BIO-BASED ORTHODONTIC DEVICE AND PROCESS FOR THERMOFORMING THE SAME

Abstract

For improving the quality of use of intraoral orthodontic devices (1) such as dental splints (2) to be worn on teeth as well as for increasing their functionality, such devices (1) are fabricated at least in part, but preferably fully from bio-based materials (5). In particular when using a design featuring a cap layer (4) covering an inner stiff core (3) and including a bio-based material (5), which can be additionally chosen such that it can take-up a significant amount of liquid by swelling, both the micro-deformability of the device (1) can be improved—resulting in increased wearing comfort for the patient and less microplastic contamination for the patient through fossil-based plastic abrasions—and novel functions can be realized, for example releasing substances (9) such as drugs or flavor molecules or bio-based antimicrobial or protective agents from the device (1).

Claims

1. An intraoral orthodontic device (1) to be worn on teeth, the orthodontic device comprising: a bio-based material (5) that forms an outer surface (7) of the device (1), and wherein the bio-based material (5) comprises a non-fossil carbon content containing a detectable portion of the carbon isotope .sup.14C.

2. The intraoral orthodontic device (1) according to claim 1, further comprising a core (3) and a cap layer (4) at least partially covering the core (3), and wherein the cap layer (4) comprises cellulose acetate butyrate (CAB) (5).

3. The intraoral orthodontic device (1) according to claim 2, wherein the core (3) is made from Polyethylenterephthalat (PET).

4. The intraoral orthodontic device (1) according to claim 2, further comprising at least one of: an agent (9) derived from a bio-based material (5) embedded into the cap layer (4), cinnamaldehyde embedded into at least one of the cap layer (4) or the bio-based material (5) as an antimicrobial agent (9), or at least one of triacetin or polycaprolactone-triol (PCL-T) embedded into the cap layer (4) or the bio-based material (5) as a softening agent (9).

5. The intraoral orthodontic device (1) according to claim 1, further comprising a core (3) and a cap layer (4) at least partially covering the core (3), wherein the cap layer (4) comprises a liquid-absorbing material (6) with a volumetric liquid absorption ratio of at least 1.5%.

6. The intraoral orthodontic device (1) according to claim 5, further comprising a liquid-soluble substance (9) which is releasable through or from the cap layer (4) into an oral cavity of a patient wearing the device (1).

7. The intraoral orthodontic device (1) according to claim 1, further comprising a multilayer sandwich structure (10) including a core (3) sandwiched between a top cap layer (4a) and a bottom cap layer (4b).

8. The intraoral orthodontic device (1) according to claim 7, wherein thicknesses of the top cap layer (4a) and bottom cap layer (4b) are asymmetric with the top cap layer (4a) adapted to be facing away from the teeth on which the device (1) is worn, and the top cap layer (4a) is at least 10% thicker than the bottom cap layer (4b).

9. The intraoral orthodontic device (1) according to claim 2, wherein the core (3) is a rigid layer (12) providing at least one of structural stability or shape stability, and the core (3) is elastic and provides a resilient force adapted for aligning single teeth, when the device (1) is worn by a patient as a dental splint (2) on a patient's teeth.

10. The intraoral orthodontic device (1) according to claim 2, further comprising an intermediate layer (13), that is softer than at least one of the cap layer (4) or the core (3), separates the core (3) from the cap layer (4).

11. The intraoral orthodontic device (1) according to claim 2, wherein a glass transition temperature T.sub.g,core of the core (3) and a glass transition temperature T.sub.g,cap of the cap layer (4) differ by less than 80° C., such that when heating the device (1) from outside, the core (3) reaches the glass transition temperature T.sub.g,core before or when the cap layer (4) reaches the cap layer glass transition temperature T.sub.g,cap, and a melting temperature of the core (3) T.sub.m,core and a melting temperature of the cap layer (4) T.sub.m,cap differ by at least 20° C., such that a compound material is adapted to be produced at an interface (19) between core (3) and the cap layer (4) during thermoforming of the device (1).

12. A method of forming the intraoral orthodontic device (1) according to claim 1, comprising heating a film (14) or a multi-layer-sandwich structure (10) comprising a core (3) and top and bottom outer cap layers (4a, 4b) from two opposing sides during thermoforming, such that the core (3) sandwiched between the top and the bottom cap layer (4a, 4b) reaches a glass transition temperature T.sub.g,core before the top and bottom cap layers (4a, 4b) reach glass transition temperatures T.sub.g,cap thereof, respectively; and thermoforming the device.

13. The method of claim 12, further comprising at least partly fabricating the device by an additive-manufacturing process.

14. A method for thermoforming an intraoral orthodontic device (1), the method comprising heating a film (14) or a multi-layer-sandwich structure (10) comprising a core (3) and top and bottom outer cap layers (4a, 4b) from two opposing sides, such that during heating outer sides of the film (14) or the outer cap layers (4a, 4b) of the multi-layer-sandwich structure (10) are synchronously heated towards respective glass transition temperatures thereof, using a thermoforming apparatus featuring two separate heat sources; and thermoforming the device.

15. A method for equipping an intraoral orthodontic device (1) with a substance (9) which is releasable into a patient's oral cavity, the method comprising: embedding the substance (9) into a liquid-absorbing bio-based cap layer (4) of the device (1) prior to use of the device (1), including mixing the substance (9) with bio-based material (5) of the cap layer (4) using a solvent such as acetone, the solvent modifying a surface of core (3) of the device, by reducing an interaction of molecular chains of the material of the core (3), such that the core (3) and the cap layer (4) interlock on a nanometer scale, resulting in improved adhesion of the cap layer (4) on the core (3), or thermally fusing the cap layer (4) and the core (3) of the device (1) at an interface (19) between cap layer (4) and the core (3) after thermoforming of the device (1) forming a compound material at the interface (19).

16. The intraoral orthodontic device according to claim 5, wherein an elastic modulus of the cap layer (4) is reduced by at least 10% by absorption of water.

17. The intraoral orthodontic device according to claim 6, wherein the substance (9) is embedded into the device (1) through or into the cap layer (4) prior to use.

18. The intraoral orthodontic device according to claim 7, wherein the core (3) is fully encapsulated by the top and bottom cap layers (4a, 4b).

19. The intraoral orthodontic device according to claim 7, wherein the top and bottom cap layers (4a, 4b) form an outer surface (7) coating (11) less than 0.3 mm in thickness.

20. The intraoral orthodontic device according to claim 10, wherein an elastic modulus of the intermediate layer (13) is a factor of 10 lower than an elastic modulus of the core (3), the cap layer (4) is softer than the core (3) at least after swelling in water, and a thickness of the cap layer (4) and a thickness of the intermediate layer (13) are limited such that a maximum combined deformation of the cap layer (4) and the intermediate layer (13) after swelling in liquid and due to wearing the device (1) on the teeth is less than 50% of a total thickness of these two layers (4, 13).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0125] With reference to the accompanying drawings, where features with corresponding technical function are referenced with same numerals even when these features differ in shape or design:

[0126] FIG. 1 illustrates a fabrication process for a first intraoral orthodontic device according to the invention based on a single film, and

[0127] FIG. 2 illustrates a fabrication process for a second intraoral orthodontic device according to the invention based on a multilayer sandwich structure,

[0128] FIG. 3 illustrates a preferred embodiment of an orthodontic device according to the invention, and

[0129] FIG. 4 illustrates the definition of non-fossil carbon content and bio-based content used herein to describe bio-based materials.

DETAILED DESCRIPTION

[0130] FIG. 1 illustrates the fabrication of an intraoral orthodontic device 1 according to the invention, which is shown in the lower left subfigure. As is visible, the device 1 is designed as a dental splint 2 to be worn on teeth inside the oral cavity by a patient. The device 1 is fabricated by first thermoforming 16 a film 14 using heat 17 and vacuum or pressure to achieve a complex 3d-shape fitting the teeth of an upper jaw of an individual patient, as shown in the left center subfigure of FIG. 1. For thermoforming of the film 14, a 3d-model 18 is used, as illustrated in FIG. 1. After thermoforming 16 of the film 14, the resulting 3d-shape is cut into the final shape of the dental splint 2, as visible in the lower left subfigure of FIG. 1.

[0131] The film 14 consists of a bio-based material 5. This material 5 is rapidly degradable outside of the oral cavity. During wear, however, the device 1 is protected both from UV-radiation and also from fungi, which are responsible for the rapid decay of the bio-based material 5 in normal ambient conditions. Therefore, the device 1 can be worn over several weeks inside the oral cavity by a patient without any significant degradation of performance.

[0132] As the device 1 consists entirely of a bio-based material 5, during wear only uncritical natural particles such as fiber fragments are produced, in particular when the teeth of the lower jaw are grinding on the device 1. Thus, the generation of microplastic particles inside the mouth is avoided, which is a problem in state-of-the-art orthodontic devices based on plastic materials.

[0133] As indicated by the lower right subfigure in FIG. 1, the bio-based material 5 is actually a liquid-absorbing material 6, which can take up a significant volumetric ratio of water, namely more than 2.5%. Hence, it is possible to embed water-soluble substances 9 such as flavor molecules into the material 5, 6. When a patient is wearing the device 1, it will come in contact with saliva, which will then wash-out the flavor molecules over time. As a result, the embedding of the flavor molecules 9 into the liquid-absorbing material 6 prior to use of the device 1 results in a pleasant taste of the device 1 during wear.

[0134] FIG. 2 illustrates the fabrication of another example of an intraoral orthodontic device 1 according to the invention, again using a 3d-model 18 being an accurate copy of a topography of a patient's oral cavity. Different from the first example illustrated in FIG. 1, the device 1 is fabricated not only from a single film 14 but from a complex multilayer sandwich structure 10, whose cross-section is shown on the right half of FIG. 2. As is visible in the upper cross-sectional view on the right of FIG. 2, the multilayer sandwich structure 10 consists of a central core 3, which may have a thickness in the range 300-1100 μm, sandwiched between an upper cap layer 4a and a lower cap layer 4b. Each of these cap layers 4a, 4b is separated from the core 3 by an additional soft intermediate layer 13a/13b.

[0135] The core 3 can be made from hard polymers such as polycarbonate or polyurethane. Preferably however, the core 3 is also made from a bio-based and hence biodegradable material. As the core 3 is elastic, with an elastic modulus of 0.5 GPa, it provides structural stability as well as shape stability to the device 1. Hence, when the dentals splint 2 is properly fitted to the teeth of a patient it can exert a resilient force onto single teeth for re-aligning them to a desired position.

[0136] The two cap layers 4a, 4b, visible in the cross-sections on the right of FIG. 2, consist entirely of a bio-based polymer, comprising cellulose fibers 8 and cellulose acetate (CA). Moreover, the two cap layers 4a, 4b form a coating 11 defining the entire outer surface 7 of the device 1. In other words, the core 3 is fully encapsulated, at least indirectly, by the cap layers 4a, 4b. In fact, the cap layers 4a, 4b can be considered as one uniform outer layer defining the outer surface 7 of the device 1.

[0137] As is visible in the cross-sectional views on the right of FIG. 2, it is actually preferable for a slim design that is comfortable to wear, if the upper cap layer 4a, which is facing away from the teeth on which the device 1 is worn, is thicker (for example with a thickness in the range of 100-300 μm) than the lower cap layer 4b (which may have a thickness in the range 5-75 μm), which is in direct contact with the teeth on which the device 1 is worn.

[0138] The intermediate layers 13a, 13b are based on a soft polymer such as silicone and hence elastically deformable. Moreover, these layers 13a, 13b are almost impermeable to water (water-repelling). Their thickness can be in the range 10-100 μm.

[0139] In contrast, the bio-based material 5 of the cap layers 4a, 4b is a liquid-absorbing material 6, with a volumetric water absorption ratio of more than 2.5%. As a result, the cap layers 4a, 4b are capable of taking up a substantial amount of liquid, and can also change their shape due to swelling in various liquids, in particular in water. Due to the swelling, the outer cap layers 4a, 4b, which are hard polymer layers in air ambient, are rendered soft with their elastic modulus being reduced below 0.5 GPa. As a secondary effect, the outer cap layers 4a, 4b are rendered plastically deformable.

[0140] The specific material choice for the cap layers 4a, 4b can also be slightly different, allowing fine-tuning of the thermal and/or mechanical properties of the single layers 4a, 4b. This is particularly relevant for designs, in which the cap layers 4 cover the inner core 3 only partially, which is also possible.

[0141] The benefits of this multi-layer-sandwich-design with a stiff inner core 3 and outer bio-based cap layers 4a, 4b are manifold:

[0142] Due to the presence of non-crosslinked but entangled fibers 8 in the cap layers 4a, 4b, the outer surface 7 of the device 1 can adapt its shape on a micrometer scale, as the fibers 8 render these layers 4a, 4b plastically deformable, as soon as they have taken up enough liquid.

[0143] Due to the stiff core, which may show an elastic modulus being 5 times or even up to a factor of 10 higher than an elastic modulus of the cap layer 4 (after soaking in liquid), the device 1 can be used as a dental splint exerting forces on the teeth. At the same time, the much higher softness and deformability of the outer cap layers 4a, 4b in comparison to the stiff core 3 guarantees a highly comfortable fit. In particular, irritation of the gingiva can be effectively avoided.

[0144] As the device 1 is fabricated at least in part from bio-based materials, the environmental impact of the device 1 is reduced, as these materials can be easily decomposed.

[0145] As another important advantage, liquid soluble substances 9 such as flavor molecules or drugs, can be embedded into the device, either directly into the liquid-absorbing material 6 or through this material 6 into deeper lying layers of the device. Hence, the device 1 can feature such substances 9 as they can be embedded into the device 1 prior to use.

[0146] During use of the device 1 in the mouth, these substances 9 can then be released, either from a cap layer 4, in case the substance is embedded directly into the cap layer 4, or through the cap layer 4, in case the substance 9 is embedded in a deeper-lying layer of the device. A very convenient way of equipping the device 1 with such substances 9 is to soak the device 1 in a liquid containing the desired substance 9. This liquid may be an oil/a water solution containing the substance.

[0147] To guarantee, that the intended function of the dental splint 2, namely re-alignment of teeth, is not compromised by an excessive deformability of the cap layers 4a, 4b and the intermediate layers 13a, 13b, the thicknesses of these individual layers 4a, 4b, 13a and 13b can be limited such that a maximum combined deformation, for example a change of the total thickness of the device 1, in reaction to swelling of the outer layers in liquid (in particular when the device 1 is immersed in saliva in the mouth) and due to wearing the device 1 on the teeth is less than 50% of a total thickness of these layers 4a, 4b, 13a and 13b. For example if this combined deformation is below 50 μm, the proper working mechanism of the dental splint can still be guaranteed, as a typical value for a desired re-adjustment of the teeth positions is 200-500 μm per aligner splint.

[0148] For the same reason, i.e. to avoid excessive deformations of the total device 1, it is of advantage to limit the amount of water that reaches the inner core 3, in particular if the core 3 is also fabricated from a liquid-absorbing material 6. This may be achieved, for example, by encapsulating the core 3 in water-impermeable layers, which is achieved in the design of FIG. 2 by using the water-impermeable intermediate layers 13a, 13b.

[0149] Concerning the fabrication of the device 1 according to FIG. 2, it is visible in the upper left subfigure of FIG. 2 that the 10 multilayer sandwich structure 10 is actually heated from both sides. This approach avoids, that the inner core 3 is still rigid, when one of the cap layers 4a, 4b is already softened because it has reached its own glass transition temperature. For the same reason, the material of the core 3 is chosen such that its glass transition temperature is actually lower than the glass transition temperature of the material 5, 6 used for the cap layers 4a, 4b.

[0150] To fully exploit such a design, it is recommended to heat the outer layers of the device 1 synchronously towards their individual glass transition temperatures during thermoforming. This can be safely achieved using two separate and individually adjustable heat 17 sources, placed on the respective side of the device 1.

[0151] Therefore, using the two-sided heating approach illustrated in FIG. 2, the core 3 will reach its glass transition temperature before the cap layers 4a, and 4b reach their own. This means that as soon as the outer cap layers 4a, 4b are rendered soft by the heating, the multilayer sandwich structure 10 will be ready to be shaped by thermoforming. Thermoforming can be done in particular by deep-drawing the sandwich structure 10 over a 3d-model 18 of a patients oral cavity (cf. FIG. 2). Such a 3d-model 18, which may be cast from plaster or made from a polymer material, can be obtained easily by a casting process or by optically scanning the oral cavity and 3d-printing of the 3d-model 18 based on the obtained data.

[0152] Alternatively or additionally, at least part of the device 1, for example the core 3, can be fabricated by additive manufacturing techniques such as 3d-printing. The cap layer 4 and, if necessary an intermediate layer 13, can then be added onto the core 3, using various techniques, including thermoforming and various coating processes.

[0153] FIG. 3 illustrates a preferred embodiment of an orthodontic device according to the invention: the device consists of a multi-layer-structure 10 with a core 3 sandwiched between a top cap layer 4a and a bottom cap layer 4b, forming a coating 11 completely covering the core 3. The layers 4a, 4b are made from cellulose acetate butyrate (CAB). The CAB is first mixed with acetone to yield a carrier liquid.

[0154] Next, an agent liquid containing an agent 9, in particular an antimicrobial agent 9 such as cinnamaldehyde and/or an softening agent such as triacetin or polycaprolactone-triol (PCL-T), is mixed with the carrier liquid, which is then applied as a liquid film onto the core 3 made from a glycol modified Polyethylenterephthalat (PETG)-foil with a thickness in the range of 200 to 700 μm. After drying of the liquid film (by evaporation of the acetone), a mechanical interlocking occurs at the interface 19, because the acetone softens the PETG surface such that the molecular chains of the CAB can interlock with the PETG on a nanometer scale leading to improved adhesion of the CAB on the PETG.

[0155] The resulting CAB coating 11 (on both sides of the PETG-foil) may have a thickness between 5 to 100 μm, but preferably between 10 to 50 μm, depending on the viscosity of the carrier liquid. The multi-layer-structure 10 is then deepdrawn (by thermoforming) to yield the final orthodontic device 1.

[0156] Importantly, during the thermoforming process, a thermal fusion is produced between the CAB and the PETG, which further increases the chemical and/or mechanical interaction of the CAB coating 11 on the core 3. In fact, a compound material will be formed at the interface 19 during thermoforming.

[0157] The CAB used for the coating 11 encapsulating the core 3 as illustrated on the right of FIG. 3 is in fact a bio-based material 5, as it is produced by blending organic materials derived from fossil sources with organic material, in particular cellulose, derived from non-fossil natural sources such as plants.

[0158] As FIG. 4 illustrates schematically, “bio-based material” as understood herein may mean that the material 5 contains a significant portion of non-fossil carbon content 20, for example at least 40%. This non-fossil carbon content 20 is characterized in that it contains the carbon isotope .sup.14C in a detectable fraction (e.g. more than 10 ppq). There may also be a fossil carbon content 21 (cf. FIG. 4) which is based on fossil sources and containing the isotope .sup.12C but no detectable fraction of .sup.14C any more, as the .sup.14C has been diminished by radioactive decay over thousands of years. As illustrated in FIG. 4, there can be defined a further quantity namely the so-called bio-based content 22. This fraction of the material 5 comprises the non-fossil carbon content 20 as well as all hydrogen H-, oxygen O-, and nitrogen N-atoms 23 bound to the non-fossil carbon content 20.

[0159] In summary, for improving the quality of use of intraoral orthodontic devices 1 such as dental splints 2 to be worn on teeth as well as for increasing their functionality, it is proposed to fabricate such devices 1 at least in part, but preferably fully from bio-based materials 5. In particular when using a design featuring a cap layer 4 covering an inner stiff core 3 and comprising a bio-based material 5, which can be additionally chosen such that it can take-up a significant amount of liquid by swelling, both the micro-deformability of the device 1 can be improved—resulting in increased wearing comfort for the patient and less microplastic contamination for the patient through fossil-based plastic abrasions—and novel functions can be realized, for example releasing substances 9 such as drugs or flavor molecules or bio-based antimicrobial or protective agents from the device 1.

LIST OF REFERENCE NUMERALS

[0160] 1 intraoral orthodontic device [0161] 2 dental splint [0162] 3 core [0163] 4 cap layer [0164] 5 bio-based material [0165] 6 liquid-absorbing material [0166] 7 outer surface (of 4) [0167] 8 entangled fibers [0168] 9 substance/agent (e.g. flavor molecules or drugs) [0169] 10 multilayer sandwich structure [0170] 11 coating [0171] 12 rigid layer [0172] 13 intermediate layer (e.g. in between 3 and 4) [0173] 14 film [0174] 15 liquid [0175] 16 thermoforming [0176] 17 heat [0177] 18 3d-model [0178] 19 interface [0179] 20 non-fossil carbon content (containing .sup.14C) [0180] 21 carbon content based on fossil sources (containing no detectable fraction of .sup.14C any more) [0181] 22 bio based content (i.e. non-fossil carbon content plus hydrogen, nitrogen, and oxygen bound to this content) [0182] 23 hydrogen, nitrogen, and oxygen bound to non-fossil carbon