Hi Pyr1, I dont have a pyr, but have had danes who were real finicky. Have you always had him on the same food?? Sometimes if you find THAT food for a dog, that will help the appetite. They also have the "ready made" sauces to pour over food, I have never tried them myself but hear they work well, but we have such big dogs so they should make it gallon size

There is also a variety of appetite boosting tabs,drops,liquid out there. One simple thing you could try is to use bullion cubes and warm water, and pour it over his food right before he is eating. There has been other threads about finicky eaters with lots of good advice. I know there were plenty of ideas about things to pour over the food.
The teeth, my vets have told me that certain dogs are more prone to tartar buildup. How often are you cleaning them yourself??? I like the toothbrushes and the paste for dogs, and they have a liquid you put in the water that helps keeping the teeth clean. An easy thing is to give carrots and other harder veggies to them to chew on, that gives them a great supplement to the diet and also helps clean the teeth. Chewing on bones.
I try and brush the teeth every other week, sometimes I give it a try every week and sometimes I neglect their teeth. But once every other week seems to be an okay way to go, at least for me.
Marit