I did a 7 days veg-juice only cleanse 4 weeks ago. No solid food for 1 week. Amougst other veggies, I drank 1-2 beetroots per day and that stuff really stains, BIG time. Plus my teeth where not that clean in the first place, the beets just stained them real bad.
It’s all to do with PH alkaline / acid balance of your body. If you have acid Ph saliva, tooth decay can happen, the more acidic, the more decay. If alkaline saliva no decay is possible.
The veg-cleanse alkalised my body but stained my teeth.