WO2025068405A1 - Optical impression-capturing device - Google Patents

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

Title: Optical impression taking device

The present invention relates to an optical impression holder device usable for taking three-dimensional and temporal impressions in the dental field, and which consists of a device of the same type as traditional impression holders operating with molding materials, but comprising opto-electronic image-taking systems using light sources and optical measurement sensors in order to digitize at least part of a dental arch. Such a device must then be connectable, by cable or by wave, to a hardware and software system firstly for transmitting the information collected by said sensors, and then capable of carrying out their ordering and/or their storage, their processing and/or their visualization to allow an optical impression to be taken in one or more shots. The field of use of the devices of the invention also involves particular constraints, for example a protective hermeticity of the electro-optics due to the existence of mandatory disinfection products in the medical field.

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, in the mouth or on a reproduction model. One of the objectives pursued is to simplify the positioning of the device so as to maintain it in the ideal focal zone to ensure good shots without preventing any movements necessary for a correct three-dimensional reconstruction. One of the difficulties is that the captured 3D surface information is likely to include blind zones originating in particular from parasitic reflections and light artifacts that can be caused by lighting by light sources in the dark environment of the mouth.

The device of the invention must in practice limit these blind zones by significantly reducing light reflections on the different locations/walls of the device which are on the path of the light rays, but which also appear on the surfaces of the teeth, the gum or the bone, all while maintaining the conditions for good disinfection of its surfaces.

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

If these documents actually correspond to the needs of modern dentistry, in particular what is described in the latter, 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 the present application.

We also know of numerous documents in which solutions are proposed to problems relating to the same overall objective of digitizing optical data.

This is the case, for example, of document US 2017100219 Al, which proposes an impression tray comprising assemblable and detachable elements consisting, among other things, of sensors capable of taking the impression of a tooth or an arch, these electro-optical means being associated with a traditional molding material. Document US 2015118638 Al also discloses an impression tray, in this case consisting of a tray and a chute, equipped with optical sensors making it possible to obtain images which, combined, are intended to determine the depth of the sulcus in an edentulous patient with a view to manufacturing his appliance. Such an impression tray was not, however, designed for the surface capture of images of the mouth. Also known, from document US 2017128173 A1, is an optical scanning device comprising a handle intended to be held by an operator and a mouthpiece comprising a mobile 3D scanner. This document describes means for moving said 3D scanner inside the mouthpiece. The latter comprises a partly transparent casing, inside which mirrors move in order to perform a scan to digitize the mouth. If such a device can be considered at first glance as simple to use, its use has major clinical limitations. Indeed, whatever the possibilities of movement of the 3D scanner inside the mouthpiece, not all dental surfaces can be reached, and they cannot therefore be measured with the same precision. Moreover, not all of them can be reached. Furthermore, for all the teeth to be visible, a long adjustment process is necessary, in particular depending on the size of the mouths. Finally, all devices that have sought to use this type of mechanical movement encounter sterilization problems.

In the same vein, document US 2002/064752 Al describes a mechanically displaced carriage that is very complex to implement, mainly in the mouth. This device comprises a rail following the shape of the dental arch, on which a device capable of scanning the vestibular and lingual surface of the teeth in the arch moves again. In practice, it is difficult to use in the mouth due to the anatomical varieties of shapes in human jaws. Document US 2015/079534 Al presents a well-known articulated solution in impression trays, allowing the three-dimensional reconstruction of dental arches, but which requires complex calibrations, and consequently that advanced training be given to practitioners: it is therefore not a user-friendly and easy-to-use tool.

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 practically no movement in the optical impression tray supporting the cameras if the minimum precision required in dental clinics is to be preserved, which must be a few dozen microns, so as not to have to recalibrate the device for each measurement and for each patient.

Most of the above documents struggle to meet the objectives sought by the clinician, namely to have a system covering the entire mouth and gum, without any mechanism that could become unregulated during use and/or, above all, not requiring calibration at each shot. While a slight movement of a few millimeters is acceptable and even desirable during the shot to compensate for the natural and physiological movement of any patient, one of the objectives is that the device itself can be static, ensuring a very rapid shot, lasting a few seconds. Furthermore, such a device must require very little training, be user-friendly for the dentist and comfortable for the patient, in its use and in its space requirement in the mouth. Finally, its cost must remain accessible to the daily practice of a dental office or that of a laboratory, which is particularly impossible in the so-called "mechanical displacement" systems seen previously.

The aim of the present invention is to propose an optical impression tray that is simple to use, with spontaneous placement in the mouth for the dentist and allowing a precision of a few tens of microns in the measurements taken. A non-traumatic shape, close to traditional impression trays using molding products such as those always used by dentists, is used because it has proven satisfactory for both patients and dentists, without changing their habits.

As explained in document FR 18 50689 by the same inventor, the objectives of such devices also consist of collecting and measuring, at the same time or in a very short time, the shape of the dental surfaces and their shades, but also the gingival surfaces and possibly the bone contours for surgical purposes. It may also prove necessary to measure the meshing of the maxillary teeth with respect to the mandible in occlusion, and possibly their movements.

The context of intraoral shots being very particular, notably in terms of brightness and humidity, There are multiple obstacles in the design and development of such a device. For example, some cameras are "dazzled" by the lighting LEDs in front of them when the picture is taken. Similarly, the specular reflections of these same LEDs on the surface of the teeth, which are generally white and very bright, often saturate the sensors, making them unable to detect certain useful information. Also, cameras that are too far away from the focal plane of the shot, which is of course located at the level of the teeth, result in a reduction in the accuracy of the system. Finally, the variation of colors in a mouth, particularly between the gum and healthy or damaged teeth, can lead to measurement errors.

The present invention aims to propose industrially acceptable solutions to all the problems mentioned, clinically usable, at low cost, with the objective of achieving the already mentioned precision of the order of a few tens of microns, whatever the surface of the body measured. The necessary information must be captured with a minimum of blind zones, which often correspond to specular reflections of the lighting sources on the teeth, resulting in zones without information. The expected results are a permanent diagnostic quality and a good adaptation of the prostheses resulting from the model constructed using the optical impressions made with the invention, without requiring the practitioner to carry out overly complex manipulations or training.

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 lighting (LED, plasma, laser, etc.) or natural lighting (sun).

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 part of the dental impression tray type or fraction of a tray dental impression adapted to at least partially cover the dental object, an optical assembly having: a light emission system comprising light sources for illuminating the dental object; optical modules with light measurement sensors distributed in a back wall of the support part oriented, during shooting, towards the dental object, said optical modules being capable of capturing direct light radiation emitted by the light emission system, and indirect radiation coming from the optical assembly and the dental object.

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

In a few words, the present invention consists of an impression tray comprising cameras and light projections whose internal arrangement, the subject of the invention, has been organized to limit, or even eliminate, the areas of reflection and light brilliance on the teeth in order to allow the sensors to best collect the information necessary for a good 3D reconstruction by stereoscopy in structured or non-structured light. Taking into account the humid environment of the mouth and the existence of disinfection chemicals, means of protecting the opto-electronic components are provided.

More precisely, what can be described as an optical impression tray within the meaning of the invention, usable for diagnosis and taking two-dimensional, three-dimensional and temporal measurements in the dental and medical field to ensure good capture of information in the mouth or on a plaster model or obtained by stereolithography, actually consists of a device comprising, in a shell (the support part comprising the optical assembly) adapting to the shape of the object to be analyzed, a certain number of optical and optoelectronic components. These components are distributed in one or more planes and/or on a left shape of regular or non-regular shape, the “field of view” of which covers all or part of one or more teeth, one or two arches to be viewed or measured by means of one or more lighting sources. These can be identical or different, Lambertian or/and direct specular or indirect, the intensity and exposure time of which are automatically adjusted by software controlling the device of the invention.

The optical rays are transmitted either directly or by means of optical systems which may include fibers, diffusing materials, reflectors and/or mirrors, in association or not. As will be seen later, the device may include LED type sources, but also radially diffusing glass fibers, or even molded optics.

The means of protection required in such an environment may be of several types. Thus, according to a first variant of the device, the means of protection of the optical modules consist precisely of at least one non-reflective flat transparent plate intended to be placed on the dental object and to separate the back wall from the dental object, the lateral edges of said plate joining the back wall. It must allow a position of spontaneous support and/or sliding of the assembly on the teeth and ensure the partial or total hermeticity of the opto-electronic system with respect to external aggression factors. It therefore also has a mechanical function of positioning on the dental object, guaranteeing a correct focal distance for the optical modules, by allowing the exercise of slight movements (by sliding) to allow the taking of several shots which may be useful in a photogrammetry approach.

It should be noted that we know from document US 2021/0045852, a system for performing intraoral scanning, the sensors of which are retained by a rigid body which may be opaque with the exception of 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.

To address the previously mentioned problem relating to the areas of reflection and light brilliance, the transparent plate which is used in the context of the invention is a non-reflective glass. It may be a transparent plate covered with an anti-reflective film on at least one of its faces, in order to eliminate reflections as much as possible, and to improve the signal-to-noise ratio. The transparent plate can also be a polarizing glass.

Various configurations are possible for the light sources of the light emission system. Thus, at least some of the light sources of the light emission system can be integrated into the back wall around the optical modules. There is then direct lighting consisting of sources, for example LEDs, placed around the cameras and directly illuminating the scene with or without a transparent plate, the protection of the electronic system being located in the second case directly at the level of and in front of the cameras and the LEDs (see below).

Alternatively or in combination, at least some of the light sources may be placed in the support part so as to emit light towards the back wall of said support, said back wall or at least one layer which covers it having reflective properties. This involves the implementation of indirect lighting of the dental object, which may be added to direct lighting.

According to yet another possibility, at least some of the light sources of the light emitting system can be placed in the support part so as to emit light simultaneously towards the bottom wall of the support and towards the dental object, said bottom wall or at least one layer which covers it having reflective properties.

In the latter case, indirect lighting is useful in suppressing specular reflections, and direct lighting is useful in suppressing parasitic reflections which 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, etc.).

According to the invention, the light sources of the light emission system can be placed in the holder next to the two side edges of the transparent plate.

In this case, preferably, the light sources are positioned in the plane of the transparent plate, at least along a lateral edge of said plate, opposite a reflector located on the opposite side of the transparent plate relative to 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 sent towards the back wall of the support piece, and direct lighting is in reality a lateral lighting of the dental object.

According to a possible configuration, the reflector has a flat reflective surface inclined relative to the transparent plate at an angle of between 30° and 60°, preferably 45°. In addition, preferably, a diffusing translucent porthole is interposed between the reflector and the dental object: the diffuse lateral lighting that it provides helps to eliminate parasitic reflections.

The configuration of the device can however change depending on the portion of the support considered, and the dental object facing it. Thus, the optical treatment of molars is not done 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 has a form of symmetry, and the two lateral faces (vestibular and lingual) of the tooth are treated, optically speaking, substantially in 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 emission system are placed on the opposite side of the transparent plate relative to the back wall, and facing the dental object. These components are therefore placed, during a shooting phase, directly laterally to a face of the tooth, in this case the vestibular face.

In addition to the type of tooth lighting configuration as seen so far, the surface condition of certain parts of the device is also a parameter to consider, since they may be diffusing bodies within the optical assembly of the invention. Thus, preferably, the bottom wall of the support is provided in white color. The granularity of the surface also plays a role, so that the white diffusing body is effective, in particular to avoid concentrations of reflections, which is the opposite of the diffusing character. The reflection must be as random as possible, that is to say not distinguish the sources incident light. For this purpose, the bottom wall of the support preferably has a fine-grained granulometry.

In order to limit or attenuate reflections, according to the invention, the device is provided such that the light spectrum of the light sources and the light spectrum of the light measuring sensors of the optical modules are between 380 nm and 550 nm, that is to say that they are in practice selected to be close. This aims to improve the signal/noise ratio without reducing the light power of the light source.

According to a possible configuration, particularly suitable for devices for treating dental arches or portions thereof, the bottom wall of the support piece is, in section, arch- or dome-shaped. Such a curve generates a left surface which allows the support piece to cover the teeth, and for the optical rays to have access to their occlusal faces as well as to the lateral faces, with a view to a complete reconstruction without inaccessible areas.

According to a variant of the device of the invention, the protection means may consist of overmolding on the bottom wall of the support, forming a molded optical layer covering the optical modules, said layer being reflective. There is then no longer a transparent flat plate, and the problems mentioned linked to reflections or spots of light on said plate disappear. The overmolded layer ensures sealing and consequently protects the optical modules, and it does not disrupt their operation, it moreover becomes an element in its part which covers them.

The speculars on the tooth enamel are also attenuated with this second variant, but the conservation of the distance between the latter and the optical modules is no longer assured.

This is the reason why this variant can include at least one mechanical stop for support on 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 particular optical properties, encroaches on the dental object and results in creating blind zones which are detrimental to data analysis, which must then be deleted during software processing: said areas are however easy to recognize, in particular following movements occurring between several captures, and therefore relatively easy to “erase” by software.

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

According to one possible configuration, the light emission system may consist of a matrix of light sources, for example LEDs included in a transparent matrix or in a diffusing matrix. Grids may also be placed in front of the light sources to constitute structured light. The light is then structured in the form of the projection of such a grid onto the dental object. The grid can take many forms. In this configuration, the light sensors are not provided with them, so as not to reduce the intensity of the signal.

As an additional possibility, Fresnel lenses can be placed in front of the light sources. The homogenization of the radiation resulting from the passage of the radiation through Fresnel lenses makes it possible to reduce its specularity.

The light measuring 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 comprise at least one static or dynamic optical system of the lens or fiber type associated with the light measuring sensors. These means make it possible to better control the depth of field when capturing optical information.

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 filtering the light signal in a direction perpendicular to the filtering direction of the filters placed in front of the light sources. This is a solution which applies in particular if there is direct lighting, and when the means of protection consist of overmolding of the opto-electronic components.

In short, the device of the invention functions as an optical impression tray schematically comprising information capture cameras and light projections and whose internal arrangement, the subject of the invention, has been organized to limit, or even eliminate the areas of light reflection and brilliance 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 non-structured light.

Other aims and advantages of the present invention will become apparent during the description which follows, relating to embodiments which are given only as indicative examples. Understanding of this description will be facilitated in particular with reference to the figures attached in the appendix and 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 to the treatment of premolars and molars, comprising direct light sources and a transparent protective plate; Figure 2 represents the same sectional view of another variant with direct light sources and without a protective wall;

- Figure 3 shows said 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 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 according to which the means of protection of the optical modules with light sensors are overmolded directly in contact with the latter.

In the configurations shown, the support part of the optoelectronic components is intended to take pictures of at least a portion of a dental arch, and it is consequently of canal appearance so that the optical rays access not only the occlusal faces of the teeth, but also their vestibular and lingual lateral faces. The optical modules 1 acting as cameras or image capture sensors are integrated into a back wall 4 forming in this case - in section - a dome or an arch, in which they are distributed angularly. The view is in section, it is therefore necessary to represent rows of cameras 1 in the canal shape that the support part takes in three dimensions. Their positioning in the back wall 4, marking their distance from the dental object to be observed, depends on their angular position, so as to adapt their focal distance to said object appropriately. A transparent plate 2, for example made of glass, can be fixed to the support part at the lateral edges of the back wall 4. This is the case in the configuration of figure 1. It is used to position the device on the teeth, and helps to control the depth of field. It also makes it possible to achieve a seal with respect to the external environment. Movements obtained by slight sliding of the plate 2 on the teeth are possible, to be coupled with the triggering of the shots so that several images of the dental object can be captured, making it possible to improve its 3D reconstruction by photogrammetry.

Plate 2 (which can be made of natural crystal such as quartz, glass or synthetic material) is only a mostly passive protective glass. It is also preferably treated, at least by adding at least one anti-reflective layer on one of its faces. The physical characteristics and chemical protection, positioning and sliding plates are an important element of the device of the invention, because said plates 2 must facilitate the use of the device while reducing parasitic reflections on the teeth, the gum and the palate, but also on the very walls of the device. They must also not increase the reflections on their own internal and external walls during the passage of the radiation, and in particular be free as much as possible from the effects of reflection and refraction.

Physically, these protective plates must be as little deformable as possible. They must allow the practitioner to lean on the teeth to position the cameras 1 and/or the light sources 3 spontaneously and intuitively in an area with the correct depth of field. This allows for the ideal position to have the best precision and resolution.

Chemically and to resist scratches from teeth naturally composed of hydroxyapatite crystals, but also of ceramics which can be very hard (Zirconia) in prosthetic reconstructions, these transparent plates 2 for protection, positioning and sliding are made from a very hard natural material (for example quartz, crystalline charged silica, etc.) or synthetic material, for example cast silica such as JGS1 UV quality,

To also reduce reflections on the 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 deposits on one or more of the surfaces of the plates 2. These deposits can be placed on the outside and/or inside the device, on all the walls that can be crossed by the radiation leaving the light sources 3' towards the teeth and/or returning towards the sensors 1.

These walls and these treatments must resist as well as possible to external physical, chemical or bacteriological attacks, such as scratches from teeth, or to attacks thermal and plasma, or even cleaning and disinfection chemicals.

These walls can also contain a heating and/or cooling thermal system limiting the appearance of fog inside and/or outside the device and possibly participating in the internal thermal regulation of the electronics.

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

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, he captures the information. This presents perfectly measurable areas and very good quality in terms of information, especially since the position of the protection/sliding plate is not modified too much. On the other hand, some areas do not have information, because the sensors are "dazzled" by reflections on the teeth and on the external and internal surfaces of the sliding walls. In a second step, the operator slightly moves the device by sliding on the teeth, which has the effect of moving the reflections and making perfectly measurable areas that were not. As these new areas are wholly or partly connected to the previously measured areas, the total and precise 3D reconstruction is made possible by this simple clinical gesture, making the blind areas disappear.

In this configuration of the device, in direct lighting (which can also be implemented in at least partially indirect lighting, as will be seen below), polarizing filters can also be used, for example integrated into the protective wall and which eliminate reflections on the teeth and on the transparent plate 2 serving as protection, positioning and sliding. These filters can also be placed in front of the light sources 3' and, with an angle depending on the type of composition of the polarization filter, generally of the order of 90°, in front of the information recovery cameras 1. More precisely, the first filter placed in front of the emitted light polarizes it while the second, placed in front of the camera 1 for example at 90° relative to the first, filters a large part 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 sources, they require increasing the power of the lighting system, but this also leads to a reduction of reflections on the teeth, which harmonizes the lighting a little and allows a good overall measurement of the surfaces. The plate 2 located against the teeth, if it is in the configuration, then serves only for protection, positioning and sliding.

In Figure 2, the device is practically identical, without the protective plate 2. The protective wall for the optoelectronic components is placed directly at the level of and in front of the cameras 1 and the LEDs 3'. It can cover a single sensor unit 1 or LED 3', or a group combining one or more LEDs 3' and sensors 1. This configuration makes it possible to avoid reflections directly on a sliding glass, which does not exist, but forces the practitioner to hold the device in suspension. This is a configuration particularly suited to use in a prosthesis laboratory or in dedicated rooms of dental practices, especially if the use of a support arm holding the device is allowed.

It corresponds to a field of application of the device corresponding to measurements and diagnosis (ODF and periodontology) on supports made of plaster or various synthetic materials (additive method for example by stereolithography or subtractive for the manufacture of implant guides, ODF splints or whitening trays, etc.). These materials having little or no specular reflections, the problem of reflections on the measured surface is significantly reduced, which simplifies and accelerates the treatment while increasing precision. The use of polarizing filters is of course also possible in this variant without plate. In the configuration of Figure 3, the light sources 3' are in indirect lighting. There are no more light sources around the cameras 1, but they are in front of the back wall 4, on which their rays are reflected to be redirected towards the teeth. Said wall 4 consequently becomes a reflector which directs the light from the light sources 3' towards the teeth after reflection. It can be a reflecting mirror (as in car headlights) and the reflected light will be specular and perfectly circumscribed, or made up of a diffusing matrix restoring in a Lambertian manner the light which has struck its density. The light sources 3' are placed around the periphery of the support, either inside the arched back wall 4, as in the figure, or outside it.

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

It is obviously possible to associate the direct light sources 3' placed around the cameras 1 as in the first variant with the indirect sources located on the periphery as in this figure 3. This makes it possible to reduce the very specular aspect of the incident rays and the reflected rays thanks to the interference resulting from the crossing of the direct and indirect radiation, and therefore to reduce the reflections leading to the aforementioned blind zones.

In the configuration of Figure 4, light matrices 3 comprising the light sources, for example light-emitting diodes 3' LED, are placed on either side of the transparent plate 3, fixed in border zones of the support part. They are located substantially in the same plane as the plate 2, the light sources illuminating downwards, towards reflectors 5 which return the light on the one hand towards the dome 4, which must consequently be reflective, and on the other part towards the dental object through a diffusing wall or porthole 6. The dome 4 itself can also be a reflecting mirror or made of a diffusing matrix restoring the light in a Lambertian manner. In this case, surface treatments mentioned previously can be implemented: bottom wall 4 of white color, fine grain size of the surface of said bottom wall 4 etc.

The homogeneity of the radiation of the sources 3' is significantly increased by adding a reflector 5 behind the source 3', and by a diffuser 6 placed in front of this same source. The presence of the diffuser 6 in front of the light source 3' causes a random exit of the radiation increasing the Lambertian character of the light, which has the effect of drastically reducing the reflections on the teeth. The thicker the diffuser 6, the more this character will be accentuated, which makes it possible to increase the light power without degrading this phenomenon which is very favorable in reducing blind zones.

The presence of the diffusing body 6 is very important in reducing the specularity of the light, but also in its homogenization at the level of all or part of the measured arch. The diffuser 6 is characterized by its color, but also by its surface condition, which defines the degree of random reflection of the radiation, therefore how much any light source will be Lambertian. The surface condition is therefore very important if we want to significantly reduce the specularity and therefore the blind zones not measured in 3D topographic surveys by stereoscopy. This surface condition is a function of the roughness/granulometry of the surface, generally obtained by sandblasting, and the type of source used. It will not be the same, for example, in coherent laser light, which is very specular in principle, or in incoherent LED light, which is less specular but less powerful.

This diffusing body 6 can have all colors, including black. This absorbs all radiation according to the black body principle, and therefore obviously specular radiation, but it erases the granulometry of the few rays which come out of it quite little, which will be erased very moderately if the surface is in the form of a mirror, for example. chrome (which provides good reflection, but highlights surface defects too much).

Light colors, preferably white, best erase specularity. Combined with a good choice of roughness, always as fine as possible, these colors are best suited to three-dimensional readings in the mouth.

The reflector 5 located behind the source 3' allows, by creating an additional degree of freedom for the radiation axes, to adjust differently - depending on the area where it is located in the impression tray - the part of direct lighting striking the teeth laterally and the indirect part reflecting on the wall 4 to arrive on the occlusal surfaces of the dental object. Thus, the same inclination or the same surface is not provided in the incisor areas compared to the molar areas, in order to better detach the profiles.

These irradiation gradients make it possible to effectively dose the overall illumination and harmonize it according to its position on the arch. The elimination of overexposed or underexposed areas makes it possible to adjust the overall intensity of the whole by a much simpler control at the electronic level or at the human-machine interface level, and thus to control the overall saturation over the entire arch. In practice, a control of the light intensity is provided which is manual and/or automatic with feedback to avoid under-exposures or overexposures of light.

The advantages of the mixed lighting configuration (direct + indirect) of the dental object are multiple, and we can notably cite:

- Sufficiently uniform lighting;

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

- The speculars resulting from this type of lighting are acceptable;

- Reflections perceived by cameras other than those placed on the side ends are acceptable;

- For cameras placed on the lateral ends, the anti-reflection film(s) on plate 2 make it possible to significantly reduce the 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.

In this approach, the indirect lighting coming from the wall 4 can also be modulated (as it is possible to do with the LEDs distributed on the wall 4 in direct lighting, by acting for example on the intensity at the power supply, on the distribution in the geometry of the back wall 4, or even on the wavelength, by a set of filters or by the choice of the emitting material). As this indirect lighting can be less important than the direct lighting, this leads to a possible reduction of the reflections of the direct or indirect radiations which are annoying for the cameras 1, mainly the most peripheral ones, those which are subject to grazing radiations. The reduction of these radiations obviously leads to a significant reduction of the reflections on the teeth, and therefore to a limitation of the blind zones.

Since the lateral and grazing illumination is direct on the lateral parts of the teeth, this leads to a significant increase in the signal/noise ratio (between 3 and 5), which is very favorable for the detection of tooth profiles for stereoscopic reconstruction. This amplification of the texture by the direct grazing light largely compensates for the decrease in intensity from the dome.

Similarly, the use of this device, by increasing the grazing lighting compared to indirect lighting on surfaces with little relief such as the vestibular or lingual surfaces of teeth, produces an amplification of the bumps and hollows of the texture very favorable to the detection of points which rely on these relief references to correlate the stereoscopic views between them. 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 "crush" the relief while maintaining good homogeneity in the distribution of light over the entire scene viewed. With reference to Figure 5, a slightly different configuration is implemented, suitable for portions of the dental arch including the incisors and canines, the configuration of Figure 1 being more particularly suitable for the treatment of premolars/molars. The differences concern both the lighting of the dental object and the image capture part. An optical impression taking device according to the invention comprises, for the entirety of a dental arch or a half-dental arch, the two configurations, which makes it possible to cover all the areas necessary for a good 3D reconstruction of the teeth.

In fact, when scanning the arch area, the teeth do not have the same implantation in the arch. This means that a camera, associated or not with lighting sources, which is well oriented to visualize the occlusal face of a molar (that is to say which is placed at the top of the wall 4) will only measure the incisal edge of the incisors if it keeps this same orientation in the anterior part of the mouth.

It is therefore necessary to provide different orientations depending on the areas of the dental arch. The device in fact reconstructs the teeth using the principle of photogrammetry. By definition, the reconstruction is done from the spatial measurement, which is based on precise points which must be seen at least from two different directions. The more each point is seen from different angles, the more numerous the reconstruction beams are for each point, and the more precise and verifiable the 3D reconstruction is. One of the characteristics of the invention therefore lies in the orientations of the light source assemblies 3' and/or cameras 1. They are different depending on the areas of the mouth, and different in the areas of the incisors, the areas of the molars or those of the palate.

In particular, by way of example, the LEDs 3' and/or the cameras 1 located at the top of the bottom wall 4 of the support part of the optical impression tray of the invention are placed in a plane close to the horizontal of the mouth (corresponding to the Camper plane for example) in the molar zone while these same cameras 1 and/or light sources 3' are placed at 90° in relation to this plane in the incisor areas. One or more additional camera assemblies and/or 3' LEDs can also be provided in certain areas that are difficult to access, such as the frontal region, facing the vestibular plane of the incisor, to increase the number of reference points and provide good, harmonious lighting during measurement.

Specifically, the device of Figure 5 differs from that of Figure 4 in that, in the vicinity of a lateral edge of the glass plate 2, a camera 1' (this is true in section, in reality it is a row of cameras if we reason 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, in particular at the level of the opposite edge of the plate 2, with the exception, therefore, of this more significant outgrowth of the support part under the plate 2, integrating the aforementioned opto-electronic components, on one side.

The research and optimization of the suppression of the specularity of the light while maintaining good power has led to the development of a variant using radially diffused optical fibers on the internal and/or external periphery on all or part of the impression tray. Thus, the variant illustrated in Figure 6 does not include matrices of discrete light sources, such as LEDs, but optical fibers 300 which illuminate radially, and consequently send light rays towards the tooth, also via a diffusing wall 6, and towards the reflecting dome 4. It should be noted that this variant considerably simplifies the industrialization of the device of the invention, and therefore reduces the cost of the system, since it is sufficient to replace the LEDs or any other light sources, but also the diffusing reflective walls 4, with one or more diffusing fibers placed at different levels of the device.

The use of several fibers also makes it very easy to have several wavelengths available during the impression taking (see below the comments on the importance of the different wavelengths). It then becomes It is also possible to change the wavelength during the impression taking. This allows for a good and rapid colorimetric analysis, but also to facilitate the search for pathologies of the mouth and the arch at a lower cost.

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

Finally, the variant of figure 7 does not include a transparent plate 2, but an overmolding 2' which results in the same level of protection and hermeticity, but does not allow the depth of field to be controlled as well as in the previous configurations. It is in reality a molded optic 2' surrounding the cameras, and which follows the shape of the dome 4. It can have a simple role of molded optical lens, or a simple role of light diffuser if it is transparent enough to allow the scene measured by the cameras to be viewed, or even a dual optical and light diffuser role as in figure .

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

The importance of the type of light used has been mentioned previously. In all these configurations, to attenuate reflections, it is necessary to choose both a wavelength with a spectrum close to the optimal zone of sensitivity of the sensors of the camera 1 to limit the emissive energy necessary for the source 3', but also the wavelength which leads the tooth to have the least reflective structural behavior possible. The tooth has a chalky appearance erasing almost all specular reflections in the low wavelength (high energy) zones 300-480 nm, but these are not the best reading zones to obtain beautiful colors in order to make good diagnoses. A good result is preferably obtained with light sources, for example pulsed LEDs, emitting in the zone 380-550 pm. The optimization of wavelength and intensity has the advantage, in dentistry, of allowing very fast shots (in frames per second "fps") which avoid blurring which is not only due to the operator's movements, but also, and above all, to the uncontrollable movements of the patients. This makes it possible to increase the quality and quantity of the information sought over the entire surface of the tooth, the arches and/or the gums (including the palate).

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

It is indeed well known today that carious areas, gingival tumors, etc., have a particular behavior under certain radiations such as UV or red, or even IR. (fluorescence effects, phosphorescence, erasures, etc.). For use in diagnostics for use in dental and medical practices, hospitals, pharmacies, but also for the general public, this set of variable wavelengths makes it possible to study, map, store and/or quickly transmit the complete analysis of these pathologies. This possibility of lighting specific to the device of the invention allows manual or automatic surface and/or temporal diagnostics by artificial intelligence. This also allows the determination, by colorimetry, of the shade of the teeth by playing on the Mayer principle at the pixel level of our sensors.

It should be noted that the configuration examples which are the subject of the figures should not be considered as exhaustive of the invention, which on the contrary encompasses structural variants, relating for example to the shape and positioning of the opto-electronic components, or even to the nature of the light sources etc. Claims

1) [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 support part of the dental impression tray type or fraction of a dental impression tray adapted to at least partially cover the dental object, an optical assembly having: a light emission system (3, 30, 300) comprising light sources (3') for illuminating the dental object; optical modules (1) with light measuring sensors distributed in a bottom wall (4) of the support part 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 radiation coming from the optical assembly and the dental object, characterized in that it comprises protection means (2, 2') for the optical modules (1), said protection means (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 distance for the optical modules.

2) Optical impression taking device according to the preceding claim, characterized in that the means for protecting the optical modules (1) consist of at least one non-reflective, flat, transparent plate (2) intended to be placed on the dental object and to separate the bottom wall (4) from the dental object, the lateral edges of said plate joining the bottom 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 at least on 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 window. 5) Optical impression taking device according to one of the preceding claims, characterized in that at least some of the light sources (3') of the light emission system are integrated in the bottom wall (4) around the optical modules (1).

6) Optical impression taking device according to one of the preceding claims, characterized in that at least some of the light sources (3') are placed in the support part so as to emit light towards the bottom wall (4) of said support, said bottom wall (4) or at least one layer which covers it having reflective properties.

7) Optical impression taking device according to 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 part so as to emit light simultaneously to the bottom wall (4) of the support and to the dental object, said bottom wall (4) or at least one layer which covers 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 a lateral edge of said plate (2), opposite a reflector (5) located on the opposite side of the transparent plate (2) relative to the bottom wall (4) and oriented so as to reflect the light rays simultaneously towards the dental object and towards the bottom 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 relative to The transparent plate (2) is at an angle of between 30° and 60°, preferably 45°.

11) Optical impression taking device according to one of claims 9 and 10, characterized in that a translucent diffusing porthole (6) is interposed between the reflector (5) and the dental object.

12) Optical impression taking device according to 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) relative to the bottom wall (4), and opposite the dental object.

13) Optical impression taking device according to one of the preceding claims, characterized in that the bottom wall (4) of the support is provided in white 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-grained granulometry.

15) Optical impression taking device according to one of the preceding claims, characterized in that the light spectrum of the light sources (3') and the light spectrum of the light measuring 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 part 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 one of the preceding claims, characterized in that the sources of light 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 one of the preceding claims, characterized in that the light emission system consists of a matrix (3, 30) of light sources (3').

21) Optical impression taking device according to 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 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 one of the preceding claims, characterized in that the light measuring sensors of the optical modules (1) are of the CCD or Cmos type.

24) Optical impression taking device according to 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 measuring sensors.

25) Optical impression taking device according to 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').

Claims

25 Claims 1) [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 support part of the dental impression tray type or fraction of a dental impression tray adapted to at least partially cover the dental object, an optical assembly having: a light emission system (3, 30, 300) comprising light sources (3') for illuminating the dental object; optical modules (1) with light measuring sensors distributed in a bottom wall (4) of the support part 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 radiation coming from the optical assembly and the dental object, characterized in that it comprises protection means (2, 2') for the optical modules (1), said protection means (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 distance for the optical modules. 2) Optical impression taking device according to the preceding claim, characterized in that the means for protecting the optical modules (1) consist of at least one non-reflective, flat, transparent plate (2) intended to be placed on the dental object and to separate the bottom wall (4) from the dental object, the lateral edges of said plate joining the bottom 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 at least on 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 window. 5) Optical impression taking device according to one of the preceding claims, characterized in that at least some of the light sources (3') of the light emission system are integrated in the bottom wall (4) around the optical modules (1). 6) Optical impression taking device according to one of the preceding claims, characterized in that at least some of the light sources (3') are placed in the support part so as to emit light towards the bottom wall (4) of said support, said bottom wall (4) or at least one layer which covers it having reflective properties. 7) Optical impression taking device according to 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 part so as to emit light simultaneously to the bottom wall (4) of the support and to the dental object, said bottom wall (4) or at least one layer which covers 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 a lateral edge of said plate (2), opposite a reflector (5) located on the opposite side of the transparent plate (2) relative to the bottom wall (4) and oriented so as to reflect the light rays simultaneously towards the dental object and towards the bottom 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 relative to The transparent plate (2) is at an angle of between 30° and 60°, preferably 45°. 11) Optical impression taking device according to one of claims 9 and 10, characterized in that a translucent diffusing porthole (6) is interposed between the reflector (5) and the dental object. 12) Optical impression taking device according to 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) relative to the bottom wall (4), and opposite the dental object. 13) Optical impression taking device according to one of the preceding claims, characterized in that the bottom wall (4) of the support is provided in white 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-grained granulometry. 15) Optical impression taking device according to one of the preceding claims, characterized in that the light spectrum of the light sources (3') and the light spectrum of the light measuring 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 part 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 one of the preceding claims, characterized in that the sources 28 of light 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 one of the preceding claims, characterized in that the light emission system consists of a matrix (3, 30) of light sources (3'). 21) Optical impression taking device according to 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 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 one of the preceding claims, characterized in that the light measuring sensors of the optical modules (1) are of the CCD or Cmos type. 24) Optical impression taking device according to 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 measuring sensors. 25) Optical impression taking device according to 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').