Cranberries may help prevent tooth decay and cavities, research suggests.
Cranberries also fight bladder infections
Scientists have found a compound in the fruit can stop bacteria from clinging to the teeth, blocking the formation of damaging plaque deposits.
However, researcher Dr Hyuan Koo warned many cranberry-containing products were loaded with sugar and consuming large amounts could lead to tooth decay.
The study, by the University of Rochester Medical Center in New York, will be published in Caries Research.
Dr Koo said the goal was to extract the berry's protective properties and add them to toothpaste or mouthwash.
He said it was still unclear why the fruit was so effective at protecting the teeth.
Cranberries have previously been found to reduce the risk of urinary tract infections that are also caused by harmful bacteria.
Dr Koo said people should not eat or drink excessive amounts of cranberry-containing products in an attempt to improve their dental health.
He said many cranberry products contained large amounts of sugar, which is the leading cause of tooth decay.
In addition, the fruit contains a natural acid that can strip away essential minerals in the teeth.
During the study, researchers coated a synthetic material that acts like tooth enamel, called hydroxyapatite, with cranberry juice.
They then applied the cavity-causing bacteria streptococcus mutans, or plaque.
S. mutans creates cavities by eating sugars and then excreting acids that cause dental decay.
Plaque is a gooey substance formed by bacteria from bits of food, saliva, and acid.
It covers the tooth and gives bacteria a safe haven to munch on sugar, and churn out more damaging acid.
The results, which took about seven months to obtain, showed cranberries were about 80% effective in protecting teeth.
Not only were new bacteria prevented from sticking to the teeth, the cranberry compound also appeared to block bacterial enzymes that play a key role in plaque formation.
Dr Koo said more laboratory tests were needed to try to isolate the active compounds before clinical trials with patients can be considered.
He said: "Scientists believe that one of the main ways that cranberries prevent urinary tract infections is by inhibiting the adherence of pathogens on the surface of the bladder.
"Perhaps the same is true in the mouth, where bacteria use adhesion molecules to hold onto teeth."
Dr Nigel Carter, chief executive of the British Dental Health Foundation, said: "Cranberries are naturally very acidic, while manufacturers also tend to add sugar to cranberry products.
"Every time you eat or drink something acidic the enamel on your teeth is softened temporarily.
"If given time to recover, then your saliva will neutralise this acidity in your mouth and restore it to its natural balance.
"However, if this attack happens too often the mouth does not have the chance to repair itself and tiny particles of enamel can be brushed away. This is called erosion.
"Tooth decay is caused by sugar, and erosion can leave you even more open to this.
"So while cranberries can be enjoyed, they should be limited to mealtimes only to avoid potential problems."