Polymer-based burn-out material for the lost-wax technique

Abstract

Modelling material which includes (a) at least one radically polymerizable monomer, (b) at least one initiator for the radical polymerization and (c) at least one inert component. The inert component (c) is soluble in the polymer formed by polymerization of the monomer (a), wherein the solubility of component (c) decreases as the temperature increases, with the result that a phase separation takes place above a particular temperature. The material is suitable in particular for the production of models of dental restorations for investment casting processes.

Claims

1. Process for the production of dental restorations in which, (A) a model of a tooth to be restored or of teeth to be restored is moulded, wherein the model is fabricated of a composition comprising a radically polymerizable composition which comprises (a) at least one radically polymerizable monomer, (b) at least one initiator for the radical polymerization and (c) at least one inert component, characterized in that the inert component (c) is soluble in the polymer formed by polymerization of the monomer(s) (a), wherein the solubility of component (c) decreases as the temperature increases, with the result that a phase separation takes place above a particular temperature, (B) the model is then invested in an investment material, (C) after the investment material has set, the invested model is heated in a furnace so that the modelling material is completely removed from the mould, (D) an alloy or a ceramic or glass ceramic material is poured or pressed into the mould.

2. Process according to claim 1, in which the radically polymerizable composition comprises as component (a), at least one (meth)acrylate and/or (meth)acrylamide.

3. Process according to claim 2, wherein the at least one (meth)acrylate and/or (meth)acrylamide comprises one or more mono- or multifunctional (meth)acrylates or a mixture thereof.

4. Process according to claim 1, which comprises, as initiator (b), a photoinitiator.

5. Process according to claim 4, which comprises, as the photoinitiator, benzophenone, benzoin or a derivative thereof, an *α-diketone or a derivative thereof, 9,10-phenanthrenequinone, 1-phenyl-propane-1,2-dione, diacetyl, 4,4′-dichlorobenzil, camphorquinone (CQ), 2,2-dimethoxy-2-phenyl-acetophenone, an *α-diketone in combination with an amine as reducing agent, a Norrish type I photoinitiator, a monoacyl- or bisacylphosphine oxide, a monoacyltrialkyl- or diacyldialkylgermanium compound, benzoyltrimethylgermanium, dibenzoyldiethylgermanium, bis(4-methoxybenzoyl)diethylgermanium (MBDEGe), a mixture of bis(4-methoxybenzoyl)diethylgermanium in combination with camphorquinone and 4-dimethylaminobenzoic acid ethyl ester, camphorquinone (CAS No. 10373-78-1) in combination with ethyl 4-(dimethylamino)benzoate (EMBO, CAS No. 10287-53-3), 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO, CAS No. 75980-60-8), ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate (TPO-L, CAS No. 84434-11-7), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (Irgacure 819, CAS 162881-26-7), bis(2,6-difluoro-3-(1-hydropyrrol-1-yl)phenyl)titanocene (Irgacure 784, CAS No. 125051-32-3), 2-benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone (Irgacure 369, CAS No. 119313-12-1), 1-butanone, 2-(dimethylamino)-2-(4-methylphenyl)methyl-1-4-(4-morpholinyl)phenyl (Irgacure 379, CAS No. 119344-86-4) and/or bis(4-methoxybenzoyl)diethylgermanium (MBDEGe; K69).

6. Process according to claim 1, which comprises, as inert component (c), at least one phthalate, polyethylene glycol (PEG), polypropylene glycol (PPG), PEG-PPG copolymer, glycerol derivative, ethoxylated and/or propoxylated glycerol, ethylenediamine tetrakispropoxylate, ethylenediamine tetrakisethoxylate or a mixture thereof.

7. Process according to claim 6, in which the radically polymerizable composition comprises, as component (c) at least one of PPG with a molecular weight of 1000 to 4000 g/mol, PPG with a molecular weight of 1500 to 3000 g/mol, co-PEG-PPG with a molecular weight of 1000 to 10,000 g/mol, co-PEG-PPG with a molecular weight of 1500 to 5000 g/mol and/or polypropylene glycol with a molecular weight of approx. 2000 g/mol.

8. Process according to one of claim 1, in which the radically polymerizable composition additionally comprises at least one colorant and/or one inhibitor.

9. Process according to claim 1, in which the radically polymerizable composition comprises 20 to 90 wt.-% component (a), 0.1 to 5 wt.-% (photo)initiator (b) and 9.9 to 79.9 wt.-% inert component (c), in each case relative to the total mass of the composition.

10. Process according to claim 1, in which the radically polymerizable composition comprises 42.5 to 82.5 wt.-% component (a), 0.3 to 2.5 wt.-% (photo)initiator (b) and 15 to 55 wt.-% inert component (c), in each case relative to the total mass of the composition.

11. Process according to claim 1, in which the radically polymerizable composition comprises 50 to 79.3 wt.-% component (a), 0.5 to 1.5 wt.-% (photo)initiator (b) and 20 to 48.5 wt.-% inert component (c), in each case relative to the total mass of the composition.

12. Process according to claim 8, in which the radically polymerizable composition comprises 54.7 to 77.7 wt.-% component (a) comprising UDMA, TEGDMA, a mixture of UDMA and TEGDMA or a mixture of UDMA, TEGDMA and bis-GMA, 0.5 to 1.5 wt.-% (photo)initiator (b) and 23.8 to 44.8 wt.-% inert component (c) comprising one or more of PPG with a molecular weight of 1000 to 4000 g/mol, co-PEG-PPG with a molecular weight of 1000 to 10,000 g/mol, and polypropylene glycol with a molecular weight of approx. 2000 g/mol, in each case relative to the total mass of the composition.

13. Process according to claim 8, in which the radically polymerizable composition comprises 64 to 74 wt.-% component (a) comprising UDMA, TEGDMA, a mixture of UDMA and TEGDMA or a mixture of UDMA, TEGDMA and bis-GMA, 0.6 to 1.2 wt.-% (photo)initiator (b) and 24.8 to 35.4 wt.-% inert component (c) comprising one or more of PPG with a molecular weight of 1500 to 3000 g/mol, co-PEG-PPG with a molecular weight of 1500 to 5000 g/mol, co-PEG-PPG with a molecular weight of 2000 to 4000 g/mol and polypropylene glycol with a molecular weight of approx. 2000 g/mol, in each case relative to the total mass of the composition.

14. Process according to claim 9, in which the radically polymerizable composition additionally comprises 0.0001 to 1 wt.-% colorant; and/or 0.0001 to 2 wt.-% UV absorber; and/or 0 to 40 wt.-% organic filler; and/or 0 to 5 wt.-% further additive(s), in each case relative to the total mass of the composition.

15. Process according to claim 9, in which the radically polymerizable composition additionally comprises 0.0001 to 0.5 wt.-% colorant; and/or 0.0001 to 1 wt.-% UV absorber; and/or 0 to 30 wt.-% organic filler; and/or 0 to 3 wt.-% further additive(s), in each case relative to the total mass of the composition.

16. Process according to claim 9, in which the radically polymerizable composition additionally comprises 0.0001 to 0.2 wt.-% colorant; and/or 0.0001 to 0.5 wt.-% UV absorber; and/or 1 to 20 wt.-% organic filler; and/or 0 to 2 wt.-% further additive(s), in each case relative to the total mass of the composition.

17. Process according to claim 1, in which the radically polymerizable composition has a maximum linear thermal expansion below 1.5%.

18. Process according to claim 1, in which the radically polymerizable composition has a maximum linear thermal expansion below 0.7%.

19. Process according to claim 17, in which the maximum thermal expansion is reached at a temperature of below 150° C.

20. Process according to claim 17, in which the maximum thermal expansion is reached at a temperature of below 90° C.

21. Process according to claim 1, in which the model is produced in step (A) by a stereolithographic process.

22. Process according to claim 1, in which, (A) the model of the tooth to be restored or of the teeth to be restored is fabricated of a composition comprising a radically polymerizable composition which comprises (a) 20 to 90 wt.-% of at least one radically polymerizable monomer comprising at least one (meth)acrylate and/or (meth)acrylamide (b) 0.1 to 5 wt.-% of at least one initiator for the radical polymerization and (c) 9.9 to 79.9 wt.-% of at least one inert component, in each case relative to the total mass of the composition, wherein said inert component (c) is soluble in the polymer formed by polymerization of the monomer(s) (a), wherein the solubility of component (c) decreases as the temperature increases, with the result that a phase separation takes place above a particular temperature, and wherein component (c) comprises at least one of PPG with a molecular weight of 1000 to 4000 g/mol and co-PEG-PPG with a molecular weight of 1000 to 10,000 g/mol, (B) the model is then invested in an investment material, (C) after the investment material has set, the invested model is heated in a furnace so that the modelling material is completely removed from the mould, (D) an alloy or a ceramic or glass ceramic material is poured or pressed into the mould.

23. Process according to claim 22, in which the radically polymerizable composition of step (A) comprises (a) 50 to 79.3 wt.-% of at least one radically polymerizable monomer, comprising at least one (meth)acrylate and/or (meth)acrylamide, (b) 0.5 to 1.5 wt.-% of at least one initiator for the radical polymerization and (c) 20 to 48.5 wt.-% of at least one inert component, in each case relative to the total mass of the composition.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention is explained in more detail below by means of figures and embodiment examples.

(2) FIG. 1 shows the thermal expansion curve of the material according to the invention from Example 2, measured on cylinders with a 6 mm diameter and a height of 6 mm. The measurement was carried out using a Q400 measuring device from TA Instruments with a macro-expansion probe.

(3) FIG. 2 shows the thermal expansion curve of the material according to the invention from Example 4.

(4) FIG. 3 shows the thermal expansion curve of the material according to the invention from Example 5.

(5) FIG. 4 shows the thermal expansion curve of the material according to the invention from Example 6.

(6) FIGS. 5 and 6 show the expansion curves of materials customary in the trade according to the state of the art.

(7) FIGS. 7 and 8 show the thermal expansion curves of comparison materials which do not contain any inert component (c).

(8) FIGS. 9 to 11 show dental bridge frameworks made of glass ceramic which were produced using the materials according to the invention from Examples 4 (FIG. 9), 5 (FIG. 10) and 8 (FIG. 11), directly after the divesting. The bridge frameworks do not exhibit any pressing defects.

(9) FIGS. 12 to 14 show dental bridge frameworks made of glass ceramic which were produced using comparison materials without component (c) (FIG. 12, material V1; FIG. 13, material V2; FIG. 14, material V3). The bridge frameworks exhibit clearly visible pressing defects.

(10) FIGS. 15 and 16 show dental bridge frameworks made of glass ceramic which were produced using materials customary in the trade. The bridge frameworks exhibit clearly visible pressing defects.

EXAMPLES

Examples 1 to 9

(11) Modelling Materials

(12) The components listed in Table 1 were mixed with each other homogeneously in the stated quantities. The components were weighed out and stirred at approx. 50° C. for 1 hour and then at room temperature for approx. 16 h (overnight). In the case of pigment- and filler-containing compositions, the pigment and the filler respectively were stirred into UDMA, the substances were then homogenized and dispersed three times with a three-roll mill with a gap width of 10 μm and then stirred into the remaining, already dissolved organic matrix (at least 1 hour at room temperature). Finally, optional further additives such as thickeners were added to the paste and stirred again for at least 1 hour.

(13) TABLE-US-00001 TABLE 1 Modelling materials for stereolithography Composition [wt.-%] Component 1 2 3 4 5 6 7 8 9 Monomer (a) UDMA.sup.1) 42 44 49 48.95  49 36.15 34 49 32 TEGDMA.sup.2) 27 25 10.04 20    20 20.88 17 20 27 Bis-GMA.sup.3) — — — — — — — — 10 Initiator (b) Irgacure 819.sup.4) — — — 0.95 — — — — TPO.sup.5) — 0.95 0.95 — 0.95 0.92    0.95 0.95 0.95 Inert component (c) PPG 2000.sup.6) 30 30 40 30    30 30 — 20 30 PPG 1500.sup.7) — — — — — — 20 — — PPG 4000.sup.8) — — — — — —  8 — — PPG 400.sup.9) — — — — — — — 10 — Dye Sudan IV.sup.10)    0.05 — 0.01 0.05 0.05 0.05    0.05 0.05 0.05 Sudan Black B.sup.11) — 0.05 — — — — — — — White pigment (TiO.sub.2).sup.12) — — — 0.05 — — — — — Further components Wax particles.sup.13) — — — — — 10 — — — Thickener.sup.14) — — — — — 2 — — — PMMA particles.sup.15) — — — — — — 20 — — .sup.1)Urethane dimethacrylates (CAS No. 72869-86-4) .sup.2)Triethylene glycol dimethacrylate (CAS No. 109-16-0) .sup.3)Addition product of methacrylic acid and bisphenol A diglycidyl ether .sup.4)Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (CAS No. 162881-26-7) .sup.5)Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (CAS No. 75980-60-8) .sup.6)Polypropylene glycol) (CAS No. 25322-69-4), MW = 2000 g/mol .sup.7)Polypropylene glycol) (CAS No. 25322-69-4), MW = 1500 g/mol .sup.8)Polypropylene glycol) (CAS No. 25322-69-4), MW = 4000 g/mol .sup.9)Polypropylene glycol) (CAS No. 25322-69-4), MW = 400 g/mol .sup.10)CAS No. 85-83-6 .sup.11)CAS No. 4197-25-5 .sup.12)Titanium dioxide white pigment, particle size D50 <500 nm .sup.13)MC6015, micronized carnauba wax, d = 1-10 μm .sup.14)Solution of a high-molecular-weight, urea-modified, medium polar polyamide (Byk 430) .sup.15)highly crosslinked PMMA, Chemisnow MX80H3wT (Soken Chemical & Engineering Co., Ltd., Japan), D50 = 800 nm

Example 10

Modelling Materials—Comparison Examples

(14) Analogously to Examples 1 to 9, the comparison materials listed in Table 2 were prepared.

(15) TABLE-US-00002 TABLE 2 Comparison materials for stereolithography Composition [wt.-%] Component V1* V2* V3* Monomer (a) UDMA.sup.1) — 74   40 TEGDMA.sup.2) — 25   25 SR348C.sup.16) 59 — — SR480.sup.17) 40 — — Initiator (b) TPO.sup.5) 0.95 0.9 0.95 Inert component (c) — — — Dye Sudan IV.sup.10) 0.05 0.1 0.05 Further components Wax particles.sup.13) — — 34 *Comparison material .sup.1-15)see Table 1 .sup.16)Bisphenol A dimethacrylate with 3 ethoxy groups (Sartomer) .sup.17)Bisphenol A dimethacrylate; ethoxylated 10 times on average

Example 11

(16) Measurement of the Thermal Expansion

(17) For the determination of the thermal expansion of the materials, cylinders with a 6 mm diameter and a height of 6 mm were produced stereolithographically with a printer from the materials described in Tables 1 and 2. The cylinders were cured in layers and then post-exposed in a post-exposure device at a wavelength of 400 nm with an intensity of 10 mW/cm.sup.2 for 5 minutes. The cylinders were then placed in the sample chamber of a thermomechanical analyzer (Q400 type from TA Instruments with a macro-expansion probe) and heated at a heating rate of 5 K/min to 800° C. The linear thermal expansion of the cylinders during heating up and the thermal decomposition in the temperature range of from 30° C. to 800° C. was measured in an air atmosphere. The contact force of the measuring probe was 0.1 N.

(18) In FIGS. 1 to 4, the expansion curves for the materials from Examples 2, 4, 5 and 6 are shown. In all cases, the thermal expansion remained significantly below 0.7% over the whole measurement range. The tests prove that the thermal expansion of the materials is compensated for the most part by the bleeding-out of component (c). The maximum linear thermal expansion was reached in all cases at a temperature below 90° C. Thereafter, the length of the cylinders remained below the maximum value. From 300° C., the materials decomposed thermally and burned out without residue (residue on ignition in all cases <0.1 wt.-%). The decomposition manifests itself in a steep fall in the linear thermal expansion.

(19) Example 6 shows that the wax particles used as filler do not impede the bleeding-out of component (c) and have practically no influence on the expansion.

(20) The expansion curves of the other examples are similar. In Example 8, the maximum thermal expansion of <1.5% is reached at 125° C.

(21) For comparison, the expansion curves of conventional, commercially available stereolithography materials for the lost-wax technique were determined. FIG. 5 shows the expansion curve of the Bego material VarseoWax CAD/Cast. The material expands by more than 4%, and the temperature of the maximum expansion is only reached shortly before the thermal decomposition, i.e. at more than 300° C.

(22) In FIG. 6, the expansion curve is shown of a further stereolithography resin for the lost-wax technique customary in the trade (3D Systems' Visijet FTX Cast). The material expands by more than 2%, and the temperature of the maximum thermal expansion is above 200° C.

(23) FIGS. 7 and 8 show the expansion curves of comparison materials V1 and V3. Material V1 expands by more than 6% (FIG. 7); material V3 by more than 8% (FIG. 8). In both cases, the temperature of the maximum expansion was only reached shortly before the thermal decomposition, i.e. at more than 300° C. or more than 200° C., respectively.

(24) The measurements show that the maximum thermal expansion of the comparison materials is greater in all cases than that of the materials according to the invention. By adding component (c), the thermal expansion can be effectively reduced. Moreover, in the case of the comparison materials, the maximum linear thermal expansion is at significantly higher temperatures, which are determined by the decomposition temperature of the materials.

Example 12

(25) Production of Models

(26) With a 3D printer, models of a three-unit bridge were manufactured from the materials described in Examples 1 to 9 and with materials customary in the trade. In all cases, the same dataset was used to produce the models.

(27) The models were built up on a ring base with the compatible ring gauge and provided with pressing channels. The models were then invested in each case in a phosphate-based investment material customary in the trade (200 g PressVest Speed; Ivoclar Vivadent AG). The fine investment of the cavities was undertaken with a small brush. The invested ring was allowed to set without vibration for 35 minutes. The rings were then placed directly in the preheating furnace preheated to 850° C. and left there at 850° C. for 1.5 h, in order to remove the models from them completely. The rings were then taken out of the preheating furnace and the hot rings were fitted with a ceramic ingot (IPS e.max Press ingot, Ivoclar Vivadent AG), placed in the hot press furnace (Programat EP 5010, Ivoclar Vivadent) and the chosen press program was started.

(28) After the end of the pressing procedure, the rings were taken out of the furnace and placed on a cooling grid in a place protected from draughts for cooling. After cooling to room temperature, the rings were separated using a separating disc and the pressed objects were divested. The rough divesting took place using polishing jet medium at 4 bar pressure; the fine divesting using polishing jet medium at 2 bar pressure. The press results were assessed directly after the fine divesting.

(29) FIGS. 9 to 11 show bridge frameworks by way of example, which were produced using the materials according to the invention from Examples 4, 5 and 8. The pictures were produced directly after the divesting. No pressing defects are visible. The bridges produced with the other materials according to the invention were similar, in no case were pressing defects present.

(30) In contrast thereto, the bridges manufactured using the comparison materials exhibited clearly visible pressing defects, which can be attributed to cracks in the mould which formed during the expansion of the modelling materials.

(31) FIGS. 12 to 14 show the bridge frameworks obtained using the comparison materials V1 to V3. FIG. 15 shows a bridge manufactured using the Bego material Varseo Wax CAD/Cast customary in the trade and FIG. 16 shows a bridge manufactured using the 3D Systems product Visijet FTX Cast. In all cases, pressing defects are present, which make a more or less complex finishing of the restorations necessary. Some of the restorations were unusable.

(32) Even the bridge obtained using the 3D Systems product Visijet FTX Cast exhibited pressing defects, although, at approx. 2%, this material has a relatively small maximum thermal expansion. In contrast thereto, the bridge obtained with the material according to the invention from Example 8 (FIG. 11; max. expansion <1.5%) was fault-free. In the case of the material according to the invention, the maximum thermal expansion is reached at 125° C.; in the case of the comparison material only at above 200° C.

(33) The comparison material V3 contained wax particles but no component (c). The wax particles melted on burn-out, but the wax could only flow out of the surface of the component and remained trapped in the centre. The model expanded greatly on burn-out; the press results were correspondingly poor.