Can A Cavity Be Reversed Naturally?

Read so many studies that a small cavity can heal itself and decay gone by remineralization using fluoride and xylitol. Is this true? Can you actually heal a cavity by this method? Studies said rinsing with ACT( or any other fluoride rinse) & xylitol daily will actually reverse a cavity. I find it hard to believe. Once you have a cavity, small or not the only way is to fill it. But a dentist wrote that she has patients she has seen cavities gone in a few months with this method. Is this true?