AN APPARATUS FOR TRACKING AND RECORDING THE MOVEMENTS OF A PERSON'S JAW AND THE RELATIVE METHOD

Abstract

Disclosed is an apparatus for tracking and recording the movements of a person's jaw including a reference system with two parts to be fixed to the respective dental arches, an infra-red light projector, a video camera sensitive to infra-red light and a computerized system connected to the projector and to the video camera, wherein the projector projects patterns of points of light onto the face and onto the reference system and wherein the computerized system includes a processing unit configured to process the images taken by the video camera to calculate, for each of these, the distance of at least the points of light that are on the surface of the markers with respect to a pre-determined point with known coordinates, by way of a comparison of the image of the projected pattern with an image of a reference pattern.

Claims

1. An apparatus for tracking and recording the movements of a person's jaw, comprising: a reference system comprising two parts to be attached to the person's upper and lower dental arches, respectively, each part including markers positioned in front of the face; an infra-red light projector; a video camera sensitive to infra-red light, configured to frame a scene that includes at least said reference system; and a computerized system connected to the projector and to the video camera; wherein said projector is configured to project towards the person, in an area that includes at least the reference system, infra-red light beams that generate on the illuminated surfaces a pattern of points of light, wherein the video camera is configured to record with a given frequency the projected images of the afore-mentioned pattern of points of light, at least on the markers of the reference system, and wherein said computerized system comprises: a processing unit configured to receive the images taken by the infra-red video camera and to calculate, for each image, the distance of at least the points of light that are on the surface of the markers with respect to a pre-determined point with known coordinates, by means of a comparison of the image of the projected pattern with an image of a reference pattern; a storage unit for storing at least the images taken by the video camera and the data calculated by the processing unit.

2. The apparatus according to claim 1, wherein generation of the infra-red light beams is of a pseudo-random nature.

3. The apparatus 100) according to claim 1, wherein each part of the reference system comprises three hemispherical markers.

4. The apparatus according to claim 1, wherein the markers have an outer surface consisting of or coated with a reflecting material.

5. The apparatus according to claim 1, wherein the markers are mounted on a rigid support and are positioned at the vertices of an isosceles triangle arranged with its the isosceles triangle's height substantially vertical.

6. The apparatus according to claim 5, wherein, when the reference system is applied to the person, the lower part has the apex of the triangle turned upwards while the upper part of the reference system has the apex turned downwards.

7. The apparatus according to claim 5, wherein the supports and relative markers of the upper and lower parts are identical in terms of shape and size.

8. The apparatus according to claim 5, wherein said support comprises a plate made of an opaque material or a material of a uniform color.

9. The apparatus according to claim 5, wherein said supports are each carried by a rigid supporting element that can be directly fixed to the upper or lower dental arch, respectively.

10. The apparatus according to claim 9, wherein said supporting element comprises a fastening plate, to be fixed to the teeth by means of an adhesive product or by mechanical means, and a rod j (15, 25) that extends from the fastening plate and carries the support at the end.

11. A method for tracking and recording the movements of a person's jaw comprising at least the following steps: providing at least one infra-red projector and at least one video camera sensitive to infra-red wavelengths; providing a reference system comprising two parts, where each part comprises markers; fixing the two parts of the reference system to a person's upper and lower dental arches, respectively, in such a way that the markers are positioned in front of the face; positioning the person in front of the video camera and the infra-red projector; projecting towards the person's face infra-red light beams adapted to form a pattern of points of light, and at the same time to record with a certain frequency images of a scene that includes at least the reference system or the whole face of the person onto which the pattern of points of light is projected; processing the images taken in real time with a computerized system configured to compare each image with an image of a reference pattern and to calculate the distance of at least the points of light projected onto the surface of the markers with respect to a pre-determined point with known coordinates.

12. The apparatus 100) according to claim 1, wherein each part of the reference system comprises three hemispherical markers.

13. The apparatus according to claim 2, wherein the markers have an outer surface consisting of or coated with a reflecting material.

14. The apparatus according to claim 3, wherein the markers have an outer surface consisting of or coated with a reflecting material.

15. The apparatus according to claim 2, wherein the markers are mounted on a rigid support and are positioned at the vertices of an isosceles triangle arranged with the isosceles triangle's height substantially vertical.

16. The apparatus according to claim 3, wherein the markers are mounted on a rigid support and are positioned at the vertices of an isosceles triangle arranged with the isosceles triangle's height substantially vertical.

17. The apparatus according to claim 4, wherein the markers are mounted on a rigid support and are positioned at the vertices of an isosceles triangle arranged with the isosceles triangle's height substantially vertical.

18. The apparatus according to claim 6, wherein the supports and relative markers of the upper and lower parts are identical in terms of shape and size.

19. The apparatus according to claim 6, wherein said support comprises a plate made of an opaque material or a material of a uniform color.

20. The apparatus according to claim 7, wherein said support comprises a plate made of an opaque material or a material of a uniform color.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Further characteristics and details of the invention will be more apparent from the following description, provided by way of non-limiting example, and from the accompanying drawings, wherein:

[0055] FIG. 1 is a perspective view of the reference system of the apparatus according to the invention;

[0056] FIG. 2 is a perspective view of the reference system applied to a person's dental arches;

[0057] FIG. 3 is a schematic view of the apparatus according to the invention in the condition of use.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] With reference to FIG. 1, this illustrates the reference system 1 of the apparatus according to the invention. The reference system comprises two parts 10, 20 to be attached to the upper and lower dental arch, respectively. Each part comprises a supporting element 11, 21 with a curved fastening plate 12, 22 that has a concave supporting surface 13, 23 adapted to be placed against the front surfaces of the teeth D, as shown in FIG. 2. Fixing of the plate 12, 22 typically takes place by means of gluing, although alternative fixing means, for example of mechanical type, would also be possible.

[0059] A curved rod 15, 25, and more precisely curved in a substantially vertical plane, extends from the fastening plate 12, 22. A support 16, 26 comprising a plate in the shape of isosceles triangle is connected to the end of the rod. Preferably, the plate and the rod, which are typically disposable, are connected movably to the support so that the latter can be re-utilized several times for the same person or for different people.

[0060] Three hemispherical markers 18, 28 are applied to the vertices of the triangle, on the front surface 17, 27 of the support 16. 26. Said markers have a reflective surface, for example coated with aluminum powder or with a colored reflective paint, preferably of a uniform color.

[0061] FIG. 3 schematically illustrates the apparatus 100 according to the present invention in an example of use.

[0062] In the example in the figure, the reference system 1 is applied to the teeth of a person P whose jaw kinematics require to be tracked. The apparatus 100 further comprises a projector 40 adapted to project infra-red light beams according to a pseudo-random pattern and a video camera 50 of RGB type sensitive to infra-red wavelengths. The video camera 50 and the projector 40 are positioned side by side, facing towards the person's face, as shown in FIG. 3.

[0063] The projector 40 and the video camera 50 are connected to a computerized system 60 adapted to receive and process the images taken by the video camera.

[0064] The computerized system typically comprises at least a processing unit, a storage unit and preferably also a video interface.

[0065] The computerized system is further equipped with a computer program that allows the processing unit to process the images taken to obtain a three-dimensional digital reconstruction of the movement of the person's jaw.

[0066] The method implemented through said computerized system involves applying a selective filter to the images to search, in succession, for the greatest brightness and color levels.

[0067] Unlike prior art methods commonly used in movement analysis, which are based on calculation of the 2D centers of gravity with subsequent calculation of the three-dimensional coordinates, by means of triangulation, in the present invention three-dimensional data are processed directly.

[0068] In detail, the analysis involves the processing of clouds of three-dimensional points of the scene illuminated with the infra-red light beams and recorded by the video camera. The pattern of light beams projected is of a pseudo-random nature and makes it possible to obtain a set of 3D points of coordinates X, Y, Z, which form the hemispherical surfaces of the markers.

[0069] The processing method of the images then involves applying a filter to all the 3D points by means of statistical operators to eliminate those that do not satisfy certain criteria.

[0070] In particular, the distribution of the distances between the nearby points is calculated and more precisely for each point the average distance between it and all its nearby points is calculated. Assuming that the resulting distribution is of Gaussian type with a mean and standard deviation, all the points whose mean distances are outside a range defined by the global mean of the distances and by the standard deviation are considered as abnormal values and hence removed from the set of data.

[0071] Euclidean clustering analysis is applied to the remaining data, i.e., the data are grouped into sub-groups, or clusters, which comprise the points with mathematical properties “similar” to one another, specifically those belonging to the hemispherical surfaces of the markers. This algorithm makes it possible to identify the clusters in which the elements belonging to them are more “similar” to one another with respect to the elements belonging to other sub-groups. The measurement of similarity is a function of the Euclidean distance between the objects and allows the construction of spherical clusters with similar sizes and densities. These spherical clusters correspond to the markers of the reference system.

[0072] The subsequent processing is the reconstruction of the effective spherical shape, for example by means of the MLS (Moving Least Squares) technique, which performs smoothing and resampling filtering of the data, to eliminate any discontinuities.

[0073] However, the distances calculated and used in the preceding step can, in some cases, be affected by small errors that lead to irregularities in the data that are difficult to eliminate with the statistical method alone. To overcome this, a resampling is preferably carried out to attempt to recreate the missing parts of the surface of the marker by means of polynomial interpolation of higher degree between the surrounding data points.

[0074] In the scientific literature, processes for reconstructing surfaces based on polynomial approximation methods (least squares approximation) are frequently described, but not to obtain interpolated data. Therefore, in the analysis method, the MLS Moving Least Squares approximation variant, associated with appropriate weights, is implemented.

[0075] At this point, the centers of these hemispheres are calculated by means of an algorithm for estimation of the parameters of the spherical surface and for estimation of the normal directions of each point.

[0076] Once the centers of the markers of the two parts of the reference system applied to the person have been defined, the center of the Cartesian coordinate system attached to the lower dental arch and to the upper dental arch is calculated.

[0077] The systems are referred with respect to the movement space of the patient and can provide data relating to the movement between them.

[0078] With the algorithm implemented in the present invention, measuring as reference parameter a distance between two markers, a precision in the order of units per thousand is obtained.

[0079] The invention has been described purely for non-limiting illustrative purposes, according to some preferred embodiments. The person skilled in the art may make many other embodiments and variants, all falling within the scope of protection of the appended claims.