When our dogs have their teeth cleaned, they have to be sedated and I really don't like that unless they have to have a tooth extracted. So we bought some dog toothbrushes (no I'm not kidding) and some dog toothpaste that they love the taste of. Every night we brush their teeth, We also try to give them treats that will help their teeth. Our Akita is 12 yrs old and has no dental problems. Ever since she was a puppy, she has been chewing on "Cheweeze" or "Denti-Bone".
Hope everything works out with your shih tzu. We have a shih tzu too and he hates having his teeth brushed.
Here's how I tell the difference: Let your dog chew/play with a STUFFED toy. Then immediately smell the toy....If the odor is on the toy, it's from the teeth/mouth and it's time for a dental/teeth cleaning. If not, then it's coming from somewhere else.(Farther down). Sometimes it's just an overgrowth of bacteria in the digestive system. In this case, a Probiotic is helpful, to counter-act the bad bacteria in the gut. Otherwise, a bloodtest is in order to look for organ problems. Hope some of this helps....Karla
P.S. As of right now, 83% of dogs in the U.S. have some kind of dental disease by the age of 3 yrs. old. Most of these dogs are fed dry kibble. That will probably answer your question about food... If it's actually Dental Disease...Please address it, now. It's unbelieveable what it can lead to.....Trust me on this one!!!!!!!
Bad breath does not always originate from dental problems. If a dog has a problem with internal organs like kidneys or the liver for example, it can result in some horrific-smelling breath. Untreated diabetes can harm the kidneys and result in bad breath too. If your dog has consitent bad breath, it's time for your vet to do an exam and get to the bottom of it. Hopefully it's only a matter of needing some tartar removal. :-)
My Bichon Frise also has foul breath I started giving him a half of a Tums a day for tear stains on his face that I read about hear it is working along with a vinigar wash. I also notice his breath is quite a bit better. It's worth a try and cant hurt him.