I have brothers Zachary and Kuma both had not lost their baby canines an several molars which had not fallen out by 4 months. Kuma belonged to my son and he had Kuma neutered at 4.5 months and all 7 of his teeth were removed. However, I do not believe in neutering Yorkies before at least 6 months of age. I waited until Zachary was 8 months old because he was so little (less that 4lbs). I spent several weeks playing rough tough of war with Zachary and wiggling his eye teeth with my fingers. He didn't mind this playing and within 3 weeks all of his baby teeth were out! Thus his stay under general anesthesia was shortened quite a bit compared to his brother and the $ price was much less! Hope this helps! Dogs in the wild play very roughly when it comes to tug of war and doing this with toys meant for tug of war usually does the trick!
BTW- My son's vet did charge by the tooth because it is more medicine used and more of their time. At least that was his comment as to why!