## 2 Materials and Methods  
The objective of this present study was to examine alterations in surface hardness, roughness, and absorption of the denture base polymer Thermosens (Vertex Dental, 3D Systems, Soesterberg, The Netherlands) following immersion in artificial saliva for varying durations (7, 14, 28 days). The sample size calculation and study design were determined prior to the experiment. An a priori power analysis was conducted using the specialized software G*Power version 3.1.9.7. (Heinrich--Heine University, Dusseldorf, Germany), setting a significance level (\(p\) value) of 0.05 and a power of 0.70 for a balanced 2-group design. The analysis indicated that 20 specimens were needed per testing group, to meet the specified criteria. The specimens (\(n=20\)) were fabricated in a rectangular shape (dimensions: length--20 mm, width--20 mm, thickness--3 mm), using the injection molding technique. Dental stone Type III (Elite Model, Zhermack, Badia Polesine, Italy) was employed for investingthe experimental samples, with the flask being preheated to 30 \({}^{\circ}\)C before the injection molding process. Injection processing took place at a polymer temperature of 290 \({}^{\circ}\)C, operating under a pressure of 6 bar, and maintaining the pressure for approximately 3-4 min for polymer solidification within the flask. The arrangement of the experimental specimens within the flask is depicted in Figure 1.  
Following the completion of the curing process, the test samples underwent a cleaning procedure to eliminate any residual particles of dental stone. Subsequently, measurements were conducted both prior to submersion in artificial saliva and after immersion periods of 7, 14, and 28 days. Additionally, measurements were performed 7 days after the removal of the test specimens from the glass container (Figure 2). A Mitutoyo Surftest 4 roughness meter (Mitutoyo, Aurora, IL, USA) was applied to measure the roughness of the test samples. The Surftest(r) SJ-310 (Mitutoyo, Aurora, IL, USA) enhances productivity through its adaptability and efficiency, boasting precise measurements (with a resolution of 0.002 \(\upmu\)m within a 25 \(\upmu\)m range), rapid measurement capabilities (up to 0.75 mm/s), and a variety of 11 interchangeable detector tips. Additionally, it offers features such as the ability to detect gear tooth surfaces, further contributing to its overall versatility and increased throughput (Figure 3). The roughness measuring instrument comes with a diamond-tipped needle that, as it moves, records changes in the surface profile by detecting the lowest and highest points. These data are then sent to the writing device, and the surface's roughness characteristics are shown on the display. Once the measurements are complete, the device calculates and displays the average roughness value based on the collected data. The surface roughness of the test specimens on Surface 1 and Surface 2 was assessed in two orientations: along the injection direction (1.1 and 2.1) and perpendicular to it (1.2 and 2.2). Figure 1: The position of the specimen in the injection mold. Figure 2: Test specimens before and after immersion in artificial saliva. The hardness evaluation of the ThermoSens polymer test samples, was conducted using the Shor method, employing the D--HSD scale. This technique, classified as elastic-dynamic, involves dropping a tip from a specific height and then measuring the rebound distance (Figure 4). The measurements were executed utilizing an EQUOTIP hardness testing device (Screening Eagle Technologies AG, Zurich, Switzerland) as illustrated in Figure 4. This device allows for convenient assessment of hardness in various items, including polished components and surfaces that have undergone heat treatment. Hardness evaluations are conducted through three techniques: dynamic rebound testing based on the Leeb method, the static Portable Rockwell hardness test, and the Ultrasonic Contact Impedance (UCI) approach.