Method and device for the automatic localization of condylar points in a patient model

Abstract

A method for locating the condylar points (2) of a patient (1), comprising: determining (S1) a first position of a bicondylar axis in a first position of the patient's mandible; obtaining (S2) at least a second position of the bicondylar axis in a second position of the mandible after a right lateral displacement; obtaining (S3) at least a third position of the bicondylar axis in a third position after a left lateral displacement; obtaining (S4) a right, or respectively left, condylar point by determining a point minimizing a distance measurement between the first position and at least a second, or respectively third, position. Figure for the abstract: Fig. 2

Description

Title of the invention: Method and device for the automatic localization of condylar points in a model of a patient FIELD OF THE INVENTION

[0001] The present invention relates to an automatic method and a device for precisely determining the location of condylar points in a digital model of a patient, including the facial mass.

[0002] This determination is important in order to allow precise modeling of the patient's facial mass, and in particular of his face and, above all, of its kinematics. The term "face" can be understood here as including all the cutaneous, osteoarticular, neuromuscular parts, the dental arches, etc. of the front hemisphere of the patient's head.

[0003] For example, precise knowledge of the face and its kinematics can allow optimal adjustment of articulators or other tools used in dentistry.

[0004] A mechanical articulator has long been used as an essential tool in laboratory procedures in different fields of dentistry, such as orthodontics, denture design, maxillofacial, or orthognathic surgery, etc., to assist in both diagnosis and treatment planning. A mechanical articulator is a physical instrument that facilitates the reproduction of the relationship between the jaws and the base of the skull, as well as the mandibular articulation.

[0005] With technological advances, the articulator is moving from a mechanical device to its digital equivalent, a "virtual articulator" (VA). A virtual articulator is a computer tool that can reproduce the relationship between the jaws and simulate the movement of the jaws.

[0006] For this type of tool, it is clear that there is a need to improve the modeling of the kinematics of the patient's face, and not just its static anatomy.

[0007] Among the essential joints of the human face are the temporomandibular joint, which allows movement of the mandible.

[0008] This joint includes a mandibular condyle (hereinafter abbreviated to simply "condyle") which is the rounded eminence at the end of the mandibular bone and which articulates with the mandibular fossa via the articular disc.

[0009] The condyles, left and right, form a bi-condylar axis which passes through these two condyles, respectively left and right.

[0010] In the existing literature, different bi-condylar axes could be defined, for example the hinge axis, the kinematic axis, or anatomical axes.

[0011] The location of the condyles is therefore essential in order to be able to determine a bi-condylar axis allowing in particular the modeling of mandibular kinematics.

[0012] Historically, the study of mandibular kinematics is carried out by taking cutaneous points (i.e. on the surface of the face) as reference.

[0013] For example, a practitioner can, by palpation, feel the bony outgrowths corresponding to the mandibular condyles.

[0014] Other techniques for locating condyles rely on statistical conventions.

[0015] Indeed, the general location of the condyles is known, but their actual position on an individual patient may vary and the condyles may lack precise visual indicators. Thus, several definitions of the condylar point may be used.

[0016] Thus, mechanical articulators, proposed in the past, were based on distinct locations of the condyles.

[0017] [Fig.5] illustrates some locations of the condyles established by the state of the art: - Guichet Point, PI, corresponding to the Denar® articulator by N. Guichet, in 1960 - Gy point si, P2, corresponding to the Dentatus® articulator - Monson Point, P3, - Duminil Point, P4,

[0018] For example, the Duminil condylar point P4 can be located 9.5 mm forward from the angle of the tragus PT and 7.5 mm vertically downward from a straight line formed between the ectocanthion PO and the angle of the tragus.

[0019] In another example, to ensure the transfer of models of the dental arches by referencing them in relation to the bi-condylar axis, systems such as facial bows with ear tips have become the norm. The positioning of these same tips in the auditory canal will make it possible to deduce the location of the condyles and therefore that of their mechanical representation during assembly on the articulators.

[0020] Yet another technique is to use pointing styluses and look for the place where it only moves in rotation during mandibular movements.

[0021] Still other methods of locating the condyles are described in the prior art. For example, we can cite the thesis of Mathilde Bapelle, “Posterior determinants of mandibular kinematics: literature review and analysis of Modjaw@ recordings”, Human Medicine and Pathology. 2020. dumas-02976829.

[0022] However, all of these methods are based on the determination of a cutaneous condylar point, i.e. located on the surface of the face. However, the condyles are under- cutaneous (i.e. under the skin) and it is important to locate these points precisely in order to obtain a good modeling of the mandibular kinematics.

[0023] A poor approximation of a condylar point can lead to poor modeling of mandibular kinematics. This poor modeling can then lead to poor parameterization of an articulator, or any other simulation tool.

[0024] It can also induce a misinterpretation of mandibular kinematics, and thus cause the determination of dyskinesia that does not exist.

[0025] We therefore understand the need to improve the precision in determining the location of the condylar points. Summary of the invention

[0026] According to a first aspect, the invention proposes a method for locating the condylar points of a patient, comprising: - determining a first position of a bicondylar axis in a first position of the mandible of said patient, - obtaining at least a second position of said bi-condylar axis in a second position of said mandible after a right lateral displacement; - obtaining at least a third position of said bi-condylar axis in a third position of said mandible after a left lateral displacement; - obtaining a right, respectively left, condylar point by determining a point minimizing a distance measurement between said first position of said bi-condylar axis and said at least one second, respectively third position of said bi-condylar axis.

[0027] Thus, the method makes it possible to determine condylar points which are not constrained by the surface of the face, but are as close as possible to the true location of the condyles.

[0028] Furthermore, as seen previously, different cutaneous condyles have been proposed in the literature. The method makes it possible to free oneself from these subjective choices.

[0029] The method makes it possible to free oneself from the patient's anatomy by basing itself solely on the kinematic behavior of the mandible.

[0030] This kinematic movement can be represented by a modeling of the kinematics (which makes it possible to obtain a position for each instant), or by a discrete sequence of different positions of the movement captured at different instants. These captures can be carried out via images, radiographs, etc. Movement simulation mechanisms can also be implemented.

[0031] Furthermore, the method is agnostic on the determination of an initial bi-condylar axis: whatever the type of bi-condylar axis chosen, the method will make it possible to optimize the location of the condylar points on this axis.

[0032] Still other advantages will appear in the description which follows.

[0033] According to different implementations, this method may comprise one or more of the following features, taken individually or in combination. - said first, second and third positions of said bi-condylar axis are obtained from a modeling of the mandibular kinematics; - said first, second and third positions of said bi-condylar axis are displayed on a human-machine interface in order to allow an operator to select a second, respectively third position of said bi-condylar axis, from among said at least one second, respectively third, position of said bi-condylar axis; - said point is determined by the intersection of said first position of said bicondylar axis with said at least one second, respectively third position of said bicondylar axis, in a plane; - said positions of said bi-condylar axis are displayed on a human-machine interface in order to allow an operator to select said point; - said condylar points are used to configure an articulator, or any other simulation tool;

[0034] According to another aspect, the invention proposes a computer program comprising instructions adapted for the implementation of a method as previously described when said program is deployed on an information processing platform.

[0035] According to another aspect, the invention proposes a device for locating the condylar points of a patient, comprising processing means and a human-machine interface, adapted to, in collaboration, implement the method as previously described.

[0036] According to different implementations, this device may further comprise a camera substantially oriented towards said patient. BRIEF DESCRIPTION OF THE FIGURES

[0037] Other characteristics and advantages of the invention will now be described in the following description of different implementations in conjunction with the appended figures. - [Fig.l] illustrates a face of a patient on which different elements have been positioned for understanding embodiments of the invention. - [Fig.2] shows a diagram of a functional architecture of a device according to a embodiment of the invention - [Fig.3] illustrates a flowchart of a process according to a mode of realization of the invention. - [Fig.4] illustrates an axial view of the upper surface of a dental arch lower and mandibular bone according to one embodiment of the invention - [Fig.5] illustrates different condylar points proposed in the state of the technical.

[0038] DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0039] The proposed method is based on the search for condylar points on a bi-axis condylar based on positions of the bicondylar axis corresponding to different moments of a movement of the mandible.

[0040] In [Fig.l] a face 1 of a patient is illustrated.

[0041] The mandible 5 is schematically represented in dotted lines. This articulates with the mandibular fossa at the level of the condyles 2 via the articular disc.

[0042] More precisely, the temporomandibular joint, abbreviated TMJ, is a diarthrosis (or synovial, of the bi-condylar type) which unites the mandibular fossa of the temporal bone with the condyle of the mandible by means of a fibrocartilaginous articular disc and closed by an articular capsule.

[0043] This temporomandibular joint is described in more detail in the scientific literature to which the following Wikipedia page can form an access point:

[0044] https: / / fr.wikipedia.org / wiki / Articulation_temporo-mandibulaire

[0045] The invention aims to locate the condylar points 2.

[0046] As seen previously, it is known and customary to determine cutaneous condylar points, 4, that is to say located on the surface of the skin of the face.

[0047] As can be seen, however, in [Fig.l], there is a substantial gap between the sought condylar points 2 and the cutaneous condylar points 4. This gap is notably linked to the particular anatomy of patient 1.

[0048] In order to best estimate the condylar points, a device and a method are proposed, illustrated by figures 2 and 3.

[0049] The method is based on obtaining different positions of the bi-condylar axis 3 in different positions of the mandible. The positions of the mandible can for example correspond to a reference position and to one or more positions corresponding to a lateral movement.

[0050] The changes in position of the bi-condylar axis 3 are used to deduce the position of the condyles 2, in particular its orientation.

[0051] The positions of the bicondylar axis can be obtained in different ways. It is important here to have different "views", each corresponding to different positions of the mandible.

[0052] When the patient makes a lateral movement, these different views can correspond to different moments of this movement.

[0053] These views may correspond to images representing the jaw in at least two different positions. These images may come from optical cameras, infrared cameras, 3D scanners, intraoral scanners, ultrasonic sensors, magnetic sensors, inertial sensors, etc.

[0054] The positions of the bi-condylar axis can also be obtained from a modeling of the mandibular kinematics.

[0055] Thus, in particular, the determination of the first position of the bi-condylar axis can be determined from a modeling of the mandibular kinematics, or statically from for example an analysis of the face or from anthropometric analyses or from different medical imaging techniques: superposition of “cone beams” (or cone beam volume tomography), X-rays, images from a facial scanner, association of 2D photos, etc.

[0056] The modeling of mandibular kinematics can be carried out according to different methods known in the state of the art.

[0057] The thesis report “Posterior determinants of mandibular kinematics: literature review and analysis of Modjaw® recordings” by Mathilde Bapelle, Human Medicine and Pathology. 2020. dumas-02976829 provides an overview of different technologies for determining a model of a patient's mandibular kinematics.

[0058] We can thus cite mechanical axiography, electronic axiography, digital pantography, and new 3D technologies.

[0059] The Modjaw® system is a mandibular kinematics recording device based on infrared technology. It is part of a process of dematerialization of dental practice, which is increasingly geared towards digital technology.

[0060] A helmet and a mandibular fork equipped with reflective pads are installed on the patient. The camera emits and receives infrared by reflection, which allows the software to calculate the location of the condyles and the mandibular landmarks. The pointing stylus makes it possible to locate, at the start of the manipulation, the positioning of the mandibular condyles (identified by palpation) and the dental landmarks. The software then ensures the reliability of the pointing, and will subsequently recalculate the positioning of the real axis of rotation of the condyles, after recording the rotation axis by manipulation or not, in order to adjust the values ​​as close as possible to reality.

[0061] Another example of implementation is described by French patent FR3027205B1. This document describes a method for modeling the mandibular kinematics of a patient based in particular on capture by stereoscopic camera.

[0062] Other mechanisms for recording movement exist and can also be used. For example, we can cite electromagnetic systems, systems based on ultrasound, systems using inertial sensors IMUs (for "Inertial Motion Unit" in English) ...

[0063] [Fig.2] illustrates a device 20 adapted for locating the condylar points 2 of a patient 1.

[0064] The device 20, illustrated in [Fig.2], may comprise a sensor 21. This sensor may for example be a camera 21 substantially oriented towards the face 1 of the patient. This camera may be a normal optical camera, or an infrared camera. It may also be a stereoscopic camera, such as in patent FR3027205B1 for example.

[0065] The device 20 also comprises processing means 22. These processing means may conventionally comprise one or more processors and one or more memories coupled to the processor(s). Additional circuits may also be provided to collaborate with this or these processor(s) and this or these memories.

[0066] A human-machine interface 24 may also be provided allowing interactions with an operator, a practitioner or the patient himself. This human-machine interface may be adapted to guide the patient so that he performs the actions required of him (for example lateral movements, opening / closing of his mandible), and / or to allow the operator (practitioner) to view and possibly select the detected positions of the bi-condylar axis and the condylar points.

[0067] The device 20 can be adapted to provide the locations of the determined condylar points to an external device 23, for example a virtual articulator or any other simulation tool. These can thus be based on a precise estimation of the location of the condylar points.

[0068] This device 20 is suitable for implementing a method for locating the condylar points (2) of a patient (1), a possible embodiment of which is illustrated by the flowchart in [Fig.3].

[0069] The proposed method comprises - a step SI of determining a first position of the bi-condylar axis in a first position of the patient's mandible; - a step S2 of obtaining at least a second position of the bi-condylar axis in a second position of the mandible after a right lateral displacement 11; - a step S3 of obtaining at least a third position of the bi-condylar axis in a third position of said mandible after a left lateral displacement 12; then, - a step S4 of obtaining a right condylar point, respectively left, by determining a point minimizing a distance measurement between the first position of the bi-condylar axis and at least a second position, respectively third position, of this bi-condylar axis.

[0070] As seen previously, these positions of the bi-condylar axis can for example be obtained from a modeling of the mandibular kinematics.

[0071] Steps S1-S3 can be performed in any order, although it seems more natural to perform step S1 first. Focusing on the left or right condylar point first is obviously ineffective. Different variations of the illustrated flowchart are thus possible.

[0072] Typically, the first position of the mandibular arch 5 is the natural resting position. The position itself is not critical because the method is essentially based on obtaining the positions of the axis for different positions, whatever these positions may be.

[0073] In one embodiment, the first position of the mandible may be a position easily reproducible by a patrician, such as the occlusion position in centric relation, ORC.

[0074] In this first position, a first position of the bicondylar axis can be determined, for example by means of modeling the mandibular kinematics.

[0075] [Fig.4] illustrates an axial view of the upper surface of a mandible 5. The mandible here comprises the lower dental arch and the mandibular bone. The mandible is shown in occlusion, without laterality, which in this example corresponds to the first position.

[0076] In this first position, a first position A1 of the bi-condylar axis can be determined.

[0077] We then search for the right and left condylar points in positions of the mandible after right and left lateral displacement respectively.

[0078] The patient is asked to perform a lateral movement of his mandible, first on one side (with the aim of locating a first condylar point, then on the opposite side (with the aim of locating the second condylar point), as indicated by arrows 11 and 12 in [Fig.l].

[0079] Thus, in a step S2, the patient performs a right lateral displacement and a second position of the bi-condylar axis is thus obtained.

[0080] In a step S3, the patient performs a left lateral displacement and a third position of the bi-condylar axis is thus obtained.

[0081] [Fig.4] illustrates such a second position A2 of the bi-condylar axis after laterality of the mandible 5 (the position of the mandible after laterality is not shown for the clarity of the figure).

[0082] It is therefore understood that the position of the bicondylar axis follows the movement of the mandible.

[0083] In particular, at the level of the skull, the medial side of the joint is formed by a bony wall which continues anteriorly by the temporal condyle. This anatomy has a consequence on the movement: one of the condyles, when the mandible is moved by muscular action, during a lateral displacement must, in order to avoid this bony wall, lower and move forward. It is called the orbiting condyle. This mechanism opens an angle, and on this side, the bicondylar axis moves away from its original position. On the other side, however, the axes tend to move closer together.

[0084] It is also understood that the distance between two positions of the bi-condylar axes (each position forming an axis) corresponding to two positions of the same lateral movement is minimal at the position of the working condylar point 2. According to certain anatomical parameters, the two positions of the axis may or may not intersect.

[0085] Different choices are possible for the second and third positions (which can also be different on one side and the other).

[0086] It may be interesting, however, for these positions to be far enough from the first position in order to involve a significant excursion of the angle between the two positions of the bi-condylar axis.

[0087] In step S4, from each pair of positions of the bi-condylar axis, one of the two condylar points can be determined.

[0088] Thus, a right condylar point is obtained as a point minimizing a distance measurement between the first position of the bi-condylar axis A1 and a second position A2 of the bi-condylar axis determined in a mandibular position in translation to the right.

[0089] And we obtain a left condylar point as a point minimizing a distance measurement between the first position of the bi-condylar axis A1 and the third position A3 of the bi-condylar axis determined in a mandibular position in translation to the left.

[0090] Different methods can be used to calculate the distance measurement and thus determine the respective condylar points.

[0091] According to one embodiment of the invention, the condylar points are located on one of the two positions of the axis of the respective pairs. Each condylar point can be on the first position A1 of the bi-condylar axis, or on respectively the second or third position of the bi-condylar axis, respectively A2, A3.

[0092] According to another embodiment, the condylar points can be the points minimizing the distance to each of the two respective axis positions (this point then not belonging to either of these two axis positions).

[0093] The point of positions of the bi-condylar axis minimizing the distance to the other position of the bi-condylar axis of the couple can be determined algorithmically, via an equation of the respective positions of the bi-condylar axis.

[0094] It can also be determined visually and manually: the positions of the bi-condylar axis can be displayed on a human-machine interface 24 in order to allow an operator to select said point. The operator can visually determine the two points of each position of the axis where the distance is minimal and choose one or the other, if the condylar point belongs to the first position of the axis or to the second or third position of the axis.

[0095] According to one embodiment, the condylar point can be determined as the point of intersection of the first position A1 of the bi-condylar axis A1 with the second A2, or respectively third A3, position of the bi-condylar axis, in a given plane. This plane can be the axial plane, but also the axio-orbital plane, the Frankfurt horizontal plane, the axial plane resulting from the recording of the natural position of the head, the frontal plane, etc.

[0096] The axial plane can be defined as a horizontal plane, when the patient is in a standing position. On such a plane, the positions of the bi-condylar axis, or their projection, necessarily intersect at a point PC which can be defined as the desired condylar point.

[0097] According to embodiments, several second and third positions of the bicondylar axis can be determined. Indeed, it is possible to define intermediate positions between the first and, respectively, second or third positions of the mandible, in order to determine a set of second and third positions of the bicondylar axis.

[0098] According to one embodiment, these positions of the bi-condylar axis can be displayed on a human-machine interface in order to allow an operator to select a second, respectively third, position of the bi-condylar axis, from among said at least one second, respectively third, position of the bi-condylar axis.

[0099] According to one embodiment, the distance to be minimized can then be a distance between each position taken two by two.

[0100] Whatever the implementations, the method makes it possible to obtain an estimation of the right and left condylar points, 2, which is much more precise than the cutaneous condylar points 4, generally used.

[0101] The condylar points thus determined can be used for subsequent treatments.

[0102] This provides more precise modeling of mandibular kinematics that can be used in different ways.

[0103] For example, this modeling can make it possible to configure a virtual articulator 23, or any other digital simulation tool.

[0104] One of the advantages of virtual articulators compared to mechanical articulators of previous generations is that they can have greater precision because they are less constrained by physical aspects.

[0105] But the transition to digital technology allows for greater precision in modeling, and therefore makes it necessary to better determine the different parameters allowing modeling, including the condylar points.

[0106] As seen previously, the proposed method makes it possible to overcome the anatomical particularities of each patient. This axis is also universal in the sense that it does not depend on a choice of a particular cutaneous condylar point (Guichet point, Gysi point, Monson point, Duminil point, etc.), and is less subject to human errors when determining these points by the practitioner.

[0107] It can be validly used to allow the repositioning of other characteristic elements of the “face” or the skull, whether they are other characteristic points, or axes, planes, etc. (sagittal plane, Frankfurt plane, Camper plane, axio-orbital plane, etc.)

[0108] Of course, the present invention is not limited to the examples and the embodiment described and shown, but is defined by the claims. It is in particular susceptible of numerous variants accessible to those skilled in the art.

Claims

Claims

1. Method for locating the condylar points (2) of a patient (1), comprising: - determining (SI) a first position of a bi-condylar axis in a first position of the mandible of said patient, - obtaining (S2) at least a second position of said bi-condylar axis in a second position of said mandible after a right lateral displacement; - obtaining (S3) at least a third position of said bi-condylar axis in a third position of said mandible after a left lateral displacement; - obtaining (S4) a right, respectively left, condylar point by determining a point minimizing a distance measurement between said first position of said bi-condylar axis and said at least a second, respectively third position of said bi-condylar axis.

2. Method according to the preceding claim, in which said first, second and third positions of said bi-condylar axis are obtained from a modeling of the mandibular kinematics.

3. Method according to one of the preceding claims, in which said first, second and third positions of said bi-condylar axis are displayed on a human-machine interface in order to allow an operator to select a second, respectively third position of said bi-condylar axis, from among said at least one second, respectively third, position of said bi-condylar axis.

4. Method according to one of the preceding claims, wherein said point is determined by the intersection of said first position of said bi-condylar axis with said at least one second, respectively third position of said bi-condylar axis, in a plane.

5. Method according to one of the preceding claims, in which said positions of said bi-condylar axis are displayed on a human-machine interface in order to allow an operator to select said point.

6. Method according to one of the preceding claims, in which said condylar points (2) are used to parameterize an articulator, or any other simulation tool (23).

7. Computer program comprising instructions adapted for implementing a method according to one of the preceding claims when said program is deployed on an information processing platform.

8. Device for locating the condylar points (2) of a patient (1), comprising processing means (22) and a human-machine interface (24), adapted to, in collaboration, implement the method according to one of claims 1 to 6.

9. Device according to the preceding claim, further comprising a camera (21) substantially oriented towards said patient (1).

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