First of all, the canine carnassial tooth has to be checked out. This is located on both sides of the upper jaw and it is the one much larger than the rest of your dog’s teeth because it’s made for crushing and breaking up the food. When you notice swelling in front of your dog’s eye, it’s probably that.
A dog that has a painful infection will also chew only when necessary and this is not their usual behavior as any good owner will know. Suddenly dropping food from their mouths can represent the same thing, too.
Bad breath can be another telltale sign so if you suddenly can’t stand your buddy licking you, check for any underlying causes.