Periodontitis, like other biofilm infections, is refractory to antibiotic agents and host defenses because, as explained previously, the causative microbes live in complex communities that persist despite challenges that range from targeted antibiotic agents to phagocytosis–the ingestion of bacteria or other material by phagocytes and amoeboid protozoans. The American Dental Association describes periodontitis as an archetypical biofilm disease. https://jada.ada.org/article/S0002-8177(14)64499-8/fulltext

To read more about biofilms visit the US National Library of Medicine National Institutes of Health.