Method for manufacturing a dental prosthetic workpiece, workpiece manufactured using the method, and software for controlling the manufacturing process for manufacturing the workpiece.

Abstract

Method for manufacturing a dental prosthetic workpiece(5), comprising the steps: (a) Creating a data set using CAD software for a three-dimensional dental prosthetic workpiece(5); (b) virtual placement of the workpiece (5) in a workpiece holder (1); (c) virtual application in the created data set of the workpiece (5) of a preselectable layer thickness of material in at least one preselectable area of ​​the surface of the workpiece (5); (d) Producing an intermediate product of the workpiece (5) based on the data set generated in step (c) in a numerically controlled device (40) using an additive manufacturing process, wherein the additive manufacturing process is a laser melting process or 3D printing; (e) Positioning the workpiece (5) in a second numerically controlled device (60) for carrying out a subtractive manufacturing process; and (f) Reworking by removing material from at least one area of ​​the surface of the workpiece (5) with increased layer thickness.

Description

Field of the invention

[0001] The invention relates to a method for producing a dental-prosthetic workpiece, a workpiece produced by the method, and software for controlling the production process for producing such a workpiece. State of the art

[0002] Dental constructions such as model cast frameworks, telescopic dentures, crowns, and bridge frameworks were originally manufactured using investment casting. Since the introduction of computer technology into dental manufacturing processes in the late 1990s, this field has been undergoing constant change. Gradually, all manual processes and tasks performed by dental technicians are being digitalized. Almost the entire range of dental services has now been virtualized. Crowns and bridges, implant work, splints and model frameworks, working models and wax-ups, and even full dentures are increasingly being designed virtually. Many dental laboratories already use CNC machines to manufacture the designed parts.

[0003] Milling is a subtractive manufacturing process because it involves removing material from a blank until the desired geometry of the molded part is achieved. Milling is a machining process in which almost any shaped workpiece surface can be created using mostly multi-tooth tools in circular cutting movements and a feed that can be adjusted perpendicular or oblique to the rotational axis. When using a CNC (Computerized Numerical Control) machine, the molded part is first designed using CAD software and then loaded as a three-dimensional data set into CAM (Computer-Aided Manufacturing) software. This software creates an NC (Numerical Control) code that controls the CNC machine to produce the desired molded part.

[0004] A suitable blank for the molded part is first selected in the CAM software, and the molded part is then placed in a favorable position (nesting). A milling strategy is then created that is suitable for the existing CNC machine, the material, and the geometry to be manufactured. This strategy determines which tool and method will be used to remove the material from the blank. Material- and tool-specific settings are made for the speed, feed, and tool infeed. Furthermore, the paths and intervals at which the milling cutter should be guided through the material are determined. Such milling strategies consist of several sub-steps, which can be roughly divided into roughing and finishing steps.

[0005] Roughing is a process in which as much material as possible is removed in the shortest possible time to achieve the desired geometry of the molded part as closely as possible. Large, coarse, and stable tools are used for this purpose. The resulting molded part has a rough surface and high dimensional tolerances.

[0006] During finishing, the geometry of the molded part is then precisely machined using smaller and finer tools, and the rough surface is smoothed. Once the tool paths have been defined with the appropriate milling parameters, a virtual simulation of the milling process is performed to determine whether the result meets the requirements in terms of mold accuracy and surface quality.

[0007] The CAM software then outputs the NC code, which is loaded into the CNC machine's control software. The CNC machine can then be set up by clamping the blank and the corresponding tools into the machine and starting the NC program. The production machine then begins to machine the molded part from the blank fully automatically. Once the process is complete, the blank can be removed and the molded part separated.

[0008] Laboratories that don't have such production facilities send the virtually designed data sets over the internet to outsource the blanks. The finished pieces are then quickly delivered to the company via express delivery for further processing. Milling machines are primarily used in such processes, which mill the desired parts from prefabricated blanks.

[0009] During the turn of the millennium, additive manufacturing processes found their way into dental manufacturing technology. These SLM (selective laser melting) processes are currently used in the production of dental frameworks. Of particular note here are the frameworks for model cast dentures and, consequently, telescopic dentures, as the production of these frameworks using milling is uneconomical due to their size and low volume. The SLM process results in higher-quality end products with perfect chemical and physical properties. However, the surface quality after production is not yet sufficient for use in the mouth and for the production of precision-mechanical dental fitting elements. Therefore, these frameworks must be reworked by hand. Precision-mechanical fitting elements are currently not feasible and can only be produced using investment casting or milling. Description of the invention

[0010] The invention is based on the object of developing a method and associated software with which dental prosthetic workpieces with precision mechanical fits can be manufactured in a material-saving and economical manner.

[0011] This object is achieved by a method for producing a dental-prosthetic workpiece having the features of claim 1. The software used is described by the features of claim 8. The workpiece produced by the method according to the invention is the subject of claim 6. Preferred embodiments of the invention are described in the remaining claims.

[0012] The method according to the invention for producing a dental-prosthetic workpiece comprises the steps of creating a data set using CAD software for a three-dimensional, dental-prosthetic workpiece, virtually placing the workpiece in a workpiece holder, virtually applying a preselectable layer thickness of material in at least one preselectable region of the surface of the workpiece in the created data set of the workpiece, producing the workpiece on the basis of the data set thus generated in a numerically controlled device using an additive manufacturing process, positioning the workpiece in a second numerically controlled device for carrying out a subtractive manufacturing process; and post-processing by removing material in the at least one region of the surface of the workpiece with an increased layer thickness.After positioning the workpieces, the milling machine "knows" within the CNC software where they will be during the subsequent milling process. This eliminates the need for subsequent re-calibration of the workpiece (positioning / locating).

[0013] Using the method according to the invention, all workpieces can be manufactured. The method according to the invention is particularly suitable for the production of workpieces such as model cast frameworks, telescopic denture frameworks including telescopes, attachment denture frameworks including attachments, bars with additional retaining elements, bar riders with model cast structures, crowns, bridges, implant abutments, drilling templates, and bite splints made of metal and plastics.

[0014] After the data set has been created, an intermediate product of the workpiece to be manufactured is first produced using an additive manufacturing process. The intermediate product has an increased layer thickness in at least one preselectable area of ​​the surface, which, like the at least one area of ​​the surface, can be preselected by the user. The intermediate product thus produced is then post-processed using a subtractive manufacturing process. The subtractive manufacturing process processes the preselectable area of ​​the workpiece's surface, bringing it to the desired final dimension and achieving the desired surface quality.

[0015] A particular advantage of the method according to the invention is that by increasing the layer thickness of material in at least one preselectable area of ​​the workpiece surface, the intermediate product manufactured using the additive process does not have to be fixed to the micrometer in the device for carrying out a subtractive manufacturing process in order to be able to machine the workpiece precisely using the subtractive manufacturing process. By increasing the layer thickness, any possible offset between the milling paths and the workpiece can be compensated. The individually adjustable layer thickness, which is applied to the surface of the workpiece beyond the nominal dimension using the additive process, makes it possible to compensate for varying degrees of offset.

[0016] A further advantage of the method according to the invention is that the subtractive manufacturing process of the workpieces eliminates the need for material-removing roughing paths, which place a strain on the machine and tools and would increase both the duration of the manufacturing process and the material required for the production of the workpieces. Subtractive post-processing can often be performed in a single machining step by finishing on surfaces already produced in the additive process with a contour-parallel finish. Only with larger preselected layer thicknesses does the material removal need to be performed in stages.

[0017] A further advantage of the process according to the invention is that the workpieces can be manufactured as a single piece. There is no need to laser, solder, or glue individual parts together. This eliminates joint edges, which are often the weak points of telescopic systems. Furthermore, material combinations that can promote corrosion are avoided.

[0018] Finally, an advantage of the method according to the invention is that the surfaces of the workpieces that receive an increased layer thickness and are subsequently reworked can be freely selected by the user. Not all elements and surfaces of dental constructions require high surface quality. Surfaces that do not require rework in the second device for performing a subtractive manufacturing process can, in some cases, significantly reduce the time required to perform the subtractive manufacturing process.

[0019] According to a preferred embodiment of the invention, the post-processing is carried out by milling, preferably by finishing, while according to another preferred embodiment of the invention, the device for carrying out an additive manufacturing process uses a laser melting process.

[0020] When positioning the workpiece in the device for performing a subtractive manufacturing process, the workpiece is preferably clamped in a tool holder using a frame (round blank). This is a tool holder that is already specified when the data set for the device for performing an additive manufacturing process is created. The frame is additively manufactured together, i.e. in one piece, with the workpiece to be reworked. The 3D data set for this is created in the CAM software. The workpiece to be manufactured is fixed to the frame using holding webs. The frame is used to position the intermediate workpiece product as precisely as possible in the device for performing a subtractive manufacturing process.Alternatively, a frame can be used which is formed in one piece with the workpiece to be produced in the additive manufacturing process and can be attached directly to the machine holder of the device for carrying out the subtractive process by means of a suitable fastening geometry.

[0021] According to a preferred embodiment of the invention, the method comprises the additional step of thermally stress-relieving the intermediate workpiece prior to performing the subtractive manufacturing process. This avoids unwanted stresses in the workpiece that could later lead to undesirable deformation of the workpiece or an increased tendency for the workpiece to fracture.

[0022] Preferably, the method according to the invention comprises the additional step of determining the position of the clamped intermediate product of the workpiece in the device for carrying out the subtractive manufacturing process by means of detecting the position of a position reference body in the tool holder.

[0023] The dental prosthetic workpiece produced by the method according to the invention is a one-piece and preferably a framework part, bar, bar rider, implant abutment, a crown, bridge, drilling template or bite splint.

[0024] According to a preferred embodiment, the workpiece consists of a CoCr alloy or a TiAlV alloy, such as Ti6Al4V or Ti6Al4Nb. These alloys are free of precious metals and exhibit good mechanical properties. This also allows for the post-processing of plastic parts produced using 3D printing. The TiAlV alloy, in particular, is suitable for allergy sufferers.

[0025] The software according to the invention for controlling the manufacturing process for producing a dental prosthetic workpiece comprises two software modules. A first software module serves to control a device for performing an additive manufacturing process for an intermediate product of the workpiece, while a second software module serves to control a device for performing a subtractive manufacturing process for the intermediate product of the workpiece. In the first software module, the user can preselect at least one surface of the workpiece via an input prompt, which will receive an increased layer thickness exceeding the nominal dimension during additive manufacturing.

[0026] The software is thus used to allow the user to control both the device for performing the additive manufacturing process, for example, a laser melting device, and the device for performing a subtractive manufacturing process, for example, a milling device. The software according to the invention is preferably embedded in CAM software. The CAM software generates the NC code that controls the CNC machines.

[0027] The software according to the invention is preferably characterized in that, in the first software module, the intermediate workpiece product to be manufactured is positioned in a virtual frame in the data set of geometric data for transmission to the device for carrying out the additive manufacturing process. The frame is positioned relative to the intermediate workpiece product to be manufactured in the device for carrying out the additive manufacturing process, thereby enabling precise positioning of the intermediate workpiece product within the device for carrying out the subtractive manufacturing process.

[0028] Preferably, the software generates an STL file for the device for carrying out the additive manufacturing process and NC codes for the device for carrying out the subtractive manufacturing process.

[0029] According to a preferred embodiment, the software further comprises a user prompt with which the layer thickness can be preselected. Short description of the characters

[0030] The invention is explained below with reference to the accompanying figures, in which Fig. 1 schematically shows the holder for a workpiece with a round blank in the mounted state; Fig. 2 the bracket Fig. 1 in an exploded view; Fig. 3 the bracket Fig. 1 shows a detailed cross-sectional view; Fig. 4 the bracket Fig. 3 in an exploded view; Fig. 5 schematically illustrates the production process; and Fig. 6 and Fig. 7 schematically shows a frame manufactured in one piece with the dental-prosthetic workpiece to be produced. Ways to implement the invention

[0031] First, Fig. 5, which schematically illustrates the process for producing a dental prosthetic workpiece.

[0032] First, in step 10, the desired workpiece is designed using a conventional CAD program. The data sets for the 3-dimensional workpiece are then transferred in step 20 to the CAM software, which contains the software according to the invention, which has a modular structure and includes a module 31 for the laser melting process (SLM module) and a module 32 for milling.

[0033] In SLM Module 31, the user is prompted to select the surface or surfaces of the workpiece to be reworked, as well as the additional layer thickness to be applied. According to the STL format, the surfaces of 3D bodies are described by triangular facets, each characterized by its three vertices and the corresponding surface normal. The additional layer thickness is therefore always defined in the direction of the surface normal pointing outward from the body. Furthermore, the CAM software virtually fixes the workpiece using individually positionable retaining bars in a frame (round blank), in which the intermediate part of the workpiece is positioned during laser melting.

[0034] In module 32 for milling, the CAM software generates the milling paths for the subtractive production of the workpiece.

[0035] Finally, the NC codes for controlling the CNC machines are generated in an NC module 33 in the CAM software.

[0036] The STL file generated in module 31 of the CAM software is transferred to the CNC machine 40 for laser melting, which creates an NC code using NC software and, starting from the desired material, produces the intermediate product of the workpiece and the retaining webs serving as a support structure for attachment to the frame in one piece using the additive manufacturing process.

[0037] The intermediate product of the workpiece with frame and support structure is then stress-relieved in a thermal process 50 and freed from the support structures required for production using the laser melting process.

[0038] The intermediate product with frame is precisely positioned on CNC machine 60. The CNC machine also receives the NC codes required for the production process and is equipped with the necessary tools. The CNC machine specifically mills those areas of the intermediate product that received an increased layer thickness during laser melting on CNC machine 40.

[0039] When milling in the CNC machine 60, a conventional milling machine from the dental sector can be used. This requires a holder and the associated frame to which the workpiece is attached. For example, a Wieland 98 mm blank holder is used to clamp a holder for the SML frame. However, various holders from other manufacturers can also be used, or holders manufactured directly using the additive manufacturing process can also function as frames.

[0040] The Fig. The holder shown in Figures 1-4 with an SLM blank for use in a laser melting process comprises a holder 1, a clamping device 2 and a frame 3. With the help of the clamping device 2, the frame 3 is fixed in the correct position on the holder 1, as best seen from Fig. 3. The workpieces are fixed to frame 3 using individually positionable holding bars.

[0041] In order to increase the positioning accuracy of the SLM blank of the CNC machine 60 and minimize the offset between the milling path and the workpiece, it is additionally possible within the software according to the invention to incorporate standardized position reference bodies into the SLM blank. These can then be located by the CNC machine 60 using a digital, tactile measuring probe before the workpieces are post-processed in the CNC machine 60. The software of the CNC machine 60 then takes the orientation of the workpiece into account by aligning the milling paths to the previously located position reference bodies. In this way, the manufacturing accuracy can be further increased, allowing the layer thickness of the layers applied during the additive manufacturing process to be kept low.This has the additional advantage that the milling of these layers can be carried out by finishing, preferably in a single work step, which accelerates the production of the dental prosthetic workpiece.

[0042] In the Fig. 6 and Fig. 7 shows a view from two different perspectives of a frame 6 manufactured in one piece with the dental-prosthetic workpiece 5 to be produced. The frame 6 has fastening projections 7, with the aid of which the frame 6 can be screwed directly onto the machine holder of the device for carrying out a subtractive manufacturing process. Thus, in the variant according to the Fig. 6 and Fig. 7 the separate provision of the holder 1, the clamping device 2 and the frame 3.

[0043] The Fig. 6 and Fig.The holders shown in Figure 7 are particularly suitable for producing implant connection geometries. In the normal milling process, placeholders, so-called spacers, are inserted onto the implant connection geometries to be manufactured so that the implant connection geometries of the dental prosthesis are not affected during the subtractive manufacturing process. This is necessary because dental prosthesis restorations consist of free-form surfaces manufactured using STL data sets, whereas implant connection geometries consist of defined geometric shapes. After the dental prosthesis restoration has been milled out, the implant geometry is then milled out using a subprogram integrated into milling software suitable for defined geometric shapes. In this process, placeholders, so-called spacers, are placed onto the implant connection geometries to be manufactured.The individual data sets are combined with the restoration dataset using a Boolean union, resulting in a single volume file, which is then used to create the intermediate product in the subsequent additive manufacturing process. The intermediate product, preferably produced using laser melting, is then subtractively milled to produce the desired dental prosthesis. The corresponding implant connection geometry can then be created using milling software suitable for defined geometric shapes.

[0044] What all embodiments have in common is that the intermediate product manufactured using the additive process does not need to be fixed to the micrometer in the fixture used for subtractive manufacturing. Furthermore, time-consuming and wear-intensive roughing paths are no longer required during the production of the workpieces in the subtractive manufacturing process. The workpieces can be manufactured as a single piece, and the surface quality of individual surfaces can be freely selected by the user.

Claims

[1] Method for producing a dental prosthetic workpiece (5), comprising the steps: (a) creating a data set using CAD software for a three-dimensional dental prosthetic workpiece(5); (b) virtually placing the workpiece (5) in a workpiece holder (1); (c) virtually applying in the created data set of the workpiece (5) a preselectable layer thickness of material in at least one preselectable area of ​​the surface of the workpiece (5); (d) producing an intermediate product of the workpiece (5) on the basis of the data set generated in step (c) in a numerically controlled device (40) by means of an additive manufacturing process, wherein the additive manufacturing process is a laser melting process or 3D printing; (e) positioning the workpiece (5) in a second numerically controlled device (60) for carrying out a subtractive manufacturing process; and (f) Reworking by removing material from at least one area of ​​the surface of the workpiece (5) with an increased layer thickness. [2] Method according to claim 1, characterized by that in step (f) the finishing is carried out by milling, preferably by finishing. [3] Method according to one of the preceding claims, characterized by that in step (e) the workpiece (5) is clamped in a tool holder (1) by means of a circular blank (3) or a frame (6) produced in step (d) and formed in one piece with the dental-prosthetic workpiece to be produced. [4] Method according to claim 3, further comprising the step (e1) of determining the position of the clamped workpiece (5) by detecting the position of a position reference body in the frame. [5] Method according to one of the preceding claims, characterized by that between steps (d) and (e) the additional process step (d1) takes place: (d1) Thermal relaxation of the workpiece (5). [6] One-piece, dental-prosthetic workpiece (5), preferably a framework part, bar, bar rider, implant structure, a crown, bridge, drilling template or bite splint, which is produced by a method according to one of the preceding claims. [7] One-piece, dental-prosthetic workpiece (5) according to claim 6, characterized by that the workpiece (5) consists of a CoCr alloy or a TiAlV alloy. [8] Software for controlling the manufacturing process for producing a dental prosthetic workpiece (5), comprising: - a first software module (31) for generating geometric data for transmission to a device (40) for carrying out an additive manufacturing process for producing an intermediate product of the workpiece (5); and - a second software module (32) for generating data for controlling a device (60) for carrying out a subtractive manufacturing process for machining the intermediate product of the workpiece (5); wherein - in the first software module (31), at least one surface of the workpiece (5) can be preselected by the user via an input prompt, which surface receives an increased layer thickness exceeding the nominal dimension in the additive manufacturing process. [9] Software according to claim 8, characterized byin that in the first software module (31) in the data set of the geometric data for transmission to the device (40) for carrying out an additive manufacturing process for producing the intermediate product of the workpiece (5), the intermediate product to be manufactured is positioned in a virtual frame. [10] Software according to claim 8 or 9, characterized by that the software creates an STL file for the device (40) for carrying out an additive manufacturing process and NC codes for the device (60) for carrying out a subtractive manufacturing process.

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