In vitro antibacterial activity of green tea–loaded chitosan nanoparticles on caries-related microorganisms and dentin after Er:YAG laser caries removal

This study aimed to determine the inhibitory effects of green tea (Gt), EGCG, and nanoformulations containing chitosan (Nchi) and chitosan+green tea (Nchi+Gt) against Streptococcus mutans and Lactobacillus casei. In addition, the antibacterial effect of nanoformulations was evaluated directly on dentin after the selective removal of carious lesion. At first, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against S. mutans and L. casei isolates were investigated. In parallel, dentin specimens were exposed to S. mutans to induce carious lesions. Soft dentin was selectively removed by Er:YAG laser (n=33) or bur (n=33). Remaining dentin was biomodified with Nchi (n=11) or Gt+Nchi (n=11). Control group (n=11) did not receive any treatment. Dentin scraps were collected at three time points. Microbiological analyses were conducted and evaluated by agar plate counts. Gt at 1:32 dilution inhibited S. mutans growth while 1:16 was efficient against L. casei. EGCG at 1:4 dilution completely inhibited S. mutans and L. casei growth. Independently of the association with Gt, Nchi completely inhibited S. mutans at 1:4 dilution. For L. casei, different concentrations of Nchi (1:32) and Nchi+Gt (1:8) were required to inhibit cell growth. After selective carious removal, viability of S. mutans decreased (p<0.001), without difference between bur and Er:YAG laser (p>0.05). Treatment with Nchi and Nchi+Gt did not influence the microbial load of S. mutans on dentin (p>0.05). Although variations in concentrations were noticed, all compounds showed antibacterial activity against S. mutans and L. casei. Both bur and Er:YAG laser have effectively removed soft dentin and reduced S. mutans counts. Nanoformulations did not promote any additional antibacterial effect in the remaining dentin.