s bone loss and gum disease BESIDES not brushing correctly and not flossing?(corrected post) What cause

(This is a corrected post. In the one I just sent, I mistakenly said "bone disease" when I meant "gum disease."  I've restated my post correctly below, and also corrected the Title for this post.

Dear Doctors--What causes bone loss and gum disease BESIDES not brushing correctly and not flossing?
I'm 74 and have been flossing every day for many many years, and brushing after eating. I also haven't had a cavity for many many years, yet my dentist tells me I have some gum disease and bone loss. Thank you.