Oil pulling using coconut oil can stop the progression of cavities but it will not reverse already made cavities.
If you start noticing a small cavity in your teeth then oil pulling can help get rid of the bacteria in your mouth and prevent further progression of those cavities.
The oil pulling with coconut oil also helps to prevent gum disease and gingivitis and helps to keep your teeth healthy by killing and removing bacteria in your mouth.
If you have small cavities you can use some demic toothpaste to help fill in the small tooth cavity but if the tooth cavity has progressed too far and is now too big then a dentist will need to fill the cavity in with a filling.