I brush my dogs teeth about once a week. We have done this since he was a little pup (he's now 2) so he has no problem with me brushing them. I think he actually enjoys it because I only have to call him once and get his toothbrush out and he will come
I have heard it is very important to keep your dogs dental hygiene in good condition as it can affect their lifespan. I know a few people who had dogs that eventually couldn't eat in their old age because of bad teeth.
I also use the dental stick treats too to help out a little. You don't have to brush them every day but once a week is recommended.