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.
Have you looked in your cats mouth to see if there is any infection ? Is the cat eating normal like usually ? If not I would go to the vet with the cat to see what is going on .