@edouard You live in a very beautiful place.

My 3-and-a-half-year-old nephew has these black marks on his teeth. He eats a pretty normal diet to other kids. I would say better than the average considering the family has homecooked food most days and avoids junk. Drinks milk, eats fruits etc. Gets his teeth brushed twice a day. They did show it to a dentist, who did not give any particular cause or solutions other than brushing, which helped reduce it a bit. But it's back now. Does anyone know what could be causing this? Any remedies to get rid of this?