Three-dimensional dental scanning method

Abstract

To solve the following problem, in which scanning a cast dental model may result in missing crucial areas of detail which may be more readily visible in the dental impression, for example, areas of detail in the interproximal regions and the retracted gingival sulcus around a crown preparation may not be captured accurately, conversely, regions which may be difficult to accurately scan in a dental impression may be more readily visible in the cast model.SOLUTION: A three-dimensional scanning method includes the steps of: a region for replacement in a first point cloud of a dental object; and patching the region for replacement with a corresponding region from a second point cloud of a dental object.SELECTED DRAWING: Figure 12

Description

[Technical field]

[0001] The present invention relates to a 3D dental scanning method for scanning dental objects. [Background technology]

[0002] In a wide range of applications, it is desirable to accurately capture three-dimensional (3D) models of a patient's intra-oral structures (i.e., teeth and gums). For example, such 3D models are useful in the manufacture of dental prostheses or implants, where a laboratory may use computer-aided design (CAD) software to design such prostheses based on the 3D models and then manufacture the prostheses or implants. As such, it is highly desirable that the captured 3D model accurately reflect the patient's intra-oral structures and that the manufactured prostheses or implants properly fit the patient.

[0003] In a typical workflow, a dentist takes a dental impression of a patient's intraoral structures at an oral surgery clinic. This is achieved by placing the impression in the patient's mouth and having the patient bite down on it to deform it, creating a negative imprint of the intraoral structures. This impression is then sent (posted) to a dental lab, where a model is made from the impression. The cast is then fixed into a dental scanner, which can move the cast relative to the scanning head to capture the model. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2016 / 161250 [Non-patent literature]

[0005] [Non-Patent Document 1] Richard Hartley and Andrew Zisserman (2003), "Online Chapter: Trifocal Tensors (PDF)", Multiple View Geometry in computer vision, Cambridge University Press, ISBN 978-0-521-54051-3 Summary of the Invention [Problem to be solved by the invention]

[0006] Dental impression materials can be distorted during transportation or storage, for example due to temperature changes, which can lead to difficulties in compromising the accuracy of the resulting cast models and captured 3D models. Furthermore, the process of casting the model can cause deformation of the impression material.

[0007] A further difficulty arises because 3D scanners tend to use pre-programmed motion paths to completely cover the scanned object, but regions of the object may be missed, requiring the operator to manually add scans to cover the missing regions. Thus, training may be required to perform relatively accurate scanning.

[0008] In another typical workflow, an intraoral 3D scanner is placed inside a patient's mouth in a dental surgery and moved around the patient's mouth to capture a 3D model, but such equipment can be prohibitively expensive and lack accuracy.

[0009] It is an object of the present disclosure to overcome the above-mentioned difficulties, as well as other difficulties that will be apparent to one of ordinary skill in the art from the description herein. It is a further object of the present disclosure to provide a cost-effective and accurate 3D scanner for scanning dental objects, such as dental impressions, that does not require specialist skill or training to operate. [Means for solving the problem]

[0010] According to the present invention there is provided an apparatus and method as set out in the accompanying claims. Other features of the invention will become apparent from the dependent claims and the description that follows. According to a first aspect of the present disclosure, there is provided a three-dimensional (3D) dental scanning system for scanning a dental object, the system comprising: a scanning surface configured to support a dental object; a scanning section configured to capture a 3D scan of a dental object; and and a motion section configured to move the scanning surface and the scanning section relative to each other in five axes of motion while maintaining the scanning surface in a substantially horizontal plane.

[0011] The system may comprise a control unit configured to control the operating unit and the scanning unit to obtain a 3D scan of the dental object. The control unit identifying regions of the point cloud of the dental object captured at a level of detail less than a predetermined level of detail; identifying a scan location for capturing the identified area; and and controlling the motion unit to move the scanning plane and the scanning unit to scan the identified area.

[0012] The controller may be configured to generate a 3D model by surfacing the point cloud and uniformly sample the surfaced model to generate a uniformly sampled point cloud. The controller may be configured to identify a nearest point in the point cloud for each point in the uniformly sampled point cloud and, in response to a distance between the point in the uniformly sampled point cloud and the identified nearest point exceeding a threshold distance, flag a point in the uniformly sampled point cloud as being below a predetermined level of detail.

[0013] The controller may be configured to determine an optimal viewing position for each flagged point. The optimal viewing position may be based on an optimal focal length of the scanning component. The optimal viewing position may be based on a normal extending from the flagged point. The controller may be configured to examine each optimal viewing position to determine that the flagged point is not occluded when viewed from the scanning component.

[0014] The controller may be configured to determine that the optimal viewing position is occluded and to adjust the optimal viewing position so that it is an unoccluded position. The optimal viewing position may be adjusted by adjusting an angle of the normal. The optimal viewing position may be adjusted by adjusting a position along the normal. The optimal viewing position may be adjusted iteratively until an unoccluded position is reached. The controller may be configured to rank each optimal viewing position according to the number of flagged points that are visible from it.

[0015] The control unit may be configured to identify regions of the point cloud of the dental object captured at a level of detail less than the predetermined level of detail, identify a scanning position for capturing the identified region, and control the movement unit to move the scanning plane and the scanning unit to scan the identified region of the second aspect iteratively. Thus, the point cloud of the dental object may be a point cloud obtained by a previous iteration of the process defined herein. The point cloud of the dental object may be an initial point cloud or may be obtained by a pre-programmed scanning sequence.

[0016] The motion unit may include a plurality of actuators configured to move the scanning surface and the scanning unit relative to each other. The control unit may be configured to control the plurality of actuators.

[0017] The five axes of motion may comprise translation in a first horizontal direction, preferably translation of the scan plane, which may be in the X direction. The actuation portion may comprise a first linear actuator configured to translate the scan plane in the X direction.

[0018] The five axes of motion may comprise translation of the scan plane in a second horizontal direction, preferably translation of the scan plane. The second horizontal direction may be perpendicular to the first horizontal direction and may be a Y direction. The actuation portion may comprise a second linear actuator configured to translate the scan plane in the Y direction. The first linear actuator may be configured to translate the second linear actuator in the X direction.

[0019] The five axes of motion may comprise translation, preferably of the scanning part, in a vertical direction. The vertical direction may be the Z direction. The movement part may comprise a vertical linear actuator configured to translate the scanning part in the Z direction. The scanning part may be movable to a vertical position that is substantially in the same horizontal plane as the dental object and / or the scanning surface. A lower end of the vertical linear actuator may extend to a position in the same horizontal plane as the dental object and / or the scanning surface or below.

[0020] The five axes of motion may comprise a rotation of the scan plane. The rotation of the scan plane may be a rotation about a substantially vertical axis perpendicular to the plane of the scan plane. The motion unit may comprise a rotational actuator for rotating the scan plane.

[0021] The five axes of motion may include tilt of the scanning part. The motion part may include a tilt actuator configured to tilt the scanning part. The tilt actuator may be configured to change the pitch of the scanning part. The tilt actuator may be configured to tilt the scanning part about a substantially horizontal axis. The substantially horizontal axis may be located below the scanning part.

[0022] The actuator may be configured to allow freedom of movement of the scanning unit relative to the center of the scanning plane. The actuators may be independently operable. The scanning plane and the scanning unit may be in a fixed relationship, preferably such that the center of the scanning plane is held in the center of the view of the scanning unit, but may not be held in a fixed relationship.

[0023] The scanning unit may comprise a projector configured to project a structured light pattern onto the dental object. The scanning unit may comprise a camera, preferably two cameras. The cameras may be arranged on the same horizontal plane.

[0024] The scanning unit may comprise a projector configured to project a structured light pattern onto the dental object. The scanning unit may comprise a camera, preferably two cameras. A first of the two cameras and the projector may be connected by a first notional line. A second of the two cameras and the projector may be connected by a second notional line. The first and second notional lines may be non-colinear. The first and second notional lines may be orthogonal. The first of the two cameras and the projector may be arranged in the same horizontal plane. The second of the two cameras and the projector may be arranged in the same vertical plane. The two cameras and the projector may be arranged in an L-shape, with the projector being arranged at the vertex of the L.

[0025] The scanning unit may be configured to operate in a first mode in which a first camera and a projector are activated. The first camera and the projector may form a stereo pair having a first baseline extending therebetween. In the first mode, the projector may project a structured light pattern orthogonal to the first baseline. The first mode may be referred to herein as a horizontal mode. The first baseline may be a horizontal baseline.

[0026] The scanning unit may be configured to operate in a second mode in which a second camera and a projector are activated. The second camera and the projector may form a stereo pair having a second baseline extending therebetween. In the second mode, the projector may project a structured light pattern orthogonal to the second baseline. The second mode may be referred to herein as a vertical mode. The second baseline may be a vertical baseline.

[0027] The scanning unit may be configured to operate in a third mode in which the first camera, the second camera, and the projector are activated. The first camera and the second camera may form a stereo pair having a third baseline extending therebetween. In the third mode, the projector may project a structured light pattern orthogonal to the third baseline. The third mode may be referred to herein as a diagonal mode. The third baseline may be a diagonal baseline.

[0028] The scanning unit may be configured to operate in a trifocal mode, where the first camera, the second camera, and the projector are activated and each of the first camera, the second camera, and the projector form an opticcentre. The system may be configured to determine the trifocal tensor in the trifocal mode.

[0029] The scanning portion may be selectively operable in a horizontal mode and a vertical mode. The scanning device may include a housing having a scanning surface, a scanning portion, and an operating portion. The scanning surface may be substantially planar. The scanning system may not comprise a fixing means for fixing the dental object to the scanning surface.

[0030] The scanning surface may include a high friction surface to hold the dental object in place during movement (operation) of the scanning surface. In some examples, the elements of the system or parts thereof may be located remotely from each other and connected by a suitable communication medium. For example, the elements or parts may be connected through a network connection. The network connection may comprise one or more of a local area network (LAN), a wide area network (WAN), leased lines, or the Internet. The network connection may comprise wired and / or wireless links. In other examples, the elements may be linked by a wired communication protocol, such as a USB link or a FireWire link.

[0031] The system may comprise a scanning device and a controller operable to control the scanning device. The scanning device may comprise a scanning surface, a scanning portion, and a motion portion. According to a second aspect of the present disclosure, there is provided a three-dimensional (3D) scanning method comprising capturing a 3D scan of a dental object by using a 3D dental scanning system as defined in the first aspect.

[0032] 3D scanning methods include: Identifying regions of the point cloud of the dental object that are captured with a level of detail less than a predetermined level of detail; identifying a scan location for capturing the identified area; and The method may further include a step of controlling the operation unit to move the scanning surface and the scanning unit and scan the identified area.

[0033] The method may comprise generating a 3D model by surfacing the point cloud, and uniformly sampling the surfaced model to generate a uniformly sampled point cloud.

[0034] The method comprises: for each point in the uniformly sampled point cloud, identifying a closest point in the point cloud; and flagging a point in the uniformly sampled point cloud as being below a predetermined level of detail if a distance between the point in the uniformly sampled point cloud and the identified closest point exceeds a threshold distance.

[0035] The method may comprise determining an optimum viewing position for each flagged point. The optimum viewing position may be based on an optimum focal length of the scanning unit. The optimum viewing position may be based on a normal extending from the flagged point.

[0036] The method may comprise examining each optimal viewing position to determine that the flagged points are not occluded when viewed from the scanning portion. The method may comprise ray casting.

[0037] The method may comprise determining that the optimal viewing position is occluded and adjusting the optimal viewing position to reach an unoccluded position. The optimal viewing position may be adjusted by adjusting an angle of the normal. The optimal viewing position may be adjusted by adjusting a position along the normal. The optimal viewing position may be adjusted iteratively until an unoccluded position is reached.

[0038] The method may comprise ranking each optimal viewing position according to the number of flagged points that are visible from it. The method of the second aspect may be performed iteratively, so that the point cloud of the dental object may be a point cloud obtained by a previous iteration of the method.

[0039] The point cloud of the dental object may be an initial point cloud or may be obtained by a pre-programmed scan sequence. According to a third aspect of the present disclosure, identifying an area for replacement in a first point cloud of the dental object; and and patching the areas for replacement with corresponding areas from a second point cloud of the dental object.

[0040] One of the first and second clouds of points may be a cloud of points of a dental impression material, and the other of the first and second clouds of points may be a cloud of points of a cast from the dental impression material.

[0041] The method may comprise surfacing the first point cloud, and uniformly sampling the surfaced model to generate a uniformly sampled point cloud. The method comprises: identifying a closest point in the first cloud of points to each point in the uniformly sampled cloud of points; and flagging a point in the uniformly sampled point cloud for replacement if a distance between the point in the uniformly sampled point cloud and the identified closest point exceeds a threshold distance.

[0042] The method may comprise inverting and aligning the second cloud of points with the first cloud of points. The method may comprise determining a closest point in the uniformly sampled point cloud to each point in the flipped and aligned (flipped and aligned) point cloud of the impression material point cloud, and in response to the determined closest point being a point flagged for replacement, adding the point to the temporary point cloud.

[0043] The method may comprise editing the temporary point cloud to include neighbouring points of the second point cloud. The method may comprise clustering the temporary point cloud to form a plurality of patches. The method may comprise aligning each patch to the first point cloud.

[0044] The method of the third aspect may be executable by the three-dimensional (3D) dental scanning system of the first aspect. According to a fourth aspect of the present invention there is provided a computer readable storage medium comprising instructions which, when executed by a computer, cause the computer to perform any of the methods defined herein. The computer readable storage medium may be tangible and / or non-transitory.

[0045] According to a fifth aspect of the present invention there is provided a computer program product comprising instructions which, when executed by a computer, cause the computer to perform any of the methods defined herein.

[0046] The invention also extends to a computing device having a memory and a processor configured to carry out any of the methods disclosed herein. For a better understanding of the invention and to show how embodiments thereof may be carried into effect, reference will now be made, by way of example, to the accompanying perspective drawings in which: FIG. [Brief description of the drawings]

[0047] [Figure 1] 1 is a schematic block diagram of an exemplary 3D dental scanning system. [Diagram 2] FIG. 2 is a perspective view of an exemplary scanning device of a 3D dental scanner. [Diagram 3] 3 is a perspective view of the exemplary scanning device of FIG. 2 with a portion of the housing removed to reveal the interior of the scanner. [Figure 4] FIG. 4 is a top cross-sectional view of the exemplary scanning device of FIGS. [Diagram 5] FIG. 5 is a cross-sectional side view of the exemplary scanning device of FIGS. [Figure 6] FIG. 2 is a side view through a door of an exemplary scanning device in use. [Figure 7] FIG. 7 is a perspective view of a first exemplary scanning portion of the exemplary 3D dental scanner of FIGS. 1-6. [Figure 8A] FIG. 7 is a perspective view of a second exemplary scanning portion of the exemplary 3D dental scanner of FIGS. 1-6. [Figure 8B] FIG. 7 is a perspective view of a second exemplary scanning portion of the exemplary 3D dental scanner of FIGS. 1-6. [Figure 9] 4 is a schematic flow chart of a first exemplary scanning method. [Figure 10] 10 is a schematic flow chart illustrating in further detail the first exemplary scanning method of FIG. 9; [Figure 11] 10 is a schematic flow chart illustrating in further detail the first exemplary scanning method of FIG. 9; [Figure 12] 10 is a schematic flow chart showing a second example scanning method. [Figure 13] 13 is a schematic flow chart illustrating in further detail the second example scanning method of FIG. 12; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] In the drawings, corresponding reference characters indicate corresponding components. Those skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to enhance an understanding of the various illustrative embodiments. Also, common but well-understood elements that are useful or necessary in commercially feasible embodiments are often not depicted so as to not obscure too much the view of these various embodiments.

[0049] In summary, embodiments of the present disclosure provide a 3D dental scanner for scanning a dental object, where the scanner provides 5-axis relative motion between the dental object and a scanning unit while holding the dental object in a substantially horizontal plane. As a result, no clamps, jigs, or other fixturing mechanisms are required to hold the dental object in place. This allows accurate scanning of dental objects, such as dental impressions, that would be deformed if clamped.

[0050] 1 to 6 show a 3D dental scanning system 1 according to one embodiment of the present disclosure. The 3D dental scanning system 1 includes a scanning device 100 and a control device 200. The scanning device 100 is shown in detail in Figures 2 to 5. The scanning device 100 comprises a housing 110 which holds and supports the other components of the scanning device 100. In the example shown, the housing 110 takes the form of a substantially cubic housing having a bottom wall 111, a top wall 112, and four substantially vertical side walls 113a to 113d. The front wall 113a of the side walls 113 comprises a door 114 for accessing the interior of the housing 110. For example, the door 114 may be a sliding door.

[0051] The dimensions of the housing 110 may be approximately 440 mm in height between the bottom wall 111 and the top wall 112, approximately 580 mm between the left and right side walls 113b and 113d, and approximately 450 mm between the front wall 113a and the rear wall 113c. These dimensions allow the scanning device 100 to be placed on a desktop or work surface, for example in a dental surgery.

[0052] 3 to 5, the scanning device 100 includes a motion section 120. The motion section 120 may include a number of actuators. The operating portion 120 is configured to include a first linear actuator 121. The first linear actuator 121 is attached to the bottom wall 111, and configured to be movable in a first horizontal direction (hereinafter referred to as the X direction).

[0053] Moreover, the operating unit 120 is configured to include a second linear actuator 122 mounted on the first linear actuator 121. Therefore, the first linear actuator 121 is configured to translate the second linear actuator 122 in the X direction.

[0054] The plate support element 123 is attached to the second linear actuator 122. The plate support element 123 is configured to support a plate 124, which can be best seen in Figure 6. The plate 124 defines a scan surface 124a on which a dental object D can be placed. The plate 124 can take the form of a substantially planar surface that is circular in plan view and disposed in a substantially horizontal plane.

[0055] In one embodiment, the scanning surface 124a comprises a high friction surface. For example, a non-slip mat may be placed on the scanning surface 124a. The high friction surface may comprise, for example, ridges, bumps, or other protrusions that increase friction between the scanning surface 124a and the dental object D placed thereon. Thus, the dental object D remains in position on the scanning surface 124a during the movement of the plate 124.

[0056] The second linear actuator 122 is configured to move the plate support element 123, and thus the plate 124, in a second horizontal direction, which is perpendicular to the first horizontal direction and is hereinafter referred to as the Y direction. Thus, the first linear actuator 121 and the second linear actuator 122 cooperate to translate the plate support element 123 and the plate 124 horizontally in the X and Y directions.

[0057] Furthermore, the operating unit 120 is configured to include a rotary actuator 125. The rotary actuator 125 is configured to rotate the plate 124 in a rotation direction R1 about a vertical axis V. This axis (vertical axis V) may pass through the center of the scanning surface 124a, for example.

[0058] The operating unit 120 further includes a third linear actuator 126. The third linear actuator 126 is attached vertically, for example, to the inside of the side wall 113d. The third linear actuator 126 has a scanning unit attachment portion 127, and the scanning unit 130 can be attached to the scanning unit attachment portion 127. The scanning unit 130 will be described in further detail herein. The third linear actuator 126 is configured to move the scanning unit attachment portion 127 in a vertical direction that is substantially perpendicular to the X direction and the Y direction. Hereinafter, the vertical direction (perpendicular direction) may be referred to as the Z direction.

[0059] The third linear actuator 126 is configured to move the scanning unit attachment portion 127 to a position where the scanning unit 130 is in substantially the same horizontal plane as the dental object D. For example, the lower end of the third linear actuator 126 may terminate in approximately the same horizontal plane as the plane of the plate 124 or below the plane of the plate 124. This allows the scanning unit 130 to scan in a substantially horizontal direction, thereby accurately capturing (photographing) the side of the dental object D.

[0060] Further, the operating unit 120 includes a tilt actuator (not shown) configured to tilt the scanning unit mounting unit 127. Thus, the tilt actuator is configured to change the pitch of the scanning unit 130. In particular, as shown by the dotted line in FIG. 5, the scanning unit mounting unit 127 can be moved between a first position and a second position. In the first position, the scanning unit mounting unit 127 is disposed in a vertical plane substantially parallel to the plane of the third linear actuator 126. In the second position, the top of the scanning unit mounting unit 127 is rotated away from the plane of the third linear actuator 126 in a rotation direction R2. Thus, the scanning unit mounting unit 127 is configured to tilt about a horizontal tilt axis T. In one example, the horizontal tilt axis T passes through the bottom of the scanning unit mounting unit 127.

[0061] Thus, the plate 124 and the scanning portion 130 are configured for relative movement in five axes of motion: translation in the X-, Y-, and Z-directions, rotation of the plate 124, and tilt of the scanning portion 130.

[0062] Additionally, the plate 124 and the scanning unit 130 may be configured for independent relative movement; that is, each actuator may be independently actuated. Thus, the plate 124 and the scanning unit 130 are not held in a fixed relationship, such as a relationship in which the center of the plate 124 (and thus the dental object D) is held in the center of the field of view of the scanning unit 130. Thus, the scanning unit 130 has a degree of freedom of movement relative to the center of the plate 124, allowing the scanning unit 130 to be moved to a position offset from the center of the plate 124. This, in turn, may allow for the capture of a region of interest that would not be captured if the scanning unit 130 could only capture an image centered around the center of the plate 124.

[0063] It will be appreciated that the actuators may comprise any suitable mechanism for translating or rotating the plate 124 or the scanning portion 130. For example, the actuators may comprise a drive screw, a piston jack, or a screw jack. In some examples, the actuators are driven by motors. It will be appreciated that in some embodiments, each actuator is driven by a respective motor, while in other embodiments, two or more actuators may be driven by one motor.

[0064] 7, an example of a scanning unit 130 is shown in greater detail. The scanning unit 130 comprises a structured light scanner that includes a projector 131 and a pair of cameras 132,133.

[0065] The projector 131 is configured to project a structured light pattern onto the dental object D. The cameras 132 and 133 are disposed above the projector 131. The cameras 132 and 133 are disposed in the same horizontal plane. Each of the cameras 132 and 133 is disposed at an equal distance from the projector 131. Thus, the lenses of the cameras 132 and 133 and the projector 131 can be connected by an imaginary inverted triangle with a horizontal upper side. The cameras 132 and 133 have angles such that their focal positions converge.

[0066] Returning to Fig. 1, the scanning device further includes a control unit 140. The control unit 140 is configured to control the operation of the scanning unit (scanning device) 130. For example, the control unit 140 is configured to obtain a 3D scan of a dental object by controlling the operation unit 120 and the scanning unit 130.

[0067] The control unit 140 includes a computing element such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an FPGA (Field Programmable Gate Array). The scanning device 100 further comprises storage 150. The storage 150 may temporarily or permanently store any data and / or instructions required for the operation of the scanning device 100. The storage may comprise volatile and / or non-volatile memory including ROM, RAM, EEPROM, solid state drives and hard disk drives.

[0068] In one embodiment, the control unit 140 and the storage 150 may be included in a mini PC 141. The control unit 140 and the storage may also be included in a microcontroller (e.g., Arduino (registered trademark)). For example, the mini PC 141 may control the scanning unit 130 and send control instructions to the microcontroller, which in turn may control the operation of the operating unit 120.

[0069] The scanning device 100 may further include a communication interface 160. The communication interface 160 is configured to receive and transmit data and instructions from the control device 200. For example, the communication interface 160 may include a network interface, such as a wired or wireless network interface. In other examples, the communication interface 160 may include a serial connection, a USB connection, or any other suitable data transmission mechanism.

[0070] 1, the control device 200 includes a control unit 210, a storage 220, a communication interface 230, and a user interface 240. The control unit 210 includes a computing element such as a central processing unit (CPU), a graphics processing unit (GPU), and a field programmable gate array (FPGA). The storage 220 may temporarily or permanently store any data and / or instructions required for the operation of the control device 200. The storage may include volatile and / or non-volatile memory including a ROM, a RAM, an EEPROM, a solid state drive, and a hard disk drive.

[0071] The communications interface 230 is configured to receive and transmit data and instructions from the scanning device 100. For example, the communications interface 230 may comprise a network interface, such as a wired or wireless network interface. In other examples, the communications interface 230 may comprise a serial connection, a USB connection, or any other suitable data transmission mechanism.

[0072] The user interface 240 may take the form of any suitable input and output devices that allow a user to input control instructions to the scanning apparatus 100 and / or view the result model resulting from a scan. For example, the user interface 240 may include one or more of a monitor or other screen, a keyboard, a mouse, and a touch screen interface. The controller 200 may take the form of a desktop or laptop computer.

[0073] In use, the door 114 of the scanning device 100 is opened and a dental object D, such as a cast model or dental impression material, is placed on the plate 124. A dental object scanning routine is then initiated, for example by a user providing appropriate user input via the user interface 240.

[0074] The control unit (controller) 140 then controls the operating unit 120 and the scanning unit 130 to move them to the desired scanning position, while at the same time making the desired portion of the dental object visible to the scanning unit 130 at the desired viewing angle.

[0075] The operating unit 120 can translate the plate 124 in the X direction or the Y direction by operating the first or second linear actuator 121 or 122. The operating unit 120 may also rotate the plate 124 using a rotary actuator 125. Furthermore, the operating unit 120 may translate the scanning unit 130 in the Z direction using a third linear actuator 126, and may tilt the scanning unit 130 using a tilt actuator.

[0076] As the operating unit 120 moves the plate 124 and the scanning unit 130 to a desired scanning position, the projector 131 projects a light pattern onto the dental object while images are captured by one or both of the cameras 132, 133.

[0077] From the captured image or images, a 3D point cloud is derived according to a structured light scanning technique. It will be appreciated that part of the processing of deriving the 3D point cloud from the captured images is performed by controller 140, while further processing may be performed by controller 210.

[0078] The process of controlling the operating unit 120 to position the dental object D and the scanning unit 130 at the desired scanning position may be repeated multiple times to capture scans of the model from multiple desired scanning positions. Point clouds obtained from different scanning positions may be combined to form a point cloud of the dental object D. An example of a scanning method in which multiple scans are captured and combined is described in further detail below with respect to Figures 9 and 10.

[0079] Thus, the motion unit 120 and the scanning unit 130 may be moved relative to one another in five axes of motion. This allows the scanning unit 130 to capture scans from a very wide range of positions, and therefore provide highly detailed and extensive scans. Furthermore, scans can be captured without the need to clamp or otherwise secure the dental object D to the plate 124.

[0080] 8A and 8B show a scanning unit 1130 of the second embodiment. Similar to the scanning unit 130, the scanning unit 1130 includes a projector 1131 and a pair of cameras 1132 and 1133. The first camera 1132 of the two cameras 1132 and 1133 and the projector 1131 are disposed in the same horizontal plane. The second camera 1133 of the two cameras and the projector 1131 are disposed in the same vertical plane. Therefore, the lenses of the two cameras 1132 and 1133 and the projector 1131 are disposed in an assumed "L" shape.

[0081] The scanning unit 1130 is configured to operate in a first mode, which may be referred to herein as a horizontal mode, in which a first camera 1132 and a projector 1131 are used for scanning. Thus, the first camera 1132 and the projector 1131 form a stereo pair having a horizontal baseline extending therebetween. In the horizontal mode, the projector 1131 may project a structured light pattern (e.g., a series of lines) that is orthogonal to the horizontal baseline.

[0082] The scanning unit 1130 is also configured to operate in a second mode, sometimes referred to herein as a vertical mode, in which the second camera 1133 and the projector 1131 are used for scanning. The second camera 1133 and the projector 1131 thus form a stereo pair having a vertical baseline extending therebetween. In the vertical mode, the projector 1131 may project a structured light pattern (e.g., a series of lines) that is orthogonal to the vertical baseline.

[0083] The scanning unit 1130 is also configured to operate in a third mode (sometimes referred to herein as a diagonal mode) in which both the first camera 1132 and the second camera 1133 are used for scanning. In this mode, the first camera 1132 and the second camera 1133 form a stereo pair with a diagonal baseline extending between them. The projector 1131 projects a structured light pattern orthogonal to the diagonal baseline.

[0084] In one embodiment, the scanning unit 1130 is configured to operate in a trifocal mode. In this mode, instead of utilizing a stereo scanning pair with two optical centers, the first camera 1132, the second camera 1133, and the projector 1131 each form an optical center. In the trifocal scanning mode, instead of calculating a fundamental matrix (also called a bifocal tensor) based on two images, a trifocal tensor is calculated that represents the point-wise correspondence between images captured from three optical centers. The trifocal tensor can be calculated, for example, as shown in Non-Patent Document 1, the contents of which are expressly incorporated herein by reference.

[0085] In use, the controller 140 controls the scanning unit 1130 to selectively operate in either a vertical mode or a horizontal mode, thereby enabling the scanning device 100 to accurately scan areas of the dental model that would otherwise be hidden when scanned using the scanning unit 130, thereby improving the scanning coverage and accuracy of the 3D model.

[0086] It will be appreciated that the scanning unit 1130 is an example configuration in which a first imaginary line connecting the first camera 1132 and the projector 1131 and a second imaginary line connecting the second camera 1133 and the projector 1131 are non-collinear. In the example scanning unit 1130, the first imaginary line and the second imaginary line are orthogonal, and the first imaginary line is substantially horizontal. However, in further examples, the scanning unit may include other ways in which the first imaginary line and the second imaginary line are non-collinear. For example, the angle between the lines may be acute or obtuse. Furthermore, the imaginary lines need not coincide with a horizontal and / or vertical plane.

[0087] 9 is a flow chart of an exemplary scanning method that generates a sequence of scan positions to provide a high coverage scan of a dental object. In step S901, an input point cloud of a dental object is analyzed and regions of the object scanned at a level of detail less than a predetermined sufficient level of detail are identified. In step S902, a scan position for capturing the identified regions is determined. In step S903, the operating unit 120 and the scanning unit 130 are moved to a scan position and the identified regions are captured.

[0088] 10 is a diagram illustrating the process of step S901 in more detail. In a first step S1001, the input point cloud is surfaced. This is a process of reconstructing a three-dimensional surface (3D surface) of the dental object based on the points in the point cloud. For example, a Poisson surfacing algorithm is used to generate a surface from the 3D model. This results in a surfaced mesh.

[0089] The surfaced mesh is then sampled at a uniform distance to generate a uniformly sampled point cloud in step S1002. In one example, the sampling distance is 0.5 mm. This distance may be varied, with smaller distances providing greater accuracy at the expense of processing speed.

[0090] Next, in step S1003, for each point in the uniformly sampled point cloud, the closest point in the input point cloud is identified. Then, in step S1004, if the distance between a point in the uniformly sampled point cloud and the identified closest point exceeds a threshold distance, indicating that this region of the input point cloud has not been captured with a sufficient level of detail, each point that exceeds the threshold distance is flagged, for example by changing the color of the point.

[0091] The threshold value is for example 0.3 mm, but as with the sampling distance, smaller or larger distances can be employed. Also, if the nearest point in the input point cloud is a relatively large distance away (e.g., 10 mm or more), that point may be removed from the uniformly sampled point cloud. Such a large distance may indicate an area of ​​the uniformly sampled point cloud where the surfacing of the model is inaccurate and therefore should not be used.

[0092] In one embodiment, the dental model may have unscannable regions, e.g., having black or highly reflective parts. Regions of the uniformly sampled point cloud that correspond to unscannable regions will not have a nearby corresponding point in the input point cloud. So, to avoid repeatedly scanning unscannable regions, a list of all previous scan positions where a scan of the dental object has already been obtained is maintained. Ray casts are performed from each of these previous scan positions, and a check is made to see if a previous view should have already captured the unseen point. If the ray cast indicates that the unseen point was visible from a previous scan position, the point may be determined to be unscannable. In some examples, a point may be determined to be unscannable if there are a predefined number (e.g., 2) previous views that should have captured the point but did not. This avoids discarding an unscannable point due to an abnormal reflectivity in only one view.

[0093] FIG. 11 is a diagram for explaining the process of step S902 in more detail. In the first step S1101, an optimal viewing position is determined for a given flagged point. In one example, the optimal viewing position is determined by first projecting a normal line from the flagged point. The normal line is a line perpendicular to the tangent plane of the flagged point. Then, a point on the normal line that is at a distance from the flagged point that corresponds to the optimal focal length of the scanning unit 130, 1130 is determined to be the optimal viewing position of the flagged point.

[0094] In a second step S1102, the optimal viewing position is verified so that the flagged points are not hidden when viewed from the camera of the scanning unit 130, 1130. For example, the scanning unit is virtually placed at the optimal viewing position, and a ray-cast is performed from the virtual position of the center of the camera to the flagged points.

[0095] If the raycast shows that the camera has a clear line-of-sight to the flagged point, then this camera position is stored in a list of potential scanning unit positions (S1103).

[0096] As mentioned above, it will be appreciated that the scanning unit 1130 may operate in one of a number of modes in which one or more cameras and projectors are operating. Thus, in one example, a clear line of sight from all cameras used in the current scanning mode is required. In a further example, if a clear line of sight is available in one of the scanning modes, the camera positions are stored along with a record of the mode in which a clear line of sight is available. Thus, the scanning method can automatically select the most appropriate scanning mode to capture a particular point. In some examples, a predefined ranking may be defined so that the best available scanning mode is used. For example, if both cameras and projectors have a clear line of sight, the method can select the trifocal or diagonal mode, with the horizontal and vertical modes acting as fallbacks.

[0097] Since the projector is active in all scanning modes, in one embodiment the line of sight from the projector may be determined before the line of sight from any of the cameras, which acts as an effective first filter to avoid computing raycasts to the cameras if the projector is occluded.

[0098] On the other hand, if there is no clear line of sight, the normal angle is iteratively adjusted. For example, the normal angle is adjusted by one degree for each axis to reach a position where the line of sight is ensured (S1104). This traces a cone pattern where a point at the apex of the cone and the camera position form the base of the cone. By gradually increasing the radius of the base of the cone, a clear line of sight can be found. Thus, the method effectively combines a brute force search with optimization based on an ideal position.

[0099] In another example, in the absence of a clear line of sight, the camera position can be iteratively adjusted along the normal and closer or less close to the point than the optimal focal distance, providing another possible means of arriving at a position closer to the ideal position without obstructing the view of the point.

[0100] The adjusted position is then stored in a list of possible scanning position (S1103). In step S1105, the potential scanning position locations are ranked according to the number of flagged points that are visible from them.

[0101] For example, for each candidate location, all flagged points visible from that location are stored. This list of flagged points may then be pruned to remove one or more of the following:

[0102] A point that is not within the 2D screen coordinates of any camera. Points whose 3D normals point away from each camera. Points can be discarded using a threshold angle, such as 70 degrees from the camera.

[0103] Points that are too far away or too close to either camera, based on the camera's stored depth of field parameters. A point that is hidden from the projection of either camera.

[0104] The candidate scan locations are then ranked based on the number of flagged points. In one embodiment, if the list of candidate locations exceeds a predefined threshold size, the list size is reduced by randomly sampling the candidate locations before step S1105 is performed. Random sampling may result in a particular point being missed, but repeated iterations of the algorithm will result in that point being more likely to be captured in a later iteration. The threshold may be, for example, 1000.

[0105] As an example, the ranking may ensure that a particular flagged point is not repeatedly counted once it has appeared in a particular scan, i.e., a point that has already appeared in one scan position does not subsequently contribute to the count of a point that is visible in another lower ranking scan position.

[0106] In one example, a complete list of candidate scan locations may be returned. In another example, the first n views may be returned. In some implementations, a list may be returned that includes scan locations that correspond to a predetermined percentage of the flagged points. The operating unit is then moved to the scan location to scan the identified areas of insufficient level of detail.

[0107] In some embodiments, the method of Figure 9 is performed iteratively, such that the point cloud obtained as the output of one iteration of the method forms the input point cloud for a subsequent iteration of the method. In some examples, an initial point cloud may be obtained by a pre-programmed scanning sequence, which may then form the input point cloud for the method.

[0108] 9-11 may be implemented by the 3D dental scanning system 1. It may be implemented by the controller 200, for example. Another exemplary scanning method will now be described with reference to FIG.

[0109] As mentioned above, a dental impression is a negative imprint of a patient's intra-oral structure from which a dental model may be cast. Scanning a cast dental model may miss important areas of detail that may be more easily seen in a dental impression. For example, detailed areas of the interproximal area and receding gingival sulcus around a crown preparation may not be accurately captured. Conversely, areas that are difficult to accurately scan in a dental impression may be easily seen in a cast model.

[0110] The scanning method allows for the combination of a 3D model obtained by scanning a dental impression (hereinafter, "impression 3D model") with a 3D model obtained by scanning a dental model cast from the impression (hereinafter, "cast 3D model"). However, due to differences between the cast 3D model and the impression 3D model, e.g. due to the model pouring process, it may be inaccurate to simply invert the impression 3D model and combine it with the cast 3D model.

[0111] The method of this example includes a step S1201 of detecting defective regions in a 3D model obtained by scanning a dental model cast from a dental impression material.

[0112] In one embodiment, defective regions are detected in a manner similar to detecting regions scanned with insufficient level of detail in step S901 above. For example, the point cloud of the cast 3D model may be surfaced and then uniformly sampled to generate a uniformly sampled point cloud. Points in the uniformly sampled point cloud that are more than or equal to a threshold distance from the closest point in the cast 3D model point cloud are flagged as defective. In this example, a smaller threshold may be used because there is less risk of large regions of the model being missing during the scanning process. For example, the threshold may be 0.1 mm.

[0113] In a further example, edge detection techniques can be used to identify holes in the point cloud of a casting 3D model. The exemplary method includes step S1202, in which the defect areas are patched with corresponding areas from a 3D model of the dental object obtained from a scan of the dental impression.

[0114] FIG. 13 shows step S1202 in further detail. In a first step S1301, the normals of the impression 3D model are flipped and aligned to the cast 3D model using a global registration algorithm.

[0115] In a second step S1302, the closest point in the uniformly sampled point cloud to each point in the inverted and aligned point cloud of the impression 3D model is identified. If the closest point in the uniformly sampled point cloud is flagged as a defect, the point in the inverted and aligned point cloud of the impression 3D model is added to a new temporary point cloud. This temporary point cloud is thus populated with all points in the inverted and aligned point cloud of the impression 3D model that correspond to the defect area of ​​the cast 3D model.

[0116] In the next step S1303, the temporary point cloud is swollen to include the neighboring points of the impression 3D model. Each point in the inverted and aligned point cloud of the impression 3D model that has a nearest neighbor in the temporary point cloud less than a predetermined distance (e.g. 0.5 mm) is also added to the temporary point cloud.

[0117] In a next step S1304, the temporary point cloud is clustered into a number of smaller point clouds. This may be based on a nearest neighbor search, with an example search criterion being 0.3 mm. It will be appreciated that other clustering algorithms may be applied to the division of the temporary point cloud. Each of the resulting smaller point clouds forms a patch that is applied to the casting 3D model.

[0118] In the next step S1305, each patch is aligned to and incorporated into the cast 3D model, for example an alignment algorithm such as an iterative closest point algorithm may be employed.

[0119] It will be appreciated that the methods of Figures 12 and 13 can similarly be practiced by patching the impression 3D model with a cast 3D model, if desired. In a further example, the methods of Figures 12 and 13 may be applied to combine two scans of different dental objects.

[0120] In one example, the method may be used to combine two impression scans where the impressions are from the same patient. For example, a practicing dentist may take a second impression where it is clear that the first impression did not capture a particular area of ​​the tooth with a sufficient level of detail.

[0121] In another example, the method can be applied to combine two scans of a cast model. For example, a dental laboratory may take a first scan of a cast model. The cast model may then be worked on by the lab, for example to fit a prosthesis to it. As the cast model is handled in the process of preparing the prosthesis, small damage may occur to areas of the model, especially areas not in close proximity to the prosthesis. It may therefore be desirable to combine the first scan of the cast model with a subsequent scan, and the method patches the first scan with a second scan of the cast model with the prosthesis.

[0122] In some examples, a region of the model may be marked by a user as a donor region to serve as a region to be patched into another model. For example, the region may be selected via user interface 240. Regions of the model that do not correspond to a donor region or are not within a predetermined distance of a donor region may be cropped from the model prior to applying the methods outlined above.

[0123] 9-11 may be implemented by the 3D dental scanning system 1. For example, it may be implemented by the controller 200. Various modifications or variations may be made to the embodiments described herein. For example, it will be understood that the functions of the controllers of the scanning device 100 and the control device 200 may be interchanged. In other words, in some embodiments, functionality described herein as being performed by the control unit 140 may be performed by the control unit 210, and vice versa. In some embodiments, the functionality of the control unit 200 may be integrated into the scanning device 100, such that a control unit is not required. It will be understood that the shape and configuration of the housing 110 may vary.

[0124] The scanning system and method described herein advantageously allows accurate scanning of a wide range of perspectives of soft materials, such as dental impression materials, without clamping the impression material, which can cause distortion thereof. Moreover, the structure of the scanning system allows for easy installation in a dental operating room.

[0125] Furthermore, the scanning methods described herein can automatically derive high quality models of dental objects with minimal intervention from an operator of the scanning system. Thus, the scanning system can be easily operated with minimal training, for example by a dental nurse or dentist in a surgery. The fact that the scanner can be used with minimal training and with dental impressions can eliminate the need to post dental impressions to a dental lab. Thus, an accurate model of the patient's teeth can be quickly created.

[0126] At least some of the embodiments described herein may be constructed, in part or in whole, using dedicated, special-purpose hardware. Terms such as "component," "module," or "unit" as used herein may comprise, but are not limited to, hardware devices such as circuits in the form of discrete or integrated components, field programmable gate arrays (FPGAs) or application specific integrated circuits (ASICs) that perform specific tasks or provide related functionality. In some examples, the described elements may be configured to reside on tangible, persistent, addressable storage media and may be configured to execute on one or more processors. These functional elements may comprise, in some examples, components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables, such as software components, object-oriented software components, class components, and task components, by way of example only. Although the embodiments are described with reference to components, modules, and units discussed herein, such functional elements may be combined into fewer elements or separated into additional elements. Although various combinations of optional features have been described herein, it will be understood that the described features may be combined in any suitable combination. In particular, features of any one embodiment may be combined with features of any other embodiment, as appropriate, unless such combinations are mutually exclusive. Throughout this specification, the terms "comprising" or "including" mean the inclusion of the specified component(s) but not excluding the presence of other components.

[0127] Attention is directed to all articles and documents in connection with this application that are filed contemporaneously or prior to and published herewith, and the contents of all such articles and documents are incorporated herein by reference.

[0128] All of the features disclosed in this specification (including the accompanying claims, abstract, and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except where at least some of such features and / or steps are mutually exclusive.

[0129] Each feature disclosed in this specification (including the accompanying claims, abstract, and drawings), unless expressly stated otherwise, may be replaced by alternative features serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features.

[0130] The invention is not limited to the details of the foregoing embodiments. The invention extends to any novel or combination of features disclosed in this specification (including the accompanying claims, abstract and drawings), or any novel or combination of method or process steps so disclosed.

Claims

1. A method as a three-dimensional scanning method, the method comprising: identifying a replacement region in a first point cloud of the dental object as a region for replacement; patching the replacement area with a corresponding area from a second point cloud of the dental object; The method comprises:

2. one of the first cloud of points and the second cloud of points is a cloud of points of a dental impression material; the other of the first and second clouds of points is a cloud of points of a cast from the dental impression material; The method of claim 1.

3. The method further comprises: surfacing the first cloud of points and uniformly sampling the surfaced model to generate a uniformly sampled cloud of points; identifying a closest point in the first cloud of points to each point in the uniformly sampled cloud of points; flagging a point in the uniformly sampled point cloud for replacement if the distance between the point in the uniformly sampled point cloud and the identified closest point exceeds a threshold distance; The method according to claim 1 or 2, comprising:

4. The method further comprises: inverting the second cloud of points to align it with the first cloud of points; determining a closest point in the uniformly sampled point cloud to each point in the flipped and aligned point cloud of the second point cloud; in response to determining that the closest point is a point flagged for replacement, adding the point to a temporary point cloud; The method of claim 3 , comprising:

5. The method further comprises editing the temporary point cloud to include neighboring points of the second point cloud. The method according to claim 4.

6. The method further comprises: clustering the temporary point cloud to form a plurality of patches; aligning each of the patches to the first cloud of points; The method of claim 5 , comprising:

7. comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of claims 1 to 6, A computer-readable storage medium.

8. comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of claims 1 to 6, Computer program.

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