We have been wondering exactly the same thing. One of Bradleys teeth at the front still hasnt come through, either that or it was there and has fallen out., he looks like an old man who didnt ever visit his dentist! lol.
What do you feed? I raw feed, and have found in the past that my pups seem to teeth earlier than those fed kibble or wet foods, my 5 month old pup has lost all her puppy teeth now and is on with pushing through adult teeth. But I wouldn't worry if your diet is different, it may take a few months more.