Method of machining a dental restoration with reduced contour falsification

Abstract

A method of machining at least one dental restoration (1) from a workpiece (2) using one or more dental took (3), including a step of defining, a target contour (4) of the dental restoration (1); also including a step of predicting the deflection of the dental tool (3) during pre-machining through a model based on one or more machining parameters; a step of determining based on the prediction step one or more primary locations (5) at which the target contour (4) would have been damaged during pre-machining; a step of modifying the target contour (4) or the corresponding machining path by adding an oversize of material (6) substantially only at the primary locations (5) for preventing damage; and a step of pre-machining the workpiece (2) based on the modified target contour (17) or the corresponding modified machining path.

Claims

1. A computer-implemented method of machining a dental restoration from a workpiece using a dental tool, comprising: defining a target contour of the dental restoration; further comprising: predicting a deflection of the dental tool during pre-machining through a model based on one or more machining parameters, wherein the one or more machining parameters include a length of an overlap between the dental tool and the workpiece, and a machining force between the dental tool and the workpiece; determining based on the predicting, one or more primary locations at which the target contour would have been damaged during pre-machining; modifying the target contour or a corresponding machining path by adding an oversize of material substantially only at the one or more primary locations for preventing damage; and pre-machining the workpiece based on the modifying the modified-target contour or the corresponding machining path.

2. The method according to claim 1, further comprising: determining one or more secondary locations at which an excess of material will be left after the pre-machining the workpiece; and post-machining the workpiece substantially only at the one or more secondary locations for removal of the excess of material.

3. The method according to claim 2, further comprising: determining based on a sensor feedback the one or more secondary locations.

4. The method according to claim 2, further comprising: a step of dispensing with the post-machining of the workpiece at one or more of the secondary locations for removal of the excess of material if at these secondary locations the post-machining is clinically irrelevant.

5. The method according to claim 2, wherein an infeed in the pre-machining is larger than an infeed in the post-machining.

6. The method according to claim 2, wherein in the pre-machining the dental tool is configured for rough machining, and in the post-machining the dental tool is configured for fine machining.

7. The method according to claim 3, further comprising: a step of dispensing with the post-machining of the workpiece at one or more of the secondary locations for removal of the excess of material if at these secondary locations the post-machining is clinically irrelevant.

8. The method according to claim 3, wherein an infeed in the pre-machining is larger than an infeed in the post-machining.

9. The method according to claim 3, wherein in the pre-machining the dental tool is configured for rough machining, and in the post-machining the dental tool is configured for fine machining.

10. A dental machining system comprising: a dental tool machine comprising one or more carriages each for driving the dental tool for machining the dental restoration from the workpiece; and a control means for individually controlling the one or more carriages to perform the machining according to the method of claim 1.

11. A non-transitory computer-readable storage medium storing a program which, when executed by a computer system, causes the computer system to perform the method step as defined in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the subsequent description, further aspects and advantageous effects of the present invention will be described in more detail by using exemplary embodiments and by reference to the drawings, wherein

(2) FIG. 1is a schematic partial perspective view of a dental machining system according to an embodiment of the present invention;

(3) FIG. 2is a schematic enlarged partial side view of a dental tool according to an embodiment of the present invitation, used in the dental machining system of FIG. 1;

(4) FIG. 3is a schematic enlarged partial side view of a workpiece according to an embodiment of the present invitation, used in the dental machining system of FIG. 1;

(5) FIG. 4is a schematic enlarged partial sectional view of an experimental set up showing the deflection of the dental tool of FIG. 2 during machining of the workpiece of FIG. 3;

(6) FIG. 5is a diagram showing the deflection of the dental tool with respect to two machining parameters including the overlap and the machining force.

DETAILED DESCRIPTION OF THE INVENTION

(7) The reference numbers shown in the drawings denote the elements as listed below and will be referred to in the subsequent description of the exemplary embodiments: 1. Dental restoration 2. Workpiece 3. Dental Tool 4. Target Contour 5. Primary location 6. Oversize of material 7. Modified target contour 8. Secondary location 9. Excess of material 10. Dental tool machine 11. Carriage

(8) FIG. 1 partly shows a dental machining system according to an embodiment. The dental machining system has a dental tool machine (10) which has two carriages (11) each for driving a dental tool (3) for machining a dental restoration (1) from a workpiece (2). FIG. 2 shows partly a dental tool (3) which can be mounted to any one of the carriages (11). FIG. 3 shows an unused workpiece (2) which can be mounted into the dental tool machine (10). The dental machining system has a control means for individually controlling the carriages (11) during the machining. The control means controls the carriages (11) in accordance with 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 subsequent description, the method will be described.

(9) FIG. 1 shows the dental machining system in operation. In a defining step, the target contour (4) of the dental restoration (1) is defined. The target contour (4) has been depicted as a cylinder in FIG. 1 for the ease of illustration. In a predicting step, the deflection of the dental tool (3) that will occur in the pre-machining is predicted beforehand through a model based on one or more machining parameters. The model will be described later in more detail with reference to FIG. 4 and FIG. 5. In a determining step, one or more primary locations (5) at which the target contour (4) would have been damaged during the pre-machining is determined based on the prediction step. In a modifying step, the target contour (4) or the corresponding machining path is modified by adding an oversize of material (6) to the target contour (4) substantially only at the primary locations (5) for preventing any damage. In the present application the term substantially is to be interpreted as referring to the limits of technical tolerance of the present machining method. In the pre-machining step, the workpiece (2) is pre-machined based on the modified target contour (7) or the corresponding modified machining path. The defining step, the predicting step, the determining step, and the modifying step are preferably performed in the CAD/CAM module. The pre- and post-machining steps are performed through the control means. The CAD/CAM module can also be integrated into the control means.

(10) FIG. 4 partly shows an experimental set up used for preparing the model that predicts 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 and upper dashed lines respectively show the target position and the real position of the dental tool (3) during pre-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 has been removed by the dental tool (3) down to the target position through pre-machining repeatedly several times until the measured machining force between the dental tool (3) and the workpiece (2) has become zero. With this experimental set up, the deflection of the dental tool (3) has been measured for various values of the overlap and various values of the machining force to produce the 3D characteristic map as shown in FIG. 5. The 3D characteristic map in FIG. 5 can be used as a model to predict the deflection of the dental tool (3) during a pre- and post-machining.

(11) In an embodiment, the method has in addition to the pre-machining step also a post-machining step. In this embodiment, in an additional determining step, one or more secondary locations (8) at which an excess of material (9) will be left after the pre-machining step is determined based on the prediction step. And in the post-machining step, the workpiece (2) is post-machined substantially only at the secondary locations (8) for removal of the excess of material (9).

(12) In an alternative embodiment, in the additional determining step, one or more secondary locations (8) at which an excess of material (9) will be left after the pre-machining step is alternatively determined based on a sensor feedback during the pre-machining step. And in the post-machining step, the workpiece (2) is post-machined substantially only at the secondary locations (8) for removal of the excess of material (9).

(13) In an embodiment, in a dispensing step, it is dispensed with the post-machining of the workpiece (2) at one or more of the secondary locations (8) for removal of the excess of material (9) if at these secondary locations (8) the post-machining is clinically less relevant or irrelevant. The clinical relevance of the secondary locations (8) of the dental restoration (1) can be input by the user through marking on a display of the dental restoration (1) such secondary locations (8). Alternatively, an algorithm for artificial intelligence can be employed.