Antibacterial activity and bonding performance of carboxymethyl chitosan–containing dental adhesive system

Objectives Develop an antibacterial adhesive by adding appropriate concentration of carboxymethyl chitosan (CMC), to prevent secondary caries on the bonding surface, meanwhile, ensuring the bonding performance. The addition of polyelectrolyte into the bonding system will provide a new idea for the development of antibacterial adhesives. Methods CMC was incorporated into the primer at the concentration of 5, 10, and 20 mg/ml. An etched-and-rinse adhesive without CMC was used as the negative control. Antibacterial activity against Streptococcus mutans was evaluated using the direct contact test, XTT assay, live/dead bacteria staining and fluorescence analysis. The degree of conversion, microtensile bond strength (μTBS) before and after thermocycling were also evaluated. The results were compared at the significant level of 0.05 (α = 0.05). Results The polymerized CMC-modified adhesive significantly decreased the adherent S. mutans amount. The inhibitory effect was more significant when the CMC concentration increased; There was no significant difference observed between the 10 and 20 mg/mL groups. The XTT and live/dead bacteria staining results indicated that the polymerized CMC-modified adhesive interfered with the adherence of S. mutans poliand biofilm integrity. Reduction in metabolic activity was more significant when the CMC concentration increased. The ratio of green/red fluorescence mean intensity showed no significant difference between the experiment group and control group, but the fluorescence area and bacterial viability of CMC-containing group was significantly lower than control group. There were no significant differences in the degree of conversion and μTBS among each group before or after thermocycling. Conclusions The adhesive system containing 20 mg/mL CMC demonstrated reliable antibacterial activity against S. mutans and did not adversely affect bonding performance. Clinical significance The CMC-modified adhesive inhibits S. mutans whilst preserving bond strength to dentine. Incorporation of the antibacterial agent endows the modified adhesive with the potential of combating secondary caries.