The photosensitive resin used in additive manufacturing is cured by free radical polymerization by UV irradiation. However, undesired reaction with oxygen during polymerization inhibits polymerization and results in an under-cured polymer. Therefore, in this study, the hypothesis that successful oxygen shielding in the post-polymerization step could affect the properties of the final polymer was tested. 3D printed specimens using denture base resin were post polymerized either by immersion in glycerin for oxygen shielding (GL group) or placed in a medium-low vacuum chamber at 5 × 10⁻² Torr (VA group). Specimens cured with no additional conditioning served as the control (CON group). To consider the effect of temperature, all groups were additionally compared with 80 °C and without an increase in temperature (room temperature) during post-polymerization. Fourier transform infrared spectroscopy was used to measure the monomer conversion ratios between different groups. In addition, the mechanical properties were quantified by the micro-hardness, flexural strength, and elasticity of the surface, and the water sorption and solubility. Dynamic mechanical analysis (DMA) was conducted to observe the trend in storage and loss modulus between the groups against temperature. Differences in the surface as a function of the post-polymerization conditions were qualitatively observed by scanning electron microscopy (SEM).