The results of the experiments on contact angle and QCM suggested that a novel polydopamine-induced-PEG coating on the dentine surface was developed in this study. This polydopamine-induced-PEG coating had the anti-biofouling effect in inhibiting salivary mucin absorption and cariogenic biofilm formation. The substrates used in this study are hydroxyapatite disks and human dentine blocks. The hydroxyapatite disks were standardized and made from hydroxyapatite powder. They were used for the assessment of the contact angle and mucin absorption because these two assessments require high test–retest variability. Autoclaving was used to sterilize both hydroxyapatite disks and dentine blocks because this would render the teeth free of viable microorganisms . Although autoclaving of teeth may reduce dentine microhardness, an in vitro study has shown that it did not significantly alter the physical properties . Contact angle quantifies the wettability of the polydopamine-induced-PEG-coated hydroxyapatite by water via the Young equation. Spectrophotometry is widely used for the study of chemical substances and can determine the amount of mucin absorbed on the hydroxyapatite disk through calculations of observed wavelengths. The early stage of bacterial invasion in the caries process involves Streptococci, Lactobacilli, and Actinomycetes. Streptococcus mutans is the most important odontopathogens involved in the initiation and progression of caries. Actinomyces israelii has the potential to invade dentinal tubules and is associated with root surface caries. Lactobacillus acidophilus is one of the most abundant species frequently found in both superficial deep carious lesions . For the foregoing reasons, these three cariogenic species were chosen to form a multi-species cariogenic biofilm. It is noteworthy that dental caries is a polymicrobial infection process caused by over 700 species of oral bacteria . In addition, this study incubated the bacteria on the root dentine surface with no prior saliva contamination. The results of this in vitro study need to be interpreted with caution.