Is the dog exactly 5 m/o ? if a little younger or even not it very well coulda been his puppy teeth and not his perm ones....take a good pic of his mouth/teethe and post it....look real close and see if his grown teeth are comming in through the gums.
x3 Have a bmc male about the same age, he lost one playin with another pup. If they came out pretty easy I'd say they were baby teeth and his adults will come in.
Anthony