From The Guardian, 11 July 2011:
Teeth with neat parallel grooves have been found in Viking graves in Sweden, Denmark and England, and farther afield.
Filed Viking teeth are piling up. Caroline Arcini, an osteologist at the archaeology department of the Swedish National Heritage Board, was fascinated to learn from Oxford Archaeology of the men with neat horizontal lines filed into their teeth who ended up in a pit in Dorset: she has scores more such teeth on her desk.
The epicentre of Viking teeth filing appears to be a Viking cemetery at Kopparsvik on Gotland, which has produced more examples than any other site so far examined. Most had neat parallel marks only on their two upper front teeth – which may originally have had charcoal or other colouring rubbed in to increase the impact – but some had lines incised into three, four or even more teeth. Further research on the Wessex teeth may reveal whether they had any connections with Gotland.