Izzy was the same way...we got her at 20 weeks and she had tiny teeth and my husband would laugh and ask me where her teeth are. She just turned 1 on 12/29 and I can tell that her teeth (especially her caninnes) have grown to adult. At first when she would bark you couldn't even see that she had teeth..lol. Now when she barks or takes a treat from you you can at least see her pearly whites.
I wouldn't worry she is still young. Oh and Izzy is only 2.8 so I wonder if it's because they are so tiny to begin with.
