Intraoral Devices as Potential Reservoirs of Pathogens: Effect of Acrylic Resin Manufacturing Technique, Printed and Milled on Susceptibility to Polymicrobial Biofilm Colonization

Biofilm development on intraoral devices represents a relevant challenge in clinical practice, especially in immunocompromised patients or those at increased risk of opportunistic infections. We evaluated the influence of surface properties of acrylic resins used in the fabrication of occlusal splints on biofilm formation derived from human saliva, as a representative model of the complexity of oral microbiota. Cylindrical acrylic resin (PMMA) specimens (4.0 × 1.5 mm) were fabricated under three conditions: heat-polymerized (RAT group, control), milled (RAF group), and 3D-printed (RAI group), with n=120 per group. After standardized finishing and polishing, surface free energy (contact angle, θ), roughness (Ra), total biofilm quantification, biofilm extracellular matrix, and surface morphology by scanning electron microscopy (SEM) were evaluated. Statistical analysis used ANOVA with Tukey’s test for physicochemical data and the Mann-Whitney test for microbiological variables (α=0.05). The RAI group had a significantly more hydrophilic surface (55.10 ± 5.82°) than RAF (73.30 ± 4.71°) and RAT (71.70 ± 4.08°) (p<0.001). Although roughness was similar among RAT (13.3 ± 1.44), RAI (13.8 ± 1.52), and RAF (16.1 ± 1.78) (p=0.067), biofilm formation was significantly higher in RAI from day 4 onwards (0.53 ± 0.2) (p<0.05), with marked production of carbohydrate-rich extracellular matrix, which was absent in RAF. The RAF group remained less susceptible to microbial colonization over six days of incubation. SEM images showed that biofilm formation varied according to resin type: RAI had the highest number of bacterial cells at all three time points; RAF showed greater morphological diversity on day 4; and RAT had overall lower colonization, although with an increase on day 4. Manufacturing method influences biofilm formation on PMMA intraoral devices, with relevant implications for the prevention of device-associated infections. 3D printing generates surfaces more prone to bacterial adhesion and extracellular matrix accumulation, potentially representing a risk factor for persistent infections in the oral environment, whereas milling appears to be a more suitable alternative from the standpoint of microbial control.