Hi Gerald,
This is quite common in cats and can be resolved with a number of options. The smell comes from the mixture of saliva and bacteria in your cats mouth so if we can limit the bacteria (it's not necessarily bad don't worry!) then the smell will ease!
there are numerous gel/ pastes (if they will tolerate you brushing their teeth) designed to combat bad breath aswell as some chews if not. Proden have a product called plaque off that aims to remove plaque from teeth aswell, just sprinkle it over their biscuits!
a build up of plaque and tartar can lead to periodontal disease so best to keep an eye on it!
