The team at King's College London showed that a chemical could encourage cells in the dental pulp to heal small holes in mice teeth.
A biodegradable sponge was soaked in the drug and then put inside the cavity.
The study, published in Scientific Reports, showed it led to "complete, effective natural repair".
Teeth have limited regenerative abilities. They can produce a thin band of dentine - the layer just below the enamel - if the inner dental pulp becomes exposed, but this cannot repair a large cavity.
Normally dentists have to repair tooth decay or caries with a filling made of a metal amalgam or a composite of powdered glass and ceramic.
These can often need replacing multiple times during someone's lifetime, so the researchers tried to enhance the natural regenerative capacity of teeth to repair larger holes.