The invention relates to a method of and an apparatus for determining the colour of teeth.

Determining the correct colour of a tooth is important for the dentist for many reasons:

a) When making fillings\crowns\bridges\dentures

b) Showing the patient the results after tooth bleaching

c) Classification of enamel\dentin defects

d) Research, for example: quantitative caries classification or tooth colour prevalence in a population.

Most commonly, to determine a tooth colour a dentist looks at the tooth and compares its colour to a colour scale {for example: VITA colour scale). The problem with this method is that the colour matching is subjective, therefore prone to error. Today there are high-tech solutions to this problem such as the: X-Rite

ShadeVision™ System and VITA Easyshade™. These systems rely on expensive specialised equipment. In addition, these systems give a colour output for only one tooth at a time. The X-Rite ShadeVision™ System and VITA Easyshade™ system can give only the average colour of a tooth due to their technical design. They cannot "see" or distinguish between colours on different parts of a tooth.

Viewed from a first aspect, the present invention provides a method of determining the colour of teeth comprising: providing a lip spreader with an integral colour chart positioned on the lip spreader, wherein the colour chart comprises at least three different colours with known characteristics; using the lip spreader to expose the patient's teeth; by virtue of the integral colour chart, locating the colour chart at a predetermined position relative to the teeth; capturing a digital image of the colour chart and teeth of interest, the digital image hence including image colours for the teeth and image colours for the colour chart at a known position relative to the teeth; electronically processing the digital image using the image colour for a selected tooth or tooth area, the image colours for the colour chart, and the known characteristics of the actual colours of the colour chart; and thereby determining the actual colour of the selected tooth or tooth area.

This method is able to determine the true colour of any or all of the patient's anterior teeth objectively and with no expensive equipment. The colour detection resolution allows for accurate colour readings on all parts of a tooth, and not just the average colour, since the image contains image colour information for all parts of the teeth in the image. With present camera technology even cheap cameras have a high enough resolution to capture a detailed image of the teeth's surface. A user (dentist, dental technician, researcher or any individual) can take a picture of teeth together with the lip spreader plus colour chart with, for example, their cell phone camera or any other camera. The method does not require a camera of any particular quality, and does not require any special attention to lighting conditions. Instead, it can be possible to use any image captured by any camera in a well lit area or with the use of the camera's flash. Different cameras detect colours siightly differently. In addition, the camera's sensor is not necessarily stable over time. This means that the same camera might detect the same colour differently when taking a picture at a later time. The colour chart and electronic processing software effectively re-calibrate the camera during processing of each image automatically, solving ail of these problems at once. This is because the electronic processing of the digital image can correct for differences between the image colour and actual colour based on the known characteristics of the actual colours in the colour chart and the colour of the colour chart in the image.

The final steps of the method can be repeated as required to determine the actual colour for multiple teeth or multiple parts of teeth. The colour information can then be:

• Used by the dentist in direct restoration of the teeth

• Used by a researcher

• Used by the dentist directly and inputted into an automated crown

manufacturing machine

· Sent by email to a dental lab that will manufacture the crown\dentures.

• Printed and sent to a dental lab by regular mail.

The colour chart may include a known set of standard colours as defined in any given color space (or coordinate system), such as red- green-blue (RGB), cyan-magenta-yeilow-key(black) (CMYK), or CIELAB. Other colours may also be present, such as white for example. What is important for the invention is that multiple known colours are used enabling the electronic processing to identify and correct any differences between the image colours and the known colours for the colour chart. One preferred technique for correcting the image colours is polynomial regression of the colour values. Two cases may make different yet similar colours on a colour chart be indistinguishable: a) poor lighting, b) automatic image parameters and processing in cameras such as auto exposure and white balance. Customer satisfaction is partially based on product reliability. In order to reduce errors the preferred colour chart should have colours discernable from each other even in dark lighting conditions. Hence, as well as comprising at least three different colours, the colour chart may preferably consist of colours that are easily distinguishable in a digital image, for example colours that are far apart in a given color space (or coordinate system), such as red-green-blue (RGB), cyan-magenta-yellow-key(black) (CMYK), or CIELAB.

It should be understood that natural lighting or lamps in a dental office do not shine pure white light. The light source may contain (in fact usually does contain) tints of green, blue, red, yellow or another colour. Any reference colours (or colour charts) that only contain one or two colours (such as black and white and/or gray) cannot account for this. Such reference colours can only correct the white balance in the image and not the colour the teeth have when viewed under different light sources that emit tints of for example green, blue, red or yellow. This is because a camera's sensor can detect different wavelengths of light (i.e. different colors) with varying accuracy. These systems are not reliable under all lighting conditions. The present invention uses a lip spreader with an integral colour chart containing multiple different colours. This allows the invention to work under almost any lighting conditions.

It is also important to note that contrary to many known methods, it is not necessary for the colour chart to include any tooth colours, as used in known colour matching charts for teeth (the VITA colour scale, for example). In a preferred embodiment therefore, the colour chart does not include such tooth colours.

The colour chart may comprise patches of different colours set out next to each other or in an array or grid with several rows and colours of colour patches. The colour patches may be circles or squares or any other shape suited to automatic image recognition.

The colour chart is provided integrally with the lip spreader. Thus, the lip spreader may have the colour chart printed on it or formed as a part of its structure. This ensures that the colour chart is in a known position for each patient, which improves the accuracy and ease of automation for the colour determining process. Another advantage is that this design does not require patient education of the device or patient cooperation (holding known tooth colour matching charts steadily and in the proper location by hand can be especially difficult for the elderly, handicapped and children). Finally, since the integral colour chart is always the same shape and located in the same position, the design also decreases the image recognition processing time and allows more effective automation of the electronic image processing. This allows the user the get the results as fast as possible.

The preferred embodiment uses a specially created lip spreader. The lip spreader is designed to hold the lips away from the teeth, as with a conventional lip spreader. Preferably, the part of the lip spreader containing or holding the colour chart is located such that it crosses the lips as close as possible to the teeth while in the same time providing a clear view of the teeth. This is important since this design allows the customer to take a close-up picture of the teeth while in the same time keeping the colour chart on the lip spreader in frame. For example, the colour chart may be across an upper arch of the lip spreader.

Preferably, the part of the lip spreader containing the colour chart is arranged to have the same angle facing the camera as the anterior teeth of an average person have. Thus, in preferred embodiments when the lip spreader is in use the part of the lip spreader containing the colour chart is arranged to be at the same angle as the angle of the anterior teeth of an average person, thereby allowing the colour chart to face a camera at the same angle as the anterior teeth The lip spreader and/or colour chart may incorporate a bar code. This enables identification of the image with the particular lip spreader and/or colour chart. A remote processing station or iab can hence easily and/or automatically identify the owner of the image since each dentist may have a different bar code or set of bar codes for their apparatus. The bar code may be any known type of bar code including linear/one-dimensional codes such as the Universal Product Code (UPC) type bar code, matrix/two-dimensional bar codes and other similar machine readable codes.

The material used for the lip spreader and/or colour chart is preferably a plastic that tolerates disinfection with alcohol. Preferably the lip spreader and/or colour chart have a low reflectivity.

In a preferred method the digital image can be sent via e-mail or MMS to an online server that will process the image with special software to determine the colour of selected teeth or tooth areas. This software processing takes a few seconds. The server may then return details of the determined colour(s) to the user, for example by sending an email or MMS back to the customer with the image and information about the tooth colour(s). The software may for example be located on a remote server connected to a cell phone network. Thus, in one preferred embodiment a cell phone is used to transmit the digital image and to receive details of the determined tooth colour(s) after the image processing. A camera on the cell phone may advantageously be used to capture the image of the teeth and colour chart. The interaction with the server may occur via a dedicated telephone number or web address, or via an application running on the phone, which may be a smart phone such as an iPhone™.

The software preferably uses image recognition the locate the colour chart, its individual colour patches, and a bar code, if present. The bar code is used to store information about what batch the lip spreader and colour chart came from. The information from the colour chart is used to transform the colours in the image to their "true" values. Advantageously, the software can be arranged to

automatically identify teeth on the image using edge recognition techniques, and to then determine the colour of each tooth that is identified. This enables the user to be automatically provided with information about the colour of all teeth in the image.

Each time a consumer uses the product, the software may run a quality control check on the colour chart to check for any anomalies. The lip spreader may have a batch number identification, for example incorporated in a bar code, which may be the same bar code as that mentioned above.

Viewed from a second aspect the invention provides an apparatus for determining the colour of teeth comprising: a lip spreader including a colour chart provided integrally with the lip spreader, wherein the colour chart comprises at least three different colours with known characteristics.

The apparatus may also include any feature mentioned above in relation to the method of the invention.

Thus, the colour chart may include a known set of standard colous in a given color space (or coordinate system), such as red-green-blue (RGB), cyan- magenta-yel!ow-key(black) (CMYK), or CIELAB. Other colours may also be present, such as white for example. The colour chart may preferably consist of colours that are far apart in a given color space (or coordinate system), such as red-green-blue (RGB), cyan-magenta-yellow-key(black) (CMYK), or CIELAB. In a preferred embodiment therefore, the colour chart does not include standard tooth colours, such as those found in a VITA tooth colour chart. The lip spreader may have the colour chart printed on it or formed as a part of its structure.

The preferred embodiment comprises a specially created lip spreader with integral colour chart. The lip spreader is designed to hold the lips away from the teeth, as with a conventional iip spreader. Preferably, the part of the lip spreader containing or holding the colour chart is located such that it crosses the lips as close as possible to the teeth while in the same time providing a clear view of the teeth. For example, the colour chart may be across an upper arch of the lip spreader. Preferably, the lip spreader is arranged such that when the lip spreader is in use the part of the lip spreader containing the colour chart is at the same angle as the angle of the anterior teeth of an average person. Hence, in use, the part of the lip spreader containing the colour chart has the same angle facing the camera as the anterior teeth of an average person have.

The lip spreader and/or colour chart may incorporate a bar code. The material used for the lip spreader and/or colour chart is preferably a plastic that tolerates disinfection with alcohol, Preferably the lip spreader and/or colour chart have a low reflectivity.

It will be appreciated from the above that the invention provides an alternative and/or improved method and apparatus for determining the colour of teeth. The colour of all teeth can easily be determined without special equipment. Any camera can be used under virtually any lighting condition, since the colour chart of the invention enables effective self-calibration. The whole process may be automated so that no extra input from the user is necessary. The invention is designed to be so simple to use that a customer needs to only know how to do 3 things: 1 ) Insert the colour chart and lip spreader into the mouth, 2) Take a picture with any digital camera, and 3) Send the image to the remote server (for example using a cell phone and an MMS message). No special training is required and the user can still quickly obtain an accurate indication of the true tooth colour.

Certain preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which:

Figure 1 A shows a schematic of an image of a patient's mouth and teeth with an embodiment of the invention; and

Figure 1 B shows the same image with information about the tooth colour, as added by the electronic processing software. The Figures illustrate the preferred form of the invention wherein the colour chart 1 is integrated with the lip spreader 2. The lip spreader 2 is shown inserted into the patient's mouth 3 and in use to expose the anterior teeth 4.

The upper image, Figure 1A is before image processing by the software. The lower image, Figure 1B is after the processing and contains information about the tooth colour of all the anterior teeth 4, as indicated by the codes A2, A3 and C2.

The colour chart 1 includes multiple colours, 5-13, which are far apart on an RGB scale, in the preferred embodiment the colours are green 5, black 6, yellow 7, blue 8, orange 9, gray 10, purple 11 , white 12 and brown 13, the different colours being illustrated in the Figures by different hatching and shading, it should be noted that the colours of the colour chart used in the Figures are just an example and are not the only colours that may be used in the colour chart of the invention. The colour chart 1 includes a bar code 14. The bar code 14 may contain information about the batch for the lip spreader 2 and colour chart 1, as well as data used to identify the particular Hp spreader 2, so that images can be identified as being from a particular source or a particular dental surgery.

In use, the lip spreader 2 is placed in the mouth 3 to expose a patient's teeth 4. This locates the colour chart 1 at a predetermined position relative to the teeth 4. A digital image is taken using a digital camera, and this shows the colour chart 1 and teeth 4 of interest, as in Figure 1 A. The digital image is sent to a server, e.g. via MS or e-mail, where it is electronically processed. The software uses image recognition the locate the colour chart 1 and the bar code 14. The information from the known characteristics of the colour chart 1 is used to transform the colours in the image to their "true" values. The software automatically identifies teeth on the image using edge recognition techniques, and then determines the colour of each tooth that is identified. The user is then automatically provided with information about the colour of all teeth in the image, as shown in Figure 1 B.