Antimicrobial hard denture reliners using quaternary ammonium methacryloxy silicate (K18 QAMS) and K18-functionalized filler

Objective: To determine the effects of adding a quaternary ammonium methacryloxy silicate (K18) and K18-functionalized filler (K18-Filler) on the material and antimicrobial properties of a hard denture reline material. Materials and methods: 30% K18 in methyl methacrylate (K18-MMA; 0–20 wt% of reliner) and K18-Filler (0–30 wt% of reliner) were incorporated into Kooliner^TM hard denture reliner. Kooliner^TM served as the control. The cure (Shore A hardness), hydrophilicity (contact angles), mechanical (3-point bend test), water sorption, and antimicrobial properties against Streptococcus mutans, S. sanguinis, and Candida albicans were determined. Results: Most K18 groups cured well and had comparable Shore A hardness values (range ~52 to 70 DHN) to that of controls (67.2 ± 1.8 DHN; Bonferroni corrected p > 0.0003). Even the softest group had hardness values within the range of commercial products. Half of the K18 groups had comparable contact angles to that of controls (range ~75° to 80° vs 83.41° ± 2.66°; Bonferroni corrected p > 0.0003), and most were within the range of commercial liners. K18-MMA and K18-Filler increased modulus but decreased ultimate transverse strength (UTS). All experimental groups had comparable or higher moduli than controls (range ~966 to 2069 MPa vs 1340 ± 119 MPa; Bonferroni corrected p < 0.0003), but only half of the experimental groups had comparable UTS to that of controls (range ~41 to 49 MPa vs 55.8 ± 1.5 MPa; Bonferroni corrected p > 0.0003). The 15% and 20% K18-MMA with 30% K18-Filler groups had significant antimicrobial activity against all three microbes (p < 0.05). However, the 15% and 20% K18-MMA with 30% K18-Filler groups had significantly higher water sorption at early time points (p < 0.05). After 8 weeks, they were comparable to each other (p > 0.05). Conclusions: K18-MMA and K18-Filler are promising antimicrobial additives that produce hard denture liners with material properties within the range of commercial products and significant antimicrobial properties against S. mutans, S. sanguinis, and C. albicans. Further development is needed to reduce water sorption.