French scientists said the gel works by prompting cells in teeth to start multiplying.
They claim that in laboratory studies it took just one month to restore teeth back to their original state.
A team of scientists at the National Institute for Health and Medical Research in Paris tested if melanocyte-stimulating hormone, or MSH, could stimulate tooth growth, according to the Daily Mail.
The French team mixed MSH with a chemical called poly-L-glutamic acid. The mixture was then turned into a gel and rubbed on to cells taken from extracted human teeth.
In a separate experiment, the scientists applied the gel to the teeth of mice with dental cavities.
In just one month, the cavities had disappeared. The gel is still undergoing testing but could be available for use within three to five years.
Their findings are published in the American Chemical Society journal ACS Nano.
“There are a lot of exciting developments in this field, of which this is one,” said Professor Damien Walmsley, the British Dental Association’s scientific adviser.
“It looks promising, but we will have to wait for the results to come back from clinical trials and its use will be restricted to treating small areas of dental decay.”
Tooth decay is a major public health problem in Britain with around £45m a year spent treating decayed teeth.