# Accuracy of 3D-Printed Master Cast Workflow Using a Digital Light Processing Primer
## Materials and Methods  
Preparation of a Reference Cast  
As described by [PERSON] et al. [20], a maxillary reference cast was produced (Figure 1):  
Initially, selected teeth of a maxillary typodont (Basic Study Model, KaVo Dental GmbH, Biberach, Germany), missing the right first molar, were prepared for all-ceramic restorations. The left first premolar was prepared for an inlay, whilst the left first molar, the right first premolar, and the right second molar were prepared for crowns. The typodont model was digitized by an intraoral scanner (Cerec Primescan, software v5.1 Dentsply Sirona, Bensheim, Germany) to create a digital cast. Prior to separating the digital cast into an alveolar base and single teeth, the acquired data were extracted as a standard tessellation language (STL) file and uploaded into a 3D software (Blender v2.78, Blender Foundation, Amsterdam, The Netherlands). The base, consisting of yttrium-stabilized zirconium oxide (IPS e.max ZirCAD Prime, A3, Ivoclar Vivadent AG, Schaan, Liechtenstein), was milled using a 5-axis milling machine (Coritec 250i; imes-icore GmbH, Eiterfeld, Germany). The teeth were produced from lithium disilicate glass-ceramic blocks (IPS e.max CAD LT A2, Ivoclar Vivadent AG, Schaan, Liechtenstein) by another milling machine (Cerec MC XL,  
Figure 1: Reference cast with an yttrium-stabilized zirconium oxide base and lithium disilicate glass-ceramic teeth; prepared surfaces of the teeth were non-glazed. Dentsply Sirona, Bensheim, Germany). After milling, the teeth were crystallized (Programt P500, Ivoclar Vivadent AG, Schaan, Liechtenstein) and the coronal parts of the teeth, except for the prepared areas, were glazed (IPS Ivocolor Glaze Paste FLUO and mixing liquid allround, Ivoclar Vivadent AG, Schaan, Liechtenstein). The root segments of the teeth were etched with fluoric acid and silanized (IPS Ceramic Etching Gel and Monobond plus, Ivoclar Vivadent AG, Schaan, Liechtenstein). The sockets of the base were airborne particle abraded with \(\leq\)50 \(\upmu\)m aluminum oxide at 0.1 MPa. Then, the root segments of the teeth were adhesively cemented into the sockets using a phosphoric acid-containing composite (Panavia 21 Ex, Kuraray Europe GmbH, Hattersheim am Main, Germany). After applying a scanning spray (Scan Spray Stone, Dentaco GmbH & Co. KG, Essen, Germany), the reference cast was scanned by an industrial structured light scanner (ILS) (GOM ATOS III Triple Scan, topometric GmbH, Goppingen, Germany). The cast was scanned five times to check precision. The scans were provided as standard tessellation language (stl) files. For trueness evaluation, one of the casts was randomly selected. Conventional Workflow  
Cast Preparation and Scan  
The interproximal spaces of the reference cast were blocked out with wax. To check for any wax residues on the teeth surfaces a microscope (ZEISS OPMI pico, Carl Zeiss Surgical GmbH) was used. Rim-Lock Trays, size U2 (Orbi-Lock, Orbis Dental), were coated with a universal adhesive (Kulzer GmbH, Hanau, Germany). Single-step two-phase silicone elastomeric impressions were taken. A high-viscosity and low-viscosity material consisting of polyvinyl siloxanes (HEAVY Regular Set DECA and Aquasil Ultra+ XLV Regular Set, Dentsply DeTrey GmbH, Konstanz, Germany) were used. The impressions were removed from the cast after five minutes and disinfected for 10 min (Kanipur, KANIEDENTA, Dentalmedianische Erzeugnisse GmbH, Herford, Germany) to simulate the clinical workflow. Thirty minutes post disinfection, the impressions were poured with type IV gypsum (20 mL water/100 g gypsum, vacuum mixed for 30 s) (BEGO Stone plus, BEGO, Bremen, Germany) by an experienced technician. The impressions were removed from the gypsum cast after a setting time of 30 min. Under dry conditions, sharp edges of the base were trimmed. A total of ten casts were made and then digitized with an ILS (GOM ATOS Triple Scan, topometric GmbH, Goppingen, Germany).