Plaque detection using specular reflection patterns

Abstract

The present invention relates to a computer-implemented method for detecting plaque on a tooth using intensity patterns. The method comprises illuminating a surface of the tooth with a light source, receiving an image of the illuminated surface of the tooth with a camera, and determining an indication for a presence of plaque on the surface of the tooth based on intensity patterns caused by the illumination of the surface of the tooth with the light source.

Description

[0001] 2025PF00039

[0002] 1

[0003] PLAQUE DETECTION USING SPECULAR REFLECTION PATTERNS

[0004] FIELD OF THE INVENTION

[0005] The present invention relates to a computer-implemented method for detecting plaque on a tooth using intensity patterns, a data processing apparatus, an intra-oral camera system, a computer program, and a computer-readable storage medium.

[0006] BACKGROUND OF THE INVENTION

[0007] Plaque detection is of strong interest to provide users of toothbrushes like powered toothbrushes with feedback where to brush better. For example, quantitative light-induced fluorescence (QLF) can be used to detect red auto-fluorescent plaque, which is older neglected plaque. However, such intraoral cameras for quantitative light-induced fluorescence need high-intensity violet light sources and special optical fdters making it more expensive than normal intraoral cameras. Moreover, the light integration time with QLF systems needs to be longer, making the scanning speed slower. Additionally, QLF cameras only detect red auto-fluorescent plaque, and not younger plaque that fluoresces green, similar to the teeth.

[0008] With normal white-light intraoral cameras, sometimes the plaque can be distinguished as slightly different colored mass on the teeth, but the contrast to clean teeth and therefore the sensitivity is low. Thus, there is a need for improved methods of detecting plaque on teeth.

[0009] SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide an improved method that solves at least a part of the problems of the state of the art.

[0011] The inventors of the present invention have developed a method that provides a better contrast mechanism for plaque on teeth using the difference in roughness between plaque-covered and clean teeth.

[0012] The object of the present invention is solved by the subject matter of the independent claims, wherein further embodiments are incorporated in the dependent claims.

[0013] The described embodiments pertain to a computer-implemented method for detecting plaque on a tooth using intensity patterns, a data processing apparatus, an intra-oral camera system, a computer program, and a computer-readable storage medium. The embodiments described further may be combined in any possible way. Synergistic effects may arise from different combinations in various ways of the embodiments described further although these combinations might not be described explicitly in detail.2025PF00039

[0014] 2

[0015] Further on, it shall be noted that all embodiments of the present invention concerning a method might be carried out with the order of the steps as described, nevertheless this has not to be the only and essential order of the steps of the method. The herein presented methods can be carried out with another order of the disclosed steps without departing from the respective method, unless explicitly mentioned to the contrary hereinafter.

[0016] According to a first aspect of the invention, there is provided a computer-implemented method for detecting plaque on a tooth using intensity patterns. The method comprises illuminating a surface of the tooth with a light source, receiving an image of the illuminated surface of the tooth with a camera, and determining an indication for a presence of plaque on the surface of the tooth based on intensity patterns caused by the illumination of the surface of the tooth with the light source.

[0017] Plaque is composed of a layer of micro-colonies giving it a rough mountainous surface compared to clean teeth. This roughness can advantageously be employed by looking at the intensity patterns like specular reflection patterns or shadow patterns of the plaque on the surface of a tooth if illuminated with a light source, which are different from clean teeth. On clean smooth surfaces of teeth, the specular reflection pattern of a light source gives large over illuminated spots in a distinct pattern depending on the tooth curvature. Where plaque is present on a tooth, the specular reflection spots are much smaller, reflecting the small dimensions of the structure of the microcolonies.

[0018] In an embodiment of the invention, determining an indication for a presence of plaque on the surface of the tooth comprises analyzing the intensity patterns to determine a plurality of deviating spots in the image, each deviating spot of the plurality of deviating spots having an intensity that differs significantly from an intensity of a region of the image surrounding the deviating spot, estimating an area of each deviating spot of the plurality of deviating spots, determining the indication for a presence of plaque on the surface of the tooth based on the area of each deviating spot of the plurality of deviating spots.

[0019] This utilizes the fact that specular reflection patterns are well visible in intra-oral camera images as over-illuminated or high intensity spots on the teeth. On clean surfaces, this gives large spots with a predictable pattern based on the light source design and the expected tooth curvatures. On plaque covered surfaces, the pattern becomes irregular with smaller high intensity spots. The same applies to shadow patterns of a lights source illuminating the tooth from the side.

[0020] In an embodiment of the invention, the plurality of deviating spots comprises a plurality of bright spots, the plurality of bright spots corresponding to a specular reflection pattern caused by the illumination of the surface of the tooth with the light source, and / or the plurality of deviating spots comprises a plurality of dark spots, the plurality of dark spots corresponding to a shadow pattern caused by the illumination of the surface of the tooth with the light source.

[0021] Thus, according to the invention, it is possible to determine the presence of plaque on the surface of the tooth based on over-illuminated high-intensity spots on the surface of the tooth caused by specular reflection. Further, dark spots that correspond to shadows caused by the plaque microcolonies in2025PF00039

[0022] 3

[0023] side illumination can be used to determine the presence of plaque on the surface of the tooth. Of course, it is possible to use both bright spots of specular reflection and dark spots of shadows simultaneously.

[0024] To enhance the difference in the patterns between smooth and plaque covered surfaces in this invention it is preferred to place the light sources like LEDs more to the side or have them illuminate at lower incidence angles over the teeth. Further, also the shadow patterns may be used for further contrast. In some embodiments multi-color light sources, e.g. red, green and blue LEDs at different sides, may be used to have different patterns in the different channels of an RGB camera which can be combined to enhance detection sensitivity.

[0025] In an embodiment of the invention, determining a plurality of deviating spots in the image comprises applying a predefined intensity threshold to the image, and the area of a deviating spot of the plurality of deviating spots is defined as an area of a subregion of the image, wherein each pixel in the subregion of the image has an intensity higher or lower than the predefined intensity threshold. Thus, brights spots of specular reflection and / or dark spots of shadows can be determined by discriminating the image brightness or intensity by applying a high or a low threshold, respectively.

[0026] In an embodiment of the invention, determining the indication for a presence of plaque on the surface of the tooth comprises comparing an average deviating spot area in a region of the image with a predefined area threshold, and setting the indication for the presence of plaque on the surface of the tooth to positive in case the average deviating spot area is smaller than the predefined area threshold in the region of the image, wherein the average deviating spot area in the region of the image is determined by averaging over the areas of each deviating spot of the plurality of deviating spots in the region of the image.

[0027] Thus, regions of the surface of the tooth having a plurality of small bright spots are more likely determined as covered with plaque, than regions comprising a large bright spot. Since plaque colonies have a typical size range it is expected that the bright spots are also in a certain size range, so the bright spot area may be smaller than a certain predefined threshold but also higher than a certain predefined lower threshold. This can exclude large specular reflection spots on, for example, curved tooth surfaces.

[0028] In an embodiment of the invention, determining the indication for a presence of plaque on the surface of the tooth comprises determining a frequency distribution of the areas of each deviating spot of the plurality of deviating spots in a region of the image, and determining the indication for the presence of plaque on the surface of the tooth in the region based on the frequency distribution.

[0029] Thus, the presence of plaque on the tooth surface is detected based on the distribution of the areas of the bright or dark spots. In particular, a plurality of small bright spots in close proximity might be interpreted as high probability for plaque, while a larger spot may most likely be interpreted as clean tooth surface, as well as regions of the tooth without any spots.2025PF00039

[0030] 4

[0031] In an embodiment of the invention, determining an indication for a presence of plaque on the surface of the tooth comprises determining an indication for the presence of plaque on the surface of the tooth for a plurality of regions of the surface of the tooth.

[0032] Thus, the determination of plaque can be performed for different section of a tooth separately, for example, indicating that plaque may be present close to the gums, while the rest of the tooth is clean.

[0033] In an embodiment of the invention, the method further comprises segmenting the image of the illuminated surface of the tooth to discriminate between the tooth and the gums. Thus, the method needs only to be applied to the regions of the image that are segmented as tooth surfaces.

[0034] In an embodiment of the invention, illuminating a surface of the tooth with a light source comprises illuminating the surface of the tooth with a plurality of light sources, each light source of the plurality of light sources having a different central axis of an illumination direction, and each light source of the plurality of light sources has a different wavelength, and the camera is a multi-color camera configured for detecting light of the different wavelength of the plurality of light sources.

[0035] Thus, embodiments with illumination from multiple sides may enhance this creating of specific reflection and / or shadow patterns that are typical for plaque colony sizes. More advanced embodiments with multi-color illumination, e.g. red, green, and blue LEDs, would enable to distinguish reflection and shadow patterns in different camera channels.

[0036] In an embodiment of the invention, a central axis of an illumination direction of the light source and a viewing direction of the camera form an angle in the range of from 45 degrees to 90 degrees. Thus, a low incidence angle of the light from the light source, i.e., illumination of the tooth surface from the side, can improve the contrast of the specular reflection pattern. Additionally, this will create specific shadows of the plaque peaks.

[0037] In an embodiment of the invention, determining an indication for a presence of plaque on the surface of the tooth comprises utilizing a machine learning algorithm for analyzing the intensity patterns to determine the indication for the presence of plaque on the surface of the tooth.

[0038] More elaborate algorithms may be used such as machine learning algorithms that can separate the typical specular reflection patterns of plaque from those of clean teeth. This can be achieved by training such models on annotated images.

[0039] According to another aspect of the invention, there is provided a data processing apparatus for carrying out the steps of the method according to any one of the preceding embodiments.

[0040] According to another aspect of the invention, there is provided an intra-oral camera system comprising the data processing apparatus according to the preceding embodiment, and a sensing head, wherein the sensing head comprises a light source configured for illuminating the surface of a tooth and a camera configured for receiving an image of the illuminated surface of the tooth.2025PF00039

[0041] 5

[0042] According to another aspect of the invention, there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method according to any one of the preceding embodiments.

[0043] According to another aspect of the invention, there is provided a computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method according to any one of the preceding embodiments.

[0044] Thus, the benefits provided by any of the above aspects equally apply to all of the other aspects and vice versa.

[0045] In summary, the invention relates to a computer-implemented method for detecting plaque on a tooth using intensity patterns. The method comprises illuminating a surface of the tooth with a light source, receiving an image of the illuminated surface of the tooth with a camera, and determining an indication for a presence of plaque on the surface of the tooth based on intensity patterns caused by the illumination of the surface of the tooth with the light source.

[0046] One of the advantages of embodiments of the present invention of detecting plaque on a tooth using intensity patterns is that the sensitivity of plaque detection with light reflection, preferably white light, is improved. As plaque is not a smooth layer but a mountain landscape, the specular reflection pattern can advantageously be utilized to detect plaque. This will have typical patterns on plaque due to the smaller colony sizes compared to the curvature of clean smooth teeth. This allows intraoral cameras to detect plaque by analyzing the specular reflection of light illuminating the surface of the tooth under a low angle of incidence. Further, also shadows caused by the mountain landscape of the plaque layer can be analyzed.

[0047] These advantages are non-limiting and other advantages may be envisioned within the context of the present application.

[0048] The above aspects and embodiments will become apparent from and be elucidated with reference to the exemplary embodiments described hereinafter. Exemplary embodiments of the invention will be described in the following with reference to the following drawings:

[0049] BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Fig. 1 shows a block diagram of a computer-implemented method for detecting plaque on a tooth using intensity patterns according to an embodiment of the invention.

[0051] Fig. 2 shows a schematic setup of a sensing head of an intra-oral camera system according to an embodiment of the invention.

[0052] Fig. 3 shows a schematic setup of an intra-oral camera system according to an embodiment of the invention.

[0053] Fig. 4A shows an image of a clean tooth surface that is not covered with plaque.

[0054] Fig. 4B shows an image of a tooth surface that is covered with plaque.2025PF00039

[0055] 6

[0056] DETAILED DESCRIPTION OF EMBODIMENTS

[0057] Fig. 1 shows a block diagram of a computer-implemented method for detecting plaque 140 on a tooth 130 using intensity patterns according to an embodiment of the invention. The method comprises step SI 10 of illuminating a surface of the tooth 130 with a light source 110, and step S 120 of receiving an image of the illuminated surface of the tooth 130 with a camera 120. The method comprises further step S130 of determining an indication for a presence of plaque 140 on the surface of the tooth 130 based on intensity patterns caused by the illumination of the surface of the tooth 130 with the light source 110.

[0058] Fig. 2 shows a schematic setup of a sensing head 100 of an intra-oral camera system 200 according to an embodiment of the invention. The sensing head 100 comprises a light source 110 that illuminates a surface of tooth 130 that is covered with plaque 140. The light illuminates the surface under a small angle of incidence, i.e., by side illumination. A camera 120 receives an image of the illuminated surface of the tooth 130. As a viewing direction 111 of the camera 120 is directed towards the tooth 130, the viewing direction 111 forms an angle 160 with a central axis of the illumination direction 111 of the light source 110 that is in the range of from 45 degrees to 90 degrees.

[0059] Thus, basically, the invention provides a method that analyzes an oral reflection image looking at the size of the bright spots on the tooth surfaces, defined as spots with a significantly higher intensity than the surroundings, by using a threshold for this intensity difference, for example. First, tooth surfaces can be segmented out, for example based on a color threshold to discriminate between the teeth and the gums. Then bright spots are discriminated using an intensity threshold and the areas of the bright spots on the tooth surface are determined. When the bright spot areas are below a certain threshold this tooth area can be classified as a tooth covered with plaque.

[0060] Alternatively, more elaborate algorithms may be used such as machine learning algorithms that can separate the typical specular reflection patterns of plaque from those of clean teeth. This can be achieved by training such models on annotated images.

[0061] The hardware of the intra-oral camera system 200 can be optimized for this invention by positioning the light sources 110 to obtain more specular reflections. Light sources 110 can for example be positioned to radiate on the teeth with shallower angles, for example by placing them further away from the camera 120 or by angulating them towards the center of the field of view of the camera 120 on the tooth 130. They might also be placed on for example an extension, such as a spacer, where they would illuminate the field of view mostly from the sides. If the angles are shallow enough the microcolonies could additionally create shadows, which would create an additional different pattern from clean teeth having darker spots instead of lighter spots. Plaque colonies may be recognized by having a bright specular reflection on one side and a darker shadow on the other side. This is best visible if the light source incidence is from one side. Possibly different light sources can be activated for different video frames, to better differentiate plaque 140 from clean surfaces of a tooth 130. Light sources 110 could be switched from different shallow directions, but also for example a switch could be made between shallow2025PF00039

[0062] 7

[0063] and steep direction of the incoming light to become more specific for shadows, as darker spots that are not a shadow would be easily identified in this way.

[0064] A further embodiment that does not need switching but still delivers light input from different positions could be an intra-oral camera system 200 that uses a red, a green and a blue LED at different positions, e.g. two shallow from each side and one steep from the top. Since a multi-color camera like an RGB camera has a red, a green and a blue channel, a single instant image frame would contain the separated information provided by the three light sources.

[0065] Fig. 3 shows a schematic setup of an intra-oral camera system 200 according to an embodiment of the invention. In addition to the sensing head 100 comprising the light source 110 and the camera 120 as described above, the intra-oral camera system 200 comprises a data processing apparatus 210 that is configured for executing the method as described in detail above.

[0066] Fig. 4A shows an image of a clean tooth 130 that is not covered with plaque 140. This is a white light image created with an intra-oral camera. On clean smooth surfaces as shown in Fig. 4A, the specular reflection pattern gives large over-illuminated spots as deviating spots 150 in a distinct pattern depending on the tooth curvature and the shape of the light source 110. The deviating spots 150 deviate in their intensity in the image from its surrounding regions.

[0067] Fig. 4B shows an image of a tooth 130 that is covered with plaque 140. Where plaque 140 is present on the surface of the tooth 130, the deviating spots 150 of the specular reflection pattern are much smaller than shown in Fig. 4A, reflecting the small dimensions of the microcolonies.

[0068] Thus, specular reflection patterns are well visible in intra-oral camera images as overilluminated or high intensity spots on the teeth. On clean surfaces as shown in Fig. 4A, this gives large spots with a predictable pattern based on the light source design and the expected tooth curvatures. In this exemplary image, a light source 110 comprising a plurality of LEDs arranged in a light ring is used, the ring shape of the light source is visible in the reflection pattern on the surface of the tooth. On plaque covered surfaces as shown in Fig. 4B, the specular reflection pattern becomes irregular with smaller high intensity spots, due to the surface structure of the plaque 140.

[0069] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed invention, from a study of the drawings, the disclosure, and the dependent claims.

[0070] In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

[0071] It is to be understood that any of the previous steps described in relation to embodiments and / or training steps described above can be performed by a specific-purpose computer system or2025PF00039

[0072] 8

[0073] general-purpose computer system, or a computer-readable medium, or data carrier system configured to carry out any of the steps described previously. The computer system can include a set of software instructions that can be executed to cause the computer system to perform any of the methods or computer-based functions disclosed herein. The computer system may operate as a standalone device or may be connected, for example using a network, to other computer systems or peripheral devices. In embodiments, a computer system performs logical processing based on digital signals received via an analogue-to-digital converter.

[0074] However, all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussion, it is appreciated that throughout the description, discussions utilizing terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system memories or registers or other such information storage devices. Portions of the present disclosure include processes and instructions that may be embodied in software, firmware, or hardware, and when embodied in software, may be downloaded to reside on and be operated from different platforms used by a variety of operating systems.

[0075] In a networked deployment, the computer system operates in the capacity of a server, or as a client user computer in a server-client user network environment, or as a peer computer system in a peer-to-peer or distributed network environment. The computer system can also be implemented as or incorporated into various devices, such as a server or another type of computer such as a workstation that includes a controller, a stationary computer, a mobile computer, a personal computer (PC), a laptop computer, a tablet computer, or any other machine capable of executing a set of software instructions sequentially or non-sequentially that specify actions to be taken by that machine. The computer system can be incorporated as an integrated system part of a larger system that includes additional devices. In an embodiment, the computer system can be implemented using electronic devices that provide voice, video, or data communication possibilities. Further, while the computer system is illustrated in the singular, the term “system” shall also be taken to include any collection of systems or sub-systems that individually or jointly execute a set or multiple sets, of software instructions to perform one or more computer functions.

[0076] The computer system may also include a processor. The processor executes instructions to implement some, or all aspects of methods and processes described herein. The processor is tangible and non-transitory. As used herein, the term “non-transitory” is to be interpreted not as an eternal characteristic of a state, but as a characteristic of a state that will last for a period. The term “non-transitory” specifically disavows fleeting characteristics such as characteristics of a carrier wave or signal or other forms that exist only transitorily in any place at any time. The processor is an article of manufacture and / or a machine component. The processor is configured to execute software instructions to perform functions as described in the various embodiments herein. The processor may be a general-2025PF00039

[0077] 9

[0078] purpose processor or may be part of an application specific integrated circuit (ASIC). The processor may also be a microprocessor, a microcomputer, a processor chip, a controller, a microcontroller, a digital signal processor (DSP), a state machine, or a programmable logic device, a logical circuit, including a programmable gate array (PGA), such as a field programmable gate array (FPGA), or another type of circuit that includes discrete gate and / or transistor logic. The processor may be a central processing unit (CPU), a graphics processing unit (GPU), or both. Additionally, any processor described herein may include multiple processors, parallel processors, or both. Multiple processors may be included in, or coupled to, a single device or multiple devices. The processor can include one or more internal levels of cache, and a bus controller or bus interface unit to direct interaction with a bus. The term “processor” as used herein encompasses an electronic component able to execute a program or machine executable instruction. References to a computing device comprising “a processor” should be interpreted to include more than one processor or processing core, as in a multi -core processor. A processor may also refer to a collection of processors within a single computer system or distributed among multiple computer systems. The term computing device should also be interpreted to include a collection, or network, of computing devices each including a processor or processors. Programs have software instructions performed by one or multiple processors that may be within the same computing device or which may be distributed across multiple computing devices. Further, the software instructions, when executed by the processor, perform one or more steps of the methods and processes as described herein.

[0079] The computer system can further include a communications interface by way of which the computer system can connect to networks and receive data useful in executing the methods and system set out herein as well as transmitting information to other devices. The computer system further includes a video display unit as an output device by which information can be output, such as a liquid crystal display (UCD), an organic light emitting diode (OUED), a flat panel display, a solid-state display, or a cathode ray tube (CRT), for example. Additionally, the computer system includes an input device, such as a keyboard / virtual keyboard or touch-sensitive input screen or speech input with speech recognition, and a cursor control device, such as a mouse or touch-sensitive input screen or pad. The computer system also optionally includes a disk drive unit, a signal generation device, such as a speaker or remote control, and / or a network interface device.

[0080] The processes and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may also be used with programs in accordance with the teachings herein, or it may prove convenient to construct more specialized apparatus to perform one or more method steps. The structure for a variety of these systems is discussed in the description below. In addition, any programming language that is sufficient for achieving the techniques and implementations of the present disclosure may be used. In addition, the language used in the specification has been principally selected for readability and instructional purposes and may not have been selected to delineate or circumscribe the disclosed subject matter. Accordingly, the present disclosure is intended to be illustrative, and not limiting, of the scope of the concepts discussed herein.2025PF00039

[0081] 10

[0082] In accordance with various embodiments of the present disclosure, the methods described herein may be implemented using a hardware computer system that executes software programs. Further, in an exemplary, non-limited embodiment, implementations can include distributed processing, component / object distributed processing, and parallel processing. Virtual computer system processing may implement one or more of the methods or functionalities as described herein, and a processor described herein may be used to support a virtual processing environment.

[0083] The illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The illustrations are not intended to fully describe all the elements and features of the disclosure described herein. Many other embodiments may be apparent to those of skill in the art upon reviewing the disclosure. Other embodiments may be utilized and derived from the disclosure, such that structural and logical substitutions and changes may be made without departing from the scope of the disclosure. Additionally, the illustrations are merely representational and may not be drawn to scale. Certain proportions within the illustrations may be exaggerated, while other proportions may be minimized. Accordingly, the disclosure and the figures are to be regarded as illustrative rather than restrictive.2025PF00039

[0084] LIST OF REFERENCE SIGNS:

[0085] 100 sensing head

[0086] 110 light source

[0087] 111 central axis of illumination direction 120 camera

[0088] 121 viewing direction

[0089] 130 tooth

[0090] 140 plaque

[0091] 150 deviating spot

[0092] 160 angle

[0093] 200 intraoral camera system

[0094] 210 data processing apparatus

Claims

2025PF0003912CLAIMS:

1. A computer-implemented method for detecting plaque (140) on a tooth (130) using intensity patterns, the method comprising:illuminating (SI 10) a surface of the tooth (130) with a light source (110);receiving (120) an image of the illuminated surface of the tooth (130) with a camera (120); anddetermining (S130) an indication for a presence of plaque (140) on the surface of the tooth (130) based on intensity patterns caused by the illumination of the surface of the tooth (130) with the light source (110).

2. The method according to claim 1, wherein determining an indication for a presence of plaque (140) on the surface of the tooth (130) comprises:analyzing the intensity patterns to determine a plurality of deviating spots (150) in the image, each deviating spot (150) of the plurality of deviating spots (150) having an intensity that differs significantly from an intensity of a region of the image surrounding the deviating spot (150);estimating an area of each deviating spot (150) of the plurality of deviating spots (150); anddetermining the indication for a presence of plaque (140) on the surface of the tooth (130) based on the area of each deviating spot (150) of the plurality of deviating spots (150).

3. The method according to claim 2, wherein the plurality of deviating spots (150) comprises a plurality of bright spots, the plurality of bright spots corresponding to a specular reflection pattern caused by the illumination of the surface of the tooth (130) with the light source (110), and / or wherein the plurality of deviating spots (150) comprises a plurality of dark spots, the plurality of dark spots corresponding to a shadow pattern caused by the illumination of the surface of the tooth (130) with the light source (110).

4. The method according to any of claims 2 or 3, wherein determining a plurality of deviating spots (150) in the image comprises applying a predefined intensity threshold to the image, and wherein the area of a deviating spot (150) of the plurality of deviating spots (150) is defined as an area of a subregion of the image, wherein each pixel in the subregion of the image has an intensity higher or lower than the predefined intensity threshold.2025PF00039135. The method according to any of claims 2 to 4, wherein determining the indication for a presence of plaque (140) on the surface of the tooth (130) comprises comparing an average deviating spot area in a region of the image with a predefined area threshold, and setting the indication for the presence of plaque (140) on the surface of the tooth (130) to positive in case the average deviating spot area is smaller than the predefined area threshold in the region of the image, wherein the average deviating spot area in the region of the image is determined by averaging over the areas of each deviating spot (150) of the plurality of deviating spots (150) in the region of the image.

6. The method according to any of claims 2 to 4, wherein determining the indication for a presence of plaque (140) on the surface of the tooth (140) comprises determining a frequency distribution of the areas of each deviating spot (150) of the plurality of deviating spots (150) in a region of the image, and determining the indication for the presence of plaque (140) on the surface of the tooth (130) in the region based on the frequency distribution.

7. The method according to any of the preceding claims, wherein determining an indication for a presence of plaque (140) on the surface of the tooth (130) comprises determining an indication for the presence of plaque (140) on the surface of the tooth (130) for a plurality of regions of the surface of the tooth (130).

8. The method according to any of the preceding claims, further comprising segmenting the image of the illuminated surface of the tooth (130) to discriminate between the tooth (130) and the gums.

9. The method according to any of the preceding claims, wherein illuminating a surface of the tooth (130) with a light source (110) comprises illuminating the surface of the tooth (130) with a plurality of light sources, each light source (110) of the plurality of light sources having a different central axis of an illumination direction; and wherein each light source (110) of the plurality of light sources has a different wavelength, and wherein the camera (120) is a multi-color camera configured for detecting light of the different wavelength of the plurality of light sources.

10. The method according to any of the preceding claims, wherein a central axis of an illumination direction (111) of the light source (110) and a viewing direction (121) of the camera (120) form an angle (160) in the range of from 45 degrees to 90 degrees.

11. The method according to any of the preceding claims, wherein determining an indication for a presence of plaque (140) on the surface of the tooth (130) comprises utilizing a machine learning algorithm for analyzing the intensity patterns to determine the indication for the presence of plaque (140) on the surface of the tooth (130).2025PF000391412. A data processing apparatus (210) for carrying out the steps of the method according to any one of claims 1 to 11.

13. An intra-oral camera system (200) comprising:the data processing apparatus (210) according to claim 12; anda sensing head (100), wherein the sensing head (100) comprises a light source (110) configured for illuminating the surface of a tooth (130) and a camera (120) configured for receiving an image of the illuminated surface of the tooth (130).

14. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method according to any of claims 1 to 11.

15. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method according to any of claims 1 to 11.

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