I always send folks here, to Dr. Laura's advice on toddler tooth brushing: [=http://www.ahaparenting.com/ask-the-doctor-1/how-to-get-toddler-to-brush-teeth?A=SearchResult&SearchID=5297307&ObjectID=3594596&ObjectType=35][/
] ( I am on mobile if that link doesn't work go to www.ahaparenting.com
and search under "how to get a toddler to brush teeth")
What worked for us for awhile was asking him what was in there and open so we could see, and I would look and say "Is there a dump truck in there?! Oh wait, I think I see a giraffe, let me get him!" That kind of thing, and he was amused and would open up. It also helped somewhat when I made a game out of it and asked him to brush my teeth and then pretended like I didn't want to and ran away and made a big scene and let him "get" me as I playfully struggled. He thought that was hilarious and would then open up for a few seconds and I could get a few swipes. He also really liked the banana brush...at first....over time we got quite a toothbrush collection going and now he has about 8 to choose from. He also really likes the Lavera kids strawberry toothpaste.
But honestly we only had moderate success with those things and I thank my lucky stars every day that somehow, overnight, literally from one day to the next, when he was maybe just two or a few months past his birthday....he just started opening up and letting me get a good solid brushing in. Just like that! He always has to do it himself first (which i model as i brush my teeth and he's actually getting kinda good!) and then he lets me do it. I still have to make a big deal out of which toothbrush and sometimes use the old tricks when he is not as willing, but it just isn't a struggle anymore he always opens up. I hope it stays this way! I also think this was made possible because I rarely ever forced him, I would say maybe once a week or even less than that, I would just say ok we're doing this and hold him firmly on my lap and do it while he screamed...but it never felt right. It felt like a violation of trust and I just didn't have the nerve for that every day, I may be wrong but I believe if I had gone down the road of forcing him with brute physical force every day, he would not have had this turnaround to willingness. I feel it's crucial to try very hard everything you can and if you must then occasionally force it but every day.....I wouldn't.
I wish you the best of luck and if nothing else may your child suddenly become cooperative as mine did....it does happen, take heart!