I have a patient who struggles with staining. It’s not the typical coffee/tea/cigarette staining. It is marginal and slightly green/brown. The patient doesn’t use any particular toothpaste or mouthwash (I told her to stay away from Crest Pro Health due to staining capabilities), and she brushes/flosses two times a day. She has a regular, healthy diet, including a lot of vegetables. Does anyone know what could be causing this?