Method of machining a dental restoration having reduced profile distortion

Abstract

The present invention relates to a method for machining at least one dental restoration (1) from a workpiece (2) using one or more dental tools (3), comprising the following steps: defining a target profile (4) of the dental restoration (1); characterized in that it also comprises the following steps: predicting the deflection of the dental tool (3) during pre-machining by a model based on one or more machining parameters; determining one or more first positions (5) at which the target profile (4) will be damaged during pre-machining based on the prediction step; in order to prevent damage, modifying the target profile (4) or a corresponding machining path by adding a residual size (6) of material substantially only at the first positions (5); and pre-machining the workpiece (2) based on the modified target profile (7) or the corresponding modified machining path.

Description

Technical Field

[0001] The invention relates to a method for machining a dental restoration from a workpiece using one or more dental tools. The invention also relates to a dental machining system for machining a dental restoration from at least one workpiece. Background Art

[0002] When a workpiece is machined using a rotationally symmetrical tool such as a milling cutter or a grinder, the tool is bent or deflected (sometimes referred to as flexing) due to the action of the machining forces. Reference is made to WO2007 / 110655A2, which discloses a method for machining a blank. The tool deflection in the radial direction is similar in nature to the deflection of a bent beam clamped on one side with a longitudinally variable diameter. During machining, the deflection of the tool causes profile distortion at each working point. The extent of the profile distortion depends primarily on the overlap between the tool and the workpiece and the feed rate. The feed rate is typically 50 μm for fast grinding and 25 μm for fine grinding. In the case of fast grinding, the maximum local profile distortion at full overlap is typically about 300 μm. The portion of the profile distortion independent of the overlap causes a profile shift, and the portion dependent on the overlap causes a profile deformation. Despite the considerable displacement of 300 μm, the usable dental restoration can be machined in a single-step machine. However, in the case of dental restorations (such as inlays and partial crowns) produced with strongly fluctuating tool / workpiece overlaps during machining, the quality of the dental restorations is reduced and they receive, for example, uneven supports, missing edge closure, edge breakage, etc. In general, contour distortions are accepted or compensated by two-step machining. In two-step machining, the entire restoration is first covered with a spherical excess size and pre-machined (i.e. by fast grinding or rough machining) to remove most of the excess material and thus reduce the tool load by one or more orders of magnitude for the second step (i.e. post-machining, i.e. fine grinding or finishing). However, the two-step process leads to a significant increase in the processing time. Summary of the invention

[0003] The object of the present invention is to overcome as many of the problems of the prior art as possible and to provide a method for machining a dental restoration from a workpiece by using one or more dental tools, in which method geometric deformations of the dental restoration can be avoided or reduced as much as possible and the processing time can be relatively shortened.

[0004] This object is achieved by a computer-implemented method as defined in claim 1 and a dental machining system as defined in claim 7. The other claims relate to further developments.

[0005] The present invention provides a method for machining at least one dental restoration from a workpiece by using one or more dental tools. The method comprises the following steps: defining a target profile of the dental restoration; predicting the deflection of the dental tool during pre-machining by a model based on one or more machining parameters; determining one or more first positions where the target profile will be damaged during pre-machining based on the prediction step; modifying the target profile or a corresponding machining path by adding an excess size of material only at the first position to prevent damage; and pre-machining the workpiece based on the modified target profile or the corresponding modified machining path.

[0006] The main advantageous effect of the present invention is that by using a model that predicts tool deflection and the resulting profile deformation and profile shift, the problem of profile distortion caused by tool deflection can be overcome or reduced as much as possible. Unlike the prior art mentioned above, in the pre-machining step of the present method, the excess size of material is basically only produced at the target profile where local tool deflection will damage the final profile. Therefore, the quality of the dental restoration can be improved and the processing time can be reduced. Therefore, manufacturing costs can also be saved. Other main advantageous effects of the present invention are that the accuracy of the fit can be improved, any details on the dental restoration can be selectively increased by using a thinner tool, the retaining pins of the dental restoration can be made thinner, and the preparation line can be completed with higher accuracy.

[0007] According to the present invention, the method may optionally provide a two-step machining with a pre-machining step and an additional post-machining step as described above. Therefore, in an embodiment of the present invention, the method may optionally include the following steps: based on the prediction step, determining one or more second positions where excess material will remain after the pre-machining step; and post-machining the workpiece substantially only at the second position to remove the excess material. Unlike the prior art mentioned above, in the post-machining step of the present method, substantially only the second position is machined. Therefore, the dental restoration can be completed with higher precision and the processing time can be relatively reduced. Therefore, the manufacturing cost can be further saved.

[0008] In an alternative embodiment, the step of determining one or more second positions where excess material will remain after the pre-machining step is based on sensor feedback during the pre-machining step. The force between the tool and the workpiece may be measured directly by a sensor to establish the sensor feedback. The sensor may be arranged in a holder for the workpiece. Alternatively, the current supply to the tool motor may be monitored to establish the sensor feedback.

[0009] According to the present invention, the post-machining step may optionally be based on clinical relevance. Therefore, in an embodiment, the method further comprises the following step: if at these second positions, the post-machining is clinically less relevant or irrelevant, then the post-machining of the workpiece at one or more second positions for removing excess material is exempted. For example, the front and back sides of a dental restoration may be considered to be clinically less relevant than the left and right sides of a dental restoration, which generally must be precisely fitted to adjacent teeth with good precision. A poor fit may complicate the insertion of the dental restoration into the proper position, or lead to the accumulation of residual food, etc. The computer-implemented method may include a neural network that identifies the positions of dental restorations that are clinically less relevant or irrelevant based on artificial intelligence.

[0010] According to the present invention, the value of the feed amount for two-step machining can be flexibly set according to the processing time and the desired accuracy. In an embodiment, the feed amount for the pre-machining step is set to be greater than the feed amount for the post-machining step. Because the risk of damaging the dental restoration is prevented or reduced as much as possible due to the damage prediction based on the model, the feed amount in the pre-machining step can be relatively increased. Therefore, the processing time can be safely further reduced. Since the relatively high feed amount speeds up the pre-machining, the feed amount can be relatively reduced in the post-machining. Therefore, the quality of the dental restoration can be further improved without extending the total machining time.

[0011] According to the present invention, different dental cutters can be used in the pre-machining step and the post-machining step. Therefore, in an embodiment, a dental cutter for rough machining is used in the pre-machining step. And in the post-machining step, a dental cutter for fine machining is used. Therefore, the quality of the dental restoration can be improved with a relatively low machining time.

[0012] According to the present invention, the machining parameters of the model include the length of overlap between the dental tool and the workpiece and the machining force between the dental tool and the workpiece. The deflection depends on these two machining parameters. The values ​​of the machining parameters can be obtained according to the machining path reconstructed from the target geometry so as to predict the tool deflection during the entire machining process. Instead of the machining force, the current supply of the tool motor can also be used as the machining parameter in the model. The model is prepared before the entire pre-machining step and the post-machining step. The model can be provided in the form of a lookup table or a 3D feature map.

[0013] The present invention also provides a dental machining system. The dental machining system has a dental machine tool, which includes one or more slides for driving one or more dental tools, and the one or more dental tools are used to machine a dental restoration from at least one workpiece. The dental machining system has a control device for controlling the slides separately. The control device controls the slides according to the method of the present invention. The dental machining system may also have a CAD / CAM module for performing at least some steps other than the pre-machining step and the post-machining step. The CAD / CAM module preferably includes a computer station or microprocessor unit provided separately from the dental machine tool. Communication between them can be performed via a network or the like. The CAD / CAM module can also be provided as part of the dental machine tool. The present invention also provides a computer program for implementing the method. The computer program has a computer readable code for causing a computerized dental machining system to perform the steps of the method. The computer program is stored in a computer readable storage medium. The storage medium can be portable or integrated. The storage medium can be located outside or inside the dental machining system. The storage medium can be accessible via a network or the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In the following description, further aspects and advantageous effects of the present invention will be described in more detail by using exemplary embodiments and with reference to the accompanying drawings, in which

[0015] Figure 1 is a schematic partial perspective view of a dental machining system according to an embodiment of the present invention;

[0016] Figure 2 is Figure 1 A schematic enlarged partial side view of a dental tool according to an embodiment of the present invention used in a dental machining system;

[0017] Figure 3 is Figure 1 A schematic enlarged partial side view of a workpiece according to an embodiment of the present invention used in a dental machining system;

[0018] Figure 4 is a schematic enlarged partial cross-sectional view of the experimental setup, showing Figure 2 Dental tools in Figure 3 deflection of the workpiece during machining;

[0019] Figure 5 is a graph showing the deflection of a dental tool with respect to two machining parameters including overlap and machining force.

[0020] The reference numerals shown in the drawings denote the elements listed below and will be referenced in the subsequent description of the exemplary embodiments:

[0021] 1. Dental restorations

[0022] 2 Workpiece

[0023] 3. Dental Knives

[0024] 4. Target outline

[0025] 5. First position

[0026] 6. Material excess size

[0027] 7. Modified target profile

[0028] 8. Second Position

[0029] 9. Excess Materials

[0030] 10. Dental machine tools

[0031] 11. Sliding seat. DETAILED DESCRIPTION

[0032] Figure 1 A dental machining system according to an embodiment is partially shown. The dental machining system has a dental machine tool (10) having two slides (11), each of which is used to drive a dental tool (3) for machining a dental restoration (1) from a workpiece (2). Figure 2 A dental cutter (3) is partially shown, which can be mounted to any one of the slides (11). Figure 3 An unused workpiece (2) is shown which can be mounted in a dental machine tool (10). The dental machining system has a control device for controlling the slide (11) separately during machining. The control device controls the slide (11) according to the method of the invention. The dental machining system preferably has a CAD / CAM module separate from the control device for implementing the method. The method will be described in the subsequent description.

[0033] Figure 1 The dental machining system is shown in operation. In a definition step, a target contour (4) of a dental restoration (1) is defined. For ease of illustration, the target contour (4) is defined in Figure 1 In the prediction step, the deflection of the dental tool (3) that will occur during pre-machining is predicted in advance by a model based on one or more machining parameters. Figure 4 and Figure 5The model is described in more detail. In the determination step, one or more first positions (5) at which the target profile (4) will be damaged during pre-machining are determined based on the prediction step. In the modification step, in order to prevent any damage, the target profile (4) or the corresponding machining path is modified by adding the material excess size (6) to the target profile (4) essentially only at the first position (5). In the present application, the term "essentially" is interpreted as referring to the limit of the technical tolerance of the machine machining method. In the pre-machining step, the workpiece (2) is pre-machined based on the modified target profile (7) or the corresponding modified machining path. The definition step, the prediction step, the determination step and the modification step are preferably performed in a CAD / CAM module. The pre-machining step and the post-machining step are performed by a control device. The CAD / CAM module can also be integrated into the control device.

[0034] Figure 4 Partially shows the experimental setup used to prepare a model that predicts Figure 2 Dental Knives (3) Figure 3 The deflection of the workpiece (2) during machining. Figure 4 In the figure, on the left side of the workpiece (2), for a specific overlap and a specific machining force between the dental tool (3) and the workpiece (2), the lower dotted line and the upper dotted line respectively show the target position and the actual position of the dental tool (3) during pre-machining. On the right side of the workpiece (2), by repeating the pre-machining multiple times until the measured machining force between the dental tool (3) and the workpiece (2) becomes zero, the material is removed by the dental tool (3) until the target position. Using this experimental device, the deflection of the dental tool (3) is measured for various overlap values ​​and various machining force values ​​to produce the following results: Figure 5 3D feature map shown in . Figure 5 The 3D feature map in can be used as a model to predict the deflection of the dental tool (3) during pre-machining and post-machining.

[0035] In an embodiment, the method has a post-machining step in addition to the pre-machining step. In this embodiment, in an additional determination step, based on the prediction step, one or more second positions (8) are determined where excess material (9) will remain after the pre-machining step. And in the post-machining step, the workpiece (2) is post-machined substantially only at the second positions (8) to remove the excess material (9).

[0036] In an alternative embodiment, in an additional determination step, one or more second locations (8) where excess material (9) will remain after the pre-machining step are determined, optionally based on sensor feedback during the pre-machining step, and in a post-machining step, the workpiece (2) is post-machined substantially only at the second locations (8) to remove the excess material (9).

[0037] In an embodiment, in the exemption step, post-machining of the workpiece (2) at one or more second positions (8) for removing excess material (9) is exempted if post-machining at these second positions (8) is clinically less relevant or irrelevant. The clinical relevance of the second positions (8) of the dental restoration (1) may be input by a user by marking such second positions (8) on a representation of the dental restoration (1). Alternatively, an algorithm of an artificial intelligence may be employed.

Claims

1. A computer-implemented method for machining at least one dental restoration (1) from a workpiece (2) using one or more dental tools (3), the method comprising the following steps: defining a target contour (4) of the dental restoration (1); It is characterized in that it also includes the following steps: predicting the deflection of the dental tool (3) during pre-machining by a model based on one or more machining parameters, wherein the machining parameters include the length of overlap between the dental tool (3) and the workpiece (2) and the machining force between the dental tool (3) and the workpiece (2); determining, based on the prediction step, one or more first locations (5) at which the target contour (4) will be damaged during pre-machining; To prevent damage, modifying the target profile (4) or the corresponding machining path by adding an excess size (6) of material only at the first position (5); Pre-machining the workpiece (2) based on the modified target profile or the corresponding modified machining path; determining one or more second locations (8) where excess material (9) will remain after the pre-machining step based on the predicting step or based on sensor feedback during the pre-machining step, and post-machining the workpiece (2) only at the second locations (8) to remove the excess material (9); and Post-machining of the workpiece (2) at one or more of the second locations (8) for removing the excess material (9) is dispensed with if, at these second locations (8), the post-machining is not clinically relevant.

2. The method according to claim 1, characterized in that The feed amount in the pre-machining step is greater than the feed amount in the post-machining step.

3. The method according to claim 1, characterized in that In the pre-machining step, a dental cutter (3) for rough machining is used, and in the post-machining step, a dental cutter for fine machining is used.

4. A dental machining system comprising: A dental machine tool (10) comprising one or more slides (11), each of the slides (11) being used to drive one or more dental tools (3) for machining a dental restoration (1) from at least one workpiece (2); and A control device for controlling the slides (11) separately; It is characterized in that The control device is further adapted to control the carriage (11) according to the steps of the method according to any one of claims 1 to 3.

5. A computer program product comprising computer readable code for causing a computerized dental machining system to perform the steps of the method according to any one of claims 1 to 3.

6. A computer-readable storage medium having stored thereon a computer program for causing a computerized dental machining system to perform the steps of the method according to any one of claims 1 to 3.

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