Dental scanning apparatus and method

Abstract

A system, method and device for performing extra-oral scanning of a dental object 200 via projection 102 of a pattern, which may take the form of structured light, 108 onto said object, the pattern be

Description

TECHNICAL FIELD This present invention relates to a system for scanning a scan object. More specifically, the present invention relates to a system for performing freehand three-dimensional scanning of dental scan objects including dental models, impressions, dentures, and the like. The present invention also relates to a device for, and method of scanning a scan object. BACKGROUND In dentistry, it is desirable to capture accurate three-dimensional (3D) data of a patient’s intra-oral structures, such as the teeth and gums. From this data, 3D models can be generated for subsequent use in developing prosthetic parts and for developing surgical or treatment plans. For example, such 3D models find utility in the production of dental prostheses and implants, wherein laboratories will use computer-aided design (CAD) software to design prostheses based on the obtained 3D models, and then subsequently manufacture the prosthesis or implant. Therefore, it is highly desirable that the captured 3D model accurately reflects the patient’s intra-oral structures, so that any manufactured prosthesis or implant properly fits the patient. It is important to accurately determine and record the position of the upper and lower teeth, as well as their relationships relative to one another. Furthermore, a reliable understanding of these intra-oral structures and their interaction is necessary to ensure that prosthetics and implants do not have a negative impact on the patient’s bite. Intra-oral scanners (IOS) have been developed to perform scanning of the upper and lower dental arches without the need to obtain a physical dental impression or cast. IOS devices can be placed in a patient’s mouth and slowly moved around, capturing image data as the IOS device is moved. From this scan data, 3D models or digital impressions can be generated for subsequent use. However, this arrangement can be prone to errors because tracking overtime is required which can lead to areas being missed. Distortion of the dental arches is also a common issue, thereby affecting the reliability of the generated 3D models. In some cases, where data cannot be accurately obtained, IOS devices / systems may generate false data, further reducing the reliability of any subsequently generated 3D models. Alongside the accuracy and reliability limitations, IOS devices and systems are prohibitively expensive and require specialist training to use effectively. Since data can only be obtained intra-orally, the usefulness of the generated 3D models is reduced when trying to understand the dynamic movement of the upper and lower dental arches relative to one another. Furthermore, the use of bulky intra-oral scanners can be uncomfortable for patients. As an alternative, dental impressions can be taken to capture a patient’s intra-oral structures. This is often achieved by placing an impression material, such as silicon, in the patient’s mouth, whereupon the patient bites the impression material and deforms it, producing a negative imprint of the intra-oral structures. Based on the impression, a model may then be cast. The impression and / or cast can then be mounted in a 3D scanning system. The scanning system will move the dental model relative to a camera to obtain 3D structural information relating to intra-oral structures and features. These systems typically use a pre-programmed motion path to fully cover the scanned object and hence, do not offer much adaptability. For example, if a region of an impression or model is not scanned to the required standard, further manual scanning may be required. This is a time-intensive process and requires the operator to be trained to perform accurate scanning. Motorised scanning systems, as may be used in extra-oral scanning systems as referred to above, are typically large and occupy a significant amount of valuable worktop space. Existing systems are generally only able to provide 2-axis, 3-axis, and 5-axis movement, wherein 2-axis movement includes tilting and rotating; 3-axis movement includes tilting, rotating, and movement in the Z axis; and 5-axis movement includes titling, rotating, and movement the X, Y, and Z axes. Typically, these X / Y / Z translations are achieved using eccentric rotation motions and so do not provide true 5-axis movement. The systems may further enable rotation or tilting of a model or impression, but these may not be used in conjunction with other movement operations. These systems are also expensive due to their complexity. Furthermore, existing extra-oral scanning systems can be slow because they rely on mechanical systems to move the dental model. Therefore, there is a desire to provide a faster, less complex, and inexpensive alternative for obtaining high-quality oral scan data. It is an aim of this disclosure to overcome at least some of the above-mentioned deficiencies, and any other difficulties that may be apparent to the skilled reader from the description herein. It is a further aim of the disclosure to provide a more cost-effective and accurate system for performing extra-oral scanning of dental objects, such as dental models, which does not require specialist skills or training to operate. STATEMENT OF INVENTION The present invention aims to address at least some of the shortcomings of existing dental scanning systems. Unlike existing extra-oral dental scanning devices and systems, the system of the present invention is configured to allow a user to orientate the scan object freehand, thereby providing a greater range of motion with more degrees of freedom of movement and manipulation. Further, the system comprises a relatively simple construction and therefore lacks many of the components of current systems, thereby making the system less expensive and easierto maintain. Further, the avoidance of using complex mechanical systems for 3D scanning means that the system is much smaller than other currently available systems. The lack of mechanical elements removes the risk of mechanical breakages occurring that would otherwise put the scanning system out of use until fixed by a trained technician - as such, upkeep and maintenance of the system is simpler. Furthermore, the system described herein may be capable of providing immediate feedback, to a user, regarding the state of a scanned dental model. Display of a 3D model or representation may enable a user to quickly identify which areas of the dental model require further scanning. A further benefit of the invention disclosed herein is that a metal bite frame, or adhesive e.g., Blu Tack ®, is not required to perform a bite scan. Rather, scan objects, are simply held together by hand and scanned, making the process simpler, more accurate, and quicker. Of course, a bite frame or articulator may be used in some situations. According to the present invention, there is provided a system and method, as set forth in the appended claims. Otherfeatures ofthe invention will be apparent from the dependent claims, and the description which follows. According to a first aspect of the disclosure there is provided a system for performing extra-oral scanning of a scan object. The scan object may be a dental cast, impression, prosthesis, or the like. The scan object may also be a bite registration material, denture, or wax. A dental model may include an upper or lower dental arch, or a combination of upper and lower dental arches positioned together to replicate the interaction between the upper and lower dental arches. The system comprises a projecting means. The projecting means is configured to project a pattern onto at least a portion ofthe scan object. The projecting means may be a light, such as light emitting diode (LED), such as a focused LED, or a laser. The projecting means may comprise a filter capable of forming the pattern. The filter may be interchangeable to enable different patterns to be used. Alternatively, the pattern may be formed as part ofthe output signal ofthe projecting means. The system further comprises a first visual recording means. The first visual recording means is configured to obtain surface scan data of at least a portion ofthe scan object, based on the position and orientation ofthe scan object relative to the projected pattern. The first visual recording means may be a camera, or any other suitable recording device capable of obtaining three-dimensional surface scan data from the scan object. The first visual recording means is configured to obtain surface scan data of at least a portion ofthe scan object while the scan object is moved through six degrees of freedom relative to the first visual recording means. The scan object may also be moved through six degrees of freedom relative to the projecting means projecting means. In other words, the first visual recording means and / or the projecting means may be static or in a fixed position relative to the scan object while the scan object is moved. Movement through six degrees of freedom may include movement in the X, Y, and Z directions, in addition to pitch, roll, and yaw rotational movements. The system described herein may enable these movements and rotations to be used in any combination to facilitate the scanning of a scan object. The first recording means may continuously obtain surface scan data during operation while a scan object is being moved and / or manipulated. As referred to herein, movement may refer to the movement or manipulation of a scan object. Movement ofthe scan object may be provided by a user simply holding the scan object and changing its position and / or orientation of relative to the first visual recording means and / or projecting means. Surface scan data may include data relating to the surface topography and features of a scan object. This may include, but may not limited to, the position, orientation, and spacing of teeth, the shape and / or structure of the gums, the extent of the gums relative to the teeth, and other appropriate features that may be necessary to consider for the preparation of prosthetics and / or surgical procedures. In other words, the surface scan data may include any relevant topographical and surface feature information of a scan object. The system further comprises a processor. The processor may be a central processing unit, or any suitable equivalent known to the skilled person in the art. The processor is configured to generate a three-dimensional (3D) model on-the-fly, and / or substantially in real time based on the obtained surface scan data. The 3D model generated by the processor may also be referred to herein as a 3D representation of the scan object. The system may further comprise a memory and / or storage for storing surface scan data obtained by at least the first visual recording means, thereby enabling said stored surface scan data to be retrieved and used by the processor as appropriate, for example, to update a 3D model or representation of a scan object based on obtaining additional surface scan data. For example, the processor may continuously update the generated 3D model or representation based on newly obtained or reobtained surface scan data obtained by at least the first visual recording means. The processor may generate or update the generated 3D model or representation in substantially real-time while scanning is being performed. The system may further comprise a display. The display may be configured to display the generated 3D model. The user may view the display during movement or manipulation of the scan object and use the 3D model to determine which areas of the scan object have not been scanned, or which areas may require further scanning to capture relevant features or details. The display may be updated in substantially real-time to provide the user with up-to-date and accurate feedback. Use of the system described herein may enable a scan object to be scanned quickly, for example, a complete scan of a top or bottom dental arch model may be achieved more quickly than an equivalent scanning operation could be performed when using an intra-oral scanning system or motorised extra-oral scanning system. The system may comprise a single visual recording means and projecting means. A single visual recording means and projecting means arrangement may be used in the same or a substantially similar way to arrangements including more than one visual recording means and a projecting means. This arrangement may further require the projecting means to be calibrated as an inverse visual recording means (or inverse camera) with a known image. The surface scan data obtained from this known image is warped by the relief of the surface that is being scanned and from this, a depth estimation can be made to enable a stereo-matching to be performed. As such, the use of a single visual recording means requires minimal technical differences compared to the use of more than one visual recording means. Deep learning and Al techniques may be further applied to improve the accuracy and robustness of a system comprising only a single visual recording means and a projecting means, such that the quality of surface scan data and the generated 3D models created from this data may have an equivalent accuracy to those obtained if the same scan object were to be scanned using a system including two visual recording means and a projecting means. Advantageously, the system disclosed herein may provide a simple and effective means of scanning a scan object. The system may enable comparatively fast scanning of a scan object compared to existing extra-oral or intra-oral scanning devices. By enabling A scan object to be manipulated by a user, a greater range of movement may be achieved without the need for mechanical means, thereby improving the speed of scan data acquisition and the adaptability of scanning while scanning is taking place. By displaying the generated 3D model or representation, the scan object may be adaptively manipulated during a scanning procedure to improve scan quality. The relatively simple construction of the system may further reduce the cost and size of the system, thereby making it more suitable for use on worktop benches and more widely accessible. A further advantage of the system described herein is that a larger area is captured in each image frame, therefore, fewer frames may be required to complete a scan, thereby making the scanning process faster. In addition, the use of larger scan patches may also improve global alignment and accuracy of the scan data compared to intra-oral scanning systems. The system may further comprise a second visual recording means. The second visual recording means may be configured to obtain surface scan data from the scan object based on the position and orientation of the scan object relative to the projected pattern. The second visual recording means is configured to obtain surface scan data of at least a portion of the scan object while the scan object is moved through six degrees of freedom relative to at least the second visual recording means. The scan object may also be moved through six degrees of freedom relative to the projecting means. In other words, the second visual recording means and / or the projecting means may be static or in a fixed position relative to the scan object while the scan object is moved. The scan object may be moved as described relative to the projecting means and the first and second visual recording means. Movement through six degrees of freedom may include movement in the X, Y, and Z directions, in addition to pitch, roll, and yaw rotational movements. The system described herein may provide accurate tracking of the scan object while the scan object is moved or rotated as in any combination. The second recording means may continuously obtain surface scan data during operation while a scan object is being scanned. Movement and / or manipulation of the scan object may be provided by a user simply holding the scan object and manipulating the position and / or orientation of the scan object relative to at least the second visual recording means and / or projecting means. Surface scan data obtained by the first and second visual recording means may be combined to provide more detailed or more accurate data tracking and scanning of the scan object. Although only the first and second visual recording means are referred to herein, the system may comprise additional visual recording means. The system may comprise a plurality of visual recording means. Advantageously, the use of two separate visual recording means may enable more information to be obtained from the scan object, in the form of surface scan data. Further, the use of at least two visual recording means allows use as a stereo pair, which may enable stereomatching and depth ranging to be applied to the obtained data, thereby improving the accuracy of the obtained surface scan data and 3D models and representations derived from the collected surface scan data. The first and second visual recording means may be arranged to obtain surface scan data from a scan object from different perspectives. In other words, the first and second visual recording means may be positioned at different locations within the system relative to a scan object to be scanned, such that each visual recording means obtains a different view of the scan object. Where additional visual recording means are also included, these may be arranged to give further perspectives of the scan object. Advantageously, obtaining surface scan data from different perspectives may improve the accuracy and / or reliability of the obtained surface scan data. Further, by using surface scan data from different perspectives, more accurate feature tracking may be enabled. Additionally, by obtaining surface scan data from different perspectives, more accurate stereo-matching and depth ranging may be achieved. The processor may be further configured to perform stereo-matching and / or depth ranging based on the surface scan data obtained by the first and second visual recording means. Stereomatching may involve identifying data points within the surface scan data obtained by the first and second visual recording means that correspond to the same 3D point or feature of the scan object. For example, stereo-matching may make use of notable or landmark features to do this. In doing so, the surface scan data obtained by the first and second visual recording means may be more accurately combined. Meanwhile, performing depth ranging may enable determination between the scan object and the first and / or second visual recording means. Depth ranging may also enable the size of features of the scan object to be obtained, thereby providing any generated 3D models with appropriate sizing and scaling. As described herein, stereo-matching and depth-ranging may be achieved by performing stereo-correspondence which can be achieved by using rectified images and a one-dimensional search. Correspondence may be found using deep learning feature matching, or other traditional methos including those commonly used and found in vision libraries, such as OpenCV. One such example is OpenCV Semi-Global Block matching. Non-rectified image searches performed in two-dimensions may also be performed using epipolar constraints to improve accuracy. The projecting means may be calibrated as an inverse camera to improve accuracy in all regions of a scan object such that the first visual recording means, second visual recording means, and projecting means, may be arranged to provide high-quality 3D surface scan data that includes occluded regions of the scan object where only one of the visual recording means or projecting means has a visual line of sight. This arrangement may therefore improve robustness and accuracy of the surface scan data obtained, and the 3D models generated form this data. Advantageously, by performing stereo-matching, more reliable 3D data i.e., 3D models or representations, may be obtained or generated. Stereo-matching may further reduce the likelihood of false recognition of features within a scanned scan object. By performing depth ranging, more accurate sizing and scaling of a scan object may be achieved. This may provide any generated 3D models or representations with the relevant sizing and scaling, thereby improving the accuracy of development of any dental implants or the like that may be produced based on the 3D model or representation. The first visual recording means may be configured to obtain surface scan data from a first field of view. The second visual recording means may be configured to obtain surface scan data from a second field of view. The first field of view and the second field of view may at least partially overlap. The first field of view may extend outwards from the first visual recording means to cover an area in which a scan object is to be moved and / or manipulated. The second field of view may extend outwards from the second visual recording means to cover an area in which a scan object is to be moved and / or manipulated. There may be an area or volume where the first and second fields of view overlap i.e., an overlap region. In this overlap region, each camera may have a different perspective view of the same part of the scan object being imaged. Therefore, stereomatching and / or depth ranging may be performed based on surface scan data obtained by the first and / or second visual recording means in relation to features of the scan object that are within the overlap region. Advantageously, this may enable improved stereo-matching and depth ranging to be achieved. The projecting means may be configured to project a pattern within a substantially cone-shaped volume that extends outwards from the projecting means. In other words, the projecting means may project the pattern within a specifically defined volume and / or onto a defined area. The pattern may cover at least part of a presented surface of the scan object. The presented surface may be the surface of the scan object that faces the projecting means. The relevant volume or area projected through by the projecting means may be sized to accommodate a scan object. The relevant volume or area projected by the projecting means may be larger than the scan object so that the scan object may remain within the relevant volume or area while a user moves and / or manipulates the scan object. The projecting means may be adjustable to change the shape and / or size of the cone-shaped volume or area. For example, the projecting means may be adjusted so that a differently shaped volume i.e., not a cone-shaped volume, is produced instead, for example, a cylindrical volume. Advantageously, this arrangement may ensure that the pattern is only projected within a defined volume so that the pattern primarily covers at least part of the surface of the scan object, and not onto background objects. The first visual recording means may be configured to obtain surface scan data of at least a portion of the scan object from within a first field of view having a substantially cone-shaped volume that extends outwards from the first visual recording means. In other words, the first visual recording means may obtain visual information in the form of surface scan data from the scan object from within a specifically defined volume or area i.e., a first field of view. The first field of view may be sized to fully cover the scan object from the perspective of the first visual recording means. In otherwords, the first field of view may be sized such that the whole of the presented surface of the scan object can be observed by the first visual recording means. The presented surface of the scan object may be the surface of the scan object that faces the first visual recording means. The presented surface may not include surfaces of the scan object that are obscured from the viewpoint of the first visual recording means. The first field of view may cover a volume or area that is larger than the scan object so that the scan object may remain within the first field of view while a user moves and / or manipulates the scan object. Advantageously, the first visual recording means and the first field of view may be arranged to allow relevant surface scan data from the scan object to be captured. The second visual recording means may be configured to obtain surface scan data for at least a portion of the scan object from within a second field of view having a substantially cone-shaped volume that extends outwards from the second visual recording means. In other words, the second visual recording means may obtain visual information in the form of surface scan data from the scan object from within a specifically defined volume or area i.e., a second field of view. The second field of view may be sized to fully cover the scan object from the perspective of the second visual recording means. In otherwords, the second field of view may be sized such that the whole of the presented surface of the scan object can be observed by the second visual recording means. The presented surface of the scan object may be the surface of the scan object that faces the second visual recording means. The presented surface may not include surfaces of the scan object that are obscured from the viewpoint of the second visual recording means. The second field of view may cover a volume or area that is larger than the scan object so that the scan object may remain within the second field of view while a user moves and / or manipulates the scan object. Advantageously, the second visual recording means and the second field of view may be arranged to allow relevant surface scan data from the scan object to be captured. The processor may be configured to process the surface scan data obtained by the first and second recording means using deep learning to provide accurate stereo-matching and depth ranging for the 3D topography of the scan object. As referred to herein, deep learning may include using techniques from at least one of ACVNet, GWC Net, IGEV Net, or other deep learning techniques that support stereovision. Advantageously, the use of deep learning may improve the accuracy of stereo-matching and depth ranging of a scan object, thereby improving the accuracy of the generated 3D model or representation. The first and second visual recording means may be arranged on opposite sides of the projecting means. For example, the first visual recording means may be located on a first side of the projecting means and the second visual recording means may be located on a second side of the projecting means. The first and second visual recording means may be arranged to face in a similar, or substantially the same direction. Advantageously, the relative locations of the first and second visual recording means relative to the projecting means may enable improved stereo-matching and depth ranging. At least the projecting means and first visual recording means may be static elements. The static elements may be configured to not move, translate, rotate, or otherwise change the position or orientation during use. In other words, the system may not comprise any moving elements. Instead, all relative movement between the scan object and the system may be provided by a user holding the scan object and moving or manipulating the scan object. The second visual recording means may also be a static element, as referred to above. In other words, the second visual recording means may not be moveable. Advantageously, this may provide a simpler construction compared to other intra and extra-oral scanning devices and systems. The simpler construction may provide an inexpensive system that is less likely to break due to the absence of mechanical parts. During use, the processor may be configured to continually update the generated three-dimensional model and display the updated three-dimensional model, in response to further surface scan data being obtained by first and / or second recording means. The first and / or second visual recording means may continually obtain surface scan data about a scan object. The processor may continually receive the obtained surface scan data from at least one of the first and / or second visual recording means and incorporate new or re-scanned features into a generated 3D model. The processor may therefore be configured to generate an updated 3D model in substantially real time. The updated 3D model may be displayed, thereby enabling a user to adaptively move the scan object relative to the first and / or second visual recording means to provide comprehensive scanning of the scan object. Advantageously, the processor may generate an up-to-date 3D model based on the most recent surface scan data obtained from the scan object. The up-to-date 3D model may then be used or displayed, the user may utilise this up-to-date model to move and / or manipulate the scan object relative to the first and / or second visual recording means such that areas requiring further scanning may be scanned. Hence, this arrangement may provide a more adaptable scanning system. The pattern may be a point cloud comprising a plurality of points arranged in at least one of a texture, a grid, ora starfield. The pattern may be any appropriate arrangement of a plurality of points or shapes that may enable the first and / or second visual recording means to track features of the 3D model relative to the pattern. It may therefore be preferable to use points having a distinguishing shape that may be easily identified by the first and / or second visual recording means or the processor. Advantageously, the use of a pattern such as the types described above may enable features of a scan object to be accurately identified and / or tracked during the movement of the scan object relative to the at least one of the first and / or second visual recording means and / or the projecting means. Feature identification and tracking may enable a more accurate 3D model or representation to be generated. According to a second aspect of the disclosure there is provided a method of scanning of a scan object. The method comprises the step i) of projecting a pattern onto at least a portion of the surface of a scan object. The pattern may be projected using a projecting means as described above. The pattern may be continuously projected onto at least a portion of the surface of the scan object during a scanning operation. The pattern may be projected statically, in other words, the pattern may not move, rotate, or otherwise change during a scanning operation. The method further comprises the step ii) of obtaining surface scan data of at least a portion of the scan object relative to the projected pattern. Surface scan data may be obtained by a visual recording means. Surface scan data may be obtained by at least one visual recording means. The at least one visual recording means may be a camera. The method further comprises the step iii) of moving the scan object through six degrees of freedom while obtaining surface scan data. Movement through six degrees of freedom may include movement in the X, Y, and Z directions, in addition to pitch, roll, and yaw rotational movements. The method may utilise these movements and rotations in any combination to facilitate the scanning of a scan object. Surface scan data may be obtained continuously while a scan object is being moved and / or manipulated. The method further comprises the step iv) of generating a 3D model of the scan object from the obtained surface scan data. The 3D model generation may be performed by a processor. The processor may receive surface scan data from at least one visual recording means and translate this into a 3D model or representation. Obtained surface scan data may be stored for subsequent use by the processor, for example, to enable subsequent iterations of the 3D model or representation to be generated in response to new or additional surface scan data being obtained and received. The method further comprises the step v) of displaying the generated 3D model of the scan object to provide substantially real-time feedback. The generated 3D model may be displayed via a display. Displaying the generated 3D model may enable a user to adaptively move and / or manipulate a scan object to obtain missing surface scan data, or to re-scan previously scanned areas. Generating the 3D model of the scan object may include involve aligning the surface scan data. This alignment may be performed in substantially real time. This may be achieved by combining local 3D alignment to align the most recently acquired surface scan data to the previously generated 3D model. Alignment may be achieved using a combination of local 3D alignment and global refinement or loop closure. Local 3D alignment may involve performing alignment between the mostly recently acquired surface scan data and the previously generated 3D model. Global refinement or loop closure may correct alignment errors, such as accumulated alignment errors resulting from successive updates to the generated 3D model. This 3D generation and alignment may be achieved using any relevant off the shelf method and the general principles will be known to the skilled person. Advantageously, the method disclosed herein may provide a simple and effective way of scanning a scan object, or the like. The method may enable efficient and comparatively fast scanning of a scan object compared to existing extra- and intra-oral scanning methods. Further, by displaying the generated 3D model, the scan object may be adaptively moved and / or manipulated during a scanning procedure to improve scan quality and the completeness of the scan data that is acquired. The scan object may be moved through six degrees of freedom by a user. Movement through six degrees of freedom by a user may include movement in the X, Y, and Z directions, in addition to pitch, roll, and yaw rotational movements. Movement and / or manipulation of the scan object may be provided by a user simply holding the scan object and manipulating the position and / or orientation of the scan object relative to at least one visual recording means and / or projecting means. For example, the movement may be provided by a user moving their wrist whilst holding the scan object. Advantageously, a greater range of movement can be achieved without the need for mechanical means, thereby improving the speed of scan data acquisition and the adaptability of scanning while scanning is taking place. This arrangement may further reduce the complexity of the scanning system because no mechanical elements are required for moving or manipulating the scan object. The method may include repeating steps ii) to v) until the relevant surface of the scan object has been appropriately captured. As used herein, “appropriately captured” may refer to capturing surface scan data until a specific proportion of the surface of the scan object has been captured e.g., a scan completeness value. Alternatively, this may involve capturing surface scan data until specific features have been captured in a relevant amount of detail so as to be useful. The user may set relevant thresholds before a scanning operation is started, based on the intended use of the surface scan data or the model generated from the obtained surface scan data. The skilled person in the art will appreciate that various parameters and / or metrics may be used to determine whether a scan object has been “appropriately captured”. In other words, the pattern may continue to be projected onto a scan object, and surface scan data may be continuously obtained during the movement of the scan object until a 3D model or representation is generated containing sufficient. Sufficient detail may include obtaining surface scan data in relation to a majority of the scan object, i.e., at least 50% of the model. A sufficient extent of scanning may also be reached when a specific region or regions have been scanned. The skilled person will appreciate that various metrics may be used to determine when adequate scanning has been performed. Advantageously, this may ensure that a sufficient extent of a scan object has been scanned such that the generated 3D model contains the required amount of information. The surface scan data is obtained using at least a first visual recording means. The surface scan data is obtained using at least a second visual recording means. The surface scan data obtained by the first and second recording means is stereo-matched, and depth ranged. The first and second visual recording means may be positioned such that each provides a different perspective view of the scan object, thereby enabling stereo-matching and depth ranging to be performed. Advantageously, by performing stereo-matching, more reliable 3D data i.e., 3D models or representations, may be obtained and / or generated. Stereo-matching may further reduce the likelihood of false recognition of features within a scanned scan object. By performing depth ranging, more accurate sizing and scaling of a scan object may be achieved. This may provide any generated 3D models or representations with the relevant sizing and scaling, thereby improving the accuracy of development of any dental implants or the like that may be produced based on the 3D model or representation. The surface scan data obtained by the first and second recording means may be processed using deep learning to provide accurate stereo-matching and depth ranging for the 3D topography of the scan object. As referred to herein, deep learning may include using techniques from at least one of ACVNet, GWC Net, IGEV Net, or other deep learning techniques that support stereovision. Advantageously, the use of deep learning may improve the accuracy of stereo-matching and depth ranging of a scan object, thereby improving the accuracy of the generated 3D model or representation. The method is performed using the system described herein. Advantageously, this may provide a comparatively cheaper and simpler way of performing extra-oral scanning of scan objects while enabling high-quality 3D models to be generated. The smaller system comprising fewer components may further reduce the size of the system, making it more affordable and requiring less space on a worktop. Any of the above features may be combined in various combinations. According to a third aspect of the disclosure there is provided a device for scanning of a scan object. The device for performing extra-oral scanning of a scan object comprises a projecting means and a first visual recording means. The projecting means is configured to project a pattern onto at least a portion of the scan object. The first visual recording means is configured to obtain surface scan data of at least a portion of the scan object, based on the position and orientation of the scan object relative to the projected pattern. In use, the first visual recording means is configured to obtain surface scan data of at least a portion of the scan object while the scan object is moved through six degrees of freedom relative to at least the first visual recording means. The projecting means and first visual recording means may have the same characteristics, features, capabilities, and relative arrangement as already described above in relation to the system. The device may include other discussed above in relation to the system. For example, the device may further comprise a second visual recording means having the same characteristics, features, capabilities, and relative arrangement as already described above in relation to the system. BRIEF DESCRIPTION OF THE DRAWINGS Features of examples of the present disclosure will become apparent by reference to the following detailed description and drawings, in which like reference numerals correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals or features having a previously described function may or may not be described in connection with other drawings in which they appear. FIG. 1 shows an illustration of an extra-oral scanning device of an extra-oral scanning system. FIG. 2 shows a block diagram of the system for performing extra-oral scanning of a scan object. FIG. 3A shows a top view of the device for performing extra-oral scanning of the scan object, showing the field of projection of a pattern. FIG. 3B shows a top view of the device for performing extra-oral scanning of the scan object, showing the field of view of a first visual recording means. FIG. 3C shows a top view of the device for performing extra-oral scanning of the scan object, showing the field of view of a second visual recording means. FIG. 3D shows top view of the device for performing extra-oral scanning of the scan object, showing the fields of view of the first visual recording means and the second recording means. FIG. 3E shows top view of the device for performing extra-oral scanning of the scan object, showing the field of projection of a pattern alongside fields of view of a first visual recording means and a second recording means. FIG. 4 shows a flow chart of a method of performing extra-oral scanning of the scan object. DETAILED DESCRIPTION Hereinafter, various examples will be described with reference to the accompanying figures. The examples described below may be modified and implemented in various forms. To more clearly describe features of the examples, detailed descriptions of matters well known to those skilled in the art to which the following examples belong will be omitted. In the present disclosure, when an element is described as "connected" or “coupled” with another element, this includes not only “directly connected” or “directly coupled”, but also “connected with another element therebetween” or “coupled with another element therebetween”. In addition, when one element is described to "include" another element, this means that, unless specifically stated otherwise, the one element may further include other elements rather than excluding other elements. Figure 1 shows a perspective view of an illustrated example of an extra-oral scanning device 101 of an extra-oral scanning system 100 for performing extra-oral scanning of a scan object 200, according to the present invention. The system 100 includes a projecting means 102 located in a substantially central position disposed between a first visual recording means 104 and a second visual recording means 106. The projecting means 102, first visual recording means 104, and second recording means 106 are arranged on a baseplate 118. The baseplate 118 provides a fixed support, upon which various other components can be attached. The projecting means 102, first visual recording means 104, and second recording means 106 are orientated in substantially the same direction. The projecting means 102 is configured to project a pattern 108 outwards. The pattern 108 is projected from the projecting means 102 in a substantially cone-shaped volume. The surface of any external object, such as a scan object 200, that is located within the first cone-shaped volume will be at least partially covered by a plurality of points from the pattern 108. In Figure 1, the scan object 200 is held by a user and positioned within the cone-shaped volume of the projected pattern 108. During use of the system 100, the user moves and / or manipulates the scan object 200 through six degrees of freedom of movement whilst keeping the scan object 200 within the pattern 108 projection. As the model 200 is moved within the pattern 108, the first visual recording means 104 and the second recording means 106 obtain surface scan data. This is achieved by tracking features of the scan object 200 relative to the plurality of points of the pattern 108. The first visual recording means 104 and second recording means 106 are arranged to have respective fields of view 110, 112 that overlap, as discussed in more detail in relation to Figures 3A-3E. By providing an overlapping field of view, the surface scan data obtained by each of the first and second recording means 104, 106 can be correlated and used to perform stereo-matching, thereby enabling more accurate tracking of features of the scan object 200, and more accurate depth ranging. Preferably, the pattern 108 is one of a grid, star field or point cloud, or texture. Figure 2 shows a block diagram of the system 100 for performing extra-oral scanning of a scan object 200, according to the present invention. Figure 2 provides an overview showing how the various components of the system 100 are connected. As shown, the system 100 includes the projecting means 102, first visual recording means 104, and second visual recording means 106, which are all connected to a processor 114. The processor 114 is configured to instruct the projecting means 102 to project the pattern 108 onto the scan object 200. The processor 114 is further configured to receive surface scan data from the first and second visual recording means 104,106. The processor is configured to collate the received surface scan data and collate this to generate a 3D representation of the scan object 200. The system 100 further comprises a display 116. The processor 114 is configured to send the generated 3D representation of the scan object 200 to the display 116. The display 116 is configured to display the generated 3D representation of the scan object 200. The generated 3D representation can be displayed to a user. The user can then use the displayed 3D model to identify which areas of the scan object 200 require further scanning to capture necessary details and can adjust the position and / or orientation of the scan object 200 relative to the first and second visual recording means 104, 106 to capture the relevant details. Figure 3A shows a top view of the device 101 for performing extra-oral scanning of the scan object 200, showing the field of projection of the pattern 108. As shown, the projecting means 102 is centrally located within the system 100 between the first and second visual recording means 104, 106 and is configured to project the pattern 108 outwards within a first substantially cone-shaped volume, as shown by the dashed region. The scan object 200 is positioned, by a user, within the first substantially cone-shaped volume to enable the projected pattern 108 to fall across the at least part of the surface of the scan object 200. The projected pattern 108 will remain static while the scan object 200 is moved relative to the projected pattern 108, thereby enabling features of the scan object 200 to be tracked during the movement of the scan object 200 relative to the stationary pattern 108. Figure 3B shows a top view of the device 101 for performing extra-oral scanning of the scan object 200, showing the field of view of the first visual recording means 104. As shown, the first visual recording means 104 is located adjacent to the projecting means 102 i.e., offset to one side. The first visual recording means 104 is configured to obtain image data, such as surface scan data, from a first field of view 110 having a substantially cone-shaped volume, as shown by the dashed region. The scan object 200 is positioned, by a user, within the first field of view 110 to enable the first visual recording means 104 to obtain surface scan data based on the position and orientation of the scan object 200 relative to the projected pattern 108. Figure 3C shows a top view of the device 101 for performing extra-oral scanning of the scan object 200, showing the field of view of the second visual recording means 106. As shown, the second visual recording means 106 is located adjacent to the projecting means 102 i.e., offset to one side. The second visual recording means 106 is configured to obtain image data, such as surface scan data, from a second field of view 112 having a substantially cone-shaped volume, as shown by the dashed region. The scan object 200 is positioned, by a user, within the second field of view 112 to enable the second visual recording means 106 to obtain surface scan data based on the position and orientation of the scan object 200 relative to the projected pattern 108. Figure 3D shows a top view of the device 101 or performing extra-oral scanning of a scan object 200, showing the first and second fields of view 110, 112 of the first and second visual recording means 104, 106, respectively. As shown, the first and second visual recording means 104, 106 are arranged such that the respective first and fields of view 110, 112 overlap with one another at least partially. The first and second visual recording means 104, 106 are arranged such that the respective first and second fields of view 110, 112 overlap in a region that contains the scan object 200. The first and second visual recording means 104, 106 are configured to obtain image data, such as surface scan data, from the first and second fields of view 110, 112 respectively. Since the first and second visual recording means 104, 106 are offset relative to each other and the projecting means 102, the fields of view 110, 112 are provided with different vantage points that enable a combination of matching surface scan data and different surface scan data first to be obtained. For example, both fields of view 110, 112 may enable surface scan data to be captured for a central portion of the scan object 200. Meanwhile, the side portions of the scan object 200 may only be visible from the perspective of one of the first or second visual recording means 104, 106. The use of two visual recording means 104, 106 enables stereo-matching and depth ranging to be used to improve the reliability and accuracy of the surface scan data. Figure 3E shows a top view of the device 101 for performing extra-oral scanning of the scan object 200, showing the overlap between the projected pattern 108, the first field of view 110, and the second field of view 112. As shown, scan object 200 is optimally positioned within an overlap zone between the projected pattern 108 and the first and second fields of view 110, 112 to enable maximum amount and quality of surface scan data to be captured by the first and second visual recording means 104, 106. Figure 4 shows a flow chart of a method of performing extra-oral scanning of the scan object 108. The method 300 shown can be performed using the system 100 described above. The method 300 includes the step 302 of projecting a pattern 108 onto at least a portion of a scan object 200. The pattern 108 is projected onto the scan object 200 by the projecting means 102. The pattern 108 is projected within a substantially cone-shaped volume that at least partially covers the scan object 200. The method 300 further includes the step 304 of obtaining surface scan data related to the scan object 200. The surface scan data is obtained by the first and second visual recording means 104, 106. The first and second visual recording means 104, 106 have second and third substantially cone-shaped a field of view 110, 112, respectively. The first and second substantially cone-shaped fields of view 110, 112 at least partially overlap. By using first and second visual recording means that are spaced apart, surface scan data is obtained from two different perspectives, thereby enabling stereo-matching and ranging to be applied to obtain more accurate feature recognition and tracking. The surface scan data obtained by the first and second visual recording means 104, 106 can be processed for stereo-matching and / or depth ranging using, for example, OpenCV: Depth Map from Stereo Images; 3D or 4D cost volume aggregation and processing methods, and the like. The skilled person will appreciate that various stereo-matching and depth ranging calculations may be usable with the surface scan data obtained by the system described herein. The OpenCV: Depth Map from Stereo Images example operates using the distance between points (x and x’) within an image plane that correspond to the 3D point of interest and their visual recording means centre. The distance (B) between two visual recording means is known, along with the focal length (f). Therefore, the depth of a point within a scene is inversely proportional to the difference in distance of corresponding image points and their visual recording means centres. From this, a disparity value is calculated and the depth (Z) of all pixels within an image can be derived. This calculation uses the following equation: , Bf Disparity = x — x = — The method 300 further includes the step 306 of moving the scan object 200 through six degrees of freedom. During this movement, the pattern 108 is continually projected onto the scan object 200 and surface scan data is obtained by the first and second visual recording means 104, 106. The scan object 200 is moved through six degrees of freedom of movement by a user. The method 300 further includes the step 308 of generating a 3D model, or 3D representation, of the scan object 200 based on the surface scan data. In other words, a 3D representation of the scan object 200 will be developed based on surface scan data obtained by the first and second visual recording means 104, 106 so far. The 3D representation will be updated based on newly acquired surface scan data that is obtained as the scan object 200 is moved by the user. Finally, the method 300 includes the step 310 of displaying the generated 3D model or representation. For example, the generated 3D model or representation can be displayed via a display 116. The display 116 may enable a user to view, in substantially real-time, the current state of the 3D model or representation. Based on the 3D representation of the scan object 200 that is displayed, the user can move and orient the scan object 200 so that additional surface scan data can be obtained for features or areas of the scan object 200that are lacking adequate detail or that have not been covered yet. This enables the 3D representation of the scan object 200 to be updated quickly. Reference in the specification to “an example”, “an embodiment”, “an aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example, but not necessarily in other examples. The various instances of the phrase “in one example” or similar phrases in various places in the specification are not necessarily all referring to the same example. In describing and claiming examples disclosed herein, the singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. As used herein, unless otherwise expressly specified, all numbers such as those expressing values, ranges, amounts or percentages may be read as if prefaced by the word “about”, even if the term does not expressly appear. The term “about” when used herein means +1-10% of the stated value. While several examples have been described in detail, it is to be understood that the disclosed examples may be modified. Therefore, the foregoing description is to be considered non-limiting. It should be understood that the examples described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each example should typically be considered as available for other similar features or aspects in other examples. While one or more examples have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made.

Claims

1. A system for performing extra-oral scanning of a scan object, the system comprising:a projecting means;a first visual recording means;a processor; anda display;wherein the projecting means is configured to project a pattern onto at least a portion of the scan object,wherein the first visual recording means is configured to obtain surface scan data of at least a portion of the scan object, based on the position and orientation of the scan object relative to the projected pattern,wherein the first visual recording means is configured to obtain surface scan data of at least a portion of the scan object while the scan object is moved through six degrees of freedom relative to at least the first visual recording means,wherein the processor is configured to generate a three-dimensional model substantially in real-time based on the obtained surface scan data, andwherein the display is configured to display the generated three-dimensional model.

2. The system of claim 1, wherein the system further comprises a second visual recording means, configured to obtain surface scan data of at least a portion of the scan object, based on the position and orientation of the scan object relative to the projected pattern.

3. The system of claim 2, wherein the first and second visual recording means are arranged to obtain surface scan data from the scan object from different perspectives.

4. The system of claim 2 or claim 3, wherein the processor is further configured to perform stereo-matching and / or ranging based on the surface scan data obtained by the first and second visual recording means.

5. The system of claim 2, wherein the first visual recording means is configured to obtain surface scan data from a first field of view, and the second visual recording means is configuredto obtain surface scan data from a second field of view, wherein the first field of view and the second field of view at least partially overlap.

6. The system of any preceding claim, wherein the projecting means is configured to project a pattern within a substantially cone-shaped volume that extends outwards from the projecting means.

7. The system of any preceding claim, wherein the first visual recording means is configured to obtain surface scan data of at least a portion of the scan object from within a first field of view having a substantially cone-shaped volume that extends outwards from the first visual recording means.

8. The system of claim 2, wherein the second visual recording means is configured to obtain surface scan data for at least a portion of the scan object from within a second field of view having a substantially cone-shaped volume that extends outwards from the second visual recording means.

9. The system of claim 2, wherein the processor is configured to process the surface scan data obtained by the first and second recording means using deep learning to provide accurate stereo-matching and depth ranging for the 3D topography of the scan object.

10. The system of claim 2 or claim 3, wherein the first and second visual recording means are arranged on opposite sides of the projecting means.

11. The system of any preceding claim, wherein at least the projecting means and first visual recording means are static elements, wherein the static elements are configured to not move, translate, rotate, or otherwise change the position or orientation during use.

12. The system of claim 11, wherein the static elements also include the second visual recording means.

13. The system of any preceding claim, wherein during use, the processor is configured to continually update the generated three-dimensional model and display the updated threedimensional model, in response to further surface scan data being obtained by first and / or second recording means.

14. The system of any preceding claim, wherein the pattern is a point cloud comprising a plurality of points arranged in at least one of a texture, a grid, or a star field.

15. A method of scanning of a scan object, comprising the steps of:i) projecting a pattern onto at least a portion of the surface of a scan object;ii) obtaining surface scan data of at least a portion of the scan object relative to the projected pattern;iii) moving the scan object through six degrees of freedom while obtaining surface scan data;iv) generating a 3D model of the scan object from the obtained surface scan data; andv) displaying the generated 3D model of the scan object to provide substantially real time feedback.

16. The method of claim 15, wherein the scan object is moved through six degrees of freedom by a user.

17. The method of claim 15 or claim 16, wherein steps ii) to v) are repeated until the relevant surface of the scan object has been appropriately captured.

18. The method of claim 15, wherein surface scan data is obtained using at least a first visual recording means.

19. The method of claim 18, wherein surface scan data is obtained using at least a second visual recording means.

20. The method of claim 19, wherein the surface scan data obtained by the first and second recording means is stereo matched, and depth ranged.

21. The method of claim 20, wherein the surface scan data obtained by the first and second recording means is processed using deep learning to provide accurate stereo-matching and ranging for the 3D topography of the scan object.5 22. The method of any one of claims 15 to 21, wherein the method is performed using thesystem of any one of claims 1-14.

23. A device for performing extra-oral scanning of a scan object, the device comprising:a projecting means;10 a first visual recording means;wherein the projecting means is configured to project a pattern onto at least a portion of the scan object,wherein the first visual recording means is configured to obtain surface scan data of at least a portion of the scan object, based on the position and orientation of the scan object 15 relative to the projected pattern,wherein, in use, the first visual recording means is configured to obtain surface scan data of at least a portion of the scan object while the scan object is moved through six degrees of freedom relative to at least the first visual recording means.

Images