What a cute vid!
I am really neurotic about Thor's teeth; we brush every night. I do my teeth, and then I do his. There have already been some great tips, but I wanted to share my technique to get Thor brush ready (I got this from LilMissy originally).
Thor used to HATE getting his teeth brushed, and it was such a struggle that his breath was really bad even right after we'd finished. I got beef-flavored tooth paste, and started by rubbing my pinky finger along his teeth. I did this every night for about a month. I didn't push it too hard, but as he got more comfortable, I started rubbing the front ones, making him open his mouth so I could get the back ones, etc.
Then I re-introduced the brush. I actually got one for cats because Thor's mouth is so small. The brush is about three inches long. I started by letting him lick a little paste off the brush, and then I would do a couple teeth very softly. After a week, I was doing all his teeth, + gums!
It was so worth it to train Thor to accept the brush. It literally takes five minutes, so I think it's very worthwhile to make it a daily habit.