JP2005199084A - System and method of removing gingiva from tooth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system and a method to remove a gingiva from a tooth. <P>SOLUTION: The method executed with a computer to detach the gingiva from the tooth comprises a process to determine a severing surface along the gingiva, and a process to provide the tooth with the severing surface to detach the gingiva from the tooth with single severance. In one embodiment, the severing surface curves. In another embodiment, the severing surface is expressed with a function. In another embodiment, the severing surface is expressed with a spline function and a quadratic function. In another embodiment, the severing surface is expressed with a spline function and a parabolic function. Moreover, in another embodiment, the severing surface is adjusted reciprocally. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

(Background of the Invention)
(1. Field of the Invention)
The present invention relates generally to the field of orthodontics, and more particularly to computer automated separation of tooth models.

(2. Description of background art)
A tooth retainer for finishing orthodontic treatment is disclosed in Am. J. et al. Orthod. Oral. Surg. 31: 297-304 (1945) and 32: 285-293 (1946). The use of silicone tooth restraints for comprehensive orthodontic realignment of patient teeth is described in Warunek et al. (1989) J. MoI. Clin. Orthod. 23: 694-700. Transparent plastic tooth retainers for finishing and maintaining tooth retainers are available from Raintree Essix, Inc. New Orleans, Louisiana 70125, and Tru-Tain Plastics, Rochester, Minnesota 55902. The manufacture of orthodontic tooth retainers is described in US Pat. Nos. 5,186,623; 5,059,118; 5,055,039; 5,035,613; 4,856,991; 4,798,534; and 4,755,139.

  Other publications describing the manufacture and use of dental tooth retainers are described by Kleemann and Janssen (1996) J. MoI. Clin. Orthodon. 30: 673-680; Cureton (1996) J. MoI. Clin. Orthodon. 30: 390-395; Chiaphone (1980) J. MoI. Clin. Orthodon. 14: 121-133; Shilidday (1971) Am. J. et al. Orthodontics 59: 596-599; Wells (1970) Am. J. et al. Orthodontics 58: 351-366; and Cottingham (1969) Am. J. et al. Orthodontics 55: 23-31.

  Kuroda et al. (1996) Am. J. et al. Orthodontics 110: 365-369 describes a method of laser scanning a plaster dental cast and generating a digital image of this cast. See also US Pat. No. 5,605,459.

  U.S. Pat. Nos. 5,533,895 assigned to Ormco Corporation; 5,474,448; 5,454,717; 5,447,432; 5,431,562 Nos. 5,395,238; 5,368,478; and 5,139,419 are for manipulating digital images of teeth to design orthodontic appliances. Describes the method.

  US Pat. No. 5,011,405 describes a method for digitally imaging teeth and determining optimal bracket positioning for orthodontic treatment. Laser scanning of shaped teeth to produce a three-dimensional model is described in US Pat. No. 5,338,198. U.S. Pat. No. 5,452,219 describes a method for laser scanning a tooth model and planing a tooth mold. Digital computer manipulation of tooth contours is described in US Pat. Nos. 5,607,305 and 5,587,912. Computerized digital imaging of the jaw is described in US Pat. Nos. 5,342,202 and 5,340,309. Other important patents are: US Pat. Nos. 5,549,476; 5,382,164; 5,273,429; 4,936,862; 3,860, No. 803; No. 3,660,900; No. 5,645,421: No. 5,055,039; No. 4,798,534; No. 4,856,991; 5,035,613; 5,059,118; 5,186,623; and 4,755,139.

(Item 1) A computer-implemented method for separating gingiva from teeth, comprising:
Defining a cutting surface along the gingiva; and applying the cutting surface to the tooth to separate the gingiva from the tooth in a single cut.
2. The method of claim 1, wherein the cutting surface is curved.
3. The method of claim 1, wherein the cutting surface is expressed as a function.
4. The method of claim 1, wherein the cutting surface is represented as a spline function and a quadratic function.
5. The method of claim 1, wherein the cutting surface is represented as a spline function and a parabolic function.
6. The method of claim 1, wherein the cutting surface is adjusted interactively.
7. The method of claim 4, wherein the interactive adjustment of the cutting surface alters a function that defines the cutting surface.
8. The method of claim 4, further comprising the step of interactively enhancing the separated portions.
9. The method of claim 8, further comprising interactively highlighting the boundaries of the separated portions.
10. The method of claim 1, wherein the cutting surface is defined by identifying the tooth foundation.
11. The method of claim 1, further comprising the step of finding a gingival line separating the tooth surface and the gingiva.
12. The method of claim 11, further comprising finding a high curvature position on the tooth surface.
13. The method of claim 11, further comprising fitting a spline to the gingival line.
14. The method of claim 1, wherein the cutting surface further comprises a plurality of surfaces.
15. The method of claim 14, wherein the tooth root is modeled as a parabolic surface below the gingival line.
16. The method of claim 14, further comprising defining an enclosing surface for encircling the dental crown.
(Item 17) The method according to claim 14, wherein:
Displaying the surface identified by a plurality of nodes;
Adjusting the one or more nodes to modify the surface; and applying the surface to separate the gingiva from the tooth.
18. The method of claim 17, further comprising providing a handle to adjust each orientation of the cutting shape.
19. The method of claim 17, wherein adjusting the one or more nodes further comprises moving the one or more nodes.
20. The method of claim 17, wherein the cutting surface is formed using a function in a cylindrical coordinate system.
21. A system for separating gingiva from a tooth comprising:
Means for defining a cutting surface along the gingiva; and means for imparting the cutting surface to the tooth to separate the gingiva from the tooth in a single cut.
22. A computer program residing on a tangible storage medium for use in separating gingiva from a computer model of a tooth, comprising:
On the computer:
A program comprising executable instructions operable to define a cutting surface along the gingiva; and to impart the cutting surface to the tooth to separate the gingiva from the tooth in a single cut.
23. A computer program residing on a tangible storage medium for use in separating gingiva from a computer model of a tooth, comprising:
On the computer:
Defining a cutting surface along the gingiva, wherein the cutting surface is represented as a spline function and a quadratic function; and the cutting of the tooth to separate the gingiva from the tooth in a single cut A program comprising executable instructions operable to cause a surface to be applied.
(Item 24) A computer:
Processor;
A data storage device connected to the processor, the data storage device including code for use in separating gingiva from a dental computer model, wherein a program is stored on a computer:
Defining a cutting surface along the gum, wherein the cutting surface is represented as a spline function and a quadratic function, wherein the cutting surface further comprises a plurality of surfaces, and wherein the tooth The root of the tooth is modeled as a parabolic surface below the gingival line; and is feasible to apply a cutting surface to the tooth to separate the gingiva from the tooth in a single cut Computer with various instructions.
25. The system of claim 24, further comprising instructions defining an enclosing surface surrounding the dental crown.
26. A computer-implemented method for separating teeth from gums, comprising:
Defining a cutting surface along the gingiva; and separating the gingiva and imparting the cutting surface to the tooth to reconstruct the root of the tooth with a single cut. .

(Simple Summary of Invention)
In one aspect, the computer-implemented method includes defining a cutting surface along the gingiva; and applying the cutting surface to the tooth to separate the gingiva from the tooth in a single cut. Separate the gingiva from the tooth model.

  Implementation of this method may include one or more of the following. The cutting surface can be curved. The cutting surface may be represented as a function such as a spline function and a quadratic function. The quadratic function may be a parabolic function. The cutting surface can be adjusted interactively, where the interactive adjustment of the cutting surface modifies the function defining the cutting surface. The method may include interactively highlighting the separated portion and the boundary of the separated portion. The cutting surface may be defined by identifying the tooth foundation. A gingival line separating the tooth surface and the gingiva can be determined. The method may include the step of finding a high curvature position on the tooth surface. The spline can be adapted to the gingival line. The cutting surface may include a plurality of surfaces. The root of the tooth can be modeled as a parabolic surface below the gingival line. The method can include defining an enclosing surface for enclosing the dental crown. The method also includes displaying the surface identified by a plurality of nodes; adjusting one or more nodes to modify the surface; and separating the surface to separate the gingiva from the tooth Including the step of imparting.

  In another aspect, a system for separating gingiva from a tooth includes means for defining a cutting surface along the gum; and the cutting on the tooth to separate the gum from the tooth in a single cut. Means for providing a surface are provided.

  In another aspect, a computer program on a tangible storage medium for use in separating gingiva from a computer model of a tooth, the program comprising: a computer: defining a cutting surface along the gingiva And executable instructions operable to impart the cutting surface to the tooth to separate the gingiva from the tooth in a single cut.

  In another aspect, a computer program on a tangible storage medium for use in separating gingiva from a computer model of a tooth, the program comprising: a computer: defining a cutting surface along the gingiva Where the cutting surface is represented as a spline function and a quadratic function; and to cause the tooth to impart the cutting surface to separate the gingiva in a single cut from the tooth Contains executable instructions that are operable.

  In yet another aspect, a computer comprising: a processor; a data storage device connected to the processor, the data storage device including code for use in separating gingiva from a computer model of a tooth A program causing a computer to define a cutting surface along the gingiva, wherein the cutting surface is represented as a spline function and a quadratic function, wherein the cutting surface further defines a plurality of surfaces And wherein the root of the tooth is modeled as a parabolic surface below the gingival line; and providing a cutting surface to the tooth to separate the gingiva from the tooth in a single cut. Includes executable instructions operable to cause

  In yet another aspect, a computer-implemented method for separating a tooth from a gingiva: defining a cutting surface along the gingiva; and separating the gingiva and singly rooting the tooth Including providing a cutting surface to the tooth for reconstruction by cutting.

  The benefits of this system may include one or more of the following. This system provides a flexible cutter that can be modified to follow the gingival line, where the user can cut the gingiva in one single cut. Here, the gingival line defined by the user can also be reused later for the gingival reconstruction process.

  Advantages of the invention may include one or more of the following. This system separates the gingiva from the teeth with a single cut. This system also reconstructs the teeth and provides tooth roots in the same orientation. The system also generates the crown surface portion of the tooth model relatively quickly by applying a computerized function. The speed in drawing the crown surface allows real-time shaping by the user when the user moves the crown and tip control points or when the user edits the gingival line. It also facilitates the cross-insight itself. This is because the system can quickly determine whether a given point, such as the apex of the tooth mesh, is inside or outside the gingival cutting surface.

(Detailed description of the invention)
Referring to FIG. 1A, a representative jaw 100 includes 16 teeth, at least some of which should be moved from the initial tooth arrangement to the final tooth arrangement. An optional center line (CL) is drawn through one of the teeth 102 to understand how the teeth can be moved. With reference to this center line (CL), the teeth can be moved in orthogonal directions represented by axes 104, 106, and 108 (where 104 is the center line). This centerline may be rotated about axes 108 (root angulation) and 104 (torque), indicated by arrows 110 and 112, respectively. In addition, the teeth can be rotated around the center line, as represented by arrow 114. Thus, all possible free form movements of the teeth can be performed.

Referring now to FIG. 1B, the magnitude of any tooth movement is defined with respect to the maximum linear translation of any point P on the tooth 102. Each point P _i undergoes a cumulative translation as its teeth move in any orthogonal or rotational direction as defined in FIG. 1A. That is, this point usually follows a non-linear path, but when measured at any two times during the procedure, there is a linear distance between any points in the tooth. Thus, arbitrary point P ₁ may actually perform a side-by-side translation as indicated by arrow d ₁ , while the second arbitrary point P ₂ may move along an arcuate path and finally Produces a translation d ₂ of In many situations, the maximum allowable movement of point P _{i on} any particular tooth is defined as the maximum linear translation of that point P _i on the tooth that makes the maximum movement for that tooth in any treatment step.

  One tool for progressively repositioning teeth is a set of one or more adjustment tools. Suitable appliances include any known tooth retainer, retainer, or other removable appliance used to finish and maintain the position of the teeth in combination with conventional orthodontic procedures. As described below, a plurality of such appliances may be worn continuously by the patient to achieve gradual tooth repositioning. A particularly advantageous appliance is an appliance 100 as shown in FIG. 1C, which typically receives and elastically repositions teeth from one tooth arrangement to another. A polymeric shell having a shaped cavity is provided. This polymeric shell typically fits over all teeth present in the upper or lower jaw. Often only some teeth are repositioned while other teeth provide a foundation or anchoring area to hold the repositioning instrument in place. This is because it provides a resilient repositioning force to the tooth (s) to be repositioned. However, in complex cases, many or most of the teeth are repositioned at specific points during the procedure. In such cases, the moved tooth can also serve as a foundation or anchoring area for holding the appliance to be repositioned. The gums and pallets are also served as anchoring areas in some cases, thus relocating all or nearly all of the teeth simultaneously.

  The polymeric device 100 of FIG. 1C is preferably a suitable elastomeric polymer thin sheet, such as the Tru-Tain 0.03 inch thermoformable dental material marketed by Tru-Tain Plastics, Rochester, Minnesota 55902. Formed from. In many cases, no wires or other means are provided to hold the appliance in place on the teeth. In some cases, however, it is necessary to provide individual attachments on the teeth with corresponding containers or apertures in the appliance 100, and the appliance may be applied without such attachments. A force may be applied that may or may not be possible to do.

  FIG. 2 shows a process 200 for generating an incremental positioning device for subsequent use by the patient to reposition the patient's teeth. As an initial step, an initial digital data set (IDDS) representing an initial tooth arrangement is obtained (step 202). This IDDS can be obtained in various ways. For example, the patient's teeth can be scanned or imaged using x-rays, three-dimensional x-rays, computer-assisted tomography images or data sets, or in particular magnetic resonance images. Further details regarding contact or non-contact scanners can be found in Application No. 09 / 169,276, filed on Oct. 8, 1998, which is co-pending for sharing, the contents of which are incorporated by reference.

  A plaster image of a patient's teeth is obtained by well-known techniques as described in Graber, Orthodontics: Principle and Practice, 2nd edition, Saunders, Philadelphia, 1969, 401-415. After the dental cast is obtained, the casting is digitally scanned by a scanner such as a non-contact laser or a destructive scanner or a contact scanner to generate an IDDS. The data set generated by the scanner can be presented in any of a variety of digital formats to ensure compatibility with the software used to manipulate the image represented by this data. In addition to 3D image data collected by laser scanning or resolving scans of the exposed surface of the tooth, the user can collect data on hidden features such as the patient's tooth root and the patient's jawbone. May be hoped. This information is used to build a detailed model of the patient's dentition and to show more accurately and precisely how the tooth responds to the treatment. For example, information about the root allows modeling of all surfaces of the tooth, not just the crown, which in turn simulates the relationship between the crown and root as they move during the procedure. Enable. Information about the patient's jaw and gums also allows for a more accurate model of tooth movement during the procedure. For example, x-rays of the patient's jawbone can assist in identifying tough teeth, and MRI can provide information about the density of the patient's gum tissue. Furthermore, information regarding the correlation between the patient's teeth and other skull features allows for accurate alignment of the teeth with respect to the rest of the head at each of the treatment steps. Data about these hidden features can be collected from a number of sources including 2D and 3D x-ray systems, CT scanners, and magnetic resonance imaging (MRI) systems. Using this data to introduce visually hidden features to the tooth model is described in more detail below.

  The IDDS is operated using a computer with a suitable graphical user interface (GUN) and suitable software for viewing and modifying images. More detailed aspects of this process are described in detail below.

  Individual teeth and other components may be segmented or isolated in this model to allow their individual rearrangement or removal from the digital model. After segmenting or isolating components, users often reposition teeth in the model by following prescriptions or other written specifications provided by the treatment professional. Alternatively, the user can reposition one or more teeth based on visual appearance or based on rules and algorithms programmed into the computer. Once the user is satisfied, the final tooth array is captured in the final digital data set (FDDS) (step 204).

  This FDDS is used to create an appliance that moves teeth in a specified sequence. Initially, the center of each tooth model can be aligned using a number of methods. One method is a standard arc. The tooth model is then rotated until their roots are in the proper vertical position. The tooth models are then rotated around their vertical axis to the proper orientation. The tooth model is then observed from the side and translated vertically to their proper vertical position. Finally, the two arcs are placed together and the tooth model is moved slightly to ensure that the upper and lower arcs are properly captured together in the mesh. The meshing of the upper and lower arcs together is visualized using a collision detection process that emphasizes the tooth contact points.

  In step 204, the final positions of the upper and lower teeth in the patient's masticatory system are determined by generating a computer representation of the masticatory system. The bite of the upper and lower teeth is calculated from this computer display; and the functional bite is calculated based on the interaction in the computer display of this masticatory system. This bite can be determined by generating an ideal set of tooth models. Each ideal model in this set of ideal models is a summary model of idealized tooth placement, which is customized to the patient's teeth, as will be discussed below. After applying the ideal model to the computer display, the tooth position is optimized to fit this ideal model. This ideal model can be specified by the form of one or more arcs or can be specified using various features associated with the teeth.

  Based on both IDDS and FDDS, a plurality of intermediate digital data sets (INTDDS) are defined and correspond to incremental adjustment instruments (step 206). Finally, a set of incremental adjusters is generated based on INTDD and FDDS (step 208).

  FIG. 3 shows an exemplary 3D surface model of one tooth. The surface topology of the 3D model of the teeth on the jaw can be modeled as a set of polygons of appropriate size and shape connected at their edges. This set of polygons defining the 3D object is referred to as the “model” or “mesh” of the 3D object. In one embodiment, the polygon is a triangle. In this embodiment, the triangular mesh is a piecewise linear surface with triangular faces connected along their edges.

Many types of scan data, such as obtained by an optical scanning system, provide a 3D geometric model of a tooth (eg, a triangular surface mesh) when acquired. Other scanning techniques, such as the above-described decomposition scanning technique, provide data in the form of capacitive elements (“voxels”) that can be converted into a digital geometric model of the tooth surface. In one implementation, a marching cube algorithm is applied to convert this voxel into a mesh, which can be subjected to a smoothing operation to reduce jaggedness on the surface of the tooth model caused by the marching cube transformation. One smoothing operation moves the vertices of individual triangles to a position that represents the average of neighboring vertices connected to reduce the angle between triangles in the mesh.

  Another optional step is the application of a thinning operation to the smoothed mesh to eliminate data points, which improves processing speed. After smoothing and decimation operations are performed, an error value is calculated based on the difference between the resulting mesh and the original mesh or original data, and the error is compared to an acceptable threshold. . This smoothing and decimation operation is applied once again to the mesh if this error does not exceed an acceptable value. The last set of mesh data that satisfies the threshold is stored as a tooth model.

  The triangles in FIG. 3 form a connected graph. In this context, two nodes in a graph are connected if there is a sequence of edges that form a path from one node to another (edge direction is ignored). The connectivity defined in this way is an equivalent relationship on the graph: if triangle A is connected to triangle B and triangle B is connected to triangle C, then triangle A is connected to triangle C. The set of nodes that are connected is then called a patch. A graph is fully connected if it consists of a single patch. The process discussed below maintains a connected triangle.

  The mesh model can also be simplified by removing undesired or unnecessary sections of the model, increasing data processing speed and visual display. Unnecessary sections include sections that are not necessary for the generation of a tooth repositioning device. Removal of these undesired sections reduces the complexity and size of the digital data set and thus accelerates the processing of the data set and other operations. After the user positions the erase tool, determines the size, and instructs the software to erase the undesired section, all triangles in the box set by the user are removed, and the bounding triangle is modified and smoothed Leave a straight line boundary. The software deletes all triangles in the box and clips all triangles that intersect the box boundary. This requires creating new vertices on the box boundaries. The holes created in the model at the face of the box are made rectangular and closed with the newly created vertices.

  In an alternative embodiment, the computer automatically simplifies the digital model by performing functions directed to the user. The computer uses the corresponding knowledge of orthodontics to determine which parts of the digital model are unnecessary for image processing.

  Once a 3D model of the tooth surface is constructed, a model of the patient's individual teeth can be derived. In one approach, individual teeth and other components are “cut” using a cutting tool to allow individual repositioning or tooth removal in or from digital data. After the component is “free”, the teeth are repositioned according to a prescription or other written specification provided by a processing specialist. Alternatively, the teeth can be repositioned based on visual appearance or based on rules and algorithms programmed into the computer. Once an acceptable final sequence is generated, the final tooth sequence is captured in the final digital data set (FDDS).

Referring now to FIG. 4, a process 211 that separates all teeth into individual units is shown. Initially, the process 211 customizes the cutting tool (step 212). Next, using the cutting tool, the user or automated process applies the cutting tool to repeatedly divide the group of teeth into two smaller groups until the teeth are reduced to individual units (step 214). The viewer program displays an initial image of the tooth and, if requested by the user, an isolated tooth image. The user can rotate these images in three dimensions to observe various tooth surfaces, and the clinician can take images to any number of predetermined viewing angles. These viewing angles are specific to orthodontics such as standard front, back, top, bottom and side views, as well as tongue, buccal, facial, occlusal, and incision views Including a wide viewing angle.

A saw tool is used to define the individual teeth (or possibly a group of teeth) to be moved. This tool divides the scanned image into individual geometric components that allow the software to move the tooth or other component image independently of the rest of the model. In one embodiment, the saw tool uses two cubic B-spline curves lying in space, possibly constrained to either parallel planes that are either opened or closed, to generate a graphic image. Specify the route to be disconnected. A set of straight lines connects the two curves and presents the user with a general cutting path. The user can edit the control points on the cubic B-spline, the thickness of the saw cut, and the number of erasers used, as described below.

  In an alternative embodiment, the teeth are separated by using a saw as a “coring” device and cutting the teeth from above with a vertical saw cut. The dental crown and the gingival tissue immediately below the crown are separated from the rest of the geometric shape and treated as individual units, referred to as teeth. As this model is moved, the gingival tissue moves relative to the crown, producing an initial sequential approximation of the manner in which the gingiva is remodeled in the patient's mouth.

  Each tooth can also be separated from the original cutting model. In addition, a base can be generated from the original cut model by cutting the crown of the tooth. The resulting model is used as a base for moving the teeth. This facilitates the final manufacture of the physical mold from the geometric model, as described below.

  Thickness: When using a cut to separate teeth, the user usually wants this cut to be as thin as possible. However, the user may want a thicker cut when scraping the surrounding teeth, for example, as described above. Graphically, this cut appears as a curve bounded by the thickness of the cut on one side of the curve.

Number of erasers: The cut consists of a plurality of eraser boxes arranged next to each other as a piecewise linear approximation of the saw tool's curve path. The user selects the number of erasers, which determines the sophistication of the curve that is generated: the more segments, the more accurate the cut following this curve. The number of erasers is indicated graphically by the number of parallel lines connecting two cubic equations B-spline curves. Once the saw cut is fully identified, the user applies this cut to the model. This cutting is performed as an erasure sequence as shown in FIG. 4A. FIG. 4B shows the single erasure iteration of the cut as described in the algorithm for the open end B-spline curve. For vertical cuts, the curve is closed, P _A [O] and P _A [S] are the same point, and P _B [O] and P _B [S] are the same point.

In one embodiment, the software automatically partitions the saw tool into a set of erasers based on smoothness criteria input by the user. The saw is adapted and subdivided until the error metric is less than the threshold specified by the smoothness setting, the deviation from the ideal representation to the approximate representation. One error metric compares the straight line length of the subdivided curve with the arc length of the ideal spline curve. When this difference is greater than the threshold calculated from the smoothness setting, a subdivision point is added along the spline curve.

  A preview feature may also be provided in the software. This preview feature visually displays the saw cut as two surfaces representing the opposite sides of the cut. This allows the user to consider the final cut before applying it to the model dataset.

  In one embodiment, a flexible plane can be used to splice two more teeth into two groups of teeth. This process allows a user to view a flexible plane with multiple control grid nodes and display one or more teeth that display it. This flexible plane is formed by many surface patches called bicubic Bezier patches. The equation for such patches is well known and can be described as:

ここで、ｕ、およびｖは、２つの歯の間の真っ直ぐな平面に沿って選択された３Ｄスペース中の座標であり、そしてＳは、この真っ直ぐな平面に対して正規直交方向に沿った関数であり、ｂ_ｉ，ｋは、パッチのＢｅｚｉｅｒ点を表し、そして

Where u and v are the coordinates in 3D space selected along a straight plane between the two teeth, and S is a function along the orthonormal direction relative to this straight plane And b _{i, k} represents the Bezier point of the patch, and

は、Ｂｅｒｎｓｔｅｉｎ多項式を示す。

Indicates a Bernstein polynomial.

  This process accepts user adjustments to the position of the various grid nodes and modifies the flexible plane. The cutting curve and tooth portion associated with the flexible plane is then updated in real time. The user can perform these operations repeatedly, dividing all teeth into individual teeth that are prepared for treatment.

  FIG. 5 shows a process 220 for cutting or splicing gingiva from a tooth model. Initially, the user selects a tooth to be cut. Next, process 220 determines whether the gingival line can be positioned, and if so, a cutter is applied to follow the gingival line. Referring now to FIG. 5, the gingival line is the line that separates the clinical crown surface of the tooth from the gingival surface in the computer model of the tooth (step 230). The process 220 then generates a closed surface model of the cut line that passes through the gingival line found above (step 250). This surface should not be cut through the clinical crown portion and should produce an approximate root shape. This cutting line is part of the closed surface model that passes exactly through the gum line of the tooth.

  Next, this process 220 is a US patent application Ser. No. 09 / 539,185, filed Mar. 30, 2000, entitled “System for Separating Teeth Models,” the contents of which are incorporated by reference. And the gingiva from the teeth using the curved clipping algorithm described in US patent application Ser. No. 09 / 539,021, filed Mar. 30, 2000, entitled “Flexible Plane for Separating Teeth Models”. Clip.

  Process 220 cuts the gingival parts of the teeth that have already been separated in a single cutting operation and simultaneously reconstructs a relatively closed root shape.

  The cutter of FIG. 5 embeds itself in the tooth to be cut. In the embodiment of FIG. 6, the cutter is shaped like an ice cream cone, with the top of the crown of the tooth 301 to be extracted and the bottom embedded inside the gum 300 defining the root of the tooth 301. Have. The gum line or curve defines the rim 304 for this ice cream cone shaped cutter. This cutter is formed by several sets of control points. A point on the rim 304 (gingival curve) control gives a definition of the gingival line. This set of control points can be moved over the surface of the tooth 301. One or more crown control points 308 define the upper portion of the cutter. This set of crown control points 308 can be adjusted to surround the crown portion of the tooth with the upper portion of the cutter. The crown control point 308 is also adjusted so that the crown portion of the gum cutter does not cut any gum 300.

  In addition, a root control point 306 is provided. The behavior of these control points differs from the crown control point 308 in that the set of control points 306 can only be moved in and out in one direction, except that the pivot control points are also moved up and down. By doing so, you can actually move all the root controls up and down with it. The purpose of adjusting the set of root control points 306 is to define the starting root structure for the cutting teeth.

  The system also provides one top control that defines the height of the top portion and one bottom control that defines the depth of the root portion. Both can be moved up and down. The purpose of adjusting the top control point is consequently that all crown parts of the tooth are surrounded within the cutter, while the purpose of adjusting the bottom control point is to set the proper root depth. is there. In addition, the gingival line can be visualized with a distinguishing color and drawn more emphasized than the other lines, allowing better visualization during editing of the gingival section. The gingival curve generated during this process can also be reused in gingival reconstruction. Further details regarding gingival reconstruction can be found in the application entitled “Digital Modeling of Gingival Tissue Deformation During Orthodontic Treatment” filed May 14, 1999, the contents of which are incorporated herein by reference. May be found in a co-pending application having the number 09 / 311,716.

  FIG. 7 shows step 230 of FIG. 5 in more detail. The process of FIG. 7 performs automatic discovery of gingival lines. Initially, the user selects a tooth having a properly defined basis (step 232) and identification number. For example, the z-axis traverses along the top of the tooth, the center is set to approximately the center of the tooth, and the y-axis starts from the tongue to the lip surface. Thus, the defined dental foundation can also be used in other parts of the treatment process. The process of FIG. 7 generates a spline curve that approximates the periphery of the tooth surface and gingival surface in the computer model of the tooth (step 234). Next, the process of FIG. 7 generates an EDF surface for a given tooth (step 236).

  Next, along the preset number of angles around the z-axis of the tooth, the maximum bending point along the z-axis direction is found (step 238). These inflection points are found only in areas where a given tooth type may have a gingival line. This eliminates the discovery of many high curvature points, which are elsewhere due to noise and tooth characteristics themselves. A filtering procedure is used to find points generated by noise in the data (step 240). Since the gingival line is often not very smooth, a smoothing procedure is applied to adjust certain points and eliminate noise points on the curve (step 242). A smooth spline curve is fitted along the final set of points available after the filtering and smoothing procedure (step 244). This spline curve represents the gingival line of this tooth. The spline curve can be edited as necessary by moving one or more control points on the curve (step 246).

  FIG. 8A shows in more detail the process for step 250 of FIG. 5 to generate a surface model with cut gingiva. The input to this process is a generic tooth identification that identifies the type of gingival line, tooth bounding box, and teeth themselves found in the above steps. This process generates a closed surface model that passes through the gingival line. This surface consists of three distinct surfaces: a) a crown surface that begins with a gingival line and surrounds all clinical crown parts of the tooth; b) a parabolic surface with a gingival interior at approximately the base of the tooth root; and c ) Having a curved surface connecting this parabolic root to the crown surface; In one embodiment, these surface pieces are modeled in a cylindrical coordinate system (r, θ, Z).

  The process of FIG. 8A models the crown surface as a spline surface that passes through a set of points around the gingival line and the clinical crown portion of the tooth (crown point), and a point above the top of the crown. (Step 252). Initially, at a predetermined angle (phi) around the z-axis, the gingival curve is intersected with a half-plane that begins at the z-axis angle phi. Another point is calculated depending on the type of tooth, the bit away from the tooth surface, and on the gingival line. A quadratic curve is constructed at each angle from the top control point to the gingival point and through the crown control point. The spline is then fitted around the z-axis through all points thus found for crown control. Thus, the crown surface is defined by generating grid points that are quadratic along the z-axis and cubic on the z-axis. The crown control points can be edited to change the shape of the surface crown portion (step 254). For example, a point on the top of the tooth can be moved in the z direction, changing the shape of the crown surface portion.

  FIG. 8B shows a description of the construction of the cutter surface. This figure shows the four meridians of the surface around the z-axis. The portion of each meridian above the gingival line is called a crown portion 771. This is modeled as a quadratic function in polar coordinates. In one embodiment, the mathematical representation of this curve is

であり、ここで「ａ」および「ｂ」は定数である。この関数を用いて、任意の所定のｚ値についてｚ軸から等距離にある点の半径を見出し得る。定数ａおよびｂは、カーブが通過する点、すなわち、頂部点７７４、歯冠点７７６および歯肉点７７７によって決定される。

Where “a” and “b” are constants. Using this function, the radius of a point that is equidistant from the z-axis for any given z value can be found. The constants a and b are determined by the points through which the curve passes, namely the top point 774, crown point 776 and gingival point 777.

  The portion of the meridian curve that lies under the gingival line 770 has two curves 772 and 773. Curve 772 is linear from gingival point 777 to root control point 778. A curve 773 is a parabola whose apex is the bottom control point 775. In one embodiment, this curve is a function.

によって表され、ここで、ｄ＿ａ、ｄ＿ｂおよびｄ＿ｃは定数であり、そしてこのカーブが、根コントロール点７７８および底コントロール点７７５を通過しなければならない条件から算出され得る。

Where d_a, d_b and d_c are constants, and this curve can be calculated from the conditions that must pass through the root control point 778 and the bottom control point 775.

Meridian curves 771, 772 and 773 are determined for each of the control angles that divide 360 degrees into a predetermined number of intervals around the z-axis. Then a point on the meridian curve of uniform z increment is found. Using these points at each elevation, a cubic periodic Hermite curve around the z-axis 779 is constructed. Next, each of these elevation curves, such as curve 779, is evaluated for a preset number of points evenly distributed around the z-axis. Thus, using a grid of points generated by these elevation curves, the meridian curve is used to generate an overall grid for the cutter.

  The crown surface portion can be generated relatively quickly. Because it is based on a function. The speed of drawing the crown surface allows real-time shaping by the user when the user moves the crown control point and the top control point or when the user edits the gingival line. It also facilitates the intersection discovery itself. This is because the system can quickly determine whether a given point, such as the apex of the tooth mesh, is inside or outside the gingival cutting surface.

  The initial placement of the crown control points is performed using the approximate tooth shape estimated from the tooth identification information (step 256). For example, for molars, these points should be far from the z-axis than for incisors. Next, a root portion of the gingival cutting surface is generated (step 258). The root portion may be composed of a parabolic surface at the bottom of the surface and a defined surface that connects the parabolic surface to the crown surface.

  FIG. 9 shows in more detail step 260 of FIG. 5 using the gingival cutting surface to extract gingiva from the teeth. The inputs to the process of FIG. 9 are a triangular mesh model of the tooth and a triangular mesh model of the gingival cutting surface. The process of FIG. 9 generates a cut-out gingival part and a crown part of the tooth (step 262). Cut the gums from the teeth using a curved clipping procedure. The process then reconstructs the root using the gingival cutting surface (step 264). Root reconstruction occurs as part of the cutting process, and the root portion of the cut tooth is part / all of the root portion of the gingival cutting surface. The process then cuts the gingival portion of the tooth and generates a crown portion (step 266).

  If the gingival line is deep, the crown surface constructed using the tooth type information can be cut through a portion of the gingiva. For this purpose, the “Auto Crown” procedure shown in FIG. 10 can be used. The process of FIG. 10 produces a gingival cut compact crown part, which does not cut through the crown part of the tooth. Returning to FIG. 10, in each direction away from the z-axis, the tangential direction is calculated from the corresponding point on the gingival line to the crown portion of the tooth (step 272). These tangents are selected so that they are furthest away from the z-axis (step 274). In other words, this tangent does not intersect the crown portion of the gingival cut, but touches the crown portion at one or more points. FIG. 11 shows one particular (z, phi) plane. These tangents are used to automatically locate the crown control points that define the crown surface of the gingival cut (step 276).

  FIG. 11 illustrates one exemplary operation of the process of FIG. 10 on the tooth model 301. The tooth model 301 is stationary on the gingiva 300. The root model 301 is in contact with the gingiva 300 at the gingival line 316. Further, the crown surface 310 covers the teeth 301. Tangent line 312 exits gingival line 316 and points to a corresponding point on crown surface 310. The process of FIG. 11 calculates an alternative tangent 314 by shifting the tangent 312 by a small offset. The intersection of this alternative tangent 314 with the crown surface 310 is a new crown point 318 according to the process of FIG.

FIG. 12 shows an exemplary user interface of a cutter 500 that can remove gums 504 from a tooth model. The cutter 500 provides a shafting 502 that allows the user to rotate and move the cutter 500 in and around the three main directions (x, y and z). Ball control 506 is provided along the gingival line 508, where the user can edit the gingival line 508. Control cubes 510 are provided that allow the user to change the shape of the cutter 500, and these cubes 510 can be edited by moving them. All user changes cause a recalculation of the surface of the cutter 500 and cause this surface to pass through the gingival line 508.

  This user interface allows the user to turn on and off the solid line option so that the surface of the gingival cutter 500 can be visualized from its wireframe model. The roots can be displayed or remain hidden using a transparency setting and are useful for viewing the root structure inside the teeth. The geometric structure of the intersection can be shown and the root point and crown point and root depth can be identified.

  Once the intermediate data set and the final data set are generated, the instrument can be fabricated as shown in FIG. Conventional fabrication methods employ a rapid prototype manufacturing device 201 such as a stereolithography machine. A particularly suitable rapid prototype production machine is the Model SLA-250 / 50 available from 3D System, Valencia, California. This rapid prototyping machine 201 separates liquid or other non-solidified resin from the remaining non-solidified resin, cleans it, and either directly as an instrument or indirectly as a mold to produce the instrument. Selectively solidify into a three-dimensional structure that can be used in The rapid prototype manufacturing machine 201 receives individual digital data sets and generates one structure corresponding to each desired instrument. In general, this rapid prototyping machine 201 may utilize a resin with non-optimal mechanical properties, and typically this may not be generally acceptable for patient use, so typically a rapid prototyping machine Is used to produce a mold in a valid positive tooth model for each successive stage of treatment. Once the positive model has been prepared, a more suitable material (eg, 0.03 inch thermoformable dental material available from Tru-Tain Plastics, Rochester, Minnesota 55902, using conventional pressure or vacuum forming machine 251. ) To create an instrument. Suitable pressure forming equipment is described by Great Lakes Orthodontics, Ltd. Available from Tonawanda, New York 14150 under the trade name BIOSTAR. The molding machine 251 generates each appliance directly from the positive tooth model and the desired material. Suitable vacuum forming machines are available from Raintree Essix, Inc. Is available from

  After manufacture, the instrument can be supplied to the treatment professional all at once. These instruments are marked in several styles, typically directly on or on each instrument, or by sequential numbering on a tag, pouch, or other item that wraps each instrument. , Show the order of their use. If necessary, written instructions accompany the system, which presents the patient to wear the individual devices in a marked order somewhere in the device or packaging. The use of this type of appliance gradually repositions the patient's teeth toward the final tooth arrangement.

  Because the patient's teeth may react differently than originally expected, the treating clinician may wish to assess the patient's progress during the course of the treatment. The system can also do this automatically, starting with a newly measured ongoing dentition. If the patient's teeth do not progress as planned, the clinician may revise the treatment plan as necessary, returning the patient's treatment to the intended direction, or designing an alternative treatment plan. The clinician may provide oral or written comments for use in revising the treatment plan. The clinician may also form another set of casts of the patient's teeth for digital imaging and manipulation. The clinician may wish to delay production on the next aligner until patient progression is assessed, and limit initial aligner production to only a few aligners.

  FIG. 14 is a simplified block diagram of a data processing system 800 that may be used to develop an orthodontic treatment plan. The data processing system 800 typically includes at least one processor 802 that communicates with a number of peripheral devices via a bus subsystem 804. These peripheral devices typically include a storage subsystem 806 (memory subsystem 808 and file storage subsystem 814), a set of user interface input devices and user interface output devices 318, and an external including a public switched telephone network. Includes an interface to network 316. This interface is illustrated as a “modem and network interface” block 816 and is coupled via a communication network interface 824 to a corresponding interface device in other data processing systems. The data processing system 800 can be a terminal or low-end personal computer or a high-end personal computer, workstation or mainframe.

  Typically, the user interface input device includes a keyboard and may further include a pointing device and a scanner. The pointing device can be an indirect pointing device such as a mouse, trackball, touch pad, or graphic tablet, or a direct pointing device such as a touch screen embedded in a display, or as described in US Pat. No. 5,440,326. Other types of user interface input devices such as a three-dimensional pointing device, such as a gyroscope pointing device, a speech recognition system may also be used.

  Typically, a user interface output device includes a display subsystem including a printer and a display controller and a display device connected to the controller. The display device can 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 a non-visual display such as an acoustic output.

  The storage subsystem 806 maintains the basics necessary for programming and data construction. The program modules discussed above are typically stored in the storage subsystem 806. The storage subsystem 806 typically includes a memory subsystem 808 and a file storage subsystem 814.

  The memory subsystem 808 typically includes a main random access memory (RAM) 810 for storing instructions and data during program execution, and a read only memory (ROM) 812 in which fixed instructions are stored. Includes a lot of memory including. In the case of a Macintosh compatible personal computer, this ROM contains part of the operating system; in the case of an IBM compatible personal computer, this may include a BIOS (Basic Input / Output System).

File storage subsystem 314 stores persistent (non-volatile) program and data files, and typically at least one hard disk drive and at least one floppy disk drive (associated removable media). Together with). Other devices such as CD-ROM drives and optical drives (all with their associated removable media) may also exist. In addition, the system may include a type of drive having a removable media cartridge. The removable media cartridge can be, for example, a hard disk cartridge such as that marketed by Syquest et al., And a flexible disk cartridge such as that marketed by Iomega. One or more drives may be located at a remote location, such as at a server in a local area network, or a site on the Internet's World Wide Web.

  In this context, the term “bus system” is used to generally include any mechanism that communicates with each other as intended by the various components and subsystems. Other than the input device and the display, the other components need not be in the same physical location. Thus, for example, portions of a file storage system can be linked via various local area or wide area network media including telephone lines. Similarly, the input device and display need not be co-located with the processor, although typically a personal computer and workstation are expected to be used.

  Although the bus subsystem 804 is illustrated as a single bus, a typical system is a local bus and one or more expansion buses (eg, ADB, SCSI, ISA, EISA, MCA, NuBus, or PCI), And many buses such as serial and parallel ports. Usually, network communication is established through a device such as a network adapter on one of these expansion buses or a modem on a serial port. The client computer can be a desktop system or a portable system.

  The scanner 820 is responsible for the scan cast of the patient's teeth, either from the patient or from the orthodontist, and provides the scanned digital data set information to the data processing system 800 for further processing. In a distributed environment, the scanner 820 can be located at a remote location and communicates the scanned digital data set information to the data processing system 800 via the network interface 824.

  The production machine 822 produces dental instruments based on the intermediate and final data set information received from the data processing system 800. In a distributed environment, the production machine 822 can be located at a remote location and receives data set information from the data processing system 800 via the network interface 824.

  The invention has been described with reference to specific embodiments. Other embodiments are within the scope of the appended claims. For example, the three-dimensional scanning technique described above can be used to analyze material properties such as shrinkage and expansion of the material forming the teeth and aligners. Also, the 3D tooth model and graphical interface described above treat patients with conventional fixators or other conventional orthodontic appliances when constraints are applied and therefore tooth movement is altered. Can be used to assist clinicians to do so. In addition, the tooth model can be provided on the Hypertext Transfer Protocol (http) website for limited access by the corresponding patient and treating clinician.

FIG. 1A shows the patient's jaw and generally shows how the teeth can be moved. FIG. 1B shows one tooth from FIG. 1A and defines how the tooth travel distance is determined. FIG. 1C shows the jaw of FIG. 1A with an incremental position adjustment device. FIG. 2 is a block diagram illustrating steps for generating a system of incremental position adjustment devices. FIG. 3 is a diagram of a 3D model of a tooth using a triangular mesh. FIG. 3-2 is a continuation of FIG. 3-1. FIG. 4 is a flowchart illustrating a process for repeatedly separating a group of teeth into two groups of teeth. FIG. 5 is a flowchart illustrating a process for cutting or stitching gingiva from a tooth model. FIG. 6 shows an exemplary circular vertebral body shaped cutter and control points for this cutter. FIG. 7 is a flowchart showing automatic discovery of a gingival line. FIG. 8A is a flowchart showing the generation of a cut gingival surface model. FIG. 8B shows an exemplary surface model of a cut gingiva. FIG. 9 is a flowchart illustrating the use of a gingival cutting surface to remove gingiva from a tooth. FIG. 10 is a flow chart showing the creation of a compact crown portion for gingival cutting (not yet cut through the crown portion of the tooth). FIG. 11 illustrates one exemplary operation of the process of FIG. 10 on a tooth model. FIG. 12 shows an exemplary user interface for a cutter that can remove gingiva from a tooth model. FIG. 13 is a diagram of a system for making an instrument. FIG. 14 is a diagram of a computer system that supports the manufacture of the instrument.

Claims (1)

A computer-implemented method for separating gingiva from teeth.

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