Assessment of Surface Roughness and Bacterial Adhesion of Occlusal Splints Fabricated with Different Layer Thicknesses, Polishing Techniques and Build Orientations

This study evaluated the combined effects of build orientation, layer thickness, and polishing protocols on surface roughness and bacterial adhesion of occlusal splints. Ten disc-shaped specimens (Ø16 × 3 mm) were fabricated for each group using a digital light processing (DLP)-based 3D printer. Specimens were printed at two orientations (0° and 90°) and two layer thicknesses (50 and 100 µm) using a splint resin. Surface roughness was measured with a contact profilometer, and bacterial adhesion was measured by optical density (OD) readouts for Streptococcus mutans using a spectrophotometer. Surface morphology was examined by field-emission scanning electron microscopy (SEM). Statistical analyses were performed using jamovi. Because normality and/or homogeneity assumptions were not met, robust analysis of variance was applied. Polishing protocol significantly affected surface roughness (Ra) values. Unpolished specimens showed the highest Ra values, whereas mechanical polishing combined with centrifugation produced the lowest values. No significant main effects of polishing protocol, layer thickness or orientation were observed for bacterial adhesion. SEM findings supported the roughness results. Surface roughness was primarily influenced by polishing protocols and their interactions, whereas bacterial adhesion remained relatively stable. The weak Ra–OD correlation indicated that surface roughness alone was not a reliable predictor of bacterial adhesion.