I have not heard of breath mints for cats. I imagine if it is made for them then one or two would not hurt, but I would research it before I started giving it too them regularly.

I agree that if it just started and is not just the result of having just eaten something like tuna like PIF said. Then I would definately talk to the vet. Dental issues can be the result of or turn into something bad. Not all the time, but better safe then sorry.