Gum receded after cleaning by dentist? (Photo)

I'm 31 old im putting braces since one year and a month ago I cleaned my front lower teeth from inside my mouth but my gum directly went down even doctor herself was shocked as me also I thought she was too hard on my teeth so please tell me what to do with problem and I have gum disease since years and still red even after mouth wash and antibiotics I have now black triangle gabs..I don't want ant crown s.

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