My grandmother chewed betel leaves with a small amount of tobacco, betel nuts, lime (calcium hydroxide aka chuna/chun), multiple times a day all her life. Her other diet consisted of tea just as many times per day, and for actual food a diet of rice, fish, and vegetables. For the majority of her life I don't think she actually had access to fluoridated toothpaste and probably used neem twigs or even charcoal at times to brush her teeth. Her teeth were gross, tinted red and brown. She lived to 93 and I never heard of her ever getting cavities or fillings or going to a dentist. In the place where she lived the only reason you go to a "dentist" is to have teeth removed.

Basically what I'm saying is that diet and genetics are a huge factor.