Preschoolers who have cavities in their baby teeth are three times as likely as other preschool children to develop cavities in their permanent teeth, according to an often-quoted study published in the Journal of Dental Research in 2002. A 5-year-old’s oral health can even predict greater decay and disease at 26, especially for poor children, another study found.

This may be caused partly by not brushing with fluoride twice daily and sipping sugary drinks over long periods. But it’s also because the bacteria that causes cavities, called caries, signify an infectious disease. So even if one decayed, brown-mottled tooth falls out, an infection may continue ravaging that child’s mouth.