Sewing Pup,
I know a couple of people like that. It's frustrating when you care for them and know that a couple of visits to the dentist each year will reduce their pain.
My granddaughter doesn't really like to brush her teeth. She was going to meet a first date after corresponding for a while on internet. Before she left I asked if she had brushed her teeth. The answer was no.
My response to that was, "Well, if I was meeting someone for the first time, I would not be impressed if their teeth weren't clean.". She turned around, went to the bathroom and brushes her teeth. They are in a relationship now and she brushes her teeth more often. Yay!