It might just be tarter build up. They may not have gotten him used to brushing his teeth. You can try to take a wet washcloth and clean his teeth. I'd mention it to the vet next time you bring him in. As far as I know, vet's don't fill caveties. They just pull the teeth. Dogs and cats can do quite well without some of their teeth. I had to have my dog's tooth pulled in the front because it was abcessed. You wouldn't know it the way he eats! He's a piggy! :)
Hope you enjoy your new doggy!
Does your dog have what we cal "Wicked dog breath?" If so, it's probably tartar build up. Have him get a cleaning. I'm not up on pet dentistry but I think if you're wiling to pay, you can have them filled. Ain't medicine grand?!! :)