Long-term antibacterial activity and cytotoxicity of BAC incorporated 4-META/MMA-TBB resin

Objectives: The aim of this study wasto produce an safe antibacterial adhesive for orthodontic bonding without compromising the mechanical property.

Methods:Superbond C&B (4-META/MMA-TBB) resin was mixed with benzalkonium chloride (BAC) to obtain final BAC concentrations of 0.25%, 0.75%, 1.25%, 1.75%, 2.5% and 5.0% (wt/wt). Long-term antibacterial activity against Streptococcus-mutans and Streptococcus-sobrinus was evaluated by soaking the BAC incorporated-resin (BAC-resin) in distilled water at 37°C for periods of 180 days. Antibacterial activity of the BAC-resin was measured by disk diffusion method. For evaluating cytotoxicity, BAC-resin samples were put in cell culture inserts placed above human gingival cells and incubated at 37°C for 1, 3 and 6 days. Cytotoxicity was determined with tetrazolium bromide reduction assay. The bond strengths of orthodontic metal bracket to enamel surface of human premolars using BAC-resin were measured after immersion in water at 37°C for 24 hours.

Results:The antibacterial activity of BAC-incorporated resin samples decreased significantly after immersion in water for 180 days, regardless of BAC concentration. The antibacterial activity of non-immersed resin containing 0.25% or 1.75% BAC was comparable to 5.0% BAC resin immersed for 180 days. In cytotoxicity tests, most of cells died when exposed to resins containing 1.75%, 2.5% and 5% BAC-resin. No difference was observed between resins containing 0.25% and 0.75% BAC at 1, 3 and 6 days of culture. The shear bond strength of orthodontic bracket bonded to enamel by BAC-resins containing 0.25% or 0.75% BAC was compatible with the shear bond strength of original 4-META/MMA-TBB resin.

Conclusions:These results confirm that the addition of BAC to 4-META/MMA-TBB resin confers an antibacterial effect even after long-term immersion in water, and that 4-META/MMA-TBB resin containing 0.25% to 0.75% BAC has no significant cytotoxic effect. 4-META/MMA-TBB resin containing 0.25% to 0.75% BAC has a possibility for clinical application as orthodontic bonding adhesive.