Method for machining a dental restoration with reduced contour 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), characterized in that the method comprises a step of defining a target contour (4) of the dental restoration (1), and further comprises a step of predicting deflections of the dental tool (3) during pre-machining by means of a model based on one or more machining parameters, a step of determining one or more primary locations (5) where the target contour (4) will be damaged during pre-machining based on the prediction step, a step of modifying the target contour (4) or a corresponding machining path by adding oversized material (6) substantially only at the primary locations (5) to prevent damage, and a step of pre-machining the workpiece (2) based on the modified target contour (7) or the modified corresponding machining path.

Description

Technical Field

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

Background Art

[0002] When machining a workpiece using a rotationally symmetric tool such as a milling cutter or a grinder, the tool bends or deflects due to the action of the machining force. See WO2007 / 110655A2, which discloses a method of machining a blank. The radial deflection of the tool is qualitatively similar to the deflection of a bent beam clamped on one side and having a longitudinally variable diameter. The deflection of the tool causes contour falsification at each working point during machining. The degree of contour falsification essentially depends on the amount of overlap between the tool and the workpiece and the infeed. The infeed is typically 50 μm for high-speed grinding and 25 μm for fine grinding. The maximum local contour falsification by high-speed grinding at complete overlap is typically approximately 300 μm. The portion of the contour falsification that does not depend on the overlap causes contour displacement, and the portion that depends on the overlap causes contour distortion. Despite such a significant displacement of 300 μm, a usable dental restoration can be machined in a single-step machining. However, when dental restorations such as inlays and partial crowns are fabricated with a largely varying tool / workpiece overlap during machining, the quality of the dental restoration deteriorates and is subject to, for example, non-uniform support, missing edge closure, and edge breakout. Generally, the contour falsification is either acceptable or compensated for by two-step machining. In two-step machining, the restoration AllIt is first covered with an overall oversized size and pre-processed, i.e., pre-processed by high-speed grinding or rough cutting to remove a substantial portion of the excess material, thereby reducing the tool load for the second step, i.e., post-processing, i.e., finish grinding or finishing, by one digit or more. However, the two-step process leads to a significant increase in processing time.

Summary of the Invention

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

[0004] This object is achieved by the computer-implemented method according to claim 1 and the dental processing system according to 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 defining a target contour of the dental restoration, predicting the deflection of the dental tool during pre-processing by a model based on one or more processing parameters, determining, based on the prediction step, one or more primary positions where the target contour would be damaged during pre-processing, modifying the target contour or the corresponding machining path by adding oversized material only at the primary positions to prevent damage, and pre-processing the workpiece based on the modified target contour or the modified corresponding machining path.

[0006] The main advantageous effects of the present invention are that the problem of contour distortion caused by tool deflection can be overcome or reduced as much as possible by using a model that predicts the tool deflection and thereby predicts the resulting contour distortion and contour displacement. Different from the above-mentioned prior art, in the pre-processing step of the present method, substantially, local tool deflection damages the final contour. would be At the target contour only , oversized material is generated. Thereby, the quality of the dental restoration can be improved, the processing time can be reduced. Thereby, the manufacturing cost can also be saved. Another main advantageous effect of the present invention is that the fitting accuracy can be improved, the details of the dental restoration can be selectively improved by using a thinner tool, the retaining pins of the dental restoration can be reduced, and the machining line can be finished with higher accuracy.

[0007] According to the present invention, the method may optionally be provided with a two-step machining having the above-mentioned pre-processing step and an additional post-processing step. Therefore, in one embodiment of the present invention, the method optionally includes, based on a prediction step, determining one or more secondary positions where excess material will remain after the pre-processing step, and substantially at the secondary positions only post-processing the workpiece to remove the excess material. Different from the above-mentioned prior art, in the post-processing step of the present method, substantially the secondary positions only are machined. Thereby, the dental restoration can be finished with higher accuracy, and the processing time can be relatively reduced. Thereby, the manufacturing cost can be further saved.

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

[0009] According to the present invention, the post-processing step can optionally be based on clinical relevance. Thus, in one embodiment, the method further comprises the step of omitting post-processing the workpiece at one or more of the secondary positions to remove excess material if the post-processing at these secondary positions is clinically less relevant or irrelevant. For example, the front and rear sides of a dental restoration may be considered to be clinically less relevant than the left and right sides of a dental restoration that generally need to fit accurately and precisely to adjacent teeth. If it does not fit well, the insertion of the dental restoration into its proper position may become complicated, or food residues may accumulate. The computer-implemented method may comprise a neural network that recognizes the positions of dental restorations that are clinically less relevant or irrelevant by artificial intelligence.

[0010] According to the present invention, the infeed value for two-step machining can be flexibly set according to the processing time and the desired accuracy. In one embodiment, the infeed for the pre-processing step is set larger than the infeed for the post-processing step. Since the risk of damaging the dental restoration is prevented or reduced as much as possible due to the model-based damage prediction, the infeed in the pre-processing step can be relatively increased. Thereby, the processing time can be safely further reduced. Thanks to the accelerated pre-processing with a relatively high infeed, the infeed in the post-processing can be relatively reduced. Thereby, the quality of the dental restoration can be further improved without extending the overall machining time.

[0011] According to the present invention, different dental tools can be used in the pre-processing step and the post-processing step. Therefore, in one embodiment, in the pre-processing step, a roughing dental tool is used. And in the post-processing step, a finishing dental tool is used. Thereby, the quality of the dental restoration can be improved in a relatively short processing time.

[0012] According to the present invention, the machining parameters of the model include the length of the overlap between the dental tool and the workpiece, and the machining force between the dental tool and the workpiece. The amount of deflection depends on both machining parameters. In order to predict the deflection of the tool throughout the machining, the values of the machining parameters can be obtained from the machining path reconstructed from the target geometry. Instead of the machining force, the current supply to the tool motor can also be used as a machining parameter in the model. The model is created prior to the overall pre-processing step and post-processing step. The model can be provided in the form of a look-up table or a 3D property map.

[0013] The present invention also provides a dental processing system. The dental processing system has a dental tool machine including one or more carriages for driving one or more dental tools for machining a dental restoration from at least one workpiece. The dental processing system has control means for individually controlling the carriages. The control means controls the carriages according to the method of the present invention. The dental processing system may also have a CAD / CAM module for performing at least some of the steps other than the pre-processing step and the post-processing step. The CAD / CAM module preferably includes a computer station or a microprocessing unit provided separately from the dental tool machine. Communication between these may be performed via a network or the like. The CAD / CAM module may also be provided as part of the dental tool machine. The present invention also provides a computer program for implementing the present method. The computer program has computer-readable code for causing a computerized dental processing system to execute the steps of the present method. The computer program is stored in a computer-readable storage medium. The storage medium may be portable or built-in. The storage medium may be located outside or inside the dental processing system. The storage medium may be reachable through a network or the like.

[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 referring to the drawings.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

[0016] The reference numbers shown in the drawings indicate the elements listed below and are referred to in the following description of the exemplary embodiments. 1. Dental restoration 2. Workpiece 3. Dental tool 4. Target contour 5. Primary position 6. Oversized material 7. Modified target contour 8. Secondary position 9. Excess material 10. Dental tool machine 11. Carriage

[0017] FIG. 1 partially shows a dental machining system according to an embodiment. The dental machining system has a dental tool machine (10) having two carriages (11) for driving a dental tool (3) for machining a dental restoration (1) from a workpiece (2), respectively. FIG. 2 partially shows a dental tool (3) that can be attached to any one of the carriages (11). FIG. 3 shows an unused workpiece (2) that can be installed in the dental tool machine (10). The dental machining system has control means for individually controlling the carriages (11) during machining. The control means controls the carriages (11) according to the method of the present invention. The dental machining system preferably has a CAD / CAM module separately from the control means for implementing the method. In the following description, the method will be described.

[0018] Figure 1 shows a dental machining system in operation. In a definition step, a target contour (4) of a dental restoration (1) is defined. The target contour (4) is illustrated as a cylinder in Figure 1 for ease of illustration. In a prediction step, the deflection of a dental tool (3) that will occur during pre-machining is predicted in advance by a model based on one or more machining parameters. This model will be described in more detail later with reference to Figures 4 and 5. In a determination step, the target contour (4) is damaged during pre-machining would be one or more primary positions (5) are determined based on the prediction step. In a correction step, the target contour (4) or the corresponding machining path is corrected by adding oversized material (6) to the target contour (4) substantially only at the primary positions (5) in order to prevent damage. In the present application, the term "substantially" should be construed as referring to the limits of the technical tolerances of this machining method. In a pre-machining step, the workpiece (2) is pre-machined based on the corrected target contour (7) or the corresponding corrected machining path. The definition step, the prediction step, the determination step, and the correction step are preferably performed in a CAD / CAM module. The pre-machining step and the post-machining step are performed by control means. It is also possible to incorporate the CAD / CAM module into the control means.

[0019] FIG. 4 partially shows an experimental apparatus used to create a model for predicting the deflection of the dental tool (3) of FIG. 2 during machining of the workpiece (2) of FIG. 3. In FIG. 4, on the left side of the workpiece (2), the lower dashed line and the upper dashed line respectively indicate the target position and the actual position of the dental tool (3) before machining for a specific overlap and a specific machining force between the dental tool (3) and the workpiece (2). On the right side of the workpiece (2), the material is removed to the target position by pre-machining several times by the dental tool (3) until the measured machining force between the dental tool (3) and the workpiece (2) becomes zero. To produce a 3D characteristic map as shown in FIG. 5, using this experimental apparatus, the deflection of the dental tool (3) was measured for various values of the overlap and various values of the machining force. The 3D characteristic map of FIG. 5 can be used as a model for predicting the deflection of the dental tool (3) during pre-machining and post-machining.

[0020] In one embodiment, the method also has a post-machining step in addition to the pre-machining step. In this embodiment, in an additional determination step, one or more secondary positions (8) where excess material (9) will remain after the pre-machining step are determined based on the prediction step. Then, in the post-machining step, the workpiece (2) is post-machined substantially only at the secondary positions (8) to remove the excess material (9).

[0021] In an alternative embodiment, in an additional determination step, one or more secondary positions (8) where excess material (9) will remain after the pre-machining step are alternatively determined based on sensor feedback during the pre-machining step. Then, in the post-machining step, the workpiece (2) is post-machined substantially only at the secondary positions (8) to remove the excess material (9).

[0022] In one embodiment, in the omission step, if post-processing at these secondary positions (8) is clinically less relevant or irrelevant, post-processing the workpiece (2) at one or more of the secondary positions (8) to remove excess material (9) is omitted. The clinical relevance of the secondary positions (8) of the dental restoration (1) can be input by the user by marking such secondary positions (8) on the display of the dental restoration (1). Alternatively, an artificial intelligence algorithm can be used. The following matters described in the claims of the original application are appended as they are for reference purposes only. [1] A computer-implemented method for machining at least one dental restoration (1) from a workpiece (2) using one or more dental tools (3), comprising: defining a target contour (4) of the dental restoration (1); In a method comprising: a prediction step of 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); a determination step of determining one or more primary positions (5) at which the target contour (4) would be damaged during pre-machining based on the prediction step; a correction step of correcting the target contour (4) or the corresponding machining path by adding oversized material (6) only substantially at the primary positions (5) in order to prevent damage; a pre-machining step of pre-machining the workpiece (2) based on the corrected target contour (7) or the corrected corresponding machining path; The method is characterized by further comprising the above steps. [2] A step of determining one or more secondary positions (8) at which excess material (9) will remain after the pre-machining step based on the prediction step; a post-machining step of post-machining the workpiece (2) only substantially at the secondary positions (8) in order to remove the excess material (9); The method according to [1], characterized by further comprising the above steps. [3] A step of determining one or more secondary positions (8) at which excess material (9) will remain after the pre-machining step based on sensor feedback during the pre-machining step; a post-machining step of post-machining the workpiece (2) only substantially at the secondary positions (8) in order to remove the excess material (9); The method according to [1], characterized by further comprising the above steps. [4] When the post-processing is not clinically relevant at the secondary position (8), further comprising the step of omitting post-processing the workpiece (2) at one or more of the secondary positions (8) to remove the excess material (9). [2] The method according to [2] or [3]. [5] The method according to any one of [2] to [4], characterized in that the feed in the pre-processing step is greater than the feed in the post-processing step. [6] The method according to any one of [2] to [5], characterized in that in the pre-processing step, a dental tool (3) for roughing is used, and in the post-processing step, a dental tool for finishing is used. [7] A dental processing system, A dental tool machine (10) comprising one or more carriages (11) each driving one or more dental tools (3) for machining a dental restoration (1) from at least one workpiece (2), Control means for individually controlling the carriage (11), In a dental processing system comprising: The control means is further adapted to control the carriage (11) according to the steps of the method according to any one of [1] to [6]. Dental processing system. [8] A computer program comprising computer-readable code for causing a computerized dental processing system to execute the steps of the method according to any one of [1] to [6]. [9] A computer-readable storage medium storing the computer program according to [8].

Claims

1. A computer-implemented method for machining one dental restoration (1) from a workpiece (2) using one dental tool (3), the method comprising a defining step of defining a target contour (4) of the dental restoration (1), the method further comprising: a predicting step of predicting deflection of the dental tool (3) during pre-machining by a model based on one or more machining parameters, wherein the one or more machining parameters include a length of overlap between the dental tool (3) and the workpiece (2) and a machining force between the dental tool (3) and the workpiece (2), a determining step of determining one or more primary positions (5) at which the target contour (4) will be damaged during pre-machining based on the predicting step, a modifying step of modifying the target contour (4) or a corresponding machining path such that oversized material (6) is added only substantially at the one or more primary positions (5) to prevent damage, a pre-machining step of pre-machining the workpiece (2) based on the modified target contour (7) or the modified corresponding machining path, A method, characterized in that it comprises.

2. a determining step of determining one or more secondary positions (8) at which excess material (9) will remain after the pre-machining step based on the predicting step, a post-machining step of post-machining the workpiece (2) only substantially at the one or more secondary positions (8) such that the excess material (9) is removed, The method according to claim 1, further characterized in that it further comprises.

3. The method according to claim 2, further characterized in that it further comprises a determining step of determining the one or more secondary positions (8) based on sensor feedback.

4. When the post-processing is not clinically relevant at the secondary position (8), an omission step of omitting post-processing the workpiece (2) at one or more of the secondary positions (8) so that the excess material (9) is removed is further provided. The method according to claim 2 or 3.

5. The method according to any one of claims 2 to 4, characterized in that the feed in the pre-processing step is larger than the feed in the post-processing step.

6. The method according to any one of claims 2 to 5, characterized in that a dental tool (3) for rough machining is used in the pre-processing step, and a dental tool for fine machining is used in the post-processing step.

7. A dental processing system, A dental tool machine (10) comprising one or more carriages (11) each for driving a dental tool (3) for machining the dental restoration (1) from the workpiece (2); Control means for individually controlling the one or more carriages (11); In a dental processing system comprising: The control means is further adapted to control the carriage (11) according to the steps of the method according to any one of claims 1 to 6. Dental processing system.

8. A computer program comprising computer-readable code for causing a computerized dental processing system to execute the steps of the method according to any one of claims 1 to 6.

9. A computer-readable storage medium storing the computer program according to claim 8.

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