## 2 Materials and Methods  
This research used a PEEK filament (Peek Ketaspire KT-820 NT Filament, Medphen, Madrid, Spain) for Class I Medical Devices (ISO 10993-1) [33]. Following the manufacturer's instructions, the filament was dried in an oven at 150 \({}^{\circ}\)C (Visnec DW25, Moretec, Hoorn, The Netherlands) for 4 h before the printing process and after printing to prevent water absorption. An adhesive (Nano Polymer Adhesive, Vision Miner, Irvine, CA, USA) was applied on the surface of the print table to promote the adhesion of the specimens to the table and prevent the printed pieces from warping. Printing was performed on the FDM 3D printer AON-M2 (AON3D, Montreal, QC, Canada), on which initial tests were carried out to assess the technical parameters (printing path, printing speed, print layer thickness, extruder temperature), as recommended by the manufacturer. The final specimens and the stabilization gutter prototype were printed with the printer-adjusted parameters summarized in Table 1. The selected printing path is shown in Figure 1.  
The specimens (10 mm \(\times\) 10 mm \(\times\) 1.5 mm) were designed using the software Solidworks (Version 2021) (Dassault Systemes Solidworks Corporation, Waltham, MA, USA). Four specimens were printed--two specimens (A1 and A2) with 0.1 mm and two specimens (B1 and B2) with 0.3 mm of print layer thickness--to evaluate whether changing this parameter modifies the specimen's surface roughness. The surface roughness of all specimens was assessed after the printing process without any surface finishing. Subsequently, these specimens were polished with a series of silicon carbide (SiC) sandpapers of increasing grain (P80, P180, P320, P800, P1200, and P4000, Struers, Ballerup, Denmark) [18; 34; 35; 36]. For this procedure, the specimens were first placed in a support material (Polyvinyl Siloxane, Aquasil Ultra, Dentsply Sirona, Charlotte, NC, USA) (Figure 2) to allow safe and uniform polishing. The polishers (Rotopol-21, Struers, Denmark) were used with tap water lubrication at 300 rotations per minute (rpm) for 60 s (Figure 3). After this procedure, the specimens' roughness was measured again. \begin{table}
\begin{tabular}{c c} \hline
**Parameters** & **Technical Specifications** \\ \hline Extruder diameter & 0.6 mm \\ Printing layer thickness & 0.1 mm or 0.3 mm \\ Print speed & 10 mm/s \\ Printing table temperature & 160 \({}^{\circ}\)C \\ Chamber temperature & 100 \({}^{\circ}\)C \\ Extruder temperature & 380 \({}^{\circ}\)C \\ \hline \end{tabular}
\end{table} 
Table 1: Printing parameters used. Figure 1: Printing path. The control group for comparison consisted of 3 specimens produced in PMMA (Aidite Temp, Aidite Technology Co, Qinhuangdao, China). Another STL file was created using computer software (Exocad DentalCAD, Exocad GmbH, Darmstadt, Germany) for specimens with the same dimensions as the PEEK specimens (10 \(\times\) 10 \(\times\) 1.5 mm). These PMMA specimens were then milled (DWX-52D, Roland DGA Corporation, Irvine, CA, USA). After milling, different surface treatments were carried out on these specimens: one specimen was left unfinished (P1), another was polished with the SiC sandpaper used for the PEEK specimens (P2), and another was subjected to a conventional finish with polishing drills and diamond paste (P3). Then, their roughness was evaluated. A Hommelwerke T8000 controller with an LV-50 linear unit (Hommelwerke GmbH, Villingen-Schwenningen, Germany) was employed to obtain the specimens' surface topography (see Figure 4a). A TKL 300 pickup was used as the stylus probe, with a vertical measurement range of \(\pm\)300 \(\upmu\)m, a tip radius of 5 \(\upmu\)m, and a cone angle of 90 degrees. A support structure was created in polylactic acid (PLA) using the FDM 3D printer to fix the specimens in place securely, ensuring accurate and repeatable readings from the stylus profilometer (see Figure 4b).