METHOD FOR THE POST-TREATMENT OF PRINTED 3D OBJECTS

Abstract

The invention relates to a method for the post-treatment of 3D objects (10) printed from a light-curing resin formulation. A 3D object (10) removed from a 3D printer is post-treated according to the following steps: a) exposing the surface (11) of the 3D object (10) to a post-treatment liquid (16) comprising a light-curing resin formulation for a prescribed exposure time, wherein the post-treatment liquid (16) and the exposure time are chosen such that the post-treatment liquid (16) can penetrate into a crack (12) or a pore (13) on the surface (11) of the 3D object within the exposure time as a result of capillarity; b) removing the post-treatment liquid (16) remaining on the surface of the 3D object (10); and c) irradiating the 3D object (10) with light for post-curing the light-curing resin formulation used for the printing of the 3D object (10) and curing the post-treatment liquid (16) that has penetrated into cracks (12) and/or pores (13) on the surface (11) of the 3D object (10).

Claims

1. A method of aftertreatment of 3-D objects (10) printed from a light-curing resin formulation, wherein a 3-D object (10) taken from a 3-D printer is aftertreated by the following steps: a) exposing the surface (11) of the 3-D object (10) to an aftertreatment fluid (16) comprising a light-curing resin formulation for a given contact time, where the aftertreatment fluid (16) and contact time are chosen such that the aftertreatment fluid (16) can penetrate into a fissure (12) or a pore (13) on the surface (11) of the 3-D object (10) within the contact time owing to capillarity; b) removing the aftertreatment fluid (16) remaining on the surface of the 3-D object (10); and c) irradiating the 3-D object (10) with light for post-curing of the light-curing resin formulation used to print the 3-D object (10) and curing the aftertreatment fluid (16) that has penetrated into fissures (12) and/or pores (13) at the surface (11) of the 3-D object (10).

2. The method as claimed in claim 1, characterized in that the surface (11) of the 3-D object (10), before being exposed to the aftertreatment fluid (16), is cleaned with a detergent (15) distinct from the aftertreatment fluid (16) to remove residues (14) of uncured or incompletely cured resin formulation adhering to the surface of the 3-D object, wherein the detergent (15) has preferably completely evaporated or is removed prior to exposure of the 3-D object (10) to the aftertreatment fluid (16).

3. The method as claimed in claim 2, characterized in that the detergent (15) is a volatile organic solvent, preferably comprising isopropanol and/or ethanol.

4. The method as claimed in claim 2 or 3, characterized in that the detergent (15) at 23 C. has a volatility index of 1 to 15.

5. The method as claimed in claim 1, characterized in that the exposing of the surface (11) of the 3-D object (10) to the aftertreatment fluid (16) includes cleaning of the surface (11), for which the aftertreatment fluid (16) has a lower viscosity than the viscosity of residues (14) of uncured or incompletely cured resin formulation used in the 3-D printing that adhere to the surface of the 3-D object (10).

6. The method as claimed in any of the preceding claims, characterized in that the exposing of the surface (11) of 3-D object (10) to the aftertreatment fluid (16) comprises the coating of the surface (11) of the 3-D object (10) with aftertreatment fluid (16) or dipping it into an aftertreatment fluid bath, wherein, in the case of cleaning of the surface (11) of the 3-D object (10) with aftertreatment fluid (16), the aftertreatment fluid bath is preferably configured as an ultrasound bath or has a stirrer system for washing the 3-D object (10) with aftertreatment fluid (16).

7. The method as claimed in any of the preceding claims, characterized in that the removing of the aftertreatment fluid (16) remaining on the surface of the 3-D object (10) and/or the removing of detergent (15) is effected by blowing away the aftertreatment fluid (16) and/or the detergent (15).

8. The method as claimed in any of the preceding claims, characterized in that the aftertreatment fluid (16) at 23 C. and a shear rate of 1 s.sup.1 has a viscosity of 2 Pa s to 0.005 Pa s, preferably of 1.5 Pa s to 0.01 Pa s, further preferably of 1 Pa s to 0.01 Pa s, where the viscosity in a shear rate range of 0.01-10 s.sup.1 is preferably not more than 10 Pa s, preferably 5 Pa s, more preferably 2 Pa s.

9. The method as claimed in any of the preceding claims, characterized in that the aftertreatment fluid (16) comprises at least one free-radically photopolymerizable monomer, preferably more than one free-radically photopolymerizable monomer.

10. The method as claimed in claim 9, characterized in that the at least one free-radically photopolymerizable monomer is selected from the group of the (meth)acrylates, preferably comprising monomers consisting of two or more, preferably two, (meth)acrylate groups and one group which has 2 to 12 carbon atoms and is selected from linear or branched alkyl and alkylene groups, aliphatic cyclic hydrocarbyl groups, polyoxyalkylene groups and a combination of these groups, for example PRDMA, propane-1,3-diol dimethacrylate; BDMA, butane-1,3-diol dimethacrylate; BDDMA, butane-1,4-diol dimethacrylate; PDDMA, pentane-1,5-diol dimethacrylate; NPGDMA, neopentyl glycol dimethacrylate; HDDMA, hexane-1,6-diol dimethacrylate; NDDMA, nonane-1,9-diol dimethacrylate; DDDMA, decane-1,10-diol dimethacrylate; DDDDMA, dodecane-1,12-diol dimethacrylate; PRDA, propane-1,3-diol diacrylate; BDA, butane-1,3-diol diacrylate; BDDA, butane-1,4-diol diacrylate; PDDA, pentane-1,5-diol diacrylate; NPGDA, neopentyl glycol diacrylate; HDDA, hexane-1,6-diol diacrylate; NDDA, nonane-1,9-diol diacrylate; DDDA, decane-1,10-diol diacrylate; DDDDA, dodecane-1,12-diol dimethacrylate; EGDMA, ethylene glycol dimethacrylate; DEGDMA, diethylene glycol dimethacrylate; TEDMA, triethylene glycol dimethacrylate; TEGDMA, tetraethylene glycol dimethacrylate; EGDA, ethylene glycol diacrylate; DEGDA, diethylene glycol diacrylate; TEDA, triethylene glycol diacrylate; TEGDA, tetraethylene glycol diacrylate; PEG200DMA, polyethylene glycol 200 dimethacrylate; PEG300DMA, polyethylene glycol 300 dimethacrylate; PEG400DMA, polyethylene glycol 400 dimethacrylate; PEG600DMA, polyethylene glycol 600 dimethacrylate; PEG200DA, polyethylene glycol 200 diacrylate; PEG300DA, polyethylene glycol 300 diacrylate; PEG400DA, polyethylene glycol 400 diacrylate; PEG600DA, polyethylene glycol 600 diacrylate; PPGDMA, polypropylene glycol dimethacrylate; PPGDA, polypropylene glycol diacrylate; NPG (PO) 2DMA, propoxylated (2) neopentyl glycol dimethacrylate; NPG (PO) 2DA, propoxylated (2) neopentyl glycol diacrylate; from the group of the (meth)acrylates, preferably comprising monomers consisting of a (meth)acrylate group and a radical which has 2 to 12 carbon atoms and is selected from linear or branched alkyl and alkylene groups, aliphatic cyclic hydrocarbyl groups, polyoxyalkylene groups and a combination of these groups, for example EMA, ethyl methacrylate; allyl methacrylate; allyl acrylate; n-BMA, n-butyl methacrylate; IBMA, isobutyl methacrylate, t-BMA, tert-butyl methacrylate; EHMA, 2-ethylhexyl methacrylate; LMA, lauryl methacrylate; TDMA, tridecyl methacrylate; CHMA, cyclohexyl methacrylate; BZMA, benzyl methacrylate; IBOMA, isobornyl methacrylate; HEMA, 2-hydroxyethyl methacrylate; HPMA, 2-hydroxypropyl methacrylate; DMMA, dimethylaminoethyl methacrylate; DEMA, diethylaminoethyl methacrylate; GMA, glycidyl methacrylate; THEMA, tetrahydrofurfuryl methacrylate; ETMA, ethoxyethyl methacrylate; AIB, isobutyl acrylate; TBA, tert-butyl acrylate; LA, lauryl acrylate; CEA, cetyl acrylate; STA, stearyl acrylate; CHA, cyclohexyl acrylate; BZA, benzyl acrylate; IBOA, isobornyl acrylate; 2-MTA, 2-methoxyethyl acrylate; ETA, 2-ethoxyethyl acrylate; EETA, ethoxyethoxyethyl acrylate; PEA, 2-phenoxyethyl acrylate; THFA, tetrahydrofurfuryl acrylate; HEA, 2-hydroxyethyl acrylate; HPA, 2-hydroxypropyl acrylate; 4HBA, 4-hydroxybutyl acrylate; DMA, dimethylaminoethyl acrylate; 3F, trifluoroethyl acrylate; 17F, heptadecafluorodecyl acrylate; 2-PEA, 2-phenoxyethyl acrylate; TBCH, 4-tert-butylcyclohexyl acrylate; DCPA, dihydrodicyclopentadienyl acrylate; EHA, 2-ethylhexyl acrylate; and 3EGMA, triethylene glycol monomethacrylate; and/or from the group of the (meth)acrylates comprising monomer(s) consisting of two or more, preferably two, (meth)acrylate groups and one group comprising at least one group selected from a urethane group, a bisphenol A group, an aliphatic polycyclic group and an oligoester group, for example bis-MA, bisphenol A dimethacrylate; bis-GMA, bisphenol A glycerol dimethacrylate; BPA (EO) DMA, ethoxylated bisphenol A dimethacrylate (EO=130); BPA (PO) DMA, propoxylated bisphenol A dimethacrylate (PO=130); BPA (EO) DA, ethoxylated bisphenol A diacrylate (EO=130); BPA (PO) DA, propoxylated bisphenol A diacrylate (PO=130); BPA (PO) GDA, propoxylated bisphenol A-glycerol diacrylate; UDMA, diurethane dimethacrylate; TCDD (M) A and PEM-665.

11. The method as claimed in any of the preceding claims, characterized in that the aftertreatment fluid (16) comprises at least one additive.

12. The method as claimed in claim 11, characterized in that the aftertreatment fluid (16) comprises one or more additives, preferably selected from the group of (photo) initiators, stabilizers, dyes and nanoscale fillers.

13. The method as claimed in any of the preceding claims, characterized in that the 3-D object (10) is composed of a light-curing resin formulation for 3-D printing comprising 5% to 65% by weight of insoluble filler particles.

14. The method as claimed in any of the preceding claims, characterized in that the aftertreatment fluid is chosen such that it is subject to immediate concomitant curing on irradiation of the 3-D object for post-curing.

15. A method of printing 3-D objects, in which the 3-D printing of a 3-D object from a light-curing resin formulation is followed by a method as claimed in any of the preceding claims.

Description

[0043] FIG. 1a-f: diagrams of the method of the invention.

[0044] Before later addressing specific working examples of 3-D objects aftertreated with the aid of the method of the invention, the principle the method of the invention will first be elucidated with reference to FIG. 1 and an illustrative method sequence.

[0045] In a 3-D object 10 printed from a light-curing resin formulation, of which FIG. 1 shows, in each case only in significantly enlarged form, a small surface section in a section view, there are generally already fissures 12 and/or pores 13 at the surface 11 immediately after the 3-D object 10 has been removed from a 3-D printer. In addition, there are also residues 14 of uncured resin formulation from the 3-D printer sticking to the surface 11 (cf. FIG. 1a). The resin formulation of the 3-D object 10 is already basically firm at this juncture, albeit not yet finally cured, and so the 3-D object 10 has not yet reached its final strength. Intensive mechanical processing of the surface 11 of the 3-D object 10 at this stage of the method is therefore not an option.

[0046] In order nevertheless to remove the residues 14 of uncured resin formulation, therefore, a liquid detergent 15 is used first of all, which is applied to the surface 11 of the 3-D object 10, and dissolves the residues 14 from the surface 11 (cf. FIG. 1b). The detergent 15 may, for example, be isopropanol or ethanol, which, as shown in FIG. 1b, can also penetrate into the fissures 12 and pores 13. Even though a corresponding detergent is able to efficiently remove residues 14 of uncured resin formulation, there is the risk that the detergent also attacks resin formulation that has properly cured during the 3-D printing, and hence, for example, increases the size of the fissures 12 or pores 13 or even creates new fissures or pores.

[0047] The cleaning can therefore preferably also be effected with the aftertreatment fluid 16 described in detail hereinafter. For this purpose, the aftertreatment fluid 16 has a lower viscosity than the viscosity of residues 14 of uncured or incompletely cured resin formulation used in the 3-D printing that adhere to the surface of the 3-D object 10. It has been found that the residues 14, given sufficient contact time and especially given induced movement of the aftertreatment fluid 16 by means of an ultrasound generator or a stirrer system, a sufficient cleaning effect can be achieved. This is also true if, as the case may be, the aftertreatment fluid 16 (unlike the case shown in FIG. 1b) is unable to penetrate directly into the fissures 12 or pores 13, which means that the cleaning effect in these regions is fundamentally limited.

[0048] If cleaning was effected with a liquid detergent 15 distinct from the aftertreatment fluid 16, the detergent 15 is first removed completely before the surface 11 of the 3-D object 10 is subsequently exposed over the full area to the aftertreatment fluid 16 (FIG. 1c). Depending on the detergent 15, it is also possible to wait for a certain time until the detergent 15 has evaporated completely.

[0049] The aftertreatment fluid 16 comprises a light-curing resin formulation and is chosen such that the aftertreatment fluid 16 penetrates into the fissures 12 and pores 13 as a result of capillarity within a suitably chosen and defined contact time (cf. FIG. 1d). It is directly possible here for the person skilled in the art to discover an aftertreatment fluid 16 with the required properties and to fix a contact time suitable for the aftertreatment fluid 16. For exposure of the 3-D object 10 to the aftertreatment fluid 16, the 3-D object may be coated with the aftertreatment fluid or dipped into a bath of the aftertreatment fluid 16.

[0050] After the contact time has elapsed, the aftertreatment fluid 16 remaining on the surface 11 of the 3-D object 10 is blown away with compressed air, leaving the aftertreatment fluid 16 that has penetrated into the fissures 12 and/or pores 13 therein (cf. FIG. 1e).

[0051] Finally, the 3-D object 10 is post-cured by irradiation with light in the suitable wavelength for the resin formulation used for printing. If the resin formulation of the aftertreatment fluid 16 has been suitably chosen to cure at the same wavelength, the result is a continuous surface 11 in which previously existing fissures 12 and/or pores 13 have been eliminated (cf. FIG. 1f).

[0052] The fundamental principle of the method of the invention that has been illustrated in FIGS. 1a-f was verified by specific working examples.

WORKING EXAMPLES

[0053] In each of the working examples and tests conducted that are described hereinafter, a 3-D object is used as test specimen, where the test specimen has a cuboidal shape or the shape of a tooth crown depending on the test to be conducted. The 3-D objects were produced in a known 3-D printer available on the marketnamely the D20 II model from Rapid Shape GmbH, Heimsheim, Germanyfrom the LuxaPrint ProCB 3-D printing resin, likewise available on the market, from DMG, Hamburg, Germany. The 3-D printing resin in question contains SiO.sub.2 filler particles in a matrix of UDMA (diurethane dimethacrylate), TEDMA (triethylene glycol dimethacrylate), HDDMA (hexane-1,6-diol dimethacrylate), bis-GMA (bisphenol-A-glycerol dimethacrylate), IBOMA (isobornyl methacrylate), Omnirad TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide) and additives. Omnirad TPO is a trade name from IGM Resins B. V., Waalwijk, the Netherlands.

[0054] In the working examples, the two aftertreatment fluids below are used as alternatives.

[0055] The aftertreatment fluid 1 is a mixture of the following components:

TABLE-US-00001 Proportion Component [% by wt.] TEDMA 33.97 HDDMA 23.62 UDMA 21.23 IBOMA 19.50 Omnirad TPO, IGM Resins 01.20 Tinuvin 622 SF - HALS, BASF 00.20 TMPM (2,2,6,6-tetramethyl-4-piperidyl methacrylate) 00.20 BHT (2,6-di-tert-butyl-4-methylphenol) 00.08
Tinuvin 622 is poly(4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol-alt-butane-1,4-dioic acid). The name Tinuvin 622 is a trade name of BASF, Ludwigshafen, Germany.

[0056] The mixture of this composition was stirred until the solution was homogeneous.

[0057] The aftertreatment fluid 2 used was the commercially available photopolymerizable lacquer LuxaGlaze from DMG, Hamburg, Germany.

[0058] The dynamic viscosity of the two aftertreatment fluids was ascertained. For this purpose, a measurement device of the Kinexus Pro KNX 2100 type from Malvern Instruments Ltd., Malvern, United Kingdom, with a plate-plate geometry at a diameter of 25 mm for the upper plate was used. For the measurement, the shear stress range from 0.01 to 50 Pa was traversed in a logarithmic step method with 2 points per decade, keeping the shear stress constant at each measurement points for a duration of 1.00 min. What are reported in each case are the value of dynamic viscosity ascertained at a shear stress of 50 Pa and at a shear rate of 1 s.sup.1. The viscosity at a shear rate of 1 s.sup.1 was ascertained by linear interpolation of the viscosity between the respectively adjacent points calculated by the device software along the shear rate scale. The measurement was effected at a constant sample temperature of 23 C., which was monitored by the measurement device.

[0059] For the aftertreatment fluid 1, a dynamic viscosity of 16 mPa s was thus found at shear stress 50 Pa and shear rate 1 s.sup.1.

[0060] The dynamic viscosity of the aftertreatment fluid 2 was found to be 390 mPa s at shear stress 50 Pa and to be 960 mPa s at a shear rate of 1 s.sup.1.

[0061] In a first series of experiments, flexural strength of test specimens produced for the purpose was tested to ISO 4049:2009. The test specimens were of cuboidal shape with dimensions of x40 mm, y=1.90.1 mm and z=1.950.15 mm; these dimensions were each ascertained after the aftertreatment steps that follow were implemented.

[0062] On completion of printing, all test specimens were taken from the 3-D printer with a layer thickness of 0.050 mm and subjected to preliminary cleaning with compressed air. Subsequently, the test specimens were cleaned in an automatic cleaning device of the 3Dewash type from DMG, Hamburg, Germany, with isopropanol as detergent and dried with compressed air. The support structures remaining from the 3-D printing on one side of the test specimen were removed.

[0063] Test specimens from a comparative example 1 were not subjected to an aftertreatment of the invention. Instead, the test specimens, immediately after cleaning, were subjected to post-exposure from all sides in an exposure unit of the 3Decure type from DMG, Hamburg, Germany, at full light output and a pressure of 50 mbar for 15 minutes. Then the test specimens were aftertreated, in which the binding sites of the support structure on one side of the test specimens were ground, before the complete surface of the test specimens was then polished. The test specimens were then stored in water at 37 C. for 24 hours.

[0064] In the case of the test specimens from a working example 1, after removal from the 3-D printer, the aftertreatment fluid 1 was applied to the surface of the test specimens with the aid of a microscale brush. After a contact time of 30 seconds, the aftertreatment fluid 1 present on the surface was blown away by means of compressed air, before the test specimens were then subjected to post-curing, further processing and storage in an identical manner to comparative example 1.

[0065] The test specimens from a working example 2 were aftertreated analogously to working example 1, with the sole difference that the aftertreatment fluid 2 was used rather than the aftertreatment fluid 1.

[0066] For working example 3, the test specimens were dipped into a dip bath of aftertreatment fluid 1 and removed again after a contact time of 30 seconds. Immediately thereafter, the aftertreatment fluid 1 on the surface was blown away by means of compressed air, before the test specimens were then subjected to post-curing, further processing and storage in an identical manner to comparative example 1.

[0067] For the test specimens thus produced from comparative example 1 and working examples 1 to 3, flexural strength was then ascertained to ISO 4049:2009. The measurements were effected on Z010 or Z2.5 universal testers from ZwickRoell GmbH & Co. KG, Ulm, Germany, at a constant advance rate of 0.8 mm/min until fracture. For the three-point load specified in ISO 4049:2009, a bending device provided for the purpose with steel rolls in a parallel arrangement was used, using two steel rolls of diameter 2 mm and at an axial separation of 20 mm as base and a third steel roll of diameter 2 mm as die in the middle between the two other steel rolls. If a cuboidal test specimen is deflected until fracture, the formula

[00001]$=\frac{3Fl}{2b{h}^2}$

gives the flexural strength , where F is the maximum force exerted on the test specimen (in newtons), l is the support width, i.e. the distance between the first and second steel rolls (in mm), b is the width of the test specimen before the test (in mm) and h is the height of the test specimen before the test (in mm).

[0068] Various test series were conducted for comparative example 1 and working examples 1 to 3. In a first test series 1, the test specimens from comparative example 1, working example 1 and working example 2 were each placed into the bending apparatus with the ground side on which the support structure originating from the 3-D printing was disposed upward, i.e. facing the third steel roll. In the second test series 2, the test specimens of comparative example 1, working example 1 and working example 3 were each inserted into the bending apparatus with the said ground side downward, i.e. facing the first and second steel rolls. For each comparative example or working example, six test specimens were examined in each case, which gave the following picture:

TABLE-US-00002 Test series 1 Test series 2 Flexural Flexural strength [MPa] strength [MPa] Comparative example 1 67.6 19 62.2 6.83 Working example 1 108 13.8 113 11.5 Working example 2 102 7.83 Working example 3 99.58 17.84

[0069] As is immediately apparent, the test specimens or 3-D objects aftertreated by the method of the invention have a distinct improvement in flexural strength compared to test specimens without corresponding aftertreatment.

[0070] In a further test series, the dimensional accuracy of printed tooth crowns on employment of the method of the invention was verified.

[0071] For this purpose, identical tooth crowns were created by 3-D printing with a layer thickness of 0.05 mm, with a support structure on the occlusal face. The support structure was removed and the tooth crowns were subjected to preliminary cleaning with compressed air.

[0072] The tooth crown from a comparative example 2 was treated analogously to comparative example 1. Immediately after cleaning in an automatic cleaning device of the 3Dewash type from DMG, Hamburg, Germany, with isopropanol as detergent and subsequent drying with compressed air, the tooth crown was thus subjected to further exposure from all sides in an exposure unit of the 3Decure type from DMG, Hamburg, Germany, at full light power and a pressure of 50 mbar for 15 minutes. The tooth crown was then aftertreated, in which the occlusal face of the tooth crowni.e. the face to which the support structure was boundwas ground, before the complete surface of the tooth crown was then polished. The tooth crown was then stored in water at 37 C. for 24 hours.

[0073] In the case of the tooth crown of comparative example 3, the tooth crown, by contrast with comparative example 2, was cleaned not in an automatic cleaning device but merely with a cloth and isopropanol. The subsequent post-exposure, further processing and storage were then once again analogous to comparative example 2 and hence also to comparative example 1.

[0074] The tooth crown of comparative example 4, after preliminary cleaning with a cloth, was cleaned with a microbrush and ethanol. The subsequent post-exposure, further processing and storage were analogous to the other comparative examples 1 to 3.

[0075] The tooth crown from a working example 4 was cleaned and aftertreated corresponding to working example 1.

[0076] The tooth crown from a working example 5 was cleaned and aftertreated corresponding to working example 2.

[0077] In a working example 6, the tooth crown, for cleaning purposes, was first placed into an ultrasound dip bath of 50 ml of TEDMA as aftertreatment fluid for 3 minutes, with the tooth crown completely surrounded by the aftertreatment fluid. Subsequently, the tooth crown was removed, cleaned briefly with compressed air and then placed again into an ultrasound bath of 50 ml of TEDMA for two minutes. This was fresh TEDMA, and not, for instance, the aftertreatment fluid used previously for cleaning. Subsequently, the tooth crown was removed, and the aftertreatment fluid still adhering on the surface of the tooth crown was blown away with compressed air. The subsequent post-exposure, further processing and storage were analogous to the other comparative/working examples.

[0078] In order to verify dimensional accuracy, some of the comparative and working examples were measured with a 3-D scanner of the ATOS Core type from GOM GmbH, Braunschweig, Germany, after they had been rendered detectable by the 3-D scanner by spraying with the Nord-Test Entwickler U89 from Helling GmbH, Heidgraben, Germany. The scan data were evaluated on the basis of the 3-D data used for 3-D printing (here in STL data format). In order to determine dimensional accuracy, the percentile of the area below a variance of 60 m compared to the 3-D data was ascertained.

[0079] The dimensional accuracy of comparative example 2 and of working example 6 can be assessed as being very good at 94.1% and 95.8% respectively. By contrast, the dimensional accuracy of comparative example 3 is low at only 86.9%. Elevations in particular (of up to 0.5 mm) on the inner surfaces of the tooth crown of comparative example 3, which suggest incomplete removal of 3-D printing resin adhering to the crown, which has been cured by the post-exposure, make the tooth crown virtually unusable. The same applies to comparative example 4, in which comparable elevations were detected. Just like comparative example 2 and working example 6, working examples 4 and 5 do not show any such elevations either. In view of visual comparisons between the tooth crowns from the various comparative and working examples, even without 3-D detection of working examples 4 and 5 that was dispensed with for reasons of expediency, good dimensional accuracy of these working examples can be assumed.

[0080] Even though comparative example 2 achieves good dimensional accuracy, the surface quality of comparative example 2 is inadequate. Thus, white deposits and fissures are apparent by the naked eye on the surface of the tooth crown. The surface of working examples 4 to 6, by contrast, can be described as very good. Thus, there are neither deposits nor fissures. Nor are any other faults on the surface apparent.