Introduction: For the 3D FDM printing of working models, not only the selection of the optimal material are of interest, but also the print settings.
Objective: Optimisation of the printing process using FDM printers with regard to the print settings between mechanical stability, low material consumption, and short printing times.
Method: For the investigation, print-optimised stl files with a horseshoe base were printed with a 3D printer (TEVO Tornado, TEVO 3D Electronic Technology Co., Ltd., China) in both PETG (glycol-modified polyethylene terephthalate) and PLA (polylactide). The parameters infill (0-30%), top and bottom layers (1-4), and number of shells (1-4) were varied. From the total of 256 possible combinations, the optimisation was carried out through gradual reduction. The models were measured with a digital caliper (tooth widths, dental arch width). After that a 0.8 mm foil (Erkodent Erich Kopp GmbH, Pfalzgrafenweiler) was vacuum formed with a Scheu Biostar (Scheu-Dental GmbH, Iserlohn) and, after removing the aligner, the model was measured again. The models were also scanned at these times (S600 Arti, ZirkonZahn GmbH, Gais, It). The *.stl were compared with GOM Inspect (GOM GmbH, Braunschweig).
Results: Models without infill (0%) are in principle printable, but may have holes in the occlusal surface due to a lack of support. The bottom layers proved to be indispensable for reasons of torsional stability. Due to the better temperature stability of PETG, these models can be printed with reduced wall thickness (shells) and infill compared to PLA. With lower thicknesses, changes in shape due to vacuum forming could be observed, especially with PLA. The buccal surfaces of the teeth are susceptible to this. Metric measurements, however, remained almost unchanged.
Conclusion: With the right parameters, models that are suitable for the vacuum forming process and optimised in terms of material consumption and printing speed can be produced. Because of the heating that occurs, heat-stable filaments have an advantage.
Keywords: 3D-printing, vacuum forming, aligners
