Your big ol' dog runs up to you, jumps up on your shoulders, and then tries to kill you with his doggy breath.
If it does, you probably aren't doing your part to take care of your pup's oral hygiene. While dogs are not subject to cavities like humans, their teeth and gums still need good care if you want to avoid your pup having problems with gum disease. Gum disease can lead to serious pain and loss of teeth. With a little practice, time and patience, you can learn to brush your pup's teeth and he can learn to have it done.
Do you think your dog cares if his teeth are yellow or that his breath could drop a T-Rex at 30 feet? Not likely, but what he will care about is if his gums become painful and he starts losing teeth. The thing is, your pup doesn't understand this. The only thing he understands is that you are sticking a toothbrush laden with toothpaste in his mouth.
It's your job as your big dog's human to take care of his every need (just don't tell him that). This includes his teeth and gums. While dogs don't get cavities like we do (lucky them), they do get gum disease that can cause them to lose their teeth and suffer a great deal of pain. While it might take a bit of practice to get both of you to a point at which both of you are comfortable with the entire process.