Method for manufacturing dental crown prosthesis and computer program for creating dental crown prosthesis

Abstract

To provide a method for manufacturing a dental crown prosthesis while preventing occurrence of chipping.SOLUTION: A dental crown prosthesis 30 is formed through a pre-finishing step S30 and a finishing step S40. In the pre-finishing step S30, a workpiece 2 is cut along a margin line 100a, while maintaining a first finishing allowance 110. The first finishing allowance 110, cut along the margin line 100a, has a consistent thickness relative to a margin line section 31a. Thus, inconsistencies in force applied to the workpiece 2 are reduced, when cutting the workpiece 2. As a result, occurrence of chipping is prevented during the pre-finishing step S30 and the finishing step S40.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a dental crown prosthesis and a computer program for creating a dental crown prosthesis. [Background technology]

[0002] Conventionally, there has been known a manufacturing device for a crown prosthesis, which processes a workpiece such as a dental ceramic material into a desired shape to produce a crown prosthesis (e.g., an artificial tooth or an artificial crown). For example, Patent Document 1 discloses a manufacturing device for a crown prosthesis, which includes a grinding tool and a control means for controlling the grinding tool. In the manufacturing device for a crown prosthesis, a rough machining mode and a precision machining mode are executed by the control means. In the rough machining mode, the workpiece is roughly cut, leaving a predetermined finishing allowance. In the precision machining mode, the finishing allowance remaining in the rough machining mode is ground and finished. In the rough machining mode, the crown prosthesis can be efficiently manufactured by roughly cutting the portion other than the finishing allowance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-220714 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, a dental crown prosthesis includes a margin line portion formed along a margin line indicating the boundary with the tooth on which the dental crown prosthesis is to be placed. The margin line portion is a portion that is formed to be relatively thin. Therefore, when the machining allowance included in the vicinity of the margin line portion is cut in a rough machining mode, a part of the margin line portion may crack or chip (so-called chipping). Furthermore, chipping may occur when a cutting tool comes into contact with the margin line portion during finish machining.

[0005] The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a method for manufacturing a crown prosthesis capable of suppressing the occurrence of chipping. [Means for solving the problem]

[0006] The manufacturing method of the present invention is a method for manufacturing a crown prosthesis, and includes a three-dimensional data preparation step of preparing three-dimensional data including a linear margin line indicating the boundary between the crown prosthesis and a tooth on which the crown prosthesis is to be capped, a pre-finishing step of cutting a workpiece based on the three-dimensional data using a first cutting tool for rough processing to leave a first finishing allowance, and a finishing step of cutting the first finishing allowance using a second cutting tool for finishing processing. The pre-finishing step includes a semi-finishing step of moving the first cutting tool on the workpiece according to a tool path along the margin line, and a rough processing step of moving the first cutting tool according to a tool path for cutting a portion other than the portion along the margin line.

[0007] According to the manufacturing method of the present invention, the crown prosthesis is manufactured based on three-dimensional data. The three-dimensional data includes a linear margin line indicating the boundary between the crown prosthesis and the tooth on which the crown prosthesis is to be placed. In the pre-finishing process, the workpiece is cut using a first cutting tool for rough processing, and a first finishing allowance including a portion along the margin line is left. The first finishing allowance is cut off in the finishing process. Here, in the conventional method, the machining allowance formed in the portion along the margin line was variable, so the force applied to the workpiece during rough processing and finishing processing was variable. That is, in the portion where the machining allowance was relatively small, the force applied to the workpiece may be relatively large compared to the strength of the workpiece. Since the portion formed along the margin line tends to be formed relatively thin, when the machining allowance is relatively small, the force applied to the workpiece is relatively large. In addition, during rough processing, the cutting tool moves relatively fast, so the cutting chips may be thrown off. As a result, there was a risk of chipping occurring during rough machining or finish machining in the portion formed along the margin line. However, according to the present invention, the portion other than the portion along the margin line is cut in the rough machining process, but the portion along the margin line is cut in the semi-finishing process. In the semi-finishing process, the first cutting tool is moved according to the tool path along the margin line, so that even though the first cutting tool is a cutting tool for rough machining, the first finishing allowance has a uniform thickness along the margin line. Therefore, the force applied to the workpiece during the rough machining process and the finish process is suppressed from varying. This suppresses the occurrence of chipping. Effect of the Invention

[0008] According to the present invention, a method for producing a crown prosthesis capable of suppressing the occurrence of chipping can be provided. [Brief description of the drawings]

[0009] [Figure 1] 1 is a perspective view showing a cutting processing system according to a first embodiment. [Diagram 2] FIG. 1 is a front view showing a cutting device according to a first embodiment. [Diagram 3] FIG. 2 is a perspective view showing an object to be cut and a crown prosthesis. [Figure 4] 4(a) and 4(b) are schematic diagrams of a cutting tool. [Diagram 5] 3 is a flowchart showing a procedure for manufacturing a crown prosthesis according to the first embodiment. [Figure 6] FIG. 2 is a schematic diagram of three-dimensional data showing a crown prosthesis. [Figure 7] FIG. 4 is a diagram showing a tool path of a semi-finishing process in the first embodiment. [Figure 8] 8 is a diagram showing a workpiece when the tool path shown in FIG. 7 is executed. [Figure 9] FIG. 4 is an enlarged view of the workpiece when a first finishing allowance is formed. [Figure 10] FIG. 4 is a diagram showing a workpiece when a rough cutting step is performed in the first embodiment. [Figure 11] 10 is a flowchart showing a method for manufacturing a dental crown prosthesis according to a second embodiment. [Figure 12] FIG. 11 is an enlarged view of the workpiece when a second finishing allowance is formed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] First Embodiment Hereinafter, a method for manufacturing a dental crown prosthesis according to the first embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described here is, of course, not intended to limit the present invention in any particular way. Furthermore, the same reference numerals are used for members and parts that perform the same functions, and duplicated descriptions will be omitted or simplified as appropriate.

[0011] FIG. 1 is a schematic diagram showing a cutting system 1 according to the present embodiment. As shown in FIG. 1, the cutting system 1 includes a cutting device 10 and a CAM device 50. FIG. 2 is a front view showing the cutting device 10 according to the present embodiment. FIG. 3 is a perspective view showing an object to be cut 2 and a crown prosthesis 30 according to the present embodiment. F, Rr, L, R, U, and D in the drawings mean front, back, left, right, up, and down, respectively. However, these directions are directions defined for convenience and do not limit the present embodiment in any way. The manufacturing method of the crown prosthesis 30 according to the present embodiment is a method of manufacturing the crown prosthesis 30 using the cutting device 10 (see FIG. 1). The cutting device 10 manufactures the crown prosthesis 30 according to a computer program for manufacturing the crown prosthesis created by the CAM device 50 (see FIG. 1). A cutting tool 21 for cutting the object to be cut 2 is attached to the cutting device 10. First, the cutting device 10, the crown prosthesis 30, and the CAM device 50 will be briefly described.

[0012] As shown in FIG. 1, the cutting device 10 includes a case body 11 and a cover 12. As shown in FIG. 2, the cutting device 10 includes a spindle 13, a tool magazine 14, and a rotation support member 15. The case body 11 is formed in a box shape. The case body 11 has a space for cutting inside. The front part of the case body 11 is open. The cover 12 moves in the vertical direction along the front end of the case body 11. This allows the opening of the case body 11 to be freely opened and closed. As shown in FIG. 2, the cover 12 moves upward, so that the inside and outside of the case body 11 are connected to each other. In this embodiment, the cover 12 is provided with a window portion 12a. The interior space can be visually confirmed from the window portion 12a during cutting.

[0013] The spindle 13 rotates the cutting tool 21 to cut the workpiece 2. The spindle 13 holds the upper end of the cutting tool 21. A motor (not shown) is connected to the spindle 13. When the motor is driven while the spindle 13 holds the cutting tool 21, the rotating part 13a of the spindle 13 rotates. This causes the cutting tool 21 to rotate. The spindle 13 is configured to be movable in the left-right direction and the up-down direction by a drive mechanism (not shown). The drive mechanism is driven by, for example, a drive motor (not shown).

[0014] The tool magazine 14 is capable of housing a plurality of cutting tools 21. The tool magazine 14 is formed in a box shape extending in the front-rear direction. A plurality of holes (not shown) for housing the cutting tools 21 are formed in the upper surface of the tool magazine 14. The cutting tools 21 are inserted into the holes with their upper portions exposed. When replacing the cutting tools 21, the cutting tool 21 held by the spindle 13 is housed in the hole of the tool magazine 14 from above the tool magazine 14. Thereafter, the spindle 13 is moved above the cutting tool 21 to be used, and the cutting tool 21 to be used is held.

[0015] In this embodiment, a first cutting tool 21a for rough machining shown in FIG. 4(a) and a second cutting tool 21b for finish machining shown in FIG. 4(b) are used as the cutting tool 21. FIGS. 4(a) and 4(b) are schematic diagrams of the cutting tool 21. The first cutting tool 21a is used in a pre-finishing step S30 (see FIG. 5) described later. The second cutting tool 21b is used in a finishing step S40 (see FIG. 5) described later. As shown in FIGS. 4(a) and 4(b), the first cutting tool 21a and the second cutting tool 21b are provided with flanges 21aa and 21ba. The upper ends 21ab and 21bb of the first cutting tool 21a and the second cutting tool 21b above the flanges 21aa and 21ba are gripped by the spindle 13 (see FIG. 2). With the upper ends 21ab, 21bb held by the spindle 13, the spindle 13 moves, and the first cutting tool 21a and the second cutting tool 21b move. Below the flanges 21aa, 21ba of the first cutting tool 21a and the second cutting tool 21b, the blades 21ac, 21bc are provided. In this embodiment, the first cutting tool 21a and the second cutting tool 21b are end mills, and the blades 21ac, 21bc have an outer circumferential blade and a bottom blade. The first cutting tool 21a is an end mill with an outer diameter of 2 mm. The second cutting tool 21b is an end mill with an outer diameter of 1 mm. Therefore, the outer diameter of the second cutting tool 21b is smaller than the outer diameter of the first cutting tool 21a. However, the type and size of the first cutting tool 21a and the second cutting tool 21b are not limited to this. In the following description, when a description is common to both the first cutting tool 21a and the second cutting tool 21b, the term "cutting tool 21" will be used as appropriate.

[0016] The rotary support member 15 shown in FIG. 2 rotatably supports the workpiece 2. The rotary support member 15 rotatably supports a clamp (not shown) that holds the workpiece 2. The clamp has, for example, a substantially C-shape that opens to the left, and holds the workpiece 2 through the opening. The rotary support member 15 is equipped with a motor (not shown) and is configured to be able to rotate the shaft that supports the clamp. As a result, the rotary support member 15 rotatably supports the clamp in the front-rear and left-right directions. Therefore, the workpiece 2 is rotatably supported.

[0017] The object to be cut 2 shown in FIG. 3 is a material for a dental crown prosthesis 30. The object to be cut 2 in this embodiment has, for example, a disk-like shape. FIG. 3 illustrates a part of the disk-like object to be cut 2. The object to be cut 2 in this embodiment is formed of semi-sintered zirconia. However, the material forming the object to be cut 2 and the shape of the object to be cut 2 are not limited thereto. The object to be cut 2 may be, for example, wax, polymethylmethacrylate resin (PMMA), hybrid resin, PEEK (polyetheretherketone resin), gypsum, etc. The shape of the object to be cut 2 may be, for example, block-like.

[0018] As shown in FIG. 1, the cutting device 10 includes a control device 90. The control device 90 is a device that controls cutting of the workpiece 2. The configuration of the control device 90 is not particularly limited. The control device 90 is, for example, a microcomputer. The hardware configuration of the microcomputer is not particularly limited, but includes, for example, an interface (I / F) that receives print data and the like from an external device such as a host computer, a central processing unit (CPU) that executes instructions of a control program, a read only memory (ROM) that stores a program executed by the CPU, a random access memory (RAM) used as a working area for expanding the program, and a storage device such as a memory that stores the above program and various data. The ROM stores a computer program for creating a dental crown prosthesis, which is a program for creating a dental crown prosthesis 30 (see FIG. 3). The computer program for creating a dental crown prosthesis is created by a CAM device 50.

[0019] The crown prosthesis 30 is obtained by cutting the workpiece 2 using the cutting device 10. The crown prosthesis 30 is a dental molded product, and includes, for example, an artificial tooth or an artificial crown (for example, a crown, an inlay, an onlay, a veneer, etc.). The crown prosthesis 30 is a member that is manufactured to fit a part of a tooth that is formed into a certain shape in response to partial loss of a crown due to trauma or caries. In FIG. 3, the crown prosthesis 30 is illustrated by a two-dot chain line. The crown prosthesis 30 has a covering portion 31 and a connector portion 32. The crown prosthesis 30 obtained from the workpiece 2 has a plurality of covering portions 31 and a plurality of connector portions 32. The crown prosthesis 30 is formed by alternatingly connecting the covering portions 31 and the connector portions 32. However, here, only one covering portion 31 and the connector portions 32 at both ends thereof are illustrated.

[0020] The covering portion 31 is a portion that is attached to the patient's tooth. The covering portion 31 has a margin line portion 31a and a recessed portion 31b. The margin line portion 31a is a portion that is a boundary with the tooth on which the crown prosthesis 30 is to be covered. The margin line portion 31a has a width of about 250 μm in a plan view. In this embodiment, the margin line portion 31a has a substantially circular ring shape in a plan view. The upper surface of the margin line portion 31a is a shape that draws a three-dimensional curve. A method for forming the margin line portion 31a will be described later. The recessed portion 31b is a portion that is recessed downward from the margin line portion 31a. The patient's tooth is inserted into the recessed portion 31b, whereby the crown prosthesis 30 is attached. The recessed portion 31b may be recessed upward. The connector portion 32 is a portion that connects adjacent crown prostheses 30 to each other.

[0021] The CAM device 50 shown in FIG. 1 is a device that creates a computer program for producing a crown prosthesis 30 (see FIG. 3). The computer program for producing a crown prosthesis includes tool path data for manufacturing the crown prosthesis 30. For example, the CAM device 50 is configured to perform various settings related to processing, such as selection of the type of material and the shape of the material, and generate tool path data. The CAM device 50 holds in advance data for selecting a prosthesis required for processing, selecting the type of material, selecting the shape of the material, etc., in various settings related to processing. Such data includes data on predetermined items regarding the material or workpiece to be processed by the tool path. Processing information including data on predetermined items regarding the material or workpiece to be processed by the tool path may be prepared in advance. In addition, such information may be prepared in advance, for example, by an operator who operates the CAM device. The CAM device 50 generates tool path data based on three-dimensional data 100 (see FIG. 6), which is data on the outer shape of the crown prosthesis 30. The CAM device 50 may be configured by software or may be configured by hardware. The CAM device 50 is connected to the control device 90 of the cutting device 10 wirelessly or by wire.

[0022] Next, a method for manufacturing the crown prosthesis 30 according to this embodiment will be described. FIG. 5 is a flow chart showing the procedure for manufacturing the crown prosthesis 30 (see FIG. 3). The manufacturing method of this embodiment is a method for manufacturing the crown prosthesis 30 by moving the cutting tool 21 according to a tool path and cutting the workpiece 2 (see FIG. 3). The manufacturing method for the crown prosthesis 30 includes a three-dimensional data preparation step S10, a workpiece preparation step S20, a pre-finishing step S30, and a finishing step S40. The pre-finishing step includes a semi-finishing step S31 and a rough machining step S32. Note that other steps may be included at any stage. Each step will be described below.

[0023] First, in the three-dimensional data preparation step S10, three-dimensional data 100 (see FIG. 6) of the crown prosthesis 30 is prepared, and data of a tool path for forming the crown prosthesis 30 is generated. FIG. 6 is a schematic diagram of the three-dimensional data 100 showing the crown prosthesis 30. The three-dimensional data 100 is, for example, STL (Standard Triangulated Language) data. The three-dimensional data 100 includes, for example, three-dimensional data representing the outer shape of the crown prosthesis 30 (see FIG. 3) and three-dimensional data representing the outer shape of the workpiece 2 (see FIG. 3). The three-dimensional data 100 is usually created for each patient. However, depending on, for example, the application, three-dimensional data of a commercially available simulated crown prosthesis can be used as is. The three-dimensional data 100 of the crown prosthesis 30 is created, for example, by a computer-aided design device (CAD device). The CAD device may be configured by software or hardware. Furthermore, the CAD device may be realized by the same computer as the CAM device 50, for example.

[0024] The three-dimensional data 100 includes a margin line 100a. The margin line 100a is a virtual line indicating the boundary between the crown prosthesis 30 and the tooth on which the crown prosthesis 30 is to be placed. The margin line 100a can be obtained, for example, by applying a function for detecting an edge line to a mold of the shape of the tooth on which the crown prosthesis 30 is to be placed, taken with an impression material. However, there is no particular limitation on the method for drawing the margin line 100a. The margin line 100a is a three-dimensional curve and has a substantially circular ring shape in a plan view.

[0025] When the three-dimensional data 100 is prepared, a computer program for creating a crown prosthesis is created. The computer program for creating a crown prosthesis is created by the CAM device 50. When the computer program for creating a crown prosthesis is created by the CAM device 50, the computer program for creating a crown prosthesis is sent to the control device 90 of the cutting device 10.

[0026] A pre-finishing step S30 and a finishing step S40, which will be described later, are executed by the computer program for creating a crown prosthesis. The pre-finishing step S30 includes a semi-finishing step S31 and a rough machining step S32. The tool paths included in the computer program for creating a crown prosthesis include a path for the semi-finishing step, a path for the rough machining step, and a path for the finishing step. The path for the semi-finishing step is a path that controls the semi-finishing step S31 (see FIG. 5), which will be described later. The path for the rough machining step is a path that controls the rough machining step S32 (see FIG. 5), which will be described later. The path for the finishing step is a path that controls the finishing step S40 (see FIG. 5), which will be described later. Details of the path for the semi-finishing step, the path for the rough machining step, and the path for the finishing step will be described later.

[0027] Next, in the workpiece preparation step S20, the workpiece 2 (see FIG. 2) is prepared. The workpiece 2 is held by the clamp of the cutting device 10 described above.

[0028] Next, the pre-finishing process S30 shown in Fig. 5 will be described. The pre-finishing process S30 and the finishing process S40 are performed by the cutting device 10 shown in Fig. 2. The pre-finishing process S30 is a process in which the workpiece 2 is cut based on the three-dimensional data 100 (see Fig. 5) using the first cutting tool 21a (see Fig. 4) to leave a first finishing allowance 110 (see Fig. 8). The first finishing allowance 110 is uniformly formed along the margin line 100a shown in Fig. 6, and is a finishing allowance with a machining allowance of 0.08 mm or less. As shown in Fig. 5, the pre-finishing process S30 includes a semi-finishing process S31 and a rough machining process S32.

[0029] In the semi-finishing step S31, the workpiece 2 shown in FIG. 7 is cut according to the semi-finishing step path. FIG. 7 is a diagram showing the tool path of the semi-finishing step in this embodiment. FIG. 8 is a diagram showing the workpiece 2 when the tool path shown in FIG. 7 is executed. As shown in FIGS. 7 and 8, the semi-finishing step path is a path that forms the first finishing allowance 110 while moving the first cutting tool 21a in one direction along the shape of the margin line 100a (see FIG. 6) in the part outside the first finishing allowance 110 of the workpiece 2 before the rough machining step S32 (see FIG. 5). Here, the "outside of the first finishing allowance 110" refers to the part above the first finishing allowance 110. The semi-finishing step S31 is configured to move the first cutting tool 21a in the order of paths P1 to P6. The paths P1 to P6 are diagrams showing the tool path of the first cutting tool 21a in the semi-finishing step S31. The positions to which the first cutting tool 21a moves along the paths P1 to P6 are indicated by, for example, coordinates.

[0030] Path P1 is a path that moves the first cutting tool 21a downward from the upper surface 2a of the workpiece 2. Path P1 moves the position of the lower end of the first cutting tool 21a from position S1 to position S2. Position S1 is a position on the upper surface 2a of the workpiece 2. Path P1 moves the first cutting tool 21a to position S2 while cutting the workpiece 2 downward.

[0031] Path P2 shown in FIG. 7 is a path for moving the first cutting tool 21a along the shape of the margin line 100a (see FIG. 6). The shape of the route of path P2 is a three-dimensional curve similar to the margin line 100a shown in FIG. 6. The first cutting tool 21a moves so as to draw the three-dimensional curve of the margin line 100a, and cuts the workpiece 2. Path P2 is a path that makes one revolution in a clockwise direction in a plan view from position S2 and returns to position S2. Position S2 is, for example, the position of path P2 that is the highest in the up-down direction.

[0032] Path P3 shown in FIG. 7 is a path that moves the first cutting tool 21a downward from position S2, similar to path P1. Path P3 moves the position of the lower end of the first cutting tool 21a from position S2 to S3. The amount of lowering the first cutting tool 21a is the same as path P1. Path P4 is a path that moves from position S3 to position S4, similar to path P2. Path P5 is a path that moves from position S3 to position S4, similar to path P3. Path P6 is a path that moves from position S4 to position S4, similar to path P4. For convenience of explanation, only paths P1 to P6 have been used in the explanation, but the semi-finishing process path may include more tool paths. By performing passes similar to pass P1 and pass P2 multiple times, the workpiece 2 is cut downward along the shape of the margin line 100a. When passes P1 to P6 are completed, an approximately annular hole 2b is formed on the upper surface 2a of the workpiece 2 as shown in FIG. 8. The bottom of the hole 2b is the first finishing allowance 110 formed along the shape of the margin line 100a. FIG. 9 is an enlarged view of the workpiece 2 when the first finishing allowance 110 is formed. In passes P2, P4, and P6, cutting is performed along the shape of the margin line 100a, so that the first finishing allowance 110 having a uniform thickness is formed above the margin line portion 31a of the workpiece 2 as shown in FIG. The first finishing allowance 110 has a height of 0.08 mm or less.

[0033] The rough machining step S32 is a step of moving the first cutting tool 21a according to the rough machining step path after the semi-finishing step S31, and cutting the portion other than the margin line portion 31a. The rough machining step path is not particularly limited, but for example, is a path in which the first cutting tool 21a set at a predetermined height is moved in a circular manner in the vertical direction while moving along the outer shape of the portion other than the margin line portion 31a of the crown prosthesis 30. In addition, the portion to be the recess 31b is also cut while moving in a circular manner. FIG. 10 is a diagram showing the workpiece 2 when the rough machining step S32 is executed. When the rough machining step S32 is executed, as shown in FIG. 9, a part of the workpiece 2 is hollowed out in a cylindrical shape while leaving the covering portion 31 and the connector portion 32 of the crown prosthesis 30.

[0034] The finishing step S40 is a step of cutting the first finishing allowance 110 using the second cutting tool 21b according to the path for the finishing step. In the finishing step S40, the cutting device 10 (see FIG. 2) changes the cutting tool attached to the spindle 13 (see FIG. 2) from the first cutting tool 21a (see FIG. 8) to the second cutting tool 21b. Thereafter, as shown in FIG. 10, the second cutting tool 21b is placed on the first finishing allowance 110. After the second cutting tool 21b is moved downward by the height of the first finishing allowance 110, the second cutting tool 21b is moved once around along the shape of the margin line 100a (see FIG. 6). This cuts the first finishing allowance 110. At this time, the margin line portion 31a shown in FIG. 3 is formed. Note that the finishing process of the covering portion 31 and the connector portion 32 may be performed after the finishing step S40. This completes the crown prosthesis 30.

[0035] As described above, according to the manufacturing method of this embodiment, the crown prosthesis 30 is manufactured based on the three-dimensional data 100. The three-dimensional data 100 includes a margin line 100a. In this embodiment, in the semi-finishing step S31 of the pre-finishing step S30, the paths P1 to P6 are executed. The paths P2, P4, and P6 are tool paths along the margin line 100a. By executing the paths P2, P4, and P6, a first finishing allowance 110 having a uniform thickness along the margin line 100a is formed. Since the paths P2, P4, and P6 are tool paths along the margin line 100a, the first finishing allowance 110 has a uniform thickness along the margin line 100a, even though the first cutting tool 21a is a cutting tool for rough machining. In addition, the first finishing allowance 110 is cut by the finishing step S40. Since the first finishing allowance 110 has a uniform thickness along the margin line 100a, the force applied to the workpiece 2 is unlikely to vary in the pre-finishing step S30 and the finishing step S40. The width of the margin line portion 31a is about 250 μm in plan view, and is a portion formed relatively thinly in the crown prosthesis 30. If the thickness of the first finishing allowance 110 is not uniform, the force applied to the workpiece 2 during cutting will vary. If there is a portion of the first finishing allowance 110 with a relatively small machining allowance, there is a risk of chipping occurring in the workpiece 2. However, as in this embodiment, the first finishing allowance 110 having a uniform thickness along the margin line 100a is formed, and thus the force applied to the workpiece 2 is unlikely to vary in the pre-finishing step S30 and the finishing step S40. This suppresses the occurrence of chipping.

[0036] According to the manufacturing method of this embodiment, in the passes P2, P4, and P6 of the semi-finishing step S31, the first cutting tool 21a is moved in a clockwise direction along the shape of the margin line 100a in the portion above the first finishing allowance 110 of the workpiece 2 before the rough machining step S32. Here, if the first cutting tool 21a is moved in a clockwise direction and a counterclockwise direction when moving along the shape of the margin line 100a, the state of the machined surface of the first finishing allowance 110 may change at the point where the moving direction is switched. At this time, if the finishing step S40 is performed with the second cutting tool 21b, the force applied to the workpiece 2 may vary. Therefore, there is a risk of chipping occurring in the workpiece 2. However, as in this embodiment, by moving the first cutting tool 21a in one direction, the state of the machined surface of the first finishing allowance 110 is formed relatively uniformly. Therefore, in the finishing step S40, the force applied to the workpiece 2 is less likely to vary, thereby suppressing the occurrence of chipping of the workpiece 2.

[0037] According to the manufacturing method of this embodiment, the outer diameter of the second cutting tool 21b is 1 mm, and the outer diameter of the first cutting tool 21a is 2 mm. Therefore, the outer diameter of the second cutting tool 21b is smaller than the outer diameter of the first cutting tool 21a. In this embodiment, the second cutting tool 21b is used only in the finishing step S40, and the first cutting tool 21a is used in the pre-finishing step S30. By forming the first finishing allowance 110 using the first cutting tool 21a and using the second cutting tool 21b, which has a smaller outer diameter, only in the finishing step S40, the amount of the workpiece 2 cut by the second cutting tool 21b can be relatively reduced. This allows the life of the second cutting tool 21b to be relatively long.

[0038] According to the manufacturing method of this embodiment, the outer diameter of the first cutting tool 21a is 2 mm, and the machining allowance of the first finishing allowance 110 is 0.08 mm or less. The inventors of the present application confirmed that the occurrence of chipping can be suppressed by setting the machining allowance of the first finishing allowance 110 to 0.08 mm or less with respect to the outer diameter of the first cutting tool 21a of 2 mm. Therefore, the outer diameter of the first cutting tool 21a of 2 mm and the machining allowance of the first finishing allowance 110 of 0.08 mm or less in this embodiment are a specific aspect that can obtain the effects of the present invention.

[0039] According to the manufacturing method of this embodiment, the workpiece 2 is made of zirconia. Zirconia is preferably used for crown prostheses because of its relatively high strength. The effects of the present invention can also be applied to the workpiece 2 made of zirconia, which is suitable as a material for crown prostheses.

[0040] <Second embodiment> Next, a method for manufacturing a dental crown prosthesis according to the second embodiment will be described. FIG. 11 is a flow chart showing a method for manufacturing a dental crown prosthesis 30 according to the second embodiment. As shown in FIG. 11, the method for manufacturing a dental crown prosthesis 30 includes a three-dimensional data preparation step S10, a workpiece preparation step S20, a pre-finishing step S30A, and a finishing step S40. The pre-finishing step S30A according to the second embodiment includes a rough processing step S31A and a semi-finishing step S32A. The three-dimensional data preparation step S10, the workpiece preparation step S20, and the finishing step S40 in the second embodiment are the same as the three-dimensional data preparation step S10, the workpiece preparation step S20, and the finishing step S40 in the first embodiment shown in FIG. 5, and therefore will not be described here.

[0041] The rough machining step S31A shown in FIG. 11 is a step of cutting the workpiece 2 leaving a second finishing allowance 120 (see FIG. 12) before the semi-finishing step S32A. The second finishing allowance 120 is a finishing allowance that is larger than the first finishing allowance 110. FIG. 12 is an enlarged view of the workpiece 2 when the second finishing allowance 120 is formed. In this embodiment, the second finishing allowance 120 is a finishing allowance having a machining allowance of 1 mm or more. In the rough machining step S31A, the workpiece 2 is cut based on the three-dimensional data 100 (see FIG. 6). The rough machining step path of the rough machining step S31A cuts the workpiece 2 by moving the first cutting tool 21a arranged at a predetermined height in a circular manner, similar to the rough machining step S32 (see FIG. 5) of the first embodiment. At this time, the first cutting tool 21a is moved so that a finishing allowance of 1 mm or more, i.e., a second finishing allowance 120, remains along the margin line 100a. The second finishing allowance 120 is a finishing allowance formed by the rough machining step path 31A, and is therefore not uniform along the margin line 100a. Therefore, as shown in FIG. 12, when the rough machining step S31A is performed, the machining allowance of the second finishing allowance 120 has a shape that varies with respect to the margin line portion 31a. The average speed of the movement of the first cutting tool 21a in the rough machining step S31A is controlled to be faster than the average speed of the movement of the first cutting tool 21a in the semi-finishing step S32A described later.

[0042] The semi-finishing step S32A shown in FIG. 11 is a step of cutting the second finishing allowance 120 (see FIG. 12) remaining after the rough machining step S31A, and leaving the first finishing allowance 110 (see FIG. 12). In the semi-finishing step S32A, the first cutting tool 21a (see FIG. 12) is moved along the margin line 100a (see FIG. 6) relative to the second finishing allowance 120, thereby cutting the second finishing allowance 120. The first finishing allowance 110 is a finishing allowance with a machining allowance of 0.08 mm or less. Therefore, in the semi-finishing step S32A, cutting is performed while changing the vertical position of the first cutting tool 21a until the second finishing allowance 120 is cut and the machining allowance becomes 0.08 mm or less. In the semi-finishing step S32A, the first cutting tool 21a is moved along the margin line 100a, so that a first finishing allowance 110 having a uniform machining allowance along the margin line 100a is formed.

[0043] According to the manufacturing method of this embodiment, the second finishing allowance 120 is left by performing the rough machining step S31A. Moreover, the average speed of the movement of the first cutting tool 21a during the rough machining step S31A is faster than the average speed of the movement of the first cutting tool 21a during the semi-finishing step S32A. Since the second finishing allowance 120 is a finishing allowance with a relatively large machining allowance, the pass by the rough machining step S31A may have a lower accuracy of control of the movement of the first cutting tool 21a compared to the pass by the semi-finishing step S32A. Therefore, the pass in the rough machining step S31A can make the average speed of the first cutting tool 21a faster than the pass in the semi-finishing step 32A. Moreover, in the semi-finishing step S32A, the machining allowance of the difference between the second finishing allowance 120 and the first finishing allowance 110 is cut. The machining allowance of the difference between the second finishing allowance 120 and the first finishing allowance 110 is relatively small compared to the cutting amount by the rough machining step S31A. Therefore, by performing the semi-finishing step S32A after the rough machining step S31A as in this embodiment, the time required for the semi-finishing step S32A can be reduced, and the crown prosthesis 30 can be efficiently manufactured.

[0044] According to the manufacturing method of this embodiment, the second finishing allowance 120 is a finishing allowance having a machining allowance of 1 mm or more. If the machining allowance of the second finishing allowance 120 is too small, the difference between the second finishing allowance 120 and the first finishing allowance 110 becomes small, and it may be difficult to make the first finishing allowance 110 uniform in the semi-finishing step S32A. The second finishing allowance 120 having a machining allowance of 1 mm or more is a suitable mode for forming the first finishing allowance 110 having a uniform machining allowance along the margin line 100a.

[0045] Although the preferred embodiments of the present invention have been described above, the above-described embodiments are merely examples, and the present invention can be embodied in various forms. [Explanation of symbols]

[0046] 21a First cutting tool 21b Second cutting tool 30 Crown Prosthesis 100 3D data 100a Margin Line 110 First finishing allowance S10 3D data preparation process S30 Pre-finishing process S31 Semi-finishing process S32 Rough machining process S40 Finishing Process

Claims

1. A method for producing a dental crown prosthesis, comprising the steps of: a three-dimensional data preparation step of preparing three-dimensional data including a linear margin line indicating a boundary between the crown prosthesis and a tooth on which the crown prosthesis is to be placed; a pre-finishing process of cutting the workpiece based on the three-dimensional data using a first cutting tool for rough machining and leaving a first finishing allowance; a finishing step of cutting the first finishing allowance using a second cutting tool for finishing, The pre-finishing process includes: a semi-finishing process of moving the first cutting tool on the workpiece according to a tool path along the margin line; A rough machining process of moving the first cutting tool according to a tool path that cuts portions other than those along the margin line.

2. 2. The method for manufacturing a dental crown prosthesis according to claim 1, wherein the semi-finishing process is a process for forming the first finishing allowance by moving the first cutting tool in one direction along the shape of the margin line in a portion of the workpiece outside the first finishing allowance, prior to the rough machining process.

3. The rough machining step is a step of cutting the workpiece while leaving a second finishing allowance that is larger than the first finishing allowance, prior to the semi-finishing step; The semi-finishing step is a step of cutting the second finishing allowance remaining after the rough machining step and leaving the first finishing allowance, The method for manufacturing a dental crown prosthesis according to claim 1 , wherein an average speed of movement of the first cutting tool in the rough machining step is faster than an average speed of movement of the first cutting tool in the semi-finishing step.

4. The method for manufacturing a dental crown prosthesis according to claim 3 , wherein the second finishing allowance has a machining allowance of 1 mm or more.

5. The method for manufacturing a dental crown prosthesis according to claim 1 , wherein the second cutting tool is a cutting tool having an outer diameter smaller than that of the first cutting tool.

6. The outer diameter of the first cutting tool is 2 mm; The method for manufacturing a dental crown prosthesis according to claim 5 , wherein the machining allowance of the first finishing allowance is 0.08 mm or less.

7. 7. The method for manufacturing a dental crown prosthesis according to claim 1, wherein the object to be cut is made of zirconia.

8. A computer program for creating a crown prosthesis, which creates the crown prosthesis by controlling a cutting device based on three-dimensional data including a linear margin line indicating a boundary between the crown prosthesis and a tooth on which the crown prosthesis is to be placed, a pre-finishing process in which a first cutting tool for rough machining is used to cut the workpiece based on the three-dimensional data and a first finishing allowance is left; a finishing process for cutting the first finishing allowance by using a second cutting tool for finishing; The pre-finishing treatment is a semi-finishing process of moving the first cutting tool on the workpiece along the margin line; A rough cutting process for moving the first cutting tool according to a tool path for cutting a portion other than the portion along the margin line.

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