Bringing a new dog into the house should not change the breath of the older dog. I suspect your Yorkie has been sampling some of the puppy's food. Puppy food is more calorie rich and tends to have a stronger odor. Yorkies in general tend to have problems with dental disease. Dental tarter is bacteria mineralized to the tooth, leads to gingivitis, gum recession, and abscessed teeth. Have your veterinarian examined the dog's mouth to determine if periodontal disease is present and if your dog needs a dental cleaning.
Would Introducing A Week Old Puppy To Our 4 Year Old Yorkshire Terrier Make Her Breath Smell Stronger?
We found these treats for our pomeranians called greenies and they work fantastic. The breath problem cleared up in a few days . Ask for greenies at your pet store.