Development and Characterization of a Phthalate-Free Antifungal Soft Denture Lining Material Incorporating a Quaternary Ammonium Monomer

Soft denture lining materials are widely used to improve patient comfort; however, their susceptibility to fungal colonization and concerns regarding phthalate plasticizer use remain major limitations. This study aimed to develop and evaluate a phthalate-free acrylic soft lining material incorporating 2-phenylethyl benzoate (PhB) as a safer plasticizer and 2-(methacryloyloxy)ethyl-2-decylhydroxyethylmethylammonium bromide (QAHAMA-10), a quaternary ammonium-functionalized monomer, as an antifungal component. The synthesized materials with increasing QAHAMA-10 content (7%, 11%, 15% and 18%) were evaluated for their physico-mechanical properties (Shore A0 hardness, tensile strength, tensile bond strength, water sorption, water solubility, and water contact angle), antifungal activity against Candida albicans using adhesion and agar diffusion assays, and cytotoxicity using L-929 fibroblast cells. Incorporation of QAHAMA-10 reduced hardness and surface contact angle while increasing water sorption and solubility; however, tensile strength remained within an acceptable range. The absence of inhibition zones may suggest a predominantly contact-dependent antimicrobial mechanism. All modified materials significantly reduced C. albicans adhesion, with no recoverable CFU detected for SLM3 after both 24 h and 28 days of water storage under the applied assay conditions. All formulations exhibited cell viability above 70%, indicating the absence of cytotoxic effects. Among the tested formulations, SLM3 demonstrated the most favorable balance between antifungal activity, cytotoxicity, and mechanical properties.