Mucins are the fundamental organic components of mucus in human saliva. It remains controversial whether mucin reduces or enhances cariogenic bacterial adhesion . However, mucin may act as a receptor for accumulation and biofilm formation, and it plays an important role in the agglutination/aggregation of a number of microorganisms . The mucin absorption measured by a spectrophotometer in this study demonstrated that polydopamine-induced-PEG coating inhibited mucin adhesion to hydroxyapatite. This can be one of the main reasons for the biofilm-inhibitory effect of polydopamine-induced-PEG. Likewise, polydopamine-induced-PEG showed an inhibitory effect on cariogenic biofilm formation on dentine. The total bacterial amount of the polydopamine-induced-PEG group was significantly lower than that of the other three groups, and the quantity of the biofilm does increase with time. The reason might be that the “micro-brush” effect of polydopamine-induced-PEG coating is a mechanical effect rather than a chemically antimicrobial function. It is plausible that the accumulation of bacteria on the dentine surface weakened the “micro-brush” effect by occupying the space for PEG movement, which in turn caused more bacteria to settle on the dentine surface. Thus, it is difficult to rely completely on this function to protect the tooth surface due to the complex environment of oral biofilm. The polydopamine-induced-PEG should be applied more frequently to sustain the anti-biofouling effect. Polydopamine-induced-PEG may be used as an anti-biofouling agent in mouth rinse and to prevent cariogenic biofilm formation after teeth cleaning. Another clinical application involves adding it to a varnish to protect the tooth from biofilm adhesion. This in vitro study demonstrated the promising results of a novel anti-biofouling method to help control cariogenic biofilm formation. Further studies aiming to simplify the coating process and to sustain the coating are needed.