Primary source of anaerobic bacteria in diseased periodontal tissue

 # Which of the following is the primary source of anaerobic bacteria in diseased periodontal tissue?

A. Supragingival plaque

B. Blood

C. Subgingival plaque

D. Calculus

The correct answer is C. Subgingival plaque. 

Subgingival plaque is most likely to contain the anaerobic bacteria that cause periodontal disease.

Remember that although calculus is a secondary etiologic factor, the primary etiologic factor of periodontal disease is dental plaque.