Just as you brush your teeth and have them professionally cleaned for good overall health and appearance, your cat requires the same care.
Cats are predators by nature.
As such, their teeth are designed to kill prey and shear small, easy to swallow pieces of flesh from the carcass. Their teeth are not made to grind and gnaw things. Cats that eat moist food generally will need dental care earlier than cats who have a diet of dry food. Adding to the problem, many of our purebred cats seem to have inherited poor quality tooth enamel. Plaque builds up more rapidly on a purebred's teeth than it does for a genetically diverse cat.