Their teeth should ideally be brushed every day. Brushing 2-3 times a week may help a little, but not much as plaque hardens within 48 hours, thus making it very difficult to try to brush off. My vet did get me a tip for brushing the cats teeth if they are difficult. The cat/dog toothpastes that you buy are (should be) enzymatic cleaners, therefore they will still clean if you aren't scrubbing the teeth. If you're having a hard time with that tiny kitten mouth just rub the toothpaste over his teeth. Of course, brushing is best, but I guess you can introduce that in a few months when he's more comfortable, and things may be easier.