GB2504471A

GB2504471A - Method for optimized dental component milling

Info

Publication number: GB2504471A
Application number: GB1213398.9A
Authority: GB
Inventors: Matts Andersson; Timo Kero; Glenn Svensson; Mats Myremark
Original assignee: Nobel Biocare Services AG
Current assignee: Nobel Biocare Services AG
Priority date: 2012-07-27
Filing date: 2012-07-27
Publication date: 2014-02-05
Also published as: GB201213398D0

Abstract

A method of milling a dental component from a material block, such as using computer control and CAD/CAM assistance, comprises the steps of providing a dental component geometric data having a plurality of reference regions 540 which may be in the form of dome-shaped or n-gonal pyramid protrusions extending from the surface of the component. The reference regions 540 may be support points positioned to provide optimal robustness for fitment to a tooth. The component is milled to a first accuracy and then the reference regions 540 are milled to a second accuracy greater than said first milling operation - saving time and tool wear.

Description

Method for Optimized Component Milling

Field

The invention relates to a method of optimizing the manufacture of a dental component and apparatus for carrying out said method.

Background

A well understood problem in the field of manufacturing individualised components is the length of time taken by a milling machine to mill a customized component from a material block and the resulting wear on the milling tool.

In one example, a 5-axis milling machine is controlled by a computer to produce a physical representation of a model component. The milling machine must first remove the bulk of the excess material from a material block before beginning the more fine-grained work of finishing the surface of the component to the accuracy required by the model. Producing the surface usually occurs in a series of progressively more accurate milling steps, where each step refines the surfaces of the component closer and closer to the model stored in the computer. Dental components typically require a very high precision (e.g. to within 10 pm) for the surface which fits against the tooth or teeth of the recipient patient.

The problem with this process is that it takes a long time for the milling to be completed. Accurately milling a titanium customized dental component from a block of titanium can take up to 20-30 minutes for a typical crown, or up to 30-1 00 minutes for a bridge structure or prosthesis. Alternatively, milling a ceramic customized dental component from a block of pre-sintered pressed powder can take up to 15-25 minutes for a typical crown, or up to 30-120 minutes for a bridge structure or prosthesis.

Furthermore, the more milling work a milling machine is required to do, the more physical wear on the milling tool used to do the milling.

What is needed is a method of reducing the time required to perform the milling of a customized component whilst retaining the accuracy and fit of the surfaces intended to fit the patient's oral situation. This will allow a greater number of components to be produced by the milling machine over a period of time whilst reducing the milling tool wear on a per milled component' basis.

Summary

The invention is defined in the independent claims. The dependent claims describe preferred embodiments of the invention.

An embodiment of the invention describes a method of milling a dental component from a material block comprising the steps of: providing a dental component geometric data having a plurality of reference regions, milling, to a first accuracy, the dental component according to said dental component geometric data, said dental component having physical reference regions corresponding to the reference regions of the dental component geometric data, milling, to a second accuracy greater than said first tolerance, the physical reference regions of the dental component.

Figures Aspects of the present invention will now be described by way of example with reference to the accompanying drawing. In the drawings: Figure 1 shows the process flow for the milling process.

Figure 2 shows the oral situation of the patient before applying a component.

Figure 3 shows the surface data of the surface scan.

Figure 4 shows the virtual component.

Figure 5 shows the addition of the reference regions to the virtual component.

Figure 6 shows an embodiment of a reference region.

Figure 7 shows the surface of the component after the first milling step.

Figure 8 shows the surface of the component after the second milling step.

Figure 9 shows the finished component as applied to a tooth stem.

Description of embodiments

Specific embodiments of the invention will now be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

The terminology used in the detailed description of the embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements.

The following description focuses on an embodiment of the present invention applicable to the accurate milling of individualised dental components. However, it will be appreciated that the invention is not limited to the use of individualised dental components, but may be applied to the dental components in general, or even any manufactured component.

The following is a description of a preferred embodiment of the invention.

Figure 1 shows the process flow for the milling of a dental component.

In step 10, data determining the necessary shape of the dental component is obtained. In the preferred embodiment shown in figure 2, the dental component is a dental crown 210 configured to fit to an existing tooth stem 220 of a patient.

Consequently, the surface of the tooth stem 230 will define at least part of the shape of the dental component, the surface to fit against the tooth stem. Therefore, in step 10, the surface of the tooth stem is imaged with a high degree of accuracy (e.g. to a tolerance of 10 pm) using a 3D surface scanner and the resulting surface data 330 shown in figure 3 is provided to a CAM/CAM system.

In an alternative embodiment, the dental component is a bridge, denture or partial denture. Any customised component that is designed to fit a specific patient may benefit from the present invention.

The surface data could be in the form of a point cloud, triangulated data or any common data format such as IGES or STL data formats.

In step 20, a virtual dental component 410 is designed by a technician using the CAD/CAM system. In the preferred embodiment shown in figure 4, the virtual dental component is designed, using the tooth stem surface data, to have a surface 430 to fit to the tooth stem. The body 420 of the virtual dental component is then designed by the technician to provide a good aesthetic outcome and suitable occlusal surface in order to make a corresponding physical crown comfortable in the patient's mouth.

In step 30, as shown in figure 5, a number of reference regions 540 are added to surface 430 of the virtual dental component 410. This step maybe performed by the technician by selecting suitable sites on the surface 430 of the virtual component and placing them manually using the CAD/CAM software. In the preferred embodiment, the reference regions are placed only on the portion of the surface 430 of the component which is configured to fit against the surface of the tooth stem.

Alternatively, the reference regions may be placed automatically. In the preferred embodiment, the reference regions are support points used to provide optimal robustness for the fit of the component to the tooth. In this embodiment, the position of the reference regions are chosen to match those of ideal support points for providing optimal robustness for the fit of the component to the tooth. In these embodiments, determining the positions of the support points may include performing the algorithm of Wang et al., Optimizing Fixture Layout in a Point-Set Domain, IEEE Transactions on Robotics and Automation, Vol. 17, No3, June 2001. Alternatively, a configuration of random seed positions as prospective marker positions may be generated and then the marker positions iteratively moved to find an optimal configuration with the best support robustness.

In the preferred embodiment, a total of 6 reference regions are employed. In other embodiments, up to a total of 50 reference regions may be employed.

In the preferred embodiment shown in figure 6, the reference regions are dome shaped and extend 25 pm from the surface of the virtual component. In one embodiment, the reference regions are also markers suitable for use in for performing geometric quality control. In another embodiment, the reference regions are n-gonal pyramid (i.e. Tetrahedron, Square pyramid, Pentagonal pyramid, Hexagonal pyramid). The apex point provides a very precise reference region for high resolution scanners. The reference regions could have any size from 5 to 100 microns in orthogonal direction of the surface and could also be extended to a surface.

Once the design of the virtual component is complete, the virtual component and reference regions are recorded as component geometric data.

In steps 40-60 showing a preferred embodiment of the present invention, the dental component is milled according to the component geometric data. In the preferred embodiment, the component is first milled from a pre-sintered pressed powder bar in dependence on the component geometric data. The pre-sintering allows sufficient hardness to allow good accuracy of the milling tool, without hardening the bar too much to mill. The resulting milled component is then sintered to further shrink and harden it, making it suitable for placement in the patient's mouth. In an alternative embodiment, the component is milled from a titanium block or other suitable milling material.

In step 40, the bulk of the excess material is removed by the milling machine using a a a tool designed for removing a lot of material..

In step 50, a milling tool is used to prepare the surface of the component to a low resolution. In this operation high cutting speed could be used and thereby using high feed rate. The fast milling is performed so that there is no interference with the surface of the milled coping and the geometry of the prepared tooth. As shown in figure 7, the surface of the roughly milled coping has a layer of excess material 720 above the nominal surface of the coping 710.

In step 60, the milling tool is then used to more accurately mill physical reference regions of the component, corresponding to the reference regions of the geometric data, to a high degree of accuracy (e.g. greater than in step 50). Figure 8 shows nominal surface 710 being accurately milled around the locations of the reference regions 810 of the component.

Where the reference regions are used as support points to provide optimal robustness for the fit of the component to the tooth, the technique allows the high precision milling to be limited to only the portion of the surface of the component critical to the fit. This could significantly reduce the amount of time required for step 60. Where the support points only, for example, cover 5% of the surface of the component, the length of time required to perform step 60 is reduced to little more than 5% of its previous length. Furthermore, the wear on the tool used to perform the higher accuracy milling of step 60 is also reduced to little more than 5% of its previous amount.

Where the reference regions are also used for assessing geometric coping quality, such as determining any inconsistent shrinkage or distortion during the sintering process, the accurately milled reference regions allow a precise and clear position for the reference marker in any subsequent digital image obtained of the component.

Claims

CLAIMS1. A method of milling a dental component from a material block comprising the steps of: providing a dental component geometric data having a plurality of reference regions, milling, to a first accuracy, the dental component according to said dental component geometric data, said dental component having physical reference regions corresponding to the reference regions of the dental component geometric data, milling, to a second accuracy greater than said first tolerance, the physical reference regions of the dental component.
2. The method according to claim 1, wherein the dental component is a dental crown configured to fit to an existing tooth stem of a patient
3. The method according to claim 2, wherein the dental component geometric data having a plurality of reference regions is formed at least in part in dependence on a surface of the existing tooth stem of the patient.
4. The method according to any previous claim, wherein the step of obtaining an image of the dental component including said physical reference regions is performed using a 3D surface scanner.
5. The method according to any previous claim, wherein the step of obtaining an image of the dental component including said physical reference regions is performed to an accuracy of 10pm.
6. The method according to claim 1, wherein the dental component is a bridge, denture or partial denture.
7. The method according to any preceding claim, wherein the plurality of reference regions are added to the dental component geometric data using CADICAM software.
8. The method according to any of claims 1-6, wherein the plurality of reference regions are added to the dental component geometric data according to an iterative optimal fit algorithm.
9. The method according to any preceding claim, wherein the plurality of reference regions are added to the dental component geometric data using CADICAM software.
10. The method according to any preceding claim, wherein the plurality of reference regions dome shaped.
11. The method according to any preceding claim, wherein the plurality of reference regions have an n-gonal pyramid shape and comprise an apex end.
12. The method according to any preceding claim, wherein the plurality of reference regions extend 25 pm from the surface of the virtual component.
13. The method according to any preceding claim, wherein the step of milling, to a first accuracy, the dental component, comprises leaving an excess of material above a nominal surface of the dental component.
14. The method according to claim 13, wherein the step of milling, to a second accuracy, the dental component, comprises removing the excess of material above the nominal surface of the dental component in the physical reference regions.