digital images are perfectly repeatable. Nevertheless, standardized photography implies the following problems:

1 .- Sensors (CCD) and screen

Digital sensors perceive the light differently and each screen displays the images with slight differences compared to other screens.

2 -. Light source

LEDs and flash lights are extremely sensitive to the fabrication process and power supply. They are also sensitive to lenses and their coating protections and the color temperature of the light changes largely between flashes. Such a difference is even bigger in the LED industry and therefore this factor is extremely difficult to be standardized.

3 -. Distance

Images that are artificially lit are extremely sensitive to distance, especially in case of macro-photography, such as in the dental field. If the distance changes by 5 mm, the image will lose an important quantity of light (underexposure). On the contrary, if the subject to be photographed is 5 mm closer than the ideal distance, the image will receive excessive light (overexposure). Even with very small distance variations (+ or - 2mm), the changes in equalized images can be dramatic and they will surely make standardization impossible. The distance must be always the same with all instruments.

4 -. TTL balance

The "Through The Lens" (TTL) technology is the capability of the camera software to analyze the received light and adjust the entrance of the light in a very short time. The TTL can analyze a scene either partially or totally, changing the result of the photo in an extremely easy way, especially if the background changes or if the subject becomes darker or lighter. In case of very dark teeth, the camera will probably set off the dark color with a stronger light; on the contrary, in case of very white teeth, the camera will operate in the opposite way, making the scene darker and changing the standardized photograph.

5 -. Exposure

In automatic cameras exposure is controlled by the TTL technology and is based on the following parameters:

Aperture -. The aperture of the diaphragm determines the entrance of the light. The more open the diaphragm is, the lower the depth of field will be (difficult focusing); the more closed the diaphragm is, the higher the depth of field will be (easy focusing).

b) Speed -. The speed indicates the speed of the shutter when closing or opening to let the light pass or the length of time for which the sensor will be exposed to the light. When the speed is lower, a higher amount of light will enter the scene, but the image risks to become "blurred". On the contrary, if the speed increases, less light will enter in the scene and the image will be more stable.

c) ISO -. It is the light sensitivity of the sensor. Normally such a sensitivity increases in poor lighting conditions and decreases in strong lighting conditions. A different ISO will affect the final result of the photograph: a low ISO will give a better brightness and contrast, whereas a high ISO will have the opposite effect.

6 -. White balance

Automatic cameras measure the light of the scene and regulate the temperature of the light with the average measurement of the total light quantity. White balance according to the scene is completely different and similar scenes are always different.

7 -. Focusing

The automatic focusing of digital cameras operates according to the same base of exposure and white balance, analyzing an average value of the complete or partial scene and thus relying on the scene characteristics for correct focusing. This function makes standardized photography almost impossible, unless the subject is at the same distance and in the same position with respect to the camera.

In conclusion, because of the aforementioned problems, it is impossible to obtain a standardized digital photograph.

EP1528380 discloses a digital imaging system that comprises a spacer acting as dark room disposed in a camera of a cellular phone. Polarization filters and a calibration label are disposed in the spacer. The digital images of teeth taken by the device of the invention are sent to a database.

The spacer of EP1528380 has a cylindrical cavity with a truncated- conical end with decreasing diameter. The shape of the spacer implies some inconveniences caused by the radial rebound of the light on the internal cylindrical wall of the spacer that creates reflections that cannot be eliminated with polarization filters. Moreover, it must be considered that a tooth has a rectangular shape and therefore the circular section of the spacer cavity does not allow for discriminating contour elements that are not part of the tooth, such as gums and palate.

It must be considered that the tooth color is related to a combination of an enamel layer and a dentin layer, i.e. two layers of materials with a different thickness and a different color that are overlapped in parallel direction. Consequently, multiple reflections and diffractions of the light are generated between the enamel layer and the dentin layer, thus causing an incorrect color perception with the naked eye and with a camera. Such an error is accentuated in the device of EP1528380, wherein no effective suppression of light reflections in the spacer is provided.

The calibration label of EP1528380 is of standard type and these types of standard calibration labels are not able to calibrate a correct tooth color according to the enamel and dentin layers of the tooth.

EP1528380 does not contain any precepts about how to remedy the color assessment error caused by the overlapped layers of enamel and dentin on the tooth.

WO2009/013687 and WO2007/034300 disclose the use of different calibration labels to correct the color of a digital image taken with a camera, such as for example the image of a tooth. However, also these documents do not contain any precepts about how to remedy the color assessment error caused by the overlapped layers of enamel and dentin on the tooth.

The purpose of the present invention is to eliminate the inconveniences of the prior art, by devising a device for dental use for discriminating the color of teeth, which is accurate, reliable, versatile, inexpensive and easy to use.

These purposes are achieved according to the invention with the characteristics claimed in independent claim 1 .

Advantageous embodiments of the invention appear from the dependent claims.

Further characteristics of the invention will appear clearer from the detailed description below, which refers to merely illustrative, not limiting, embodiments, illustrated in the attached drawings, wherein: Fig. 1 is an exploded perspective view of the parts of the device according to the invention ;

Fig. 2 is a bottom view of a case of the device of Fig. 1 ;

Fig. 3 is a top view of the case of Fig. 2;

Fig. 4 is a front view of the case of Fig. 2;

Fig. 5 is a side view of the case of Fig. 2;

Fig. 6 is a top view of the calibration label of the device of Fig. 1 ;

Fig. 7 is a block diagram that shows the operation of the device of the invention ;

Fig. 8 is a block diagram that shows the buttons used to activate the functions of the device of the invention ; and

Fig. 9 is a flow diagram that illustrates the tooth color discrimination process of the invention.

With reference to the figures, the device for dental use according to the present invention is disclosed, which is generally indicated with reference numeral (1 ).

Referring now to Fig. 1 , the device (1 ) comprises a cellular phone (2) and a case (3).

The cellular phone (2) is provided with a digital photo or video camera (20). Therefore the back side of the cellular phone (2) is provided with a lens (21 ) of the camera and a light source (22) acting as flash. The cellular phone (2) is of known type and can be any cellular phone provided with a digital photo camera that is normally available on the market. Preferably the cellular phone (2) is a cellular phone produced by Apple and known with the trade name Iphone™.

Also referring to Figs. 2 to 5, the case (3) comprises a base plate (30) with rectangular shape and with the same dimensions as the cellular phone.

Lateral walls (31 ) protrude from the base plate (30) in such manner to define a parallepiped housing adapted to receive the cellular phone (2). The height of the lateral walls (31 ) is substantially the same as the thickness of the cellular phone (2). As shown in Figs. 1 and 4, some lateral walls (31 ) of the case are provided with openings (32, 33, 34) to leave the services of the cellular phone provided on the borders of the cellular phone, such as buttons, connectors and the like, uncovered.

Optionally, the base plate (30) may be provided with an opening (35) with circular shape in order to make the logo of the cellular phone (2) visible.

Referring to Fig. 2, a first polarization filter (4) and a second polarization filter (5) are disposed in proximity to a corner of the base plate (30) of the case, in such manner to be respectively in correspondence of the lens (21 ) and the light source (22) of the digital camera of the cellular phone, when the cellular phone (2) is inserted into the case. The filters (4, 5) cover the lens (21 ) and the light source (22) of the cellular phone independently. The filters (4, 5) are linear polarization filters disposed in such manner to polarize the light in orthogonal directions in order to produce light with zero reflections. For example, the first filter (4) is disposed in such manner to obtain a vertical polarization, wherein the second filter (5) is disposed in such manner to obtain a horizontal polarization.

The polarization filters (4, 5) pass through the base plate (30) of the case and protrude externally from the base plate (30). A holding plate (6) is mounted on the base plate (30) of the case in such manner to hold the polarization filters (4, 5).

Onto the polarization filters (4, 5) a spacer (7) is mounted, having an axial cavity (70) with axis orthogonal to the base plate (30) and a border (71 ) adapted to come in contact with the tooth to be photographed. The axial cavity (70) of the spacer has a tapered truncated-pyramidal shape with increasing dimensions going from the case (3) outwards. The truncated pyramidal shape of the cavity (70) of the spacer (7) creates orthogonal light reflections that are totally suppressed by the polarization filters (4, 5) in mutual orthogonal position.

The spacer acts as dark room and therefore the lateral walls of the spacer are black or opaque in order to prevent the light from passing. Preferably the spacer (7) is coated with black neoprene foam. Preferably the spacer (7) has a length of approximately 80 mm, in such manner that the distance between the lens (21 ) of the digital photo camera (20) of the cellular phone and the tooth to be photographed is higher than 78 mm. Such a distance is the ideal distance to guarantee the best performance of the macro lenses of cellular phones.

The combination of the spacer length, the truncated-pyramidal shape of the cavity of the spacer (7) and the crossed polarization of the polarization filters (4, 5) allows for completely eliminating the reflections of the light inside the spacer and flatten the image of the enamel and dentin layers, thus obtaining a single color.

Referring to Figs. 1 and 3, a calibration label (8) for color control is disposed inside the spacer (7), in correspondence of the border (71 ) of the spacer. The calibration label (8) has a rectangular shape and occupies approximately half surface with respect to the cross-section of the spacer (7).

Referring to Fig. 6, the calibration label (8) comprises a square central portion (80) with pure white color, provided with a focusing target (81 ) having a circular shape with 12 mm diameter. The focusing target (81 ) is provided in correspondence of the lens (21 ) of the camera of the cellular phone.

On the left of the central portion (80) a lateral band with three rectangular flags (82, 83, 84), respectively with Yellow, Magenta and Cyan color, is provided. On the right of the central portion (80) a lateral band with three rectangular flags (85, 86, 87), respectively with Black, 50% gray and 18% gray color, is provided.

The label (8) is used for balancing whites and colors and for exposure and focusing before and after taking the photograph. The label (8) is obtained with silk-screening technique on paper with opaque silicone inks, without coloring agents or other metameric pigments.

The calibration label (8) is not a standard label, being personalized according to colors that are especially studied for reconstructing the colors of the tooth enamel and dentin.

The calibration label (8) has a rectangular shape and the opening of the border (71 ) of the spacer has a square shape. The dimensions of the calibration label (8) and of the opening of the border (71 ) of the spacer are such that a rectangular shooting range is obtained with dimension 20 mm x 12 mm. Such shape and size of the shooting range is essential to follow the rectangular shape of teeth and allows for discriminating foreign elements, such as palate and gums.

Going back to Fig. 1 , the device (1 ) comprises an anti-contamination protection (9) adapted to be disposed on the border (71 ) of the tip of the spacer (7) with snap-on coupling, such as a removable cap. Clearly, the anti- contamination protection (9) has a transparent portion (90) to allow for taking a photograph. The anti-contamination protection (9) is made of plastic and is of disposable type. The protection (9) is used to prevent the spacer (7) from getting in contact with the oral tissues and with humidity, and acts as barrier for infections.

In addition to being provided with a space for the polarization filters (4, 5), the case (3) is designed according to the specifications of the cellular phone (2) in order not to cover the devices of the cellular phone, such as: distance sensors, earplugs connectors, battery charge and mini-plug audio cable, switch-on button and volume buttons, screen-locking button, Home button, front camera and loudspeaker.

With the hardware of the case (3) the following problems of standardized photography have been solved:

Distance -. The minimum distance for perfect focusing with the macro function of the iPhone is 78 mm. The length of the spacer is 80 mm because this distance allows for focusing an object with the maximum resolution and enlargement possible, thus allowing for 2 mm tolerance. The images are taken through a spacer having an axial cavity with truncated-pyramidal shape that guarantees a constant distance and a minimum variation.

The following characteristics: Diaphgram - Depth of field - Speed - ISO - White balance will be always the same for each photograph because they are calibrated with respect to a sample of known characteristics (label 6), with the same light (i-Phone flashes (22)), the same distance (imposed by the spacer (7)) and therefore the same shooting conditions. Light sources -. External lights are eliminated because of the cone design, the black material and the opaqity that blocks the external light that may alter the measurement result.

TTL -. All measurements are made through the lenses (TTL) concentrating them on the same sample. The quantity of light and lighting on the scene will always be the same, although small variations of the flash temperature are possible.

Focusing -. It will be always the same because the measurement is made in the calibration label (8) where a special focusing target (81 ) is provided, with the same light, distance and scene conditions.

White balance -. It is done in the central portion (80) of the calibration label (8) with paper colored with pure white. Therefore white balance will be always the same because it is calibrated in the balance label, with the same light, the same distance and the same shooting conditions.

Digital sensors (CCD) - The digital sensors (CCD) used in digital camera can have small variations from device to device. However digital sensors are digitally calibrated with the calibration label (8) in order to set off luminous deviation.

Light temperature -. The light source (22) can have slight variations from device to device. Therefore the light source (22) is calibrated digitally with the calibration label (8) to set off any luminous deviation.

The device (1 ) of the invention comprises the following functions:

1 -. Focusing target. It consists in an especially designed grid (81 ) that is similar to an aim and provides the autofocus in order to calilbrate efficiently and exactly in the same way every time a photograph is taken.

2 -. Image standards and normalization. Reflected colors can be measured using any digital camera that makes measurements in the visible spectrum (and a little beyond) of a color sample. The reflected colors of the device must not be considered to be 100% precise given the fact that flashes and sensors can surely have minor variations. In order to fine-balance the images, the photographs must be calibrated every time with the sample label (8). 3 -. Crossed polarization -. This type of polarized light is obtained with the orthogonal layout of the two linear polarization filters (4, 5) respectively disposed on the lens (receiver) (21 ) and on the flash (source) (22). This filter layout produces a light that creates zero interference and therefore a light without specular or diffused reflections. These types of reflection-free images can be analyzed numerically, having eliminated any undesired reflection. Moreover, they allow the user to observe the tooth and assess the tooth color more easily, with a better understanding of depth and transparency. Hyper- contrast images, i.e. images with brighter colors, are obtained with this light.

4 -. Elimination of external light sources -. The spacer (7) is coated with black neoprene foam that eliminates the interference of internal light and insulates the external light. The close distance between the subject and the spacer (7) also blocks the external light efficaciously.

5 -. Exposure balance -. I is made on the calibration label (8), always obtaining the same exposure balance.

6 -. Focus constancy -. I is made on the calibration label (8), always obtaining the same focusing. The object will be out of focus only if it is not placd at the correct distance, i.e. in contact with the cone.

7 -. Color correspondence with seven reference colors -. Seven colors will be captured in each single photo. This will allow the software to balance each color in a specific order in order to balance a photograph up to the smallest details and standardize with a database. With reference to the calibration label 8, shown in Fig. 6, the seven colors are the following:

1 ) Black -. When it is found it can inform the digital sensor about a possible condition of excessive exposure;

2) 50% Gray-. When it is found it indicates green and blue traces;

3) 18% Gray-. When it is found it indicates yellow, green and red traces;

4) White -. When it is found it indicates underexposure (shadow) and heavy traces of other colors;

5) Cyan -. Control color for 90% correspondence

6) Magenta -. Control color for 95% correspondence 7) Yellow -. Control color for 100% correspondence

Colors 1 , 3 and 4 are the standard for the classical white balance. Color 2 is added to improve the elimination of undesired colors. Colors 5, 6, and 7 are the purest expression of the primary colors in the subtractive color system, i.e. pure colors without any mixture of other colors. When all colors are found in a digital image, each single variation will appear on at least one of the colors contained in these standards, given the fact that all color ranges are covered. The normalized image will be analyzed and compared in a large database of standardized images.

8 -. Lighting-. In spite of being a characteristic of the cellular phone (2), the device (1 ) will allow the light to act without interferences, providing the ideal lighting in order to obtain standardized images easily.

9 -. Aperture -. It is a characteristic of the camera (20) of the cellular phone (2). Because of the small diameter of the video camera (20), the aperture is very small and therefore a correct depth of field is always obtained with the standardized light conditions obtained with the device of the invention.

10 -. Speed -. The speed is rather quick because lighting is quite strong, making images very stable every time a photo is taken.

The cellular phone (2) is provided with a software application to control the operation of the device (1 ) of the invention.

Referring to Fig. 7, a database (100) is stored in the cellular phone, which comprises digital sample images that univocally identify sample colors.

The sample colors of the database are calibrated with a three-dimensional element comprising an enamel layer with thickness of 0.5mm and a dentin layer with thickness of 2mm. Such a calibration of the sample colors in the database allows for taking into account the color detection error possibly made by the device (1 ).

Moreover, the cellular phone (2) is equipped with a comparison software (101 ) that compares a digital image (D) taken with the device (1 ) with the digital sample images stored in the database (100). Therefore, the comparison software (101 ) provides information (I) to discriminate the color of the photographed image (D) according to the sample colors of the digital sample images stored in the database (100).

Discrimination is made by reading the color values of pixels in the digital photographed image (D) and by comparing them with the values of the sample colors contained in the database (100). In fact, each pixed has a color value that is compared with the color values of the sample colors in the database (100).

Referring to Fig. 9, the comparison and discrimination method provides for a continuous cycle statistic analysis, which comprises the following steps: a) select, wherein an area comprising a plurality of pixels of the digital image (D) photographed with the device (1 ) is selected,

b) delete, wherein the pixels of the colors that are not stored in the database (100) are deleted and the pixels of the remaining colors are sent to step (c),

c) frequency, wherein the pixels of the most frequent colors among the remaining pixels are selected and said pixels of the most frequent colors are sent to step (d),

d) average, wherein an average value of the most frequent colors is calculated,

e) comparison, wherein the average values of the most frequent colors are compared with the values of the sample colors of the database; if the average value does not correspond to any value of the sample colors of the database, the method returns to step b),

f) the process proceeds until a correspondence is found between the most representative pixels of the selected area and the sample colors of the database.

Referring to Fig. 8, the software of the device (1 ) comprises the functions activated with the buttons shown in Fig. 8.

Take photo: it activates the entire system to take a photo, it switches the LED flash (22) on and it calibrates the focusing, white balancing and exposure on the calibration label (8). Right/left keys: keys used to take a photo, which can be accessed from the left and the right side of the screen for a better ergonomics while taking a photo.

Accelerometer: The accelerometer will automatically determine whether the cellular phone (2) is positioned to photograph either the upper or the lower teeth.

Pop-up: If desired, before making the photo session, a pop-up window is displayed in order to enter the patient's data. After taking the photo, another pop-up window is displayed, which allows the user to save, delete or analyze the captured image. The "Save" function will store the photo in the archive and will return to the camera mode, the "Delete" function will delete the image and return to the camera mode. The "analyze" button will start the analysis of the image, which will be compared with the images in the database to find the correct correspondence.

View: when the image is displayed in full screen (either selecting an image from the archive or the image that has just been captured) the 3 buttons "Save", "Delete" or "Analyze" will be displayed. The "Save" function will store the photo in the archive and will return to the camera mode, the "Delete" function will delete the image and return to the camera mode. The "analyze" button will start the analysis of the image, which will be compared with the images in the database to find the correct correspondence.

Archive: the photographic archive is ordered in folders with a label with the patient's name and a sub-label with the file number. The label of images without pre-entered data will include the date and the hour as sub-label. Each session will be considered as a new patient. The session will expire when the user leaves the "camera mode" (all the images of the session will be saved in the same folder). The user can edit the patient's name and the file number at any time. The list of folders can be sorted by alphabetical order or by date.

Patient: After selecting the folder to be examined, the user will have access to the images. The extension of the images contains the date and the tooth reference number. Analyze: When this button is pressed by the user, the system makes a comparison in different points of the digital image of the photographed tooth, inside a defined area of the tooth, and searches for the most repeated values of colors that correspond to the sample colors of the images in the database. Then a diagnosis of the color is given and a list of equivalence for the tooth color is provided.

Image anatomical centering: When the analysis is started, different pre-loaded anatomical figures will appear to determine the tooth contour.

Enlarge/reduce: The tooth pre-loaded contour can be enlarged or reduced in order to increase and decrease the size according to the tooth.

Tooth sliding shapes: The pre-loaded tooth shapes can be browsed with the "slide" movement, which will take the user to the following shape. For instance, if tooth 1 1 is displayed and the user slides to the right, the following tooth to be displayed on the screen will be tooth 12.

Variations and modifications can be made to the present embodiments of the invention, within the reach of an expert of the field, while still falling within the scope of the invention.

Claims

1 . Device (1 ) for dental use to discriminate teeth color, comprising:

- a cellular telephone (2) comprising a digital camera (20) comprising a lens (21 ) and a light source (22) acting as flash,

- a case (3) adapted to be applied on the cellular telephone (2) in such manner to leave said lens (21 ) and light source (22) uncovered,

- a spacer (7) mounted on said case (3) on said lens (21 ) and light source (22), said spacer being provided with an axial cavity with tapered shape with increasing dimensions from the case outwards and opaque lateral walls to prevent light from passing and a final edge (71 ) adapted to go in contact with the tooth to be photographed,

- a first polarization filter (4) and a second polarization filter (5) disposed inside said spacer (7), respectively on said lens (21 ) and said light source (22), wherein said polarization filters (4, 5) are linear, and

- a calibration label «»8) disposed inside said spacer (7) in the border of the spacer in order to balance the whites and the colors and calibrate the exposure and the focusing of the digital camera (20),

characterized by the fact that it comprises

- a database (100) stored in the cellular phone (12) containing a plurality of values of sample colors calibrated with a three-dimensional element comprising an enamel layer having thickness of 0,5 mm and a dentin layer having thickness of 2 mm,

- a comparison software (101 ) installed in said cellular phone to analyze the pixels of the tooth digital image (D) photographed with the device (1 ) and compare the color values of the pixels with said values of sample colors of the database (100) to discriminate the color of the photographed tooth among the sample colors of the database,

wherein

said spacer (7) has a length of 80 mm,

said spacer (7) having an axial cavity (70) with truncated-pyramidal shape with increasing dimensions going from the case outwards and said polarization filters (4, 5) are disposed in such manner to have two orthogonal light polarization directions in order to avoid reflected light,

said calibration label (8) comprises a central portion (80) with pure white color, provided with a focusing target (81 ), a first lateral band with three rectangular flags (82, 83, 84) respectively with Yellow, Magenta and cyan color, and a second lateral band with three rectangular flags (85, 86, 87) respectively with Black, 50% Gray and 18% Gray colors, and

the border (71 ) of the spacer defines an opening and the dimensions of the calibration label (8) and of the opening of the border (71 ) of the spacer are such that a rectangular shooting range is obtained with dimension 20 mm x 12 mm.

2. The device (100) of claim 1 , also comprising an anti-contamination protection (9) disposed on the border (71 ) of the tip of the spacer (7) with snap-on coupling.

3. The device (100) of any one of the preceding claims, also comprising a locking plate (6) mounted on said case (3) in order to lock said first and second polarization filters (4, 5).

4. The device (100) of any one of the preceding claims, wherein said focusing target (81 ) disposed on the central portion of the calibration label has a circular shape with 12 mm diameter.

5. The device (100) of any one of the preceding claims, wherein said calibration label is obtained by means of silk-screening on paper with opaque silicone inks without fluorescent colorants or other metameric pigments.

6. The device (100) of any one of the preceding claims, wherein said comparison software searches for the most repeated color values of the photographed image that correspond to the values of the color samples of the (100).

7. The device (100) of any one of the preceding claims, wherein said cellular phone (2) is a cellular phone produced by Apple and known with the trade name of Iphone™.

8. Method for discriminate the color of teeth with a device (1 ) according to any one of the preceding claims, said method comprising the following steps:

a) selection, wherein an area comprising a plurality of pixels of a digital image (D) photographed with the device (1 ) is selected,

b) deletion, wherein the pixels of the colors that are not stored in the database (100) are deleted and the pixels of the remaining colors are sent to step (c),

d) average, wherein an average value of the most frequent colors is calculated,

e) comparison, wherein the average values of the most frequent color are compared with the values of the sample colors of the database (100), if the average value does not correspond to any value of the sample colors of the database (100), the method returns to step b),

f) the method proceeds until a correspondence is found between the remaining pixels of the selected area and the sample colors of the database.