Please help? what is the difference of regular teeth cleaning vs a full mouth debridement?

Simple explanation: A "routine" cleaning is performed on a patient every few months or so, and as such the patient's teeth are relatively easy to clean. Patients who have poor oral hygiene and have not seen a dentist in years have so much calculus that they need debridement to remove all the hardened material. It is next to impossible to thoroughly clean years of hardened calculus in one visit.

Debridement/Cleaning: A debridement is a mid-level dental cleaning that provides deeper cleaning for patients that have not been to the dentist in a while. Patients diagnosed with a healthy mouth and healthy gums receive a prophylaxis or regular cleaning. Hope it helps.