Abstract:
A method is set forth for making a computer model of patient&#39;s jaws, face, teeth and removable dentures on the basis of digital information. Three dimensional digital data about the soft tissues, artificial teeth, supporting bone and position of nerves is combined in a virtual computer model to create an aesthetic and functional plan for the creation of surgical drill guides and the creation of new dentures and teeth. A key component of this method, the accurate positioning of dental casts in a physical articulator, is simplified using three dimensional virtual and physical measurements and movements. Surgical guides used to position dental implants are manufactured using computer milling, layered manufacturing or conventional laboratory techniques with the aid of mechanical tools that reproduce the position of the dental cast or digitally produced replica in the same orientation to the virtual implant position. This method eliminates the need to create radiographic templates of proposed restorations or damaging a patient&#39;s removable prosthesis to use it for imaging.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 (e) to U.S. Provisional Patent Application No. 61/257,974 filed Nov. 4, 2009, the disclosure of which is incorporated herein by reference. 
    
    
     FIELD 
     The present application generally relates to a dental apparatus and method, and more particularly to methods of orienting dental casts in an articulator based digital models, and the construction of devices using such techniques. 
     BACKGROUND 
     Many methods of planning and guiding the proper position of dental implants have been revealed. Frequently a radiographic template is made to fit to the patient&#39;s teeth, and radiographic markers are attached to the template. Klein (U.S. Pat. No. 5,967,777) revealed a method that uses a plastic replica of the prospective teeth to be supported by dental implants. This is a time consuming process since a dental laboratory technician must set or carve teeth to fit in the ideal position for a given patient. The patient is then scanned with the radiographic template, preferably using computed tomography (CT). If the patient has teeth that will be removed at the time of implant placement, it is difficult to image these areas since the teeth are still present and radiographic scatter frequently makes it difficult to determine the actual shape of the teeth. It is also difficult to position the template in a predictable position after the teeth to be removed. Other methods have been revealed that require the patient&#39;s teeth be removed first and removable dentures made. 
     The NobelGuide™ (Nobel Biocare) system uses this technique. After healing, radiographic markers are placed in the dentures and the patient is imaged using CT. A second scan of the patient&#39;s denture is made of the denture alone, and then the radiographic markers are used to align the two CT scans in the same computer space. The Nobel system allows for planning of the dental implant position in relation to the patient&#39;s denture and the supporting bone, but it requires that the patient&#39;s dentures be damaged by placing gutta percha markers in the plastic to align the images. If the dentures are not used, then they are duplicated to make a new set with radiographic markers. Generally, the duplicate set is less accurate, which involves an additional cost and source of errors. 
     Thus, there is a need for an improved method of imaging a patient and planning for implant placement that provides for the virtual positioning of artificial teeth in harmony with the patient&#39;s facial structure and appearance and the virtual positioning of implants in relation to the remaining bone. There is also a need for a method of communicating this information easily to the surgeon, restorative dentist and laboratory. It is also desirable that changes can be made in the virtual plan such that the surgeon, restorative dentist or laboratory can modify the treatment plan as needed. 
     SUMMARY 
     A method of positioning a model of a patient&#39;s dentition may comprise receiving first digital data representative of a patient&#39;s dentition; receiving CT data of the patient&#39;s fossae and a CT bite plate having three or more non-linear radiographic markers, said dentition being oriented with respect to said fossae in an actual orientation, said CT bite plate being engaged with said dentition; creating a virtual model of said dentition, said fossae, and said radiographic markers from said first digital data and said CT data, said virtual model comprising a virtual representation of said dentition, a virtual representation of said fossae, and a virtual representation of said radiographic markers, wherein said virtual representation of said dentition is oriented with respect to said virtual representation of said fossae in a virtual orientation, said virtual orientation being substantially the same as said actual orientation; mounting an actual model of said dentition in a positioning device using said CT bite plate, said positioning device comprising a removable mounting plate, said mounting plate being attachable to an actual articulator in a known orientation; orienting said actual model of said dentition with respect to said mounting plate in said positioning device; attaching said actual model to said mounting plate; removing said actual model and said mounting plate from said positioning device; and positioning said actual model in said actual articulator using said mounting plate. 
     U.S. patent application Ser. No. 11/674,956 entitled Method of Making a Virtual Computer Model of the Jaws, which is herein incorporated by reference, reveals a method of using computed tomography (CT) to image the hard and soft tissues of the head and neck. It also reveals a method of imaging dental casts of a patient using non-radiographic techniques to eliminate radiographic scatter caused by dental restorations in CT scans. 
     U.S. patent application Ser. No. 11/739,310 Computer Milled Dental Tooth System, which is herein incorporated by reference, reveals a method of tracking the positional relationship of the upper and lower jaws with static records (wax bites), average measurements, and a digital recording device called ARCUSdigma digital recorder (KAVO Company). It also reveals a method of virtually positioning artificial denture teeth and using computer milling to shape the teeth and the dental cast to construct immediate dentures using digital technology. 
     U.S. patent application Ser. No. 11/851,105 Method and Process for the Virtual Design and Computer Manufacture of Intra Oral Devices, which is herein incorporated by reference, reveals a method of imaging dental casts, recording spatial relationships, and creating virtual movement of the models such that actual devices can be made with computer technology. 
     U.S. patent application Ser. No. 11/867,590, Surgical Guides and Method for Positioning Artificial Teeth and Dental Implants, which is herein incorporated by reference, reveals methods of evaluating and treating a patient&#39;s anatomy prior to tooth removal and planning ideal position of artificial teeth. It also is directed to methods for the computer manufacturing of artificial teeth attached to dental implants. 
     U.S. Pat. No. 7,322,824 issued Jan. 29, 2008, and U.S. patent application Ser. No. 12/048,047 filed Mar. 13, 2008 and Ser. No. 12/208,163 filed Sep. 10, 2008 are incorporated herein by reference. 
     The methods and apparatus taught in the foregoing applications and patent may be used as a basis for creating virtual models as described herein. 
     In some embodiments, methods are presented to create a digital image of a patient using the patient&#39;s existing teeth or removable dentures to record the spatial orientation of the jaws and shape of the soft tissues in relation to the supporting bone without damaging or altering the dentures or natural teeth. 
     In some embodiments, methods are presented for positioning physical dental casts or digital replicas of dental casts in an articulator in the same spatial orientation to the patient&#39;s rotational centers, planned incisal edge position, and anatomic planes as existed in the digital imaging. 
     In some embodiments, methods are presented to create a virtual computer model of a patient&#39;s mouth and to ideally position virtual artificial teeth in proper spatial orientation to the supporting tissues, teeth, and the opposing arch. The positioning of teeth may be determined by the use of virtual planes, curved surfaces, or other digital references. 
     In some embodiments, methods are presented to virtually determine the ideal position to place implants in the remaining supporting bone. 
     In some embodiments, methods are provided for the restorative dentist, surgeon, and laboratory to communicate and change, if needed, the actual 3D virtual plan for any given patient via the Internet. 
     In some embodiments, methods are provided to use advanced computer manufacturing techniques (e.g., milling and layered manufacturing) to make drill guides, immediate dentures, and immediate load prostheses with minimal manual labor. 
     In some embodiments, methods are provided to use mechanical positioning devices to reproduce the spatial orientation of the dental cast or replica of the dental cast to the virtual dental implant position and to use conventional laboratory techniques to make the surgical template. 
     In some embodiments, methods are provided for evaluating the aesthetic appearance of a patient prior to tooth removal and to use virtual techniques that allow for the selection of ideal replacement teeth, shaping the supporting bone, placing implants, construction of surgical guides and immediate prosthesis all via the Internet such that many individuals in different parts of the world can communicate and support the process of planning and treating patients that require implant therapy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a CT bite plate. 
         FIG. 2A  illustrates a CT bite plate.  FIG. 2B  illustrates the CT bite plate in the patient&#39;s mouth positioned between removable dentures.  FIG. 2C  illustrates a CT bite plate attached to dentures. 
         FIG. 3  illustrates a patient being imaged in a CT scanner 
         FIG. 4A  is a side perspective view that illustrates the three dimensional rendering of CT data locating radiographic markers, rotational centers, and anatomical markers for the ideal placement of teeth;  FIG. 4B  is a coronal view that illustrates alignment of a virtual image of upper teeth and boney structures to a corresponding position and boney structures in a virtual representation of an articulator;  FIG. 4C  is a frontal view of virtual image data that illustrates a nasion point and an anterior nasal spine point; and  FIG. 4D  is a coronal view of virtual image data that illustrates coronal rotation about a point which is the center of a rotational axis. 
         FIG. 5  illustrates a complete denture, a dental cast attached to the denture, a vacuum formed template, and a template filled with cured material to create a replica of a denture. 
         FIG. 6  shows a mechanical device for positioning the CT bite plate and upper denture/cast in the same relationship to the rotational centers as recorded in the CT image. 
         FIG. 7  illustrates a five-axis mill used to create bores in the dental cast to position guide tubes. 
         FIG. 8  illustrates the tool of a five-axis mill and bore holes in a dental cast. 
         FIG. 9  is an illustration of a three-piece device for positioning guide tubes in the correct position on a dental cast. 
     
    
    
     DETAILED DESCRIPTION 
     The term “dental cast” as used herein means a structure composed of any material that is shaped to model a patient&#39;s natural teeth or denture. A dental cast may correspond to the upper jaw, the lower jaw or both. 
       FIG. 1  illustrates a CT bite plate assembly  12 . The bite plate assembly  12  has a U-shaped rigid section attached to a thin bite surface  13  made of a radiolucent material that will mate with the patient&#39;s teeth and yet have minimal opening of the jaws. The assembly  12  has central forward projections  5  that extend between the lips when the assembly is placed in the mouth. The forward projections  5  join a vertical portion that extends above or below the plane of occlusion. Wings  20  extend laterally from the vertical portion and generally follow the contour of the face but do not contact it. Three or more non-linear radiographic markers  25  are attached to the vertical and wing portions of the CT bite plate. These markers have a radiographic density that makes them visible in CT data, such as may be collected as shown in  FIG. 3 , and also have a geometric shape that can be converted to a digital image with non-radiographic imaging, including for example contact, light, laser, or holographic techniques. Bite registration material  28  records the indentations  30  of any of the upper and lower teeth of a patient, or of a denture, when the patient bites into the CT bite plate. Note the indentation  101  made by one of a patient&#39;s incisor teeth, or associated portion of a denture. The indentation  101  may, as described below, become associated with a virtual image of an incisor and may be a useful reference point for movement of a virtual model as discussed with respect to  FIG. 4B . 
       FIG. 2A  illustrates the CT bite plate assembly  12  with radiographic markers  25 .  FIG. 2B  illustrates the CT bite plate assembly positioned between the patient&#39;s dentures in his mouth.  FIG. 2C  illustrates that the dentures can be altered with impression material  30  to provide a better adaptation to the soft tissues and shape for new dentures. In some embodiments, bite registration material  28  may be placed on the CT bite plate to record the position of the patient&#39;s existing teeth or dentures and jaws using a CT scan. In some embodiments, bite registration material  28  may be placed on the CT bite plate to record the position of the patient&#39;s existing teeth or denture and jaws using non-radiographic means. 
       FIG. 3  illustrates a CT bite plate  12  placed in the patient&#39;s mouth and the patient positioned in a CT machine  46 . An x-ray source  48  projects radiation across the patient&#39;s head and is detected on a sensor  50 . 
     In some embodiments, in addition to the CT scan data collected as shown in  FIG. 3  a second scan using, for example, non-radiographic techniques may be made. Non-radiographic techniques may include, for example and without limitation, contact, light, laser, or holographic imaging. The second scan may be made of the dentures or a dental cast wherein the CT bite plate is disposed outside of the patient&#39;s mouth to record the patient&#39;s occlusal and tissue surfaces. The two scans can then be aligned in a computer model using the radiographic markers  25 . Such techniques are described in more detail in U.S. patent application Ser. No. 11/851,105, of which Applicant is the sole inventor. 
     Imaging an impression of the patient&#39;s existing teeth or denture and the CT bite plate may be performed in a manner that does not damage the denture, any existing teeth, or both. In some embodiments, the undamaged denture may be returned to the patient. In some embodiments the denture and any impression material may be altered, such as by injecting a contrast agent into either the denture or the impression material. 
       FIG. 4A  illustrates the 3D rendering of the CT data to record the shape of bone, dentition, CT bite plate, radiographic markers  25 , rotational centers  17  and axis of rotation  19 . The rotational centers  17  are identified using 3D data such as the skin and tragus of the ear, external auditory meatus, condylar head, condylar fossae or actual digital recording of the axis points. The location of the incisor tooth before treatment can also be located from the indentation  101  on the CT bite plate or in the CT data. 
       FIG. 4B  is a coronal view and illustrates the alignment of data representing a virtual image of the upper teeth and upper boney structures A to the precise corresponding position and boney structures in a virtual representation of an articulator B. The alignment of a virtual image of the upper teeth and upper bony structures to the virtual articulator may be accomplished using related points. For example, point  102  may be a virtual representation of the left fossae in the virtual image of the upper teeth and upper boney structures A and may relate to point  106 , a virtual representation of the left mechanical fossae, in a virtual representation of an articulator. Point  121  may be a virtual representation of the right fossae in the virtual image of the upper teeth and upper boney structures A and may relate to point  122 , a virtual representation of the right mechanical fossae, in a virtual representation of an articulator. Thus, the virtual model may include the locations of the anatomic fossae. Point  103  may be a virtual representation of the incisor and may relate to point  105 , a virtual representation of the vertical position of the incisal pointer, in the virtual representation of an articulator. Ideally, at least three related points may be used to align a virtual image of the upper teeth and upper boney structures A to the precise corresponding position of a virtual representation of an articulator B. 
     Once a virtual image of the upper teeth and upper boney structures is oriented with a virtual representation of the articulator, the virtual data of either object may be modified in any number of ways, including for example, by translation or rotation, and modification of the other object may be correlated. In some embodiments, an origin point, located in three dimensional space, may be used to relate translation or rotation of a virtual object. In some embodiments, the alignment of data representing a virtual image of the upper teeth and upper boney structures A to the precise corresponding position and boney structures in a virtual representation of an articulator B (as shown in  FIG. 4B ) may be followed by defining a common origin point for both objects. In some embodiments, a common origin point may be related to two virtual objects, and the trigonometric relationship of the common origin points may be known with regards to the reference points for an object and markers, including radiographic markers  25 . In some embodiments, motion of a virtual object may be correlated with movement of the physical object represented by that virtual object through knowledge of the physical location of radiographic markers  25 . For example, as further shown below in  FIG. 6 , three non-linear markers  25  are shown, and those markers  25  may serve to relate data in virtual space to physical objects. 
       FIG. 4C  is a frontal view of the virtual image data showing the nasion point  114  and the anterior nasal spine point  110  from the CT data. This data may be rotated in the frontal plane of the virtual representation of an articulator around the anterior nasal spine to position the nasion in a vertical position directly over the anterior nasal spine. 
       FIG. 4D  is a coronal view of the virtual data of the patient identifying the coronal rotation about the point  116  which is the center of the rotational axis  19 , which may be a line connecting the anatomic fossae  102 ,  121 . 
       FIG. 5A  illustrates a complete denture  35  after the CT scan has been made. In  FIG. 5B  the inside of the denture  35  is filled with dental stone to record the shape of the patient&#39;s soft tissue and to create a dental cast  42 .  FIG. 5C  illustrates vacuum formed material  43  placed over the patient&#39;s denture to record the shape of the denture and create a replica of the denture.  FIG. 5D  illustrates the vacuum formed template filled with a curable material  36  to reproduce the shape of the denture. Such procedures are described in more detail in U.S. Pat. No. 7,322,824, of which Applicant is the sole inventor. 
     In some embodiments, the denture is a physical object that correlates with the virtual image of the teeth as shown in relation to  FIG. 4 . It should also be understood that the orientation of the upper denture with regards to the three non-linear radiographic markers is known, irrespective of whether or not dentition is imaged using radiographic or non-radiographic methods. 
       FIG. 6  illustrates a device  18  for positioning the dental cast or denture  36  in the precisely corresponding relationship to the rotational axis of the patient. This eliminates the need for a face bow and allows the completed computer generated prosthesis to be placed in an articulator for physical evaluation. The CT scan image data is used to determine the positional relationship of the three radiographic markers  25  and rotational centers in the virtual image. These positional relationships are then reproduced for the physical models using simple trigonometric functions. Rotational centers  17  are located in relation to the physical positioning device. In some embodiments, motion of the bottom portion  57  of the positioning device  18  may be tracked, such that the relative positions of the top portion  55  and bottom portion  57  of the device are known. In some embodiments, the CT bite plate  12  may be attached to the bottom portion  57  of the positioning device  18  in a known and reproducible manner. Positioning of the radiographic markers  25  with respect to the bottom portion  57  of the device is therefore also reproducible and known. In that light, the position of the radiographic markers  25  and denture  36 , or dental cast, are known with respect to the bottom portion  57  of the device, and the position of the mounting plate  49  is known with respect to the top portion  55  of the device  18 , and thus the relative positions of the radiographic markers  25 , denture  36  and mounting plate  49  are all known and can be tracked as the jig  44  is moved. In addition, the position of the radiographic markers  25  are known with respect to the rotational centers  17  in virtual space. Therefore, physical components on the device  18 , including the mounting plate  49 , denture  36  and radiographic markers  25 , can all be positioned with respect to the virtual image data of the patient&#39;s upper teeth and upper bony structures and to reference points on the virtual articulator. Furthermore, the mounting plate  49  may, in some embodiments, have a known orientation to the mechanical fossae of an actual physical articulator when mounted in an actual physical articulator. In some embodiments, the mounting plate  49  may be constructed such that it may be attached to and removable from the top portion  55 , or alternatively, mounting plate  49  and top portion  55  may be removable from the positioning device together. 
     The CT bite plate  12  and upper or lower cast/denture  36  is attached to a jig  44  that allows for movement around a multiple axes. The jig rotates the CT bite plate  12  about the Z axis and allows tilting about the X and Y axis. This makes it possible to orient the CT bite  12  in the same angulations as existed in the CT scan or any position that is needed for the diagnostic process. The linear slides allow movement  54 ,  52 ,  50  along the X, Y, and Z axes, respectively. After the CT bite plate  12 , denture replica  36  and cast  42  are positioned correctly, the cast is joined to the mounting plate  49 . In some embodiments, movements of the jig may be accomplished manually by an operator. In some embodiments, movement of the jig maybe accomplished in an automated manner, such as by computer control. An operator, therefore, can maneuver the mounting plate  49  in any desired orientation with regards to other structures shown in  FIG. 6 . In some embodiments, the mounting plate  49  would be oriented with regards to the cast  42  such that when the mounting plate is removed and placed on an actual physical articulator, it is in a desired orientation. Such a desired orientation may, for example, orient the dental cast  42  with regards to the mechanical fossae. In some embodiments, the mounting plate  49  and cast  42  are fixed in a desired orientation by adding an acceptable fixing agent or glue, including for example mounting stone to gap  62 . Mounting stone may be, for example, a fast setting gypsum-based material with minimal expansion, or other suitable material. In some embodiments, this allows the cast  42  to be transferred to a mechanical articulator, thus eliminating the need for a face bow. 
       FIG. 7  is an illustration of a five-axis mill used to create bore holes in a dental cast  42  in the correct positions in relation to the virtual model. The mill allows for linear movement  54 ,  52 ,  50  along the X, Y, and Z axes, respectively. Rotational motion  63  is capable around the Z axis, and rotational motion  58  is capable about the X axis. A magnetic receiver  60  holds the mounting plate  49  and cast  42  in the proper orientation with respect to the machine tool  56 . 
       FIG. 8  shows the machine tool  56  and bore holes  70  created in the dental cast for placement of guide tubes. 
       FIG. 9  illustrates a tube retaining device  125  for positioning guide tubes in the bore holes and allows for the removal of the guide tubes and template from the cast even though the tubes are at divergent angles.  FIG. 9A  illustrates the tube retaining device  125  screwed together.  FIG. 9B  illustrates an exploded view of the tube retaining device  125  with the retaining screw  79 , guide tube  77  and bore receiver  81 . The bore receiver  81  is cemented into the bore holes created with the five-axis mill to record the exact position and angle for placing a specific implant from the CT imaging and planning process. The bore receiver has a threaded internal bore hole that matches the retaining screw  79 . Next, the guide tube  77  and retaining screw  79  are attached to the bore receiver  81 . Acrylic resin  75  or other types of curable or thermoplastic materials are then placed on the cast  42  and around the guide tubes  77  to record their position. After the resin has cured, the retaining screws  79  are removed and the surgical template  75  is separated from the cast  42 . 
     Although the foregoing specific details describe certain embodiments of this invention, persons reasonably skilled in the art will recognize that various changes may be made in the details of this invention without departing from the spirit and scope of the invention as defined in the appended claims and considering the doctrine of equivalents. Therefore, it should be understood that this invention is not to be limited to the specific details shown and described herein.