3D-PRINTED ORTHODONTIC SPLINT MADE OF CROSSLINKED POLYMERS

Abstract

The present invention relates to an orthodontic splint made of a crosslinked polymer, wherein the crosslinked polymer has a glass transition temperature T.sub.g, determined by means of dynamic-mechanical analysis at a frequency of 1/s DMA as peak tan δ, of ≥25° C. and ≤60° C., a modulus of elasticity, determined by means of dynamic-mechanical analysis as the storage modulus E′ at a frequency of 1/s at 35° C., of ≥500 MPa and ≤4000 MPa, and a loss factor tan δ, determined by means of dynamic-mechanical analysis at a frequency of 1/s at 35° C., of ≥0.08. The invention further relates to a process for producing such splints.

Claims

1. An orthodontic aligner, comprising a crosslinked polymer having a glass transition temperature T.sub.g, determined by dynamic mechanical analysis at a frequency of 1/s as peak tan δ, of ≥25° C. and ≤60° C., an elasticity modulus, determined by dynamic mechanical analysis as storage modulus E′ at a frequency of 1/s at 35° C., of ≥500 MPa and ≤4000 MPa, and a loss factor tan δ, determined by dynamic mechanical analysis at a frequency of 1/s at 35° C., of 0.08.

2. The aligner as claimed in claim 1, wherein the crosslinked polymer is a copolymer which comprises units based on a first monomer and a second monomer, said first monomer being a (meth)acrylic monomer whose homopolymer has a glass transition temperature, determined by dynamic mechanical analysis at a frequency of 1/s as peak tan δ, of s 0° C., and said second monomer being a (meth)acrylic or styrenic monomer whose homopolymer has a glass transition temperature, determined by dynamic mechanical analysis at a frequency of 1/s as peak tan δ, of ≥60° C., and where units based on the first monomer are present in a fraction of ≥5 to ≤40 weight %, based on a total weight of the crosslinked polymer, and units based on the second monomer are present in a fraction of ≥20 to ≤80 weight %, based on the total weight of the crosslinked polymer.

3. The aligner as claimed in claim 1, wherein the crosslinked polymer comprises a crosslinked polyurethane.

4. The aligner as claimed in claim 1, wherein the crosslinked polymer has an isocyanurate fraction, ascertained via .sup.13C NMR, of ≥3%.

5. The aligner as claimed in claim 3, wherein the crosslinked polymer has a urethane fraction, ascertained via .sup.13C NMR, of ≥3%.

6. The aligner as claimed in claim 1, wherein the crosslinked polymer has a refractive index, measured with an Abbe refractometer, of ≥1.48 RI and ≤1.58 RI.

7. The aligner as claimed in claim 1, wherein the crosslinked polymer has a mean network arc length according to Flory and Huggins of ≥300 g/mol and ≤5000 g/mol.

8. The aligner as claimed in claim 1, wherein the polymer is a transparent polymer having a light transmittance, measured in a UV-VIS spectrometer on a sample with a thickness of 1 mm in a wavelength range of 400-800 nm, of ≥50%.

9. The aligner as claimed in claim 1, wherein the polymer is a transparent polymer comprising polyurethanes and/or polysilicones and has an Abbe number of ≥20.

10. A method for producing an orthodontic aligner, comprising: i) selecting a crosslinkable resin; and ii) shaping the aligner by crosslinking the crosslinkable resin to form a crosslinked polymer, wherein selecting the crosslinkable resin includes a criterion that a crosslinked polymer obtained after crosslinking of the crosslinkable resin has a glass transition temperature T.sub.g, determined by dynamic mechanical analysis at a frequency of 1/s DMA as peak tan δ, of 25° C. and ≤60° C., an elasticity modulus, determined by dynamic mechanical analysis as storage modulus E′ at a frequency of 1/s at 35° C., of ≥500 MPa and ≤4000 MPa, and a loss factor tan δ, determined by dynamic mechanical analysis at a frequency of 1/s at 35° C., of ≥0.08.

11. The method as claimed in claim 10, wherein the crosslinkable resin comprises a first monomer and a second monomer, said first monomer being a (meth)acrylic monomer whose homopolymer has a glass transition temperature, determined by dynamic mechanical analysis at a frequency of 1/s as peak tan δ, of ≤0° C., and said second monomer being a (meth)acrylic or styrenic monomer whose homopolymer has a glass transition temperature, determined by dynamic mechanical analysis at a frequency of 1/s as peak tan δ, of ≥60° C., and where the first monomer is present in a fraction of ≥5 to ≤40 weight %, based on a total weight of the resin, and the second monomer is present in a fraction of ≥20 to ≤80 weight %, based on the total weight of the resin.

12. The method as claimed in claim 10, wherein the aligner is shaped by crosslinking the crosslinkable resin in a casting mold corresponding to the aligner.

13. The method as claimed in claim 10, wherein the aligner is shaped via an additive manufacturing method.

14. The method as claimed in claim 10, wherein the crosslinkable resin has free isocyanate groups, measured by .sup.13C NMR, in a concentration ≥1 wt %, based on a total weight of the crosslinkable resin.

15. The method as claimed in claim 10, wherein the crosslinkable resin has free alcohol groups, measured by .sup.13C NMR, in a concentration ≥0.5 wt %, based on a total weight of the crosslinkable resin.

Description

EXAMPLES

[0091] The present invention is more particularly elucidated hereinbelow with reference to the subsequent examples without, however, being limited thereto. Experiments according to the invention in tables 1 and 2 are marked with an asterisk (*).

[0092] DMA measurements were carried out in accordance with the DIN EN ISO 6721 standard. A specimen of known geometry was subjected to mechanical nonresonant vibration in tension at a constant frequency of 1 Hz and a temperature of 0° C. to 80° C. in a Mettler Toledo DMA 861 instrument. As described in the standard, using the force and deformation measurements and the phase shift between force and deformation signal, the tensile storage modulus (E′) and tensile loss modulus (E″) were calculated. The test setup corresponded to Part 4 of ISO 6721.

Example 1: Production of Urethane Acrylate 1 from Desmodur® N3600 and Hydroxypropyl Acrylate

[0093] In a glass flask, 100 g of the trifunctional isocyanate crosslinker Desmodur® N3600 (HDI trimer; obtained from Covestro Deutschland AG, Germany) were initially charged at room temperature. Added first to the isocyanate was 0.040 g of dibutyltin laurate, after which hydroxypropyl acrylate obtained from Sigma-Aldrich, Germany was added in an equimolar proportion, the addition taking place dropwise over a period of around 30 minutes. The reaction mixture was then heated to 60° C. using a temperature-controlled oil bath until the theoretical residual NCO content of 0% was achieved. To this end, samples were withdrawn from the reaction vessel at regular intervals and subjected to titrimetric determination according to DIN EN ISO 11909.

[0094] After attainment of the theoretical residual NCO content, 0.20 g of the inhibitor butyl hydroxytoluene was added, and the mixture was homogenized for 15 minutes. After cooling to 50° C., the reaction mixture obtained was then diluted to 80% using hexamethylenediol diacrylate (HDDA).

Example 2: Production of Urethane Acrylate 2, a Prepolymer with Blocked Isocyanates and Acrylate Functions

[0095] In a glass flask, 130.0 g of the linear polypropylene ether polyol Desmophen® 1111BD (obtained from Covestro Deutschland AG, Germany) were initially charged at room temperature. Added first to the polyol was 0.043 g of dibutyltin laurate, after which 101.9 g of the hexamethylene diisocyanate-based uretdione Desmodur® N3400 (obtained from Covestro Deutschland, AG, Germany) were added dropwise over a period of around 30 minutes. The reaction mixture was then heated to 80° C. using a temperature-controlled oil bath until the theoretical residual NCO content of 4.71% was achieved. To this end, samples were withdrawn from the reaction vessel at regular intervals and subjected to titrimetric determination according to DIN EN ISO 11909.

[0096] After attainment of the theoretical residual NCO content, 0.20 g of the inhibitor butyl hydroxytoluene was added, and the mixture was homogenized for 15 minutes. After cooling to 50° C. had taken place, 33.8 g of hydroxyethyl methacrylate were then added dropwise and the mixture continued to be stirred until the residual NCO content had reached 0%. The reaction mixture obtained was diluted to 65% with isobornyl methacrylate (IBOMA).

Example 3: Production of the Radically Crosslinkable Resin

[0097] In a plastic beaker with lid, the urethane acrylate, the photoinitiator, and optionally inhibitor were weighed out in accordance with weight fractions from tables 1 and 2. These input materials were mixed in a Thinky ARE250 planetary mixer at 2000 revolutions per minute at room temperature for about 2 minutes. Then the quantities of n-butyl acrylate and/or isobornyl acrylate (IBOA) indicated in tables 1 and 2 were added, following by manual mixing with a spatula.

[0098] Where appropriate, in a further step, butanediol was heated to 40° C. and added, with manual mixing with a spatula.

Example 4: Curing of the Radically Crosslinkable Resin

[0099] The radically crosslinkable resin was applied to a glass sheet, using coaters with different slot sizes, one above another. This simulated a 3D printing process in the sense of a DLP 3D printer. The glass sheet had previously been treated with a 1% solution of soy lecithin in ethyl acetate and dried. The soy lecithin acted as a release agent to allow the cured films to be detached from the substrate again later. The slot sizes were 300 μm, 200 μm, and 100 μm.

[0100] The respective layers applied were each cured in a Superfici UV curing unit with mercury and gallium radiation sources at a belt speed of 5 m/min. The lamp output and belt speed resulted in a radiation intensity of 1300 mJ/cm.sup.2 acting on the coated substrates. This produced a three-layer system with a total thickness of around 600 μm. The samples were conditioned, after curing, in a forced-air oven at 60° C. for 12 hours.

[0101] The cured films were carefully removed from the glass substrates, to give specimens for the mechanical characterization. In addition, tactile and optical assessments were made of the cured films.

TABLE-US-00005 TABLE 1 Formulas of UV-curable resin mixtures with urethane acrylate 1 (containing isocyanurate). The quantities are reported in parts by weight. Experiment No. 1a 1b 1c 1d 1e* 1* 2 3 4 5 6 7 8 Urethane acrylate 1 20 21 21 20 20 21 20 20 20 20 20 20 21 (including HDDA) IBOA 80 75 70 65 60 55 50 45 40 35 30 25 20 n-butyl acrylate 0 5 10 15 20 25 30 35 40 45 50 55 60 photoinitiator 5 5 5 5 5 5 5 5 5 5 5 5 5 tactility at 35° C. hard, hard, hard, hard hard, hard, tough tough soft soft tacky to tacky to tacky to brittle brittle light tough tough touch touch touch brittle T.sub.g (tan δ)/DMA [° C.] 78 69 47 E′ 35° C./DMA [MPa] 2095 2023 1456 tan δ 35° C./DMA 0.037 0.040 0.254 All of the samples were clear and had high transparency. FIG. 1 shows DMA curves of a sample from the inventive experiment No. 1. FIG. 2 shows DMA curves from experiment No. 1b (comparative example). FIG. 3 shows DMA curves from experiment No. 1c (comparative example).

TABLE-US-00006 TABLE 2 Formulas of UV-curable resin mixtures with urethane acrylate 2 (containing uretdione). The quantities are reported in parts by weight. Experiment No. 9a 9b 9c 9e 9f* 9* 10 11 12 13 14 15 16* Urethane acrylate 2 21 22 21 20 20 21 20 21 20 20 20 20 20 (including IBOMA) IBOA 80 75 70 63 60 55 50 45 40 35 30 25 65 n-butyl acrylate 0 5 10 17 20 25 30 35 40 45 50 55 15 butanediol 0 0 0 0 0 0 0 0 0 0 0 0 5 photoinitiator 0 5 5 5 5 5 5 5 5 5 5 5 5 tactility at 40° C. hard, hard, hard, hard, hard, hard, tough soft soft tacky to tacky to tacky to hard, tough, brittle brittle slightly tough tough tough touch touch touch tacky brittle T.sub.g (tan δ)/DMA 71 38 [° C.] E′ 35° C./DMA 2041 534 [MPa] tan δ 35° C./DMA 0.05 0.136 All of the samples were clear and had high transparency. FIG. 4 shows DMA curves from the inventive experiment No. 9. FIG. 5 shows DMA curves from experiment No. 9c (comparative example).