Method for producing dental prosthesis.

The invention relates to a method for the production of dentures.

The previously used method to make dentures, based on the fact reproduce the individually different clinical oral conditions with footprints and models obtained thereafter. A process for the preparation of dental prostheses must make it possible to achieve a good fit of the denture as this requirement is precision fit for safe anchoring and the permanent seat of the denture. All tissues involved in the chewing process are then able to compensate for the physiological loads acting without injury.

All dental and all subsequent dental operations carried out by decades conventional methods, which are to be described using the example of a single crown briefly:<ul><li>1.) impression of the prepared tooth stump with a rubber-elastic or hydrocolloid impression material; </li><li>2.) Provisoriche supply;</li><li>3.) pouring the impression in die stone and producing a working model and a Gegenbißmodells;</li><li>4.) introducing the models in an articulator;</li><li>5.) preparing an artificial tooth crown to wax and metal casting;</li><li>6) fitting of the casting in the mouth on the tooth stump and definitive incorporating the artificial crown.</li></ul>

This conventional production of metal or other materials requires a variety of dental and dental procedures, which include a large number of inaccuracies and errors possibilities. Inaccurate fit may result, making the repetition of workflows required.

Material properties such as gypsum expansion, metal shrinkage and the like, as well as improper handling and difficult mouth conditions are to blame.

Be a while efforts are underway, after which using other techniques, the conventional impression method and numerous subsequent operations are to be replaced. These techniques are mechanical or optical three. dimensional measuring and sensing devices based. The information thus collected will be stored and control devices already in use in the machine tool industry NC machines (numerically controlled loading processing machines) passed.

US Patent 4,182,312 shows a mechanical scanning of three-dimensional surface information of teeth and surrounding tissues directly on the patient. Here, a probe from the handler is performed in the patient's mouth. However, a mechanical scanning involves certain inaccuracies with it.

U.S. Patent 3,861,044 describes a method which detects the cavity of the tooth photographically. A Wachsfüllkörper is placed by the dentist in the desired final shape.

The method described in the European patent 0054785 requires constructive corrections before the necessary accuracy of fit is achieved. Previously surfaces of organs in their spatial and topographical shape are detected without contact by optical means.

The-indicated in European patent EP-0040165 methods tried using the holographic interferometry to detect and transmit data of a prepared tooth stump. generated with laser light is processed optoelectronically and fed to a computer. This method is 040,165 been described in EP-0; However, such a method could not be carried out in practice until now.

The object of the invention is to provide an actual executable, simple and rapid method for the production of dental prostheses.

This object is achieved in that Höhenschicht- or contour lines on the ground tooth and its surroundings are created, that the lines are detected with an optoelectronic device that from the detected values, the spatial structure of the tooth and the tooth replacement is calculated and that the denture is then fabricated by known per se methods.

Essential for the invention is that contour lines or contour lines on the tooth stump is applied. The present invention differs from the method described in the European patent EP-0040165 in principle in that it is based is an optical method for generating contour lines or contour lines.

The shape of the ground tooth stump that of the adjacent teeth and the antagonist is detected by contour lines or contour lines. The creation of these contour lines or contour lines is done by already known methods such as projection method or moire.

Biem projection method are directly Koturlinien, ie lines that describe the outer shape of the tooth stump, projected onto (Figure 1). The contour lines can be generated by interferometry using a laser or by shadows. When moire method of the tooth stump is illuminated by a grid, and observed through the same grating on a television camera at a distance from the light source. By superimposing the aufprojizierten Schattenmusterns on the tooth stump with the lattice creates a moire that the contour of the tooth stump describes (Figure 2).

The contour lines can be detected with a video camera, where this can be done directly or through optical fibers.

The evaluation of contour lines is carried out in an image processing system. In contrast to line tracking programs, the evaluation on an intensity measurement is fed back, which can be easily performed via a television camera. The intensity is included in the video signal for each pixel.

The calculated contour can then be transferred directly to a numerically controlled milling machine, so that the dentures can be angeferigt exact fit. The dentures can be firmly secured and / or removable.

The inventive method brings with it the advantage that a tooth stump, the adjacent teeth and the antagonists optically detected, evaluated immediately and the shape of the dental prosthesis can be calculated. The process is actually executed, quickly and easily. The production of the dental prosthesis is performed directly without any time gap without contact prints. The denture can therefore be used during treatment.

An advantageous development of the invention is characterized in that at least three different Höhenschicht- or contour line patterns are generated. This procedure allows fully automated manufacture of the denture.

The calculation of the spatial structure of the tooth and the tooth replacement is the following formula based on: (1) I = ax (1 + mx cos θ) In this formula:     I - intensity     a - ground brightness     m - Contrast     θ - angle

The intensity I can be measured. It lies at the Aufnah me with a video camera for each pixel determined. If the video image of 512 x 512 pixels is, so it can be clearly identified and measured, this intensity for each of the pixels from the video signal. In the equation thus remain three unknowns: the underground brightness a, the contrast m and the angle θ. The unknown quantity is the angle θ. If the angle θ for each individual pixel, it is clear from the height coordinate (Z coordinate) can also be calculated for each individual pixel. This height Koordiante z is a function of θ. With the determination of the height coordinate z for each pixel x, y the spatial shape of the tooth and the dental prosthesis is clearly. So the goal is to calculate the height coordinate for each point x, y. To this end it is necessary and sufficient to calculate the angle θ for each pixel x, y. This is achieved not by the equation (1), because this equation contains three unknowns. So you need three equations. To obtain these three equations, one first moves the Höhenschicht- or contour lines pattern by a certain distance in order to obtain in this way a that differs from the first sample pattern of Höhenschicht- or contour lines. then the following equation applies for this second pattern: (2) I (2) = ax (1 + mx cos (θ + θ (2))

The displacement angle θ (2) is known, since it corresponds to the dimension of the line shift. It remains in the previous three unknowns a, m and θ. Then the Höhenschicht- or contour line pattern is shifted one more time. Preferably, the heights of these displacements amount to a quarter to a third of the grid spacing; but there are also other (well-defined) shifts possible. The equation for the third pattern is: (3) I (3) = ax (1 + mx cos (θ + θ (3))

Also, the angle θ (3) is known as predetermined. That from the equations (1), (2) and (3) resulting system of equations thus now allows the calculation of the unknowns θ and thus the calculation of the height coordinate z. When this procedure has been performed for each of the pixels, the overall spatial structure calculated.

The method just described the "phase shift" or "line shift" to produce the prosthetic automatically enables. If only a single Höhenschicht- or contour line pattern is detected and evaluated, must in fact be additionally entered manually, in which direction ascending contour lines and direction extend Descending contour lines. Further still have to enter the areas where shade or fissures lie. The inventive method thus works even if only a single Höhenschicht- or contour lines pattern is taken; but it is then necessary, then fill in the information on the rise direction of the contour lines and the shadows and fissures by hand, which can be done interactively on the screen.

When working with three different contour line patterns or Höhenschicht-, this additional information need not be specially inputted. By the method described above can then y from the three equations (1), (2) and (3) the Z-coordinates for each image point x can be calculated. A separate information on the increase in the course of contour lines is not necessary. The shadows and fissures can be seen that they always lie in each of the three different sample images at the same location.

The evaluation of the contour is effected in that at least three images are input into the computer, wherein each of the line pattern is shifted by a predetermined amount. From the distance of the shift and the change in intensity in each pixel, the contour can be clearly calculated.

An embodiment of the invention will be explained below with reference to the accompanying drawings. In the drawings<ul><li>Figure 1 shows the production of contour lines by projecting and</li><li>Figure 2 shows the generation of contour lines by Moire.</li></ul>

As seen in Figure 1, a projector 1 generates light beams that strike a grid. 2 This grating 2 has opaque regions and horizontal light transmissive portions 3 in a predetermined, preferably equally spaced. Thus, the light beams leave the grid 2 in horizontal, mutually parallel planes 4. hit the tooth stump 5 and there generate contour lines 6. These contour lines 6 on the tooth stub 5 are picked up by the TV camera 7 and the monitor 8 and to the computer 9 forwarded. On the monitor 8, the contour lines 6 can be made visible, as indicated by the reference number 10. The computer 9 calculated from the intensity values ​​for each of the pixels of the monitor the spatial structure of the tooth stump 5. The monitor can consist for example of 512 x 512 pixels.

If only a single image with contour lines is taken, the computer or the information must be entered, in which direction the higher and in which direction the deeper parts of the tooth are. Furthermore the computer or the information must be entered which include areas shadow and / or fissures.

In order to make the system fully automatically, a phase shift or line shift is needed. First, an image is taken with certain contour lines. Then, the projector 1 is vertically moved to the projection axis 11, ie perpendicular to the planes 4, namely by a well-defined height, which preferably corresponds to approximately one quarter to one third of the lattice spacing, that is the distance between the light transmissive portions 3 of the grid second In this way, an offset second line pattern is formed on the tooth stub 5 and taken by the TV camera. 7 This process is then repeated a third time. In this way, get three different contour patterns in the computer 9. The computer 9 can calculate therefrom the spatial tooth stump form completely automatic self. The shade and / or fissures are detected, they are all three shots in the same place and not - as the contour lines - move. These shadows and / or fissures can therefore be later automatically omitted from the calculation by the computer. 9

If only a single layer line image is recorded, the computer must 9 otherwise the information will be given, where is "up" and "down" and where shadows and / or fissures lie. This can be done interactively through the monitor. 8

Figure 2 shows the generation of contour lines by Moire. From the light source 21 light beams are emitted and thrown on a grid 22nd This grid is made of opaque areas and from line-shaped light transmissive preparation surfaces 23. The line-shaped light-transmitting regions are arranged parallel to each other and in a well-defined, preferably equally spaced. The grating plane perpendicular to the axis 24 of the tooth stub 5. Through the grating 5 contour lines are generated on the tooth stub, of which only a single contour line 25 is shown in the picture the second The television camera 7 is located at a distance from the light source 21. The tooth stump 5 is thus illuminated by the grid 22, and observed through the same grating 22 via the television camera 7th By superimposing the aufprojizierten shadow pattern (contour lines 25) on the tooth stump 5 to the grid 22 produces a Moire describing the contour of the tooth stump fifth This Moiré can be made visible on the screen 8, as indicated by the lines 26th The television camera 7 is connected with the monitor 8 and to the computer. 9

The procedure shown in Figure 2 differs from that of the image 1 only in that are generated by the projection image 1 contour lines, while contour lines are generated by the moiré image. 2 So for the process of Figure 2, the statements about the method in other respects to figure 1.