I have dealt with many heavy perio cases and one of my patients that came to the clinic was a heavy type IV.  she had generalized bone loss and mobility.  Here are the radiographs taken on the patient, that was used to help evaluate the severity of bone loss.

With these radiogrpahs I saw the amount of generalized alveolar bone loss.  There was also generalized mobility.  I scaled lower arch very carefully because as I was scaling the teeth, they became more mobile.