What happens if a cat swallowed a human teeth?

Yes. It is, however, unlikely that a cat would have only one tooth; I suspect you are talking about the big teeth, the so-called "canines", of which most cats have two in the upper jaw. These teeth are spaced to assist in rapidly killing rodents like rats and mice. With only one canine, a cat will be hindered somewhat in hunting; but as hunting is so little of a modern domestic cat's life, losing one of them actually poses very little handicap to a domestic cat.

If in fact you mean only one tooth, then the answer is still yes, though a cat with only one tooth would have significant trouble chewing anything. Soft, canned cat food would be advised, or dry cat food that comes in small, rounded rather than angular "kibbles", would be required.