LASER CUTTING HOLDING DEVICE, LASER CUTTING DEVICE AND CUTTING METHOD

Abstract

LASER CUTTING HOLDING DEVICE, LASER CUTTING DEVICE AND CUTTING METHOD Holding device (1) for laser cutting of a thermoformed sheet (2) comprising a hollow dental groove (3) substantially in the shape of a U attached to a peripheral edge (4), comprising: - a workpiece holder (5) with a bearing surface (6) intended to receive said thermoformed sheet (2) in support, and with a lateral surface (7) intended to engage forcefully along at least part of its periphery in a receiving cavity (8) formed in the thermoformed sheet (2), - first means for injecting a gas (9), opening onto the bearing surface (6) and shaped to inject said gas into a volume (V) provided between the bearing surface (6) and the thermoformed sheet (2),- Exhaust means with a shaped passage (11) to establish fluidic communication with the external environment (12) of the volume (V) provided between the support surface (6) and the thermoformed sheet (2). Figure to be published with the abbreviation: Fig. 10,

Description

Title of the invention: SUPPORT DEVICE LASER CUTTING, LASER CUTTING DEVICE AND CUTTING METHOD TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the field of orthodontics, and more particularly to dental trays (also called dental aligners) intended to be worn by a patient on one or the other of his dental arches to realign his teeth according to a progressive treatment plan aimed at progressively moving the patient's teeth.

[0002] To produce such dental splints, an intraoral scan of the patient's mouth is performed to take a 3D impression of the current configuration of his dentition.

[0003] Using software, the current configuration of the patient's dentition is virtually replicated, and a progressive treatment plan is then established aimed at progressively moving (in several stages) the patient's teeth from their current configuration in the patient's mouth to a predetermined final configuration.

[0004] Master models of the patient's tooth configuration are then generated for each step. These master models can, for example, be manufactured by 3D printing.

[0005] These master models are then used to plastically deform thermoformable sheets (generally transparent or at least translucent): a thermoformable sheet is overmolded onto each of the master models. After thermoforming, each thermoformed sheet has a hollow dental groove substantially in the shape of a U attached to a peripheral rim.

[0006] A cut is then made to separate the dental gutter from the peripheral sidewalk.

[0007] Manual cutting has sometimes been carried out. This is a lengthy, difficult, and arduous process, and prone to errors. Furthermore, it generally results in dental splints with sharp edges that can be harmful to the patient and must be removed by a subsequent (again, manual) operation. All these manual operations make the dental splint too expensive.

[0008] In document EP 2 760 624 Bl, the cutting is carried out using a laser, maintaining a ratio between the laser energy applied to the thermoformed sheet and the thickness of said thermoformed sheet along a cutting path in such a way The process involves cutting the thermoformed sheet on both sides while preserving the integrity of the master model, which is still overmolded by the thermoformed sheet. The cutting path generally takes into account the soft tissues (gums) located in the immediate vicinity of the teeth. The applicant has never been able to implement such a process, which proves to be very complex in practice because the thickness varies along the cutting path. Furthermore, when the master model is damaged by the laser, the material it is made of (unsuitable for use in a patient's mouth) can contaminate the dental tray, rendering it unusable.

[0009] The applicant has thus carried out laser cutting tests on a thermoformed sheet by first removing the master model from the thermoformed sheet.

[0010] The dental splint obtained after cutting often exhibits yellowed or slightly browned areas. Furthermore, the dental splint frequently has sharp edges that could potentially injure the patient and must be removed by a revision procedure. Description of the invention

[0011] One problem proposed by the present invention is to provide a holding device that allows a thermoformed sheet comprising a hollow dental tray substantially in the shape of a U attached to a peripheral edge to be reliably held during laser cutting, while limiting the risks of yellowing or browning of the dental tray.

[0012] Simultaneously, the present invention aims to limit the need for reworking dental splints after cutting, in particular by limiting the risk of having overly sharp edges that could injure the patient.

[0013] To reach these objects and others, the invention proposes a holding device for laser cutting a thermoformed sheet comprising a hollow dental tray substantially in the shape of a U attached to a peripheral edge; according to the invention, the holding device comprises: - a coin holder including: a. a support surface intended to receive the said thermoformed sheet in support, b. a lateral surface designed to engage forcefully along a part of less of its periphery in a receiving cavity formed in the thermoformed sheet, - the first means for injecting a gas, opening onto the support surface and shaped so as to inject said gas into a volume provided between the support surface of the workpiece holder and the thermoformed sheet, - escape means comprising at least one shaped passage to put into fluidic communication with the external environment the volume provided between the support surface of the part holder and the thermoformed sheet.

[0014] The applicant has observed that injecting a gas (air, for example) during cutting into the space between the workpiece holder's support surface and the thermoformed sheet simultaneously limits the risk of yellowing or browning of the dental tray and promotes the production of a dental tray free of excessively sharp edges along the cutting path. The gas injected by the first injection methods is substantially at ambient temperature, substantially between 15 and 30 degrees Celsius, and in any case below the glass transition temperature of the thermoformable material.

[0015] Without being bound by any theory, it appears that the fumes generated by laser cutting (produced by local melting of the thermoformed sheet) are carried away by the gas introduced by the first injection means and flow to the exhaust means, thus preventing their stagnation in the hollow of the dental tray and the yellowing / browning of the latter. Simultaneously, and again without being bound by any theory, it appears that the gas introduced by the first injection means helps to "smooth" the edges along the cutting path.

[0016] Preferably, it can be provided that: - the lateral surface of the part holder is shaped to obtain a seal around the perimeter of the hollow gutter after the thermoformed sheet is forcefully inserted into the receiving cavity. - the passage of the escape means includes a through-hole provided in the part holder.

[0017] This provides reliable support for the thermoformed sheet by the holding device, while promoting good channeling of the fumes generated by the laser cutting for their efficient evacuation via the exhaust means.

[0018] Advantageously, the first means for injecting a gas include a first injection orifice located in the central part of the support surface and / or positioned on the support surface so as to be located in the central part of the U-shape formed by the dental tray when said thermoformed sheet is engaged on the workpiece holder. The placement of the first injection orifice substantially in the central part of the U-shape formed by the dental tray allows the injected gas to distribute itself rapidly and in a nearly homogeneous manner within the volume created between the support surface of the workpiece holder and the thermoformed sheet. The placement of the first injection orifice in the central part of the support surface helps to limit the risk of the workpiece holder coming out of the receiving cavity along part of its periphery during gas injection.

[0019] Preferably, the first gas injection means comprise at least one auxiliary injection orifice disposed between the first injection orifice and the lateral surface of the workpiece holder, preferably arranged so as to be aligned with the U-shaped groove when the thermoformed sheet is engaged on the workpiece holder. This at least one auxiliary injection orifice allows for faster injection of gas into the U-shaped groove.

[0020] Advantageously, the holding device can be arranged at the end of a robotic arm that can be moved along at least 5 axes. Such a robotic arm makes it possible to move the holding device (and therefore the thermoformed sheet) satisfactorily in relation to a laser beam to perform a cutting trajectory that is sometimes made complex by the patient's soft tissues, which must not be covered by the dental tray.

[0021] According to another aspect, the present invention proposes a laser cutting device that may include: - a holding device as previously described, - a cutting laser, - means of movement configured to move the holding device relative to the cutting laser.

[0022] Preferably, to move the holding device (and therefore the thermoformed sheet) satisfactorily in correspondence with the cutting laser to perform a cutting trajectory sometimes made complex by the patient's soft tissues which must not be covered by the dental tray, it can be provided that: - the cutting laser is fixed relative to a machine frame, - the means of movement are configured to move the holding device relative to the cutting laser, preferably by means of a robotic arm movable along at least 5 axes.

[0023] Advantageously, it can be foreseen that: - a laser beam is emitted through an outlet orifice of an emission conduit, - second means for injecting a gas are configured to inject a gas into the emission conduit.

[0024] The second means of injecting a gas make it possible to generate a gas flow limiting the risk that the fumes generated by the laser cutting (produced by local melting of the thermoformable sheet) will alter and / or damage one or more components of the generation of the laser beam.

[0025] Preferably, the laser cutting device may include gas extraction means disposed in the external environment of the holding device. These extraction means make it possible to create a slight negative pressure in the environment in which the holding device is located. The volume provided between the surface The support of the workpiece holder and the thermoformed sheet are thus also in slight depression, which helps to convey the fumes generated by the laser cutting to the exhaust means.

[0026] Advantageously, it can be foreseen that: - The laser cutting device includes a machine frame, - the laser cutting device comprises a containment enclosure inside the machine frame, said containment enclosure containing the cutting laser and being suitable for containing the holding device during laser cutting, - the suction equipment is arranged within the containment enclosure.

[0027] The containment enclosure allows for the definition of a restricted volume enabling better efficiency of the suction means.

[0028] The containment enclosure can in practice take the form of a rectangular parallelepiped at least partially open along one of its faces.

[0029] Preferably, the suction means can be arranged around the periphery of the laser emission duct, preferably all around the laser emission duct. This results in a relatively compact structure.

[0030] According to another aspect, the present invention proposes a cutting method using a laser cutting device as previously described, for cutting a thermoformed sheet comprising a hollow dental tray substantially in the shape of a U attached to a peripheral edge; during said cutting method: - the thermoformed sheet is forcefully attached to the workpiece holder, - a gas is injected, via the first means of gas injection, into the volume created between the support surface of the workpiece holder and the thermoformed sheet, - the laser is positioned on the convex side of the hollow gutter and performs a cutting path.

[0031] Preferably, to ensure good results, the volume provided between the support surface of the workpiece holder and the thermoformed sheet can include the internal volume of the gutter.

[0032] Advantageously, it can be predicted that: - The laser cutting device includes gas extraction means located in the external environment of the holding device, - During the laser cutting of the thermoformed sheet, gases are drawn into the external environment of the holding device.

[0033] The suction during cutting creates a slight negative pressure in the environment surrounding the holding device. The volume between the workpiece holder's support surface and the thermoformed sheet is thus also in slight depression, which contributes to the routing of fumes generated by laser cutting towards the exhaust means.

[0034] During treatment, it is important that the patient use the dental aligners in the order prescribed by the treatment plan. However, dental aligners corresponding to two successive treatment stages sometimes differ very little from one another and can therefore be easily confused.

[0035] To avoid confusion and allow for the correct ordering of dental trays, each tray is generally marked with a unique identifier made of the thermoformable material from which it is made. This identifier is, however, relatively small (so as not to interfere with the shapes designed to accommodate the patient's teeth) and therefore often difficult to read. Consequently, the same identifier is generally repeated on a portion of the outer edge: as space is less limited, the identifier is usually larger to ensure better legibility and facilitates the orderly filing of the thermoformed trays.

[0036] When a laser cutting device is supervised by an operator responsible for retrieving each dental tray immediately after it is cut, a well-ordered sorting can be ensured. This is not the case with a laser cutting device operating without operator supervision (for example, during a weekend) and successively cutting a plurality of dental trays, which are then collected loosely in a cutting bin at the output of the laser cutting device.

[0037] According to yet another aspect, the present invention aims to facilitate the cutting of a plurality of thermoformed sheets autonomously by a laser cutting device, without systematic recovery of the dental tray immediately after its cutting by an operator, while facilitating an orderly and reliable reclassification after cutting a series of dental trays.

[0038] To reach these objects and others, the invention proposes a cutting method as previously described, in which: - Before the cutting path is executed, the dental tray is held in place on the peripheral edge using an initial holding force. - after the cutting path is completed, the dental tray is held on the peripheral sidewalk by a second retention force which is less than the first retention force and not zero.

[0039] Following this cutting process, the dental tray remains attached (albeit precariously) to the peripheral edge, so that an operator can easily reclassify the thermoformed sheets after cutting based on the marking of the peripheral edge.

[0040] The reclassification can even be carried out by an automated system (with a robotic arm and a marking reading device). Indeed, the fact that the dental tray remains attached to the peripheral edge allows for better handling by an automated system.

[0041] Once the thermoformed sheets have been reclassified, an operator can separate the dental trays from the peripheral sidewalks, and classify them as they go in the appropriate order.

[0042] To achieve the second desired holding force, it is preferable, during the laser cutting of the thermoformed sheet, to adjust the gas injection conditions using the first gas injection means according to the laser power. A person skilled in the art is naturally able to adjust these injection conditions (in particular flow rate, temperature, and pressure) to achieve a satisfactory result.

[0043] To obtain a satisfactory second holding force while maintaining a high-quality cut (absence of excessively sharp edges), it is advantageous to provide that, during the cutting process, the thermoformed sheet is a composite sheet comprising at least a first layer of thermoformable material coated with a peelable protective film, said protective film having a thickness less than that of the first layer. Good results have been obtained with a peelable polyethylene protective film.

[0044] Preferably, the thermoformed sheet can be placed on the workpiece holder so that the protective film is between the first layer and the workpiece holder.

[0045] To achieve the second desired retention force, discontinuous cutting can advantageously be performed along the cutting path. For example, discontinuities in the cutting path can be incorporated in the areas of dental trays intended to cover the patient's molars (areas where a less refined finish is acceptable). Alternatively, discontinuities can be incorporated along the entire cutting path. SUMMARY DESCRIPTION OF THE DRAWINGS

[0046] Other objects, features and advantages of the present invention will become apparent from the following description of particular embodiments, made in relation to the accompanying figures, among which:

[0047] [Fig.1] Fig.1 is a schematic and perspective view of a particular embodiment of a holding device according to the present invention;

[0048] [Fig.2] The [Fig.2] is a schematic and top view of the holding device of the [Fig.1];

[0049] [Fig.3] The [Fig.3] is a schematic and cross-sectional view of the holding device of the [Fig.1], taken along a first cross-sectional plane;

[0050] [Fig.4] The [Fig.4] is a schematic and cross-sectional view of the holding device of the [Fig.1], taken along a second cutting plane perpendicular to the first cutting plane;

[0051] [Fig.5] The [Fig.5] is a schematic and perspective view of an example of a thermoformed sheet intended to be received on the holding device of the [Fig.1];

[0052] [Fig.6] The [Fig.6] is a schematic and perspective view of the thermoformed sheet of the [Fig.5] on which an example of a cutting path is illustrated;

[0053] [Fig.7] The [Fig.7] is a schematic and perspective view of the thermoformed sheet of the [Fig.5] after its cutting along the cutting path of the [Fig.6];

[0054] [Fig.8] The [Fig.8] is a schematic and perspective view of the assembly of the thermoformed sheet of the [Fig.5] and the holding device of the [Fig.1];

[0055] [Fig.9] The [Fig.9] is a schematic and cross-sectional view of the assembly of the [Fig.8], taken along the first cutting plane;

[0056] [Fig. 10] The [Fig. 10] is a schematic and cross-sectional view of the assembly of the [Fig.8], taken along the second cutting plane;

[0057] [Fig. 11] The [Fig. 11] is a schematic and perspective view of the holding device of the [Fig.1] arranged at the end of a robotic arm;

[0058] [Fig. 12] The [Fig. 12] is a schematic and perspective view of a laser cutting device including the assembly of the [Fig.8] disposed at the end of a robotic arm;

[0059] [Fig. 13] [Fig. 13] is a detailed cross-sectional view of the laser cutting device of [Fig. 12]; and

[0060] [Fig. 14] The [Fig. 14] is a detailed and cross-sectional view of different structures 14a to 14d of thermoformed sheet. DESCRIPTION OF PREFERRED IMPLEMENTATION METHODS

[0061] When identical numerical references are used in several figures, embodiments or variants of the invention, these numerical references designate identical or similar elements in each of the figures, embodiments or variants.

[0062] Figures 1 to 4 illustrate a particular embodiment of the holding device 1 according to the present invention.

[0063] The holding device 1 is designed to receive and support a thermoformed sheet 2 as illustrated in Figures 5 to 7 so that the latter may be cut by a laser along a cutting path T. The thermoformed sheet 2 comprises a hollow dental tray 3, substantially U-shaped, attached to a peripheral edge 4. The dental tray 3 was formed by plastic deformation of the thermoformable material of the thermoformed sheet 2 by overmolding a master model representative of a particular stage of treatment of a patient.

[0064] Here, the dental splint 3 has been represented in a very simplified way, but in reality it has a shape similar to that of [Fig.3] of document EP 2 760 624 Bl. The cutting path T is also represented in a very simplified way, but in reality it has a more complex shape (as illustrated on [Fig.5] of document EP 2 760 624 Bl), taking into account the soft tissues (gums) of the patient and which the dental splint 3 must not cover.

[0065] Figures 1 to 4 show in particular that the retaining device 1 comprises a workpiece holder 5, which workpiece holder 5 includes: - a support surface 6 intended to receive said thermoformed sheet 2 in support, - a lateral surface 7 intended to engage by force along at least part of its periphery in a receiving cavity 8 formed in the thermoformed sheet 2.

[0066] The retaining device 1 further comprises: - of the first means for injecting a gas 9, opening onto the support surface 6 and shaped so as to inject said gas into a volume V provided between the support surface 6 of the workpiece holder 5 and the thermoformed sheet 2, - means of escape 10 comprising at least one passage 11 shaped to put in fluidic communication with the external environment 12 the volume V.

[0067] Here, the lateral surface 7 of the workpiece holder 5 is shaped so as to engage forcefully around its entire periphery in the receiving cavity 8 of the thermoformed sheet 2. This provides a seal around the periphery of the hollow dental tray 3 after forceful engagement in the receiving cavity 8 of the thermoformed sheet 2. The thermoformed sheet 2 is engaged on the workpiece holder by fitting it along an axial direction II.

[0068] The passage 11 of the escape means 10 includes in practice a through-hole provided in the workpiece holder 5 which itself is substantially in the form of a plate of thickness E. For a good seal between the workpiece holder 5 and the thermoformed sheet 2, the (lateral) gap between the workpiece holder 5 and the receiving cavity 8 is adjusted, as well as the height h according to which the workpiece holder 5 engages in the receiving cavity 8.

[0069] The first means for injecting a gas 9 include a first injection orifice 9a disposed in the central part of the support surface 6. Here, the first injection orifice 9a is further disposed on the support surface 6 so as to be in the central part of the U (between the arms of the U) formed by the dental tray 3 when said dental tray 3 is engaged on the workpiece holder 5.

[0070] In the embodiment of the holding device 1 illustrated in the figures, the first means for injecting a gas 9 comprise two injection orifices auxiliaries 9b and 9c arranged between the first injection port 9a and the lateral surface 7 of the part holder 5.

[0071] It is observed more particularly on [Fig. 10] that the two auxiliary injection ports 9b and 9c are arranged so as to be in correspondence with the U-shaped dental tray 3 when the latter is engaged on the workpiece holder 5. Each of the auxiliary injection ports 9b and 9c is located substantially in correspondence with one arm of the U formed by the dental tray 3.

[0072] The three ports 9a to 9c are supplied with gas (air for example) by a common supply line 13.

[0073] Opposite the first injection port 9a, the peripheral sidewalk 4 is located away from the support surface 6. The volume V formed between the support surface 6 of the workpiece holder 5 and the thermoformed sheet 2 includes the internal volume V3 of the dental tray 3. The gas injected via the first injection port 9a spreads into the volume V formed between the support surface 6 of the workpiece holder 5 and the thermoformed sheet 2 until it reaches the internal volume V3 of the dental tray 3, as illustrated by the arrows 14 (figures 9 and 10).

[0074] The gas injected via the two auxiliary injection ports 9b and 9c enters directly into the internal volume V3 of the dental tray 3, as illustrated by the arrows 15 ([Fig. 10]).

[0075] After traveling through volume V, the gas injected through orifices 9a to 9c can escape into the external environment 12 through passage 11 of the exhaust means 10, carrying away out of volume V the fumes (and any debris) generated by the laser cutting (produced by local melting of the thermoformed sheet 2), as illustrated by arrow 16 ([Fig.9]).

[0076] In [Fig. 11], the holding device 1 is arranged at the end of a robotic arm 17 movable along at least 5 axes in order to be able to move the holding device 5 and the thermoformed sheet 2 satisfactorily in correspondence with a laser beam to carry out a cutting trajectory T sometimes made complex by the soft tissues of the patient which must not cover the dental tray 3. Here, the robotic arm is movable along 6 axes (6 rotations RI to R6).

[0077] Compared to figures 1 to 4, the holding device 1 further comprises two ejectors 18a and 18b which can be moved in translation in a bidirectional manner along the axial direction II. When they come to rest on the peripheral sidewalk 4, and are moved in the direction illustrated by arrow 19, the ejectors 18a and 18b allow the workpiece holder 5 to be removed from the receiving cavity, which has the effect of removing the thermoformed sheet from the workpiece holder 5.

[0078] Figure 12 illustrates a laser cutting device 20, comprising: - a holding device 1 as described above, - a 21-inch laser cutter, - means of movement 22 configured to move the holding device 1 relative to the cutting laser 21.

[0079] More precisely: - the cutting laser 21 is fixed relative to a machine frame 23, - the movement means 22 are configured to move the holding device 1 relative to the cutting laser 21.

[0080] It can be seen more particularly in [Fig. 13] that: - a laser beam 21a is emitted through an outlet orifice of an emission conduit 24, - second means for injecting a gas 25 are shaped to inject a gas into the emission line 24.

[0081] In practice, the second means for injecting a gas 25 include a conduit 25a opening into the emission conduit 24. To exit the emission conduit 24, the gas (air for example) injected via the second means for injecting a gas 25 passes through the outlet orifice 24a, as illustrated by the arrow 31.

[0082] The laser cutting device 20 further includes gas extraction means 26 disposed in the external environment 12 of the holding device 1.

[0083] In figures 12 and 13, a containment enclosure 27 is particularly distinguished inside the machine frame 23, said containment enclosure 27 containing the cutting laser 21. The containment enclosure 27 is in the general form of a rectangular parallelepiped at least partially open along one of its faces 27a, which allows it to receive (thanks to the robotic arm 17) and contain the holding device 1 during laser cutting.

[0084] The gas suction means 26 are arranged in the containment enclosure 27: this increases their efficiency.

[0085] It can be seen more particularly in [Fig. 13] that the gas suction means 26 are arranged on the periphery of the laser emission conduit 24. Here, the gas suction means 26 have a collector 26a with a ring-shaped inlet face 26b completely surrounding the laser emission conduit 24.

[0086] The gas injected via the first gas injection means 9, the fumes generated by the laser cutting, as well as the gas injected via the second gas injection means 25, are collected by the collector 26a with inlet face 26b in a ring of the gas suction means 26 and are extracted out of the machine frame 23. The gas injected via the second gas injection means 25 prevents the fumes generated by the laser cutting from entering the emission duct 24 of the laser beam 21a, to preserve the components of the cutting laser 21 from any degradation.

[0087] When a thermoformed sheet 2 comprising a hollow, substantially U-shaped dental groove 3 attached to a peripheral edge 4 is cut using a laser cutting device 20, the thermoformed sheet 2 is forcefully engaged on the workpiece holder 5 (as illustrated in Figures 8 to 10). The robotic arm 17 inserts the holding device 1 into the containment chamber 27 and presents the thermoformed sheet to the laser beam 21a (Figures 12 and 13). The cutting laser 21 is positioned on the convex side of the hollow dental groove 3. The robotic arm 17 moves the holding device 1 so that the laser beam 21a follows the cutting path T ([Fig. 6]) and forms a cutting line between the dental groove 3 and the peripheral edge 4.

[0088] During cutting, a gas (air for example) is injected via the first gas injection means 9 into the volume V formed between the support surface 6 of the workpiece holder 5 and the thermoformed sheet 2 (Figures 9 and 10). Injected via the first injection port 9a and the auxiliary injection ports 9b and 9c, the gas diffuses throughout the volume V (including the internal volume V3 of the dental tray 3) before exiting through the passage 11 of the exhaust means 10 ([Fig.9]), carrying with it the fumes (and any debris) generated by the laser cutting by local melting of the thermoformable sheet 2 along the cutting path T.

[0089] Simultaneously with the injection of gas into volume V during cutting, gases are drawn from the external environment 12 of the holding device 1 by gas extraction means 26 which are located in the external environment of the holding device 1 ([Fig. 13], arrows 30). This extraction facilitates the removal of gases contained in volume V.

[0090] Before the cutting path T is carried out, the dental gutter 3 is held on the peripheral sidewalk 4 by a first holding force (which here results from the fact that the dental gutter 3 and the peripheral sidewalk 4 are formed in one and the same piece by the thermoformed sheet 2).

[0091] According to an advantageous method of the present invention, after making the cutting path T, the dental tray 3 is retained on the peripheral ledge 4 by a second retention force which is less than the first retention force, but said second retention force is non-zero.

[0092] The dental tray 3 is thus held together with the peripheral edge 4 after the cutting of the thermoformed sheet 2. The second retaining force must be high enough to prevent any untimely separation of the dental tray 3 and the peripheral edge 4, but must be low enough to allow a simple and quick separation by an operator (preferably manually).

[0093] A plurality of thermoformed sheets 2 can thus be cut autonomously by a laser cutting device 20, without systematic recovery of the dental tray 3 immediately after its cutting by an operator, while facilitating an orderly and reliable reclassification after cutting a series of dental trays 3.

[0094] To obtain a second satisfactory restraint force, the injection conditions of a gas by the first gas injection means 9 can be adapted, taking into account several factors, including, for example: - the power of the laser, - the material of the thermoformed sheet 2 (and its thickness), - the flow rate, temperature and pressure of the gas injected by the first means of gas injection 9.

[0095] The applicant experimented with different structures 14a to 14d of thermoformed sheet 2 ([Fig. 14]) during cutting tests to evaluate the importance of the structure of the thermoformed sheet 2 in order to obtain after cutting a dental splint 3 held together with the peripheral edge 4 after cutting the thermoformed sheet 2.

[0096] The structure 14a is a single-layer structure 28a of thermoformable material(s). The layer 28a of thermoformable material(s) may consist of several sub-layers.

[0097] The structure 14b has two layers, namely a first layer 28a of thermoformable material(s) covered with a peelable protective film 28b. The first layer 28a of thermoformable material(s) may consist of several sub-layers. The protective film 28b has a thickness E28b that is less than the thickness E28a of the first layer 28a. The protective film 28b is located on the inner side of the dental tray 3 and is therefore intended to be positioned between the first layer 28a and the workpiece holder 5 when the thermoformed sheet 2 is received on the workpiece holder 5.

[0098] The structure 14c has two layers, namely a first layer 28a of thermoformable material(s) covered with a peelable protective film 28c. The first layer 28a of thermoformable material(s) may consist of several sub-layers. The protective film 28c has a thickness E28c that is less than the thickness E28a of the first layer 28. The protective film 28c is located on the outer side of the dental tray 3. The first layer 28a is therefore intended to be positioned between the protective film 28b and the workpiece holder 5 when the thermoformed sheet 2 is received on the workpiece holder 5.

[0099] The structure 14d has three layers, namely a first layer 28a of thermoformable material(s) coated on its upper surface with a peelable protective film 28c and coated on its lower surface with a peelable protective film 28b. The first layer 28a of thermoformable material(s) may consist of several sub- layers. The protective films 28b and 28c have respective thicknesses E28b and E28c that are less than the thickness E28 of the first layer 28a. The protective film 28b is located on the inner side of the dental tray 3 and is therefore intended to be positioned between the first layer 28a and the workpiece holder 5 when the thermoformed sheet 2 is received on the workpiece holder 5.

[0100] A protective film 28b or 28c is peelable, that is to say it can be separated from the layer 28a on which it is located by a simple pull.

[0101] Cutting tests were carried out with thermoformed sheets 2 of structures 14a to 14d, under identical cutting, gas injection, and gas extraction conditions. Layers 28a to 28c were identical between structures 14a to 14d of thermoformed sheet 2. The results are summarized in Table 1 below.

[0102] [Tables 1] 14a 14b 14c 14d Second holding force insufficient satisfactory not high enough satisfactory Edges along the cutting path too aggressive satisfactory satisfactory very satisfactory

[0103] A first observation is that a composite thermoformed sheet 2, comprising at least a first layer 28a of thermoformable material(s) coated with a peelable protective film 28b and / or 28c, is preferable to a thermoformed sheet 2 with a first layer 28a of thermoformable material(s) without a protective film.

[0104] A second observation is that in the case of a thermoformed sheet 2 with a first layer 28a of thermoformable material(s) coated with a single protective film 28b or 28c, it is preferable to place said single protective film 28b or 28c on the inner side of the dental tray 3, so that said single protective film 28b or 28c is placed between the first layer 28a and the workpiece holder 5 when the thermoformed sheet 2 is received on the workpiece holder 5 for cutting.

[0105] Excellent results have been obtained using thermoformable sheets marketed under the reference "0893.2" and trade name "CA® Pro+" by the German company SCHEU-DENTAL GmbH. These thermoformable sheets have a 14d structure with: - a layer 28a of thermoformable material(s) consisting of three sub-layers, namely a central sub-layer 0.25 mm thick made of a thermoplastic elastomer, two outer sub-layers 0.25 mm thick made of a copolyester respectively arranged on the two opposite faces of the central sub-layer; - two protective films 28b and 28c made of polyethylene, respectively placed on the two outer sub-layers of layer 28a.

[0106] It should be noted that the fact of carrying out a cut at the end of which the dental splint remains attached to the peripheral sidewall by a second retention force which is less than the first retention force by which the dental splint is held on the peripheral sidewall before carrying out the cutting path, constitutes in itself a technical solution solving a technical problem independent of the technical problem of yellowing / browning of the dental splint and / or of edges too sharp likely to injure the patient.

[0107] The applicant therefore reserves the right to obtain independent protection for a method of cutting a thermoformed sheet, said thermoformed sheet comprising a hollow dental tray substantially in the shape of a U attached to a peripheral edge, by means of a laser performing a cutting path, in which method: - Before the cutting path is executed, the dental tray is held in place on the peripheral edge using an initial holding force. - after the cutting path is completed, the dental tray is held on the peripheral sidewalk by a second retention force which is less than the first retention force and not zero.

Claims

Demands

1. Holding device (1) for laser cutting of a thermoformed sheet (2) comprising a hollow dental tray (3) substantially in the shape of a U attached to a peripheral edge (4), said holding device (1) comprising: - a workpiece holder (5) comprising: a. a bearing surface (6) intended to receive said thermoformed sheet (2) in support, b.a lateral surface (7) intended to engage forcefully along at least part of its periphery in a receiving cavity (8) formed in the thermoformed sheet (2), - first means for injecting a gas (9), opening onto the support surface (6) and shaped so as to inject said gas into a volume (V) provided between the support surface (6) of the workpiece holder (5) and the thermoformed sheet (2), - exhaust means (10) comprising at least one passage (11) shaped to put into fluidic communication with the external environment (12) the volume (V) provided between the support surface (6) of the workpiece holder (5) and the thermoformed sheet (2).

2. Retaining device (1) according to claim 1, characterized in that: - the lateral surface (7) of the piece holder (5) is shaped so as to obtain a seal around the periphery of the dental tray (3) after force engagement in the receiving cavity (8) of the thermoformed sheet (2), - the passage (11) of the escape means (10) includes a through-hole provided in the piece holder (5).

3. Retaining device (1) according to any one of claims 1 or 2, characterized in that the first means for injecting a gas (9) comprise a first injection orifice (9a) disposed in the central part of the support surface (6) and / or disposed on the support surface (6) so as to be in the central part of the U formed by the dental tray (3) when said thermoformed sheet (2) is engaged on the workpiece holder (5).

4. Holding device (1) according to claim 3, characterized in that the first means for injecting a gas (9) include at least one auxiliary injection port (9b, 9c) disposed between the first injection port (9a) and the lateral surface (7) of the piece holder (5), preferably disposed so as to be in correspondence with the U-shaped dental tray (3) when the thermoformed sheet (2) is engaged on the piece holder (5).

5. Holding device (1) according to any one of claims 1 to 4, characterized in that the holding device (1) is disposed at the end of a robotic arm (17) movable along at least 5 axes.

6. Laser cutting device (20), characterized in that the laser cutting device (20) comprises: - a holding device (1) according to any one of claims 1 to 5, - a cutting laser (21), - displacement means (22) configured to move the holding device (1) relative to the cutting laser (21).

7. Laser cutting device (20) according to claim 6, characterized in that: - the cutting laser (21) is fixed relative to a machine frame (23), - the movement means (22) are configured to move the holding device (1) relative to the cutting laser (21), preferably by means of a robotic arm (17) movable along at least 5 axes.

8. Laser cutting device (20) according to any one of claims 6 or 7, characterized in that: - a laser beam (21a) is emitted through an outlet orifice (24a) of an emission conduit (24), - second means for injecting a gas (25) are shaped to inject a gas into the emission conduit (24).

9. Laser cutting device (20) according to any one of claims 6 to 8, characterized in that the laser cutting device (20) comprises gas suction means (26) disposed in the external environment (12) of the holding device (1).

10. Laser cutting device (20) according to claim 9, characterized in that: - the laser cutting device (20) comprises a machine frame (23), - the laser cutting device (20) includes a containment enclosure (27) inside the machine frame (23), said containment enclosure (27) containing the cutting laser (21) and being suitable for containing the holding device (1) during laser cutting, - the gas extraction means (26) are arranged in the containment enclosure (27).

11. Laser cutting device (20) according to any one of claims 9 or 10 taken in dependence thereof from claim 8, characterized in that the gas suction means (26) are arranged on the periphery of the emission conduit (24) of the laser beam (21a), preferably all around the emission conduit (24).

12. A cutting method using a laser cutting device (20) according to any one of claims 6 to 11, for cutting a thermoformed sheet (2) comprising a hollow dental tray (3) substantially in the shape of a U attached to a peripheral edge (4), characterized in that, during said cutting method: - the thermoformed sheet (2) is forcibly engaged on the workpiece holder (5), - a gas is injected, via the first gas injection means (9), into the volume (V) provided between the bearing surface (6) of the workpiece holder (5) and the thermoformed sheet (2), - the cutting laser (21) is positioned on the convex side of the hollow dental tray (3) and performs a cutting path (T).

13. Cutting method according to claim 12, characterized in that the volume (V) provided between the support surface (6) of the workpiece holder (5) and the thermoformed sheet (2) includes the internal volume (V3) of the dental tray (3).

14. Cutting method according to any one of claims 12 or 13, characterized in that: - the laser cutting device (20) includes gas extraction means (26) disposed in the external environment (12) of the holding device (1), - during the cutting of the thermoformed sheet (2) by the cutting laser (21), gases are extracted from the external environment (12) of the holding device (1).

15. A cutting method according to any one of claims 12 to 14, characterized in that: - before the cutting path (T) is carried out, the dental tray (3) is held on the peripheral sidewalk (4) by a first holding force, - after the cutting path (T) is carried out, the dental tray (3) is held on the peripheral sidewalk (4) by a second holding force which is less than the first holding force and not zero.

16. Cutting method according to claim 15, characterized in that, during the cutting of the thermoformed sheet (2) by the cutting laser (21), the conditions for injecting a gas by the first means for injecting a gas (9) are adapted according to the power of the laser to achieve the second desired retention force.

17. Cutting method according to any one of claims 15 or 16, characterized in that discontinuous cutting is carried out along the cutting path (T).

18. Cutting method according to any one of claims 12 to 17, characterized in that the thermoformed sheet (2) is a composite sheet comprising at least a first layer (28a) of thermoformable material(s) coated with a peelable protective film (28b, 28c), said protective film (28b, 28c) having a thickness (E28b, E28c) less than the thickness (E28a) of said first layer (28a).

19. Cutting method according to claim 18, characterized in that the thermoformed sheet (2) is arranged on the workpiece holder (5) so that the protective film (28b, 28c) is located between the first layer (28a) and the workpiece holder (5).

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