## 2 Materials and Methods  
Determination of the strain fields that occurred during the setting time of the tested cements was performed using the 3D optical system Aramis 2M (GOM, Braunschweig, Germany). The measuring system recorded the image of the tested object with the help of two high-resolution cameras (1600 \(\times\) 1200 pixel resolution, 1 um displacement sensitivity and 12 Hz maximum frame rate) that provide images for 3D measuring (Figure 1). Automatic measurements can be performed thanks to a previous system calibration. Calibration was performed by using the calibration panel according to the volume of the measured object or according to the dimensions of the specimen surface. By adjusting the frequency and time intervals of recording, the resulting series of images were analyzed for determining displacement, which was used to calculate the surface strain of the object. In this research, 30 intact upper premolars, extracted due to orthodontic reasons, were used. Teeth were cleaned of debris, and kept in 0.02% chloramine solution for one month prior to the experiment. The use of extracted teeth in this research was approved by the Ethical Board of the Faculty of Dentistry in Pancevo (reference number 1139/2-2022). Dentine disks were sectioned transversely from the middle third of the tooth crowns, in order to obtain 2 mm-thick sections. In each section, the central space was enlarged with a 4 mm diameter cylindrical diamond bur to obtain standardized cavities within each disc. Dentine discs were divided into three groups with ten samples each, and then filled with MTA+ (Cerkamed Company, Stalowa Wola, Poland), Biodentine (Septodont, Saint-Maur-des-Fosses, France) or Well-Root PT (Vericom, Chuncheon-si, Korea). Materials were prepared according to the manufacturer's instructions. An additional ten samples of each cement were made within ring-like Teflon molds of 4 mm diameter and 2 mm height. The samples were placed on a wet cotton gauze. The upper surface of each specimen was sprayed with a thin layer of matte white and matte black spray and dried within 10-20 s (Figure 2). In this way, a field of contrast was created, which allowed the specialized software Aramis 6.2.0 (GOM, Braunschweig, Germany) to more easily track the surface points. The software automatically defined the reference coordinate system and recorded reference points on the surface by assigning coordinates to them. Each change was compared with the previous pictures in the sequence by using the digital image correlation method (DIC). Collecting digital images began immediately upon the placement of materials and continued automatically every five seconds. Three sections were observed on each specimen. The first section was circular, positioned on a peripheral segment of each sample (SO). The remaining two sections were linear, positioned perpendicularly to each other and they measured the central deformation (SS). The sections were obtained according to the locations of the largest measured deformations in the selected regions. Software analysis of the images was used to determine the von Mises strain (%). The period of imaging for each material was chosen in accordance with the manufacturer's predetermined setting time. Biodentine offers an initial setting time of 12 min. The setting time of Well-Root PT is within ten minutes. MTA+ cures for six to ten minutes after mixing with water. Figure 1: Scheme of the experimental set-up. (**A**) Cameras, (**B**) Dentin/Teflon mold, (**C**) Sample, (**D**) Glass plate and (**E**) Sample holder. Results obtained in this experiment were analyzed using the IBM SPSS Statistics 25 program (IBM, Armonk, NY, USA). Nested (hierarchic) ANOVA was used for testing the differences between the means of the three cements. The Scheffe post hoc test was used after significant F-statistic determination in ANOVA, to find out which pairs of means were significantly different. In order to look for significant differences between means of SS and SO, the paired t-test was used.