Optical impression-capturing device

Abstract

The invention relates to an optical impression-capturing device that is capable of capturing images for the three-dimensional reconstitution of a dental object representing at least part of at least one dental arch, the device comprising: in a support part of the dental impression tray type suitable for at least partially covering the dental object, an optical assembly having: - a light-emitting system comprising light sources (3') for illuminating the dental object; - optical modules (1) having light-measuring sensors distributed in a bottom wall (4) of the support part oriented, during image capture, towards the dental object, the optical modules (1) being capable of capturing the direct light rays emitted by the light-emitting system and indirect light rays originating from the optical assembly and from the dental object; and also means (2) for protecting the optical modules (1) that allow the passage of light rays.

Description

[0001] Title: Optical Impression Taking Device

[0002] The present invention relates to an optical impression tray device usable for taking three-dimensional and temporal impressions in dentistry. This device is similar to traditional impression trays that operate with molding materials, but includes optoelectronic imaging systems using light sources and optical measurement sensors to digitize at least a portion of a dental arch. The device must then be connectable, by cable or wirelessly, to a hardware and software system that first transmits the information collected by the sensors, and then performs the sequencing, storage, processing, and / or visualization of this information to enable the taking of an optical impression in one or more captures.The field of application of the devices of the invention also implies particular constraints, for example a protective hermeticity of the electro-optics due to the existence of mandatory disinfection products in the medical field.

[0003] The present invention is intended to facilitate and optimize the capture of at least one three-dimensional view of all or part of a dental arch, either in the mouth or on a reproduction model. One of the objectives is to simplify the positioning of the device so as to maintain it in the ideal focal zone to ensure good image capture without hindering any movements necessary for correct three-dimensional reconstruction. One of the difficulties lies in the fact that the captured 3D surface information may contain blind spots resulting in particular from stray reflections and light artifacts that can be caused by illumination from light sources in the dark environment of the mouth.

[0004] The device of the invention must in practice limit these blind spots by significantly reducing light reflections on the different locations on the walls of the device which are in the path of the light rays, but which also appear on the surfaces of the teeth, gums or bone, while preserving the conditions for good disinfection of its surfaces.

[0005] For 50 years, one of the inventors of this application has proposed several devices or methods using optical or ultrasonic measurements in a patient's mouth as a means of making diagnoses, for example, in the clinical study of orthodontic movements using brackets or aligners, or for designing and manufacturing dental prostheses and implants by combining a computer with a numerically controlled machine tool. Work has also been carried out on the remote fabrication of prostheses based on data derived from digitized dental objects. The corresponding inventions have been the subject of patents such as documents EP 0040165 and EP 0091876, relating to taking impressions by optical means, and, more recently, documents WO2011 / 154656 and WO 2019 / 145658, which also relate to an optical impression tray.

[0006] If these documents do indeed correspond to the needs of modern dentistry, in particular what is described in the latter cited, it turns out that in practice, the implementation of these inventions has required additional research to facilitate their exploitation, which is in particular the subject of this application.

[0007] We also know of many documents in which solutions are proposed to problems falling under the same overall objective of digitizing optical data.

[0008] This is the case, for example, with US patent 2017100219 A1, which describes an impression tray comprising assembleable and detachable elements, including sensors capable of taking an impression of a tooth or arch. These electro-optical devices are used in conjunction with a traditional molding material. US patent 2015118638 A1 also discloses an impression tray, specifically consisting of a platform and a channel, equipped with optical sensors for obtaining images which, when combined, are intended to determine the sulcus depth in an edentulous patient for the purpose of fabricating their prosthesis. However, such an impression tray was not designed for surface imaging of the mouth. US patent 2017128173 A1 also describes an optical scanning device comprising a handle for an operator and a mouthpiece incorporating a mobile 3D scanner.This document describes methods for moving the 3D scanner inside the mouthpiece. The mouthpiece contains a partially transparent casing within which mirrors move to scan and digitize the mouth. While such a device may initially appear simple to use, its application has major clinical limitations. Indeed, regardless of the 3D scanner's movement capabilities within the mouthpiece, not all dental surfaces can be reached, and therefore not all can be measured with the same precision. Furthermore, not all surfaces can be reached at all times. Moreover, to ensure all teeth are visible, extensive adjustments are necessary, particularly depending on the size of the mouth. Finally, all devices that have attempted to use this type of mechanical movement have encountered sterilization problems.

[0009] Similarly, US patent 2002 / 064752 A1 describes a mechanically driven trolley that is very complex to operate, primarily in the mouth. This device consists of a rail that follows the shape of the dental arch, along which a device moves that is capable of scanning the buccal and lingual surfaces of the teeth in the arch. In practice, it is difficult to use in the mouth due to the anatomical variations in the shapes of human jaws. US patent 2015 / 079534 A1, on the other hand, presents a well-known articulated solution for impression trays, allowing for the three-dimensional reconstruction of dental arches, but which requires complex calibrations and, consequently, extensive training for practitioners: it is therefore not a user-friendly or easy-to-use tool.

[0010] However, as shown by one of the inventors of the device of the present invention, in document US 11,357,601 B2 (WO2019 / 145658), there must be virtually no movement in the optical impression tray supporting the cameras if one wants to preserve the minimum accuracy required in dental clinics, which must be a few tens of microns, so as not to have to recalibrate the device for each measurement and for each patient.

[0011] Most of the above-mentioned devices struggle to meet the clinician's objectives, namely to have a system that covers the entire mouth and gums, without any mechanisms that could malfunction during use and / or, above all, without requiring calibration for each image. While a slight movement of a few millimeters is acceptable and even desirable during the image capture to compensate for the natural and physiological movement of any patient, one of the objectives is for the device itself to remain static, ensuring very rapid image capture, lasting only a few seconds. Furthermore, such a device must require minimal training, be user-friendly for the dentist, and comfortable for the patient, both in its use and its size within the mouth.Finally, its cost must remain affordable for the daily practice of a dental practice or laboratory, which is notably impossible in the so-called "mechanically moving" systems seen previously.

[0012] The aim of the present invention is to provide an easy-to-use optical impression tray that allows for spontaneous insertion by the dentist and provides measurement accuracy to within a few tens of microns. A non-traumatic shape, similar to traditional impression trays using molding materials as long employed by dentists, is used because it has proven satisfactory for both patients and dentists, without requiring any changes to their practices.

[0013] As explained in document FR 18 50689 from the same inventor, the objectives of such devices also include collecting and measuring, simultaneously or in a very short time, the shape and shade of the tooth surfaces, as well as the gingival surfaces and possibly the bone contours for surgical purposes. It may also be necessary to measure the intercuspation of the maxillary teeth in relation to the mandible in occlusion, and possibly their movements.

[0014] The specific conditions of intraoral imaging, particularly in terms of lighting and humidity, present numerous challenges in the design and development of such devices. For example, some cameras are "dazzled" by the LED lights positioned in front of them during image capture. Similarly, specular reflections from these same LEDs on the surface of teeth, which are generally white and very bright, often saturate the sensors, rendering them unable to capture certain useful information. Furthermore, cameras positioned too far from the focal plane of the image, which is of course located at the level of the teeth, result in reduced system accuracy. Finally, color variations within the mouth, especially between the gums and healthy or damaged teeth, can lead to measurement errors.

[0015] The present invention aims to provide industrially acceptable, clinically usable, and cost-effective solutions to all the aforementioned problems, with the objective of achieving the previously mentioned precision on the order of a few tens of microns, regardless of the surface area of ​​the body being measured. The necessary information must be captured with a minimum of blind spots, which often correspond to specular reflections of light sources on the teeth, resulting in areas without information. The expected results are consistent diagnostic quality and good adaptation of prostheses made from the model constructed using optical impressions taken with the invention, without requiring the practitioner to perform overly complex manipulations or training.

[0016] The solutions that will be given in the following are not limited to impression trays applicable to gingival and dental surfaces, but are intended to apply to all three-dimensional imaging systems using multi-camera devices operating with artificial (LED, plasma, laser...) or natural (sun) lighting.

[0017] In fact, more precisely, the invention applies to an optical impression taking device capable of taking pictures for the three-dimensional reconstruction of a dental object representing at least a part of at least one dental arch and comprising in a known manner, in a support piece of the type of dental impression tray or fraction of a dental impression tray adapted to cover at least partially the dental object, an optical assembly having: a light emission system comprising light sources to illuminate the dental object; optical modules with light measurement sensors distributed in a back wall of the support piece oriented, during the taking of pictures, towards the dental object, said optical modules being capable of capturing the direct light radiation emitted by the light emission system, and indirect light coming from the optical assembly and the dental object.

[0018] According to the invention, this device is such that it includes means for protecting optical modules, said means of protection allowing the passage of light rays.

[0019] In short, the present invention comprises an impression tray including cameras and light projections whose internal arrangement, the object of the invention, has been designed to limit, or even eliminate, areas of light reflection and brightness on the teeth in order to allow the sensors to optimally collect the information necessary for accurate 3D reconstruction by stereoscopy in structured or unstructured light. Given the humid environment of the mouth and the presence of disinfectant chemicals, means of protecting the optoelectronic components are provided.

[0020] More specifically, what can be described as an optical impression tray within the meaning of the invention, usable for diagnosis and two-dimensional, three-dimensional, and temporal measurement in the dental and medical fields to ensure accurate capture of information in the mouth or on a plaster model or one obtained by stereolithography, consists in fact of a device comprising, within a shell (the support piece containing the optical assembly) adapting to the shape of the object to be analyzed, a number of optical and optoelectronic components. These components are distributed in one or more planes and / or on a curved shape, regular or irregular, whose "field of view" covers all or part of one or more teeth, or one or two dental arches to be visualized or measured by means of one or more light sources.These can be identical or different, Lambertian and / or direct or indirect specular, the intensity and exposure time of which are automatically set by a control software for the device of the invention.

[0021] Optical rays are transmitted either directly or by means of optical systems that may include fibers, diffusing materials, reflectors, and / or mirrors, used individually or in combination. As will be seen later, the device may include LED-type sources, but also radially diffusing glass fibers, or even molded optics.

[0022] The necessary protective measures in such an environment can be of several types. Thus, according to one variant of the device, the protective measures for the optical modules consist precisely of at least one flat, non-reflective, transparent plate designed to be placed on the dental object and to separate the back wall from the dental object, with the lateral edges of said plate joining the back wall. It must allow for a position of support and / or spontaneous sliding of the assembly on the teeth and ensure the partial or total sealing of the optoelectronic system against external damaging factors. It therefore also has a mechanical function for positioning on the dental object, guaranteeing a correct focal length for the optical modules, while allowing for slight movements (by sliding) to enable the acquisition of multiple images, if necessary, for a photogrammetric procedure.

[0023] It should be noted that we know, through the US document 2021 / 0045852, of a system for performing intraoral scanning, whose sensors are held by a rigid body which may be opaque except for one or more windows located at the right of said sensors, but these windows only have the function of letting light through, and do not intervene in the positioning.

[0024] To address the previously mentioned issue of light reflection and brightness zones, the transparent plate used in the invention is a non-reflective glass. It may be a transparent plate coated with an anti-reflective film on at least one side to eliminate reflections as much as possible and improve the signal-to-noise ratio. The transparent plate may also be a polarizing glass.

[0025] Various configurations are possible for the light sources of the lighting system. For example, at least some of the light sources can be integrated into the back wall around the optical modules. This results in direct lighting composed of sources, for example LEDs, placed around the cameras and directly illuminating the scene, with or without a transparent panel. In the latter case, the protection for the electronic system is located directly at the level of and in front of the cameras and LEDs (see below).

[0026] Alternatively, or in combination, at least some of the light sources may be placed in the support piece so as to emit light towards the back wall of said support, said back wall, or at least a layer covering it having reflective properties. This constitutes the implementation of indirect lighting of the dental instrument, which may be in addition to direct lighting.

[0027] According to yet another possibility, at least some of the light sources of the light emission system can be placed in the support piece so as to emit light simultaneously towards the back wall of the support and towards the dental object, said back wall or at least a layer covering it having reflective properties.

[0028] In the latter case, indirect lighting is useful in suppressing specular reflections, and direct lighting is useful in suppressing parasitic reflections that occur during the illumination phases of the dental object, whatever it may be (a complete dental arch, a portion of such an arch, the lateral faces of two portions of arches in contact...).

[0029] According to the invention, the light sources of the light emission system can be placed in the support next to the two lateral edges of the transparent plate.

[0030] In this case, preferably, the light sources are positioned in the plane of the transparent plate, at least along one lateral edge of said plate, opposite a reflector located on the opposite side of the transparent plate from the back wall and oriented so as to reflect the light rays simultaneously towards the dental object and towards the back wall of the support. Indirect lighting is directed towards the back wall of the support piece, and direct lighting is actually lateral lighting of the dental object.

[0031] In one possible configuration, the reflector has a flat reflective surface inclined relative to the transparent plate at an angle between 30° and 60°, preferably 45°. In addition, preferably, a diffusing translucent window is interposed between the reflector and the dental object: the diffuse lateral illumination it provides helps to suppress unwanted reflections.

[0032] The configuration of the device can, however, change depending on the portion of the support being considered and the tooth facing it. Thus, the optical treatment of molars is not performed in the same way as that of incisors, for example, due to the different morphology of these two types of teeth. For molars, the device of the invention exhibits a form of symmetry, and the two lateral surfaces (vestibular and lingual) of the tooth are treated, optically speaking, in essentially the same way. For an incisor, on the other hand, for one of the lateral edges of the transparent plate, at least one additional optical module and a light-emitting system are placed on the opposite side of the transparent plate from the back wall, and facing the tooth. These components are therefore positioned, during a single imaging phase, directly lateral to one surface of the tooth, in this case, the buccal surface.

[0033] In addition to the type of tooth illumination configuration discussed so far, the surface finish of certain parts of the device is also a parameter to consider, since these parts may act as diffusing elements within the optical assembly of the invention. Therefore, the back wall of the support is preferably white. The surface grain size also plays a role in ensuring the effectiveness of the white diffusing element, particularly in preventing concentrated reflections, which are the opposite of diffusing. The reflection should be as random as possible, meaning it should not distinguish between incident light sources. To this end, the back wall of the support preferably has a fine grain size.

[0034] To limit or reduce reflections, according to the invention, the device is designed such that the light spectrum of the light sources and the light spectrum of the light measurement sensors of the optical modules are between 380 nm and 550 nm; that is, they are practically selected to be close in range. This aims to improve the signal-to-noise ratio without reducing the luminous power of the light source.

[0035] Depending on the configuration, particularly suited for devices used to treat dental arches or portions thereof, the back wall of the support piece is, in cross-section, arched or domed. This curve creates a curved surface that allows the support piece to cover the teeth, and the optical beams to access their occlusal surfaces as well as their lateral surfaces, for a complete restoration without inaccessible areas.

[0036] According to a variant of the invention, the protective means may consist of an overmolding on the back wall of the support, forming a molded optical layer covering the optical modules, said layer being reflective. There is then no longer a flat transparent plate, and the aforementioned problems related to reflections or spots of light on said plate disappear. The overmolded layer ensures a seal and consequently protects the optical modules, and it does not disrupt their operation; moreover, it becomes an integral part of them in the portion that covers them.

[0037] Specular reflections on tooth enamel are also reduced with this second variant, but the preservation of the distance between the teeth and the optical modules is no longer guaranteed.

[0038] This is why this variant may include at least one mechanical stop against the dental object, in order to preserve as much as possible the focal distance between the observed dental object and the optical modules. The physical stop, which does not necessarily have any particular optical properties, encroaches on the dental object and results in the creation of blind spots that are detrimental to data analysis, which must then be removed during software processing: these spots are, however, easy to recognize, especially following the movements that have occurred between several captures, and therefore relatively easy to "erase" in software.

[0039] In the device of the invention, the light sources of the light emission system are chosen from among coherent or non-coherent light-emitting diodes (LEDs), optical fibers, plasma sources and halogen sources. These different types of sources can also be combined with each other.

[0040] In one possible configuration, the light emission system can consist of an array of light sources, for example, LEDs embedded in a transparent or diffusing matrix. Grids can also be placed in front of the light sources to create structured light. The light is then structured as the projection of such a grid onto the dental object. The grid can take many forms. In this configuration, the light sensors are not equipped with grids, so as not to reduce the signal intensity.

[0041] Another possibility is to place Fresnel lenses in front of the light sources. The homogenization of the radiation resulting from its passage through Fresnel lenses reduces its specularity.

[0042] The light sensors of the optical modules used in the device of the present invention are, for example, of the CCD or CMOS type. Furthermore, the optical modules may include at least one static or dynamic optical system, such as lenses or fibers, associated with the light sensors. These features allow for better control of the depth of field during the capture of optical information.

[0043] According to yet another possibility, polarizing filters can be placed in front of the light sources and in front of the light sensors. The polarizing filters placed in front of the light sensors filter the light signal in a direction perpendicular to the filtering direction of the filters placed in front of the light sources. This solution is particularly applicable in cases of direct illumination, and when the protective measures consist of overmolding the optoelectronic components.

[0044] In summary, the device of the invention functions as an optical impression tray schematically comprising information capture cameras and light projections and whose internal arrangement, the object of the invention, has been organized to limit, or even eliminate, areas of light reflection and brightness on the teeth and on certain parts of the device in order to allow the sensors to best collect the information necessary for a good 3D reconstruction, by stereoscopy, in structured or unstructured light.

[0045] Other objects and advantages of the present invention will become apparent in the following description, relating to embodiments which are given only by way of illustrative examples. The understanding of this description will be facilitated in particular by reference to the figures attached in the appendix, for which: Figure 1 shows a sectional view of a first variant of the optical impression-taking device of the present invention, in its portion adapted for the treatment of premolars and molars, comprising direct light sources and a transparent protective plate; Figure 2 shows the same sectional view of another variant with direct light sources and without a protective wall;

[0046] - Figure 3 shows said cross-sectional view of yet another variant of the optical impression taking device of the present invention, comprising indirect light sources; Figure 4 illustrates a variant of the optical impression taking device of the present invention, with light sources simultaneously providing direct and indirect illumination; Figure 5 represents a cross-sectional view of the portion of the same variant of the invention intended for the treatment of incisors / canines; - Figure 6 illustrates a second variant in which the light sources are radially emitting optical fibers; and Figure 7 shows yet another variant in which the means for protecting the optical modules with light sensors are overmolded directly in contact with them.

[0047] In the configurations shown, the support piece for the optoelectronic components is designed to capture images of at least a portion of a dental arch, and is therefore canal-shaped so that the optical rays can access not only the occlusal surfaces of the teeth, but also their buccal and lingual lateral surfaces. The optical modules 1, acting as cameras or image sensors, are integrated into a back wall 4, which in this case forms—in cross-section—a dome or an arch, within which they are angularly distributed. The view is in cross-section; therefore, rows of cameras 1 must be visualized within the canal-shaped form that the support piece takes in three dimensions. Their positioning within the back wall 4, indicating their distance from the dental object to be observed, depends on their angular position, so as to adapt their focal length to said object appropriately.A transparent plate 2, for example made of glass, can be attached to the support piece at the lateral edges of the back wall 4. This is the case in the configuration shown in Figure 1. It serves to position the device on the teeth and helps to control the depth of field. It also provides a seal against the external environment. Movements obtained by slight sliding of the plate 2 on the teeth are possible, which can be coupled with the triggering of the images so that several images of the dental object can be captured, thus improving its 3D reconstruction by photogrammetry.

[0048] Plate 2 (which can be made of natural crystal such as quartz, glass, or synthetic material) is simply a mostly passive protective glass. It is also preferably treated, at least by the addition of at least one anti-reflective coating on one of its surfaces. The physical and chemical characteristics of the protective, positioning, and sliding plates are an important element of the device of the invention, as said plates 2 must facilitate the use of the device while reducing unwanted reflections on the teeth, gums, and palate, as well as on the device's walls themselves. They must also avoid increasing reflections on their own internal and external surfaces during the passage of radiation, and in particular, minimize the effects of reflection and refraction as much as possible.

[0049] Physically, these protective plates must be as rigid as possible. They must allow the practitioner to use the teeth as a guide to spontaneously and intuitively position the cameras 1 and / or light sources 3 within the correct depth of field. This ensures the ideal position for optimal precision and resolution.

[0050] Chemically, and to resist scratches from teeth naturally composed of hydroxyapatite crystals, but also of ceramics that can be very hard (Zircone) in prosthetic restorations, these transparent protective, positioning and sliding plates are made of a very hard natural material (for example quartz, crystalline filled silica...) or synthetic material, for example cast silica like JGS1 UV quality,

[0051] To also reduce reflections on surfaces, and to get closer to polarizing filters without having to use them, because they are expensive in terms of product and assembly, it is possible to use anti-reflective coatings on one or more of the surfaces of the plates 2. These coatings can be placed on the outside and / or inside of the device, on all surfaces that can be crossed by the radiation leaving the light sources 3' towards the teeth and / or returning to the sensors 1.

[0052] These walls and treatments must resist as best as possible external physical, chemical or bacteriological aggressions, such as scratches from teeth, or thermal and plasma aggressions, or even chemical cleaning and disinfection products.

[0053] These walls may also contain a heating and / or cooling thermal system limiting the appearance of condensation inside and / or outside the device and possibly contributing to the internal thermal regulation of the electronics.

[0054] In the device of the invention, the direct lighting source is composed of sources 3', for example LEDs, integrated around the cameras 1 and directly illuminating the scene. The light sources 3' induce unwanted reflections in the glass, adding to the reflections on the teeth during oral exposures, which can lead to unusable areas.

[0055] These "blind" areas can be made visible by a clinical manipulation by the operator, consisting of slightly moving the impression tray on the teeth. The operator proceeds as follows: first, they capture the information. This captures areas that are perfectly measurable and of very good quality in terms of information, especially since the position of the protective / gliding plate is not significantly altered. However, some areas lack information because the sensors are "dazzled" by reflections on the teeth and on the external and internal surfaces of the sliding walls. Second, the operator slightly slides the device on the teeth, which has the effect of shifting the reflections and making the previously unmeasurable areas perfectly measurable.Since these new areas are wholly or partly connected to previously measured areas, total and accurate 3D reconstruction is made possible by this simple clinical procedure, eliminating blind spots.

[0056] In this configuration of the device, under direct illumination (which can also be implemented under at least partially indirect illumination, as will be seen later), polarizing filters can also be used, for example integrated into the protective wall, which eliminate reflections on the teeth and on the transparent plate 2 used for protection, positioning, and sliding. These filters can also be placed in front of the light sources 3' and, at an angle depending on the type of polarizing filter composition, generally around 90°, in front of the data acquisition cameras 1. More precisely, the first filter placed in front of the emitted light polarizes it, while the second, placed in front of camera 1, for example at 90° to the first, filters a large portion of the specular rays on the shiny surfaces of the teeth according to the well-known principle of Nicol prisms.These filters reduce the brightness of the light sources, necessitating an increase in the lighting system's power, but this also leads to a reduction in reflections on the teeth, which somewhat harmonizes the lighting and allows for a good overall measurement of the surfaces. Plate 2, located against the teeth, if present in the configuration, then serves only for protection, positioning, and sliding.

[0057] In Figure 2, the device is virtually identical, without the protective plate 2. The protective wall for the optoelectronic components is positioned directly at and opposite the cameras 1 and the LEDs 3'. It can cover a single sensor unit 1 or LED 3', or a group of one or more LEDs 3' and sensors 1. This configuration avoids reflections directly onto a sliding glass panel, which is not present, but requires the practitioner to hold the device in suspension. This configuration is particularly well-suited for use in prosthetic laboratories or dedicated rooms in dental practices, especially if a support arm is used to hold the device.

[0058] This corresponds to a field of application for the device involving measurements and diagnostics (orthodontics and periodontology) on plaster supports or various synthetic materials (additive method, for example, by stereolithography, or subtractive method for the fabrication of implant guides, orthodontic splints, or whitening trays, etc.). Since these materials have little or no specular reflection, the problem of reflections on the measured surface is significantly reduced, simplifying and accelerating the process while increasing accuracy. The use of polarizing filters is, of course, also possible in this plate-free variant. In the configuration shown in Figure 3, the light sources 3' are indirectly illuminated. There are no longer any light sources around the cameras 1, but they are positioned in front of the back wall 4, from which their rays are reflected and redirected towards the teeth.This wall 4 therefore becomes a reflector that directs the light from the light sources 3' towards the teeth after reflection. It can be a reflective mirror (as in car headlights) and the reflected light will be specular and perfectly circumscribed, or it can be made of a diffusing matrix that reproduces, in a Lambertian manner, the light that has struck its density. The light sources 3' are placed around the perimeter of the support, either inside the arched back wall 4, as in the figure, or outside of it.

[0059] This configuration can lead to overexposure of certain radiations (around 60° and at grazing incidence). To limit this effect, which can lead to overemphasis of certain points used as a basis for the stereoscopic 3D reconstruction of dental surfaces, to make the cameras appear on the teeth, or to dazzle cameras close to horizontal, it is possible, in these overexposed areas, to cover the protective plate 2 with a more or less opaque mask.

[0060] It is obviously possible to combine the direct light sources 3' placed around the cameras 1 as in the first variant with the indirect sources located at the periphery as in this figure 3. This makes it possible to reduce the highly specular aspect of the incident and reflected rays thanks to the interference resulting from the crossing of the direct and indirect radiations, and therefore to reduce the reflections leading to the aforementioned blind spots.

[0061] In the configuration shown in Figure 4, light matrices 3 containing the light sources, for example, light-emitting diodes 3' LEDs, are placed on either side of the transparent plate 3, fixed in the edge areas of the support piece. They are located approximately in the same plane as the plate 2, with the light sources illuminating downwards towards reflectors 5 which direct the light on one side towards the dome 4, which must therefore be reflective, and on the other side towards the dental object through a diffusing wall or window 6. The dome 4 itself can also be a reflective mirror or made of a diffusing matrix that reproduces the light in a Lambertian manner. In this case, the surface treatments mentioned previously can be implemented: a white backing wall 4, a fine grain size on the surface of said backing wall 4, etc.

[0062] The homogeneity of the radiation from the sources 3' is significantly increased by adding a reflector 5 behind the source 3', and a diffuser 6 placed in front of the same source. The presence of the diffuser 6 in front of the light source 3' causes random emission of the radiation, increasing the Lambertian nature of the light, which drastically reduces reflections on the teeth. The thicker the diffuser 6, the more pronounced this characteristic will be, thus increasing the luminous power without degrading this highly beneficial effect in reducing blind spots.

[0063] The presence of the diffusing body 6 is very important in reducing light specularity, but also in homogenizing it across all or part of the measured arc. Diffuser 6 is characterized by its color, but also by its surface finish, which defines the degree of random reflection of the radiation, and therefore how Lambertian a given light source will be. The surface finish is thus very important if one wants to significantly reduce specularity and therefore the unmeasured blind spots in 3D stereoscopic topographic surveys. This surface finish depends on the surface roughness / grain size, generally obtained by sandblasting, and the type of light source used. It will not be the same, for example, with coherent laser light, which is inherently very specular, as with incoherent LED light, which is less specular but less powerful.

[0064] This diffusing body 6 can have all colors, including black. This color absorbs all radiation according to the black body principle, and therefore obviously specular radiation, but it does little to erase the granularity of the few radiations that emerge from it, which will be only moderately erased if the surface is in the form of a mirror, for example chromed (which ensures good reflection, but highlights surface defects too much).

[0065] Light colors, preferably white, best eliminate specular reflections. Combined with a good choice of roughness, always as fine as possible, these colors are best suited to three-dimensional readings in the mouth.

[0066] The reflector 5, located behind the source 3', allows, by creating an additional degree of freedom for the radiation axes, for the adjustment—depending on its position within the impression tray—of the proportion of direct illumination striking the teeth laterally and the indirect illumination reflected off the wall 4 to reach the occlusal surfaces of the dental object. Thus, the inclination or surface area is not the same in the incisal areas as in the molar areas, in order to better distinguish the profiles.

[0067] These irradiation gradients allow for efficient control of overall illumination and its harmonization according to its position on the arch. Eliminating overexposed or underexposed areas makes it possible to adjust the overall intensity of the entire system via a much simpler control at the electronic or human-machine interface level, thus controlling overall saturation across the entire arch. In practice, light intensity control is provided in both manual and / or automatic modes with feedback to prevent under- or overexposure.

[0068] The advantages of the mixed (direct + indirect) lighting configuration for dental instruments are numerous, and include, in particular:

[0069] - Sufficiently uniform lighting;

[0070] - The lighting does not need the full power of the LED sources to function properly;

[0071] - The specular reflections resulting from this type of lighting are acceptable;

[0072] - Reflections perceived by cameras other than those placed on the lateral extremities are acceptable;

[0073] - For cameras placed on the lateral ends, the anti-reflective film(s) of plate 2 make it possible to significantly reduce perceived reflections; - In addition, the horizontal positioning of the LED matrices makes it possible and easier to industrialize the devices of the invention, the assembly being more likely to be automated.

[0074] In this approach, the indirect lighting from wall 4 can also be modulated (as is possible with LEDs distributed on wall 4 in direct lighting, by adjusting, for example, the intensity at the power supply, the distribution within the geometry of the back wall 4, or the wavelength, using a filter or by choosing the emitting material). Since this indirect lighting can be less intense than the direct lighting, this leads to a possible reduction in reflections of direct or indirect radiation that are problematic for cameras 1, especially those furthest from the surface, which are subject to grazing radiation. Reducing this radiation obviously leads to a significant decrease in reflections on the teeth, and therefore to a reduction in blind spots.

[0075] Lateral and grazing illumination, being direct on the lateral surfaces of the teeth, leads to a significant increase in the signal-to-noise ratio (between 3 and 5), which is highly favorable for detecting tooth profiles in stereoscopic reconstruction. This amplification of texture by direct grazing light more than compensates for the reduced intensity from the dome.

[0076] Similarly, the use of this device, by increasing grazing light compared to indirect light on surfaces with little relief, such as the buccal or lingual surfaces of teeth, produces an amplification of the bumps and hollows in the texture, which is very favorable to the detection of points that rely on these relief references to correlate stereoscopic views. There is a projected shadow effect, a phenomenon widely used in electron microscopes. This phenomenon has the advantage of compensating for the indirect light coming from wall 4, which tends to flatten the relief, while maintaining good homogeneity in the distribution of light across the entire visualized scene.With reference to Figure 5, a slightly different configuration is implemented, adapted to portions of the dental arch including incisors and canines, the configuration of Figure 1 being more particularly suited to the treatment of premolars / molars. The differences concern both the illumination of the dental object and the image capture component. An optical impression device according to the invention comprises, for the entirety of a dental arch or half of a dental arch, both configurations, thus allowing coverage of all the areas necessary for a good 3D reconstruction of the dentition.

[0077] In fact, when examining the area of ​​the arch, the teeth do not have the same implantation in the arch. This means that a camera, whether or not associated with lighting sources, which is correctly oriented to view the occlusal surface of a molar (i.e., which is placed at the top of wall 4) will only measure the incisal edge of the incisors if it maintains this same orientation in the anterior part of the mouth.

[0078] It is therefore necessary to plan for different orientations depending on the areas of the dental arch. The device reconstructs the teeth using the principle of photogrammetry. By definition, the reconstruction is based on spatial measurement, which relies on precise points that must be viewed from at least two different directions. The more angles each point is viewed from, the more reconstructions are generated for each point, and the more precise and verifiable the 3D reconstruction. One of the features of the invention therefore lies in the orientations of the light source assemblies 3' and / or cameras 1. These orientations differ depending on the area of ​​the mouth, and specifically in the incisor area, the molar area, and the palate.

[0079] In particular, by way of example, the LEDs 3' and / or cameras 1 located at the top of the back wall 4 of the support piece for the optical impression tray of the invention are positioned in a plane close to the horizontal of the mouth (corresponding to Camper's plane, for example) in the molar area, while these same cameras 1 and / or light sources 3' are positioned at 90° to this plane in the incisor areas. Furthermore, one or more additional camera assemblies 1' and / or LEDs 3' may be provided in certain hard-to-reach areas, such as the frontal region, opposite the vestibular plane of the incisor, to increase the number of reference points and provide good, even illumination during measurement.

[0080] Specifically, the device in Figure 5 differs from that in Figure 4 in that, near a lateral edge of the glass plate 2, a camera l' (this is true in cross-section; in reality, it is a row of cameras if one considers it in three dimensions) is added, as well as a matrix 30 of diodes 3'. These components are therefore located, with reference to the figure, under the plate 2, and directly opposite the tooth. Almost the entire configuration remains the same, particularly at the opposite edge of the plate 2, with the exception, therefore, of this larger protrusion of the support piece under the plate 2, integrating the aforementioned optoelectronic components on one side.

[0081] Research and optimization of light specular suppression while maintaining sufficient power led to the development of a variant using radially diffused optical fibers on the inner and / or outer periphery of all or part of the impression tray. Thus, the variant illustrated in Figure 6 does not include discrete light source arrays, such as LEDs, but rather 300 optical fibers that illuminate radially, thereby sending light radiation towards the tooth, also via a diffusing wall 6, and towards the reflective dome 4. It should be noted that this variant considerably simplifies the industrialization of the device of the invention, and therefore reduces the system cost, since it is sufficient to replace the LEDs or any other light sources, as well as the diffusing reflective walls 4, with one or more diffusing fibers placed at different levels of the device.

[0082] The use of multiple fibers also makes it very easy to obtain several wavelengths during the impression taking process (see below for comments on the importance of different wavelengths). It then becomes possible to change wavelengths during the impression taking. This allows for accurate and rapid colorimetric analysis, and also facilitates the detection of oral and dental arch pathologies at a lower cost.

[0083] This fiber optic solution also has the advantage of significantly reducing the thermal problems common to any radiation source such as LEDs or other halogen sources.

[0084] Finally, the variant in Figure 7 does not have a transparent plate 2, but an overmolding 2' which achieves the same level of protection and airtightness, but does not allow for the same level of depth-of-field control as in the previous configurations. It is actually a molded optical element 2' surrounding the cameras, conforming to the shape of the dome 4. It can serve simply as a molded optical lens, or simply as a light diffuser if it is transparent enough to allow visualization of the scene measured by the cameras, or even as a dual optical and light diffuser as in the figure.

[0085] This overmolded wall, like the transparent plate, is made of a material resistant to external physical, chemical or bacteriological aggressions or is covered with a material having these characteristics.

[0086] The importance of the type of light used has already been mentioned. In all these configurations, to reduce reflections, it is necessary to choose both a wavelength with a spectrum close to the optimal sensitivity range of the camera's sensors (1) to limit the emissive energy required by the source (3'), and also a wavelength that causes the tooth to exhibit the least reflective structural behavior possible. The tooth has a chalky appearance, erasing almost all specular reflections in the low-wavelength (high-energy) 300-480 nm range, but these are not the best ranges for obtaining clear colors for accurate diagnoses. Good results are preferentially obtained with light sources, such as pulsed LEDs, emitting in the 380-550 nm range.Optimizing wavelength and intensity offers the advantage in dentistry of enabling very fast image acquisition (frames per second, or fps), thus avoiding blurring caused not only by operator movement but also, and especially, by the uncontrollable movements of patients. This allows for increased quality and quantity of information across the entire surface of the tooth, dental arches, and / or gums (including the palate).

[0087] It may be planned to use not just one type of wavelength zone, but several in the same impression tray, in order to be able to emit covering all or part of the spectrum, in order to be able to make diagnoses in the search for pathologies.

[0088] It is now well known that carious areas, gingival tumors, etc., exhibit particular behavior under certain types of radiation, such as UV, red, or even IR (fluorescence, phosphorescence, fading effects, etc.). For use in diagnostics in dental and medical practices, hospitals, pharmacies, and for the general public, this set of variable wavelengths allows for the rapid study, mapping, storage, and / or transmission of a complete analysis of these pathologies. This unique lighting capability of the device allows for manual or automated surface and / or temporal diagnostics using artificial intelligence. It also enables the determination of tooth shades through colorimetry, leveraging Mayer's principle at the pixel level of our sensors.

[0089] It should be noted that the configuration examples shown in the figures should not be considered exhaustive of the invention, which on the contrary includes structural variants, relating for example to the shape and positioning of opto-electronic components, or to the nature of the light sources, etc.

Claims

Demands 1) [Optical impression taking device capable of taking images for the three-dimensional reconstruction of a dental object representing at least a part of at least one dental arch and comprising, in a support piece of the dental impression tray type or fraction of a dental impression tray adapted to cover at least partially the dental object, an optical assembly having: a light emission system (3, 30, 300) comprising light sources (3') to illuminate the dental object;optical modules (1) with light measurement sensors distributed in a back wall (4) of the support piece oriented, during shooting, towards the dental object, said optical modules (1) being capable of capturing direct light radiation emitted by the light emission system (3, 30, 300), and indirect light coming from the optical assembly and the dental object, characterized in that it comprises means of protection (2, 2') of the optical modules (1), said means of protection (2, 2') allowing on the one hand the passage of light rays, and on the other hand, by being placed on the dental object, to ensure a mechanical positioning function and guarantee a correct focal length to the optical modules.; 2) Optical impression taking device according to the preceding claim, characterized in that the means of protecting the optical modules (1) consist of at least one flat non-reflective transparent plate (2) intended to be placed on the dental object and to separate the background wall (4) from the dental object, the lateral edges of said plate joining the background wall (4). 3) Optical impression taking device according to the preceding claim, characterized in that the transparent plate (2) is covered with an anti-reflective film on at least one of its faces. 4) Optical impression taking device according to one of claims 2 and 3, characterized in that the transparent plate (2) is a polarizing glass. 5) Optical impression taking device according to any one of the preceding claims, characterized in that at least some of the light sources (3') of the light emission system are integrated into the back wall (4) around the optical modules (1). 6) Optical impression taking device according to any one of the preceding claims, characterized in that at least some of the light sources (3') are placed in the support piece so as to emit light towards the back wall (4) of said support, said back wall (4) or at least a layer which coats it having reflective properties. 7) Optical impression taking device according to any one of the preceding claims, characterized in that at least some of the light sources (3') of the light emission system (3, 30, 300) are placed in the support piece so as to emit light simultaneously towards the back wall (4) of the support and towards the dental object, said back wall (4) or at least a layer which coats it having reflective properties. 8) Optical impression taking device according to the preceding claim, characterized in that the light sources (3') of the light emission system (3) are placed in the support next to the two lateral edges of the transparent plate (2). 9) Optical impression taking device according to the preceding claim, characterized in that the light sources (3') are positioned in the plane of the transparent plate (2), at least along one lateral edge of said plate (2), opposite a reflector (5) located on the opposite side of the transparent plate (2) with respect to the back wall (4) and oriented so as to reflect the light rays simultaneously towards the dental object and towards the back wall (4) of the support. 10) Optical impression taking device according to the preceding claim, characterized in that the reflector (5) has a flat reflective surface inclined with respect to Tl the transparent plate (2) at an angle between 30° and 60°, preferably 45°. 11) Optical impression taking device according to one of claims 9 and 10, characterized in that a diffusing translucent window (6) is interposed between the reflector (5) and the dental object. 12) Optical impression taking device according to any one of claims 2 to 11, characterized in that, for one of the lateral edges of the transparent plate (2), at least one additional optical module (1') and a light emission system (30, 3') are placed on the opposite side of the transparent plate (2) with respect to the bottom wall (4), and in front of the dental object. 13) Optical impression taking device according to one of the preceding claims, characterized in that the background wall (4) of the support is provided to be white in color. 14) Optical impression taking device according to one of the preceding claims, characterized in that the bottom wall (4) of the support has a fine grain size. 15) Optical impression taking device according to any one of the preceding claims, characterized in that the light spectrum of the light sources (3') and the light spectrum of the light measurement sensors of the optical modules (1) are between 380 nm and 550 nm. 16) Optical impression taking device according to one of the preceding claims, characterized in that the bottom wall (4) of the support piece is, in section, arch-shaped. 17) Optical impression taking device according to claim 1, characterized in that the protection means consist of an overmolding (2') on the bottom wall (4) of the support, forming a molded optical layer covering the optical modules (1), said layer being reflective. 18) Optical impression taking device according to the preceding claim, characterized in that it comprises at least one mechanical stop for support on the dental object. 19) Optical impression taking device according to any one of the preceding claims, characterized in that the sources light sources of the light emission system are chosen from coherent or non-coherent light-emitting diodes (3'), optical fibers (300), plasma sources and halogen sources. 20) Optical impression taking device according to any one of the preceding claims, characterized in that the light emission system consists of an array (3, 30) of light sources (3'). 21) Optical impression taking device according to any one of the preceding claims, characterized in that grids are placed in front of the light sources (3') to constitute structured light. 22) Optical impression taking device according to any one of the preceding claims, characterized in that Fresnel lenses are placed in front of the light sources (3'). 23) Optical impression taking device according to any one of the preceding claims, characterized in that the light measurement sensors of the optical modules (1) are of the CCD or Cmos type. 24) Optical impression taking device according to any one of the preceding claims, characterized in that the optical modules (1) comprise at least one static or dynamic optical system of the lens or fiber type associated with the light measurement sensors. 25) Optical impression taking device according to any one of the preceding claims, characterized in that polarizing filters are placed in front of the light sources (3') and in front of the light sensors, the polarizing filters placed in front of the light sensors filtering the light signal in a direction perpendicular to the filtering direction of the filters placed in front of the light sources (3').

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