Oral bacteria usually aggregate to form a biofilm or plaque on tooth surfaces. Plaque formation involves initial colonization and multiplication by pioneer species, followed by secondary colonization by other species and finally becoming a climax community1. The ‘pioneer species’ of plaque are Streptococcus oralis, Streptococcus mitis and Streptococcus sanguis. Specific bacteria are also closely related to specific dental diseases, for example, Streptococcus mutans and Porphyromonas gingivalis are associated with dental caries and periodontal disease, respectively