3D 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 three-dimensional dental scanning method for scanning dental objects. [Background technology]

[0002] For a wide range of applications, it is desirable to accurately capture three-dimensional (3D) models of a patient's intraoral structures (i.e., teeth and gums). For example, such 3D models are useful for manufacturing dental prostheses and implants, where laboratories use computer-aided design (CAD) software to design and then manufacture such prostheses or implants based on the 3D models. Therefore, it is highly desirable that the captured 3D models accurately reflect the patient's intraoral structures and that the manufactured prostheses and 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 accomplished by placing the impression in the patient's mouth and having the patient bite down on the impression, creating a negative imprint of the intraoral structures. This impression is then posted to a dental lab, where a model is made from the impression. The cast is then fixed to 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 deform during transport or storage, for example, due to temperature changes, which can cause difficulties in compromising the accuracy of the resulting cast model and the captured 3D model. 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, relatively accurate scanning may require training.

[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 devices 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 those skilled 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 scan plane and the scanning section relative to each other in five axes of motion while maintaining the scan plane 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 that are captured at a level of detail less than a predetermined level of detail; identifying a scan location for capturing the identified region; and and controlling the movement unit to move the scanning plane and the scanning unit to scan the identified region.

[0012] The controller may be configured to surface the point cloud to generate a 3D model and uniformly sample the surfaced model to generate a uniformly sampled point cloud. The controller may be configured to identify, for each point in the uniformly sampled point cloud, a nearest point in the 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 the 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 verify 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 unoccluded. The optimal viewing position may be adjusted by adjusting the angle of the normal. The optimal viewing position may be adjusted by adjusting the 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 that have been captured at a level of detail less than the predetermined level of detail, identify scanning positions for capturing the identified regions, and control the operating unit to move the scanning plane and the scanning unit to iteratively scan the identified regions of the second aspect. Thus, the point cloud of the dental object may be a point cloud obtained by a previous iteration of the steps 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 movement unit may include a plurality of actuators configured to move the scanning surface and the scanning unit relative to each other, and 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 unit may comprise a first linear actuator configured to translate the scan plane in the X direction.

[0018] The five axes of motion may include translation of the scan plane in a second horizontal direction, preferably a Y direction. The second horizontal direction may be perpendicular to the first horizontal direction and may be a Y direction. The actuator may include 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 preferably comprise vertical translation of the scanning unit. The vertical direction may be the Z direction. The movement unit may comprise a vertical linear actuator configured to translate the scanning unit in the Z direction. The scanning unit 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 that is in the same horizontal plane as the dental object and / or the scanning surface or below.

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

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

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

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

[0024] The scanning unit may include a projector configured to project a structured light pattern onto the dental object. The scanning unit may include 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 located in the same horizontal plane. The second of the two cameras and the projector may be located in the same vertical plane. The two cameras and the projector may be arranged in an L-shape, with the projector located 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 projector are activated. The second camera and 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 (oblique mode, diagonal mode). The third baseline may be a diagonal baseline.

[0028] The scanning unit may be configured to operate in a trifocal mode in which 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, and 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 that includes 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, elements of the system or parts thereof may be located remotely from one another and connected by a suitable communication medium. For example, the elements or parts may be connected via 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 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 at a level of detail less than a predetermined level of detail; identifying a scan location for capturing the identified region; 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 region.

[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 the 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 the distance between the point in the uniformly sampled point cloud and the identified nearest 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 best viewing position to determine that the flagged points are not occluded when viewed from the scanning unit. The method may comprise ray casting.

[0037] The method may include 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 the angle of the normal. The optimal viewing position may be adjusted by adjusting the 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 scanning 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 area for replacement with a corresponding area from a second point cloud of the dental object.

[0040] One of the first and second point clouds may be a point cloud of a dental impression material, and the other of the first and second point clouds may be a point cloud of a casting made 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 point cloud to each point in the uniformly sampled point cloud; 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.

[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 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 performable 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 present 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 present 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 explanation of the drawings]

[0047] [Figure 1] 1 is a schematic block diagram of an exemplary 3D dental scanning system. [Figure 2] 1 is a perspective view of an exemplary scanning device of a 3D dental scanner. [Figure 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. [Figure 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 the 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 flowchart 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 INVENTION

[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 elements in the figures may be exaggerated relative to other elements to improve 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 not to overly obstruct the view of these various embodiments.

[0049] In summary, embodiments of the present disclosure provide a 3D dental scanner for scanning dental objects, where the scanner provides five axes of 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 fixation mechanisms are required to secure the dental object in place. This allows for 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 includes a housing 110 that 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. Of the side walls 113, the front wall 113a includes 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 113 b and 113 d, and approximately 450 mm between the front wall 113 a and the rear wall 113 c. 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 multiple actuators. The operating section 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] The operating unit 120 is also 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 FIG. 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 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, for example, pass through the center of the scanning surface 124a.

[0058] The operating unit 120 further includes a third linear actuator 126. The third linear actuator 126 is mounted vertically, for example, on the inner side of the side wall 113d. The third linear actuator 126 has a scanning unit mounting portion 127, and a scanning unit 130 can be mounted on the scanning unit mounting 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 mounting portion 127 in a vertical direction that is substantially perpendicular to the X and Y directions. Hereinafter, the vertical direction may be referred to as the Z direction.

[0059] The third linear actuator 126 is configured to move the scanning unit mounting 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] The operating unit 120 further includes a tilt actuator (not shown) configured to tilt the scanning unit mount 127. The tilt actuator is thus configured to change the pitch of the scanning unit 130. In particular, as shown by the dotted line in FIG. 5 , the scanning unit mount 127 can be moved between a first position and a second position. In the first position, the scanning unit mount 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 mount 127 is rotated away from the plane of the third linear actuator 126 in a rotational direction R2. Thus, the scanning unit mount 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 mount 127.

[0061] Therefore, the plate 124 and the scanning unit 130 are configured to move relative to each other in five axes of motion: translation in the X, Y, and Z directions, rotation of the plate 124, and tilt of the scanning unit 130.

[0062] Furthermore, 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 at 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 images 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 a single motor.

[0064] 7, an example of a scanning unit 130 is shown in more 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 camera 132 and 133 is disposed equidistant from the projector 131. Therefore, the lenses of the cameras 132 and 133 and the projector 131 can be connected by an imaginary inverted triangle with a horizontal top side. The cameras 132 and 133 are angled such that their focal positions converge.

[0066] 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 control the operation unit 120 and the scanning unit 130 to obtain a 3D scan of the dental object.

[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). Scanning device 100 further comprises storage 150. Storage 150 may temporarily or permanently store any data and / or instructions necessary for operation of scanning device 100. 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. Alternatively, the control unit 140 and the storage may 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 may then 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 send and receive 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 processing 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 ROM, RAM, EEPROM, a solid state drive, and a hard disk drive.

[0071] The communications interface 230 is configured to transmit and receive 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 commands to the scanning device 100 and / or view the resultant model resulting from the 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 control device 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. The 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 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 the 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] A 3D point cloud is derived from the captured image or images according to structured light scanning techniques. It will be appreciated that part of the processing for 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. Examples of scanning methods in which multiple scans are captured and combined are described in more 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, thus providing 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 arranged in the same horizontal plane. The second camera 1133 of the two cameras and the projector 1131 are arranged in the same vertical plane. Therefore, the lenses of the two cameras 1132 and 1133 and the projector 1131 are arranged 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. The first camera 1132 and the projector 1131 thus form a stereo pair with 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. Thus, the second camera 1133 and the projector 1131 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 trifocal mode. In this mode, rather than using 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 trifocal scanning mode, rather than calculating a fundamental matrix (also called a bifocal tensor) based on two images, a trifocal tensor is calculated, which represents the point-wise correspondence between images captured from three optical centers. The trifocal tensor can be calculated, for example, as described 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, allowing 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 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 be configured in 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 an acute angle or an obtuse angle. 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 region is determined. In step S903, the operating unit 120 and the scanning unit 130 are moved to a scan position and the identified region is captured.

[0088] FIG. 10 is a diagram illustrating the process of step S901 in more detail. In the 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 the surface from the 3D model. This results in a surfaced mesh.

[0089] Next, in step S1002, the surfaced mesh is sampled at a uniform distance to generate a uniformly sampled point cloud. 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. Next, in step S1004, if the distance between a point in the uniformly sampled point cloud and the identified nearest point exceeds a threshold distance, it indicates 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 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 (e.g., 10 mm or more) apart, that point may be removed from the uniformly sampled point cloud. Such large distances may indicate areas of the uniformly sampled point cloud where the model surfacing is inaccurate and therefore should not be used.

[0092] In one embodiment, the dental model may have unscannable regions, e.g., black or highly reflective areas. Regions of the uniformly sampled point cloud corresponding to the unscannable regions will have no nearby corresponding points in the input point cloud. Therefore, to avoid repeatedly scanning unscannable regions, a list of all previous scan positions from which scans of the dental object have 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 predetermined number (e.g., two) previous views that should have captured the point but did not. This avoids discarding an unscannable point due to an anomalous 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 (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 results show that the camera has a clear line-of-sight to the flagged point, this camera position is stored in a list of candidate scanning unit positions (S1103).

[0096] As noted above, it will be appreciated that the scanning unit 1130 may operate in one of several modes, with one or more cameras and projectors 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's position is 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 predetermined 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 trifocal or diagonal mode, with horizontal and vertical modes serving 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 camera, which acts as an efficient first filter to avoid computing raycasts to the camera if the projector is occluded.

[0098] On the other hand, if there is no clear line of sight, the normal angle is adjusted iteratively. For example, by adjusting the normal angle by one degree for each axis, a position where a line of sight can be secured is reached (S1104). This traces a conical pattern in which the 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. Therefore, this method effectively combines brute force search and optimization based on the ideal position.

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

[0100] The adjusted position is then stored in a list of candidate positions for the scanning unit (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 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 predetermined 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 as the algorithm iterates, that point becomes more likely to be captured in later iterations. The threshold may be, for example, 1000.

[0105] As an example, rankings 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 will 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 embodiments, a list comprising scan locations corresponding to a predetermined percentage of the flagged points may be returned. The operating unit is then moved to the scan locations to scan the identified areas of insufficient 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 discussed above, a dental impression is a negative imprint of a patient's intraoral structure, from which a dental model can be cast. Scanning a casted dental model can miss important areas of detail that may be more easily visible in the dental impression. For example, detailed areas of the interproximal region around a crown preparation and a receding gingival sulcus may not be accurately captured. Conversely, areas that are difficult to accurately scan in a dental impression may be easily visible in a cast model.

[0110] This scanning method allows for the combination of a 3D model obtained by scanning a dental impression (hereinafter referred to as an "impression 3D model") and a 3D model obtained by scanning a dental model cast from the impression (hereinafter referred to as a "cast 3D model"). However, due to differences between the cast 3D model and the impression 3D model, for example due to the model pouring process, simply inverting the impression 3D model and combining it with the cast 3D model may be inaccurate.

[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, defect areas are detected in a manner similar to detecting areas scanned with insufficient 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 a threshold distance from the nearest point in the cast 3D model point cloud are flagged as defects. In this example, a smaller threshold may be used because there is less risk of missing large areas of the model 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 scanning the dental impression material.

[0114] FIG. 13 shows step S1202 in more 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, for each point in the inverted and aligned point cloud of the impression 3D model, the closest point in the uniformly sampled point cloud 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 defect areas in 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. For each point in the inverted and aligned point cloud of the impression 3D model, any point that has a nearest neighbor in the temporary point cloud within 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 multiple smaller point clouds. This may be based on a nearest neighbor search, with an example search criteria being 0.3 mm. It will be appreciated that other clustering algorithms may be applied to divide the temporary point cloud. Each of the resulting multiple smaller point clouds forms a patch that is applied to the cast 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 can be employed.

[0119] It will be appreciated that the methods of Figures 12 and 13 can equally be carried out by patching the impression 3D model with the 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 the cast model. The cast model may then be worked on by the lab, for example, to fit a prosthesis to it. The cast model is handled during the prosthesis preparation process, and small damage may occur to areas of the model, particularly areas not adjacent to the prosthesis. Therefore, it may be desirable to combine the first scan of the cast model with a subsequent scan, and the method involves patching the first scan with a second scan of the cast model with the prosthesis.

[0122] In some examples, a region of a 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 donor regions or are not within a predetermined distance from donor regions may be cropped from the model before 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 scanning device 100 and control device 200 may be interchanged. In other words, in some embodiments, functionality described herein as being performed by control unit 140 may be performed by control unit 210, and vice versa. In some embodiments, the functionality of control unit 200 may be integrated into scanning device 100, eliminating the need for a control unit. It will be understood that the shape and configuration of housing 110 may vary.

[0124] The scanning system and method described herein advantageously allows accurate scanning of a wide range of soft materials, such as dental impression materials, without clamping the impression material, which can cause distortion of the material. Furthermore, the scanning system's design 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 the scanning system operator. Therefore, the scanning system can be easily operated with minimal training, for example, by a dental nurse or dentist in a surgical clinic. The fact that the scanner can be used with minimal training and dental impressions can eliminate the need to post dental impressions to a dental lab. Thus, accurate models of a 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. As used herein, terms such as "component," "module," or "unit" 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 particular tasks or provide related functionality. In some examples, the described elements may be configured to reside on tangible, persistent, addressable storage media and configured to execute on one or more processors. These functional elements may, in some examples, comprise components, processes, functions, attributes, procedures, subroutines, program code segments, 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. While 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, where appropriate, except where such combinations are mutually exclusive. Throughout this specification, the terms "comprising" or "including" mean the inclusion of the specified component(s) but do not exclude the presence of other components.

[0127] Attention is directed to all articles and documents related to this application, filed contemporaneously or previously hereto, 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 combinations in which 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, and extends to any novel or novel combination of features disclosed in this specification (including the accompanying claims, abstract and drawings), or any novel or novel combination of method or process steps so disclosed.

Claims

1. A method as a three-dimensional scanning method, said method comprising: identifying a replacement region in the first point cloud of the dental object as a region for replacement; patching the replacement region with a corresponding region from a second point cloud of the dental object; It is equipped with 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 point cloud and the second point cloud is a point cloud of a casting made from the dental impression material. method.

2. The method further comprises: surfacing the first point cloud and uniformly sampling the surfaced model to generate a uniformly sampled point cloud; identifying the closest point in the first point cloud to each point in the uniformly sampled point cloud; 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 of claim 1 , comprising:

3. The method further comprises: inverting the second cloud of points to align it with the first cloud of points; determining the closest point in the uniformly sampled point cloud to each point in the flipped and aligned point cloud of the second point cloud; responsive to determining that the closest point is a point flagged for replacement, adding the point to a temporary point cloud; The method of claim 2 , comprising:

4. The method further comprises editing the temporary point cloud to include neighboring points of the second point cloud. The method of claim 3.

5. The method further comprises: clustering the temporary point cloud to form a plurality of patches; aligning each of the patches to the first point cloud; The method of claim 4, comprising:

6. comprising instructions which, when executed by a computer, cause the computer to carry out the method of any one of claims 1 to 5, A computer-readable storage medium.

7. comprising instructions which, when executed by a computer, cause the computer to carry out the method of any one of claims 1 to 5, Computer program.

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