Tooth decay is contagious from parents to children


Cavities are more complex than we thought. Sugar is still the leading culprit — and genetics, diet, immunity, susceptibility, oral hygiene and fluoride exposure play roles — but a large and growing body of research suggests that oral decay is also an infectious disease.

Numerous studies have found that cavity-causing bacteria can be passed from primary caregivers to infants and toddlers during a period in which the children’s immune systems are not fully developed — putting young children at a higher risk of cavities. Such transmission, called “vertical transmission,” is most likely from caregivers (usually mothers) with severe, untreated tooth decay.

More recently, various studies, including a 2006 study in the journal Pediatric Dentistry, have shown that the bacteria can also be passed among siblings and classmates, what’s known as “horizontal transmission.”


An earlier version of this story identified Dr. Richard Mungo as an associate professor at the USC School of Dentistry. He is a clinical instructor.

But to what degree these vertical or horizontal transmissions are responsible for cavities in young children has been “hard, if not impossible, to quantify,” says Dr. Paul Reggiardo, a pediatric dentist in Huntington Beach, Calif., and public policy advocate for the California Society of Pediatric Dentistry.

A 2000 study published in the journal Community Dentistry and Oral Epidemiology found that young children with high levels of the chief cavity-causing bacteria, Streptococcus mutans, are five times more likely to have tooth decay than those with low levels of the bacteria.

Children under age 2 appear particularly susceptible to infection with S. mutans.

“The child initially has the mother’s immunity, and then as that wears off, there’s this window of infectivity where the child does not have that resistance until they start building their own, and they’re particularly susceptible then,” says Reggiardo.

A certain amount of these bacteria are a normal part of the flora of the mouth. But when young children get an “overwhelming inoculation” of the bacteria before their immune systems are able to fend them off, the bacteria can colonize more effectively, putting the infant at a higher risk of cavities, says Dr. Richard Mungo, a pediatric dentist in Huntington Beach, Calif., and a clinical instructor at the USC School of Dentistry. “It is the timing of the transmission — a time when the infant has limited immune resources to counterbalance the presence of the bacterial colonies.”

And when excessive sugars are present in a person’s diet, the sugar fuels even more bacterial growth, allowing them to reach harmful numbers, Mungo says. If the bacteria are not properly brushed from the tongue and palate, they build up and create plaque, which is essentially food debris that turns into acid.

“Cavities are nothing more than a chemical equation,” says Mungo. “You have enamel that’s really hard, but you throw enough acid on it, it’s going to start to decompose.”


The growing understanding of the role of bacterial transmission in tooth decay in young children has, in part, led to the enormous effort by organizations including the American Academy of Pediatric Dentistry and the American Academy of Pediatrics to educate parents and even general dentists about the need to see children by the time they are 1 year of age or when their first teeth emerge.

“With this has come this huge focus that five years is too late, that we need to begin at age 1 if we truly want to prevent the disease from starting,” says Dr. Indru Punwani, professor and head of the department of pediatric dentistry at the University of Illinois at Chicago.

Punwani notes that many people are not aware of the direct link between the health of baby teeth and long-term oral health in adults. Even when baby teeth fall out, these bacteria continue to flourish. Cavity-causing bacteria are proliferating unchecked in people who have serious decay, so the bacteria are present in unhealthy numbers. When the teeth fall out, the bacteria remain.

“If you are at higher risk with baby teeth for tooth decay, you’re going to be at higher risk for decay in the permanent teeth,” says Punwani. And, he adds, “your habit patterns are what get established very early in life.”

Mungo recommends that parents rinse with Peridex (chlorhexidine gluconate), an antibacterial mouthwash, to cut down on the cavity-causing bacteria during the period when infants and toddlers do not have a fully developed immune system and to take care of their own oral health.

Reggiardo adds that one of the most important things that an expectant or new mother can do for their baby’s health is to make sure that their own teeth are healthy.


“More and more, we want to have obstetricians telling their expectant mothers that their kids’ oral health begins with their [own] oral health and it begins before the baby is born,” says Reggiardo. “Get rid of any dental decay or any periodontal problems that they may have, and then they’re going to be less likely to transmit disease to their child.”