One of my cats has lost about 2 or 3 of the teeny tiny ones on the bottom and top. I think that him playing with a toy and me pulling it too hard might have caused it but it could be any number of things. It is very unlikely that a one year old cat would be having tooth and/or gum problems. Kittens loose all of thier baby teeth at least by 7 months I'm pretty sure. I have two five month old kittens and I've been finding baby teeth all over the house!
I wouldn't worry at all unless you can see alot of tartar build up or he shows any other signs of being sick.