## 2 Materials and Methods  
### Specim Preparation  
A complete mandibular right first molar crown that had 30 \(\upmu\)m cement gap [28], 3 mm thick axial walls, 1.5 mm thick margins, and 1 mm of minimum occlusal thickness [19] was designed in standard tessellation language (STL) format using dental design software (exocad DentalCAD v3.0; exocad GmbH, Darmstadt, Germany) and the STL of a prefabricated titanium abutment. A total of 40 crowns were fabricated in additively manufactured composite resin (Crowntec; Saremco Dental AG, Rebstein, Switzerland (MS)), graphene-reinforced PMMA (G-CAM; Graphenano DENTAL SL, Valencia, Spain (GR)), PMMA (breCAM.monoCOM; bredent GmbH, Senden, Germany (PMMA)), and reinforced composite resin (Brilliant Crios; Coltene AG, Alstatten, Switzerland (BC)) (Table 1) using this crown STL (\(n=10\)). A priori power analysis (f = 0.90, 1 \(-\)\(\beta=95\%\), \(\alpha=0.05\)) performed using the results of a previous study on the wear of additively and subtractively manufactured resins [21] deemed 7 specimens to be sufficient; however, the statistical power was increased by fabricating 10 specimens, which also allowed compensation in case of specimen loss during thermomechanical aging. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Material** & **Type** & **Composition** \\ \hline Crowntec (MS) & Additively manufactured composite resin & \
\begin{tabular}{c} Esterification products of 4,4\({}^{\prime}\)-isopropylliphenol, \\ ethoxylated and 2-methylprop-2 enoic acid, silanized \\ dental glass, pyrogenic silica, initiators. Total content of \\ inorganic fillers (particle size 0.7 \(\upmu\)m) is 30–50 wt\%. \\ \end{tabular} \\ \hline G-CAM & Subtractively manufactured &
\begin{tabular}{c} Not disclosed \\ polymethylmethacrylate \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Detailed information on tested materials. A digital light processing 3-dimensional printer (MAX UV; ASIGA, Sydney, Australia) was used to fabricate MS crowns with 50 um layer thickness. A 5-axis milling unit (ProgramMill PM7; Ivoclar AG, Schaan, Liechtenstein) was used to fabricate GR, PMMA, and BC crowns [19]. A cut-off wheel was used to remove the support structures, and any remnants on the external surface were smoothened under optical magnification loupes at \(\times\)3.5 magnification using a small round carbide bur at 10,000 rpm (Figure 1). A single operator ([PERSON]) performed all fabrication and adjustments. The STL file of the abutment was used to fabricate 40 fiberglass-reinforced epoxy resin abutments (G10; McMaster-Carr, Atlanta, GA, USA) with the same 5-axis milling unit. The fit of the crowns to abutment dies was controlled with the same optical magnification loupes. Abutments were then cleaned for 10 min in an ultrasonic cleaner (Jelsonic; Jelenko, New Hyde Park, NY, USA), and autopolymerizing acrylic resin (PremEco; Merz Dental GmbH, Lutjenburg, Germany) was used to embed the crowns into the molds of the lower part of a mastication simulator. Abutment surfaces were etched with 35% phosphoric acid for 30 s (Etchant Gel S; Coltene AG, Altsattaten, Switzerland), steam-cleaned, and air-dried. Intaglio surfaces of the crowns were also steam-cleaned and air-dried. Then, an adhesive (One Coat 7 Universal; Coltene AG, Altsattaten, Switzerland) was applied with a microbrush to the abutment and crown surfaces, left undisturbed for 20 s, and gently air-dried for 5 s. A light-emitting diode curing unit (Bluephase; Ivoclar AG, Schaan, Liechtenstein), which has a power density of 950 mW/cm\({}^{2}\), was used to light-polymerize the adhesive for 10 s. The crowns were then cemented onto their respective fiberglass-reinforced epoxy resin abutments using a self-adhesive dual-polymerizing resin cement (SoloCem; Coltene AG, Altsattaten, Switzerland). A constant load of 2 N was applied during cementation with a brass holder [29].