When I was a child my parents never enforced or made sure I brushed my teeth, so I never learned to do it regularly. Like, I brushed my teeth once or twice in couple months. Now as an adult I had to learn to do it, and establishing new routines is hard (especially because I’m ADHD af). I have a rule in my head that bare minimum is once a day, good days twice a day, but I have depression days when I just don’t do it.
It’s a miracle I haven’t gotten any cavities in my life, and even tho I keep better care of my teeth nowadays, I have had a chronic salivary gland infections for years and my gums have painful blisters now and then. Apparently I have some autoimmune disease going on in my mouth area.