I was reduced to two inches when I was stared down by this vet at the clinic - it felt like one of those times when I was sent to the principal's office.
"Your dog has a bit of brown teeth. You don't feed him enough bones to chew?!", he said.
It turned out raw bones are good for your dog and his teeth. Contrary to my believe, my vet said that giving him raw bones of at least 3-4 time a week helps clean his teeth. Your dog will also has cleaner breath. If dog's teeth, especially molar teeth, look brown it is a sign that your dog's teeth is not clean - source of bad breath and other diseases. You can get him a denture treatment which is very expensive (approx. $600-$800 or more) and it might already be too late.
You can get lamb's bones (for soup) from butcher shop very cheap, about $4-5 for 1-2 kg which should last a week. My vet said to chop them up to size of about my hand, put in plastic bags and freeze them in the freezer. Before going to bed, take one out and let it thaw during the night. You can give it to him in the morning. I have a two year-old border collie and he loves them.
It works! After just one week, my dog's teeth are now back to pearly white again and his breath is so much better. I could almost kiss him now.