In 1968 Sigmund Socransky classified the bacterial species involved in the initiation and progression of periodontal disease. He classified several complexes of bacteria dividing them in groups, labeled by colors. The categories were based upon the pathogenicity of the bacteria and their role in the development of plaque (a bacterial microfilm). The red complex and the individual species in that group were also strongly associated with bleeding on probing.
The red complex is a group of bacteria that are categorized together based on their association with severe forms of periodontal disease. The three members of the red complex are:
Species in the red complex exhibited a very strong relationship with pocket depth. Sites with none of the species exhibited the shallowest mean pocket depth, while sites harboring all 3 showed the deepest. It is interesting to note that sites harboring P. gingivalis alone or in combination with the other 2 species exhibited the deepest mean pocket depths.
The red complex showed the strongest relationship with the clinical parameters considered most meaningful in periodontal diagnosis.
The orange complex is constituted by:
- Fusobacterium nucleatum
- Prevotella intermedia
- Prevotella nigrescens
- Peptostreptococcus micros
- Streptococcus constellatus
- Eubacterium nodatum
- Campylobacter showae
- Campylobacter gracilis
- Campylobacter rectus
The species in this group were closely associated with one another and this complex appeared closely related to the red complex. Ali et al. (1994) found that P. intermedia was always detected in the presence of F. nucleatum in subgingival plaque samples from deep pockets in a group of adult periodontitis subjects. Similarly to the red complex, all species in the orange complex showed a significant association with increasing pocket depth. Further, treatment that included systemically administered metronidazole decreased levels of these species and improved periodontal status.
The yellow complex is constituted by:
- Streptococcus sanguis
- Streptococcus oralis
- Streptococcus mitis
- Streptococcus gordonii
- Streptococcus intermedius