Patent Publication Number: US-2015079534-A1

Title: Apparatus for imaging dental arch in oral cavity

Description:
TECHNICAL FIELD 
     The present invention relates to an intraoral teeth image taking apparatus used to take images of a row of teeth in an oral cavity and, more particularly, to an intraoral teeth image taking apparatus capable of simultaneously taking from a plurality of directions a group of high-precision images for calculation of high-precision three-dimensional data required, for example, when artificial teeth are made. The taken images can also be used for preparation of mosaic images for diagnosis. 
     BACKGROUND ART  
     A method of calculating three-dimensional coordinates of points on an object from planar images (two-dimensional images) of the object taken with a plurality of image taking devices is known. This is called “three-dimensional reconstruction from planar images”. An apparatus for taking images from a row of teeth in an oral cavity with a plurality of image taking devices has been disclosed. This apparatus performs three-dimensional reconstruction of a row of teeth by calculation from a plurality of planar images taken (see, for example, Patent Literature 1). 
     It is necessary to take images with a plurality of image taking devices (cameras) maintained in the same state as at the time of calibration in order to obtain planar images to be used for three-dimensional reconstruction. That is, when three-dimensional reconstruction is performed by using a plurality of planar images taken in a state different from the state at the time of calibration, it is difficult to achieve a sufficiently high degree of accuracy. A state where conditions at the time of calibration are held will hereinafter be referred to as “calibrated condition holding state”. For example, if the positional relationship between the plurality of image taking devices and the base line lengths (the distances between the cameras) or the like are changed from their states at the time of calibration, the calibrated condition holding state is collapsed. 
     When images are taken while the image taking devices are moved, the images are taken in a state where the positional relationship and the base line lengths are changed and the calibrated condition holding state is collapsed, unless the images are simultaneously taken with the plurality of image taking devices. In the method disclosed in Patent Literature 1, no particular measures are taken to cope with this. When this method is used, the base line lengths are changed because the image taking devices or the image taking operator is slightly moved at all times, and it is difficult to hold the calibrated condition holding state. When three-dimensional reconstruction from planar images taken under such a condition is performed, it is difficult to achieve a sufficiently high degree of accuracy. 
     CITATION LIST  
     Patent Literature 
     Patent Literature 1: Japanese Patent Laid-Open No. 2010-069301 
     SUMMARY OF INVENTION 
     Technical Problem 
     The present invention has been achieved in consideration of the above-described problem, and an object of the present invention is to provide an intraoral teeth image taking apparatus capable of simultaneously taking from a plurality of directions a group of high-precision images for calculation of high-precision three-dimensional data required, for example, when artificial teeth are made. 
     Solution to Problem 
     To achieve the above-described object, according to the present invention, an intraoral teeth image taking apparatus described below is provided. 
     A first intraoral teeth image taking apparatus includes an image taking tray part for taking images of a tooth or a row of teeth in an oral cavity, and a grip part. In this apparatus, a plurality of image taking devices capable of simultaneously taking images from a plurality of directions and a plurality of projection devices capable of projecting a plurality of radiation patterns are provided on a surface of the tray part. 
     According to a second intraoral teeth image taking apparatus, in the first intraoral teeth image taking apparatus, the image taking tray part is formed in a U-shape in conformity with the shape of a row of teeth and the cross-sectional shape of the tray is concave such as to be capable of being put on a distal end portion of the row of teeth. 
     According to a third intraoral teeth image taking apparatus, in the first or second intraoral teeth image taking apparatus, each image taking device is provided with an electric shutter mechanism for limiting the picture taking time and a sync image taking mechanism electrically connected to the electric shutter mechanisms and capable of causing the electric shutter mechanisms to simultaneously perform image taking operations. 
     According to a fourth intraoral teeth image taking apparatus, in any of the first or second intraoral teeth image taking apparatus, each image taking device is provided with a transmitter capable of transmitting a signal transmittable wirelessly. 
     According to a fifth intraoral teeth image taking apparatus, in any of the first or second intraoral teeth image taking apparatus, each projection device is capable of changing the radiation pattern. 
     According to a sixth intraoral teeth image taking apparatus, in any of the first or second intraoral teeth image taking apparatus, the image taking tray part is divided into two arm portions swingably connected by a hinge and is provided with adjustment means for enabling adjusting the angle between the arm portions. 
     Advantageous Effects of Invention 
     According to the invention of the first intraoral teeth image taking apparatus, simultaneously taking from a plurality of directions a group of high-precision planar images for calculation of high-precision three-dimensional data required, for example, when artificial teeth are made, is enabled and the effect of enabling easy image taking in the calibrated condition holding state can be obtained. The effect of enabling use for preparing mosaic images for diagnosis is also obtained. According to the invention of the second intraoral teeth image taking apparatus, the effect of enabling taking images of a row of teeth in an oral cavity from suitable positions and directions can be obtained. According to the invention of the third intraoral teeth image taking apparatus, the effect of taking accurate images of a row of teeth under projection of a suitable pattern of light can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram schematically showing the configuration of an intraoral teeth image taking apparatus according to the first embodiment of the present invention as seen from the front side of an image taking tray part (the image taking object teeth side). 
         FIG. 2  shows the structure of the image taking tray part in the intraoral teeth image taking apparatus shown in  FIG. 1 ;  FIG. 2(   a ) is a sectional view taken along line A-A in  FIG. 1 ; and  FIG. 2(   b ) is an enlarged view of a portion B of  FIG. 2(   a ). 
         FIG. 3  is a plan view schematically showing a modified example of the intraoral teeth image taking apparatus according to the embodiment of the present invention (a view of an arrangement enabling adjustment of the angle between arm portions of the image taking tray part). 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     An embodiment of an intraoral teeth image taking apparatus according to the present invention will be described concretely with reference to  FIGS. 1 to 3 .  FIG. 1  is a diagram schematically showing the construction of an intraoral teeth image taking apparatus according to a first embodiment of the present invention as seen from the front side of an image taking tray part. As shown in  FIG. 1 , in the construction of the intraoral teeth image taking apparatus  100  according to the first embodiment of the present invention schematically shown, there is provided an image taking tray part  101  that has a plurality of image taking devices (cameras)  121  capable of simultaneously taking images of a row of teeth in an oral cavity from a plurality of directions and a plurality of projection devices  151  capable of projecting a plurality of radiation patterns. 
     As shown in  FIG. 1 , the intraoral teeth image taking apparatus  100  according to the present embodiment is further provided with a cable  102 , a sync image taking mechanism (not shown), a computer  103  and a monitor  104 . 
     The image taking devices  121  are capable of simultaneously taking images of a row of teeth in an oral cavity from a plurality of directions, as described above. In addition, the image taking devices  121  are also capable of taking images of the row of teeth in the oral cavity from a plurality of directions with passage of time. It is assumed that “simultaneous” in simultaneous image taking in the present invention is broadly interpreted as also denoting a case where image taking is performed at consecutive times while maintaining the same calibrated condition holding state. 
     X, Y and Z in  FIG. 1  and  FIGS. 2 and 3  referred to below respectively represent the coordinate axes of a three-dimensional coordinate system. The abscissa A in  FIG. 2  is a representation of line A-A in  FIG. 1  as coordinate axis A. 
       FIG. 1  is a view of the intraoral teeth image taking apparatus  100  according to the present embodiment as seen from the front side (the upper side as viewed in  FIG. 2 ) of the image taking tray part  101  having the shape of a dental impression tray. As shown in  FIG. 1 , the plurality of image taking devices  121  and the plurality of projection devices  151  are disposed so as to be capable of taking images of an image taking object at least from two directions. The projection devices  151  apply patterns of light for detecting corresponding points of a plurality of images. Data of images taken by the image taking devices  121  is sent to the computer  103  through the cable  102  for display on the monitor  104 . A grip part (with no reference numeral) is shown on the right-hand side of the image taking tray part  101  in  FIG. 1 . 
       FIG. 2(   a ) is a sectional view taken along line A-A in  FIG. 1 , showing the structure of the image taking tray part  101  in the intraoral teeth image taking apparatus  100  shown in  FIG. 1 . As shown in  FIG. 2(   a ), the image taking devices  121  and the projection devices  151  are alternately disposed on inner bottom portions of the image taking tray part  101 .  FIG. 2(   b ) is an enlarged view of a portion B of  FIG. 2(   a ). Each image taking device  121  is constituted by an image pickup element  122  and a lens  123 . Each projection device  151  is constituted by a light source  152 , a pattern generator  154  and a projection lens  155 . 
     The image pickup element  122  may be, for example, a CCD or CMOS configured in planar form. The lens  123  may be a single lens or a combination of a plurality of lenses made of glass or a plastic and formed so as to have a spherical or aspherical surface. The light source  152  may be, for example, a light emitting diode (LED) or an incandescent lamp. The pattern generator  154  may be, for example, a film or a liquid crystal. The projection lens  155  may be a single lens or a combination of a plurality of lenses made of glass or a plastic and formed so as to have a spherical or aspherical surface. 
     Each image taking device  121  has an electric shutter mechanism for limiting the image taking time, not shown. The electric shutter mechanism changes (turns on/off) an electrical signal with an electronic circuit and has no mechanical structure. The electric shutter mechanisms provided in the plurality of image taking devices  121  are electrically connected to each other and are arranged to simultaneously perform image taking operations with the sync image taking mechanism not shown. The sync image taking mechanism may be arranged to cause the electric shutter mechanisms to perform the image taking operations with passage of time. 
     Each electric shutter mechanism is operated by an electric signal. The image taking device  121  accumulates electric charge according to the lightness of the image taking object while the electric signal is being applied. It is preferable to take images by opening the shutter of the electric shutter mechanism for a sufficiently short time, e.g., 0.1 to 10.0 ms, such that the image is not blurred even if the image taking tray part  101  is shaken. 
     With the above-described arrangement, images from a plurality of directions including directions from two side surfaces of teeth are taken in synchronization with each other by means of the plurality of image taking devices  121 . The plurality of images taken are sent to the computer  103  to be processed. 
     Calibration for three-dimensional reconstruction with the plurality of image taking devices  121  can be performed, for example, by putting the image taking tray part  101  on a three-dimensionally measured teeth model (not shown) or a three-dimensionally measured standard object (not shown) as in the case of ordinary image taking and by thereafter performing image taking. Calibration may be performed at any time before or after image taking. Calibration may be omitted in the case of preparation of mosaic images. 
       FIG. 3  is a plan view schematically showing a modified example (arranged so that the angle between arms of the image taking tray part  101  is adjustable) of the intraoral teeth image taking apparatus according to the embodiment of the present invention. The configuration of a row of teeth may vary depending on the jaw size as between an adult person and a young child. For the purpose of suitably maintaining the distances between the row of teeth and the lenses in such a case, two arms  110  and  111  of the image taking tray part  101  may be made swingable on a hinge  311  as shown in  FIG. 3 , and adjustment means may be provided to enable adjustment of the arms. A potion indicated by a broken line in  FIG. 3  represents a state of the arms after the arms are adjusted by being inwardly turned. For example, as adjustment means (not shown), nuts reverse threaded relative to each other may be fixed on the two arms  110  and  111  and a threaded rod may be screw-fitted therein to enable adjustment. 
     In the first embodiment shown in  FIG. 1 , images taken with the image taking devices  121  are sent from the image taking devices  121  to the computer  103  through the cable  102  to be displayed on the monitor  104 . In another modified example of the apparatus, a transmitter that transmits a wireless signal such as an infrared signal or an electromagnetic wave signal may be connected to the plurality of image taking devices  121  to transmit the wireless signal to the computer  103 . This arrangement enables removal of the cable  102  shown in  FIG. 1  and simplification of the configuration. 
     Another modified example is conceivable in which the projection device  151  shown in  FIG. 2  is arranged so that the on/off positions in the liquid crystal (pattern generator)  154  for generating patterns can be changed to enable the image taking device  121  to take a plurality of different planar images. The accuracy with which corresponding points are detected can be improved in this way. Calculation for three-dimensional reconstruction requires detection of corresponding points in a plurality of planar images. In general, the accuracy is improved if the amount of data is larger. More specifically, detection of corresponding points by taking images is repeated a certain number of times while changing the projection pattern, and all the plurality of corresponding points thereby detected are used or the medians, averages or the like of the plurality of corresponding points are used, thereby improving the accuracy. An improvement in accuracy can also be achieved by slightly moving the image taking tray part  101  each time images are taken. 
     REFERENCE SIGNS LIST  
       88  Row of teeth in oral cavity 
       100  Intraoral teeth image taking apparatus 
       101  Image taking tray part 
       102  Cable 
       103  Computer 
       104  Monitor 
       110  Arm 
       111  Arm 
       121  Image taking device 
       122  Image pickup element 
       123  Lens 
       151  Projection device 
       152  Light source 
       154  Pattern generator 
       155  Projection lens 
       311  Hinge