Patent Application
20210393381
This patent application claims the benefit of and priority to EP Application No. 18206460.0 filed Nov. 15, 2018, which is herein incorporated by reference for all purposes.
The invention relates to a method for producing ceramic dental prosthesis parts by way of a CAD/CAM machining station, to a corresponding CAD/CAM machining station and to a computer program for controlling the CAD/CAM machining station, and to a disk-shaped blank made of a final-strength dental ceramic.
A method for producing dental restorations is known from WO2004/086999A1, in which disk-shaped blanks are processed, which are present in an unsintered form or in a form in which they have not yet undergone final sintering. According to this previously known method, it is not possible to process final-strength blanks.
In contrast, it is the object of the invention to create an improved method for producing ceramic dental prosthesis parts and a corresponding CAD/CAM machining station, a computer program and a blank.
The object underlying the invention is achieved by the features of the independent claims. Embodiments of the invention are described in the dependent claims.
A “dental prosthesis part” here shall be understood to mean a ceramic dental prosthesis, such as a crown or a bridge, for the restorative dental medicine field.
A “disk-shaped ceramic blank” here shall, in particular, be understood to mean a so-called round blank, which, for example, can have a cylindrical, and in particular a circular cylindrical, a puck-shaped or a rectangular contour or a contour resembling the human jaw (see https://www.amanngirrbach.com/index.php?id=23&news=UWC9bNZ4&no_cache=1&L=2). A “disk-shaped ceramic blank” as understood herein also encompasses a disk-shaped, plate-shaped or slice-shaped ceramic blank that may have a round, rectangular, triangular or other polygonal or curved or ellipsoid circumference and which is configured to be releasably held by a mounting device on its circumference by a press and/or form fit.
In contrast to block-shaped blanks, such as are known from DE 20 2008 018 342 U1 and EP 2 016 922 B1, for example, where they are referred to as “sub-blanks 84”, such a disk-shaped ceramic blank according to the invention does not require a holder attached to the blank (shown as “supports 86” in EP 2 016 922 B1), since the blank is intended to be surrounded on the circumference thereof by the mounting device of a CAD/CAM machining station.
Compared to a block-shaped blank, the special feature of a disk-shaped blank is that a disk-shaped blank is surrounded on the entire circumference, or on almost the entire circumference, in a mounting device for machining purposes, and more particularly in contrast to block-shaped blanks, which are generally only attached on one side, for example by an adhesively attached block holder, during machining.
The use of a disk-shaped blank is especially advantageous for long-span prostheses, such as for dental bridges, since the disadvantages of block-shaped blanks are avoided, in which the mechanical lever is accordingly high, so that a one-sided attachment by a block holder, for example by way of adhesive, is disadvantageous.
In the case of a “disk-shaped ceramic blank,” the ratio of the thickness of the blank to the diameter thereof is considerably different from 1:1, in contrast to block-shaped blanks, and the ratio of the thickness of the blank to the diameter thereof may range between 1:10 and 1:4, for example. The diameter is at least more than 40 mm, preferably more than 90 mm, and preferably less than 200 mm, and in particular between 95 mm and 110 mm. Such blanks are holderless, which is to say they do not have a holder attached to the blank, such as by adhesive bonding, but the blanks are intended to attached along the circumference thereof in a mounting device, preferably in a force-fit and/or form-locked manner. Mounting may take place along the entire circumference, or it may be interrupted by recesses along the circumference.
Round blanks having a standard format with a diameter of 98.5 mm and a thickness of 12, 14, 18 or 25 mm, for example, are commercially available in a variety of ceramic materials. However, a round blank may also have a different diameter, such as 105 mm. A round blank may also have a non-circular shape, such as a contour that is based on the shape of the human maxilla.
According to embodiments of the invention, the blank is attached in a mounting device of a CAD/CAM machining station so that the blank is surrounded on the circumference thereof. “Surrounded on the circumference thereof” herein shall, in particular, be understood to mean that the enclosure takes place along the entire circumference of the blank, or a portion of the circumference of the blank having at least one recess, the at least one recess possibly being implemented in the blank and/or in an adapter and/or in the mounting device.
The blank is detachably surrounded in the mounting device, and the enclosure may take place in a force-fit and/or form-locked manner.
A “CAD/CAM machining station” herein shall, in particular, be understood to mean a program-controlled machine for machining a blank so as to produce a dental prosthesis part.
A “grinding tool” shall, in particular, be understood to mean a tool for the CAD/CAM machining station which, in contrast to a milling cutter, does not include a defined rotating cutting edge, but an undefined blade, which is formed by an abrasive working surface. For example, the working surface may include abrasive particles, such as diamonds having a certain grain size, whereby the undefined blade is formed.
Embodiments of the invention are particularly advantageous since the disk-shaped ceramic blank is surrounded over the circumference thereof in the mounting device, and the resulting mounting is more tolerant with respect to cutting forces; this is advantageous compared to the machining of blocks, which can fall from the holder during machining if the adhesive fails under high forces and torque.
Embodiments of the invention are particularly advantageous since the production of ceramic dental prosthesis parts directly from the final-strength blank is made possible. In contrast to the state of the art, no shrinkage that would otherwise result due to final sintering has to be taken into consideration in the generation of the CAD file, which specifies the dimensions of a dental prosthesis part to be produced, but the CAD file can directly indicate the desired final dimensions of the dental prosthesis part to be produced.
The machining complexity is also reduced in that a work step, after the dental prosthesis parts have been machined from the blank, is eliminated, namely the final sintering that is otherwise required. This is advantageous both for applications in laboratories and in so-called chairside applications.
Another advantage is that the use of machining by grinding, instead of milling, allows dental prosthesis parts to be produced which have improved precision in terms of the geometric dimensions thereof, and particularly low surface roughness.
It may be furthermore of advantage in this regard that, as a result of the elimination of the sintering process after machining, a potential source of errors is eliminated, such as an incorrect shrinkage factor. Moreover, embodiments of the invention are particularly advantageous since this can take place without a tool change, which is to say using only the grinding tool.
According to embodiments of the invention, machining by grinding, instead of milling, of the final-strength ceramic blank is made possible in that an initial contact between the blank and the grinding tool is established in such a way that, due to the rotation of the grinding tool about the longitudinal axis thereof, a movement relative to the blank is carried out on the entire contact surface between the grinding tool and the blank.
In other words, the grinding tool is initially moved to the blank in such a way that a contact surface is formed between the abrasive working surface and the blank, wherein the alignment of the longitudinal axis of the grinding tool about which this tool rotates is selected, relative to the blank, in such a way that every point of the abrasive working surface carries out a relative movement with respect to the blank on the contact surface, whereby material is removed from the blank on the entire contact surface. This advantageously makes it possible to carry out a machining operation of a final-strength ceramic blank using a grinding tool while incurring low wear.
According to embodiments of the invention, the geometry of the contact surface is selected in such a way that the same relative speed is achieved over the entire contact surface. In this way, particularly uniform removal, low tool wear, and high quality and precision of the produced surfaces are made possible.
According to one embodiment of the invention, the mounting device of the CAD/CAM machining station has a recess that is open toward the blank. The recess may be a groove extending in the axial direction, having a cross-section large enough to allow the grinding tool to be introduced into the groove. Designing the groove as small as possible has the advantage that the contact surface between the blank and the mounting device, and the attendant stability of the mount, are substantially not reduced, and the local surface pressure can be kept low.
According to one embodiment of the invention, multiple of the recesses may be distributed along the circumference of the mounting device so as to allow the grinding tool to be fed to the blank in corresponding multiple locations.
According to embodiments of the invention, the grinding tool is introduced into one of the recesses of the mounting device, and more particularly without making contact with the mounting device or the blank. Only after the grinding tool has been introduced in the axial direction as far as corresponds to the thickness of the blank, or the depth of the recess, is the grinding tool moved to the blank in the radial direction for the initial contact so as to start to machine the blank.
According to one embodiment of the invention, the blank is attached in the mounting device by way of an adapter, which can have an annular design, for example. In this embodiment, the at least one recess is not formed in the mounting device, but in the adapter. This has the advantage that a CAD/CAM machining station comprising a conventional mounting device can be used for the method according to the invention.
According to one embodiment, the adapter is made of a material, such as metal or plastic material, which allows the blank to be held sufficiently firmly in the mounting device.
According to one embodiment of the invention, recesses in the adapter can be dispensed with if the adapter is made of one material that is softer than the final-strength ceramic of the blank and that, as a result, can be machined by the grinding tool without wear or with little wear. The adapter can be a plastic ring here, for example. In this embodiment, the blank can be accessed on the casing side by previously lowering the grinding tool into the adapter material on the end face. In the case of a CAD/CAM machining station comprising a tool changer, this casing-side access may also take place with a grinding tool other than the one intended for machining the dental ceramic, such as by way of a plastic milling cutter, for example.
According to one embodiment of the invention, the casing-side access of the grinding tool to the blank is implemented in that the blank has a radial flattened region, which provides a recess sufficient for a tool to engage on the casing side. Such a recess can be created during the production of the blank, for example during pressing of the ceramic, or subsequently by removing material from the casing region of the blank, for example by way of a surface grinding machine.
According to one embodiment of the invention, the blank has at least one recess, which extends across the entire thickness of the blank, so as to allow the grinding tool to be fed for the initial contact. Such a recess can, in turn, be implemented during the production of the blank by means of pressing or in a preprocessing step using machining techniques.
In the above-mentioned embodiments including a recess, the blank is likewise surrounded on the circumference, wherein the enclosure is interrupted in the region of each recess. The sum of these interruptions along the circumference is preferably substantially smaller than the length of the circumference, so that the stress introduced into the blank does not fluctuate excessively despite the interruptions along the circumference. For example, the sum of these interruptions is less than 80%, 60%, 40%, 30% or 20% of the circumference, wherein at least one of the recesses is sufficiently large for introducing the grinding tool without contact.
As an alternative, the at least one recess can also have a diameter that is smaller than that of the grinding tool. In this case, a machining operation is carried out when the grinding tool is introduced into the recess, wherein the rotational axis of the grinding tool extends through the recess, and preferably through the center thereof. In this way it is ensured that, even in this case, a relative movement relative to the blank is carried out on the entire contact surface between the grinding tool and the blank when the initial contact is established between the blank and the grinding tool, since the rotational axis (longitudinal axis) is aligned with the recess.
According to one embodiment of the invention, during the production of the blank, it is
Hipped (hot isostatically pressed) blanks are particularly advantageous since these are particularly hard and thus supply a quality dental prosthesis.
According to one embodiment of the invention, the blank is made of a final-strength dental ceramic, the blank being in particular feldspathic, feldspar-like, glass ceramic, in particular made of lithium disilicate glass ceramic, crystal ceramic, in particular made of aluminum oxide and/or zirconium oxide.
In a further aspect, the invention relates to a CAD/CAM machining station comprising a control unit that is configured in such a way that, based on the rotation of the grinding tool about the longitudinal axis thereof, a relative movement relative to the blank is carried out on the entire contact surface between the grinding tool and the blank. Following this initial contact, the blank is further machined by the grinding tool, for example, along a precalculated trajectory, so as to produce the desired ceramic dental prosthesis parts.
In a further aspect, the invention relates to a computer program for a CAD/CAM machining station for controlling the same accordingly. The computer program may be present on a memory medium, for example, in particular a data carrier, or the computer program may be kept available for downloading from a server, for example via the Internet. The computer program can be installed on the CAD/CAM machining station using a so-called firmware update, for example.
In a further concept, the invention relates to a disk-shaped blank made of a final-strength dental ceramic, and in particular what is known as a round blank, which includes a casing on the lateral surface thereof made of a material that is softer than the final-strength dental ceramic, and in particular wood or plastic material. In particular, such a round blank can have standard dimensions so as to be clampable into a corresponding standard mounting device. The feeding of the grinding tool laterally to the blank for the initial lateral contact can be prepared by previously lowering the grinding tool into the casing.
In a further aspect, the invention relates to a disk-shaped blank made of a final-strength dental ceramic, and in particular a round disk, which includes a recess extending across the entire thickness of the blank, wherein the recess can be a through-hole or the recess is located on an edge of the blank. The grinding tool can then be fed to the blank through this recess.
Embodiments of the invention will be described in more detail hereafter with reference to the drawings. In the drawings:
Elements of the following embodiments that correspond to or are identical to each other are each denoted by the same reference numerals.
For example, the CAD device 3.1 includes a scanner for acquiring 3D measurement data from the patient; as an alternative, the 3D measurement data can be received in digital form from the dentist. The CAD device 3.1 is used to execute CAD software so as to generate the CAD file 4.1 for specifying the dental prosthesis part to be produced. Appropriate scanners are commercially available, such as inEosX5 from Dentsply Sirona.
The CAD file 4.1 can be transmitted to the machining station 2 via a communication network 5, such as the Internet. Further CAD devices 3.2, 3.3 etc., which essentially have the same design, can transmit the corresponding CAD files to the machining station 2 via the communication network 5 for the generation of further CAD files 4.2, 4.3 etc., for specifying the final dimensions of further dental prosthesis parts.
The machining station 2 comprises a mounting device 6 for attaching a blank 7 in the machining station 2. For example, the mounting device 6 is designed in such a way that the blank 7 is clamped on the circumference thereof into the mounting device 6. The mounting device 6 is held rotatable about the Y axis by bearings 8, 9. The rotation about the Y axis is effectuated by a drive unit 10 of the mounting device 6, which can be controlled by a control unit 11. In addition to the rotatory alignment of the mounting device 6 about the Y axis, the drive unit 10 can be designed to carry out a positioning within the XY plane, for which purpose the drive unit 10 can be accordingly controlled by the control unit 11.
The machining station 2 furthermore comprises a spindle motor 16 for receiving a grinding tool 12, which has a pin shape in the embodiment described here. The spindle motor 16 is used to rotate the grinding tool 12 about the longitudinal axis 13. In the embodiment described here, the spindle motor 16 can be positioned relative to the mounting device 6 by a further drive unit 14, for which purpose the drive unit 14 can be controlled by the control unit 11. For example, the spindle motor 16 can position the drive unit 14 in all three spatial directions X, Y and Z.
The control unit 11 of the machining station 2 comprises at least one electronic memory 15 for storing the CAD files 4.1, 4.2, 4.3 etc. received from the CAD devices 3.1, 3.2, 3.3 etc.
The control unit 11 furthermore comprises at least one microprocessor 17 for executing a computer program, which includes the program components 18 and 19, for example.
The program component 18 is used to calculate a trajectory from the CAD files 4.1, 4.2, 4.3 etc., along which the grinding tool 12 has to machine the blank 7 to produce the specified dental prosthesis parts.
The program component 19 generates control commands for the drive units 10 and 14, and also for the spindle motor 16, so as to machine the blank 7 in keeping with the trajectory calculated by the program component 18.
In the embodiment described here, the blank 7 has a through-hole 20, which is designed in such a way that the grinding tool 12 can be introduced entirely into the through-hole 20 in the axial direction, which is to say along the Z axis here, without making contact with the blank 7. For example, the through-hole 20 has a circular cylindrical shape having a diameter that is larger than the diameter of the grinding tool 12. Other geometries are also possible.
For example, the through-hole 20 can have a shape that is not large enough to receive the grinding tool 12 such that abrasive grinding action occurs when the grinding tool is introduced into the through-hole.
The initial contact between the blank 7 and the grinding tool 12 here thus occurs in that the lateral surface 22 of the grinding tool 12 is displaced perpendicularly, which is to say in the y direction, for example, with respect to an edge 23 of the through-hole 12 extending axially, which is to say in the Z direction, so that the lateral surface 22 makes contact with the edge 23 along the entire thickness extension in the Z direction when this initial contact is established, thereby resulting in the contact surface 21.
The rotation of the lateral surface 22 about the longitudinal axis 13 results in a relative movement of the abrasive elements of the grinding tool 12 along the entire contact surface, whereby material is removed from the blank 7 along the entire contact surface 21 at essentially the same relative speed.
Proceeding from this initial contact, the control unit 11 then controls the drive units 10 and/or 14 by way of the control commands in such a way that the dental prosthesis parts specified in the CAD files 4.1, 4.2, 4.3, etc. are machined from the blank 7. It is particularly advantageous here that this takes place with particularly high precision and, due to machining by grinding, with a particularly high surface quality, and without necessitating a tool change or subsequent sintering. The dental prosthesis parts thus produced can be used directly by a dentist on a patient, without a further processing step.
This embodiment has the advantage that standard blanks having no through-hole 20 can be used.
Instead of the mounting device 6, the adapter or a casing of the blank 7 can have a geometry according to
If, in contrast, the initial contact takes place between the blank 7 and the lateral surface 22 of the grinding tool 12, as is the case in the embodiments according to
The recesses 24.1 and 24.2 can each be designed as blind holes. The depths of these blind holes, in sum, amount to at least the thickness of the blank 7. In this way, machining as follows is made possible:
1. First, the grinding tool 12 is introduced into the recess 24.1 and then forms an initial contact surface 21.1 on an edge of the recess 24.1.
2. By displacing the grinding tool 12 in the direction toward the recess 24.2, which is the Y direction here, the through-hole 20 is created, having the stepped geometry shown in
3. As soon as the recesses 24.1 and 24.2 have been connected to one another in this manner, the grinding tool 12 can be introduced into the resulting through-hole 20, and further machining can take place analogously to the embodiment according to
As an alternative to the through-hole 20, cavities that are open at the top can be formed on or milled into opposing sides of the blank 7, which is to say recesses 24.1 and 24.2 (see
As an alternative or in addition, the control unit 11 can automatically detect the position P of the through-hole 20 relative to the mounting device 6. For this purpose, the machining station 2 comprises a sensor 31, such as an optical sensor, which detects the position P of the through-hole 20. Appropriate data 32 indicating this position P is then stored in the memory 15. The position P can be ascertained and the data 32 can be stored in that the microprocessor 17 executes a program component 33. The program components 18 and/or 19 then calculate the trajectory and generate the control commands by taking this position P into consideration, which specifies the starting point of the trajectory. As an alternative or in addition, the sensor can ascertain the position of the marking 29, and thus, indirectly, also the position of the through-hole.
According to a further embodiment, the through-hole 20 can also extend axially through the center of a cylindrical disk-shaped blank 7, so that the markings 29, 30 can then be dispensed with. This is illustrated in
According to a further embodiment, the mechanical interface between the edge of the blank 7 and the mounting device 6 can be designed in such a way that the blank 7 can only be clamped in the mounting device 6 in a predefined position. For this purpose, a guide groove for rotational locking, which is to say for preventing turning, can be provided on the mounting device 6, for example.
For this purpose, the blank 7 and the conical surface 34 of the grinding tool 12 are positioned by the control unit 11 relative to one another at an angle setting in such a way that the initial contact with the conical surface 34 is formed on the surface of the blank 7, so that the contact surface 21 results there. The angle setting is made relative to the center of rotation of the grinding tool. By a relative feed of the blank 7 and the grinding tool 12 in the z direction, a through-hole 20 through the blank 7 can thus be created, proceeding from which further machining along the trajectory then takes place. In addition to the feed in the z direction, optionally an feed component may exist in the x and/or y directions, which preferably are each smaller than the feed in the z direction.
According to a further embodiment, a grinding tool having a truncated cone is used instead of a conical grinding tool, wherein the initial contact surface 21 is not formed with the top surface, but the lateral surface of the truncated cone, so that again a relative movement of the abrasive particles takes place on the entire contact surface.
The initial contact is established here in that the grinding tool is not placed at a right angle, but at an incline to the surface normal of the blank 7 onto the surface thereof. This ensures that each point of the contact surface 21 carries out a relative movement with respect to the abrasive particles on the spherical working surface of the grinding tool 12.
The grinding tool 12 is then moved back and forth in a rocking motion within the contour of the through-hole to be created, wherein the grinding tool 12 is raised when it reaches a position, during this back and forth movement, at which it is situated perpendicularly to the blank, as is shown in
Embodiments may comprise one or more of the following combinations of features that can be combined with the claimed subject matter in any combination:
A. A method for producing ceramic dental prosthesis parts by way of a CAD/CAM machining station (2), comprising the following steps:
B. The method according to item A, characterized in that the blank is round.
C. The method according to item A or B, wherein the recess is formed into the blank by pressing during manufacture of the blank.
D. The method according to item A, B or C, wherein the recess is machined by cutting technique during a preprocessing step of the blank.
E. The method according to any of the previous items, wherein the disk-shaped blank is provided with a marking (29), so that the recess can be located spatially.
F. The method according to any of the previous items, wherein the blank is feldspathic, feldspar-like, glass ceramic, in particular made of lithium disilicate glass ceramic, crystal ceramic, in particular made of aluminum oxide and/or zirconium oxide.
G. The method according to any of the previous items, wherein the blank is made of a fully-sintered, and in particular a HIPed hipped, ceramic.
H. A disk-shaped blank made of a final-strength dental ceramic, comprising a casing surrounding a perimeter of the final-strength dental ceramic, the casing made of a material that is softer than the final-strength ceramic, and in particular made of wood or plastic material.
I. A disk-shaped blank made of a final-strength dental ceramic, comprising at least one recess (20; 28), which extends through the entire thickness of the blank.
J. The disk-shaped blank according to item I, wherein the recess (28) is located on the edge of the blank.
K. The disk-shaped blank according to item J, wherein the recess is a through-hole (20) through the blank.
L. A disk-shaped blank made of a final-strength dental ceramic, wherein a respective recess (24.1, 24.2) of the final-strength dental ceramic is located on opposing sides of the blank, and the depths of the recesses, in sum, amount at least to the thickness of the blank.
M. The disk-shaped blank according to any one of items H to L, comprising a marking for the rotatory positioning of the blank.
1 CAD/CAM machining system
2 CAD/CAM machining station
3.1 CAD device
3.2 CAD device
3.3 CAD device
4.1 CAD file
4.2 CAD file
4.3 CAD file
5 communication network
6 mounting device
7 blank
8 bearing
9 bearing
10 drive unit
11 control unit
12 grinding tool
13 longitudinal axis
14 drive unit
15 memory
16 spindle motor
17 microprocessor
18 program component
19 program component
20 through-hole
21 contact surface
22 lateral surface
23 edge
24 recess
25 edge
26 end face
24.1 recess
24.2 recess
27 edge
28 recess
29 marking
30 marking
31 sensor
32 data
33 program component
34 conical surface
| Number | Date | Country | Kind |
|---|---|---|---|
| 18206460.0 | Nov 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2019/061939 | 11/18/2019 | WO | 00 |
