Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
METHOD AND APPARATUS FOR MEASUREMENT OF TOOTH PREPARATIONS AND THEIR DENTAL ENVIRONMENT
Document Type and Number:
WIPO Patent Application WO/2002/028309
Kind Code:
A1
Abstract:
An apparatus for acquiring data about a dental object are disclosed, said apparatus enabling the rotation of the dental object around at least two rotational axes and the translation along at least one translation axis. Steep surfaces, i.e. surfaces at a small angle from the light source, can then be ad-justed to improve the resolution so that they can be imaged under better conditions. It is also possible to capture data near edges under good conditions. Faulty data that will inevitably be captured in some positions can then be discarded.

Inventors:
Sjölin, Roger (Tuvagårdsvägen 62 SKELLEFTEÅ, S-931 49, SE)
Application Number:
PCT/SE2001/001984
Publication Date:
April 11, 2002
Filing Date:
September 17, 2001
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
DECIM AB (P.O. Box 753 SKELLEFTEÅ, S-931 27, SE)
Sjölin, Roger (Tuvagårdsvägen 62 SKELLEFTEÅ, S-931 49, SE)
International Classes:
A61C13/00; A61C9/00; (IPC1-7): A61C13/00; G05D1/02
Domestic Patent References:
WO1998036702A11998-08-27
WO1999062422A11999-12-09
Attorney, Agent or Firm:
ALBIHNS STOCKHOLM AB (P.O. Box 5581 STOCKHOLM, S-114 85, SE)
Download PDF:
Claims:
CLAIMS
1. A data acquisition apparatus for acquiring data about the shape of a dental object (109; 209), said apparatus comprising an imaging device for imaging said object, and a holder device (104; 204) adapted to hold the dental object when it is being imaged, wherein at least a part of said holder device is rotatable about a first ro tation axis (z; 111 ; 211), characterized in that said holder device is rotatable about at least a second rotation axis (x; 105; 205).
2. A data acquisition apparatus according to claim 1, wherein said holder device is slideable along a first translation axis (103; 203).
3. A data acquisition apparatus according to claim 1 or 2, wherein said holder de vice comprises an object foundation (107) rotatably mounted on a consol device (104b) and a mounting portion (104a), the object foundation (107) being rotatable in relation to the consol device around the first rotation axis (111), the consol device (104b) and the mounting portion (104a) being arranged perpendicularly to each other, and the mounting portion (104a) being rotatably mounted on the carrier around the second rotation axis (105).
4. A data acquisition apparatus according to any one of the preceding claims, wherein said holder device (104; 204) is provided with releasable stop means for allowing said rotation about said first rotation axis (111 ; 211) to be discontinued such that the holder device is allowed to be maintained in predetermined, discrete positions.
5. A data acquisition apparatus according to any one of the preceding claims, wherein said holder device (104; 204) is provided with a releasable stop means for allowing said rotation about said second rotation axis (105; 205) to be discontinued such that the holder means is allowed to be maintained in predetermined, discrete positions.
6. A data acquisition apparatus according to any one of the claims 25, wherein said light source (1 ; 113; 213) is adapted to emit a plane of white light.
7. A data acquisition apparatus according to any one of the preceding claims, wherein said holder device (104; 204) can be translated perpendicularly to one of the axes (105,111; 205,211) around which rotation can be performed.
8. A data acquisition apparatus according to any one of the preceding claims, wherein said holder device (104; 204) can be moved along a sliding axis (219), the orientation of said sliding axis being dependent on the rotation angle of the holder device around at least one of the first and second axes (105,111; 205,211).
9. A data acquisition apparatus for acquiring data about the shape of a dental object (109; 209), said apparatus comprising an imaging device for imaging said object, and a holder device (104; 204) adapted to hold the dental object for allowing scan ning of the light line to be performed over said surface, wherein at least a part of said holder device (104; 204) is rotatable about a first rotation axis (111; 211), characterized in that said holder device is slideable along at least a sliding axis (219).
10. An apparatus according to any one of the preceding claims, wherein the imaging device comprises comprising a source of light (1; 113; 213) adapted to project a light line (3; 114; 214) on the surface of said dental object, a viewing unit (5; 115; 215) adapted to view said light line when formed on said surface.
11. A method of acquiring data about the shape of a dental object held by a holder device, including imaging the object while performing the steps of turning said holder device about a first rotation axis to a first defined releasable stop turning said holder means about a second rotation axis to a second defined releas able stop. moving said laser line across said dental object while viewing it by said viewing unit and registering data regarding the shape of the dental object. processing the data to establish an elevation profile of said object.
12. A method of acquiring data according to claim 11, including turning said holder means about said first rotation axis and said second rotation axis to a predetermined number of defined releasable stops and moving said laser line across said dental object in each of the defined releasable stops.
13. A method of acquiring data according to claim 11 or 12, further comprising the step of moving said holder along a first translation axis parallel to the first rotation axis.
14. A method of acquiring data according to any one of the claims 1113, further comprising the step of moving said holder along a sliding axis, the direction of the sliding axis depending on the rotation angle of the holder around at least one of the first and second rotation axes.
15. A method according to any one of the claims 1114, wherein the imaging is car ried out by moving a line of light across said dental object while viewing it by a viewing unit and registering data regarding the form of the dental object.
16. A computer program product which, when run on a control system for a data acquisition apparatus comprising a holder device for an object, said holder being slideable along at least a first translation axis, and rotatable around at least a first and a second rotation axis, and an imaging device, causes the apparatus perform the following steps: turning said holder device about the first rotation axis to a first releasable stop, turning said holder means about a second rotation axis to a second defined re leasable stop, imaging the object when the holder is fixed in said first releasable stop and said second releasable stop.
17. A computer program product according to claim 16, further arranged to cause the holder to move along a first translation axis parallel to the first rotation axis.
18. A computer program product according to claim 16 or 17, further arranged to cause the holder to move along a sliding axis, the direction of the sliding axis de pending on the rotation angle of the holder around at least one of the first and sec ond rotation axes.
19. A computer program product according to any one of the claims 1618, further arranged to collect the data from at least one image of the line for at least one posi tion of the object, and to process the collected data to obtain an image of the object.
20. A computer program product according to any one of the claims 1619, further arranged to discard data that is deemed as not sufficiently good.
Description:
Method and Apparatus for Measurement of Tooth Preparations and their Den- tal Environment Technical Field The present invention relates to a data acquisition apparatus according to the pre- amble of claims 1 and also to a method of acquiring data about the shape of a dental object and a computer program product.

Description of Related Art Manufacturing of a tooth restoration at a dental laboratory often requires knowledge not only about the prepared tooth that is to be cured but also about the remaining teeth near it, that is, the dental environment. When working with CAD/CAM tech- nology it is important to get the information of the dental environment into the com- puter system. This information is generally carried from the patient's mouth to the dental laboratory in a bite impression in silicone or some other material. This im- pression is used for casting replicas of the jaws using some kind of stone or plaster.

The plaster model is then used to manufacture the restoration and ensure that it fits, with regard to the prepared tooth itself as well as regarding neighbours in the mesial and distal direction and teeth in the opposite jaw.

A method for doing this is known from W098/36702, in which a line of light is projected across the tooth and used to image the profile of the tooth along the line.

The unit projecting the light and the imaging unit are placed at an angle relative to each other and the surface to be imaged. The line, or the tooth, is then moved and another profile image is made. Finally, an interpolation is made between the profiles to create an image of the tooth.

The line will not be projected properly on parts that are shaded by another (pro- truding) part. Therefore, the apparatus of W098/36702 is also able to rotate the tooth around an axis normal to the direction of movement, before repeating the pro-

cedure of projecting the line of light and imaging in several positions across the tooth. With this rotation overlapping data is created.

Generally, the width of the line depends on the angle between the source of light and the surface on which the light is projected. Therefore, on surfaces at a too small angle in relation to the light the line will be too wide, and the accuracy of the im- aging will be low. Also, sharp edges may block part of the projected line, thus cre- ating measurement errors.

Object of the Invention It is an object of the present invention to provide a method and an apparatus for creation of measurement data from prepared teeth and their dental environment.

Summary of the Invention This object is achieved according to the invention by a data acquisition apparatus for acquiring data about the shape of a dental object, said apparatus comprising an imaging device for imaging said object, and a holder device adapted to hold the dental object when it is being imaged, wherein at least a part of said holder device is rotatable about a first rotation axis, said apparatus being characterized in that said holder device is rotatable about at least a second rotation axis.

The object is also achieved by data acquisition apparatus for acquiring data about the shape of a dental object, said apparatus comprising an imaging device for imag- ing said object, and a holder device adapted to hold the dental object for allowing scanning of the light line to be performed over said surface, wherein at least a part of said holder device is rotatable about a first rotation axis, said apparatus being characterized in that said holder device is slideable along at least a sliding axis.

The object is also achieved by a method of acquiring data about the shape of a den- tal object held by a holder device, including imaging the object while performing the steps of

-turning said holder device about a first rotation axis to a first defined releasable stop -turning said holder means about a second rotation axis to a second defined releas- able stop.

-moving said laser line across said dental object while viewing it by said viewing unit and registering data regarding the shape of the dental object.

-processing the data to establish an elevation profile of said object.

The object is also achieved by a computer program product which, when run on a control system for a data acquisition apparatus comprising a holder device for an object, said holder being slideable along at least a first translation axis, and rotatable around at least a first and a second rotation axis, and an imaging device, causes the apparatus perform the following steps: -turning said holder device about the first rotation axis to a first releasable stop, -turning said holder means about a second rotation axis to a second defined re- leasable stop, -imaging the object when the holder is fixed in said first releasable stop and said second releasable stop.

The first and second rotation axes are preferably perpendicular to each other.

With this method and apparatus it is possible to adjust steep surfaces to improve the resolution so that they can be imaged under better conditions. It is also possible to capture data near edges under good conditions. Faulty data that will inevitably be captured in some positions can then be discarded.

The second rotation axis forms an extra tilt axis, which solves the problem of gener- ating measurement data of sufficient quality in the following two situations: At surfaces that are parallel or nearly parallel to the projected light, the line or lines projected on the object will be very wide, causing a poor accuracy.

Near sharp edges only a part of the line or lines of light will be visible from the camera, while other parts will be hidden by the edge. This generates unaccept- able measurement errors.

The imaging device may comprise a source of light, preferably white light, adapted to project a light line on the surface of said dental object, and a viewing unit adapted to view said light line when formed on said surface. The method then comprises the step of imaging by moving a line of light across said dental object while viewing it by a viewing unit and registering data regarding the form of the dental object.

Said holder device is preferably also slideable along a first translation axis parallel to the first rotation axis. This enables a translational movement of the object relative to the source of light.

In a preferred embodiment, the holder device comprises an object foundation rotata- bly mounted on a consol device and a mounting portion, the object foundation being rotatable in relation to the consol device around the first rotation axis, the consol device and the mounting portion being arranged perpendicularly to each other, and the mounting portion being rotatably mounted on the carrier around the second ro- tation axis.

Preferably, the holder device is provided with releasable stop means for allowing said rotation about said first rotation axis and second rotation axis, respectively, to be discontinued such that the holder device is allowed to be maintained in prede- termined, discrete positions around these axes.

Suitably, said light source is adapted to emit a plane of white light.

In a preferred embodiment, the holder device can be moved along a sliding axis, the orientation of said sliding axis being dependent on the rotation angle of the holder device around at least one of the first and second axes.

This enables the scanning of large areas such as bridge preparations in one opera- tion, which is not possible with traditional triangulation scanners.

The computer program product is preferably arranged to perform further method steps, such as causing the holder device to move along a first translation axis paral- lel to the first rotation axis and a sliding axis, the direction of the sliding axis de- pending on the rotation angle of the holder around at least one of the first and sec- ond rotation axes.

In a preferred embodiment the computer program product is further arranged to collect the data from at least one image of the line for at least one position of the object, and to process the collected data to obtain an image of the object.

Preferably, the computer program product is also arranged to discard data that is deemed as not sufficiently good.

Brief Description of the Drawings In the following the invention will be described in more detail, by way of preferred embodiments, with reference to the appended drawings, in which: Figure 1 illustrates the principle of a prior art system; Figure 2 illustrates the principle of a first preferred embodiment of the invention; Figure 3 illustrates the principle of a second preferred embodiment of the invention ; Figure 4 shows an apparatus according to the first preferred embodiment of the in- vention; and Figure 5 shows an apparatus according to the second preferred embodiment of the invention.

Detailed Description of Embodiments Figure 1 illustrates the principle of the prior art system disclosed in W098/36702.

An object to be imaged is placed in a Cartesian co-ordinate system having axes x y

and z. A laser light source 1 is used to project a line 3 of light across the object. The profile of the line is imaged using a camera 5 connected to a computer (not shown).

As indicated two bold arrows 7,9, the object can be moved relative to the light source along the x axis and rotated around the z axis, respectively. A number of line profiles, for different positions of the object, are imaged, and processed in a com- puter to obtain an image of the object. This imaging method is known in the art and may be used in all embodiments in this document. Other known imaging methods may be used as well, such as measurements by means of fringe scanners, or using projection of a moving point, or of several points.

Figure 2 illustrates the principle of a first preferred embodiment of the invention.

The object to be imaged is placed in the same Cartesian co-ordinate system as in Figure 1, and a light source 1'emitting a plane of light is used to project a light line 3 across the object. Unlike what is disclosed in W098/36702, the light does not have to be laser light. On the contrary, it may be advantageous to use white light be- cause the speckle noise arising from interference and extinction of the laser light can be reduced in this way. Also the speckles that arise because of when using laser light are avoided. The line is imaged by a camera 5. As in Figure 1, the object may be moved along the x axis, as indicated by a bold arrow 7, and rotated around the z axis, as indicated by a bold arrow 9. In addition, as indicated by a third bold arrow 11, the object may also be tilted around a second rotation axis. In this way, the ob- ject can be imaged at a number of different angles with respect to the x and z axes, so that parts that cannot be seen from some angles will be properly imaged at other angles. The faulty data can then be discarded and the good data used. The selection may be carried out by determining the width of the projected line on the object.

When the line is wide, the conditions for measurement are not good. Such data should therefore be discarded. In Figure 2, the second rotation axis is the x axis, but another tilt axis may be preferred.

Figure 3 illustrates the principle of a second preferred embodiment of the invention.

As in Figure 2, a light source 1 projects a line 3 of light onto an object placed in a

Cartesian co-ordinate system. The profile of the line is registered by a camera 5.

The object may be translated along the x axis, as represented by a bold arrow 7, ro- tated around the z axis, as represented by a bold arrow 9 and tilted around the x axis as represented by a bold arrow 11. In addition, the object has a further sliding axis, represented by a bold arrow 13. This sliding axis 13 is dependent on the rotational angle around the z axis and the tilt angle around the x axis.

Figure 4 shows an embodiment of an apparatus functioning as illustrated in Figure 2. A carrier 101 is slideable along a first translation axis 103. A holder 104 com- prising a first plane surface 104a and a second plane surface 104b mounted perpen- dicularly to each other is mounted on the carrier 101 through the first plane surface 104A in such a way that it is tiltable around a tilt axis 105 which is parallel to the first translation axis 103. The second plane surface 104b supports a rotatable disk 107, arranged to support an object 109 to be measured. The rotatable disk 107 is rotatable around a first rotation axis 111 perpendicular to the second plane surface 104b. A light source 113 is arranged to project a line 114 of light on the object 109 when on the platform 101. A camera 115 is arranged to image the profile of the line of light on the object 109 when on the platform 101.

With the apparatus shown in Figure 4, the object 109 to be measured is slideable, relative to the light source, along the first translation axis 103, rotatable around the first rotation axis 111 and tiltable around the tilt axis 105.

Figure 5 shows an embodiment of an apparatus functioning as illustrated in Figure 3. As in Figure 4, a carrier 201 is slideable along a first translation axis 203. A holder 204 comprising a first plane surface 204a and a second plane surface 204b mounted perpendicularly to each other is mounted on the carrier 201 through the first plane surface 204a in such a way that it is tiltable around a tilt axis 205 which is parallel to the first translation axis 203. The second plane surface 204b supports a rotatable disk 207, arranged to support an object 209 to be measured. The rotatable disk 207 is rotatable around a first rotation axis 211 perpendicular to the second

plane surface 204b. A light source 213 is arranged to emit a plane of light, thus projecting a line 214 of light on the object 209 when on the platform 201. A camera 215 is arranged to image the profile of the line of light on the object 209 when on the platform 201. In this embodiment, a slideable support member 217 is mounted on the rotatable disk 207 in a fixed angular relationship with the rotatable disk, with respect to the first rotation axis 211, but slideable along an sliding axis 219 perpen- dicular to the first rotation axis 211. When the rotatable disk 207 rotates, therefore, the sliding axis 219 rotates with it.

With the apparatus shown in Figure 5, the object 209 to be measured is slideable, relative to the light source, along the first translation axis 203, rotatable around the first rotation axis 211 and tiltable around the tilt axis 205. It is also slideable along a sliding axis 219, the direction of which will depend on the rotation of the rotating disk 207 around the first rotation axis 211 and the tilting angle of the holder 204 around the tilt axis 205.

This makes the apparatus of Figure 5 particularly suitable for long irregularly shaped objects such as bridges, since it enables the scanning of an object from many different positions and angles. When single crown preparations are scanned, the cervical-occlusal axis of the tooth is positioned at the rotation centre, which means that it is possible to rotate the object and scan from different views. A preparation for a bridge has at least two portions that need to be scanned from several direc- tions. This is enabled by the movement along the sliding axis 219.

The same possibilities will be achieved if the apparatuses of Figures 4 and 5 are modified by using a fixed carrier 101, 201 and making the holder 104,204 slideable along the first translation axis 103,203 with respect to the carrier.

Of course, the embodiment shown in Figure 5 may be simplified by eliminating ei- ther the tilt axis 205 or the first rotational axis 211, which would, however, result in a less flexible apparatus.

To scan an object using the apparatus according to Figure 4 or 5, a line of light is first projected on the object. The profile of the line of light on the object is then im- aged in a number of combinations of positions along the first translation axis 103, 203 and around the tilt axis 105,205 and the first rotation axis 111,211. This is preferably done systematically, for example in the following way: First the object is held at a first rotational angle, around the first rotation axis 111, 211 and a first tilt angle, around the tilt axis 105,205, while moving it along the first translation axis 103,203 and taking a number of images. Next, the tilt angle and/or the rotation an- gle is changed, and the object is imaged again while sliding along the first transla- tion axis 103,203. With the apparatus of Figure 5, then, the object may be moved along the sliding axis 219 before it is again moved along the first translation axis and imaged a number of times. The number of positions in which to image the ob- ject may be determined by an operator depending on the size and complexity of the object.

Of course, the movements of the object may be made in a different order, for exam- ple, by first keeping the carrier fixed in a position along the first translation axis 103,203 while rotating the support member 107,207 around the first rotation axis 111,211.

This may be determined by the operator or fixed in the system, preferably by means of a computer program. A program for controlling the movements preferably com- prises functions for controlling the movements of the object to fixed positions along the first translation axis 103,203 and the sliding axis 219 and around the first rota- tion axis 111,211 and the tilt axis 105,205, and for controlling the camera so that the light profile is imaged in appropriate positions. Such a program should also comprise functions for discarding bad measurement data and for determining how many measurements are needed, and in which positions, to achieve a good image of the object.