Abstract:
An object is to provide a method for manufacturing a dental prosthesis consisting of a plurality of layers with high productivity. The method for manufacturing a dental prosthesis comprises: filling a cavity ( 21   a ) formed in a mold which has a shape of the dental prosthesis with a layered material body ( 23 ) that is made by layering materials ( 23   a,    23   b ) corresponding to the plurality of layers; and after this filling, rotating the mold on a material inlet ( 21   b ) of the mold and cutting the materials.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to a method for manufacturing a dental prosthesis, and more particularly relates to a method for manufacturing a dental prosthesis including a plurality of layers. 
       BACKGROUND ART 
       [0002]    A dental prosthesis such as a crown is one means for artificially reproducing functions of a lost natural tooth. An exterior of a natural tooth is formed hard by enamel and has a unique texture. A natural tooth affects not only the function of mastication but also impression of a human&#39;s face. Thus, preferably, a dental prosthesis having as close color and texture to a natural tooth as possible is used. As one method for improving so-called aesthetics of a dental prosthesis as described, for example, Patent Literature 1 proposes a dental prosthesis that consists of a plurality of layers having an inside layer of low transparency and an outside layer of high transparency as disclosed. According to this, the inside layer shields the color of an abutment from the exterior view, and the aesthetic property can be improved by the outer layer of high transparency and the inside layer seen through the outer layer. 
         [0003]    Patent Literature 1 discloses that the inner layer is cast first and then, the outer layer is cast on the inner layer as a method for manufacturing such a dental prosthesis having a plurality of layers. 
       CITATION LIST 
     Patent Literature 
       [0004]    Patent Literature 1: JP H6-269466A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    There is a problem that it takes some effort to form a dental prosthesis consisting of a plurality of layers with the manufacturing method as described in Patent Literature 1, and it is demanded that the productivity be improved. 
         [0006]    In view of the above problem, an object of this invention is to provide a method for manufacturing a dental prosthesis consisting of a plurality of layers with high productivity. 
       Solution to Problem 
       [0007]    The present invention will be described below. Here, reference signs attached to the drawings are described together in parentheses for easy understanding. However, the present invention is not limited thereto. 
         [0008]    The invention of claim  1  is a method for manufacturing a dental prosthesis ( 10 ) that has a plurality of layers ( 11 ,  12 ), the method comprising: filling a cavity ( 21   a ) that has a shape of the dental prosthesis with a layered material body ( 23 ) that is made by layering materials ( 23   a ,  23   b ) corresponding to the plurality of layers, the cavity being formed in a mold ( 21 ); and after said filling, rotating the mold on a material inlet ( 21   b ) of the mold and cutting the materials. 
         [0009]    In the invention of claim  2 , all of an outer circumference of the dental prosthesis is covered by one kind of the layers in the method for manufacturing a dental prosthesis according to claim  1 . 
       Advantageous Effects of Invention 
       [0010]    According to the present invention, the productivity can be improved because it is not necessary to individually make a plurality of layers of a dental prosthesis but the layers can be formed at the same time. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  is an exterior perspective view of a dental prosthesis  10 . 
           [0012]      FIG. 2  is a cross-sectional view of the dental prosthesis  10 . 
           [0013]      FIG. 3  shows a wax pattern  20 . 
           [0014]      FIG. 4  is a view to explain the scene where a mold  21  is attached to a filling device  22 . 
           [0015]      FIG. 5  is an exterior perspective view of a layered material body  23 . 
           [0016]      FIG. 6  is a view to explain one scene of molding the dental prosthesis  10 . 
           [0017]      FIG. 7  is a view to explain a process of filling with materials. 
           [0018]      FIG. 8  is a view to explain the scene where filling with the materials is completed. 
           [0019]      FIG. 9  is a view to explain the scene of rotating the mold  21  and cutting the materials. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]    The above described operation and advantage of the present invention are made clear by the embodiments described as follows. The present invention will be described below based on the embodiments shown in the drawings. However, the present invention is not limited to these embodiments. 
         [0021]    Before describing a method for manufacturing a dental prosthesis, one example of a shape of a dental prosthesis manufactured by this method is described.  FIG. 1  is an exterior perspective view of a dental prosthesis  10  that is the example.  FIG. 2  is a cross-sectional view taken along the line II-II in  FIG. 1  in the direction of the arrows. As is seen from  FIGS. 1 and 2 , the dental prosthesis  10  of this example is a crown. Intraoral side surface  10   a  and side surface  10   b  have shapes that imitate a natural tooth. In contrast, the side of the dental prosthesis  10  which faces the intraoral side surface  10   a  is an abutment side surface  10   c  that has a shape like a recess. An abutment is inserted to this portion, which is shaped to be like a recess, to retain the dental prosthesis  10  in an oral cavity. 
         [0022]    The dental prosthesis  10  of this example is formed to have an inner layer  11  and an outer layer  12  as is seen from  FIG. 2 . 
         [0023]    The inner layer  11  has color close to a natural tooth, and functions so that the dental prosthesis  10  resembles a natural tooth as a whole. The inner layer  11  is structured so as to hide an abutment from the outer view when the dental prosthesis  10  is attached to the abutment. Thereby, impression closer to a natural tooth can be given because the abutment cannot be seen. 
         [0024]    In view of the above, the inner layer  11  has color close to a natural tooth, and is constituted by a material whose transparency is kept low. Examples of a material used for the inner layer  11  in view of this include thermoplastic resin, ceramics and glass ceramics. Ceramics and glass ceramics are preferable among them in view of the strength and aesthetics of the dental prosthesis. 
         [0025]    The outer layer  12  is a layer that is formed so as to surround the outer circumference of the inner layer  11 . In this example, the outer layer  12  is layered around all the circumference of the inner layer  11 . The outer layer  12  has a function of making texture of the outer surface of the dental prosthesis  10  close to that of a natural tooth. Because of this, the outer layer  12  has color close to a natural tooth, and is constituted by a material whose transparency is higher than the inner layer  11 . 
         [0026]    Examples of a material used for the outer layer  12  in view of this include thermoplastic resin, ceramics and glass ceramics. 
         [0027]    Ceramics and glass ceramics are preferable among them in view of the strength and aesthetics of the dental prosthesis. 
         [0028]    Here, in view of easy molding and improvement of the aesthetics, preferably combination of materials of the inner layer  11  and the outer layer  12  is not combination of largely different materials in property such as thermoplastic resin and ceramics. It is more preferable to employ combination of different materials of similar properties. 
         [0029]    Specific color of the inner layer  11  and the outer layer  12  is adjusted according to a patient&#39;s natural tooth and any other requirements. Such adjustment is carried out by a known method. 
         [0030]    The dental prosthesis  10  of this example has the structure that all the circumference of the inner layer  11  is surrounded only by one kind of a layer (only by the outer layer  12 ) and thus the border between the inner layer  11  and the outer layer  12  is not exposed. Therefore, such faults can be held down that spots intrude between the inner layer  11  and the outer layer  12 , which lowers the aesthetics. 
         [0031]    Next, one embodiment will be described concerning the method for manufacturing a dental prosthesis that is formed by having a plurality of layers like the dental prosthesis  10 . Here, an example of manufacturing the dental prosthesis  10  is described. However, the present invention is not necessarily limited thereto, and for example, a dental prosthesis of such an embodiment can be manufactured that the outer circumference is not formed by one kind of a layer only, and part of the inner layer  11  is exposed.  FIGS. 3 to 9  are views for explanation. These drawings are conceptual drawings shown to explain this manufacturing method, and are not drawings showing modes and behaviors of materials precisely. 
         [0032]    In the manufacturing method of this embodiment, first, a wax pattern  20  of the dental prosthesis  10  that is to be manufactured is made as shown in  FIG. 3  by a known method. In making, an end surface for an opening  20   a  and a passage forming part  20   b  which are for forming a passage where materials pass when a mold  21  (see  FIG. 4 ) is made are provided together. 
         [0033]    Next, the wax pattern  20  is invested in dental investment. After the dental investment is cured, the wax pattern  20  is liquated out and combusted, to be removed. Thereby, the mold  21  shown in  FIG. 4  is made. Thus, in the mold  21 , a cavity  21   a  having a shape of the dental prosthesis  10 , material inlet  21   b  where materials are forced, and a passage  21   c  that is a passage linking the material inlet  21   b  with the cavity  21   a  are formed. 
         [0034]    The mold  21  formed like the above is attached to a filling device  22  as shown in  FIG. 4 . The filling device  22  includes a material insertion part  22   a  that is a space for disposing a block-like layered material body  23  (see  FIG. 5 ), a reduced diameter part  22   b  that is a space whose diameter is continuously reduced from the material insertion part  22   a , a material inlet  22   c  for filling the mold  21  with materials at an end part of the reduced diameter part  22   b , and a pressing member that presses the layered material body  23  toward the material inlet  22   e  side, which is not depicted. Here, the filling device  22  is provided with a shutter  22   d  that closes the material inlet  22   c  and cuts materials. The filling device  22  is further structured so that, assuming that a direction parallel to the pressing direction is an axis, the mold  21  can be rotated on the axis. 
         [0035]    When the mold  21  is attached to the filling device  22 , as shown in  FIG. 4 , they are arranged so that the material inlet  22   c  of the filling device  22  communicates with the material inlet  21   b  of the mold  21 . 
         [0036]      FIG. 5  is a perspective view of the block-like layered material body  23 , which is used as materials that form the dental prosthesis  10 . In this embodiment, the layered material body  23  is a columnar shape correspondingly to the shape of the material insertion part  22   a  of the filling device  22 . A material for an inner layer  23   a  and a material for an outer layer  23   b  are layered in a direction along the axis of the columnar shape. The materials each are to constitute the inner layer  11  and the outer layer  12 , and are as described above. 
         [0037]    Next, as shown in  FIG. 6 , the layered material body  23  is arranged in the material insertion part  22   a  of the filling device  22 . At this time, the material for an outer layer  23   b  faces the mold  21  side and the material for an inner layer  23   a  faces the opposite side to the mold  21  (a side of the pressing member not shown). The layered material body  23  is heated to a predetermined temperature that is lower than melting temperature in order to decrease the viscosity. 
         [0038]    The layered material body  23  is pressed by the pressing member not shown from the state shown in  FIG. 6  in the direction indicated by VI in  FIG. 6 . Thereby, the layered material body  23 , whose viscosity is decreased, passes through the reduced diameter part  22   b  and the material inlet  22   c , enters the mold  21  through the material inlet  21   b , and passes through the passage  21   c , and the cavity  21   a  is filled therewith as shown in  FIG. 7 . 
         [0039]    At this time, as shown in  FIG. 7 , the cavity  21   a  is filled with the layered material body  23 , whose viscosity is decreased, as the material for an inner layer  23   a , which is in the side further from the mold  21 , moves forward inside the material for an outer layer  23   b , which is in the side closer to the mold  21 , the material for an outer layer  23   b  covers the inner circumferential face of the cavity  21   a , and the material for an inner layer  23   a  moves forward inside the covered inner circumferential face. Thereby, as shown in  FIG. 8 , when filling (pressing) is completed, the shape and the layer structure of the dental prosthesis  10  to be obtained are simultaneously formed. 
         [0040]    Under the state shown in  FIG. 8 , the materials communicate between the mold  21  side and the filling device  22  side. Thus, it is necessary to isolate the mold  21  from the filling device  22 . Just pulling or sliding might bring the situation where the material for an inner layer  23   a  is exposed outside at this portion. In contrast, in the manufacturing method of this embodiment, as shown in  FIG. 9 , the mold  21  is rotated on the pressing axis (the axis of the pressing) as the center as indicated by IX in  FIG. 9 , and further, the shutter  22   d  provided for the filling device  22  is closed; whereby the material inlet  22   c  is closed, the materials are cut, and the mold  21  is isolated from the filling device  22 . Thereby, the material for an outer layer  23   b  covers the material for an inner layer  23   a  even at the portion of the material inlet  21   b  of the mold  21 , and the material for an inner layer  23   a  can be prevented from being exposed. 
         [0041]    At this time, the number of rotations of the mold  21  is preferably 1 rpm to 100 rpm. More preferably, 10 rpm to 70 rpm. Less than 1 rpm of the number of rotations results in bad productivity More than 100 rpm of the number of rotations might make the above described effect deteriorate. 
         [0042]    The materials with which the mold  21  is filled are cooled down and separated from the mold, and then the dental prosthesis  10  may be taken out. 
         [0043]    According to the manufacturing method as described above, a plurality of layers can be formed just once simultaneously, and a dental prosthesis can be manufactured efficiently. When the mold is removed from the filling device, the mold  21  is rotated and the shutter  22   d  is used as described above; thereby the material for an inner layer  23   a  can be properly arranged inside the material for an outer layer  23   b  even at the portion of the material inlet. 
         [0044]    In this embodiment, an example of making the mold  21  using the wax pattern  20  is described in view of matching an individual patient. This invention is not limited to this example, and when a dental prosthesis of an embodiment for multiple uses which has an average shape is manufactured, the above method may be carried out with using a die as a mold with which the dental prosthesis of an embodiment for multiple uses can be obtained. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               10  dental prosthesis 
               11  inner layer 
               12  outer layer 
               20  wax pattern 
               21  mold 
               21   a  cavity 
               21   b  material inlet 
               21   c  passage 
               22  filling device 
               22   a  material insertion part 
               22   b  reduced diameter part 
               22   c  material inlet 
               22   d  shutter 
               23  layered material body 
               23   a  material for an inner layer 
               23   b  material for an outer layer