The Oral Flora: The oral cavity is a dynamic microbiologic eco-system. From childhood to old age the numbers and types of organism that populate the mouth vary continuously. There are unique ecologic niches like tongue (Streptococcus salivarius), tooth surfaces (Streptococcus mitis, and in anaerobic gingival crevice (Bacteroides, Spirochetes) are colonized. Even within an age group factors like diet, smoking, antibiotic therapy, pregnancy and racial factors may influence composition of bacterial population. The groups of bacteria like Streptococcus, Veillonella, Lactobacillus, Corynebacterium, and Actinomyces accounts for more than half the oral flora. These exist naturally and are termed as Commensals. When the immunity of the person goes down, these commensals can attack and become pathogenic. On the hard surface of the teeth proteins from saliva are deposited and organic film called pellicle is formed. Bacteria colonize this pellicle and it can form into a loose aggregation called materia alba or a well-organized colony termed as dental plaque. Materia alba is a whitish curd like aggregation, which can be removed easily by a water spray. It normally contains groups of bacteria leukocytes and desquamated epithelial cells. There is no organized structure for this. Dental plaque is a complex bacterial colony, which helps members to survive by metabolic interdependence. We classify plaque into subgingival and supragingival on basis of its relationship to the margin of gingiva. These are likely to be the starting points for the initiation of periodontal disease. Pit and fissure and smooth surface caries are attributed to S. mutans and Lactobacillus species. The dentinal caries are attributed to Lactobacillus species and Actinomyces naeslundii. Filamentous rods, Actinomyces viscosus and Actinomyces naeslundii cause the root caries. The treatment of dental caries and periodontal diseases are specialities in themselves. We shall describe the management of some common infections. Infections of orofacial regions are common in dental practice and dentist must use healthy commonsense in prescriptions of antibiotics.