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Module 2: Dental Caries Process

2.2 Dental Caries Formation

Photo showing child with hand in father's mouth

Oral Flora

The oral cavity is home to billions of bacteria, including Mutans streptococci, which are the bacteria most often implicated in dental caries. A high burden of Mutans streptococci increases the risk for developing dental caries.


The bacteria that cause dental caries are typically transmitted from the mother or caregiver to the child. The initial transmission usually occurs after the eruption of an infant’s first tooth. Research indicates that the genetic signatures of the bacteria in the infant’s mouth frequently match those in the mother’s mouth.9–13 Mutans streptococci are usually acquired somewhere between ages 6 and 31 months, although these bacteria have been found living on the dorsum of the tongue in infants as young as 3 months old.14

Because Mutans streptococci are frequently transmitted from the mother or caregiver to the child, the following saliva-sharing practices should be avoided:15

  • The mother or caregiver places a child’s pacifier in her mouth to clean it.
  • The mother or caregiver shares food and utensils with the child (e.g., puts the child’s food in her mouth before feeding the child, to test the temperature).
  • The mother or caregiver places the child’s hand in her mouth.

The earlier a child’s mouth is colonized with Mutans streptococci, the greater the risk that caries will develop.