HK1250324B - Method for determining a map of the contacts and/or distances between the maxillary and mandibular arches of a patient - Google Patents

Description

The field of invention

The present invention relates to a method for determining a mapping of the contacts and/or distances between the teeth of the maxillary and mandibular arches of an individual.

The back-plan of the invention

The recording of an individual's mandibular kinematics has made important advances in the design of dental appliances, allowing three-dimensional models of dental arches to be animated and in particular to visualize the gear of the teeth.

US 2003/0214501 describes a method for determining a mapping of the distance between the teeth of the maxillary and mandibular arches of an individual.

WO 2013/030511 describes a design process for a dental appliance that records the patient's mandibular kinematics.

This procedure first involves either obtaining a volumetric image of the facial mass by a CT scan technique or determining the reference planes of the facial mass by locating points of interest on the patient's face.

In addition, three-dimensional models of the patient's dental arches are obtained, which are positioned relative to each other during their creation and are compared with the volumetric image of the facial masses or the reference planes determined in advance.

The recording of mandibular kinematics is carried out by equipping the patient with a marker fixed on the patient's forehead and markers fixed directly on the teeth of the mandibular arch or on the mandible by means of a support, and by detecting and recording the movements of these markers by means of a camera during the patient's mandibular movements.

The mandibular kinematics thus recorded can be applied to three-dimensional models of the arches to obtain a numerical simulation of the relative displacement of the two arches.

A criterion of interest for the practitioner designing a dental appliance is the configuration of the interdental contacts.

It would therefore be desirable to be able to exploit recorded mandibular kinematics to obtain a mapping of interdental contacts or distances between the teeth of the two arches.

However, the determination of these maps requires a significant computation time due to the size of the numerical models to be manipulated.

A brief description of the invention

One purpose of the present invention is to map the contacts and/or distances between the teeth of the two arches in a limited computation time.

In accordance with the invention, a method is proposed for determining a mapping of the contacts and/or distances between the teeth of the maxillary and mandibular arches of an individual, characterized by the following steps: obtaining the mandibular kinematics recorded on the subject, the mandibular kinematics being recorded by detecting and recording, by means of a camera, the movements of markers fixed on the patient's forehead and on the mandibular arch during the patient's mandibular movements,obtaining surface meshes of the maxillary arch and the mandibular arch and the repositioning of these meshes relative to each other,the creation of a reduced mesh of at least one of those arches, including the selection, in the mesh of that arc, of meshes whose nodes are located at a distance of less than 1 cm from the mesh of the antagonistic arc,the creation, for each mesh of that reduced mesh, of an encompassing box comprising a plurality of voxels surrounding that mesh,from the maxillary kinematics, the calculation of a network of contacts including, for each voxel of the encompassing box, information on the existence of a contact between that voxel and a node in the void of the antagonistic arc's mesh during a relative movement of the maxillary-maxilar-maxillary-arc's viscosity.

According to the invention, the process also includes: for each node of the reduced mesh, determination, from the network of contacts, of whether or not there is a contact between that node and a node of the antagonistic arcade mesh,application of a colour representative of the existence of a contact to each mesh comprising a node for which a contact has been detected, and display of that colour on each respective mesh of the arcade mesh, so as to form a map of the contacts between the teeth of the two arcades.

The invention involves the use of mandibular kinematics to animate the arcade meshes and the re-actualization of the colour display during this animation.

One method of production is to temporarily retain the previous display and gradually reduce it when the display is refreshed.

Depending on the form of implementation of the invention, the process also includes: for each node of the reduced mesh, the distance between that node and a node of the mesh of the opposing arcade shall be determined from the network of contacts,a colour representative of that distance shall be applied to each mesh comprising that node and the colour shall be displayed on each respective mesh of the mesh of the arcade so as to form a map of the distances between the teeth of the two arches.

One method of production is to use mandibular kinematics to animate the meshwork of the arcades and to refresh the color display during this animation.

The reduced mesh is partitioned into a k-d tree.

In one way, a reduced mesh is created for each of the two arcades.

In one embodiment of the invention, the limit of the displacement envelope of an arcade relative to the antagonistic arcade is determined by implementing the following steps: from the mesh of one of these arches, an appropriate volume structure is created to encompass all the positions of the said arc in relation to the antagonistic arc during the mandibular kinematics,the distance between the centre of the said arc and each node of the antagonistic arc mesh is determined for each position of the arc and for each voxel of the said structure,whether each voxel is inside or outside the antagonistic arc mesh is determined and the voxels inside the antagonistic arc mesh are memorised,the voxels bounding the teeth are translated,the contacts between the two teeth are summed for the whole set,the voxels are constructed from memory cards,a surface representing the contact between the two teeth and the surface of the arches is displayed on the map,the contact between the teeth is translated,the contact between the two teeth is constructed from memory cards,a surface representing the contact between the teeth and the arches is displayed on the map,and/or a surface representing the movements of the teeth.

In particular, it is advantageous to record the mandibular kinematics by equipping the patient with markers fixed directly to the teeth of the mandibular arch or to the mandible by means of a support.

The invention also relates to the use of the above process to design a dental prosthesis to be implanted into an individual's arch, including: the first mesh of the jaw arc,from this first mesh,the implementation of the process to generate a mapping of the contacts and/or distances between the teeth of the mandibular and maxillary arches,the adjustment of a model of the prosthesis so as to optimise the contacts and/or distances obtained when the model of the prosthesis is integrated into this first mesh.

Second, the design of the prosthesis may include: the second mesh of the arch with teeth prepared to receive the prosthesis,the application of mandibular kinematics to the second mesh,the design of the final prosthesis in such a way as to respect the contacts and/or distances obtained with the adjustment made on the first mesh.

The invention also relates to a computer program product containing a set of instructions which, when loaded onto a computer, enable the process as described above to be implemented.

The product may be on any computer medium, such as a memory or CD-ROM.

A brief description of the drawings

Other features and advantages of the invention will be shown in the following detailed description, by reference to the attached drawings on which: Figure 1 is a principle diagram illustrating the recording of mandibular kinematics,Figure 2 shows a contact map display screen,Figure 3 shows a distance map display screen,Figure 4 shows a GFP and the corresponding arcade model,Figure 5 shows a distance map display screen on a GFP.

The first two are the following: The use of the test chemical is not recommended for the treatment of the test chemical.

Before the process was implemented, dental arches were scanned in a known and reproducible gear occlusion relationship. One tool used for this purpose is an intraoral optical fingerprint camera. One arc is scanned and then the other, as well as a vestibular (on the side) impression of the gear teeth to determine the position of one arc in relation to the other. This operation is known in itself and is not part of the invention. Another method may involve using a table scanner.

The result of these scans is a superficial meshwork of the maxillary and mandibular arches, each meshwork defined in an orthorhombic reference of the scanner.

The test is performed on a test tube.

The purpose of recording mandibular kinematics is to make it possible to know how the mandible moves in space and to use this kinematics to animate three-dimensional models of dental arches in order to guide the design of a dental prosthesis or other correction device (orthodontic device, gutter, ...).

A method of recording this, as well as of shifting dental arches relative to patient reference planes or axes, has already been described in WO 2013/030511 and can be implemented in the present invention, but the invention is not limited to the techniques described in this document.

In general, recording of mandibular kinematics is carried out by equipping the patient with a marker fixed to the patient's forehead and with markers fixed directly to the teeth of the mandibular arch or to the mandible by means of a support, and by detecting and recording the movements of these markers by means of a camera during the patient's mandibular movements.

Figure 1 is a basic diagram illustrating the recording of mandibular kinematics.

A 4000-arrow is placed on the patient's jawbone, attached to the teeth, with markers detectable by a 1000-camera.

The patient is also equipped with a 2000 headset bearing 2001 markers detectable by the said camera 1000.

In the example illustrated, camera 1000 is a stereoscopic camera comprising two lenses 1001, 1002.

However, any other type of camera on the market may be used, provided that the headgear and the jaw-arm are fitted with markers detectable by the said camera.

These markers can be diodes tracked by the camera, but they can also be black and white mirrors or colours or spheres, pellets or other reflective objects. The movement of the markers in the mandible is tracked by the camera 1000 and this compared to the 2001 markers in the forehead. A rigid transformation allows the movement of the 3D mandibular arch model to be deduced from the 3D maxillary model.

The model of the maxillary arch and the reference planes are combined to animate the moving mandible.

Creating a simplified arcade mesh

The calculations require a large graphical resource, the three-dimensional models of arcades are resized to allow the implementation of the process on most computers.

For this purpose, in the three-dimensional model of an arcade, which consists of a surface mesh, only the meshes whose nodes (vertices) are located at a distance of less than 1 cm from the antagonistic arcade are retained.

This reduced mesh is obtained at least for the arcade on which the contact map and/or distance map is to be displayed, but it is also possible to create this reduced mesh for the antagonistic arcade, especially if the contact and/or distance maps are to be displayed on the models of the two arcades.

A pre-calculation step is then implemented in the background from the reduced (or simplified) mesh above. Some values are invariant, such as the distance between the meshes of the two arcs. An algorithm for calculating the distance between a point and a three-dimensional mesh (e.g. a triangle, although the shapes of the meshes may be different) is applied and stored in memory in order to later virtually materialize the contact areas.

K-d tree

In an advantageous embodiment, the network of contacts is spatially partitioned into a k-d tree (or k-d tree according to Anglo-Saxon terminology).

Map of contacts

The contact map is intended to inform the practitioner whether or not there is contact between the two arcades, without distance information.

The sensitivity can be adjusted at will. Typically, a contact sensitivity between -200 μm and +200 μm can be used.

In one embodiment, the contact map may be displayed statically on the mesh of one of the arcades, by applying a colour representative of the existence of a contact to each mesh containing a node for which a contact has been detected and displaying that colour on each respective mesh of the arcade mesh.

Another way of doing this is to display the contact map dynamically, i.e. the jaw kinematics are applied to animate the meshwork of the arcades and the colour display is updated during this animation.

The advantage of this display is that it can be combined with a shooting star effect by allowing the trace of the contact to be tracked on the arcade concerned. To this end, the display of the contact areas is temporarily retained for the previous position. This effect is achieved by calculating the color area to be displayed based on the age of the last contact.

Figure 2 shows an example of such a contact map displayed on the mesh of an arcade.

Map of distances

The distance map is intended to provide the practitioner with information on the distance between the two arcades by means of a colour code.

This colour code also indicates the proximity of a contact, so that when the two meshes are approaching a contact, the colour of the meshes of the mesh concerned is different from the colour applied when the two meshes touch.

To construct the distance map, the software processes all nodes in the respective arcade in such a way as to determine, for each of the nodes, the nearest antagonistic arcade nodes.

The colour code is then deduced for each node in the mesh, based on the distance calculated by the algorithm.

As with the aforementioned contact map, the distance map can be displayed dynamically, i.e. one applies mandibular kinematics to animate the meshwork of the arcades and one re-updates the color display during this animation.

Figure 3 shows a polychrome distance map showing the proximity of dental contacts.

Determination of the limit of the movements of an arc relative to the antagonistic arc

This envelope is also referred to by the acronym FGP, from the Anglo-Saxon term Functionally Generated Path .

This surface is used in computer-aided design of dentures to ensure that their shape fits into the movement of the opposing teeth without any bumps or discomfort.

This envelope can be calculated for either the mandibular arcade or the maxillary arcade, with the understanding that only the mandibular arcade is mobile.

To determine the FGP, the arcade from which the FGP is to be obtained is fitted with a volume structure similar to a box encompassing the complete arcade.

The volume structure must therefore be large enough to accommodate the different arcade positions that will constitute the FGP.

Then, for each voxel of the volume structure, the distance between the centre of that voxel and a mesh of the antagonistic arcade mesh is calculated, which determines whether or not there is contact, for all positions of the arcade and for each mesh of the antagonistic arcade mesh.

The normal at each mesh of the antagonistic arcade mesh allows one to determine whether the voxel is inside or outside the mesh. The voxels inside the mesh are then kept in memory, i.e. the voxels that translate a contact between the two arcades.

The application of the marching cube algorithm allows the surface of the FGP to be constructed from the voxels stored.

As with arcade meshes, a distance map or contact map relative to the antagonist arcade can be displayed on the surface of the FGP.

Figure 5 thus shows a map showing the distances between the FGP and the maxillary arch mesh.

Design of a denture

To design a dental prosthesis, it is possible to validate the contacts between arch models with restored teeth with provisional prostheses (or arch models with unprepared teeth), and then to replace these first models with second models with teeth prepared for permanent prostheses.

The first and second 3D models of arcades can be correlated, as long as there are enough points of association between two meshes. One method used is to click and position landmarks on the two meshes at recognizable areas.

Once the new model is paired, the mandibular kinematics recorded for the first model are paired with the second model to animate it in the same way.

The aim is to control and validate movement and to perform prosthetic restorations that integrate into the patient's chewing movements when the practitioner considers at the stage of the provisional prostheses that the kinematics are correct and functional.

Export of data

All data obtained during the implementation of the process can be stored and exported to computer-aided design software, including the position of the arcades relative to each other, reference planes, occlusal sheath, anatomical points, bicondyline axis and FGP.

The design of dentures, braces or occlusal gutters takes these data into account to guide the design.

On the other hand, the components provided by the software can be manufactured by means of a 3D printer. The position of the models relative to each other can be maintained by means of an occluder. Interchangeable models of the FGP can be mounted on the same occluder, which allows the prosthetist to manually modify the design to adjust the occlusion.

The Commission shall adopt implementing acts laying down the rules for the application of this Regulation.

The Commission shall be assisted by the European Parliament.

Claims (10)

1. Method for determining a mapping of contacts between the teeth of the maxillary arch and the mandibular arch of a patient, characterised in that it comprises the following steps:

   - obtaining the mandibular kinetics recorded on the patient, said mandibular kinetics being recorded by locating and by recording, by means of a camera (1000), the displacements of markers (2001) attached on the one hand to the forehead of the patient and on the other hand to the mandibular arch, during mandibular movements of the patient,

   - obtaining surface meshes of the maxillary arch and the mandibular arch and registering said meshes relative to one another,

   - creating a reduced mesh of at least one of said arches, comprising the selection, in the mesh of said arch, of the cells in which the nodes are located at a distance of less than 1 cm from the mesh of the opposite arch,

   - creating, for each cell of said reduced mesh, a bounding box comprising a plurality of voxels surrounding said cell,

   - using the mandibular kinetics, calculating a network of contacts comprising, for each voxel of the bounding box, information on the existence of a contact between said voxel and a node of the mesh of the opposite arch during a relative movement of the mandibular arch in relation to the maxillary arch,

   - for each node of said reduced mesh, determining, using the network of contacts, the existence or not of a contact between said node and a node of the mesh of the opposite arch,

   - applying a colour representative of the existence of a contact to each cell comprising a node for which a contact has been detected, and

   - displaying said colour on each respective cell of the mesh of the arch, so as to form a map of the contacts between the teeth of the two arches.

   - applying the mandibular kinetics to animate the meshes of the arches and updating the display of colour during this animation.
2. Method according to claim 1, characterised in that during the updating of the display, the previous display is temporarily conserved and it is progressively attenuated.
3. Method for determining a mapping of distances between the teeth of the maxillary arch and the mandibular arch of a patient, characterised in that it comprises the following steps:

   - obtaining the mandibular kinetics recorded on the patient, said mandibular kinetics being recorded by locating and by recording, by means of a camera (1000), the displacements of markers (2001) attached on the one hand to the forehead of the patient and on the other hand to the mandibular arch, during mandibular movements of the patient,

   - obtaining surface meshes of the maxillary arch and the mandibular arch and registering said meshes relative to one another,

   - creating a reduced mesh of at least one of said arches, comprising the selection, in the mesh of said arch, of the cells in which the nodes are located at a distance of less than 1 cm from the mesh of the opposite arch,

   - creating, for each cell of said reduced mesh, a bounding box comprising a plurality of voxels surrounding said cell,

   - using the mandibular kinetics, calculating a network of contacts comprising, for each voxel of the bounding box, information on the existence of a contact between said voxel and a node of the mesh of the opposite arch during a relative movement of the mandibular arch in relation to the maxillary arch.

   - for each node of said reduced mesh, determining, using the network of contacts, the distance between said node and a node of the mesh of the opposite arch,

   - applying a colour representative of the distance to each cell comprising said node, and

   - displaying said colour on each respective cell of the mesh of the arch, so as to form a map of the distances between the teeth of the two arches.

   - applying the mandibular kinetics to animate the meshes of the arches and updating the display of colour during this animation.
4. Method according to claim 1 characterised in that the reduced mesh is partitioned in the form of a k-d tree.
5. Method according to one of claims 1 to 4, characterised in that a reduced mesh is created for each of the two arches.
6. Method according to one of claims 1 to 5, in which:

   - using the mesh of one of said arches, a volumetric structure is created adapted to encompass all of the positions of said arch with respect to the opposite arch during the mandibular kinetics,

   - for each position of the arch and for each voxel of said structure, the distance is determined between the centre of said voxel and each node of the mesh of the opposite arch,

   - it is determined whether each voxel is located inside or outside the mesh of the opposite arch and the voxels that are located inside said mesh are memorised, said voxels translating a contact between the arches,

   - said contacts are accumulated for all of the positions,

   - using said memorised voxels, a surface is constructed representing the limit envelope of the displacements of the teeth,

   - on said surface, a map of the contacts, respectively a map of the distances, between the teeth of the two arches is displayed.
7. Method according to one of claims 1 to 6, in which, to record the mandibular kinetics, the patient is equipped with markers attached directly to the teeth of the mandibular arch or to the mandible through a support.
8. Use of the method according to one of claims 1 to 7 to design a dental prosthesis to implant on an arch of the patient, characterised in that it comprises:

   - obtaining a first mesh of said arch,

   - using said first mesh, implementing the method to generate a mapping of the contacts or a mapping of the distances between the teeth of the mandibular and maxillary arches,

   - adjusting a model of the prosthesis so as to optimise the contacts and/or distances obtained whenthe model of the prosthesis is integrated in said first mesh.
9. Use according to claim 8, characterised in that it further comprises:

   - obtaining a second mesh of the arch presenting the teeth prepared to receive said prosthesis,

   - replacing the first mesh by the second mesh,

   - applying the mandibular kinetics to the second mesh,

   - designing the definitive prosthesis so as to respect the contacts and/or distances obtained with the adjustment made on the first mesh.
10. Computer programme product including a set of instructions which, once loaded on a computer, enable the implementation of the method according to one of claims 1 to 7.