Why is our 4 year old Cocker Spaniel losing teeth?

She has horrid breath. We have had her teeth cleaned twice in the last year. It is huge expensive and I am afraid of the general anesthesia. Both times they extracted teeth, but said her remaining teeth were fine. She has horrid breath! We brush her teeth and we had adjusted her diet to a food that contains no animal by products, wheat or corn. We also give her dog bones that are supposed to clean her teeth and freshen breath. NOTHING makes a difference, she stinks! Last night she was walking through the kitchen when we heard something fall on the floor, I expected to see an earring but instead found a tooth! It is a small molar that still has all of its roots. What is going on? And what should I do now? I'm desperate for help.