We could check with the dentist!
I'll add Fromms Four Star Nutritionals to the list. It's at least worth looking into to see for yourself. Since availability is an issue, I also recommend chewy.com.
Dog Food & Treats - fromms No Corn No Wheat No Soy Dry Food for All Stages - Free Shipping at Chewy.com
If you stick with RC, run from the yorkie specific formula. Find out and use the formula Yorkiemom uses....