The microbiome has a significant impact on the host, as germfree mice have increased immune diseases, such as asthma and inflammatory bowel disease, indicating a dynamic relationship between them (Olszak et al. 2012). The oral microbiome includes bacteria, fungi, archaea, viruses, and protozoa (Dewhirst et al. 2010). The bacterial component is the best understood and is the focus of this review. The formation of dental plaque is affected by the mode of delivery (vaginal or caesarean), breast or bottle-feeding, and proximity to siblings and pets (Dewhirst et al. 2010). Bacteria can be found on all oral tissues, and there is overlap in the bacteria found on each. The most abundant bacteria are Streptococcus oralis, Streptococcus mitis, and Streptococcus peroris. Bacteria associated with periodontal health include Streptococcus, Granulicatella, Neisseria, Haemophilus, Corynebacterium, Rothia, Actinomyces, Prevotella, and Capnocytophaga (Segata et al. 2012). A biofilm forms on the tooth surface, initiated by a pellicle that promotes bacterial adhesion, with Streptococcus and Actinomyces as early colonizers (Socransky and Haffajee 2005). The latter facilitate formation of a multispecies biofilm that is spatially organized and depends on coaggregation among bacterial taxa (Socransky and Haffajee 2005). The subgingival biofilm is typically more anaerobic than the supragingival biofilm (Socransky et al. 1998). Changes in the Oral Microbiota Caused by Periodontal Disease In a National Health and Nutrition Examination Study, 47% of US adults had evidence of periodontitis, and 10% to 15% had advanced periodontitis (Kinane et al. 2017). Periodontal diseases are thought to result from opportunistic infections. The specific factors leading to changes in bacteria that cause periodontal diseases are unknown, although it is recognized that nonideal restorations, genetic conditions that alter the host response, and systemic diseases, such as diabetes and rheumatoid arthritis (RA), predispose to disease (Kinane et al. 2017). The relationships between the biofilm and the host immune response are dynamic, and the ecologic interactions between them determine local homeostasis or transition to a state of disease (Dewhirst 2010; Griffen 2012). Inflammation occurs when bacteria or their products encounter leukocytes in the 805739J DRXXX10.