Developed by a USC School of Dentistry team led by professor Paul Denny, the test quantifies the genetic component of tooth decay (caries).
Dentists have long known that even in areas with fluoridation and good oral hygiene education, some people just have bad teeth. The USC test spots the risk early, when something can be done about it.
"When we apply this to young children, it allows us to predict what might be their future caries history - the number of cavities that they'll get by, say, their late twenties or early thirties," Denny said.
The Caries Assessment and Risk Evaluation (CARE) test measures the relative proportions in saliva of different types of sugar chains, known as oligosaccharides. The same sugar chains are present on tooth surfaces.
The effect of sugar chains on the tooth's ability to resist disease is analogous to the effect of "good" and "bad" cholesterol on blood vessels. "Good" sugar chains tend to repel the bacteria that cause cavities, while "bad" sugar chains allow the bacteria to bond to a tooth and start the decay process.
Unlike cholesterol, humans' sugar chain makeup is 100 percent genetically determined and cannot be changed. The USC researchers found that the sugar chain makeup in saliva can predict a child's future cavity history to plus or minus one cavity with greater than 98 percent confidence.
Children at the far ends of the spectrum - those with exceptionally weak or strong oral hygiene and nutritional habits - may develop more or fewer cavities than the test predicts. Bad habits may cause tooth decay, but researchers caution against extreme measures: completely eliminating sugar has not been shown to prevent cavities, and over-brushing can cause enamel erosion.
The USC test suggests that genes play a greater role in tooth decay now than at any time in the past. Gross malnutrition and negligent oral hygiene are rare in developed societies: That leaves a child's genes as the prime determinant of his or her dental future.
A different version of the test identifies the particular teeth at risk, Denny said. And the test's specificity may reduce the cost and increase the effectiveness of prevention.
"It's possible that in the future - even though a kid might be at very high risk for getting a large number of caries - with the proper preventive dental care he [or she] can arrive at adulthood without any," Denny said.
A further version of the test can identify children with active tooth decay. This test has important public health implications in areas where families cannot afford routine dental exams.
"This is going to help people who are not dental professionals," said Mahvash Navazesh, associate professor in the USC School of Dentistry and co-inventor of the CARE test with USC research scientist Patricia Denny.
School nurses could administer the test, Navazesh said, though she stressed any test would not be a substitute for proper dental care.
"This is not a test to diagnose caries. This is a test that can be used to evaluate susceptibility and risk," she said. "If we can identify those people that are at risk and put in place preventive measures, it is going to prevent them from suffering."
The physical and financial burden of caries increases with age, researchers said. The cost of dental care can be prohibitive and is not covered by Medicare.
Fillings deteriorate and need to be replaced with larger fillings, often leading to root canals, crowns and even tooth loss.
That is why stopping the formation of cavities is so important, Denny said.
"It's the initial cavity or caries that we're worried about," he said. "If we can prevent that, then we prevent this whole lifelong process from occurring."
The research was supported by a grant from the National Institute of Dental and Craniofacial Research, part of the National Institutes of Health.