Abstract:A salivary-coated hydroxyapatite model was used to simulate the oral environment.competed with oral pathogens for adhesion on the surface，and Streptococcus salivarius K12（S.salivarius K12）was used as a positive control.The inhibitory effect of L.paracasei L9 on the in vitro adhesion of Streptococcus mutans 1.2499（S.mutans）and Streptococcus gordonii 1.2496 （S.gordonii）was evaluated by three indicators：the number of pathogenic bacteria adhering，the pH value of the oral environment，and the thickness of biofilm formed by pathogenic bacteria.The results showed that L.paracasei L9 could effectively inhibit the adhesion of S.mutans and S.gordonii within 6 h in the prevention group（p＜0.05）.In the treatment group，L.paracasei L9 significantly inhibited the adhesion of S.mutans within 2 h（p＜0.05）.There was no significant change in the pH value of the buffer during the adhesion process （p＞0.05）.In addition，they were able to significantly reduce the biofilm thickness and density of S.mutans on the surface of hydroxyapatite.