Abstract:
A non-invasive method for evaluating the degree of healing around a prosthetic device or implant that is obscured by tissue employs a source of imaging radiation that illuminates an area of bone or tissue around the prosthetic device or implant. The method comprises obtaining first and second images representing the bone or tissue taken at different times; determining reference points identifying similar image positions in the first and second images; registering the first and second images by utilizing the reference points, thereby producing first and second registered images; utilizing the registered images in a subtractive process to determine the differences between the first and second images; and utilizing the differences between the first and second images to generate measurements of bone or tissue growth over time around the site of the prosthetic device or implant, thereby measuring the extent of healing around the prosthetic device or implant.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    Reference is made to commonly assigned copending application Ser. No. 09/970,243, entitled “Method for Registering Images in a Radiography Application” and filed Oct. 3, 2001 in the names of J. T. Boland, J. P. Spoonhower and J. R. Squilla, which is assigned to the assignee of this application. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates generally to the field of dental imaging, and in particular to the use of subtractive radiography to measure changes in human tissues and bone over time.  
         BACKGROUND OF THE INVENTION  
         [0003]    The use and application of dental implants is well known in the art. These types of procedures are generally utilized either where typical dental crowns are not applicable or where the use of dental bridgework is difficult or otherwise undesirable to the patient. Additionally, situations such as accidents or disease often produce damage to the teeth or underlying bone structure such that applications of typical dentistry procedures are impossible.  
           [0004]    In a typical dental practice wherein a dentist deems a dental implant to be necessary for a patient, a typical procedure using the current state of the art may be described, as follows. For example, the replacement of a missing number  20  second premolar bicuspid of the lower jaw or mandible would involve first taking an x-ray of the area of the future surgical activity to reveal bone condition and the amount of space available to receive an implant. Upon evaluation of the x-ray, and all indications being positive, the area would be anesthetized, or the patient rendered unconscious. Next, an incision would be made through the soft tissue in the space between the good teeth where the implant is to be placed. After the incision that reveals the underlying jawbone, the soft tissue would be retracted and rinsed to prepare for the next step. A dental drilling burr would then be used to establish a point of entry for the implant in the form of a first indent into the surface of the jawbone. An approximately 2 mm drill would then be utilized to make the first preparatory hole into the jawbone, with depth being established at this step. Using a 2 mm depth probe, the hole is alternately drilled and measured until the desired depth is reached to receive the implant.  
           [0005]    Additionally, this procedure “sounds” the bone in an effort to establish the overall integrity of the hole and to establish that no perforations have occurred. Next, an approximately 3 mm drill or dental burr is utilized to widen the drilled hole and is again alternately checked with a 3 mm probe. Again, all indications being positive to the dentist, a guide pin is inserted into the hole to check the overall integrity of the prepared site and its proper alignment to the existing teeth. Next, the dental implant, which has a round shape and has both internal and external threads, is made ready for insertion. The implant is next carefully screwed into the prepared hole using copious amounts of irrigation to prevent overheating the underlying bone. The implant is then checked for proper depth and verified to be flush with the jawbone. After all this complete, the soft tissue surrounding the site is sutured closed, thus burying the implant. The sutures are removed about ten days after surgery and the implant is left undisturbed for about six months for solidification.  
           [0006]    After the six months, another visit is required to again incise the site to place within the implant a healing abutment or temporary crown which trains the gum tissue to grow around the future prosthesis in a collar-like fashion. The temporary crown is left in place for about eight weeks. Once the tissues are in satisfactory condition, an impression is taken with the help of transfer pins inserted into the implant. These pins transfer position of the implant to the rest of the teeth by the holes left in the impression. This impression permits the creation of custom gluing abutments from metal components which are screwed and torque pre-loaded into the implant. A permanent crown is then cemented into the abutment which also fits into the pre-grown gum tissue. This completes the implant procedure for the implant, which now only requires minor healing.  
           [0007]    As described, it is evident that this procedure is extremely time consuming, painful for the patient, and inconvenient for both the dentist and patient. Importantly, many measurements have to be taken which are obviously inexact and subject to interpretation by the dental practitioner. These measurements are needed to measure and track changes in the underlying extent of healing of both hard (bone) and soft tissue structure to assess the readiness for subsequent procedures. Moreover, such measurements may involve disturbing the tissue, not to speak of the patient, in order to see the area and/or to position the necessary measuring probes and tools.  
           [0008]    U.S. Pat. Nos. 5,664,574 and 6,058,324, which both issued in the name of B. Chance, disclose methods and systems for in vivo, non-invasive examination of a subject using non-ionizing radiation such as near Infra-Red radiation. Additionally, U.S. Pat. No. 6,419,484 B1, which issued in the name of DaSilva et al., discloses a dental drill comprising one or more single mode fibers that are used to image in the vicinity of the drill tip.  
           [0009]    Notwithstanding these imaging approaches taken in the prior art, there is a need for an intra-oral imaging methodology which is capable of removing the subjectivity and interpretation inherent in the use of such procedures. More specifically, there is a need for an intra-oral imaging system permitting measurements below the gumline and software such as subtractive radiography to reduce the error and improve the accuracy of such procedures. Such technical solutions to these problems would provide system and methodology to measure and track changes in the underlying extent of healing of both hard (bone) and soft tissue structure to better assess the readiness for subsequent procedures.  
         SUMMARY OF THE INVENTION  
         [0010]    It is an object of the invention to facilitate the measurement of teeth and/or bone dimensions in order to assist dental practitioners in the proper preparation of a prosthesis.  
           [0011]    The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a non-invasive method for evaluating the degree of healing around a prosthetic device or implant that is obscured by tissue employs a source of imaging radiation that illuminates an area of bone or tissue around the prosthetic device or implant. The method comprises obtaining first and second images representing the bone or tissue taken at different times; determining reference points identifying similar image positions in the first and second images; registering the first and second images by utilizing the reference points, thereby producing first and second registered images; utilizing the registered images in a subtractive process to determine the differences between the first and second images; and utilizing the differences between the first and second images to generate measurements of bone or tissue growth over time around the site of the prosthetic device or implant, thereby measuring the extent of healing around the prosthetic device or implant.  
           [0012]    From another perspective, the invention comprises a non-invasive system for measuring the dimensions of intra-oral tissue or bone growth around an prosthesis or implant situated below the gum line. This system includes a source of near infrared light; an intra-oral imaging device for illuminating the prosthesis or implant below the gumline with the near infrared light, wherein the imaging device also captures one or more images of the prosthesis or implant in the near infrared spectral region; and a processor using the captured images to generate reference points for registering the images of the prosthesis or implant below the gumline, said processor using the registered images to generate measurements of the dimensions of the tissue or bone growth over time around the prosthesis or implant. The measurements produced by the system may be used to generate a dental prosthesis, or to evaluate the extent of healing around the prosthesis or implant.  
           [0013]    The advantage of the invention is that it enables more rapid determination of critical dimensions for practitioners, and in particular without the need, as is the current practice, for surgery to expose the underlying bone/tooth structure to enable micrometer determination of these critical dimensions. Furthermore, the advantage of the invention is that it improves upon the use of a subtractive radiography system to enhance the application of dental implants and provides means with which to more accurately and cost effectively measure parameters that dental practitioners need to assess the progress of such procedures.  
           [0014]    These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a perspective diagram of a computer system for implementing the present invention.  
         [0016]    [0016]FIG. 2 is a pictorial illustration of an intra-oral camera that is connectable with the computer system shown in FIG. 1.  
         [0017]    [0017]FIG. 3 is a drawing of a human lower jaw or mandible detailing a missing premolar bicuspid.  
         [0018]    [0018]FIG. 4 is a drawing of a human lower jaw or mandible detailing an implanted replacement premolar bicuspid.  
         [0019]    [0019]FIG. 5 is a pictorial diagram of a fiber optic bundle system emitting near infra-red light into the area of the implant as shown in FIG. 4, and a corresponding fiber optic bundle receiving near infra-red light from the emitter.  
         [0020]    [0020]FIG. 6 is a pictorial diagram of an x-ray source emitting x-ray radiation into the area of the implant as shown in FIG. 4, and a dental x ray film for receiving the radiation from the emitter.  
         [0021]    [0021]FIG. 7 is a block diagram of the various stages of the multi-view registration method that is used in the subtractive radiography process according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    Because dental imaging devices employing electronic emitters and sensors and systems employing subtractive radiography are well known, the present description will be directed in particular to elements forming part of, or cooperating more directly with, system and method in accordance with the present invention. Elements not specifically shown or described herein may be selected from those known in the art. Certain aspects of the embodiments to be described may be provided in software. Given the system and method as shown and described according to the invention in the following materials, software not specifically shown, described or suggested herein that is useful for implementation of the invention is conventional and within the ordinary skill in such arts.  
         [0023]    Still further, as used herein, the computer program may be stored in a computer readable storage medium, which may comprise, for example; magnetic storage media such as a magnetic disk (such as a hard drive or a floppy disk) or magnetic tape; optical storage media such as an optical disc, optical tape, or machine readable bar code; solid state electronic storage devices such as random access memory (RAM), or read only memory (ROM); or any other physical device or medium employed to store a computer program.  
         [0024]    Referring to FIG. 1, there is illustrated a computer system  10  for implementing the present invention. Although the computer system  10  is shown for the purpose of illustrating a preferred embodiment, the present invention is not limited to the computer system  10  shown, but may be used on any electronic processing system. The computer system  10  includes a microprocessor-based unit  12  for receiving and processing software programs and for performing other processing functions. A display  14  is electrically connected to the microprocessor-based unit  12  for displaying user-related information associated with the software, e.g., by means of a graphical user interface (GUI)  15 . A keyboard  16  is also connected to the microprocessor based unit  12  for permitting a user to input information to the software. As an alternative to using the keyboard  16  for input, a mouse  18  may be used for moving a selector (cursor)  20  on the display  14  and for selecting an item on which the selector  20  overlays, as is well known in the art.  
         [0025]    A compact disk-read only memory (CD-ROM)  22  is connected to the microprocessor based unit  12  for receiving software programs and for providing a means of inputting the software programs and other information to the microprocessor based unit  12  via a compact disk  24 , which typically includes a software program. In addition, a floppy disk  26  may also include a software program, and is inserted into the microprocessor-based unit  12  for inputting the software program. Still further, the microprocessor-based unit  12  may be programmed, as is well known in the art, for storing the software program internally. The microprocessor-based unit  12  may also have a network connection  27 , such as a telephone line, to an external network such as a local area network or the Internet. Accordingly, the software program may be received over the network, perhaps after authorizing a payment to a network site. A printer  28  is connected to the microprocessor-based unit  12  for printing a hardcopy of the output of the computer system  10 .  
         [0026]    Images may also be displayed as part of the graphical user interface  15  on the display  14  via a personal computer card (PC card)  30 , such as, as it was formerly known, a PCMCIA card (based on the specifications of the Personal Computer Memory Card International Association) which contains digitized images electronically embodied in the card  30 . The PC card  30  is ultimately inserted into the microprocessor based unit  12  for permitting visual display of the image on the display  14 . Images may also be input via the compact disk  24 , the floppy disk  26 , or the network connection  27 . Any images stored in the PC card  30 , the floppy disk  26  or the compact disk  24 , or input through the network connection  27 , may have been obtained from a variety of sources, such as an intra-oral camera or an x-ray image scanner, which scans x-ray films, e.g., dental films, and provides scan signals corresponding to the film images.  
         [0027]    Near-infrared (NIR, i.e., 700-1000 nm) light has been shown to penetrate soft tissue and allow for a method of imaging inside soft tissue structures. Such techniques as optical coherence tomography (OCT) and NIR confocal microscopy have shown the ability to image subsurface structure with penetration depths of the order of millimeters. Furthermore, the ability of light to penetrate hard tissues such as bone or teeth is significantly different than the penetration of soft tissue so that the interface between hard and soft tissue is evident using NIR imaging technologies.  
         [0028]    An intra-oral camera for emitting near infra-red radiation is shown in FIG. 2 as a hand held fiber optic imaging device  32 . The device comprises a hand-held portion  34  by which the operator can manually manipulate the device, and a probe portion  36  that can easily be inserted into a patient&#39;s mouth. The device can be designed so that the probe is manipulated robotically or remotely, in which case a handle for an operator is unnecessary. The probe portion is comprised of a fiber bundle  42  having two optical fiber parts: the first part  42   a  terminating at a distal end thereof in an emitter tip  38  and a second portion  42   b  terminating at a distal end thereof in a pickup tip  40 , where the terminating points of the respective tips are separated by an operative spacing d. The shape of the probe portion  36  is designed to comfortably access as much of the oral cavity as possible, and in particular the optical parts  42   a  and  42   b  are curved such that a tooth, tissue or bone area may be disposed, as will be shown, within the operative spacing d.  
         [0029]    The imaging device  32  supports the fiber bundle  42 , which couples near infra-red light from the generator stage of a near IR processor  44  to the emitter tip  38 , and from the pickup tip  40  to the receiver stage of the near IR processor  44 . Near IR light is emitted from the emitter tip  38  through the distal end of the fiber part  42   a , and near IR light is collected by the pickup tip  40  through the distal end of the fiber part  42   b . The probe portion  36  may be detachable from the hand held portion  34  for ease of use, cleaning or disposal. A fiber connector  46  may be connected to the end of the hand held portion  34 . The near IR processor  44 , which generates and receives the near IR radiation, is connected to the microprocessor-based unit  12  of FIG. 1, which processes the resultant signals and produces an analysis signal for display on the display  14 .  
         [0030]    Referring now to FIG. 3, detailed is a rendition of the human lower jaw or mandible  50  before the dental restorative procedure is effected, with a missing number  20  second premolar bicuspid  51  of the lower jaw or mandible  50 . The gumline  52  shown detailed in crosshatch shows the area below which detailed measurements are desired. FIG. 4 shows the same lower jaw or mandible  50  after an implant  54  is inserted into the underlying jawbone and a crown  55  is cemented onto the implant  54 . FIG. 4 also shows an area of tissue/bone growth  56  around the implant post  54 . The dimensions, or other evidence, of the region of growth  56  is determined according to the disclosed process, as will be explained.  
         [0031]    Referring to FIG. 5, the near infra-red probe light emitted from the distal end of the emitting fiber part  42   a  is directed from the emitter tip  38  of the probe portion  36  at or onto the hard or soft tissue  56  at the appropriate location. After transmitting through the hard or soft tissue  56 , the near infra-red light is collected by the pickup tip  40  at the distal end of the pickup fiber part  42   b  and conducted back through the probe  56  to the near IR processor  44 . The signals from the near IR processor  44  may then be transferred to the computer system  10  through a direct connection, through removable media, through a network connection, such as a local are network (e.g., Ethernet) or a public network (e.g., the Internet), or by any other convenient means.  
         [0032]    [0032]FIG. 6 shows another embodiment of the imaging portion of the invention, where x-rays from a conventional x-ray source  57  are directed at or onto the hard or soft tissue  56  at the appropriate location. After transmitting through the hard or soft tissue  56 , the x-ray radiation exposes an x-ray film  58  supported in place by a film holder  59 . The holder  59  may be the conventional type of film holder, such a bite wing, for holding a film in a designated place within the intra-oral cavity. After photographic development, the developed film  58  may be scanned, or otherwise read, and the resultant signals are transferred to the computer system  10  through a direct connection, through removable media, through a network connection, such as a local are network (e.g., Ethernet) or a public network (e.g., the Internet), or by any other convenient means.  
         [0033]    An x-ray examination system can be either a traditional film system where different films can be optimized for detection of hard and soft tissue differences, or a digitally based system. In a digital system a solid state digital radiography sensor, (DR) sensor is used (in place of the film holder  59 ) where electronic means can be used to change contrast or contrast filters can be inserted before the DR sensor to achieve the same result, effectively repositioning the density curve of the resultant image.  
         [0034]    [0034]FIG. 6 also serves to illustrate a variation of the near infra-red system shown in FIG. 5, wherein the component  57  may instead be thought of as the distal end of the emitting fiber part  42   a , from which near infra-red light is directed from the emitter tip  38  of the probe portion  36  at or onto the hard or soft tissue  56  at the appropriate location. After transmitting through the hard or soft tissue  56 , the near infra-red light is then imaged upon the film  58 , which may be a specialized film adapted for the near infra-red emission with appropriate spectral sensitization of the emulsion.  
         [0035]    In dealing with images taken over time under, e.g., different exposure conditions, several problems may occur. One problem is dealing with the differences and inconsistencies between images over time, which do not relate to the tissue or bone growth, but that may be sufficient to mask the changes that we are looking for, i.e., tissue and/or bone growth. For film, such differences could be non-image related density differences. Density differences in dental x-rays taken at different times can be due to a number of sources including variations in the film, illumination differences, incidence angle of the x-ray source, and exposure differences. The use of a density target such as described in commonly-assigned, co-pending U.S. patent application Ser. No. (our Docket 85295), entitled “Incorporation of a Density Target with Dental Films to Facilitate Subtractive Radiography” and filed on even date herewith in the names of J. Squilla, J. Boland and J. Spoonhower, and which is incorporated herein by reference, can correct for these issues by allowing the places of predetermined minimum and maximum exposure values to be positively identified and measured. The density measurements from the minimum and maximum points are used by software to correct and match the dynamic range of the x-rays taken at different times.  
         [0036]    (More specifically, co-pending U.S. patent application Ser. No. (our Docket 85295) discloses a method and system for equalizing non-diagnostic differences that occur in two or more radiographic images taken of the same object at different times. The described technique utilizes an x-ray radiation source that generates a beam of radiation and an image receiver (e.g., a film) positioned to receive radiation, from the radiation source, that interacts with the object, whereby image data of the object is captured by the film receiver. The method includes the steps of interposing a graded density target in the path of the beam of radiation between the source and the image receiver such that the target is imaged upon the image receiver together with the object; using the radiation source and the receiver to capture two or more images of the object at different times; generating measurements of the targets in each of the captured images; and using the measurements to equalize the image data of the radiographic images, thereby generating two or more equalized images that have been processed to equalize the non-diagnostic differences between the images.)  
         [0037]    Another problem would be registration of the two images, in particular since the images are captured via a non-precise hand held imaging device. In other words, since the invention is useful in a subtractive radiography process where change detection is used to identify areas of differences among images of the same region that were collected at different times, registration of the images is a prerequisite for the change detection process. Registration of images taken at different times can be accomplished interactively using a process similar to that described in accordance with the cross-referenced commonly assigned copending application Ser. No. 09/970,243, which is incorporated herein by reference, and in which a series of comparative views of related images are produced and presented to a user through the graphical user interface  15  presented on the display  14 . More specifically, these comparative views enable user-friendly registration of the images prior to engaging in a subtractive process for isolating changes between the images. Automatic registration can be accomplished via software by detecting and recognizing unique points on the dental implant as they appear in each x-ray, using either existing points or points purposefully added to the implant for this purpose. Alternatively, automatic registration can be accomplished via software by matching the shape, or outline, of the dental implant in each x-ray.  
         [0038]    As also described in commonly assigned copending application Ser. No. 09/970,243, an automated method for placing reference points in a radiography application is shown in its several stages in FIG. 7 for the two images  140  and  142 , which represent before and after images of an oral object, such as a tooth (“before” and “after” is meant to represent a time sequence that would reveal, e.g., changes in the tooth, bone or tissue structure caused by a cavity or disease, or by the aforementioned implant process). The images  140  and  142  are processed by the computer system  10  and presented to a user via the graphical user interface  15 , whereupon the user manipulates and places potential tie points  144  on the images  140  and  142  by using the mouse  18  or the keyboard  16 . For example, the selector (cursor)  20  can be used to locate the potential tie points, as also represented in the view shown in FIG. 1, where the two images are shown side by side. This is done by means of conventional software in the placement stage  150  that records coordinates for the selected tie points, and which prompts the user to switch between images in a predetermined manner, i.e., once a first point has been placed in the left image  140 , the user must place a second point in the right image  142 , and so on through the other reference points. At least three reference points are selected for the subsequent registration process, and more points are preferred for a more accurate and robust registration.  
         [0039]    In the refinement stage  512 , more detailed views are processed by conventional software that isolates an area around each of the potential tie points and magnifies and presents each area in sequence to the user through the graphical user interface  15 . After the tie points are refined to the liking of the user, acceptance is signaled by an acceptance decision  154  through manipulation of the mouse  18  or the keyboard  16  (if, for any reason, the results are unacceptable, the process is returned to the refinement stage  152  until the result is acceptable). The result is a set of refined tie points that are suitable for the registration process.  
         [0040]    In other words, the placement stage  150  presents a “zoomed out” view of the full extent of the first and second images side by side in a first graphical user interface view in order to allow a user to place potential reference points in their approximate locations on each image, all the while maintaining context for the user. Thereafter, the refinement stage  152  presents a “zoomed in” view of an area of the first and second images around each of the potential tie points in a second graphical user interface view to allow the user to refine the placement of the potential reference points, thereby enabling the generation of refined reference points suitable for registration, wherein the reference points identify similar image positions in separate images of substantially the same bodily object.  
         [0041]    Once accepted, the refined tie points can be used in conjunction with optional automatically correlated points in the correlation stage  156 . These optional points may then be reviewed by the user. In the auto registration stage  158 , a polynomial function is generated to relate the tie points. In its simplest form, the polynomial (alignment equation) is of the form 
           X=α   1 +α 2   X′+α   3   Y′   
         [0042]    with only three constants (and a similar equation for Y). Hence, locating three reference (tie) points that are common to two sequential images allows one to be rotated and stretched (warped) to align with the other. (See pages 201-208 on Alignment in  The Image Processing Handbook, Second Edition , by John C. Russ, CRC Press, 1995). Typically, more tie points are involved in the registration process. For instance, in commonly-assigned U.S. Pat. No. 6,163,620 (entitled “Automatic Process for Detecting Changes Between Two Images”), which is incorporated herein by reference, between five and one hundred tie points are used. The polynomial function is then used in the auto registration stage  158  to warp the right image  142  to the left image  140  (or vice versa). Once registration is completed, the results are aligned side by side for review in the registration review stage  160 . Known alignment techniques may be employed to render the left and right images for this view with the same zoom level and image centering. (cf.,  The Image Processing Handbook ). Given the correlation between the images at this point, cursor placement in the left image can be mimicked by cursor placement at the same place in the right image. Likewise, a “zoom-in” on the left image can exactly matched by a corresponding “zoom-in” of the right image. If the user deems the registration adequate, acceptance is signaled by the acceptance decision  162  through manipulation of the mouse  18  or the keyboard  16 ; otherwise, the process is returned to the refinement stage  152  and repeated in an iterative manner until the registration results are acceptable to the user.  
         [0043]    This invention is intended to enable an accurate registration of the two images prior to a subtractive radiography process. In a subtractive process of this type, subtracting one image from another effectively removes from the difference image all features that do not change, while highlighting or otherwise denoting those that do. Details of such a subtractive process, though not used in connection with radiography, are disclosed in the aforementioned U.S. Pat. No. 6,163,620, which is incorporated herein by reference. In a dental environment, this process can be used to isolate various types of temporal changes between radiographs of the same object taken at different times, e.g., to isolate bone loss due to periodontal disease (by looking under the gum line). It should be understood, however, that the registration review stage  160  is capable of producing a visual “differencing” effect (i.e., flickering) between the two images that may be sufficient in some cases to indicate the temporal change between the two images.  
         [0044]    The techniques described herein relates in general to a non-invasive method for measuring the dimensions of a bodily object obscured by tissue in order to measure changes in the bodily object over time. While described in relation to a prosthesis implanted in a dental procedure and operation, it should be understood that the method is not to be seen as being limited in this way and would apply to any artificial device used to replace, reinforce, support or otherwise assist a missing, weakened, damaged or similarly affected body part, such as a missing, weakened or damaged limb.  
         [0045]    The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention.  
       Parts List  
       [0046]    [0046] 10  computer system  
         [0047]    [0047] 12  micro-processor-based unit  
         [0048]    [0048] 14  display  
         [0049]    [0049] 16  graphical user interface  
         [0050]    [0050] 18  keyboard  
         [0051]    [0051] 20  mouse  
         [0052]    [0052] 22  cursor  
         [0053]    [0053] 24  CD-ROM  
         [0054]    [0054] 26  compact disk  
         [0055]    [0055] 28  floppy disk  
         [0056]    [0056] 30  printer  
         [0057]    [0057] 32  PC card  
         [0058]    [0058] 34  hand-held fiber optic imaging device  
         [0059]    [0059] 36  hand held portion  
         [0060]    [0060] 38  probe portion  
         [0061]    [0061] 40  emitter tip  
         [0062]    [0062] 42  pickup tip  
         [0063]    [0063] 42   a  fiber bundle  
         [0064]    [0064] 42   b  first fiber part  
         [0065]    [0065] 44  second fiber part  
         [0066]    [0066] 46  near IR processor  
         [0067]    [0067] 50  fiber connection  
         [0068]    [0068] 51  jaw or mandible  
         [0069]    [0069] 52  bicuspid  
         [0070]    [0070] 53  gumline  
         [0071]    [0071] 54  implant  
         [0072]    [0072] 55  crown  
         [0073]    [0073] 56  tissue/bone growth  
         [0074]    [0074] 57  x-ray source  
         [0075]    [0075] 58  x-ray film  
         [0076]    [0076] 59  x-ray film holder  
         [0077]    [0077] 140  left image  
         [0078]    [0078] 142  right image  
         [0079]    [0079] 144  tie points  
         [0080]    [0080] 150  placement stage  
         [0081]    [0081] 152  refinement stage  
         [0082]    [0082] 154  acceptance decision  
         [0083]    [0083] 156  auto correlation stage  
         [0084]    [0084] 158  auto registration stage  
         [0085]    [0085] 160  registration review stage  
         [0086]    [0086] 162  acceptance decision