Yorkies do best eating hard Iams food which helps keep there gums and teeth clean.  You also will want to brush the gums and teeth of your baby to prevent plaque and tartar buildup.  Another treat that helps with this is Greenies.  They are all natural with no preservatives, help fight bad breathe and the Yorkies love them.  It's important to start brushing their teeth at a young age, grooming, and clipping their nails.  Starting young gets them use to it and becomes no big deal when it's time for grooming.