Background: Given their intraoral service for clinically relevant periods, it is important to clarify whether additive manufacturing parameters influence the surface characteristics of 3D-printed provisional restorations and thereby affect microbial colonization. Methods: This study evaluated the effects of printing orientation and layer thickness on surface roughness, wettability, and Streptococcus mutans biofilm formation of LCD-printed provisional restorations. Disk-shaped specimens were fabricated from a methacrylate-based provisional resin at two orientations (0° and 90°) and two layer thicknesses (50 and 100 µm) (n = 7 per group). Surface roughness (Ra) was measured by contact profilometry, wettability by sessile-drop contact angle analysis, and biofilm formation by crystal violet staining after 72 h. Results: Data were analyzed by two-way ANOVA, aligned rank transform (ART) ANOVA, and correlation analysis (α = 0.05). Orientation alone did not affect Ra (p = 0.992), whereas layer thickness (p = 0.012) and the orientation × layer thickness interaction (p = 0.002, η² = 0.339) were significant. At 50 µm, 90° oriented specimens showed higher Ra than 0° (p = 0.021); this pattern reversed at 100 µm (p = 0.020). Neither parameter significantly affected contact angle or biofilm formation (p > 0.05). Conclusions: Both printing orientation and layer thickness altered the surface microtopography of the specimens; however, no significant differences were observed in short-term S. mutans biofilm formation among the tested groups. Within the limitations of the present single-species 72 h in vitro model, the findings suggest that material-related characteristics may have contributed more prominently to the observed biofilm behavior than the printing-induced surface differences evaluated in this study.