By Michelle Roberts
BBC News health reporter, in Washington DC
A simple saliva test could predict how many cavities a person is likely to develop in a lifetime, say scientists.
Some people are more prone to cavities
By analysing proteins within saliva, the Southern California University team was able to predict the number of cavities a person had.
The test can also spot which teeth are most prone to decay.
Dentists might eventually be able to test children and apply protective tooth coatings before disease occurs, the researchers said.
Details of the research were given at the annual meeting of the American Association for the Advancement of Science (AAAS) held this year in Washington DC.
Professor Paul Denny's team found that certain patterns of saliva proteins were linked with a high risk of developing cavities.
From these patterns, they believe they can predict a child's future chance of getting a cavity with greater than 98% confidence.
But the test should not be seen as a replacement for seeing a dentist and going for regular check-ups, stressed Professor Denny.
Instead, it should help dentists devise individual prevention plans to keep even the most cavity-prone children decay-free.
"A version of the test may be included in a well baby check-up to provide early information on what the future oral health care needs of that child might be," said Professor Denny.
He said it might also be useful as a screening test to prioritise treatments in regions where access to dental care was limited.
He said testing saliva was attractive to patients and doctors because it did not require needles, was easy to collect and was in abundance. The average adult produces a litre a day.
Saliva contains many of the proteins and molecules that blood and urine do, so it is a good barometer of what is going on inside the body, he said.
Scientists at the University of California are already devising a saliva test for certain head and neck cancers using the same principle.
There were also saliva tests for HIV, alcohol and some of the more commonly abused drugs, experts attending the American Association for the Advancement of Science meeting said.
Professor David Wong, from the University of California-Los Angeles, said: "We will have a catalogue of the normal human salivary proteins in about two years."
Professor Denny said once this was known, it might be possible to devise a saliva "wellness" test that people could buy and use regularly as part of a health check-up.