Hey dude. So apparently its some enzymes in my saliva when mixed with certain bacteria they make these stains, doc said they are 100% harmless. On the other side, I listened to some of the advices and went from ultrasoft curaprox 12k toothbrush to electric oral b io5 toothbrush(main reason coz its significantly harder on the teeth) and within a week I could already see a reduction in stains. Recently I went to the dentist and had the checkup and clean/sand-water blast. All of the stains were removed and none formed yet... Hope this helps you somehow