The cola staining is likely due to the caramel colouring. With the energy drink, the extremely acidic nature of the liquid is to blame.

These images are from above image, a website where doctors share medical images and canvass their colleagues' opinions.  The teeth were posted by Dr Tom Bierman, a dentist at the San Diego Dental Studio in the U.S.

He had recently read a book, Rust: The Longest War by Jonathan Waldman, which claims that one in seven new energy drinks are too corrosive to put in aluminium cans.

'I thought: 'If that's what these things do to a can, what on earth are they doing to our teeth?!' ' he told Good Health. And so he set up this unique experiment.

Dr Bierman, 34, used his own wisdom teeth — extracted during his early 20s and brought home by his parents while he was too sedated to notice.