We had this done last year, on the first ewe lamb my son bought from me to begin his own flock, now an elderly pet who'll see out her life here on the farm. Our vet used a rasp generally used for equines. Turned out to be a lost bottom back tooth and the one above it growing down unchecked, making cudding almost impossible. She's still thin (and sporting a natty grey dog coat - large size - to keep her warm through this appalling weather), but bright as a button and eating well.