US 20050055118 A1 Abstract A computer-implemented method generates a computer model of one or more teeth by receiving as input a digital data set of meshes representing the teeth; selecting a curved coordinate system with mappings to and from a 3D space; and generating a function in the curved coordinate system to represent each tooth.
Claims(20) 1. A computer-implemented method for generating a computer model of one or more teeth, comprising:
receiving as input a digital data set of meshes representing the teeth; selecting a curved coordinate system with mappings to and from a 3D space; and generating a function in the curved coordinate system to represent each tooth. 2. The method of 3. The method of 4. The method of 5. The method of 6. The method of 7. The method of 8. The method of 9. The method of V=P(φ,θ)+R * Direction(φ,θ) where V is the corresponding point in three-dimensional (3D) space to (φ,θ, r), P and Direction are a vector functions expressed in terms of φ and θ. 10. The method of 11. The method of 12. The method of 13. The method of 14. The method of 15. The method of 16. The method of 17. The method of 18. The method of 19. The method of 20. The method of Description The present application is a continuation of U.S. application Ser. No. 10/359,998 (Attorney Docket No. 018563-003420US/AT-00075.2), filed on Feb. 7, 2003, which was a continuation of U.S. application Ser. No. 09/576,721 (Attorney Docket No. 18563-003400-AT-00075), filed May 23, 2000 (now U.S. Pat. No. 6,633,789), which was a continuation-in-part of U.S. application Ser. No. 09/506,419 (Attorney Docket No. 018563-004600-AT-00115), filed on Feb. 17, 2000 (now U.S. Pat. No. 6,463,344), the full disclosures of which are incorporated herein by reference. 1. Field of the Invention. The invention relates generally to the field of orthodontics and, more particularly, to computer modeling of teeth. 2. Description of the Background Art. Tooth positioners for finishing orthodontic treatment are described by Kesling in the Other publications describing the fabrication and use of dental positioners include Kleemann and Janssen (1996) Kuroda et al. (1996) U.S. Pat. Nos. 5,533,895; 5,474,448; 5,454,717; 5,447,432; 5,431,562; 5,395,238; 5,368,478; and 5,139,419, assigned to Ormco Corporation, describe methods for manipulating digital images of teeth for designing orthodontic appliances. U.S. Pat. No. 5,011,405 describes a method for digitally imaging a tooth and determining optimum bracket positioning for orthodontic treatment. Laser scanning of a molded tooth to produce a three-dimensional model is described in U.S. Pat. No. 5,338,198. U.S. Pat. No. 5,452,219 describes a method for laser scanning a tooth model and milling a tooth mold. Digital computer manipulation of tooth contours is described in U.S. Pat. Nos. 5,607,305 and 5,587,912. Computerized digital imaging of the jaw is described in U.S. Pat. Nos. 5,342,202 and 5,340,309. Other patents of interest include U.S. Pat. Nos. 5,549,476; 5,382,164; 5,273,429; 4,936,862; 3,860,803; 3,660,900; 5,645,421; 5,055,039; 4,798,534; 4,856,991; 5,035,613; 5,059,118; 5,186,623; and 4,755,139. A computer-implemented method generates a computer model of one or more teeth by receiving as input a digital data set of meshes representing the teeth; selecting a curved coordinate system with mappings to and from a 3D space; and generating a function in the curved coordinate system to represent each tooth. Advantages of the system include one or more of the following. The system reduces the amount of data storage space required for storing and communicating teeth treatment information. By utilizing space more efficiently, the system reduces the cost of the system, improves the responsiveness of the system, and allows additional functionality to be implemented. The system supports fast distance estimation from a point to the tooth's surface. This capability is needed for rapid collision detection. It also supports smoothing of the tooth surface—for noise reduction. Such rapid collision detection may support real-time manipulation of the teeth for treatment. For example, a user moves a tooth, and the tooth stops when it comes in contact with another tooth. The system can also support patching small holes in the model of the teeth that may be generated during the taking of impressions/negative impressions. The system also provides the user with a selectable range of precision in teeth geometry representation. The system also allows visualization to be used to communicate treatment information in a computer-automated orthodontic treatment plan and appliance. The invention generates a realistic model of the patient's teeth without requiring a user to possess in-depth knowledge of parameters associated with patient dental data compression. Additionally, expertise in 3D software and knowledge of computer architecture is no longer needed to process and translate the captured medical data into a realistic computer model rendering and animation. The invention allows teeth plan treatment to be generated and communicated in a simple and efficient manner. It also improves the way a treating clinician performs case presentations by allowing the clinician to express his or her treatment plans more clearly and gives a prospective patients an opportunity to visualize the facial changes associated with the proposed treatment. The invention allows multidisciplinary work teams to deal easily and efficiently with the treatment plan. Another major benefit is the ability to visualize and interact with models and processes without the attendant danger, impracticality, or significantly greater expense that would be encountered in the same environment if it were physical. Thus, money and time are saved while the quality of the treatment plan is enhanced. The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. Systems and methods are provided for modeling teeth in creating a treatment plan. The systems and methods compress data associated with the teeth model to reduce the storage size and transmission time to a treating professional. Based on the treatment plan, the teeth can be incrementally moved using a plurality of discrete appliances, where each appliance successively moves one or more of the patient's teeth by relatively small amounts. Referring now to Referring now to One tool for incrementally repositioning the teeth in a patient's jaw is a set of one or more adjustment appliances. Suitable appliances include any of the known positioners, retainers, or other removable appliances which are used for finishing and maintaining teeth positions in connection with conventional orthodontic treatment. As described below, a plurality of such appliances can be worn by a patient successively to achieve gradual tooth repositioning. A particularly advantageous appliance is the appliance The polymeric appliance A plaster cast of the patient's teeth is obtained by well known techniques, such as those described in Graber, The IDDS is manipulated using a computer having a suitable graphical user interface (GUI) and software appropriate for viewing and modifying the images. More specific aspects of this process will be described in detail below. Individual tooth and other components may be segmented or isolated in the model to permit their individual repositioning or removal from the digital model. After segmenting or isolating the components, the user will often reposition the tooth in the model by following a prescription or other written specification provided by the treating professional. Alternatively, the user may reposition one or more teeth based on a visual appearance or based on rules and algorithms programmed into the computer. Once the user is satisfied, the final teeth arrangement is incorporated into a final digital data set (FDDS) (step The FDDS is used to generate appliances that move the teeth in a specified sequence. First, the centers of each tooth model may be aligned using a number of methods. One method is a standard arch. Then, the teeth models are rotated until their roots are in the proper vertical position. Next, the teeth models are rotated around their vertical axis into the proper orientation. The teeth models are then observed from the side, and translated vertically into their proper vertical position. Finally, the two arches are placed together, and the teeth models moved slightly to ensure that the upper and lower arches properly mesh together. The meshing of the upper and lower arches together is visualized using a collision detection process to highlight the contacting points of the teeth. In step Based on both the IDDS and the FDDS, a plurality of intermediate digital data sets (INTDDSs) are defined to correspond to incrementally adjusted appliances (step Many types of scan data, such as that acquired by an optical scanning system, provide a 3D geometric model (e.g., a triangular surface mesh) of the teeth when acquired. Other scanning techniques, such as the destructive scanning technique described above, provide data in the form of volume elements (“voxels”) that can be converted into a digital geometric model of the tooth surfaces. In one implementation, a marching cubes algorithm is applied to convert the voxels into a mesh, which can undergo a smoothing operation to reduce the jaggedness on the surfaces of the tooth model caused by the marching cubes conversion. One smoothing operation moves individual triangle vertices to positions representing the averages of connected neighborhood vertices to reduce the angles between triangles in the mesh. The triangles in Once a 3D model of the tooth surfaces has been constructed, models of the patient's individual teeth can be derived. In one approach, individual teeth and other components are “cut” using a cutting tool to permit individual repositioning or removal of teeth in or from the digital data. After the components are “freed”, a prescription or other written specification provided by a treating professional is followed to reposition the teeth. Alternatively, the teeth may be repositioned based on the visual appearance or based on rules and algorithms programmed into the computer. Once an acceptable final arrangement has been created, the final tooth arrangement is incorporated into a final digital data set (FDDS). The curve network generation of step In one embodiment of Each tooth is modeled as though it were a deformed ball. The curve network is a network of M meridian lines and N parallel lines. For each meridian line, a plane is selected to contain the meridian line. A series of points representing an intersection between the plane and the triangle mesh modeling a tooth is determined. The series of points represent a curve whose length is then determined. The length of the meridian is divided by N. If M is 20 and N is 20, a 20×20 grid of points is generated, each point being represented in 3-D. In this manner, MxN 3D points can be transmitted in place of the voluminous mesh representation of the teeth. To further reduce the size of the file, the coordinates of each point are stored using integer values rather than floating point values. Alternatively, a second process Next, the process For each half plane, an intersection with the tooth mesh surface is determined (step For each meridian line, a length L is determined and S is determined as a function of L/(N−1) (step The data is saved and sent to a treating professional. To reconstruct a surface, the grid of M by N points is used to generate a surface that closely resembles a tooth. Although 20 is used in one embodiment, other values for M or N can be 30 or 40. To reconstruct a surface from a M*N grid of points, a Hermit spline is specified that maps a rectangle [0, M]*[0, N] in (u, v) parameter plane into 3D space. The Hermit spline is a bicubic 3D function on each [m, m+1]*[n, n+1] square in parameter plane. The Hermit spline F is a smooth continued function on the [0, M]*[0, N] rectangle. When restricted to any [m, m+1]*[n, n+1] unit square, the spline is a bicubic 3D function. The restriction of F onto [m, m+1]*[n, n+1] square is denoted by f (omitting the indices (m, n) that should signify that functions f are different on different squares). The function forms a continuous smooth function on the [0, M]*[0, N] rectangle. To determine a Hermit spline, 3D values F, two derivatives dF/du, dF/dv, and the second mixed derivative d2F/dudv in each nod point (m, n). Thus for each bicubic function f on [m, m+1]*[n, n+1] square, 3D values f, two derivatives df/du, df/dv, and the second mixed derivative d2f/dudv are generated for the four square corners (m, n), (m+1, n), (m, n+1), (m+1, n+1). A unique 3D bicubic function is completely determined by those values. The bicubic functions on the next squares are smoothly connected because the values and derivatives are the same on the common side. The 3D values F, two derivatives dF/du, dF/dv, and the second mixed derivative d2F/dudv in the nod points (m, n) are specified as follows:
After the Hermit spline on the rectangle [0, M]*[0, N] is determined, its values in the more dense grid of points K*L are computed to derive a K*L grid of 3D points. Each of the four points (k, l), (k+1, k), (k, l+1), (k+1, l+1) are associated with two triangles: {(k, I), (k+1, k), (k, l+1)} and {(k, l+1), (k+1, l+1), (k, l)}. In this way, 2*K*L triangles are generated that are then rendered as a reconstructed tooth. A parametric coordinate system is constructed (step The phi theta φ, θ space is represented as a regular grid. The step of the grid is determined using the following formulas
In general, the coordinate system can be specified using other parameters, and should satisfy several requirements: 1. The coordinates should parameterize the entire 3D space, or the 3D space except a small set inside the tooth. 2. Curves phi=const and theta=const should be linear functions of R (rays). The following formula must be used V(x,y,z)=P(phi, theta)+R * Dir(phi, theta). 3. Coordinate system should provide one-to-one mapping so that rays for different phi and theta do not intersect. 4. Solution should account for different types of teeth. 5. Coordinate system should be simple enough to implement inverse transformation, from 3D space to parametric coordinates. It's desired that sets phi=const be planes. In one embodiment, the (φ,θ, r)−>3D transformation is done with the following equations:
P and Direction functions should be selected to minimize the deviation between the original tooth model and the parametric surface. The formulas for P and Direction may be different for incisors and molars. In one embodiment, the formulas are as follows: 1. For incisor teeth
For molars and other types of teeth:
Additionally, a radius R representative of the tooth is constructed (step The process of Next, the process of Since maxR−minR is approximately 5-6 mm for human teeth, the error introduced by this formula is 5/255 mm=0.02 mm. The collision detection or the determination of the intersection line between two surfaces is efficient. During this process, the embodiment computes the elevation of all grid points in one tooth surface over the other one. If two next points in the grid have different sign elevations, then the segment connecting these points intersects the surface. The segment is approximately divided by the surface into parts proportional to the elevation in its ends. The intersection points on the sides of one grid cell may be connected according to the elevation signs in the vertices to generate an intersection line. This embodiment may be speeded up by first computing elevation values for sub-grid (2*2 or 3*3) of points. In some applications, tooth penetration may be estimated as the maximum of (minus) elevation of the grid points having a negative elevation. In other applications the penetration may be estimated as (minus) sum of negative elevation. Also, each negative elevation may be multiplied by the cell area. In the latter case, the result is equivalent to the volume of the 3D bodies intersection. Due to the geometry representation, certain minor collisions with small penetrations (smaller than the treatment precision) may occur and these small collisions are ignored by the system. Given a cell size and the angle between cells, the system can estimate how much a tooth may penetrate into another tooth if all its vertices are outside. The penetration may be significant only if there is a sharp outer angle. When the vertices are found with a small elevation, the mesh in those elevated areas are subdivided. (This is similar to starting with 3*3 mesh, and taking a smaller mesh in close areas only.) When a user drags a tooth model to move it, teeth penetrations are approximately computed, without subdivisions. When a user releases the tooth model, the penetration can be computed more precisely. If a collision exists, the tooth can be moved a small distance to avoid collision. The teeth penetration and “distance” (positive elevation) between two teeth are estimated quickly. When the tooth movements are small, the elevation is approximately proportional to the tooth movement (the functions are locally linear), so a touching position (a position with zero elevation) can be determined quickly. Pseudo-code for the processes of EDF2 ConvertTooth (Tooth, ResolutionPhi, ResolutionTheta) Construct the biggest box that is inside the tooth in the current basis. The box sides must be parallel to coordinate planes (XY, YZ and XY). Move the center of the coordinate system to the center of the box. Use the sides of the bounding box to construct the parameters of the coordinate system.
Sometimes XSize may be made equal to YSize and to min(XSize, YSize). This ensures that the set of 3D points “phi=const” is a plane. -
- For(theta=0; theta<resolutionTheta; theta++)
- For(phi=0; phi<resolutionPhi; phi++)
- 1. Find a point on the tooth surface that intersects with the ray for given u and v.
- 2. Using that point calculate the R value.
- R=||Point−P(φ,θ)||, using formula (1)
- Since the ray may intersect the surface in more than one point, select the point with the largest R to not make the tooth smaller. This situation should not happen at all, if the coordinate system is “good” for the tooth, but it happens sometimes in small cavities or in cut regions.
- 3. Store that value in the table.
- For(phi=0; phi<resolutionPhi; phi++)
- For(theta=0; theta<resolutionTheta; theta++)
The processes of Moreover, for every 3D point P, the system can easily detect whether the point is inside the tooth for a fast collision detection. It can be accomplished in the following way: 1. Convert P into parametric form (phi, theta, R). 2. For the above phi and theta find Rt of the tooth surface, for example, using bilinear interpolation. 3. If R>Rt, the point is outside the tooth. Although the above parametric techniques can be used to compress the storage size of a mesh model of a tooth, other techniques can be used. In another embodiment, decimation operations can be applied to the mesh of teeth to eliminate data points, which improves processing speed. After the smoothing and decimation operation have been performed, an error value is calculated based on the differences between the resulting mesh and the original mesh or the original data, and the error is compared to an acceptable threshold value. The smoothing and decimation operations are applied to the mesh once again if the error does not exceed the acceptable value. The last set of mesh data that satisfies the threshold is stored as the tooth model. Additionally, the mesh model can be simplified by removing unwanted or unnecessary sections of the model to increase data processing speed and enhance the visual display. Unnecessary sections include those not needed for creation of the tooth-repositioning appliance. The removal of these unwanted sections reduces the complexity and size of the digital data set, thus accelerating manipulations of the data set and other operations. After the user instructs the software to erase unwanted sections, all triangles within the box set by the user are removed and the border triangles are modified to leave a smooth, linear border. The software deletes all of the triangles within the box and clips all triangles that cross the border of the box. This requires generating new vertices on the border of the box. The holes created in the model at the faces of the box are retriangulated and closed using the newly created vertices. In alternative embodiments, the computer automatically simplifies the digital model by performing the user-oriented functions described above. The computer applies knowledge of orthodontic relevance to determine which portions of the digital model are unnecessary for image manipulation. In another embodiment, data associated with the 3D model includes features can be compressed based on observed characteristics of the tooth surfaces. For example, the system can use the curvature of a particular molar between the tips of the cusps and the gumline to predict the shape of the roots for that molar. Models of typical root and crown shapes also can be used to predict the shape of the tooth. The information used to arrive at the predicted shapes can be used in lieu of the original data, thus effecting data compression. Other feature detection techniques use databases of known cases or statistical information against which a particular 3D image is matched using conventional image pattern matching and data fitting techniques. One such technique, known as “Maximum a posteriori” (MAP), uses prior images to model pixel values corresponding to distinct object types (classes) as independent random variables with normal (Gaussian) distributions whose parameters (mean and variance) are selected empirically. For each class, a histogram profile is created based on a Gaussian distribution with the specified mean and variance. The prior images supply for each pixel and each class the probability that the pixel belongs to the class, a measure which reflects the relative frequency of each class. Applying Bayes' Rule to each class, the pixel values in the input image are scaled according to the prior probabilities, then by the distribution function. The result is a posterior probability that each pixel belongs to each class. The Maximum a posteriori (MAP) approach then selects for each pixel the class with the highest posterior probability. Once downloaded to a remote workstation, a treating clinician is able to view a patient's treatment plan and alter or comment on the plan. The client viewer application is implemented in a computer program installed locally on a client computer at the clinician's site. In one implementation, the viewer program downloads a data file from a remote host, such as a file transfer protocol (FTP) server maintained by the treatment plan designer, which can be accessed either through direct connection or through a computer network, such as the World Wide Web. The viewer program uses the downloaded file to present the treatment plan graphically to the clinician. The viewer program also can be used by the treatment plan designer at the host site to view images of a patient's teeth. 3-D images of various orthodontic views can then be rendered after the compressed data of the teeth has been received. In this process, an origin point, or “look from” point associated with a camera view is generated. Next, a “look at” point or a focus point associated with the camera view is determined. In this system, the line from LookFromPoint to LookAtPoint defines the direction the camera is shooting at. Additionally, a camera Z vector, or up vector, is determined. Pseudo code for generating various orthodontic views is shown below. With reference to the pseudo code, the code defines a boundingbox of one mold (2 arches) which is the smallest cube containing the molds geometry. Other settings associated with the bounding box include: -
- Z_Axis: point from lower to upper,
- Y_Axis: point from inside mouse to front teeth (incisors)
- X_Axis: point from center to left.
- FieldOfView: is the open angle, it corresponding to lens
- HalfFieldOfView: FieldOfView * 0.5
- MoldCenter: Center of the BoundingBox
- X_Length: BoundingBox×dimension
- Y_Length: BoundingBox×dimension
- Z_Length: BoundingBox×dimension
- X_MIN: minimum×value of the BoundingBox i.e. right most surface cube×value.
- X_MAX: maximum X value of the BoundingBox
- Y_MIN: minimum Y value of the BoundingBox
- Y_MAX: maximum Y value of the BoundingBox
- Z_MIN: minimum Z value of the BoundingBox
Z_MAX: maximum Z value of the BoundingBox
Once the intermediate and final data sets have been created and reviewed by an orthodontist or suitably trained person, the appliances may be fabricated as illustrated in After production, the appliances can be supplied to the treating professional all at one time. The appliances are marked in some manner, typically by sequential numbering directly on the appliances or on tags, pouches, or other items which are affixed to or which enclose each appliance, to indicate their order of use. Optionally, written instructions may accompany the system which set forth that the patient is to wear the individual appliances in the order marked on the appliances or elsewhere in the packaging. Use of the appliances in such a manner will reposition the patient's teeth progressively toward the final tooth arrangement. Because a patient's teeth may respond differently than originally expected, the treating clinician may wish to evaluate the patient's progress during the course of treatment. The system can also do this automatically, starting from the newly measured in-course dentition. If the patient's teeth do not progress as planned, the clinician can revise the treatment plan as necessary to bring the patient's treatment back on course or to design an alternative treatment plan. The clinician may provide comments, oral or written, for use in revising the treatment plan. The clinician also can form another set of plaster castings of the patient's teeth for digital imaging and manipulation. The clinician may wish to limit initial aligner production to only a few aligners, delaying production on subsequent aligners until the patient's progress has been evaluated. The user interface input devices typically include a keyboard and may further include a pointing device and a scanner. The pointing device may be an indirect pointing device such as a mouse, trackball, touch-pad, or graphics tablet, or a direct pointing device such as a touch-screen incorporated into the display, or a three dimensional pointing device, such as the gyroscopic pointing device described in U.S. Pat. No. 5,440,326, other types of user interface input devices, such as voice recognition systems, can also be used. User interface output devices typically include a printer and a display subsystem, which includes a display controller and a display device coupled to the controller. The display device may be a cathode ray tube (CRT), a flat-panel device such as a liquid crystal display (LCD), or a projection device. The display subsystem may also provide non-visual display such as audio output. Storage subsystem Memory subsystem File storage subsystem In this context, the term “bus sub-system” is used generically so as to include any mechanism for letting the various components and subsystems communicate with each other as intended. With the exception of the input devices and the display, the other components need not be at the same physical location. Thus, for example, portions of the file storage system could be connected via various local-area or wide-area network media, including telephone lines. Similarly, the input devices and display need not be at the same location as the processor, although it is anticipated that personal computers and workstations typically will be used. Bus subsystem Scanner Fabrication machine Bus subsystem Scanner Fabrication machine The invention has been described in terms of particular embodiments. Other embodiments are within the scope of the following claims. For example, the three-dimensional scanning techniques described above may be used to analyze material characteristics, such as shrinkage and expansion, of the materials that form the tooth castings and the aligners. Also, the 3D tooth models and the graphical interface described above may be used to assist clinicians that treat patients with conventional braces or other conventional orthodontic appliances, in which case the constraints applied to tooth movement would be modified accordingly. Moreover, the tooth models may be posted on a hypertext transfer protocol (http) web site for limited access by the corresponding patients and treating clinicians. Referenced by
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