Objectives: To analyze the ability of adherence and biofilm formation of certain types of oral streptococci and periodontopathogenic bacteria on dense polytetrafluoroethylene membranes (d-PTFE) used in the socket preservation process. Our goal was to examine the influence of antimicrobial agents, amoxicillin/clavulanic acid, and chlorhexidine digluconate on oral bacteria's adhesion and biofilm formation and on the bacteria in the biofilm. Materials and methods: Two d-PTFE membranes, Permamem and Cytoplast, were used in the research. The microstructure of the d-PTFE membrane was investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and infrared Fourier transform (FTIR). Surface properties were analyzed by atomic force microscopy (AFM), scanning electron microscopy (SEM) and surface free energy (SFE) measurements. Biofilm formation of selected oral bacteria in a microtiter plate model was used in the research. Adherents were quantified in individual and mixed biofilms. Qualitative analysis of the biofilm was performed using SEM and confocal laser scanning microscopy (CLSM). The effect of antimicrobial agents was determined by the broth microdilution method. Results The research demonstrated that the examined more potent bacteria adhere and form a biofilm on Cytoplast compared to Permamem membranes. A difference in the polymer's microstructure was discovered, resulting in different anti-adhesive effects of chemically identical membranes. Analysis of the mixed biofilm showed that S. salivarius K12, in interaction with other species, has an antagonistic effect on the growth and dominance of opportunistic pathogens in the dental biofilm. Significantly higher inhibitory and bactericidal concentrations of coamoxiclav and clorhexidine against bacteria in the biofilm compared to planktonic forms were found. Subinhibitory concentrations of coamoxiclav and clorhexidine can lead to an increase in the number of bacteria in the biofilm. Conclusion: Two commercial d-PTFE membranes had the same chemical composition, but their surface microstructures differed significantly, especially in the degree of crystallinity and roughness on the nanometer scale, which resulted in different bacterial adhesion. These results contribute to understanding of the adhesion of early oral microbial colonizers that may assist clinicians in membrane selection in socket preservation procedures. S. salivarius K 12 in a mixed biofilm can inhibit the growth of periodontal pathogens, help maintain the physiological balance in the oral microbiome, and improve oral health.