Most effective are the chlorhexidine based rinses.
Chlorhexidine gluconate is an antiseptic which reduces inflammation and bleeding of the gums and freshens the breath. It has no known side effects.
Chlorhexidine acetate is antibacterial, but there are some reports of staining of the teeth after prolonged usage.
Rinses may also help reduce plaque and calculus formation. They can be added to the drinking water or some come with handy applicators, enabling direct application to the mouth.
When bleeding and inflammation subside, the rinse should be stopped.
Ideally, daily brushing with cat toothpaste is the gold standard for ongoing dental care.