Patent Publication Number: US-2022233286-A1

Title: System and method for scanning an intraoral cavity

Description:
CROSS-REFERENCE 
     This application is a continuation of U.S. application Ser. No. 16/179,601 filed Nov. 2, 2018, which is a continuation of U.S. application Ser. No. 15/488,297, filed Apr. 14, 2017, now U.S. Pat. No. 10,159,546, issued Dec. 25, 2018, which is a continuation of U.S. application Ser. No. 12/980,587, filed Dec. 29, 2010, now U.S. Pat. No. 9,683,835, issued Jun. 20, 2017, which is a continuation of U.S. application Ser. No. 11/889,002, filed Aug. 8, 2007, now U.S. Pat. No. 7,890,290, issued Feb. 15, 2011, which is a continuation of U.S. application Ser. No. 11/365,589, filed Mar. 2, 2006, now U.S. Pat. No. 7,286,954, issued Oct. 23, 2007, which claims the benefit of U.S. Provisional Application No. 60/657,705, filed Mar. 3, 2005, all of which are incorporated herein by reference in their entirety and to which applications we claim priority under 35 USC § 120. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a system and method for providing guidance for scanning the intra oral cavity to provide three dimensional data that may be subsequently used in prosthodontic and orthodontic procedures in the intra oral cavity. In particular, the invention relates to such systems and methods that are computerized. 
     BACKGROUND OF THE INVENTION 
     In prosthodontic procedures designed to implant a dental prosthesis in the intra oral cavity, the dental site at which the prosthesis is to be implanted in many cases needs to be measured accurately and studied carefully, so that a prosthesis such as a crown or bridge, for example, can be properly designed and dimensioned to fit in place. A good fit is of the highest importance to enable mechanical stresses to be properly transmitted between the prosthesis and the jaw, and to prevent infection of the gums and so on via the interface between the prosthesis and the dental site, for example. 
     In the prior art, the dental site is prepared by the dental practitioner, and a positive physical model of the site is constructed using known methods. Alternatively, the dental site may be scanned to provide 3D data of the site. In either case, the virtual or real model of the site is sent to the dental lab, which manufactures the prosthesis based on the model. However, if the model is deficient or undefined in certain areas, or if the preparation was not optimally configured for receiving the prosthesis, the dental technician has a more difficult job ahead than otherwise, and the design of the prosthesis may be less than optimal. For example, if the insertion path implied by the preparation for a closely-fitting coping would result in the prosthesis colliding with adjacent teeth, the coping geometry has to be altered to avoid the collision, but this may result in the coping design being less optimal. Further, if the area of the preparation containing the finish line lacks definition, it may not be possible to properly determine the finish line and thus the lower edge of the coping may not be properly designed. Indeed, in some circumstances, the model is rejected and the dental practitioner must re-scan the dental site, or must rework the preparation, so that a suitable prosthesis may be produced. 
     In orthodontic procedures it is also necessary to provide a model of one or both jaws. Where such orthodontic procedures are designed virtually (herein also referred to as “numerically”), a virtual model of the intraoral cavity is also required, and this may be obtained, inter alia, by scanning the intraoral cavity directly, or by producing a physical model of the dentition, and then scanning the model with a suitable scanner. 
     Thus, in both prosthodontic and orthodontic procedures, obtaining a three-dimensional (3D) model of a least a part of the intraoral cavity is an initial requirement. When the 3D model is a virtual model, the more complete and accurate the scans of the intraoral cavity are, the higher the quality of the virtual model, and thus the greater the ability to design an optimal prosthesis or orthodontic treatment. 
     Prior art methods of scanning the intraoral cavity do not provide guidance to the dental practitioner on how to ensure full and accurate scanning of parts of the cavity of interest for a particular orthodontic or prosthodontic procedure. Rather, the dental practitioner uses his or her judgment on site, and it is often the case that the scans of some areas of interest may be defective, while other unimportant areas may be scanned to great accuracy with details, which is wasteful of the practitioner&#39;s and the patient&#39;s time. 
     SUMMARY OF THE INVENTION 
     Herein, “dental material” refers to any material associated with dental structures of the intra oral cavity, including but not limited to natural dental materials such as for example enamel, dentine, pulp, dental roots, and non-natural dental materials such as for example metallic and non-metallic filings, restorations, crowns, bridges, copings, preparations, and so on. 
     Herein, “dental clinic” refers to the interface between a dental practitioner and a patent, and thus includes any physical entity, in particular a clinic, in which there is interaction between a dental patient and a dental practitioner. While “dental practitioner” typically refers to a dentist, doctor or dental technician, it also includes herein all other caregivers that may interact with a dental patient during the course of a dental treatment. While “dental patient” typically refers to a person requiring the dental services of a dental practitioner, it also includes herein any person regarding whom it is desired to create a 3D numerical model of the intra oral cavity thereof, for example for the purpose of practicing the same or for carrying out research. 
     The term “prosthesis” is herein taken to include any restoration and any onlays, such as crowns and bridges, for example, and inlays, such as caps, for example, and any other artificial partial or complete denture. 
     While the term “preparation” typically refers to the stump (including the finish line and optionally the shoulder) that is left of the tooth that is to be replaced by the prosthesis—typically a crown—and on which the crown is to be mounted, the term herein also includes artificial stumps, pivots, cores and posts, or other devices that may be implanted in the intraoral cavity in such a position or in a position that is optimal for implanting the crown. 
     The term “prosthodontic procedure” refers, inter alia, to any procedure involving the intraoral cavity and directed to the design, manufacture or installation of a dental prosthesis at a dental site within the intraoral cavity, or a real or virtual model thereof, or directed to the design and preparation of the dental site to receive such a prosthesis. 
     The term “orthodontic procedure” refers, inter alia, to any procedure involving the intraoral cavity and directed to the design, manufacture or installation of orthodontic elements at a dental site within the intraoral cavity, or a real or virtual model thereof, or directed to the design and preparation of the dental site to receive such orthodontic elements. 
     The term “numerical entity” is used herein synonymously with virtual model, 3D model, and other such terms, and relates to a virtual representation in a computer environment of a real object, typically a dentition or at least a part of intraoral cavity, or of a real model thereof, for example. 
     The term “scanning” and its analogues refer to any procedure directed at obtaining 3D topographic data of a surface, particularly of a dental surface, and thus includes mechanical methods, typically based on 3D probes for example, optical methods, including for example confocal methods, for example as disclosed in WO 00/08415, the contents of which are incorporated herein in their entirety by reference, or indeed any other method. 
     The term “display” and its analogues refer to any means or method for delivering a presentation, which may include any information, data, images, sounds, etc, and thus the delivery may be in visual and/or audio form. 
     The present invention is directed to a method for scanning an intraoral cavity, and thus to a corresponding method for facilitating scanning of an intraoral cavity, the method comprising 
     (a) identifying target parts of the intraoral cavity that it is desired to have scanned; 
     (b) identifying spatial relationships between a scanning device and said target parts of the intraoral cavity suitable for enabling said target parts to be scanned by said scanning device; 
     (c) displaying said relationships; and 
     (d) using said displayed relationships as a guide for scanning the intraoral cavity. 
     The method further comprises the step of scanning said intraoral cavity in a manner substantially conforming to said relationships. 
     The scanning substantially provides 3D data of said target parts for use in a predetermined procedure. Step (a) may include identifying ancillary parts in said intraoral cavity associated with said target parts, wherein 3D data of said ancillary parts is also required for use in said predetermined dental procedure. Step (b) may comprise, for each said target part and each said ancillary part, determining for said scanning device a series of spatial parameters, each comprising a scanning station data sufficient for enabling said scanner to fully scan said corresponding target part or ancillary part. Optionally, the scanning station data of said series include a proximity and a relative orientation of said scanner with respect to said target part or ancillary part such as to enable said scanner to obtain 3D topographical data of an area of said target part or ancillary part. The series provide 3D topographical data for a corresponding plurality of said areas, wherein said spatial parameters of said series are determined such at least some adjacent said areas overlap one another. 
     In one embodiment, step (c) comprises displaying a nominal image comprising an image of at least a portion of an nominal intraoral cavity, comprising corresponding said target parts and said ancillary parts, and an image of a nominal scanner in a spatial relationship with respect to one another corresponding to the spatial relationship as determined in step (b) for at least one parameter of said series of parameters. A series of said nominal images may be provided, each image in said series corresponding to a different one of said parameters of said series of parameters. The series of images can be displayed in any predetermined sequence. Optionally, the nominal image comprises 3D attributes. The image may comprise said nominal intraoral cavity at any desired orientation with respect to a predetermined coordinate system. The coordinate system may comprise, for example, an orthogonal Cartesian axes system. The orientation may optionally correspond to a real life view of the intraoral cavity of a patient from the vantage point of a dental practitioner. Optionally, an audio and/or visual cue is provided for prompting the user to proceed to the next image. 
     In another embodiment, step (c) comprises displaying indicia on a viewfinder capable of providing a video image of the field of view of said scanner, said indicia being indicative of a desired position for associating a predetermined portion of said target parts or ancillary parts in a particular manner with respect therewith. The indicia may comprise, for example, an “+” or an “X” or any other suitable symbol, which may be, for example, geometrical, alphanumeric and so on. 
     In a variation of this embodiment, the indicia comprise a symbol representative of a profile corresponding to an expected view of said target part or ancillary part in said viewfinder. Optical or image recognition methods can be applied to said video image for providing a profile of the image, said symbol comprising said profile. For example, the profile comprises a shaped line shaped as an outline of a tooth as seen via said viewfinder. The symbol may comprise a shaped line shaped as an outline of a tooth seen in any one of top view, buccal view or lingual view, for example. 
     Optionally, a series of indicia are provided, each indicia in said series corresponding to a different one of said parameters of said series of parameters. Said series of indicia may be displayed in a predetermined sequence, a next indicia being displayed after the intraoral cavity has been scanned according to the previous said parameter and corresponding indicia. Said next indicia may be displayed together with the immediately preceding indicia. Optionally, indicia relating to different said parameters may be displayed in different colors one from another. 
     The aforesaid procedure may be, for example, a prosthodontic procedure for a crown with respect to a preparation, said target parts comprising said preparation, and said ancillary parts comprising at least a portion of the teeth adjacent to said preparation and facing said preparation from the opposed jaw. 
     The aforesaid procedure may be, for example, a procedure is a prosthodontic procedure for a bridge with respect to a plurality of preparations, said target parts comprising said preparations, and said ancillary parts comprising at least a portion of the teeth adjacent to a furthermost distal preparation and adjacent a furthermost mesial preparation, and at least a portion of the teeth facing said preparations from the opposed jaw. 
     The aforesaid procedure may be, for example, a procedure is an orthodontic procedure, and said target parts comprise the full dentition of at least one jaw of said intraoral cavity. Typically the method of the invention is a computerized method, i.e., executed partly or fully with the aid of a processing unit such as a computer. Nevertheless, at least some embodiments may be executed without the need of a computer. 
     The present invention also relates to a computer readable medium that embodies in a tangible manner a program executable for guiding the scanning of the intraoral cavity of a patient, comprising: 
     (a) a first set of data representative of target parts of the intraoral cavity that it is desired to have scanned; 
     (b) a second set of data representative of spatial relationships between a scanning device arid said target parts of the intraoral cavity suitable for enabling said target parts to be scanned by said scanning device. 
     The computer readable medium may further comprise means such as manipulation routines, computer instructions, and so on, for example, for manipulating said second set of data for enabling displaying said second data. 
     The medium may comprise any one of optical discs, magnetic discs, magnetic tapes, and so on, for example. 
     The present invention is also directed to a system for guiding the scanning of an intraoral cavity, comprising: 
     (A) input module for identifying target parts of the intraoral cavity that it is desired to have scanned; 
     (B) processing module for generating spatial relationships between a scanning device and said target parts of the intraoral cavity suitable for enabling said target parts to be scanned by said scanning device; 
     (C) display module for displaying said relationships. 
     The system preferably also comprises a suitable scanner for scanning according to said relationships. 
     INCORPORATION BY REFERENCE 
     All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to understand the invention and to see how it may be carried out in practice, a number of embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a block diagram of a scanning process according to an embodiment of the invention. 
         FIG. 2  shows a block diagram of a scanning system according to an embodiment of the invention. 
         FIG. 3  shows a virtual representation of a dentition enabling target areas to be chosen interactively. 
         FIG. 4  illustrates target parts and ancillary parts of an intraoral cavity associated with a crown prosthodontic procedure. 
         FIG. 5  shows a buccal view of an idealized virtual model of a nominal intraoral cavity showing a plurality of scanning stations. 
         FIG. 6  shows a top view of an idealized virtual model of a nominal intraoral cavity showing a plurality of scanning stations. 
         FIG. 7  shows the relationship between a scanning station and a dental surface being scanned thereat. 
         FIGS. 8 a  and 8 b    illustrate examples of display output using the system of  FIG. 2  according to one embodiment. 
         FIGS. 9 a  and 9 b    illustrate examples of display output using the system of  FIG. 2  according to another embodiment. 
         FIGS. 10 a , 10 b , 10 c    illustrate the embodiment of  FIGS. 9 a , 9 b   , used for guiding scanning from one scanning station to a next scanning station. 
         FIGS. 11 a  and 11 b    illustrate examples of display output according to a variation of the embodiment of  FIGS. 9 a   ,  9   b.    
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a block diagram of the 3D data acquisition process  100  according to an embodiment of the invention, and  FIG. 2  illustrates the main elements of a system  200  for carrying out the method according to an embodiment of the invention. The system  200  typically comprises a microprocessor or any other suitable computer, having an input interface or module  210  such as a keyboard, mouse, tablet, and so on, an output device or display means or module  220 , typically a screen or monitor but may additionally or alternatively include a printer, or any other display system, a processing unit or module  230  such as for example a CPU, and a memory  240 . In some embodiments, a suitable scanner  250  for obtaining 3D data of the intraoral cavity is also operatively connected to the system  200  and interacts therewith, while in other embodiments the scanner  250  may provide the 3D data to another system not necessarily connected in any way with system  200 . Advantageously, a probe for determining three dimensional structure by confocal focusing of an array of light beams may be used, for example as manufactured under the name of CB-CAD or as disclosed in WO 00/08415, the contents of which are incorporated herein in their entirety. Alternatively, scanning of the dental cavity to provide the 3D data may be accomplished using any suitable apparatus typically comprising a hand held probe. 
     At step  110 , the target parts of the intraoral cavity are identified. The target parts are the parts (also referred to herein as zones or areas) of the intraoral cavity which form the focus of a particular dental procedure for a particular patient and regarding which it is desired to obtain the 3D topographical or surface data thereof. The target parts typically include the part of the tooth or the teeth, or other dental material on which the particular procedure is to be performed, and in some cases may include the full mandibular or maxillary arches, or both arches. For example, the procedure may be a prosthodontic procedure involving a crown prosthesis to be designed and fabricated for fitting onto a preparation at a particular dental site. In such a case, the dental practitioner inputs into processing unit  230  the tooth which has been targeted for the procedure, identified according to any suitable convention. For example, and referring to  FIG. 3 , the display  220  may be used to display a standard image or graphical representation  211  of a nominal intraoral cavity, either with three dimensional (3D) attributes or a simple two dimensional (2D) representation. Alternatively, though, a non-graphical (for example alphanumeric) representation of the intraoral cavity may be provided. Thus, and referring to the example illustrated in  FIG. 3 , the representation  211  includes a plurality of icons or images or symbols  212 , one each corresponding to the teeth in a normal adult or child (the age of the patient having first been input to the processing unit  230 ). The tooth which is to be the target of the procedure may be identified by “clicking” with the aid of a mouse, for example, on the appropriate symbol  212 . Alternatively, any other interactive method may be used for choosing the target tooth, for example by means of a touch screen arrangement. In another example, the identity of the target tooth may be manually input to the processing unit  230  using any conventional nomenclature, a unique coding convention, by selection on a drop-down menu or the like, or in any other suitable manner, the processing unit  230  having been suitably programmed to recognize the choice made by the user. 
     Alternatively, for a prosthodontics procedure involving a bridge, the two or more teeth that are to be worked on to provide preparations to receive the bridge are identified, for example in a similar to that described above, mutatis mutandis. For orthodontic procedures typically all of the teeth in one or both jaws are required. In such a case, all of the teeth of the upper jaw, lower jaw or both jaws may be chosen by means on a single appropriate symbol, for example as indicated at  213 ,  214 ,  215 , respectively, in  FIG. 3 . 
     The manner in which the intraoral cavity needs to be scanned may depend on the procedure to be applied thereto, as will become clearer as the descriptions proceeds. Thus, the dental practitioner also inputs to the processing unit  230  the identity of the actual procedure. For this purpose, the dental practitioner may choose the procedure from a number of preset options on a drop-down menu or the like, from icons or via any other suitable graphical input interface. Alternatively, the identity of the procedure may be input in any other suitable way, for example by means of preset code, notation or any other suitable manner, the processing unit  230  having been suitably programmed to recognize the choice made by the user. By way of non-limiting example, the procedures may be broadly divided into prosthodontic and orthodontic procedures, and then further subdivided into specific forms of these procedures, as known in the art. 
     The type of scanner  250  to be used is also input to the processing unit, typically by choosing one among a plurality of options. If the scanner that is being used is not recognizable by the processing unit  230 , it may nevertheless be possible to input operating parameters of the scanner thereto instead. For example, the optimal spacing between the scanner head and the tooth surface can be provided, as well as the capture area (and shape thereof) of the dental surface capable of being scanned at this distance. Alternatively, other suitable scanning parameters may be provided. In any case, it may be desired that the virtual model of the dentition, provided using the scanners, may be dimensionally related to the real dentition in a known manner, so that dimensional measurements of the virtual model may be made. 
     In the next step  120 , the processing unit  230  identifies the required spatial relationships that are required for scanning the appropriate parts of the intraoral cavity so that complete and accurate 3D data may be obtained for the procedure in question. This step utilizes the data already provided in step  110  for 30 establishing the optimal manner for scanning the intraoral cavity, and thus will depend on the nature of the aforesaid data. Further, according to the method of the invention, additional or ancillary parts of the intraoral cavity that need to be scanned for the particular procedure are also identified, and the spatial relationship between the scanner and these parts are identified or determined. Having identified the target parts and ancillary parts, a scanning protocol is identified or determined by relating the type of scanner, resolution thereof, capture area at an optimal spacing between the scanner head and the dental surface to the target parts and the ancillary parts, either separately or together. The scanning protocol typically comprises a series of scanning stations spatially associated with the dental surfaces of the target part and the ancillary part. Preferably, significant overlapping of the images or scans capable of being obtained at adjacent scanning stations is designed into the scanning protocol to enable good registration, and the 3D data obtained at each scanning station is stitched together to provide a composite 3D virtual model, as is known in the art. A number of examples will now be described. 
       FIG. 4  illustrates an idealized portion  300  of the intraoral cavity of a patient requiring a crown prosthesis on a preparation P having teeth A, B, adjacent thereto, and teeth A′, P′ and B′ in opposed relationship thereto from the other jaw. This idealized portion  300  is typically a 3D virtual model of an idealized full dentition of an adult that is stored in the memory  240  of the system  200 . By idealized is simply meant that the idealized dentition comprises 3D models of all of the teeth of an adult in their normal relative positions, the 3D models typically being standardized according to the statistical norm regarding size, shape and so on as commonly found in the population. Of course, for the purpose of the invention, any 3D virtual model may be suitable, so long as it includes the 3D virtual models of the teeth corresponding to the teeth of the patient in the required target part and ancillary part. The memory  240  may also comprise idealized virtual models of the teeth of children or of special population groups, and thus the user typically specifies (and may optionally be prompted to 30 do so by the system  200 ) the age of the patient, or other attribute that best decides the closest idealized virtual model with respect thereto. The memory  240  also comprises, for each virtual tooth model of the 3D virtual model  300 , an idealized virtual preparation model, and according to the prosthodontics procedure required by the patient, one or more of the virtual teeth may be replaced with the corresponding one or more virtual preparations. 
     The target area or part to be scanned is represented by the dotted line T, and includes the preparation P, including the finish line LT, and part of the original tooth above the gumline. When the target area is scanned very accurately, it is possible for the internal surface of a corresponding coping or prosthesis to be accurately designed. Ancillary parts of the intraoral cavity are included in dotted line AT, and comprise parts of the adjacent and opposed teeth, principally teeth A, B, P′, and often to a lesser extent teeth A′ and B′ or parts thereof. Typically, but not necessarily, the resolution of the scanned data for the ancillary parts AT may be less than for the target part T, since the manufacturing accuracy for the external surfaces of the crown prosthesis (the design of which is dependent on the dental surfaces of the ancillary parts) may be substantially less than for the internal surface of the coping or prosthesis. According to the specific nature or properties of the scanner, including the resolution thereof, capture area at an optimal spacing between the scanner head and the dental surface to the target parts and the ancillary parts, the scanning protocol may be designed as follows. 
     Referring to  FIG. 7 , for example, at each scanning station S i  (also referred to herein as an image capture station), 3D data within an area I i ′ of the dental surface X of a tooth or preparation, for example, may be captured by the scanner  250 , and this area may be represented at the scanning station S i  by a projection I i  of area I i ′ on a plane orthogonal to the scanning axis OA of the scanner, and displaced from the dental surface by a dimension t. This dimension t is typically the optimal spacing of the particular scanner with respect to the dental surface X for providing a scan area equivalent to I i , but may be any other suitable spacing. The shape of the area I i  will generally depend on the scanner, and is herein represented by a rectangle. The orientation of the scanning axis OA can be related to a reference coordinate system, for example orthogonal Cartesian axes  320  defined with respect to the model  300 , and which are typically easily identified in the real intraoral cavity. 
     Referring to  FIGS. 5 and 6 , the processing unit  230  determines a plurality of scanning stations S i  surrounding the target part T and the ancillary part AT (referring also to  FIG. 4 ) such that the corresponding areas I i ′, in which 3D data is obtained, together cover the full extent of the dental surfaces of interest therein (wherein i=1, 2, 3, . . . 10, 11, 12, 13, 14 . . . ). For example, in  FIG. 5 , areas I 1 , I 2 , I 3  and areas I 4 , I 5 , I 6  represent two sets of three overlapping zones each at approximately two different heights with respect to the gum G which may be sufficient to define a buccal portion of the target part T and the ancillary part AT of the lower jaw of  FIG. 4 . Similar areas may be required form the lingual side. In  FIG. 6 , areas I 4 , I 5 , I 6  are represented by U-shaped symbols, wherein the arms of the U represent the direction along which the scan is taken, i.e., the spatial position of the scanning axis OA of the scanner, and the middle portion of the U represents the corresponding projection I i  as seen edge-on. Thus, exemplary additional areas I 10  and I 11  represent additional scanning stations not coplanar with the scans at areas I 4 , I 5 , I 6 . Similarly, the areas I 7 , I 8 , I 9 , I 12 , I 13 , I 14 , in  FIGS. 5 and 6  represent additional scanning areas taken from above the tooth, with greater overlap between areas being provided in the vicinity of the target part T. For example, areas I 13 , I 14 , being more face-on with respect to parts of the finish line may provide greater accuracy thereof. The location and orientation of scanning stations S i  are determined such that the areas I i ′ of the idealized model corresponding to these stations adequately cover the corresponding target parts T and ancillary parts AT thereof. Thus, by reproducing these locations and orientations of the scanner  250  with respect to the real intraoral cavity, the required 3D data of the target part T and ancillary part AT may be obtained, as will be described in greater detail hereinbelow. 
     The scanning protocol for the dental surfaces of the opposed jaw that are included in the target part T and the ancillary part AT may be obtained in a similar manner to that described above for the lower jaw, mutatis mutandis. 
     Typically, the scanning protocol will differ when different scanners are used for the same target area, depending on the capture characteristics of the scanner used. Thus, a scanner capable of scanning a larger dental area with each scan (e.g., having a larger field of view) will require less scanning stations to be defined in the scanning protocol than a scanner that is only capable of capturing 3D data of a relatively smaller dental surface. Similarly, the number and disposition of scanning stations for a scanner having a rectangular scanning grid (and thus providing projected scanning areas I i  in the form of corresponding rectangles) will typically be different from those for a scanner having a circular or triangular scanning grid (which would provide projected scanning areas I i  in the form of corresponding circles or triangles, respectively). 
     In another example (not illustrated) relating to a prosthodontic procedure for a bridge having a single or a plurality of pontics, there are generally two target parts, relating to one or the other of the two preparations on which the bridge is to be anchored, and the ancillary parts to be scanned include at least part of the teeth adjacent to the furthermost distal preparation and adjacent the furthermost mesial preparation, and at least a portion of the teeth facing the preparations from the opposed jaw. 
     In another example (not illustrated) relating to a prosthodontics procedure requiring a restoration on the buccal or lingual part of a particular tooth, only this target part may need to be scanned in the patient together with the occlusal surfaces of the some of the teeth of the opposite jaw as ancillary parts. 
     In yet another example (not illustrated) relating to an orthodontic procedure for one or both jaws, the target part may comprise the full dentition of one or both jaws, respectively. 
     According to the invention, the system  200  may calculate each time a  30  new idealized scanning protocol based on the parameters of the scanner, the procedure, the dental site of the procedure, age of the patent, and so on, and as applied to the idealized virtual model  300 . 
     Alternatively, all the necessary scanning protocols are previously calculated for every type of scanner, procedure, age group and so on, and stored in memory  240 , the most suitable protocol being retrieved therefrom when identified according to the particular patient/procedure/scanner parameters that are provided. In this case, the virtual model  300  may not be needed for the purpose of determining customized scanning protocols. Thus, it is possible to provide all the necessary guidance for a particular procedure in printed form, a printed book or pamphlet, for example, by means of a movie or video clip, or in any other communication medium, wherein the user would search for the appropriate guidance images or the like according to the particular parameters of the patient in question, via an index or the like for example, and then open the book/movie and so on at the relevant pages/scene etc., to obtain the guidance required. 
     Alternatively, the memory  240  comprises a standard scanning protocol for each different type of procedure, and this protocol is modified by the processing unit  230  to take account of at least one of the parameters including: age of dental patient, dental target part, scanner characteristics, and so on. 
     In step  130 , the spatial relationship between the scanning stations S i  and the intraoral cavity are displayed, so that in step  140  these displayed relationships may be used as a guide by the dental practitioner for scanning the intraoral cavity in a manner suitable for obtaining 3D data appropriate for the particular procedure being considered There are many ways of displaying the aforesaid spatial relationships, some examples of which will now be described. 
     Referring to  FIGS. 8 a  and 8 b   , for example, a pair of perspective view images K i  may be displayed, on a screen  220  or as printed material, for example, corresponding to the spatial relationship of the scanner  250  with respect to the idealized intraoral cavity  300  at a particular scanning station S i . Additionally or alternatively, a plurality of images showing the relationship at any other desired vantage point (viewpoint) may be provided, including for example the vantage point as would be seen by a dental practitioner with respect to a real intraoral cavity, either by default or by being chosen by the user by interacting with processing unit  230 . Optionally, a dynamic image may be provided, in which the user can change the vantage point of the image interactively, in a manner known in the art. Alternatively, a video clip or the like may be provided for providing the user with a sequence of operations of the scanner etc. 
     Images K i  may be composites of virtual models of the scanner  250  and of the intraoral cavity  300  (typically the aforesaid idealized virtual model) stored in memory  240 . These virtual models are manipulated by the processing unit  230  to provide the correct spatial relationship, in virtual space, according to the particular scanning station S i  previously determined, and can be displayed as two dimensional images in a manner known in the art. Optionally, the position of the scanning station S i  and the direction of the scanning axis OA can be displayed with respect to the intraoral cavity  300 , additionally or alternatively to the scanner. The scanning axis OA is typically defined as orthogonal to the scanning face  255  of the scanner but may be defined according to any other pre-known suitable geometric or other parameter of the scanner. The images K i  can optionally comprise a representation of the coordinate system, for example orthogonal axes  320 , in the orientation appropriate to the vantage point being viewed. 
     For the purpose of images K i , it may be possible to display the image of the dental surfaces as having 3D attributes and realistic dental morphologies, for example as illustrated in  FIGS. 8 a  and 8 b   , or alternatively, each dental surface may be represented, for example, by a geometrical form—for example simple wedges representing incisors, cones representing canines, and cylinders representing molars. Optionally, a summary composite image may be first provided (not shown) illustrating the full protocol, for example as a plurality of symbols (e.g., indicia such as “X” or “+”, or frames representing the projected areas I i , and so on) may be superposed over one or more images of the idealized dentition—for example, in a manner similar to that illustrated in  FIGS. 5 and 6 . 
     Further optionally, the idealized virtual model appearing in images K i  may be custom-modified to show a virtual preparation at each corresponding dental site where a real preparation is to be found, and also virtual teeth may be removed from the model where none are to be found in the real intraoral cavity—for example where teeth have been removed for accommodating a pontic. These features can further facilitate identification of the positions and orientations of the scanner at each of the scanning stations S i . 
     Further optionally, non-image data may be provided identifying the position and orientation of the scanner at each scanning station S i , and this data may be provided, for example, in the form of a table listing suitable corresponding geometric data, and also including, for example the spacing between the scanner scanning face  255  and the dental surface of interest, an identification of the particular surface being scanned, and so on. Alternatively, the relationships in step  130  may be displayed in alphanumeric form, as a set of instructions or statements describing the relative positions of the scanner and teeth, for example. Alternatively, the relationships in step  130  may be displayed in audible form, wherein for example such instructions or statements are broadcast by a speaker or the like, either from a prerecording, or synthetically created by the system  200 . 
     Further optionally, the scanning stations S i  may be successively displayed in any desired order, for example in an order such as to minimize displacement of the scanner between each successive scan. In this embodiment of step  130  is followed by the step  140  of using the displayed relationships as a scanning guide, and step  150  of scanning the intraoral cavity in a manner substantially conforming to said relationships. To facilitate the dental practitioner&#39;s work, the images corresponding to a next scanning station are, optionally, not displayed until the practitioner is confident that he/she has properly scanned the intraoral cavity as required by the current scanning station. This may be accomplished by operatively connecting the scanner  250  to the processing unit  230 , and prompting the user whether to display the next scanning station every time a scan is taken (and which is detected by the unit  230 ). Alternatively, it may be possible, after each scan, to display a video image as taken by the scanner with an idealized 2D virtual image of the idealized virtual model as seen from the vantage point of the scanner for this scanning station, and the user can compare the two images and decide whether or not the particular scan is likely to have sufficiently conformed with the desired relationship. 
     A second embodiment of step  130  is illustrated in  FIGS. 9 a  and 9 b   , and in this embodiment, use is made of the video image capturing capabilities of the scanner  250 , which is configured with such capabilities, for guiding the same. A suitable symbol, such as cross-hairs  400 , occlusal line  410 , and so on may be superimposed on the viewfinder of the scanner  250 , typically displayed on the screen  220  (or printed for example). In this embodiment, the spatial relationships of step  120  are displayed from the vantage point of the scanner  250 , and takes the form of providing a reference marker, such as the aforesaid cross-hairs  400 , for example, on the screen where a particular part of the dental surface (e.g., the center of a tooth viewed in the particular direction of the scanning axis) being viewed should be centered. For example, in  FIG. 9 a   , the appropriate scan for the scanning station may be taken when the upper tooth  405  and the lower tooth  406  (previously identified by the system as being the subject of the scan) as imaged from a buccal direction by the scanner are each centralized with respect to the upper and lower cross-hairs  400 . Similarly, in  FIG. 9 b   , the tooth  407  being imaged from above is centralized with respect to cross-hairs  400 . The cross-hairs may further comprise a ring  401  which further facilitates centering the tooth  407  as viewed via the scanner  250  with respect to the cross-hairs  400 . 
     Proceeding to and identifying the next scanning station is facilitated by displacing the cross-hairs  400  to a position on the screen where the last position of the cross-hairs  400  appears in the next (now current) position of the scanning station. This is accomplished automatically by the processing unit  230  when the user is satisfied that the previous scan was properly taken, for example as described earlier in connection with the embodiment of  FIGS. 8 a , 8 b   , mutatis mutandis. The scanner is then moved so that the cross-hairs  400  (still associated in virtual space with the previous scanning station, and now appearing at the relocated position on the viewfinder) is again centralized with the previous dental surface, which has been effectively displaced from the central position of the screen to a position once again associated with the now-displaced cross-hairs  400 . This automatically aligns the scanner with the next scanning station. For example, referring to  FIGS. 10 a  to 10 c   ,  FIG. 10 a    illustrates an image L in buccal view of a series of teeth, with the cross-hairs  400  centralized over one particular tooth  410 , the adjacent teeth  411  and  412  being partially visible. When the user is satisfied that a suitable scan was taken at this scanning station, this is made known to the system  200  in any suitable manner, and the cross-hairs  400  is moved from the previous position at the center of the screen to the right, such that only the left hand portion  401  of the cross-hairs  400  is now visible. The user then moves the scanner such as to renew the relative position of tooth  410  with respect to cross-hairs  400  in the viewfinder, to for example as illustrated in the image of  FIG. 10 b   , which now brings the next dental surface to be scanned, in this case tooth  411 , into the main part of the viewfinder to provide image L′. The relative position of the elements in the previous image L is shown as a dotted box. When this is accomplished to the satisfaction of the user, the old position of the cross-hairs  400  is removed from the screen, and repositioned at the center of the screen, as shown at the dotted lines  400 ′. A scan can now be performed at this position, which corresponds to a scanning station. To move to the next scanning station illustrated in  FIG. 10 c   , the new position of the cross-hairs  400  is relocated, for example to the lower part of the viewfinder, and the user correspondingly translates the scanner so as to re-locate tooth  411  to maintain the previous relative position with respect to the cross-hairs  400 , providing image L″, and the position of the previous image L′ is shown in the dotted box in this figure. This process is repeated until all the scanning stations have been passed. It may be necessary to change to direction of the scanning entirely, for example from buccal ( FIG. 9 a   ) to upper ( FIG. 9 b   ), and this can be done by guiding the user to a particular tooth where the transition is required, and then for example changing the form of the reference marker—for example, from the “+” indicia to one also including a circle  409  (e.g. as illustrated in  FIG. 9 b   )—signifying that an upper view should now be taken of the current tooth (or preparation or whatever dental surface is being considered). Additionally or alternatively, written, or graphic prompts may be provided in the screen, or vocal or other audio prompts provide via a speaker (not shown) urging the user to change position, and/or to move to a different dental site, specified according to the next scanning station. 
     In a variation of the second embodiment of steps  130  and  140  described above, optical recognition (also known as image recognition) methods may be employed for identifying features of the dental surface being scanned at the current scanning station for guiding the user to the next scanning station. For example, and referring to  FIGS. 11 a  and 11 b   , image M is a video image corresponding to the latest scan, obtained at the current scanning station. Image M shows the relative positions of various dental surfaces such as a tooth  430  in lingual view, flanked by adjacent teeth  431 ,  432 . Suitable optical or image recognition means are applied to image M, which is first isolated in processing unit  230  by means of a suitable frame grabber, and a profile of interest, MP, is determined. Such a profile MP typically comprises an external edge of one or more of teeth  430 ,  431 ,  432  as seen from the vantage point of scanner  250 , and thus typically comprises a fictitious line separating two zones that are optically different—the teeth and the background, for example. The profile MP is then reproduced as an image in the viewfinder in its original relative position in image M. Then the processing unit  230  calculates the movement of the scanner required to move to the next scanning station, and applies this movement, in a virtual manner to the profile MP, repositioning the profile MP to position MP′, or at last a part thereof, in the viewfinder, as illustrated in  FIG. 11 b   . (This is how the new position of cross-hairs  400  described above may in practice be calculated as well, for example.) The user then moves the scanner  250 , mimicking the virtual movement previously calculated, until the image seen by the viewfinder is brought into alignment with the repositioned profile MP′.  FIG. 11 b    shows image M′ obtained prior to full alignment—the scanner  250  having to be moved in the direction of arrow  450  until the profile MP′ is superposed on part of the edges MP″ of the teeth as seen via the viewfinder. 
     The guiding of the dental practitioner between the different scanning stations has been described above in graphical terms. Optionally or alternatively, the guiding may take any suitable form. For example, oral commands may be provided, asking the practitioner to now move the scanner to the left 3 mm and upwards 2 mm, for example, using any suitable speech software operating on scanning station data inputs provided by the processing unit  230 . Alternatively, non-oral audio commands may be provided, for example coded bells or beeps, the pattern and intensity thereof being capable of being interpreted by the user in terms of the required movement in a number of directions, for example. 
     Additionally or alternatively, non-graphical means may be used for guiding the user between scanning stations. For example, suitable LED&#39;s may be provided in the viewfinder, or images of arrows, for example, for guiding the user in the required directions to the next scanning station. 
     Advantageously, the scanner  250  comprises an inertial system or a suitable tracking system, that is capable of determining a change of position and/or orientation thereof relative to a datum position/orientation. Thus, the actual position/orientation of the scanner  250  can be checked automatically against the desired position for the next scan, and any suitable means—audio and/or visual for example—may be used for guiding the user to the correct position based on the difference between the current position and the desired position. For example, a beep may be sounded the frequency of which increases the closer the scanner  250  is to the desired position. Optionally, a second inertial or tracking system may be coupled to the head or jaws of the patient, so that any movement thereof may be compensated for. 
     Optionally, a series of indicia may be provided, each indicia in the series corresponding to a different scanning station. The series of indicia may be displayed m a predetermined sequence, a next indicia being displayed after the intraoral cavity has been scanned at the previous scanning station with its corresponding indicia. Optionally, the next indicia may be displayed together with the current, i.e., the immediately preceding indicia. The indicia relating to different said parameters are displayed in different colors one from another. Thus, these indicia help to identify which scanning station the user is at, and which is the next station, for example. The indicia may comprise a series of numbers (for example “1/4”, “2/4”, “3/4”, “4/4”) or symbols, for example. 
     In another aspect of the present invention, a computer readable medium is provided that embodies in a tangible manner a program executable for guiding the scanning of the intraoral cavity of a patient. The computer readable medium comprises: 
     (a) a first set of data representative of target parts of the intraoral cavity that it is desired to have scanned; 
     (b) a second set of data representative of spatial relationships between a scanning device and said target parts of the intraoral cavity suitable for enabling said target parts to be scanned by said scanning device; 
     (c) means for displaying said second data. 
     The medium may comprise, for example, optical discs, magnetic discs, magnetic tapes, and so on. 
     According to some aspects of the invention, a method and system are provided for scanning, and for facilitating scanning of, an intraoral cavity. The target parts of the intraoral cavity that it is desired to have scanned are identified, and the spatial relationships between a scanning device and the target parts of the intraoral cavity suitable for enabling said target parts to be scanned by said scanning device, are also identified or otherwise determined. These relationships are then displayed, and the displayed relationships are used as a guide for scanning the intraoral cavity. 
     In the method claims that follow, alphanumeric characters and Roman numerals used to designate claim steps are provided for convenience only and do not imply any particular order of performing the steps. 
     Finally, It should be noted that the word “comprising” as used throughout the appended claims is to be interpreted to mean “including but not limited to”. 
     While there has been shown and disclosed exemplary embodiments in accordance with the invention, it will be appreciated that many changes may be made therein without departing from the spirit of the invention.