Periodontal Disease. More Condition_symptoms Why Is Periodontal Disease A Chronic Disease?

Why is periodontal disease a chronic disease? - periodontal disease. more condition_symptoms

I read a lot about periodontal disease. I understand that this is at an advanced stage of gum disease: structure of the teeth and gums plaque attack the gum and bone.

However, the plate can be removed by cleaning and good oral hygiene, helps prevent plaque.

Why is periodontal disease, then? Why can not be treated, but can not be cured?

Thank you.