Impact of Printing Orientations on the Trueness and Precision of Additively Fabricated Complete Denture Base Before and After Thermal Aging

<b>Objectives:</b> This in vitro study assessed the accuracy (trueness and precision) of different 3D-printed resin denture bases with 0°, 45°, and 90° printing orientations. <b>Methods:</b> Denture base was designed and fabricated using three 3D-printed denture base resins (DentaBASE, Denture 3D+, and FormLabs). Each resin was printed with its own printer and fabricated with different printing orientations, resulting in a total of 72 specimens (n = 8). Trueness and precision were evaluated before and after thermal aging using the superimposition method with best-fit alignment. The data were collected and analyzed using two-way ANOVA followed by post hoc Tukey's test (α = 0.05). <b>Results:</b> The printing orientation significantly affected the trueness of 3D-printed resins (<i>p</i> < 0.001). The highest trueness was observed for NextDent at 0° printing orientation, while the lowest value was observed for ASIGA at 0° and 45° printing orientations. The precision of the denture base was significantly affected by different printing orientations for ASIGA (<i>p</i> = 0.006) and NextDent (<i>p</i> < 0.001) before thermal cycling, while the precision of FormLabs was significantly affected (<i>p</i> = 0.017) after thermal cycling. The highest precision was recorded for FormLabs at 45° printing orientation, while the lowest precision was observed for NextDent at 45° and 90° printing orientations. Moreover, the effect of thermal cycling on trueness was only significant for ASIGA at 0° printing orientation; however, the effect of thermal cycling on precision was significant for NextDent at 0° and 90° printing orientations. A 45° printing orientation provided the most accurate clinical fit. <b>Conclusions:</b> ASIGA showed the lowest trueness, while FormLabs exhibited the lowest precision, revealing performance differences between printers.