Background: Surface roughness and microbial adhesion are key determinants of the biological performance of prosthetic base resins. This study evaluated Candida albicans (ATCC 11225) and Streptococcus mutans (DSM 20523) adhesion to a conventional heat-polymerized acrylic resin (Probase Hot) and a 3D-printed resin (V-Print dentbase) fabricated at 0° and 90° build orientations. Methods: Fifteen disc-shaped specimens (10 mm × 2 mm) were polished using a standardized protocol and surface roughness was characterized by contact profilometry (Ra). After UV sterilization, specimens were incubated for 24 h with standardized suspensions of C. albicans or S. mutans. Microbial adhesion was assessed qualitatively by scanning electron microscopy (SEM). Statistical analysis was performed using one-way ANOVA with Tukey’s post hoc test after confirmation of normality (Shapiro–Wilk) and homogeneity of variances (Levene). Statistical significance was set at p < 0.05, and Cohen’s d was calculated to estimate effect size. Results: Surface roughness differed significantly among fabrication conditions (p = 0.017), with the conventional heat-polymerized resin showing the highest Ra values and the 3D-printed resin fabricated at 90° presenting the lowest roughness. SEM observations suggested a similar adhesion pattern for both C. albicans and S. mutans, with greater apparent microbial presence on 90°-printed specimens, followed by the conventional heat-polymerized resin, whereas 0°-printed specimens showed lower apparent adhesion in the analyzed fields. Conclusions: These findings suggest that printing orientation may influence surface-associated microbial adhesion patterns in 3D-printed prosthetic resins; however, further studies with larger sample sizes, orientation-specific surface characterization, and mono- and multispecies biofilm models are warranted to confirm these preliminary findings.