What is debridement and what would prompt a dentist to recommend it?

Surgical cleaning up: See prior answer regarding debridement in general, regardless of where in body. In oral cavity, debridement would be recommended if any area was very infected, macerated, extensively built up plaque. Ask the dentist why it has to be done, what is the process that it involved, and how much does it cost.

Large build-up: When there is a large amount of build-up a full mouth debridement can be done to start the cleaning process. It may be advisable to have a further type of cleaning depending on the condition of the gums.

Removal: Removal of dead, dying, or infected tissue. It's a surgical technique to help mother nature get a head start on the healing process.