A veterinarian who writes for the LA Times recommends brushing your kitties teeth every other day, never with human toothpaste, always with special pet toothpaste.
I have two 17year old cats and they never had any dental issues. But my kitty that is close to two years old had really bad breath but I didn't think to look at his teeth till recently. He had some bad plaque build up and the first times I brushed his teeth his gums would bleed (now the gums are...