TL;DR: in addition to less fuel for the bacteria to consume and therefore excrete acids that decay your teeth, the anti-inflammatory benefits of fasting extend to the mouth and may mitigate the effects of periodontal diseases.
https://pubmed.ncbi.nlm.nih.gov/34463980/
…unless you’re me and has always tied brushing to major meal times and thusly has been forgetting to brush, a lot.
I am 47 and the last time I went to the dentist was the first time ever that he commented on my increasing my cleaning. Said things look way better. I didn’t change anything with brushing/flossing etc. The only change is my weight loss, lack of drinking and IF.