The process involves removing the affected portion of the tooth and putting the filling in its place. By closing off spaces where bacteria can enter, a filling also helps prevent further decay. Generally, after the filling is in, your dentist will finish and polish it. Fillings are very durable, capable of lasting many years, but may someday need to be replaced. Only your dentist can detect whether you have a cavity that needs to be filled. The type of treatment your dentist chooses will depend on the extent of damage caused by decay.