When Bella had her first professional grooming, she had mats from her puppy coat. We worked them out as best we could by using Cowboy Magic detangler, but we couldn't get them all out. The groomer said they would have to shave her if her mats were bad, but they didn't really SHAVE her, they just cut her hair very short. She turned out great. Check out this thread to see before and after pictures:
http://www.yorkietalk.com/forums/gen...-grooming.html