Abstract:
An occlusal wear evaluation apparatus capable of evaluating quantitatively an occlusal wear of a used denture reads three dimensional data of a denture before use and three dimensional data of the denture after use, calculates a difference in a set value of an articulator allowing the maxillary dental arch and the mandibular dental arch of the denture to occlude between the denture before use and the denture after use, by way of simulating movements of a jaw in the articulator with the three dimensional data of the denture before use and the three dimensional data of the denture after use, and indicates the calculated difference.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an occlusal wear evaluation apparatus and an occlusal wear evaluation method. 
       BACKGROUND ART 
       [0002]    Generally, a denture should be re-configured periodically. Because, a condition in an oral cavity and a muscle force of a patient change over time, an optimum denture for the patient can not be made by only reconstructing a shape before occlusal wear (abrasion due to dental occlusion) of a presently used denture. Therefore, a dental technician observes a condition of the occlusal wear of the used denture to image an optimum shape of a denture for the patient so as to determine detailed configuration of a denture to be newly made. For instance, in a case of that the used denture has been unevenly worn, a cusp is adjusted in its shape and position so that a particularly worn part will be hard to be worn and the other part will be easy to be worn. 
         [0003]    When making a denture in such way, a detailed configuration of the denture is determined in a seat of the pants approach by a doctor or a dental technician. Therefore, an apparatus that can evaluate quantitatively an occlusal wear of a used denture is desired in order to allow even a less-experienced doctor or dental technician to determine an optimum denture configuration for a patient. 
         [0004]    With respect to a denture configuration, JP 2005-329055 A describes a system scanning three dimensional shape of teeth and indicating the shape of the teeth on a computer, and JP 2004-195152 A describes replicating or simulating an occlusal condition on a computer using three dimensional data of maxillary tooth and mandibular tooth. And, JP 2007-111519 A describes a system that indicates teeth in a predetermined view and at a predetermined magnification on a screen. 
       SUMMERY OF THE INVENTION 
       [0005]    The objects of the present invention is to provided an occlusal wear evaluation apparatus and an occlusal wear evaluation method that can evaluate quantitatively an occlusal wear of a used denture. 
         [0006]    In order to achieve the above object, according to the present invention, it is provided a first aspect of an occlusal wear evaluation apparatus comprising an input device, an arithmetic device and a display device, wherein the input device is configured to input three dimensional data of a denture before use and three dimensional data of the denture after use into the arithmetic device, the arithmetic device is configured to calculate a set value of an articulator allowing the maxillary dental arch and the mandibular dental arch of the denture to occlude for each of the denture before use and the denture after use by way of simulating movements of a jaw in the articulator with the three dimensional data of the denture before use and the three dimensional data of the denture after use, to calculate a difference in the set value between the denture before use and the denture after use, the set value including at least one of a distance between condyle paths, a distance between a maxillary dental arch and a mandibular dental arch, an inclination of a sagittal condylar path, an angle of a balancing side lateral condylar path, an amount of an immediate side shift, an angle of a working side lateral condylar path, an inclination of sagittal incisal path, and a guidance angle of a lateral incisal path, and the display device is configured to indicate the difference in the set value calculated by the arithmetic device. 
         [0007]    And, according to the present invention, it is provided a second aspect of an occlusal wear evaluation apparatus comprising an input device, an arithmetic device and a display device, wherein the input device is configured to input three dimensional data of a plurality of dentures used by a same patient into the arithmetic device, the arithmetic device is configured to calculate a set value of an articulator allowing the maxillary dental arch and the mandibular dental arch of the denture to occlude for the each denture, by way of simulating movements of a jaw in the articulator with the three dimensional data of the dentures, the set value including at least one of a distance between condyle paths, a distance between maxillary dental arch and a mandibular dental arch, an inclination of a sagittal condylar path, an angle of a balancing side lateral condylar path, an amount of an immediate side shift, an angle of a working side lateral condylar path, an inclination of a sagittal incisal path and a guidance angle of a lateral incisal path, and the display device is configured to indicate the set values calculated by the arithmetic device in a time series chart. 
         [0008]    In a denture, because a portion where is heavily used tends to be greatly worn, a lot of jaws inclines when an occlusion due to an uneven wear. Therefore, in the occlusal wear evaluation apparatus according to the present invention, if a relative angle between the maxillary dental arch and the mandibular dental arch of the denture in a centric occlusal position is calculated, an unevenness of the wear can be quantitatively recognized. Accordingly, a countermeasure such as to reduce unevenness of wear by increasing a contacting area in a mostly used portion can be taken. 
         [0009]    And, in the occlusal wear evaluation apparatus according to the present invention, if a relative position between the maxillary dental arch and the mandibular dental arch of the denture in a centric occlusal position is calculated, variance of an occluding position can be obtained. 
         [0010]    And, in the occlusal wear evaluation apparatus according to the present invention, if at least one of a relative moving distance and a relative moving angle of a sliding movement between the maxillary teeth and the mandibular teeth of the denture from a first occlusal condition to a second occlusal condition is calculated, a variance in a sliding movement of the teeth can be determined. 
         [0011]    And, in the occlusal wear evaluation apparatus according to the present invention, if a volume of the denture is calculated, a total worn amount can be recognized. 
         [0012]    And, in the occlusal wear evaluation apparatus according to the present invention, a height of a cusp which is often used as a reference point may be calculated. 
         [0013]    And, in the occlusal wear evaluation apparatus according to the present invention, difference of angles of planes which represent a certain area of the denture may be calculated. 
         [0014]    Further, a first aspect of an occlusal wear evaluation method according to the present invention comprises inputing three dimensional data of a denture before use and three dimensional data of the denture after use into a computer, calculating a difference between the denture before use and the denture after use in a set value of an articulator allowing the maxillary dental arch and the mandibular dental arch of the denture to occlude, by way of simulating movements of a jaw in the articulator with the three dimensional data of the denture before use and the three dimensional data of the denture after use on the computer, the set value including at least one of a distance between condyle paths, a distance between maxillary dental arch and a mandibular dental arch, an inclination of a sagittal condylar path, an angle of a balancing side lateral condylar path, an amount of an immediate side shift, an angle of a working side lateral condylar path, an inclination of a sagittal incisal path and a guidance angle of a lateral incisal path which are set values, and indicating the calculated deference on a screen. 
         [0015]    Further, a second aspect of an occlusal wear evaluation method according to the present invention comprises inputing three dimensional data of a plurality of denture used by a same patient into a computer, calculating a set value of an articulator allowing the maxillary dental arch and the mandibular dental arch of the denture to occlude for the each denture by way of simulating movements of a jaw in the articulator with the three dimensional data of the dentures on the computer, the set value including at least one of a distance between condyle paths, a distance between maxillary dental arch and a mandibular dental arch, an inclination of a sagittal condylar path, an angle of a balancing side lateral condylar path, an amount of an immediate side shift, an angle of a working side lateral condylar path, an inclination of a sagittal incisal path and a guidance angle of a lateral incisal path, and indicating the calculated set values in a time series chart on a screen. 
         [0016]    According to the present invention, a wear of a denture due to use. is quantified to be indicated, and therefore a correct diagnosis and a re-design of a denture can be made. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a schematic configuration diagram of an occlusal wear evaluation apparatus as an embodiment of the present invention; 
           [0018]      FIG. 2  is an example of a screen indication of the occlusal wear evaluation apparatus in  FIG. 1 ; 
           [0019]      FIG. 3  is a schematic view of a denture before use evaluated on the occlusal wear evaluation apparatus in  FIG. 1 ; 
           [0020]      FIG. 4  is a schematic view of a denture after use evaluated on the occlusal wear evaluation apparatus in  FIG. 1 ; 
           [0021]      FIG. 5  is an example of a chart indicated on the occlusal wear evaluation apparatus in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    Hereinafter, an embodiment of the present invention is described with referring drawings. An occlusal wear evaluation apparatus according to the present invention can be realized using a computer system that comprises an arithmetic device  1 , a data input device  2 , a display device  3  and a user input device  4  as shown in  FIG. 1 . 
         [0023]    The arithmetic device  1  can be substantialized using a personal computer and a software program, while the arithmetic device  1  may be exclusively designed. The data input device  2  can be not only an apparatus such as three dimensional scanner reading directory three dimensional shape, but also a device for inputting three dimensional data which is read by an external three dimensional scanner and the like into the arithmetic device  1 , such as a media reading device, for instance a memory device or a disc drive, or a data communication device. The display device  3  may be a common display. As the user input device  4 , a generalized input device such as a keyboard and a mouse can be used. 
         [0024]    The occlusal wear evaluation apparatus according to the present invention uses the data input device  2  to input three dimensional data of a denture before use and three dimensional data of the same denture which has been used by a patient and worn, into the arithmetic device  1 , and calculates variations in various physical quantities of the denture between before and after use so as to indicate on the display device  3 . 
         [0025]      FIG. 2  shows an example of a screen indication of the display device  3 . In this example, a sectional display portion  5  for indicating a sectional view of the denture is arranged in an upper left part of the screen, a result display portion  6  for indicating differences in physical quantities of the denture before and after use is arranged in a lower left part of the screen, and a general display portion  7  for indicating the entire denture schematically and specifying a position of a cross-section indicated in the sectional display portion  5  is arranged in right part of the screen. 
         [0026]    The sectional display portion  5  indicates a sectional shape of the denture after use and a sectional shape of the same denture before use at the same position in an overlaid manner with different line types and/or colors. As an example, in  FIG. 2 , a sectional shape of a denture after use is indicated by solid lines, and an outline of a cross-section of the same denture before use sectioned at the same position is indicated by dashed lines. Thereby, a wear of the denture in a certain cross-section is visualized in an understandable manner. 
         [0027]    The result display portion  6  indicates a difference in physical quantities between a denture before use and the denture after use (variations due to an occlusal wear). The differences in physical quantities calculated by the arithmetic device  1  and indicated in the result display portion  6  include a variation in a relative angle between a maxillary dental arch and a mandibular dental arch, a variation in a relative position between a specific reference point of a maxillary dental arch and a specific reference point of a mandibular dental arch (such as an occlusal vertical dimension). 
         [0028]    The physical quantities indicated in the result display portion  6  include a relative moving distance and a relative moving angle in a sliding movement between a maxillary teeth and a mandibular teeth from a first occlusal condition (for instance, a centric occlusal position) to a second occlusal condition (for instance, a lateral occlusal position), a volume of a denture and a height of a cusp. The differences in physical quantities indicated in the result display portion  6  may further include an angular difference (a variation in a direction of a normal line) of planes which represent a certain area of the denture, for instance, planes approximated by the method of least-square, and the like. 
         [0029]    Further, the variations indicated in the result display portion  6  may include differences between before and after use in physical quantities (for instance, sectional area and height) in the cross-section indicated on the sectional display portion  5 . 
         [0030]    Further, the occlusal wear evaluation apparatus preferably simulates movements of a jaw in an articulator by the arithmetic device  1  so that variations in set values (for instance, a distance between condyle paths, a distance between maxillary dental arch and a mandibular dental arch, an inclination of a sagittal condylar path, an angle of a balancing side lateral condylar path, an amount of an immediate side shift, an angle of a working side lateral condylar path, an inclination of a sagittal incisal path and a guidance angle of a lateral incisal path) in the articulator can be calculated to be indicated on the result display portion  6 . 
         [0031]    The general display portion  7  is mainly intended to be utilized by a user to determine a cross-sectional position to be indicated on the sectional display portion  5 , thorough the user input device  4 . Therefore, the general display portion  7  is to show dental arches schematically, and not required to show any specific shape based on an actual data. The display on the sectional display portion preferably is successively renewed together with a relocation of the cross-sectional position determined in the general display portion  7 . While it is also idealistic that the indication in the result display portion  6  is successively renewed together with a relocation of the cross-sectional position, the indication in the result display portion  6  may be renewed at a timing designated by a user via the user input device  4 , so as to reduce an arithmetic load for the arithmetic device  1 . 
         [0032]    The general display portion  7  indicates bar handles for moving cursors on the screen using the user input device  4  so as to move and rotate the displayed dental arches in respective directions of x, y, z, bar handles to designate a cross-sectional position to be displayed in the sectional display portion  5  on the dental arches displayed in the general display portion  7 , and a bar handle for zooming the display in the sectional display portion  5 . 
         [0033]    Further, the general display portion  7  preferably specifies a position in which a difference of a physical quantity as indicated in the result display portion  6  is maximized and is able to indicate the position on the screen. For instance, a position of a cusp which has most greatly varied in position, a tooth which has most greatly changed in volume and others may be specified in a manner of changing color, indicating a marker or the like. 
         [0034]      FIG. 3  schematically shows a denture before use and  FIG. 4  schematically shows the denture after use, in order to describe how to utilize the occlusal wear evaluation apparatus according to the present invention. The occlusal wear evaluation apparatus occludes the three dimensional data of the maxillary teeth and three dimensional data of the mandibular teeth respectively for the denture before use and the denture after use so as to replicate respective centric occlusal positions where contacting points are maximized. Then, difference between a relative angle of the mandibular dental arch with respect to the maxillary dental arch of the denture before use and a relative angle of the mandibular dental arch with respect to the maxillary dental arch of the denture after use is calculated, as three angles in axial directions of x, y, z, to be indicated in the result display portion  6 . For instance, x is a direction connecting both condyles, y is a direction perpendicular to the x axis and parallel to the occlusal plane, and z is a direction perpendicular to x and y. 
         [0035]    Further, the occlusal wear evaluation apparatus according to the present invention calculates relative positions of the mandibular dental arch with respect to the maxillary dental arch between the denture before use and the denture after use as in a three distances in axial directions of x, y, z, and indicates the distances in the result display portion  6 . This change in relative positions preferably is calculated in a manner assuming that three points as center points of both condyle paths and a center point between both cutting edges of central incisors are reference points. 
         [0036]    To this end, the occlusal wear evaluation apparatus specifies positions of articular fossae with respect to the maxillary teeth and positions of condyles with respect to the mandibular teeth for the three dimensional data of the denture before use. In this case, the articular fossae and the condyles in the denture before use are determined so that the articular fossae and the condyles respectively coincide with each other in the centric occlusal position. For the denture after use, positions of articular fossae and positions of condyles are calculated with assuming that the relative position between the maxillary teeth and the articular fossae and relative position between condyles and the mandibular teeth specified for the denture before use do not change. 
         [0037]    Notably, the positions of the reference points on the maxillary teeth and the positions of the reference points on the mandibular teeth coincide in  FIG. 3 , and therefore relative positions between the reference points on the maxillary teeth and the reference points are equal to the variations between the  FIG. 3  and  FIG. 4 . 
         [0038]    A denture in which relative angle between the maxilla and the mandible does not vary due to an occlusal wear is considered as being in an ideal condition where abrasions are even without an uneven wear. And, a change in a position of the condyle of the denture with respect to the articular fossa due to an occlusal wear is considered as suggesting a possibility of a temporomandibular arthrosis. Therefore, these figures give great indications to evaluate whether or not the denture is adapted to the patient. 
         [0039]    Also, a change in height of cusp of each tooth gives an indication to make a diagnosis of an occlusion. Specifically, variations of heights of a buccal cusp of mandibular first molar and a mesiolingual cusp of maxillary first molar give indications of variation in an occlusal vertical dimension. 
         [0040]    Further, the occlusal wear evaluation apparatus can determine and indicate a portion with a large variation between before and after use, i.e. a largely worn portion, so as to notify a doctor or a technician of a position to be especially attended. 
         [0041]    Further, in a case where a volume of the denture is significantly reduced, a crunching (unintentional biting) is suspected. 
         [0042]    Further, the occlusal wear evaluation apparatus according to the present invention preferably can indicate differences in a physical quantity between before and after use in comparison among plural dentures.  FIG. 5  shows a chart of variations in a relative angle between maxillary dental arches and mandibular dental arches due to wear of the respective dentures which are remade for a same patient every half year. In this example, the variation in the relative angle gets smaller gradually, and therefore it can be confirmed that newer denture is better adapted to the patient. 
         [0043]    A variation in a relative angle between a maxillary dental arch and a mandibular dental arch due to: occlusal wear can be caused by an alteration of a configuration of a denture as well as by a variation in masticatory ability due to change in muscle strength or other reasons. Therefore, this information does not lead an absolute conclusion directly, but is beneficial information contributory to make an integrated diagnosis by a doctor with an interview result and the like in mind. 
       REFERENCE SIGN LIST 
       [0000]    
       
           1  arithmetic device 
           2  data input device 
           3  display device 
           4  user input device 
           5  general display portion 
           6  result display portion 
           7  sectional display portion