These brown stained and, streaked teeth are the result of a medical condition known as "Bauxite Teeth." This condition was common to people living in and around the town of Bauxite and working the bauxite mines for Alcoa and Reynolds Metals in the early part of the 20th century. "Bauxite Teeth" might be one reason that hillbillies are often portrayed with brown, stained teeth.
The condition was so common that the mining companies brought in doctors to study the situation. Two studies were conducted, one in 1928 and one in 1938, and the doctors discovered that not only were the teeth discolored, they were perfectly healthy. In fact they were much more healthy than the average American tooth. The enamel was harder and there was a lower incidence of decay.
It turned out that the minerals in the water were responsible for the discoloration and for the strengthened enamel. If there's fluoride in your toothpaste, these teeth in this plastic box at the Bauxite Museum are part of the reason why.
To get to the Bauxite Museum, find the Bauxite post office on hwy 183 and take the turnoff south. The museum is less than a mile up the road.