Objective: The objective of this study was to investigate the effectiveness of immunoglobulin Y (IgY) antibodies as a dental caries vaccine by utilizingIgY specific to the quorum-sensing signaling receptor ComD of Streptococcus mutans combined with chitosan in the form of mouthwash.Methods: The effects of a mouthwash containing IgY anti-ComD S. mutans with and without chitosan on biofilm-forming isolates of S. mutans wereinvestigated. Subjects were assigned to rinsing twice daily for 6 days with 15–20 ml mouthwash solution for 30 s. Biofilm formation of S mutansisolated from the patiens was measured using a crystal violet method to determine the optical density at 490 nm.Results: The results indicated that mouthwash containing IgY anti-ComD S. mutans and chitosan significantly enhanced the biofilm formation ofS. mutans. In mouthwash containing IgY anti-ComD S. mutans without chitosan, a reduction in biofilm formation was observed; however, this was notstatistically significant.Conclusions: The mouthwash combination of IgY anti-ComD S. mutans and chitosan enhanced the biofilm formation ability of S. mutans isolated fromcaries and caries-free subjects. Further, research is needed to determine the appropriate concentrations of IgY anti-ComD S. mutans and chitosanrequired to effectively inhibit dental caries.