"Amy's teeth were in a pretty gross state. They were brown and stained and needed major work on them and she was determined to get them back to their sparkling best," the Sun quoted a source as saying.
"It's all major work and it's left her in almost constant pain, but she thinks the sacrifice is worth it.
"She's been given some very strong drugs to cope with the pain," the source added.
Meanwhile, Amy reportedly got involved in a furious bust-up with a punter at Soho's Jazz After Dark club.