Patent Publication Number: US-2020281698-A1

Title: Dental image acquisition apparatus and dental image acquisition method

Description:
TECHNICAL FIELD 
     The present technology relates to a dental image acquisition apparatus and a dental image acquisition method and particularly to a technology of a dental image acquisition apparatus for imaging an oral cavity by using an imaging section inserted into the oral cavity. 
     BACKGROUND ART 
     X-ray photography has been widely used to acquire diagnostic images in dental care. Further, it has become known in recent years to use a CCD camera, a CMOS camera, or other tools for briefing to patients. In the case where dentition or other areas of the oral cavity is imaged by such a camera, it is desirable to use a compact camera of a low manufacturing cost. It should be noted that a still camera or a video camera may be used for imaging. 
     Here, as a compact and inexpensive apparatus for reading a dentition image, PTL 1 discloses a dentition image reading apparatus that includes an oral cavity insertion section and an imaging optical section. The oral cavity insertion section is inserted between a cheek and dentition. The oral cavity insertion section has a light transmission portion in an area along an outer lateral surface of the dentition and a cavity portion thereinside. The imaging optical section includes a reflecting mirror, scanning means, and imaging optics. The reflecting mirror reflects light from a light source and from the outer lateral surface of the dentition outside of the oral cavity insertion section. The light source can be inserted into the cavity portion of the oral cavity insertion section and emits light to the outer lateral surface of the dentition through the light transmission portion. The scanning means moves the light source and the reflecting mirror along the outer lateral surface of the dentition. The imaging optics receives light reflected by the reflecting mirror. 
     Also, PTL 2 discloses a dentition image reading apparatus that includes an oral cavity insertion section and an imaging optical section. The oral cavity insertion section is inserted into an oral cavity having maxillary dentition and mandibular dentition. The oral cavity insertion section has a light transmission portion at least on its front or rear side and a cavity portion thereinside. The imaging optical section includes a reflecting mirror, scanning means, and imaging optics. The reflecting mirror reflects light from a light source and from the dentition outside of the oral cavity insertion section. The light source is inserted into the cavity portion of the oral cavity insertion section and emits light to the dentition through the light transmission portion. The scanning means moves the light source and the reflecting mirror along a depth direction inside the cavity portion of the oral cavity insertion section. The imaging optics receives light reflected by the reflecting mirror. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] 
     Japanese Patent Laid-Open No. 2002-191557 
     [PTL 2] 
     Japanese Patent Laid-Open No. 2002-125927 
     SUMMARY 
     Technical Problem 
     However, the technologies proposed in PTL 1 and PTL 2 are those for reading images of outer lateral surfaces of the dentition. Therefore, the acquisition of images depicting both outer and inner lateral surfaces of dentition is not assumed. 
     The present technology has been devised in light of the foregoing, and it is a main object of the present technology to provide a dental image acquisition apparatus capable of acquiring images in a plurality of imaging directions with a single captured image. 
     Solution to Problem 
     In order to solve the above problem, a dental image acquisition apparatus of an example of the present technology includes an oral cavity insertion section and an image acquisition section. The oral cavity insertion section is inserted into an oral cavity. The image acquisition section has a light source. The oral cavity insertion section has an imaging unit that includes an imaging section and a light reflection section. The light reflection section is placed at a position opposed to the imaging section via an imaging target. Also, the dental image acquisition apparatus of an example of the present technology can further include an image processing section and an image display section. The image processing section calculates three-dimensional coordinates of the imaging target on the basis of an image acquired by the image acquisition section. The image display section displays a three-dimensional image created on the basis of the three-dimensional coordinates calculated by the image processing section. 
     Also, a dental image acquisition method of an example of the present technology includes an insertion step, a placement step, and an image acquisition step. In the insertion step, an oral cavity insertion section is inserted into an oral cavity. The oral cavity insertion section has an imaging unit that includes an imaging section and a light reflection section. In the placement step, the light reflection section is placed at a position within a viewing angle of the imaging section via an imaging target. In the image acquisition step, the imaging target is observed with the imaging section, the imaging target is observed from a position opposed to the imaging section with the light reflection section, and an image of the imaging target is acquired. 
     Advantageous Effects of Invention 
     The present technology provides a dental image acquisition apparatus capable of acquiring images in a plurality of imaging directions with a single captured image. It should be noted that the effect of the present technology is not necessarily limited to that described above and may be any one of the effects described in the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an overall configuration diagram illustrating a dental image acquisition apparatus of a first embodiment according to the present technology. 
         FIG. 2  is a schematic diagram illustrating a drive mechanism as seen from a direction A in  FIG. 1 . 
         FIG. 3  is a schematic diagram illustrating the drive mechanism as seen from a direction B in  FIG. 1 . 
         FIG. 4  is an enlarged schematic diagram illustrating a camera unit depicted in  FIG. 1 . 
         FIG. 5  depicts schematic diagrams illustrating the mirror depicted in  FIG. 4 , in which  FIG. 5A  is a side view as seen from the side, and  FIG. 5B  is a plan view as seen from a diagonal direction. 
         FIG. 6  is a schematic diagram illustrating an example of a captured image captured by a camera unit of the first embodiment according to the present technology. 
         FIG. 7  depicts schematic diagrams illustrating patterned illumination of illumination optics having a mask of the first embodiment according to the present technology, in which  FIG. 7A  is a diagram illustrating the illumination optics having the mask and  FIG. 7B  is a diagram illustrating patterned illumination. 
         FIGS. 8A to 8C  are schematic diagrams illustrating generation of a three-dimensional image by the dental image acquisition apparatus of the first embodiment according to the present technology, in which  FIG. 8A  is a diagram illustrating a two-dimensional image of a tooth in one direction,  FIG. 8B  is a diagram illustrating a two-dimensional image of the tooth in another direction, and  FIG. 8C  is a diagram illustrating a three-dimensional image of the tooth. 
         FIG. 9  is a flowchart illustrating a dental image acquisition method of the first embodiment according to the present technology. 
         FIG. 10  is a flowchart illustrating a three-dimensional coordinate acquisition method of the first embodiment according to the present technology. 
         FIG. 11  is an enlarged schematic diagram illustrating a camera unit of a second embodiment according to the present technology. 
         FIG. 12  is a schematic diagram illustrating an example of a captured image captured by a camera unit of the second embodiment according to the present technology. 
         FIG. 13  is an enlarged schematic diagram illustrating a camera unit of a third embodiment according to the present technology. 
         FIG. 14  is a schematic diagram indicating a point of interest with a laser beam emitted from a camera unit of the third embodiment according to the present technology. 
         FIG. 15  depicts schematic diagrams illustrating a mirror of a working example using the present technology, in which  FIG. 15A  is a front view and  FIG. 15B  is a side view. 
         FIG. 16  is a schematic diagram illustrating the manner in which an oral cavity is observed with the mirror of the working example using the present technology. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A description will be given below of suitable modes for carrying out the present technology with reference to drawings. It should be noted that embodiments described below merely illustrate typical examples of embodiments of the present technology and that the scope of the present technology is not to be interpreted narrowly because of the embodiments. Also, the present technology permits use of respective embodiments described below and their modification examples in combination. 
     It should be noted that the description will be given in the following order. 
     1. Dental image acquisition apparatus of the first embodiment 
     (1-1) Configuration example of the dental image acquisition apparatus 
     (1-2) Configuration example of the drive mechanism 
     (1-3) Configuration example of the camera unit 
     (1-4) Example of the dental image 
     (1-5) Example of the dental image acquisition method 
     (1-6) Example of the three-dimensional coordinate acquisition method 
     2. Dental image acquisition apparatus of the second embodiment 
     3. Dental image acquisition apparatus of the third embodiment 
     4. Working example of the dental image acquisition apparatus to which the present technology is applied 
     5. Usage example of the dental image acquisition apparatus to which the present technology is applied 
     &lt;1. Dental Image Acquisition Apparatus of the First Embodiment&gt; 
     A description will be given of a dental image acquisition apparatus of a first embodiment according to the present technology by using  FIGS. 1 to 10 . The dental image acquisition apparatus of the present embodiment is an apparatus used, for example, for root canal treatment that acquires a three-dimensional image (stereoscopic image) by imaging an oral cavity. 
     (1-1) Configuration Example of the Dental Image Acquisition Apparatus 
     A description will be given first of an example of an overall configuration of the dental image acquisition apparatus according to the present embodiment by using  FIG. 1 .  FIG. 1  is an overall configuration diagram illustrating the dental image acquisition apparatus of the first embodiment of the present technology. As illustrated in  FIG. 1 , a dental image acquisition apparatus  100  of the present embodiment includes an image acquisition section, an image processing apparatus  103 , and a monitor  104 . The image acquisition section has an oral cavity insertion section  101  and a light source  102 . The oral cavity insertion section  101  is inserted into an oral cavity. The image processing apparatus  103  is an image processing section. The monitor  104  is an image display section. 
     The oral cavity insertion section  101  has a camera unit  105 , a drive mechanism  106 , and a guide rail  107 . The camera unit  105  is a movable imaging unit. The drive mechanism  106  drives the camera unit  105 . The guide rail  107  moves the camera unit  105  in an oral cavity. The guide rail  107  is inserted between a cheek and dentition and preferably includes a flexible material. This makes it possible to place the guide rail  107  along dentition of a variety of patients. A power source  108  is provided at one end of the drive mechanism  106 . It should be noted that the power source  108  may be a motor or manual means. 
     The monitor  104  displays a three-dimensional image of an imaging target created on the basis of three-dimensional coordinates calculated by a predetermined calculation. At this time, in the case where observation is made by using near infrared light that penetrates through teeth, it is possible to display, on the monitor  104 , an internal structure of a tooth in such a manner that the internal structure overlaps the tooth&#39;s appearance. It should be noted that what is displayed on the monitor  104  may be something similar to animation obtained by projecting a three-dimensional structure that connects respective coordinate points of an imaging target onto a two-dimensional plane. Alternatively, what is displayed on the monitor  104  may be something similar to three-dimensional animation obtained by pasting textures. 
     The camera unit  105  includes a camera  109 , a mirror  110 , and a connecting section  111 . The camera  109  is an imaging section. The mirror  110  is a light reflection section. The connecting section  111  connects the camera  109  and the mirror  110 . The mirror  110  is used to observe the tooth from a direction different from that of the camera  109 . The camera unit  105  can not only directly observe the tooth but also observe the tooth from two directions with the single camera  109  by capturing the mirror  110  within a field of view of the camera  109 , thus allowing for acquisition of three-dimensional coordinates of the tooth. 
     Further, the dental image acquisition apparatus  100  has a light guide  112  and a camera cable  113 . The light guide  112  connects the camera  109  and the light source  102 . The camera cable  113  connects the camera  109  and the image processing apparatus  103 . Also, as an example, the dental image acquisition apparatus  100  can image dentition  114 , which is an imaging target, with the camera  109  and the mirror  110 . 
     (1-2) Configuration Example of the Drive Mechanism 
     A description will be given next of a configuration example of a drive mechanism of the present embodiment by using  FIGS. 2 and 3 .  FIG. 2  is a schematic diagram illustrating the drive mechanism as seen from a direction A on the left in  FIG. 1 .  FIG. 3  is a schematic diagram illustrating the drive mechanism as seen from a direction B on the right in  FIG. 1 . 
     As illustrated in  FIG. 2 , the drive mechanism  106  of the present embodiment has a wire  201 , a traveling pulley  202 , and a fixture  203 . The wire  201  moves the camera unit  105  on the guide rail  107 . The traveling pulley  202  rotates the wire  201  inside the guide rail  107 . The fixture  203  fastens the camera unit  105  to any position of the wire  201 . 
     As illustrated in  FIG. 3 , the drive mechanism  106  of the present embodiment has the wire  201 , the traveling pulley  202 , the fixture  203 , and a driving pulley  204 . The traveling pulley  202  is provided at one end of the guide rail  107 . The fixture  203  fastens the camera unit  105  which is connected to the power source  108  provided at the other end of the guide rail  107 , to any position of the wire  201 . The driving pulley  204  is connected to the power source  108 . 
     The dental image acquisition apparatus  100  can successively image each tooth by moving the camera unit  105  along the dentition  114  in the oral cavity with the drive mechanism  106 . It should be noted that although the drive mechanism  106  having a wire drive is used in the present embodiment, the drive mechanism according to the present technology is not limited thereto. 
     (1-3) Configuration Example of the Camera Unit 
     A description will be given next of a configuration example of the camera unit of the present embodiment by using  FIGS. 4 and 5 .  FIG. 4  is an enlarged schematic diagram illustrating the camera unit depicted in  FIG. 1 .  FIG. 5  depicts schematic diagrams illustrating the mirror of the camera unit depicted in  FIG. 4 .  FIG. 5A  is a side view as seen from the side of the mirror, and  FIG. 5B  is a plan view as seen from a diagonal direction. 
     As illustrated in  FIG. 4 , the camera unit  105  includes the camera  109 , the mirror  110 , the connecting section  111  connecting the camera  109  and the mirror  110 , and an offset scale  401 . The offset scale  401  is a measurement section that protrudes from a mirror surface edge portion of the mirror  110  to an offset position to measure the size of an imaging target. A lens of the camera  109  and the mirror surface of the mirror  110  are placed at opposed positions to face each other via the dentition  114  in the oral cavity. Here, the mirror  110  need only be placed at a position where the imaging target and the mirror surface of the mirror  110  are within a viewing angle of the camera  109  at the same time during imaging. The camera unit  105  can emit illumination light  402  from the light guide  112  toward the imaging target and the mirror surface of the mirror  110  through the surface where the lens of the camera  109  is formed. 
     As illustrated in  FIG. 5A , the offset scale  401  is placed at a position protruding from the mirror surface of the mirror  110  at a predetermined angle. It should be noted that the predetermined angle between the offset scale  401  and the mirror surface of the mirror  110  is preferably 20° to 90° and more preferably 30° or so. Also, as illustrated in  FIG. 5B , the mirror  110  is, for example, circular in plan view, and a mirror surface scale  403 , which is engraved in a cross shape at the center of the mirror surface, is formed. With the offset scale  401  and the mirror surface scales  403 , coordinates of at least five points on the mirror surface of the mirror  110  and at least one point protruding from the mirror surface become known. It should be noted that the camera  109 , the mirror  110 , and the scales are placed such that at least six reference points (part of the scales) appear in each of a direct view image and a mirror image of the camera  109 . 
     (1-4) Example of the Dental Image 
     A description will be given next of an example of a dental image that can be captured by the dental image acquisition apparatus  100  of the present embodiment by using  FIGS. 6 to 8 . 
       FIG. 6  is a schematic diagram illustrating an example of a captured image captured by the camera unit  105  of the present embodiment. As illustrated in  FIG. 6 , an imaging target  602 , a point of interest  603  of the imaging target  602 , the mirror  110 , the offset scale  401 , and the mirror surface scale  403  appear in a captured image  601 . Further, a mirror image  604  of the imaging target  602 , a mirror image  605  of the point of interest  603 , and a mirror image  606  of the offset scale  401  appear in the mirror  110  in the captured image  601 . Here, it is necessary that six points of the offset scale  401  and the mirror surface scale  403  and the point of interest  603  should appear at the same time in both real and mirror images. It should be noted that the camera unit  105  is desirably small enough not to hinder manipulation because of its use in the oral cavity. The mirror surface scales  403  need only be formed such that coordinates of at least six points are known and may be in the shape other than a cross. 
       FIG. 7  depicts schematic diagrams illustrating patterned illumination of illumination optics having a mask of the present embodiment.  FIG. 7A  is a diagram illustrating the illumination optics having the mask, and  FIG. 7B  is a diagram illustrating patterned illumination. As illustrated in  FIG. 7A , illumination optics  701  of the present embodiment has an illumination device  702  and a lattice-shaped mask  703 . An intersection point of the lattice of the mask  703  can be used as a point of interest  704  as illustrated, for example, in  FIG. 7A . 
     In the case where patterned illumination is conducted by using the illumination optics  701 , when illumination light from the illumination device  702  is emitted to the mask  703 , a shadow  706  of the mask  703  and a shadow  707  of the point of interest are projected onto the surface of a tooth  705  illustrated in  FIG. 7B . As described above, the camera unit  105  has the illumination optics  701  that provides patterned illumination that displays a plurality of points of interest on the surface of an imaging target. 
     Here, the phrase “having a mask on illumination optics” refers to placing a patterned photomask in an illumination optical path. The photomask has an area that passes light and another area that blocks light, thus allowing projection of a pattern onto an illuminated position like a shadow picture. As described above, using a photomask produces a bright area and a dark area when illuminated. A glass plate with a printed pattern, a mask whose pattern is dynamically varied by using liquid crystal, and the like can be used as a mask. The mask is preferably inserted between the light source (lamp) and an illumination target. It should be noted that a lens may be provided in front or behind of the mask to ensure that an image is properly formed. 
       FIGS. 8A to 8C  are schematic diagrams illustrating generation of a three-dimensional image by the dental image acquisition apparatus  100  of the present embodiment.  FIG. 8A  is a diagram illustrating a two-dimensional image  801  of a tooth in one direction,  FIG. 8B  is a diagram illustrating a two-dimensional image  802  of the tooth in another direction, and  FIG. 8C  is a diagram illustrating a three-dimensional image  803  of the tooth. 
     As illustrated in  FIGS. 8A and 8B , using visible light during imaging of two-dimensional images  801  and  802  of a tooth with the dental image acquisition apparatus  100  allows for imaging of the appearance of the tooth, and using near infrared light that penetrates through the inside of the tooth allows for imaging of the inside of the tooth. Then, as illustrated in  FIG. 8C , it is possible to acquire the three-dimensional image  803  that depicts a tooth surface  804  and an inner part  805  of the tooth such as dental pulp by using the two-dimensional images  801  and  802 . 
     (1-5) Example of the Dental Image Acquisition Method 
     A description will be given next of an example of a dental image acquisition method of the present embodiment by using  FIG. 9 .  FIG. 9  is a flowchart illustrating the dental image acquisition method of the present embodiment. 
     In step S 901 , the oral cavity insertion section  101  of the dental image acquisition apparatus  100  is inserted into the oral cavity (insertion step). 
     In step S 902 , the camera unit  105  of the oral cavity insertion section  101  is moved to an observation position (placement step). Specifically, the mirror  110  is placed at a position in the viewing angle of the camera  109  via the tooth which is an imaging target. In the present embodiment, as an example, the camera unit  105  is moved to the position of the bottom left back tooth. 
     In step S 903 , all the imaging targets are imaged continuously while the camera unit  105  is gradually moved from the observation position. In the present embodiment, as an example, the camera unit  105  is gradually moved from the position of the bottom left back tooth toward the front teeth, continuously imaging the teeth until the position of the bottom right back tooth is reached. 
     In step S 904 , the image processing apparatus  103  calculates three-dimensional coordinates (real coordinates) on the basis of two-dimensional images captured in step S 903  by referring to two-dimensional coordinates of the portion where the point of interest  603  and respective points of the mirror  110  are directly visible and to two-dimensional coordinates appearing in the mirror  110 . 
     In step S 905 , a three-dimensional image (stereoscopic image) of the tooth is acquired (image acquisition step) on the basis of the three-dimensional coordinates calculated in step S 904  and displayed on the monitor  104  which is the image display section. 
     With the above configuration and action, the dental image acquisition apparatus  100  of the present embodiment can image, with the camera  109 , the dentition  114  and the mirror  110  at the same time by placing the camera  109  of the camera unit  105  and the mirror  110  to be opposed to each other with the dentition  114  provided therebetween, thus allowing for acquisition of images of both inner and outer sides of the dentition  114  with the single camera  109 . As described above, the dental image acquisition apparatus  100  of the present embodiment allows for acquisition of images in a plurality of imaging directions with a single captured image. 
     (1-6) Example of the Three-Dimensional Coordinate Acquisition Method 
     A description will be given next of an example of a three-dimensional coordinate acquisition method of the present embodiment by using  FIG. 10 .  FIG. 10  is a flowchart illustrating an example of the three-dimensional coordinate acquisition method of the present embodiment. In the present embodiment, as an example, actual three-dimensional coordinates are calculated from captured two-dimensional images by using the DLT method which is one of the photogrammetry methods used for aerial photography and other applications. 
     In step S 1001 , the imaging target  602  is imaged with visible light and/or near infrared light by using the offset scale  401  of the mirror  110  and the mirror surface scale  403 . 
     In step S 1002 , real image parameters L (l 1  to l 11 ) and mirror image parameters L′ (l 1 ′ to l 11 ′) are calculated from scaling points of real and mirror image portions of the captured two-dimensional image by using formulas 1 and 2 given below. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         
                           
                             
                               u 
                             
                           
                           
                             
                               
                                 h 
                                  
                                 
                                   ( 
                                   v 
                                   ) 
                                 
                               
                             
                           
                           
                             
                               1 
                             
                           
                         
                         = 
                         
                           
                             ( 
                             
                               
                                 
                                   
                                     I 
                                      
                                     
                                         
                                     
                                      
                                     1 
                                   
                                 
                                 
                                   
                                     I 
                                      
                                     
                                         
                                     
                                      
                                     2 
                                   
                                 
                                 
                                   
                                     I 
                                      
                                     
                                         
                                     
                                      
                                     3 
                                   
                                 
                                 
                                   
                                     I 
                                      
                                     
                                         
                                     
                                      
                                     4 
                                   
                                 
                               
                               
                                 
                                   
                                     I 
                                      
                                     
                                         
                                     
                                      
                                     5 
                                   
                                 
                                 
                                   
                                     I 
                                      
                                     
                                         
                                     
                                      
                                     6 
                                   
                                 
                                 
                                   
                                     I 
                                      
                                     
                                         
                                     
                                      
                                     7 
                                   
                                 
                                 
                                   
                                     I 
                                      
                                     
                                         
                                     
                                      
                                     8 
                                   
                                 
                               
                               
                                 
                                   
                                     I 
                                      
                                     
                                         
                                     
                                      
                                     9 
                                   
                                 
                                 
                                   
                                     I 
                                      
                                     
                                         
                                     
                                      
                                     10 
                                   
                                 
                                 
                                   
                                     I 
                                      
                                     
                                         
                                     
                                      
                                     11 
                                   
                                 
                                 
                                   1 
                                 
                               
                             
                             ) 
                           
                            
                           
                             ( 
                             
                               
                                 
                                   X 
                                 
                               
                               
                                 
                                   Y 
                                 
                               
                               
                                 
                                   Z 
                                 
                               
                               
                                 
                                   1 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                     
                       
                         ( 
                         
                           hQ 
                           = 
                           LP 
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
     
     Formula 1 is a relational formula depicting a relationship between actual coordinates (real coordinates) and coordinates on the image (image coordinates). Formula 1 associates the real coordinates (x, y, z) with the image coordinates (u, v). Here, (u, v) are image coordinates captured with the camera  109 , (x, y, z) are real coordinates, and l 1  to l 11  are constants (parameters). 
     
       
         
           
             
               
                 
                   
                       
                   
                    
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                        
                       2 
                     
                     ] 
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     ( 
                     
                       
                         
                           
                             u 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                       
                         
                           
                             v 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                       
                         
                           
                             u 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                       
                       
                         
                           
                             v 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                       
                       
                         
                           
                             u 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                       
                       
                         
                           
                             v 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                       
                       
                         
                           
                             u 
                              
                             
                                 
                             
                              
                             4 
                           
                         
                       
                       
                         
                           
                             v 
                              
                             
                                 
                             
                              
                             4 
                           
                         
                       
                       
                         
                           
                             u 
                              
                             
                                 
                             
                              
                             5 
                           
                         
                       
                       
                         
                           
                             v 
                              
                             
                                 
                             
                              
                             5 
                           
                         
                       
                       
                         
                           
                             u 
                              
                             
                                 
                             
                              
                             6 
                           
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             
                               
                                 x 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               
                                   
                               
                                
                               
                                 y 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               
                                   
                               
                                
                               
                                 z 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               1 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               
                                 
                                   - 
                                   x 
                                 
                                  
                                 
                                     
                                 
                                  
                                 1 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               
                                 
                                   - 
                                   y 
                                 
                                  
                                 
                                     
                                 
                                  
                                 1 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               
                                 
                                   - 
                                   z 
                                 
                                  
                                 
                                     
                                 
                                  
                                 1 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                         
                         
                           
                             
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               
                                 x 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               
                                 y 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               
                                 z 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               1 
                               , 
                               
                                 
                                   - 
                                   x 
                                 
                                  
                                 
                                     
                                 
                                  
                                 1 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               
                                 
                                   - 
                                   y 
                                 
                                  
                                 
                                     
                                 
                                  
                                 1 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               
                                 
                                   - 
                                   z 
                                 
                                  
                                 
                                     
                                 
                                  
                                 1 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                         
                         
                           
                             
                               
                                 x 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               
                                   
                               
                                
                               
                                 y 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               
                                   
                               
                                
                               
                                 z 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               1 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               
                                 
                                   - 
                                   x 
                                 
                                  
                                 
                                     
                                 
                                  
                                 2 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               
                                 
                                   - 
                                   y 
                                 
                                  
                                 
                                     
                                 
                                  
                                 2 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               
                                 
                                   - 
                                   z 
                                 
                                  
                                 
                                     
                                 
                                  
                                 2 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                             
                           
                         
                         
                           
                             
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               
                                 x 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               
                                 y 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               
                                 z 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               1 
                               , 
                               
                                 
                                   - 
                                   x 
                                 
                                  
                                 
                                     
                                 
                                  
                                 2 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               
                                 
                                   - 
                                   y 
                                 
                                  
                                 
                                     
                                 
                                  
                                 2 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               
                                 
                                   - 
                                   z 
                                 
                                  
                                 
                                     
                                 
                                  
                                 2 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                             
                           
                         
                         
                           
                             
                               
                                 x 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                               , 
                               
                                   
                               
                                
                               
                                 y 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                               , 
                               
                                   
                               
                                
                               
                                 z 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                               , 
                               1 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               
                                 
                                   - 
                                   x 
                                 
                                  
                                 
                                     
                                 
                                  
                                 3 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                               , 
                               
                                 
                                   - 
                                   y 
                                 
                                  
                                 
                                     
                                 
                                  
                                 3 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                               , 
                               
                                 
                                   - 
                                   z 
                                 
                                  
                                 
                                     
                                 
                                  
                                 3 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                             
                           
                         
                         
                           
                             
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               
                                 x 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                               , 
                               
                                 y 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                               , 
                               
                                 z 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                               , 
                               1 
                               , 
                               
                                 
                                   - 
                                   x 
                                 
                                  
                                 
                                     
                                 
                                  
                                 3 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                               , 
                               
                                 
                                   - 
                                   y 
                                 
                                  
                                 
                                     
                                 
                                  
                                 3 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                               , 
                               
                                 
                                   - 
                                   z 
                                 
                                  
                                 
                                     
                                 
                                  
                                 3 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                             
                           
                         
                         
                           
                             
                               
                                 x 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                               , 
                               
                                   
                               
                                
                               
                                 y 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                               , 
                               
                                   
                               
                                
                               
                                 z 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                               , 
                               1 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               
                                 
                                   - 
                                   x 
                                 
                                  
                                 
                                     
                                 
                                  
                                 4 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                               , 
                               
                                 
                                   - 
                                   y 
                                 
                                  
                                 
                                     
                                 
                                  
                                 4 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                               , 
                               
                                 
                                   - 
                                   z 
                                 
                                  
                                 
                                     
                                 
                                  
                                 4 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                             
                           
                         
                         
                           
                             
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               
                                 x 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                               , 
                               
                                 y 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                               , 
                               
                                 z 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                               , 
                               1 
                               , 
                               
                                 
                                   - 
                                   x 
                                 
                                  
                                 
                                     
                                 
                                  
                                 4 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                               , 
                               
                                 
                                   - 
                                   y 
                                 
                                  
                                 
                                     
                                 
                                  
                                 4 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                               , 
                               
                                 
                                   - 
                                   z 
                                 
                                  
                                 
                                     
                                 
                                  
                                 4 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                             
                           
                         
                         
                           
                             
                               
                                 x 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                               , 
                               
                                   
                               
                                
                               
                                 y 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                               , 
                               
                                   
                               
                                
                               
                                 z 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                               , 
                               1 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               
                                 
                                   - 
                                   x 
                                 
                                  
                                 
                                     
                                 
                                  
                                 5 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                               , 
                               
                                 
                                   - 
                                   y 
                                 
                                  
                                 
                                     
                                 
                                  
                                 5 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                               , 
                               
                                 
                                   - 
                                   z 
                                 
                                  
                                 
                                     
                                 
                                  
                                 5 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                             
                           
                         
                         
                           
                             
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               
                                 x 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                               , 
                               
                                 y 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                               , 
                               
                                 z 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                               , 
                               1 
                               , 
                               
                                 
                                   - 
                                   x 
                                 
                                  
                                 
                                     
                                 
                                  
                                 5 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                               , 
                               
                                 
                                   - 
                                   y 
                                 
                                  
                                 
                                     
                                 
                                  
                                 5 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                               , 
                               
                                 
                                   - 
                                   z 
                                 
                                  
                                 
                                     
                                 
                                  
                                 5 
                                  
                                 v 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                             
                           
                         
                         
                           
                             
                               
                                 x 
                                  
                                 
                                     
                                 
                                  
                                 6 
                               
                               , 
                               
                                   
                               
                                
                               
                                 y 
                                  
                                 
                                     
                                 
                                  
                                 6 
                               
                               , 
                               
                                   
                               
                                
                               
                                 z 
                                  
                                 
                                     
                                 
                                  
                                 6 
                               
                               , 
                               1 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               
                                 
                                   - 
                                   x 
                                 
                                  
                                 
                                     
                                 
                                  
                                 6 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 6 
                               
                               , 
                               
                                 
                                   - 
                                   y 
                                 
                                  
                                 
                                     
                                 
                                  
                                 6 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 6 
                               
                               , 
                               
                                 
                                   - 
                                   z 
                                 
                                  
                                 
                                     
                                 
                                  
                                 6 
                                  
                                 u 
                                  
                                 
                                     
                                 
                                  
                                 6 
                               
                             
                           
                         
                       
                       ) 
                     
                      
                     
                       ( 
                       
                         
                           
                             
                               | 
                               1 
                             
                           
                         
                         
                           
                             
                               | 
                               2 
                             
                           
                         
                         
                           
                             
                               | 
                               3 
                             
                           
                         
                         
                           
                             
                               | 
                               4 
                             
                           
                         
                         
                           
                             
                               | 
                               5 
                             
                           
                         
                         
                           
                             
                               | 
                               6 
                             
                           
                         
                         
                           
                             
                               | 
                               7 
                             
                           
                         
                         
                           
                             
                               | 
                               8 
                             
                           
                         
                         
                           
                             
                               | 
                               9 
                             
                           
                         
                         
                           
                             
                               | 
                               10 
                             
                           
                         
                         
                           
                             
                               | 
                               11 
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   2 
                 
               
             
           
         
       
     
     Formula 2 is used to calculate the real image parameters L (l 1  to l 11 ) and mirror image parameters L′ (l 1 ′ to l 11 ′). The real coordinates (x, y, z) are associated with the image coordinates (u, v) by using 11 parameters. The respective parameters L and L′ of the real and mirror images are calculated by substituting real and image coordinate values of the scales into formula 2. 
     In step S 1003 , the coordinates (u, v) and (u′, v′) of the real image  603  and the mirror image  605  of the point of interest are extracted by using formulas 3 and 4. It should be noted that a point of interest may be generated automatically. 
     
       
         
           
             
               
                 
                   
                       
                   
                    
                   
                     
                       [ 
                       
                         Math 
                         . 
                         
                             
                         
                          
                         3 
                       
                       ] 
                     
                      
                     
                       
 
                     
                      
                     Relational 
                      
                     
                         
                     
                      
                     formula 
                      
                     
                         
                     
                      
                     of 
                      
                     
                         
                     
                      
                     the 
                      
                     
                         
                     
                      
                     point 
                      
                     
                         
                     
                      
                     of 
                      
                     
                         
                     
                      
                     interest 
                      
                     
                         
                     
                      
                     on 
                      
                     
                         
                     
                      
                     the 
                      
                     
                         
                     
                      
                     real 
                      
                     
                         
                     
                      
                     image 
                      
                     
                         
                     
                      
                     side 
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     ( 
                     
                       
                         
                           
                             u 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                       
                         
                           
                             v 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             
                               x 
                               , 
                               y 
                               , 
                               z 
                               , 
                               1 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               
                                 
                                   - 
                                   xu 
                                 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               
                                 
                                   - 
                                   yu 
                                 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               
                                 
                                   - 
                                   zu 
                                 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                         
                         
                           
                             
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               x 
                               , 
                               y 
                               , 
                               z 
                               , 
                               1 
                               , 
                               
                                 
                                   - 
                                   xv 
                                 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               
                                 
                                   - 
                                   yv 
                                 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               , 
                               
                                 
                                   - 
                                   zv 
                                 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                         
                       
                       ) 
                     
                      
                     
                       ( 
                       
                         
                           
                             
                               I 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                         
                         
                           
                             
                               I 
                                
                               
                                   
                               
                                
                               2 
                             
                           
                         
                         
                           
                             
                               I 
                                
                               
                                   
                               
                                
                               3 
                             
                           
                         
                         
                           
                             
                               I 
                                
                               
                                   
                               
                                
                               4 
                             
                           
                         
                         
                           
                             
                               I 
                                
                               
                                   
                               
                                
                               5 
                             
                           
                         
                         
                           
                             
                               I 
                                
                               
                                   
                               
                                
                               6 
                             
                           
                         
                         
                           
                             
                               I 
                                
                               
                                   
                               
                                
                               7 
                             
                           
                         
                         
                           
                             
                               I 
                                
                               
                                   
                               
                                
                               8 
                             
                           
                         
                         
                           
                             
                               I 
                                
                               
                                   
                               
                                
                               9 
                             
                           
                         
                         
                           
                             
                               I 
                                
                               
                                   
                               
                                
                               10 
                             
                           
                         
                         
                           
                             
                               I 
                                
                               
                                   
                               
                                
                               11 
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   3 
                 
               
             
           
         
       
     
     When the real image parameters L are determined, two simultaneous equations can be obtained from image coordinates (u1, v1) of the real image of the point of interest. 
     
       
         
           
             
               
                 
                   
                       
                   
                    
                   
                     
                       [ 
                       
                         Math 
                         . 
                         
                             
                         
                          
                         4 
                       
                       ] 
                     
                      
                     
                       
 
                     
                      
                     Relational 
                      
                     
                         
                     
                      
                     formula 
                      
                     
                         
                     
                      
                     of 
                      
                     
                         
                     
                      
                     the 
                      
                     
                         
                     
                      
                     point 
                      
                     
                         
                     
                      
                     of 
                      
                     
                         
                     
                      
                     interest 
                      
                     
                         
                     
                      
                     on 
                      
                     
                         
                     
                      
                     the 
                      
                     
                         
                     
                      
                     mirror 
                      
                     
                         
                     
                      
                     image 
                      
                     
                         
                     
                      
                     side 
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     ( 
                     
                       
                         
                           
                             u 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                       
                       
                         
                           
                             v 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             
                               x 
                               , 
                               y 
                               , 
                               z 
                               , 
                               1 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               
                                 
                                   - 
                                   xu 
                                 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               
                                 
                                   - 
                                   yu 
                                 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               
                                 
                                   - 
                                   zu 
                                 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                             
                           
                         
                         
                           
                             
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               0 
                               , 
                               x 
                               , 
                               y 
                               , 
                               z 
                               , 
                               1 
                               , 
                               
                                 
                                   - 
                                   xv 
                                 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               
                                 
                                   - 
                                   yv 
                                 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               , 
                               
                                 
                                   - 
                                   zv 
                                 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                             
                           
                         
                       
                       ) 
                     
                      
                     
                       ( 
                       
                         
                           
                             
                               
                                 I 
                                 ′ 
                               
                                
                               
                                   
                               
                                
                               1 
                             
                           
                         
                         
                           
                             
                               
                                 
                                   I 
                                    
                                   
                                       
                                   
                                 
                                 ′ 
                               
                                
                               2 
                             
                           
                         
                         
                           
                             
                               
                                 
                                   I 
                                    
                                   
                                       
                                   
                                 
                                 ′ 
                               
                                
                               3 
                             
                           
                         
                         
                           
                             
                               
                                 
                                   I 
                                    
                                   
                                       
                                   
                                 
                                 ′ 
                               
                                
                               4 
                             
                           
                         
                         
                           
                             
                               
                                 
                                   I 
                                    
                                   
                                       
                                   
                                 
                                 ′ 
                               
                                
                               5 
                             
                           
                         
                         
                           
                             
                               
                                 
                                   I 
                                    
                                   
                                       
                                   
                                 
                                 ′ 
                               
                                
                               6 
                             
                           
                         
                         
                           
                             
                               
                                 
                                   I 
                                    
                                   
                                       
                                   
                                 
                                 ′ 
                               
                                
                               7 
                             
                           
                         
                         
                           
                             
                               
                                 
                                   I 
                                    
                                   
                                       
                                   
                                 
                                 ′ 
                               
                                
                               8 
                             
                           
                         
                         
                           
                             
                               
                                 
                                   I 
                                    
                                   
                                       
                                   
                                 
                                 ′ 
                               
                                
                               9 
                             
                           
                         
                         
                           
                             
                               
                                 
                                   I 
                                    
                                   
                                       
                                   
                                 
                                 ′ 
                               
                                
                               10 
                             
                           
                         
                         
                           
                             
                               
                                 
                                   I 
                                    
                                   
                                       
                                   
                                 
                                 ′ 
                               
                                
                               11 
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   4 
                 
               
             
           
         
       
     
     Further, when the mirror image parameters L′ are determined, two simultaneous equations can be obtained from image coordinates (u2, v2) of the mirror image of the real image of the point of interest. 
     In step S 1004 , the three-dimensional coordinates x, y, and z are calculated from the obtained L, L′, (u, v), and (u′, v′). For example, the coordinates (x, y, z) of the point of interest can be calculated by using the four simultaneous equations obtained from formulas 3 and 4. A three-dimensional image is generated by combining the coordinates that have been obtained. 
     In step S 1005 , it is decided whether or not three-dimensional coordinates (x, y, z) of another point of interest are further to be calculated. In the case where three-dimensional coordinates (x, y, z) of another point of interest are to be calculated, the process proceeds to Yes and returns to step S 1003 . In the case where three-dimensional coordinates (x, y, z) of another point of interest are not to be calculated, the process proceeds to No and is terminated. 
     Here, in the past, the use of X-ray CT has been known as a method of acquiring three-dimensional coordinates inside a tooth because of the need to stereoscopically see through the tooth. However, X-ray CT is conducted only once before treatment, and progress during treatment cannot be confirmed due to the problem of radiation exposure to the patient and the practitioner. Further, X-ray CT can be used only in an X-ray control area. As a result, it is necessary to prepare a separate inspection room. Also, although a technique is known that permits observation of caries inside the tooth by emitting near infrared light, the observation target is only caries, and the internal structure of the tooth is not subject to observation. Also, such an observation technique does not allow acquisition of three-dimensional coordinates. 
     In contrast, the dental image acquisition apparatus  100  according to the present embodiment allows for acquisition of images in a plurality of imaging directions with a single captured image by using a mirror and requires only a single camera, thus making it possible to capture two images at the same time with no concern for imaging timings of two cameras. As a result, it is possible to calculate position coordinates with high accuracy. 
     Also, the dental image acquisition apparatus  100  employs light, thus causing no problem of X-ray exposure during imaging. For this reason, the target can be observed even during treatment, and the treatment can be pursued while at the same time conducting verifications a number of times as necessary, thus ensuring that treatment results remain unaffected by the difference in proficiency between dentists. 
     Also, in addition to requiring no separate inspection room such as an X-ray control area and causing no risk of X-ray exposure, the dental image acquisition apparatus  100  is compact, allowing for observation of the target on the chair side. It should be noted that the dental image acquisition apparatus  100  can be used as a CAD/CAM oral cavity scanner by measuring the appearance of the oral cavity with the dental image acquisition apparatus  100 . 
     &lt;2. Dental Image Acquisition Apparatus of the Second Embodiment&gt; 
     A description will be given of a second embodiment of a dental image acquisition apparatus according to the present technology by using  FIGS. 11 and 12 .  FIG. 11  is an enlarged schematic diagram illustrating a camera unit of the second embodiment according to the present technology. The present embodiment differs from the first embodiment in that the mirror of the camera unit has a scale only at an offset spatial position from the mirror surface. It should be noted that components similar to those of the first embodiment are denoted by the same reference signs and that the description thereof is omitted. 
     As illustrated in  FIG. 11 , a camera unit  1101  of the present embodiment includes the camera  109 , a mirror  1102 , the connecting section  111  connecting the camera  109  and the mirror  1102 , and an offset scale  1103  that protrudes from a mirror surface edge portion of the mirror  1102  to an offset spatial position. The lens of the camera  109  and the mirror surface of the mirror  110  are placed at opposed positions to face each other via the dentition  114  in the oral cavity. The camera unit  1101  can emit the illumination light  402  from the light guide  112  toward the imaging target and the mirror surface of the mirror  1102  through the surface where the lens of the camera  109  is formed. 
     The offset scale  1103  is formed, for example, in the shape of a rod and placed at a position protruding from the mirror surface of the mirror  1102  at a predetermined angle. Further, the offset scale  1103  includes three rod shapes at the tip of the rod shape protruding from the mirror  1102 . The three-dimensional coordinates can be measured with respect to the three rod shapes which are orthogonal to each other. It should be noted that the predetermined angle between the offset scale  1103  and the mirror surface of the mirror  1102  is preferably 80° to 120° and more preferably 90° or so. 
     A description will be given next of an example of a dental image that can be captured by the dental image acquisition apparatus of the present embodiment by using  FIG. 12 .  FIG. 12  is a schematic diagram illustrating an example of a captured image captured by the camera unit  1101  of the present embodiment. 
     As illustrated in  FIG. 12 , the imaging target  602 , the point of interest  603  of the imaging target  602 , the mirror  1102 , and the offset scale  1103  appear in a captured image  1201 . Further, the mirror image  604  of the imaging target  602 , the mirror image  605  of the point of interest  603 , and a mirror image  1202  of the offset scale  1103  appear in the mirror  1102  in the captured image  1201 . Here, it is necessary that six points of the offset scale  1103  and the point of interest  603  should appear at the same time in both real and mirror images. It should be noted that the six scale points that define the images on the real image side and the mirror image side may be different points as long as they are in the same coordinate system. 
     The dental image acquisition apparatus of the present embodiment also provides an action and effect similar to those of the dental image acquisition apparatus  100  of the first embodiment by having the camera unit  1101  configured as described above. 
     &lt;3. Dental Image Acquisition Apparatus of the Third Embodiment&gt; 
     A description will be given of a third embodiment of a dental image acquisition apparatus according to the present technology by using  FIGS. 13 and 14 .  FIG. 13  is an enlarged schematic diagram illustrating a camera unit of the third embodiment according to the present technology. The present embodiment differs from the first embodiment in that a camera of the camera unit has a laser scanning apparatus which is a laser beam source. It should be noted that components similar to those of the first embodiment are denoted by the same reference signs and that the description thereof is omitted. 
     As illustrated in  FIG. 13 , a camera unit  1301  of the present embodiment includes the camera  109 , the mirror  110 , the connecting section  111  connecting the camera  109  and the mirror  110 , and the offset scale  401 . The offset scale  401  is a measurement section that protrudes from the mirror surface edge portion of the mirror  110  to an offset position to measure the size of an imaging target. The lens of the camera  109  and the mirror surface of the mirror  110  are placed at opposed positions to face each other via the dentition  114  in the oral cavity. The camera unit  11013  can emit the illumination light  402  from the light guide  112  toward the imaging target and the mirror surface of the mirror  1102  through the surface where the lens of the camera  109  is formed. 
     Further, a laser scanning apparatus  1302  is provided on the lateral surface of the camera  109  of the camera unit  1301 . The laser scanning apparatus  1302  can emit a laser beam  1303  in the same direction as the illumination light  402  from the light guide  112 . 
       FIG. 14  is a schematic diagram indicating a point of interest  1402  with a laser beam  1303  emitted from the camera unit  1301  of the present embodiment. The dental image acquisition apparatus of the present embodiment automatically generates the point of interest  1402  as in the first embodiment, thus making it possible to indicate a variety of points by scanning the laser beam  1303  from the laser scanning apparatus  1302 . It should be noted that the laser scanning apparatus  1302  may be incorporated in the camera unit  1301  and that a laser beam may be guided by using an optical fiber or other means. 
     The dental image acquisition apparatus of the present embodiment also provides an action and effect similar to those of the dental image acquisition apparatus  100  of the first embodiment by having the camera unit  1301  having the above configuration. 
     &lt;4. Working Example of the Dental Image Acquisition Apparatus to Which the Present Technology is Applied&gt; 
     A description will be given of a working example of a dental image acquisition apparatus to which the present technology is applied by using  FIGS. 15 and 16 .  FIG. 15  depicts schematic diagrams illustrating a mirror of the working example using the present technology.  FIG. 15A  is a front view, and  FIG. 15B  is a side view.  FIG. 16  is a schematic diagram illustrating the manner in which an oral cavity is observed with the mirror of the working example using the present technology. It should be noted that  FIG. 16  illustrates a trimmed photograph obtained by removing unnecessary portions from the original photograph. 
     As illustrated in  FIG. 15A , a mirror  1501  of the present working example is circular in plan view. As illustrated in  FIGS. 15A and 15B , the mirror  1501  has, at the center on its surface, a mirror surface scale  1502  and an offset scale  1503 . The mirror surface scale  1502  has a vertical and horizontal lines with markings that are orthogonal to each other. The offset scale  1503  protrudes perpendicularly from the mirror surface by using a wire. It should be noted that the mirror surface scale  1502  is not limited to one having a vertical and horizontal lines orthogonal to each other and may be one having a vertical and horizontal lines that intersect each other. Also, the offset scale  1503  is not limited to one protruding perpendicularly from the mirror surface and may be one protruding at a given angle. Here, upper and lower tips of the vertical line of the mirror surface scale  1502  are denoted as r 1  and r2, left and right tips of the horizontal line are denoted as r 3  and r 4 , and an intersection point of the vertical and horizontal lines is denoted as r 5 , respectively. Also, a tip of the offset scale  1503  is denoted as r 6 , and a point on the mirror surface of r 6  is denoted as r 7 . 
     As illustrated in  FIG. 16 , imaging is conducted by fastening the camera of the dental image acquisition apparatus of the present embodiment to a human chin and inserting the mirror  1501  into the oral cavity. In the present working example, the DLT method is used to calculate three-dimensional coordinates. Reference points r 1  to r 6  are used for calculation with the DLT method on the real image, and the reference points r 1  to r 5  and the point r 7  on the mirror surface are used for calculation on the mirror image. Also, three-dimensional coordinates in a real space are calculated from points of interest a and b and mirror images a′ and b′ thereof for comparison with the measured distance. Photograph coordinates obtained from the captured image are illustrated in Table 1. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Point 
                 U 
                 V 
               
               
                   
                   
               
             
            
               
                   
                 a 
                 1663 
                 2321 
               
               
                   
                 b 
                 1675 
                 2435 
               
               
                   
                 ma 
                 2148 
                 2276 
               
               
                   
                 mb 
                 2153 
                 2383 
               
               
                   
                 r1 
                 2174 
                 2137 
               
               
                   
                 r2 
                 2073 
                 2317 
               
               
                   
                 r3 
                 2120 
                 2238 
               
               
                   
                 r4 
                 2076 
                 2161 
               
               
                   
                 r5 
                 2180 
                 2325 
               
               
                   
                 r6 
                 1641 
                 2168 
               
               
                   
                 r7 
                 2136 
                 2147 
               
               
                   
                   
               
            
           
         
       
     
     Table 1 represents positions on the shot photograph as pixel positions. For example, Table 1 indicates that the point a is located at the position of the 1663rd pixel to the right and the 2321st pixel down relative to the top left corner of the shot photograph. 
     The distance between a and b is 4.58 mm from the coordinates of points of interest a (0, 2, 21) and b (2, 6, 23) obtained by the calculation using the DLT method, according to the present working example. In contrast, the measured distance between a and b is 4.7 mm as a result of the measurement using calipers. Therefore, it has been discovered that the calculation result of the distance in the present working example approximately matches the measured value. 
     &lt;5. Usage Example of the Dental Image Acquisition Apparatus to Which the Present Technology is Applied&gt; 
     A description will be given below of an application example in which the dental image acquisition apparatus according to the present technology is applied. 
     [Root Canal Treatment] 
     In root canal treatment, for example, the root canal is spread after pulp extirpation, followed by cleaning and sterilization of the inside and filling of a root canal filling agent. Because of the need for precise treatment, it is necessary to accurately grasp the root canal shape. However, the root canal shape varies from one person to another. Besides, the root canal has a complicated shape. Precise treatment is made possible by seeing through the root canal and grasping the shape thereof in advance by means of the dental image acquisition method according to the present technology. Currently, the inside is observed by using CT. However, CT is conducted only once before treatment due to the risk of X-ray exposure. The dental image acquisition method according to the present technology has no risk of X-ray exposure, thus allowing for observation any number of times during treatment on the chair side and ensuring that treatment results remain unaffected by the difference in proficiency between dentists. 
     Also, when the inside of a tooth is drilled during caries treatment or root canal treatment, perforation that is erroneous drilling of a hole in a tooth may occur due to miscalculation of the tooth thickness. The present technology has no risk of X-ray exposure, thus allowing for observation any number of times halfway through the treatment and providing a reduced risk of perforation. 
     [Cosmetic Dentistry Treatment] 
     Also, when the teeth alignment is corrected as part of cosmetic dentistry treatment, it is possible to grasp the orientation and position of each tooth, gaps between the teeth, and the like by imaging the dentition as a whole by means of the present technology, thus making it possible to determine a treatment policy, make comparison between before and after the treatment, confirm the progress of the correction, and the like. 
     [Application to CAD/CAM Crown] 
     Further, the present technology can be applied to a CAD/CAM crown. In this case, in the case where a tooth is significantly drilled as part of dental treatment, the tooth is restored by making a crown. The CAD/CAM crown has started to see widespread use in recent years, and the present technology can be used to grasp the shapes of an abutment and an opposing tooth after forming the abutment. 
     [Implant Treatment] 
     In implant treatment, it is necessary to accurately assess the direction in which to insert an implant. The present technology provides a reference for determining a treatment policy as one stereoscopically grasps the dentition as a whole by using the present technology. Also, in implant treatment, a plaster cast of dentition is made in advance, and a jig for determining the insertion direction of the implant is fabricated. However, the present technology makes it possible to fabricate a plaster cast without impression taking. 
     It should be noted that the present technology also allows for acquisition of three-dimensional coordinates and a three-dimensional image by applying the DLT method using two cameras to dentistry. 
     It should be noted that embodiments of the present technology are not limited to those described above and can be changed in various ways without departing from the gist of the present technology. For example, it is possible to combine all or some of the plural embodiments described above. Also, the effect described in the present specification is merely illustrative and not restrictive, and there may be other effects. 
     Also, the present technology can have the following configurations. 
     (1) 
     A dental image acquisition apparatus including:
         an oral cavity insertion section adapted to be inserted into an oral cavity; and   an image acquisition section having a light source, in which   the oral cavity insertion section has an imaging unit that includes an imaging section and a light reflection section, the light reflection section being placed at a position opposed to the imaging section via an imaging target.
 
(2)
       

     The dental image acquisition apparatus of feature (1), in which
         the imaging unit is movable.
 
(3)
       

     The dental image acquisition apparatus of feature (1) or (2), in which
         the oral cavity insertion section further includes a guide rail inserted between a cheek and dentition.
 
(4)
       

     The dental image acquisition apparatus of feature (3), in which
         the oral cavity insertion section further includes a drive mechanism for driving the imaging unit, and   the drive mechanism moves the imaging unit on the guide rail.
 
(5)
       

     The dental image acquisition apparatus of feature (3) or (4), in which
         the guide rail includes a flexible material.
 
(6)
       

     The dental image acquisition apparatus of any one of features (1) to (5), in which
         the light reflection section includes a measurement section for measuring a size of the imaging target.
 
(7)
       

     The dental image acquisition apparatus of feature (6), in which
         the measurement section protrudes from a reflection surface of at least one point of the light reflection section to an offset position.
 
(8)
       

     The dental image acquisition apparatus of any one of features (1) to (7), in which
         the light source uses light having a wavelength that penetrates through the imaging target.
 
(9)
       

     The dental image acquisition apparatus of any one of features (1) to (8), in which
         the light source includes a laser beam source.
 
(10)
       

     The dental image acquisition apparatus of any one of features (1) to (9), in which
         the imaging unit includes illumination optics having a mask.
 
(11)
       

     The dental image acquisition apparatus of feature (10), in which
         the imaging unit includes patterned illumination that displays a plurality of points of interest on a surface of the imaging target.
 
(12)
       

     The dental image acquisition apparatus of any one of features (1) to (11) further including:
         an image processing section adapted to calculate three-dimensional coordinates of the imaging target on the basis of an image acquired by the image acquisition section; and   an image display section adapted to display a three-dimensional image created on the basis of the three-dimensional coordinates calculated by the image processing section.
 
(13)
       

     A dental image acquisition method including:
         an insertion step of inserting an oral cavity insertion section into an oral cavity, the oral cavity insertion section having an imaging unit that includes an imaging section and a light reflection section;   a placement step of placing the light reflection section at a position within a viewing angle of the imaging section via an imaging target; and   an image acquisition step of observing the imaging target with the imaging section, observing the imaging target from a position opposed to the imaging section with the light reflection section, and acquiring an image of the imaging target.       

     REFERENCE SIGNS LIST 
     
         
           100  Dental image acquisition apparatus 
           101  Oral cavity insertion section 
           102  Light source 
           103  Image processing apparatus 
           104  Monitor 
           105 ,  1101 ,  1301  Camera units 
           106  Drive mechanism 
           107  Guide rail 
           108  Power source 
           109  Camera 
           110 ,  1102 ,  1501  Mirrors 
           111  Connecting section 
           112  Light guide 
           113  Camera cable 
           114  Dentition 
           201  Wire 
           202 ,  204  Pulleys 
           203  Fixture 
           401 ,  1103 ,  1503  Offset scales 
           402  Illumination light 
           403 ,  1502  Mirror surface scales 
           601 ,  1201  Captured image 
           602  Imaging target 
           603 ,  704 ,  1402  Points of interest a and b 
           604  Mirror image of the imaging target 
           605 , ma, mb Mirror images of the points of interest 
           606 ,  1202  Mirror images of the offset scales 
           701  Illumination optics 
           702  Illumination device 
           703  Mask 
           705 ,  1401  Teeth 
           706  Shadow of the mask 
           707  Shadow of the point of interest 
           801 ,  802  Two-dimensional images 
           803  Three-dimensional image 
           804  Tooth surface 
           805  Inner part of the tooth 
           1302  Laser scanning apparatus 
           1303  Laser beam