EP3937841A1

EP3937841A1 - Method for aligning virtual models of dental arches of an individual with a digital model of the face of said individual

Info

Publication number: EP3937841A1
Application number: EP20725892.2A
Authority: EP
Inventors: Maxime JAISSON
Original assignee: Modjaw SAS
Current assignee: Modjaw SAS
Priority date: 2019-03-12
Filing date: 2020-03-12
Publication date: 2022-01-19
Also published as: WO2020183115A1; FR3093636B1; US20220156953A1; FR3093636A1; JP2022524532A; CN113573662A; CN113573662B

Abstract

The invention relates to a method for aligning non-radiographic virtual models of a mandibular arch and of a maxillary arch of an individual with a non-radiographic digital model of the face of said individual, characterized in that it comprises: fastening a mandibular marker rigidly to the mandibular arch of the individual, said mandibular marker defining a first frame of reference; providing a non-radiographic virtual model of the mandibular arch and a non-radiographic virtual model of the maxillary arch; digitizing at least one portion of the surface of the teeth or of a prosthetic device securely fastened to said arch and at least one rigid portion of said marker by means of an intra- or extra-oral camera, so as to produce a digital record of said portions of the mandibular arch and of the marker in a given second frame of reference; on the basis of said record and of the virtual models of the mandibular arch and of the mandibular marker, matching the digital model of the mandibular marker with the marker, and the virtual model of the mandibular arch with said arch, and locating the virtual model of the mandibular arch in the first frame of reference; acquiring a non-radiographic digital model of the face of the patient; and locating the digital model of the face in the first frame of reference, so as to align the virtual models of the maxillary and mandibular arches with said digital model of the face.

Description

PROCESS FOR REGISTRATION OF VIRTUAL MODELS OF THE DENTAL ARCADES OF AN INDIVIDUAL WITH A DIGITAL MODEL OF THE FACE OF THE INDIVIDUAL

FIELD OF THE INVENTION

The present invention relates to a method for registering virtual models of the dental arches of an individual with a digital model of the face of said individual. One application of this method is the taking into account of aesthetic considerations when planning a treatment involving an acquisition of the mandibular kinematics of the individual and the application of said kinematics to virtual models of the dental arches.

STATE OF THE ART

In orthodontics or dental surgery, it is useful to animate three-dimensional (3D) virtual models of the dental arches (maxilla and mandibular) of a patient with the mandibular kinematics of said patient, in order to plan a treatment and / or determine the effects of said processing.

Recording mandibular kinematics requires equipping the patient's face with markers comprising objects detectable by a camera or inertial, magnetic or other type of position sensors, and asking the patient to perform mandibular movements. During these movements, objects are spotted in real time by a camera, or the position data of the sensors are recorded in real time.

Virtual 3D models of the mandibular and maxillary arches are generally obtained using an intraoral optical scanner or by 3D scanning of impressions of the arches or physical models of the arches. These virtual models are therefore defined in a reference which is associated with the scanning device.

The markers or sensors fitted to the face define a reference point for the patient that is different from the reference point for virtual 3D models of dental arches.

To animate the virtual models of the dental arches, it is necessary to transfer the displacement information recorded on the patient to the 3D virtual models of the dental arches. This requires knowing the rigid geometric transformation (translations and rotations) allowing to go from one frame of reference to another.

Document WO 2013/03051 1 describes a method of designing a dental appliance for an individual in which the mandibular kinematics recorded on said individual are used to animate virtual models of the dental arches of the individual.

In a first embodiment, it is proposed to register the virtual models of the dental arches to a tomodensitometric image. However, although such an image makes it possible to visualize the position of the dental arches within the facial mass of the patient, it requires irradiation of the patient with X-rays, which one wishes to dispense with. In a second embodiment, it is proposed to match the virtual models of the dental arches and a mandibular marker, by pointing in the patient's mouth at least four determined points of the dental arches by means of a stylet. The stylus includes objects that can be detected by the camera which locates the mandibular marker and arranged according to a known geometry. It is thus possible to locate the virtual model of the mandibular arch with respect to the patient's landmark attached to said arch.

An alternative to this pointing technique is presented in document WO 2016/062962, which implements a facial recognition technique. From a stereoscopic image of the patient's face on which at least three teeth of the patient's maxillary arch appear, said teeth are detected by a facial recognition process, and said teeth are put in correspondence on the surface model three-dimensional image of the patient and on the model of the maxillary arch. However, depending on the algorithms used, this facial recognition technique can still be subject to inaccuracies.

The animation of virtual models of the dental arches based on the patient's mandibular kinematics allows occlusal aspects to be taken into account in the planning of treatment.

For certain clinical applications, particularly in order to control the aesthetic implications of a treatment, it may be advantageous to visualize the effect of the treatment on a three-dimensional model of the patient's face. Such a model (“face scan” according to the English terminology) is typically obtained by digitizing the patient's face in three dimensions. In this case, the problem arises of registering the virtual models of the dental arches with the three-dimensional model of the patient's face.

DISCLOSURE OF THE INVENTION

An aim of the invention is therefore to design a robust, reliable and simple to implement process for registering virtual models of the dental arches of an individual with a three-dimensional model of the face of said individual. Given the risks associated with the exposure of an individual to X-rays, the entire process must be able to be implemented with techniques which do not use X-rays (referred to as “non-radiographic” in the following section. text).

To this end, the invention proposes a method for registering non-radiographic virtual models of a mandibular arch and of a maxillary arch of an individual with a non-radiographic digital model of the face of said individual, characterized in that it comprises :

- the fixation of a mandibular marker rigidly on the mandibular arch of the individual, said mandibular marker defining a first frame of reference,

- the supply of a virtual non-radiographic model of the mandibular arch and a virtual non-radiographic model of the maxillary arch, - the digitization of at least part of the surface of the teeth or of a prosthetic device secured to said arch and of at least a rigid part of said marker by means of an intra or extra-oral camera, so as to produce a digital recording of said parts of the mandibular arch and of the marker in the same second repository,

- from said recording and virtual models of the mandibular arch and of the mandibular marker, the matching of the digital model of the mandibular marker with the marker, and of the virtual model of the mandibular arch with said arch, and the location of the virtual model of the mandibular arch in the first frame of reference,

- the acquisition of a non-radiographic digital model of the patient's face, and

- the location of the digital model of the face in the first frame of reference, so as to register the virtual models of the maxillary and mandibular arches with said digital model of the face.

By "supply" is meant in this text the obtaining of pre-existing virtual models or the creation of said virtual models.

Preferably, the method further comprises matching the virtual model of the maxillary arch with the virtual model of the mandibular arch in a determined position of engagement of said arches, for example a maximum intercuspid occlusion.

In some embodiments, the method further includes displaying the virtual models of the maxillary and mandibular arches superimposed on the digital model of the patient's face.

In certain embodiments, the acquisition of the digital model of the patient's face is performed on the patient wearing a frontal marker rigidly secured to the forehead, a virtual model of said frontal marker being provided, and the registration of the virtual models of the maxillary and mandibular arches with the digital face model comprises matching the virtual model of the forehead marker with the forehead marker visible on said virtual model of the face.

In some embodiments, the digital model of the patient's face is textured, so that points plotted on the patient's face and / or anatomical features are visible on said digital textured model, and the registration of the virtual models of the maxillary arches and mandibular with the digital model of the face comprises the pointing of points by a stylus followed by the same localization device as a marker fitted to the patient's face, and the matching of said points and / or anatomical characteristics pointed out and visible points on the digital model of the patient's face.

In certain embodiments, the acquisition of the digital model of the patient's face is carried out on the patient wearing a frontal marker rigidly secured to the forehead, a virtual model of said frontal marker being provided, points previously drawn on the forehead. face of the patient and / or anatomical features being visible on the digital model of the patient's face, and the registration of the virtual models of the maxillary and mandibular arches with the digital model of the face comprises the pointing of said points by a stylus followed by the same device location as the frontal marker, and the mapping of said pointed points and points visible on the digital model of the patient's face.

In some embodiments, the digital model of the patient's face is untextured, and in which, upon acquiring the digital model of the face, recognizable geometric shapes are attached to the patient's face, and the registration of the virtual models. of the maxillary and mandibular arches with the digital model of the face comprises the pointing of said geometric shapes by a stylus followed by the same localization device as a marker fitted to the patient's face, and the matching of said pointed geometric shapes and geometric shapes detectable on the digital model of the patient's face.

BRIEF DESCRIPTION OF THE FIGURES

Other characteristics and advantages of the invention will emerge from the detailed description which follows, with reference to the accompanying drawings in which:

- Figure 1 is a perspective view of a mandibular fixation device equipped with a location marker,

- Figure 2 is a perspective view of the mandibular fixation device of Figure 1 in the absence of the location marker,

- Figure 3 is a block diagram of the scanning of the mandibular arch and part of the mandibular marker using an intraoral scanner;

- Figure 4A is a view of a virtual model of a frontal marker and virtual models of dental arches,

- Figure 4B is a view of a digital model of the face of an individual wearing the forehead marker of Figure 4A,

- Figure 4C is a view of the superposition of the virtual models of the dental arches and the virtual model of the frontal marker of Figure 4A on the digital model of the individual's face,

- Figure 5A is a diagram of another principle of registration of the digital models of the dental arches with the digital model of the face,

FIG. 5B is a view of the superposition of the virtual models of the dental arches on the digital model of the face of the individual after the registration of FIG. 5A. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention proposes to use on the one hand an intraoral scanner - or an extraoral camera in an alternative embodiment - to simultaneously scan the surface of the teeth of a dental arch and at least part of a marker. attached to said arch or part of the device for fixing the marker to the arch, if applicable, and on the other hand a device for scanning the face of the individual. The result of these operations is a digital recording of at least part of the arch and of at least part of the marker, in the same repository which is that of the intraoral scanner, as well as a digital recording of the face surface. As described in detail below, these recordings make it possible to register the virtual models of the dental arches with the digital model of the patient's face via the repository associated with the marker.

This registration method is implemented by a computer which includes a processor configured to implement algorithms for image analysis and for calculating rigid transformations between models defined in different marks. The computer includes a screen coupled to the processor and configured to display the virtual models of the dental arches as well as the other images implemented in the method described below.

Virtual models of dental arches

Virtual models of dental arches can be obtained by any suitable non-radiographic technique. Among the most widely used techniques, we can cite, without limitation, the digitization of impressions or physical models (for example in plaster or in resin) of the patient's arches, using a laboratory scanner, or else direct scanning in the patient's mouth, using an intraoral scanner.

When an arch is totally or partially edentulous, it is known to fix a prosthetic device, also called an occlusion model, which comprises a base covering the prosthetic bearing surface and a bead replacing the teeth and the alveolar bone . A virtual model of said device is obtained from its plan produced by computer-aided design (CAD). In this case, the virtual model of the dental arch is that of the arch provided with said device.

Regardless of the technique used, the scanning is performed for each arch taken separately, and for the two dental arches in meshing situation. In this meshing situation, the two arches are scanned in the same repository, which allows a relationship to be established between the virtual models of the two arches.

The creation of these virtual models can be carried out before the implementation of the registration method according to the invention, or concomitantly with it.

Markers To follow the movements of the mandibular arch relative to the maxillary arch, the patient is equipped with at least one mandibular marker, which defines a landmark attached to the patient's face.

According to one embodiment, the patient is also equipped with a maxillary marker. As an alternative to using a jaw marker, the patient's face itself can be used as a "marker"; thanks to a facial recognition algorithm, it is possible to follow in real time by a camera several characteristic elements of the upper part of the face, which will be associated with the model of the maxillary arch. The upper part of the face is in fact considered to be sufficiently dimensionally stable to be free from a marker as such.

According to one embodiment, each marker comprises several reflecting patches arranged according to a determined geometry. Each marker is tracked by a camera and locating the position of the pellets allows the marker to be located in space.

According to other embodiments, the markers can include pads having a two-color pattern of known geometry, diodes, inertial sensors, etc. which also allow each marker to be located in space by means of a corresponding locator device. Those skilled in the art are able to choose the appropriate location device and the associated marker (s) from the technologies present on the market.

Mandibular marker

The mandibular marker is attached to the patient's mandible rigidly, that is, it is secured so that it does not move relative to the mandible during mandibular movements made by the patient. The mandibular marker can be attached to the arch directly (the marker then incorporating a means of attachment to the arch) or through an attachment device to which it is integral.

WO 2018/158551 describes a mandibular marker which can be used in the present invention.

In the example illustrated in FIG. 1, the marker 2 comprises four reflecting patches 20, the size and relative position of which are known, detectable by an infrared camera. The shape of the pellets is not limiting. Thus, said pellets could be replaced by reflecting elements having any other suitable shape, for example balls. Alternatively, the reflecting patches could be replaced by a test pattern formed from a two-color pattern of known geometry. According to other embodiments, the reflecting pellets could be replaced by diodes, electromagnetic coils, or any other suitable localization means, such as inertial sensors (IMU, acronym for the English term “inertial measurement unit”) , accelerometers, gyroscopes, etc. The marker 2 is attached to the mandibular arch by means of a fixation device 1 on which it is removably mounted. Device 1 comprises:

- an intraoral part 10 intended to be held against the external face of the teeth of the lower jaw (not shown),

- an extraoral part 12 (better visible in FIG. 2) comprising a fixing element for the marker 2,

- A connecting part 1 1 for connecting the intraoral part 10 to the extraoral part 12.

Particularly advantageously, all of the three parts 10, 1 1, 12 are formed in one piece, by molding a biocompatible thermoplastic material.

The intraoral part 10 has a general U shape.

The material and the thickness of the intraoral part are chosen to present a certain flexibility in a direction of separation or of approach of the legs of the U in their plane. Thus, the two legs 100 can be moved apart from their initial position to be inserted into the mouth of the individual without rubbing against the teeth or the gums, and then released once they have been correctly positioned.

According to an optional but advantageous embodiment, the end of the legs of the U is made breakable by the presence of one or more notches 101 which define one or more detachable segments 102. Thus, one or more of said detachable segments can be removed until 'to obtain a length of the legs 100 adapted to the length of the jaw of the individual.

Advantageously, the mechanical strength of the intraoral part 10 on the patient's jaw is ensured at least in part by a biocompatible adhesive (not shown) deposited between the surface of the teeth and the inner face of the intraoral part. Such a biocompatible glue is frequently used in the field of dentistry.

Furthermore, the inner face 103 of the intraoral part, that is to say the face intended to come into contact with the teeth, may have a certain roughness. For example, a part resulting from 3D printing (a so-called SLS laser sintering technique, acronym for the English term “Selective Laser Sintering”) has an appropriate roughness. In the case of a part resulting from molding, the injection mold can undergo a treatment, for example sandblasting or chemical etching, giving it a non-smooth surface state. This roughness makes it possible to improve the mechanical strength of the adhesive with respect to the inner face 103.

On the other hand, the inner face 103 of the intraoral part can be provided with notches 104. Said notches are arranged so as to be located opposite parts in relief on the external surface of the teeth when the device is in place in the tooth. mouth of the individual. The notches 104 therefore fulfill a function of blocking the intraoral part, in particular in the anteroposterior direction, which stabilize the device in the mouth. Particularly advantageously, the height h of the intraoral part is chosen sufficiently low (typically less than the average height of the teeth) so as not to protrude from the plane formed by the upper surface of the teeth of the lower jaw when the device is in place. in the mouth of the individual. For example, the height h is of the order of 5 mm.

Thus, the intraoral part does not interfere with the mandibular kinematics (teeth clenching, chewing movements and others).

The extraoral part 12 has for its part a fixing element 120 for a marker.

In the example illustrated in FIGS. 1 and 2, the marker 2 is fixed by snap-fastening on the extraoral part 12. For this purpose, the mandibular marker 2 comprises, on its inner face (ie opposite the reflective patches), two arranged lugs. one above the other (considering the position of the marker when it is in place on the individual). The fixing element 120 comprises two housings 121, 122 separated by an elastic tongue 123. To place the marker 2 on the fixing device 1, the upper lug is first of all engaged in the housing, then the lower lug is engaged in the housing 122, this engagement causing a slight deformation of the tongue 123 towards the rear (that is to say on the side opposite the reflecting pads). The marker is therefore held on the extraoral part 12 by engagement of the lugs in the housings 121, 122 and by a pressure force exerted by the deformed tongue 123.

The assembly of the marker 2 on the fixation device is advantageously carried out once the fixation device has been placed in the patient's mouth and fixed using the aforementioned biocompatible glue. Thus, the marker does not hinder this positioning operation. The force required for the placement of the marker on the extraoral part is very low, so that it does not affect the mechanical strength of the fixation device vis-à-vis the mandibular arch.

The extraoral part is designed to be rigid enough to support the weight of said marker without deforming.

According to a less preferred embodiment, the marker could form an integral part of the extraoral part.

When the device 1 is in place in the mouth of the individual, the extraoral part 12 is advantageously located below the plane of the lips of the individual (the marker 20 being able for its part to protrude from this plane).

For reasons of stability of the device, the latter is substantially symmetrical with respect to the antero-posterior plane of the individual.

The part 11 of connection between the intraoral 10 and extraoral 12 parts is in the form of a bridge extending from the central region of the intraoral part 10. This bridge has a first section 1 10 extending towards the upper jaw, a second section 1 1 1 extending through the lips and a third section 1 12 for connection to the extraoral part 12. The shape and dimensions of the connecting part are chosen so that, when the device is in place in the mouth of the individual, the second section 1 1 1 extends to the level of the lift plane, without exerting pressure on the lips. Thus, the device 1 remains immobile even in the event of swallowing.

Furthermore, the connecting portion 1 1 is designed to be rigid enough not to deform when the marker 20 is attached to the extraoral portion 12.

Maxillary marker

The jaw marker is attached to the patient's jawbone or to another part of the face rigidly integral with the jawbone, for example the forehead. In the latter case, we speak of a frontal marker.

The maxillary or frontal marker is preferably based on the same technology as the mandibular marker. For example, the jaw marker comprises several reflective patches arranged in a determined pattern.

According to one embodiment, the forehead marker is in the form of an armature intended to surround the patient's forehead and adapted to rest on the ears and on the nasal ridge, which stabilizes it.

Virtual models of the mandibular and maxillary markers (and, where applicable, their fixation device if this is in the form of a separate component) are generally obtained from their plans made by computer-aided design ( CAD).

As noted above, it is possible to dispense with the use of a jaw or forehead marker by using a facial recognition algorithm to track the movements of the patient's upper face.

Recalculation of virtual models of dental arches with a patient repository

Registration involves the use of an intraoral impression camera (also called intraoral scanner) or any other suitable intraoral non-radiographic system to digitize the surface of the teeth of one or both arches (and / or, the where appropriate, a prosthetic device rigidly linked to an arch) so as to form point clouds or meshes.

However, compared to the usual use of such an intraoral device, where the practitioner only scans the surface of the teeth in order to create a virtual model of the corresponding arch, the invention involves also scanning at least part of the tooth. mandibular marker rigidly linked to the mandibular arch.

FIG. 3 is a block diagram of this operation, with a mandibular marker 2 and a device 1 for mandibular fixation of the marker as described with reference to FIGS. 1 and 2. The intraoral impression camera C is introduced into the mouth of the patient. patient, the mandibular arch having previously been equipped with the mandibular marker 2. The practitioner scans with the camera C the surface of the teeth of the mandibular arch and, where appropriate, of the above-mentioned prosthetic device, for example according to the movement shown schematically by the arrow S1.

The practitioner also performs a scan with the camera C of the connection part 1 1, shown schematically by the arrow S2. The scanned area is surrounded by dotted lines.

A digital recording is therefore obtained in the form of a cloud of points or a mesh comprising not only at least part of the surface of the teeth and / or of a prosthetic device secured to the arch but also the connecting part 1 1, in the same repository.

Knowing the geometry of this connecting part 1 1, in particular by the CAD model of the fixing device, the marker can be matched with its virtual model by correlation of the shape of the connecting part 11 on the intraoral scan and on the virtual model.

Likewise, the dental arch can be mapped to its virtual model by correlating the tooth surface on the intraoral scan and on the virtual model. In the event that a prosthetic device is integral with the arch, knowledge of the virtual model of said device makes it possible to determine the location of the edentulous gum.

The mandibular arch and the mandibular marker (or at least the connecting part 1 1) having been scanned in the same frame of reference by the intraoral scanner, the virtual model of the mandibular arch can be located in the marker of the marker mandibular, which defines the patient's landmark attached to the mandibular arch.

The complete digitization of the marker is not necessary since a sufficient non-deformable part is scanned and can be correlated with the virtual model of said part. The correlation is all the more robust as the digitized part has specific geometric characteristics. In this context, it is irrelevant whether the marker is integral with the fixing device or not, as long as the part scanned by the intraoral scanner is sufficiently rigid. By extension, in this text, the expression "digitization of at least a rigid part of the marker" covers the digitization of a rigid part of the fastening device to which the marker is rigidly and reproducibly attached.

In the case where the mandibular marker is formed integrally with the mandibular fixation device, it comprises a deformable intraoral part to adapt to the morphology of the patient and a non-deformable part provided with reflective patches or other objects. detectable. The intra-oral scan must then cover a sufficient part of the non-deformable part. On the other hand, the intraoral part is in principle not sufficient to carry out the registration because it is too deformable.

According to a particular embodiment, the creation of the virtual model of the mandibular arch can be carried out during said intraoral scanning operation; we thus obtain in a single step the virtual model of the mandibular arch and the information necessary for registration. However, the presence of the mandibular marker masks part of the surface of the teeth and is therefore likely to reduce the precision of the virtual model of the mandibular arch.

As an alternative to the use of an intraoral scanner, the scanning of the surface of part of the teeth and of a sufficient part of the mandibular marker can be carried out using an extra-radiographic camera. oral. Said extraoral camera performs a three-dimensional acquisition of the general shape of the mandibular marker and of the teeth visible from the mandibular arch, in the same frame of reference. The virtual models, more precise, of the mandibular marker and the mandibular arch can then be matched according to the same principle as explained above.

Another technique for simultaneously acquiring, in the same frame of reference, the three-dimensional shape of part of the mandibular marker and part of the mandibular arch is photogrammetry. In a manner known in itself, this non-radiographic technique consists in taking photographs from different angles where the teeth and the marker are visible. From this series of photographs, the geometry of the marker is recognized as well as that of the mandibular arch.

The same registration process can be applied to locate the virtual model of the maxillary arch in the frame of a maxillary or frontal marker. In the case of a maxillary marker (for example of the same type as the mandibular marker with a fixation device comprising an intraoral part having a general U shape), the intraoral scanner is used to simultaneously digitize at least part of the body. the surface of the teeth (and / or of a prosthetic device as described above) of the maxillary arch and a sufficient rigid part of the mandibular marker or of its fixing device). In the case of a frontal marker, the extraoral camera is used to simultaneously digitize at least part of the surface of the teeth (and / or of a prosthetic device as described previously) of the maxillary arch and the marker frontal.

According to another embodiment, a marker is rigidly linked to the patient's forehead and thus defines a mark of the maxillary arch. By placing the patient in a known arch-mesh position (usually the maximum intercuspid occlusion (MIO)), which is the one used when creating the virtual arch models, the maxillary arch model is reported. next to the mandibular arch. In this situation, the position of the maxillary marker relative to the mandibular marker is known thanks to a recording made by the extraoral camera. The maxillary arch model can therefore be associated with the maxillary marker. All the points, axes and reference planes of the patient are then associated with the virtual models of the arches. Patient face scan

A three-dimensional digital model of the patient's face is typically obtained by scanning the patient's face in three dimensions. Depending on the digitization technique used, this model may or may not include a texture of the face (in particular colors).

This digitization can be carried out by means of the following techniques: stereoscopy, photogrammetry, laser scanning associated or not with a color detection sensor (RGB, acronym of the English term “Red, Green, Blue”), structured light and / or measurement in time of flight (TOF, acronym of the Anglo-Saxon term "Time Of Flight").

During this scan, the patient can be equipped with a maxillary or frontal marker as mentioned above.

Recalaqe virtual models of dental arches with the digital model of the patient's face

The registration of the virtual models of the dental arches with the digital model of the patient's face uses the aforementioned patient frame of reference.

According to an embodiment illustrated in Figures 4A to 4C, the maxillary arch marker is arranged on the patient's forehead when scanning the patient's face. In this embodiment, this marker 3 comprises reflective patches 30 arranged according to a known geometry (cf. FIG. 4A), but, as indicated above for the mandibular marker, other localization techniques could be used. The virtual model of the marker 3 is obtained for example by its CAD plan.

The virtual models M of the dental arches are moreover obtained by one of the techniques mentioned above.

As illustrated in FIG. 4B, the marker 3 can be found on the digital model of the patient's face. It is therefore possible to match this model of the patient's face with the virtual model of marker 3.

As illustrated in FIG. 4C, the virtual models M of the dental arches having been matched beforehand with the virtual model of the frontal marker thanks to one of the methods described above, it is then possible to correlate said virtual models of the dental arches with the 3D model of the patient's face, and displaying said M models superimposed on the model of the patient's face.

Optionally, a digital model of the patient's face can be generated while the patient is not wearing the forehead marker, and is matched to the digital model of the patient's face wearing the forehead marker by recognition of the mesh shapes of the two models. As a result, the virtual models of the dental arches can be displayed on the model of the patient's face without the frontal marker.

Thus, it is possible to visualize the dental arches regardless of the position of the patient's mouth. In particular, this matching can be performed even if no tooth is visible in the image of the patient's face. In addition, this solution allows to overcome the lack of resolution of certain digital models of the face, which do not make it possible to discern the shape of the teeth even when smiling, and thus allow a correlation of the virtual models of the dental arches with the digital model of the face.

According to one embodiment that can be implemented with a textured digital model of the face, as an alternative to the use of the frontal marker or in association with it, the registration can be carried out using points drawn on the face. of the patient or placed on the face in the form of stickers, and / or anatomical features of the face, such as moles, scars, etc. These points or features are also visible on the texture of the digital model of the face. The practitioner then uses a stylus as described in the introductory part of this text, and points with the stylus to the various points or characteristics identified. Each stylus pointing action generates a corresponding point in space in the form of a sphere. The stylus being marked by the camera at the same time as the front marker, the position of the spheres is determined in the frame of the front marker.

Optionally, the registration between the facial model and the virtual models of the dental arches can be performed only using the points and anatomical features of the face, without locating the frontal marker on the facial model. In this case, the patient is equipped with a mandibular marker for the operation of registering the mandibular arch with the mandibular marker, as previously described. The pointing of the points and / or anatomical characteristics of the patient is then performed using the stylus as explained previously. This pointing makes it possible to match the spheres generated by each pointing action of the stylus with the marks associated with the mandibular and maxillary markers. Before or after this operation, the patient's face is also digitized, without any marker on the patient, so as to generate a textured digital model of the face. The points or anatomical features pointed using the stylus being visible on said textured digital model, and correlated with the virtual models of the mandibular arch and of the maxillary arch, it is thus possible to match the virtual models of the arch. mandibular and maxillary arch and digital model of the face.

This embodiment is illustrated in Figures 5A and 5B.

As illustrated in the upper part of Figure 5A, the patient is equipped with the mandibular marker and the frontal marker 3 for the acquisition of mandibular kinematics.

The digital model of the patient's face (the sides of which can be seen on the left and on the right in FIG. 5A), is obtained while the patient is not wearing either the mandibular marker or the frontal marker. However, points of color P1 -P4 located at the level of anatomical points characteristic of the face, such as respectively the two condyles, the top of the nose and the gap between the base of the nose and the upper lip are visible on the digital color model.

The matching of the models is made possible by pointing these same points P1 -P4 with the stylet 4 when the patient is equipped with the mandibular marker and the frontal marker.

These points define a reference frame of the patient RP which is common to the virtual models of the dental arches and to the digital model of the face.

FIG. 5B illustrates the result of the registration, allowing a superposition of the virtual models of the dental arches on the digital model of the patient's face.

In the event that the digital model of the face is not textured, it is possible to fix on the patient's face, before scanning the face, geometric shapes recognizable by an image processing algorithm. Advantageously, these geometric shapes include a suitable location for the stylus, for example a hollow of suitable size to receive the tip of the stylus.

Model matching is then made possible by pointing to these locations with the stylet when the patient is equipped with the mandibular marker and the forehead marker.

The combination of the registration of the forehead marker on the digital model of the face and the pointing of points or anatomical features increases the robustness of the registration process between the virtual models of the arches and the digital model of the face. In particular, since the face is less rigid than the dental arches, due to the mobility of the muscles or the depression of the skin during the application of the stylet, there may be differences between the digital model of the face with and without marker.

Naturally, the representations of the markers in the appended figures are given only by way of illustration and a person skilled in the art can choose any other form of marker having a rigid part suitable for the registration process described above.

Claims

1. Method for registering non-radiographic virtual models of a mandibular arch and of a maxillary arch of an individual with a non-radiographic digital model of the face of said individual, characterized in that it comprises:

- the supply of a virtual non-radiographic model of the mandibular arch and a virtual non-radiographic model of the maxillary arch,

- the digitization of at least part of the surface of the teeth or of a prosthetic device secured to said arch and of at least a rigid part of said marker by means of an intra or extra-oral camera, so as to produce a digital recording of said parts of the mandibular arch and of the marker in the same second repository,

2. The method of claim 1, further comprising matching the virtual model of the maxillary arch with the virtual model of the mandibular arch in a determined position of engagement of said arches.

3. Method according to one of claims 1 or 2, comprising displaying the virtual models of the maxillary and mandibular arches superimposed on the digital model of the patient's face.

4. Method according to one of claims 1 to 3, wherein the acquisition of the digital model of the patient's face is carried out on the patient carrying a frontal marker (3) rigidly secured to the forehead, a virtual model of said frontal marker being provided. , and the registration of the virtual models of the maxillary and mandibular arches with the digital model of the face comprises the matching of the virtual model of the frontal marker with the frontal marker visible on said virtual model of the face.

5. Method according to one of claims 1 to 4, wherein the digital model of the patient's face is textured, so that points plotted on the patient's face and / or anatomical features are visible on said digital textured model, and the registration of the virtual models of the maxillary and mandibular arches with the digital model of the face comprises the pointing of points by a stylus followed (4) by the same localization device as a marker (1, 3) fitted to the patient's face, and matching said pointed points and / or anatomical features to points visible on the digital model of the patient's face.

6. Method according to one of claims 1 to 4, wherein the acquisition of the digital model of the patient's face is performed on the patient carrying a frontal marker rigidly secured to the forehead, a virtual model of said frontal marker being provided, points previously drawn on the patient's face and / or anatomical features being visible on the digital model of the patient's face, and the registration of the virtual models of the maxillary and mandibular arches with the digital model of the face comprises the pointing of said points by a followed stylus by the same localization device as the frontal marker, and the matching of said pointed points and points visible on the digital model of the patient's face.

7. Method according to one of claims 1 to 4, in which the digital model of the patient's face is non-textured, and in which, during the acquisition of the digital model of the face, recognizable geometric shapes are fixed on the face. of the patient, and the registration of the virtual models of the maxillary and mandibular arches with the digital model of the face comprises the pointing of said geometric shapes by a stylet followed (4) by the same localization device as a marker (1, 3) fitted to the patient's face, and matching said pointed geometric shapes to geometric shapes detectable on the digital model of the patient's face.