Table 2.

Summary of different complexes of anaerobic bacteria species associated with periodontal health according to Socransky’s Classification.

Socransky’s Classification a	Example	Remark
Yellow	Streptococci sanguinis and Streptococci oralis	Early colonisers essential for colonization of other bacteria associated with periodontal disease
Green	Capnocytophaga spp., Campylobacter concisus, Eikenella corrodens, and Actinobacillus actinomycetemcomitans
Violet	Actinomyces odontolyticus and Veillonella parvula
Orange	Prevotella intermedia, Prevotella nigrescens, Micromonas micros, Fusobacterium periodonticum, Eubacterium nodatum and Streptococcus constellatus	Bridging colonizers that aggregate with early and later colonizing bacteria
Red	Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia	Late-colonizing bacteria, which are strongly associated with periodontitis and co-exist with the orange complex.
Ungrouped	Aggregatibacter actinomycetemcomitans, Selenomonas	More research is needed to group these bacteria properly

^a In 1998, Dr. Sigmund Socransky categorised periodontal pathogens into different colours that are associated with the disease activity of periodontitis.