## 3 Results and Discussion
### Mass and Geometry Analysis  
The average thickness and weight values given with the standard deviation and spread of the data measured immediately after printing (denoted as 0 mth) and one month after printing (denoted as 1 mth) for samples made of pure resin (denoted as resin) and with 15, 25, and 35% alcohol (denoted by the corresponding ethanol percentage) are given in Tables 1 and 2, respectively. The samples were kept at room temperature, with an average air humidity of approximately 40%, and without exposure to excessive sunlight. The average thickness for the samples made with resin was 2.09 mm, deviating from the nominal dimension by 0.09 mm. In [23], a similar phenomenon of deviation of the dimensions of the samples from the nominal dimension by a value of about 0.1 mm was observed using the same printer and the same type of calibration. Therefore, it can be concluded that this phenomenon depends not on the resin used but on the device used and its preparation, including the established parameters and calibration. As the alcohol concentration in the resin increased, the average sample thickness increased from an initial  
Figure 1: Photo of representative samples made from (from the left): resin, and resin with an alcohol content of 15%, 25%, and 35%. value of 2.09 to 2.13 mm, but with a decreasing standard deviation value from 0.03 for pure resin samples to 0.01 mm for samples with 35% alcohol content. It can be said that the thickness values for all samples were comparable but the pure resin samples had the least dimensional stability. Confirmation is also provided by the data range, which for samples made of pure resin, was 0.12 mm, and for samples with 35% alcohol content, was less than half this. After one month, the average thickness of the sample made of pure resin decreased by 0.02 mm; similarly, the range decreased from 0.12 to 0.05 mm. For samples with alcohol added, the average thickness after one month was also smaller. The more alcohol added, the greater the difference in average thickness of the samples measured immediately after manufacture and one month later, being as much as 0.14 mm for a concentration of 25% with a data range of 0.11 mm. For samples with a concentration of 35%, the thickness results after one month are not given due to the significant deformation (bending along the largest overall dimension) of the samples over time, making it impossible to measure the thickness with the chosen technique. The average resin sample mass was 2.04 g and decreased with the addition of alcohol. Initially, at an alcohol concentration of 15%, it decreased by 0.07 g, then, when increasing the alcohol concentration to 25%, the weight decreased by 0.12, and for a concentration of 35%, the weight decreased by 0.35 g, finally reaching 1.50 g. After one month, the weight of the samples decreased by an average of 0.18 g. For the pure resin samples, the data range remained constant after a month, while for the samples with alcohol, the range decreased and was smallest for the samples with maximum alcohol content, being equal to 0.2 g.  
The change in dimensions of the samples over time is most likely related to polymerization and the decrease in intermolecular spaces due to the formation of bonds within and between polymer chains (cross-links) [24]. Moreover, the addition of solvent reduces the viscosity of the solution, facilitating the migration of particles and their reaction at the initial stage of polymerization, thus increasing the effect of polymerization shrinkage due to the reduced molecular weight of polymer chains [25]. The decrease in weight of the samples with the addition of alcohol was related to the density of the ethanol, which at 0.789 g/mL, is less than that of the resin, which is about 1.1 g/mL for acrylic-urethane resins. Conversely, the change in mass over time was probably determined by the absorption of the isopropyl alcohol used to wash the samples