i got 100/100 for mine
i investiagted which beverage would cause the mose noticeable tooth stain. I collected teeth from the dentist (sterlised ofcourse) photographed them, and then put them into diff cups with diff drinks eg tea, coffee, juice, soft drink...performed seevral replicates and all that jazz
then i took photos of them , then treid to brush them with toothpaste and an old toothbrush, to see whether the stains woudl remove. after this id take photos again...and then show the before /after shots...from memory Coffee was by far the worst staining beverage for ur teeth, then creaming soda