It would probably be a good idea to take him to the vet and have this checked out. Normally the teeth will fall out but once in a while they do have to be pulled. Also, it is a very good idea to have your little Yorkie have a "dental" at least once a year starting at around a year old. Just check out a number of vet's in your area to check on the cost. In my area, I can have an excellent "dental" done for $40.00. But my sister lives in Oregon and it cost her $400
to have her little dog's teeth cleaned - both are done the same way!
Best of luck!