Antimicrobial efficacy and mechanical properties of BAC-modified hard and soft denture liners

This study investigated the antimicrobial efficacy and mechanical strength of hard and soft denture liners modified with benzalkonium chloride (BAC). The specimens (1 mm thickness, 8 mm diameter) were prepared by mixing 0.5, 1, 2 and 5 wt% BAC with soft (Sofreliner Medium, Tokuyama) and hard (Rebase II, Tokuyama) denture liners (n = 5/group). BAC was not added to the controls. Candida albicans ATCC 28366 (A ₅₅₀ = 0.5) and Streptococcus mutans Ingbritt suspensions (A ₅₅₀ = 0.35) were pipetted onto the specimens, and incubated for 4 h. The viable cells were collected, and determined by plate-culturing (CFU). The tests were repeated after the specimens were soaked in distilled water for 7 days. The mechanical strengths were evaluated by tear and 4-point flexural strength tests for soft and hard liners, respectively. The data were analyzed with ANOVA and Tukey's HSD tests at p = 0.05. C. albicans viability was lost in all groups of BAC-modified soft liners (p < 0.001), and S. mutans viability was reduced (p < 0.01), except of soaked BAC 0.5 wt% group (p > 0.05). For the hard liner, BAC 5 wt% killed the C. albicans and S. mutans cells both before and after soaked in water (p < 0.001). BAC 2 wt% showed comparable tear strength with the soft liner control (p > 0.05). BAC did not reduce the flexural strength of the hard liner (p > 0.05), except of BAC 5 wt% group (p < 0.01). BAC can be a promising agent reducing the C. albicans and S. mutans viability on the soft and hard denture liner surfaces.