METHOD AND ARRANGEMENT FOR MAKING ARTIFICIAL TEETH

Abstract: The present invention concerns a procedure and an arrangement for the remote input of the three-dimensional shape of dental objects such as teeth, casts of teeth and models of teeth. The procedure includes the steps: that the object to be measured (5) is illuminated by a laser beam that, on the surface of the object, forms a narrow trace (6) of reflected laser light (laser trace), that the laser trace (6) is imaged on a matrix of photo-detectors (9) arranged to the side of the laser beam's (4) described direction of projection, that the elevation profile of the laser trace (6) is determined from the position of the image (11) of the trace impacts on the detection matrix (9, 10), that the laser trace (6) is arranged to scan relative to the object (5) by means of which further elevation profile data is collected, that further readings are arranged after the angles between the input device (12) and the object (5) have been changed in order to achieve over-lapping surface information, and that the data about the shape obtained from the different input positions is consolidated in computer software suitable for the purpose of the objective. The arrangement includes a transmission unit, a receiver unit and a calculation unit whereby the transmitter unit includes a laser (2) and laser beam-adjusting optics (3) producing what is essentially a disc-shaped laser beam (4) directed to follow a projection to illuminate an object to be measured, whereby the receiver unit (8) is arranged to the side of and at a distance from the laser projection, and that the receiver unit includes a photo-detector matrix (9, 10) that registers laser light (11) reflected from the object to be measured.

Description: Method and arrangement for making artificial teeth The present invention concerns a procedure and an arrangement for the remote input of the three dimensional shape of dental objects such as teeth, casts of teeth and models of teeth. One current aspect of the development of dental care is seen in a desire to go over from restoration material that is shaped directly in the mouth, such as amalgam and plastic, and instead develop material suitable for shaping and finishing outside of the body, for example, by die casting, spark machining, abrasive machining or similar. By determining the shape of a dental object, such as a drilled-out tooth, in three dimensions, a suitably adapted restoration insert, such as a filling, can be produced to fit the object. There is also an increased need to be able to determine the shape of dental objects in three dimensions. It is also advantageous if the input of data can be made accurately and remotely. An arrangement for producing dental inserts that uses a mechanical means to transfer the shape from an impression of the tooth to a machining tool is known. The accuracy of the shape of such a insert is, however, often too low to achieve a reliable repair. US 4,964,770 shows an arrangement for producing an artificial tooth where the stump of the tooth is illuminated by a strip of light and where a camera is arranged to scan-in the illuminated stump of the tooth. When the scanned-in information is processed, the intensity of light at the lines and along their lengths constitutes an important factor for determining the shape of the stump of the tooth. Determination of shape can either take place directly in the mouth, from a cast impression or from a model. During optical input of natural teeth directly in the oral cavity, the measurements are impaired by saliva, and other optical imperfections on the surface of the tooth, such as different shades of colour, etc. The accuracy of inputting the three dimensional shape is, therefore, sometimes too low, which can lead to the fit of the insert being poor. For these reasons, it is still preferable when using known techniques to carry out the measurement outside of the oral cavity. During measurement, it is often sufficient to determine the shape of the surface to which the restoration body is to be adapted. Under certain conditions, however, it is also desirable to measure adjacently and oppositely located teeth. The object of the present invention is to achieve a description of the three dimensional shape of a dental object, such as teeth, cast impressions of teeth and models of teeth, by remote measurement. This objective is achieved according to the present invention by means of the procedure and arrangement according to the enclosed independent claims. Compared with previously known techniques, the invention achieves a more accurate and more cost-effective input of the three dimensional shape of dental objects. The solution that achieves the accurate and cost effective input of the three dimensional shapes includes: - that the measured object under examination is illuminated from a laser-based transmitter that generates an essentially disc-shaped beam of laser light, referred to below as the laser projection, - that when the laser projection strikes the surface of the object to be measured, it generates a narrow illuminated line, the laser trace, on the measured object. The laser trace can be 0.1 mm wide with a length preferably sufficient to extend over the surface, - that the laser trace is imaged in a position at a distance from the projection of the laser during the formation of an imaging angle α to the laser projection. Angle α is preferably in the interval, 10-45°. 22.5° is especially desirable. A larger angle gives a scan with greater accuracy but at the same time, the risk that surrounding variations in surface levels will get in the way of the illuminated points increases, - that the imaging takes place on a matrix of photo-detectors, - that the photo-detection matrix is arranged at an angle to the optical axis of the receiving optics, by means of which the laser trace is presented as a sharp image over the whole photo- detection matrix. This method results in good accuracy being obtained irrespective of where on the detector surface the laser trace strikes, - that the elevation profile along the laser trace is determined according to the images of the trace impacting on the detector matrix by means of a suitable combination of well-known geometrical algorithms, - that the laser trace is arranged to scan relative to the object, by means of which further elevation profile data is collected, - that at least one input scan is arranged after the relative positions of the input device and the object to one another have been changed, - that the data about the shape obtained from the different input positions is consolidated in a calculation unit intended for the purpose of the objective, e.g. a computer with software, plus - that the calculation unit processes and filters out measurement data that has been collected under unfavourable conditions/angles, such as close to the limits and edges of the preparation, from positions where the object to be measured has partially blocked the transmitted or received path of the laser beam, or combinations of these conditions. The additional inputs take place after the angles between the input unit and the object have been changed by rotating the object in fixed steps between the different scans of the laser. This means that only 3-D data that is registered under favourable conditions need be used. The data about the shape obtained from the different input positions is consolidated in computer software intended for the purpose of the objective. Further advantages and characteristics of the invention are made apparent by the claims listed below and the following non-limiting description of one embodiment of the invention presented with reference to the enclosed drawings, where fig. 1 is a schematic illustration of the layout of the optics of one embodiment of the arrangement according to the invention, and fig. 2 shows how a laser trace is imaged on the detector matrix. A transmitter unit 1 consisting of a laser 2 and transmission optics 3 generates a laser projection 4. Laser projection 4 generates a narrow laser trace 6 when it strikes the object to be measured 5. Part of the light scattered from the object to be measured 5 is picked up by a camera unit 8 that has its optical axis arranged at an angle to the transmitter unit's optical plane 4. The camera unit 8 includes an optical receiver 7 that images the laser trace 6 on a matrix of photo- detectors 9. By imaging the trace from the side at a known angle to the laser projection, differences in elevation on the illuminated surface can be imaged since the curve of the trace corresponds to the variations in elevation. The width of the trace (actually the width of the laser projection) and the distance between the scans determines the resolution. A narrower trace and a shorter distance between scans increases the accuracy. The elevation profile along the laser trace is determined from the position of the image 11 of the trace impacts on a detection matrix 10. By traversing the object to be measured 5 across the laser trace 6, elevation profile data for the whole of the object to be measured 5 can be obtained. As a number of positions on the surface to be measured can be shadowed because of the angle between the transmitter 1 unit and the camera unit 8, the object to be measured 5 is rotated by a known angle round a known axis, by means of which a new reading of elevation profile data can take place. This procedure is repeated until all parts of the surface of object 5 have been registered under favourable conditions/angles. Measurement data collected from the different perspectives is consolidated in a calculation unit/computer program, by means of which the complete three dimensional shape of the object to be measured (in this example, just the upper surface) can be described.

Claims: Claims 1. Procedure for the remote input of the three dimensional shape of a dental object (5) characterised by steps so that the object to be measured (5) is illuminated by a laser beam that, on the surface of the object, forms a narrow trace (6) of reflected laser light (laser trace), that the laser trace (6) is imaged on a matrix of photo-detectors (9) arranged to the side of the laser beam's (4) described direction of projection, that the elevation profile of the laser trace (6) is determined from the position of the image (11) of the trace impacts on a detection matrix (9,10), that the laser trace (6) is arranged to scan relative to the object (5) whereby further elevation profile data is collected, that further readings are arranged after the angles between the input unit (12) and the object (5) have been changed in order to achieve overlapping surface information, and that the data about the shape obtained from the different input positions is consolidated in computer software suitable for the purpose of the objective. 2. Procedure according to claim 1 characterised in that the photo-detection matrix (9,10) is arranged at an angle to the optical axis of the receiving optics (7), by means of which the imaged laser trace is sharp over the whole photo-detection matrix (9,10). 3. Procedure according to claims 1 or 2 characterised in that the object to be measured is rotated at fixed angles between the different input scans. 4. Procedure according to claims 1, 2 or 3 characterised in that the scan of the laser trace (6) over the object to be measured (5) takes place in discontinuous steps between each elevation profile. 5. Procedure according to claims 1, 2, 3 or 4 characterised in that the positions of the points of the laser trace impacts are calculated by means of triangulation algorithms. 6. Arrangement for the remote input of the three dimensional shape of a dental object including a transmission unit, a receiver unit and a calculation unit characterised in that the transmitter unit includes a laser (2) and laser beam-adjusting optics (3) producing what is essentially a disc-shaped laser beam (4) directed to follow a projection to illuminate an object to be measured, that the receiver unit (8) is arranged to the side of and at a distance from the laser projection, and that the receiver unit includes a photo-detector matrix (9,10) that registers laser light (11) reflected from the object to be measured. 7. Arrangement according to claim 6 characterised in that the laser (1) is preferably a laser diode type, that the receiver unit includes receiving optics (7) arranged with their optical axis at an imaging angle α to the projection of the laser (4), that the imaging angle is less than 60°, and that the photo-detector matrix (9,10) is arranged in the imaging projection of the receiving optics (7). 8. Arrangement according to any of claims 6 or 7 characterised in that a traversing device is arranged to scan the laser trace (6) over the object (5), and that a rotation device is arranged to change the relative positions of the transmitter/receiver (1,8) and the object to be measured (5) in pre-determined steps. 9. Arrangement according to claim 8 characterised in that the traversing device includes a track for the device holding the object to be measured, whereby the object to be measured can be displaced across the said direction of projection, that the photo-detector matrix is of what is known as an intelligent type where the position of the points where the trace strikes (11) are calculated directly on the same chip on which the photo-detector matrix is arranged.

Inventors: AAHLEN HANS, EK LEIF, WOLRATH GUSTAV, AAHLEN, HANS, EK, LEIF, WOLRATH, GUSTAV
Applicants: AAHLEN HANS, DENTRONIC AB, EK LEIF, WOLRATH GUSTAV, AAHLEN, HANS, EK, LEIF, WOLRATH, GUSTAV
Application year: 1998
Main classification: A61C13
IPC codes: A61C9, A61C13