Indeed, bacteria are the problem, just like in humans. When I was in school, there were still two thoughts on the matter of brushing your pet's teeth - since the issue arises from the constant "swallowing of" bacteria, and the dangers in swallowing globs of tartar that break off, along with the intrusion of bacteria via gingivitis.
One thought was that routine cleanings were the best route, because the pet can be anesthetized and the tartar scraped off (ultrasonically) and the mouth rinsed, and any damaged or problem teeth can be pulled.
The second way of thinking was to teach owners to brush their pet's teeth daily or weekly, to prevent tartar buildup.
Now Thought #1 didn't like Thought #2 because pets can't spit - so you're breaking up all that bacteria and having them swallow it. You're also rubbing their gums, and if gum tissue bleeds, bacteria gets inside, voiding the whole point of brushing them.
Thought #2 didn't like Thought #1 because it wasn't preventative medicine, it was old school.
Both Thoughts argue about the other being "in it for the money". Product sales vs Service costs.
My thoughts: Brush if you can, use pet toothpaste not human toothpaste, and a water bottle to "rinse" out the mouth (I can hear you laughing) But if you CAN'T brush your pet's teeth - simply keep them in mind, feed dry kibble, give dogs dental toys, cats can have crunchy treats made specifically for this, and take them in for yearly checkups.
*steps off soapbox and gives Bahamutchild a high-five*
