Demic Toothpaste or Kazue Yamagishi Toothpaste can cure small dental cavities but it cannot cure large cavities which require a dental filling by a dentist.
As long as you use the Demic or Kazue Yamagishi Toothpaste on the dental cavity before it gets too bad then the toothpaste will work to reverse and fill in the cavity but if you wait too long and it's a cavity that's too deep then the only way to fill the large cavity in is for a dentist to install the filling in your teeth.