The normal oral flora of humans is exceedingly complex and consists of more than
200 species of bacteria. The composition of the oral flora may be influenced by various
factors, including oral hygiene, genetics, age, sex, stress and diet of the individual. At birth,
the mucous membranes of the mouth and pharynx are often sterile at birth but may be
contaminated by passage through the birth canal 4-12 hours after birth. The development of
the teeth is accompanied by the appearance of other regions, which may provide suitable
conditions for growth of microorganisms.