Chitosan-Modified Dental Adhesives: Antimicrobial Activity Against S. Mutans Growth

Objectives: Resin-based materials used to fix orthodontic appliances are not anti-cariogenic in-nature. Thus, biofilm accumulation around the bracket-enamel interface is a common issue among braces users, which increases the risk of caries for these individuals. Chitosan (CS) is a natural-occurring polysaccharide with several therapeutical properties, including antimicrobial activity. This study investigated whether the addition of CS in dental adhesives could inhibit/reduce bacterial growth.
Methods: Low-molecular-weight CS was added at 0.5% concentration either in a commercial adhesive (SBU: Single Bond Universal, 3M) or experimental adhesive (EXP: BisGMA+EBP-2.5:1). Controls consisted of respective materials without CS-addition. Adhesive discs (n=3/group) were prepared using custom molds (4mm x 1mm thick) and photopolymerized for 40s (20s/side). S. mutans was mixed to brain-heart-infusion broth (BHI) and incubated at 37^oC for 24-hrs. Baseline S.-mutans-BHI dilutions were incubated at 37^oC. Twenty-ml from each dilution were spread onto blood agar plates. UV-sterilized specimens were placed on plates and incubated for 2-hrs at 37^oC/5% CO_2. This process was repeated at the 4-h, 6-h and 8-h marks. S. mutans CFUs were counted for each dilution. BHI broth without S. mutans was plated at the 2-h mark as a control. Data were analyzed by ANOVA on ranks and Student-Newman-Keuls post-hoc tests.
Results: The addition 0.5% CS showed no significant effect on the ability of commercial or experimental adhesives to prevent S. mutans growth. No statistical differences were found in CFU/mL among experimental groups.
Conclusions: The addition of 0.5% CS to dental adhesives did not reduce S. mutans growth. Experiments designed to measure the dose-response effect of higher concentrations of CS (1- 5%) in adhesives and composites are being undertaken. By using the Hill equation*, we anticipate that the half-maximal inhibitory concentration (IC50) for CS against S. mutans is ~1.5%.
*[Goutelle et al. Fundam Clin Pharmacol. 2008;22(6):633-48].