Environmental factors are more important than genetics in determining who gets cavities, a new study reports.

Australian researchers recruited 250 twin pairs when their mothers were still pregnant. They collected health and demographic data on them at 24 and 36 months’ gestational age, at birth, and at age 18 months. When they were 6 years old, the 172 twin pairs still in the study underwent dental examinations.

The comparison of identical and fraternal twins is frequently used to study the degree to which a trait is genetic as opposed to environmental. Identical twins are more alike than fraternal twins: They share 100 percent of their genes, while fraternal twins share only 50 percent. So if a condition is genetic, identical twins should look more like each other than fraternal twins look like each other.

In this study, when it came to the number of cavities, fraternal twins looked just as much like each other as identical twins looked like each other. This suggests that genetics does not play an important role in tooth decay.

The study, in Pediatrics, controlled for various health, behavioral and socioeconomic factors and found that low levels of water fluoridation, maternal obesity and a type of enamel defect in the secondary molars were associated with the risk for tooth decay. But the lead author, Mihiri J. Silva, a researcher at the Melbourne Medical School, said that she could find no evidence of a genetic contribution.

“I see a lot of patients who think they’re genetically programmed to get tooth decay,” Dr. Silva said. “It’s nice to think we can blame our genes, but most of the time we can’t.”

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