New Biocidal Additive for Resin-Based Dental Composites: Is Modification with Didodecyldimethylammonium Bromide (DDAB) Effective?

The study aimed to develop and preliminarily characterize experimental resin-based dental composites (RBCs). In addition to the composites, didodecyldimethylammonium bromide (DDAB) was used as a biocide in various concentrations (0–3 wt%). Hardness (HV), flexural strength (FS), and modulus of elasticity, as well as diametral tensile strength (DTS) of composites, were examined. Additionally, shrinkage stress, surface free energy (SFE), water sorption (Wsp), and solubility (Wsl) were determined. Cytometric analysis, including biocidal surface testing and susceptibility to colonization by Streptococcus mutans, Escherichia coli, and Candida albicans, assessed antibacterial activity. The HV of RBCs varied from 27.2 ± 1.5 to 31.5 ± 1.8 depending on DDAB amount, FS—67.0 ± 16.1 MPa for control composite and 79.2 ± 14.5 MPa for modified composite. All DTS values exceed 24 MPa. Shrinkage stress is highest for the composite with 0.25 wt% DDAB—18.5 ± 1.9 MPa—and lowest for the composite with 1 wt% DDAB—15.0 ± 2.5 MPa. Wsp is lowest in the control group (37.19 ± 1.69 µg/mm3) and highest for 1 wt% modifier (42.11 ± 2.75 µg/mm3). Wsl was at its lowest in control group (1.98 ± 1.58 µg/mm3), and highest for modification with 1 wt% (3.91 ± 1.74 µg/mm3). For RBCs modified with 3 wt% DDAB after 60 min, an increase in dead cells is observed: 51% for Escherichia coli, 71% for Streptococcus mutans, and 24% for Candida albicans. Preliminary results show that DDAB effectively reduced the presence of the tested pathogens and contraction stress; however, at certain concentrations it negatively influences hardness and water sorption of composites. The presented findings highlight both the potential and the limitations of DDAB-modified RBCs and underline the need for further studies, including cytotoxicity and genotoxicity assessments, release analyses and evaluation of composites’ ageing behavior.