The present invention relates to computer-assisted techniques for creating dental restoration models.
The art of fabricating custom-fit prosthetics in the dental field is well-known. Prosthetics are replacements for tooth or bone structure. They include restorations, replacements, inlays, onlays, veneers, full and partial crowns, bridges, implants, posts, and the like. Typically, a dentist prepares a tooth for a restoration by removing existing anatomy, which is then lost. The resultant prepared area (a “preparation”) is then digitized (or, in the alternative, a dental impression is taken) for the purpose of constructing a restoration. The restoration itself may be constructed through a variety of techniques including manually constructing the restoration, using automated techniques based on computer algorithms, or a combination of manual and automated techniques.
Computer-assisted techniques have been developed to generate three-dimensional (“3D”) visual images of physical objects, such as a dental preparation. In general, the 3D image may be generated by a computer that processes data representing the surfaces and contours of a physical object. The computer displays the 3D image on a screen or a computer monitor. The data may be generated by optically scanning the physical object and detecting or capturing the light reflected off of the object. Based on processing techniques, the shape, surfaces and/or contours of the object may be modeled by the computer. Optical scanning may be accomplished using a laser based system, such as the system described in “Laser Digitizer System for dental applications,” published Patent Application No. 20040254476, which is owned by D4D Technologies, LP. This application describes a laser digitizer having a light source, a scanner, a flat-field lens, an image capture instrument, and a processor configured to carry out instructions based on code, and to process digital data. The digitizer is used to scan a prepared area and to obtain a three dimensional (3D) data set representing the preparation as well as one or more teeth adjacent the preparation.
While computer-assisted techniques for creating a dental restoration model for a scanned preparation are known, these techniques do not always provide acceptable results. The present invention addresses this problem.
A method for generating a 3D model for a restoration is operative in a computer having a display. The method begins by obtaining a 3D model of the preparation. The preparation model may be obtained by an operator using a 3D digitizer if the model is not otherwise already available (or stored in) to the computer. A given curve on the preparation model is then determined, e.g., by the operator or the system. This curve is located at the margin where the final restoration is expected to join the preparation, and thus it is referred to herein as a “margin” curve. The method then continues by selecting a given 3D restoration cap model from a set of such models, where the set includes cap models that vary by one or more characteristics such as type, age, sex and ethnicity. The selection may be made by the operator, by the system, or in any other manner. The restoration cap model has an outer edge, which is referred to herein as a “cap edge.” The cap edge defines a cap edge curve that is then used in the modeling technique. In particular, in one embodiment, the method continues by fitting the restoration cap model over the preparation model (on the computer display) so that a minimum distance between the restoration cap and the restoration model is greater than a given minimum material thickness. The restoration cap model is then reshaped or otherwise scaled as necessary so that the restoration cap edge curve is related to the margin curve in a predetermined manner. In particular, preferably the cap edge curve is related to the margin curve by an angle from vertical that is equal or substantially equal to a given “emergence” angle at each point along the curve. To complete the model, a side surface is then created, preferably by lofting a surface from the margin curve to the cap edge curve.
The lofting process creates a well-defined tooth model. A more specific technique to generate the side surface is implemented, preferably by computer-executed program instructions, once the restoration cap has been positioned and shaped as required. In particular, preferably the side surface is formed by evaluating radial slices from the center of the restoration cap through the cap edge curve and the preparation's margin curve. Wherever the radial slice plane intersects the cap edge curve and the margin curve, a smooth curve is formed to join those two points. The curve may be formed using conventional means to join these points while maintaining a continuous first or second derivative at the cap edge. The set of smooth curves that are formed in the manner comprise the side surface of the tooth model. Each smooth curve may be further constrained to maintain a slope at the margin equal to the given emergence angle for that radial.
During the scaling operation, the restoration cap is positioned, shaped or scaled as required to enable the cap to fit between the existing teeth, as represented in the preparation. Such operations may be performed so that features in the restoration cap are aligned or otherwise line-up with features observed in the neighboring dentition, preferably as captured in the 3D scan of the preparation. For example, cusps of the cap may be lined up with cusps of the neighboring teeth. The central groove feature of the cap may be lined up with the equivalent feature in the tooth cap, and so forth.
Other features and advantages of the invention will be apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional features and advantages be included within this description, be within the scope of the invention, and be protected by the claims.
The invention may be better understood with reference to the following drawings and its accompanying description. Unless otherwise stated, the components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views.
The present invention is a method implemented, preferably in a computer. For illustrated purposes, the computer is a single machine, but this is not a limitation. More generally, the method is implemented using a set of one or more computing-related entities (systems, machines, processes, programs, libraries, functions, or the like) that facilitate or provide the inventive functionality. As seen in
More specifically, the computer 100 comprises hardware 102, suitable storage 104 and memory 105 for storing an operating system 106, one or more software applications 108 and data 110, conventional input and output devices (a display 112, a keyboard 114, a point-and-click device 116, and the like), other devices 118 to provide network connectivity, and the like. A laser digitizer system 115 is used to obtain optical scans, e.g., from preexisting anatomy. A representative digitizer system is described in commonly-owned, co-pending published application No. 20040254476, the disclosure of which is incorporated herein by reference. Using a conventional graphical user interface 120, an operator can view and manipulate models as they are rendered on the display 112.
As illustrated in
Another 3D surface, called a restoration cap model, is then selected. This selection may be made by the operator, by the system using automated techniques, by a combination of such techniques, or in any other convenient manner. As illustrated in
As illustrated in
In most cases, the restoration cap illustrated in
The cap may be further positioned, shaped or scaled as required in order for the cap to fit between the existing teeth. Such operations may be performed so that features in the cap line up with features observed in the neighboring dentition, as captured in the 3D scan of the preparation. For example, cusps of the cap may be lined up with cusps of the neighbors. The central groove feature of the cap may be lined up with the equivalent feature in the tooth cap. The cap may be adjusted so that the cap cusp height follows the curve of Spee with respect to the cusp height of the neighbors.
Once the cap has been positioned and shaped as required, the side surface is formed by looking at radial slices from the center of the cap through the cap edge curve and the margin curve. Wherever the radial slice plane intersects the cap edge curve and the margin curve, a smooth curve is formed that joins those two points, which are designated P1 and P2 in
As used herein, the side surface is created by a computer-implemented surface “lofting,” which is a known surfacing process that creates a surface using a series of curves as profiles between a starting curve and an ending curve. Further details of surface lofting are described, for example, in “The NURBS book” by Les A. Piegl and Wayne Tiller, 2d Edition.
Thus, according to the invention, a restoration cap model is positioned over the preparation model so that a minimum distance between the restoration cap model and the preparation model is greater than a given specified material thickness. The restoration cap model is then shaped to conform to the margin curve of the preparation model. Thereafter, a side surface is lofted from the margin curve to the edge curve to generate the outer surface of the three dimensional model for the restoration. The interior portion of the restoration model is of course obtained from the 3D image of the preparation itself (namely, that part of the digitized preparation contained within the margin curve). This is the part of the restoration model that is not designed; rather, it is obtained from the model itself as it is the interface between the restoration and the preparation.
In an alternative embodiment, a restoration cap model is first selected from a set of restoration cap models. The restoration cap model is then positioned, resized and reshaped as necessary to conform to the preparation model. To complete the model, the side surface is lofted, along each radial, from the margin curve of the preparation to the edge curve of the restoration cap. The resulting 3D model is then used to create the dental restoration using conventional means.
While certain aspects or features of the present invention have been described in the context of a computer-based method or process, this is not a limitation of the invention. Moreover, such computer-based methods may be implemented in an apparatus or system for performing the described operations, or as an adjunct to other dental restoration equipment, devices or systems. This apparatus may be specially constructed for the required purposes, or it may comprise a general purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including optical disks, CD-ROMs, and magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), magnetic or optical cards, or any type of media suitable for storing electronic instructions, and each coupled to a computer system bus.
While the above describes a particular order of operations performed by certain embodiments of the invention, it should be understood that such order is exemplary, as alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, or the like. References in the specification to a given embodiment indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Further, while given components of the system have been described separately, one of ordinary skill will appreciate that some of the functions may be combined or shared in given systems, machines, devices, processes, instructions, program sequences, code portions, and the like.
Having now described our invention, what we claim is as follows: