FR2635965A1 - OPTICAL PROBE FOR THREE-DIMENSIONAL MEASUREMENT OF TEETH IN THE ORAL CAVITY AND METHOD OF IMPLEMENTING - Google Patents

Abstract

An optical three-dimensional measurement probe 1 for measuring the three-dimensional geometry of the teeth in the oral cavity is designed so that it is possible to carry out on the same object several known measurement methods such as triangulation, optical cutting, phase shift, stereo-photogrammetry as well as a large number of variants of the three-dimensional optical measurement as they are known in the technique of industrial measurement, such as for example optical networks in Gray code. This is achieved by the fact that the probe 1 comprises a two-dimensional matrix light source 7, 8, punctually programmable, of high resolution, that a digitized projection model is placed in an image memory 5 and controls the matrix light source 7 , 8 via a video interface 9 and that this image is projected onto the surface of the tooth to be measured by means of image optics 6.

Description

Optical probe for three-dimensional tooth measurement

  in the oral cavity and method of implementation.

  The invention relates to three-dimensional measurement.

  teeth in the oral cavity using a probe.

  Three-dimensional optical measurement of teeth directly in the patient's mouth provides digital construction data for fabrication

  computer-assisted dental prostheses without

  semi-auto digital milling technique

  matic or fully automatic. Currently, we

  three systems are born which function according to this principle: a) A French system produced by the firm Hennson Int. of France and based on the work of Dr. Duret, uses a laser triangulation process for the punctual measurement of the distance between the surface of the teeth and the optical probe introduced into the patient's oral cavity. These distance probes are also known in the industrial measurement technique. They perform a point measurement of the distances or they can, by laser scanning along a line, measure the coordinates of the relative height of the object explored along

  of a line. Since we usually use-

  For optical sensors of CCD line sensors, we obtain point matrices from 256 to 4096

picture points.

  b) A Swiss system, from the firm BRAINS, Brandistini

  Instruments, called CEREC, also works se-

  lon the optical cutting process, known in the

  industrial measurement technique. According to this process

  From the start, a single light line or a parallel grid of light lines is projected onto the surface and observed using a two-dimensional camera at a parallax angle. The relative height can be deduced from the curvature of the cutting lines

optical.

  An improved variant of this method is known, called phase shift method. It uses a network

  optics produced by interferometry with sinu-

  brightness soid in contrast to the cuts

  binary optics. By taking pictures of the ob-

  jet for different phase relation positions of

  this network, we can obtain a specific point density

  significantly higher height values and we can

  digitally eliminate disturbances such as inconsistency

  tance of the background brightness and contrast instability

  due to local variations in the re-

bending.

  c) A method currently being developed at the Universi-

  Minnesota summer under the direction of Dr. Dianne Recow, and using a laryngoscopic probe

  takes multiple photographic views of the surface

  teeth to, after development, explore and digitize them using a document scanner

  and use them in a computer according to procedures

  dice known in photogrammetry for stereo-restitution.

  All optical dental probes used

  to date are characterized by the fact that they do not use

  read, due to their construction principle, that only one of the possible methods (triangulation by laser or optical cut or phase shift or stereo distance measurement). However, each of these methods has a series of advantages and disadvantages: a) The laser beam methods for triangulation or

  phase shifting processes suffer strongly-

  stain formation caused by coherent light. This gives rise to disturbed height images and therefore to a significant decrease in resolution.

  b) Optical cutting and phase shifting processes

  constant bucket suffer from ambiguity issues

  in the case of steep slopes. These gradients

  tions move the light line or phase relationship of the sinusoidal lattice by more than one constant

  network. It is then no longer possible to meet

truce the drop.

  The three-dimensional optical dental probes known to date determine the three-dimensional process to be used by their very construction. They are not

  editable, with the exception of a few parameters

  adjustment such as scanning frequency, phase shift, focus, magnification. It is therefore not possible

  apply with the same probe to the same object pro-

  transfer of additional measurements such as triangulation, optical cross-section, phase shift and stereo-photogrammetry of

  same as a whole series of variants of the opti-

  than three-dimensional known from industrial measurement techniques, such as, for example, networks

  optics coded in Gray code, in order to combine the advantages

  tages of these processes and avoid their drawbacks.

  This object is achieved according to the invention by the

  makes an optical dental probe for three-dimensional measurement

  teeth contains a matrix light source

  high resolution, two-dimensional, programmable

  free punctual tion, that a digital projection model

  sé is produced by a computer using a programmed mathematical or graphical process, which is put into a

  image memory and displayed on the matrix light source

  cielle via a digital / analog interface and is projected onto the surface to be measured by projection optics. According to the invention, the sources

  these light matrixes used are mo-

  niters or, video control screens, preferably,

  projection tubes with fine lines or light modulators

  spatial (in English: "spatial light modulators").

  The latter in particular exist in the form of video control screens with liquid crystals, black and

  white or colors, available at low cost in the devices

  miniature television reils and it's easy to integrate them into a dental probe like this

  of electronically controlled "slide". The light source

  dot matrix can also be formed by a scanner

  XY with optical light modulator.

  The essence of the invention will be described by way of nonlimiting example by taking the example of a probe.

  dental having a liquid crystal light modulator

  as a programmable light source. By an example of a process, we will also show how the programmability of the projection model makes it possible to project different calibration marks and / or measurement models in

  rapid succession and to process these images according to different

  many methods of interpretation to eliminate the

  above mentioned spots, ambiguities, etc.

  Advantageously, a light is projected cons-

  aunt without model for visual observation as well as

  for automatic detection of gray areas.

  Advantageously again, successive grid models of different local frequencies are projected and thus approximate and fine measurements are made.

free of ambiguities.

  Successive coded light models are

  projected and interpreted, or else we project onto the

  face of the teeth to be measured stored models and reference images, or surface images

antihomologic occlusion.

  Advantageously, local height measurements are carried out by the triangulation process, by

  spot projection of different image points.

  Advantageously also, by means of a color matrix light source, colors are projected which optimize the contrast between the surface of the teeth.

and the gum.

  Other features and advantages of the

  vention will emerge from the following description, made

  by way of nonlimiting example. Reference will be made to the appended drawings in which: FIG. 1 shows by way of example the

  logic diagram of a dental probe according to the invention

  tion. Figure 2 shows for example a series of projection models as they can be used

  in the application of the phase shift process.

  The essence of the invention will be described according to an exemplary embodiment in accordance with FIG. 1. The model to be projected is projected onto the surface of the teeth to

  measure using endoscopic optics 1. Two

  x optical line 2 conducts an image of the surface

  teeth thus identified on a two-way video camera

  sional 3 which delivers its data to the image computer 4 ensuring the operation. The model (s) to

  project are created in digital mode by the same computer

  nator or by a second image computer, put in digital mode in the projection image memory 5 and transformed, passing through a digital / analog interface and a video interface 9 into a video signal for controlling the monitor matrix liquid crystal video 7. This liquid crystal screen is, thanks to

  a lighting device 8, irradiated with a light cons-

  aunt and punctually modulated under high resolution and with a large number of possible gray degrees of constant light. The modulated light ray is, by means of an image optic 6, represented in the endoscopic optics and it is projected onto the surface

teeth.

  Figure 2 shows by way of example, a

  series of projection models which, together with the previous probes

  could not be obtained without changing the probe. In a first step, the projected model 1 is "all white". You can easily control the orientation of the probe, the sharpness adjustment, etc. on the screen of the image processing system (10,

  Figure 1) without the appearance of disturbing bands.

  On the other hand, the gray areas are signaled automatically.

  only by direct interpretation of brightness, areas in which subsequent three-dimensional measurement

  will be impossible or uncertain. A second model of pro-

  jecticn 2 can be composed of benchmarks for example, of which

  the deformation makes it possible to calculate calibration data

  ge (image ratio, distance to a reference level, etc.). From the ellipse deformation of a circular reference frame, we can obtain the image ratios, the

  position of the bottom in space and other necessary data

  calibration of the entire optical system.

  Model 3 is for example a large sinusoidal grid

  safe for implementing a phase shift process

  at low resolution. This model is taken in three different

  annuities phase relations 3a, b, c and makes it possible to obtain a rough height image of the tooth. As a result of

  the grid constant high there are no ambiguities.

  The model 4a, b, c consists of a much finer sinusoidal grid and allows a height measurement of

  high definition, but there are ambiguities.

  They can be eliminated by means of the results of the rough measurement 3. Finally, it is possible for example to

  take a series of pro-

  dental floss stored digitally and project them on the tooth to assess directly in visual mode on the connected control screen (10 in Figure 1) the quality of the agreement and possibly choose an existing model of teeth. It is not necessary to recall here the particularities of the phase shifting process because they correspond to the state of the art and are

  sufficiently published. Similarly, we will not explain

  Advantage other methods of three-dimensional measurement, such as triangulation methods, photogrammetry, coded projection model and others because they are published

in the state of the art.

  Another characteristic of the invention is to project a reference image, such as, for example, the memorized image of the occlusion surface of the tooth.

  antihomologist, to observe the occlusion problem.

  When using liquid crystal video screens

  of, for colors, as they already exist on the market, the attending physician can, independently of the three-dimensional measurement of the tooth to be treated, directly and visually assess the problem of occlusion. The example given shows the extent of the new possibilities opened by the optical three-dimensional measurement probe with free programming projection model compared to the possibilities

  rigid and limited that optical probes offer

currently naked.

Claims (16)

  1. Optical three-dimensional measuring probe for measuring the three-dimensional geometry of the teeth in the oral cavity, characterized in that the probe (1) comprises a high-resolution matrix light source (7), two-dimensional, and free   ad hoc programming, that a naked projection model   merited is put in an image memory (5) and controls the matrix light source (7) via   a video interface (9), and that this image is projected   ted on the surface of the teeth to be measured through- re image optics (6).   2. Probe according to claim 1, characterized in that the matrix light source (7) is formed by a video monitor.   3. Probe according to claims 1 and 2, charac-   terrified by the fact that the video monitor includes a video projection tube.   4. Probe according to claims 1 and 2, charac-   terrified by the fact that the matrix light source   (7) consists of a spatial light modulator.   5. Probe according to claims 1 and 4, charac-   terrified by the fact that the light modulator used   is a liquid crystal television screen.   6. Probe according to claim 5, characterized in that the liquid crystal screen is a screen black and white.   7. A probe according to claim 5, characterized in that the liquid crystal screen is a color screen. 8. Arrangement according to claim 1, characterized in that the matrix light source   (7) consists of an XY scanner with light modulator re optics.   9. Method for optical three-dimensional measurement of teeth in the oral cavity by means of a probe   optical (1) which contains a matrix light source-   the programmable according to claims 1 to 8, character-   laughed at by the fact that standard benchmarks are projected   swimming and / or successive measurement models.   10. The method of claim 9, character-   laughed at by the fact that we project a constant light without model for visual observation as well as for   automatic detection of gray areas.   11. Method according to claim 9, character-   se by the fact that we project successful grid models   different local frequencies and that   thus reads approximate and fine measurements free of ambiguities.   12. The method of claim 9, character-   se by the fact that models are projected and interpreted the successive coded lights.   13. The method of claim 9, character-   affected by the fact that we project onto the surface of the teeth   to measure memo reference models and images laughed.   14. The method of claim 9, character-   affected by the fact that it is projected onto the surface of the teeth   to measure images of the anti-occlusion surface -   counterpart. 15. Method according to claim 9, characterized   by the fact that local height measurements are exe   cut by the triangulation process, by projection   point of different image points.   16. Method according to claim 9, characterized in that by means of a matrix light source- the (7) colors are projected colors which optimize   the contrast between the surface of the teeth and the gum.