We were in your situation until right up until our son turned about 2.
Like you, we tried absolutely everything! People on the Huggies forum gave lots of good advice but in the end, only 1 thing worked for us.
The one piece of advice given to us was given early on to me by a Huggies member and at the time I thought it was too harsh. We sort of tried it but found it too upsetting for all of us. Then after many, many months of trying other things, we ended up going back to this piece of advice and now it works.
We ended up wrapping our son in a large towel(He was 2 years old - who also kicked, hit, thrashed around)This way, he couldn't move his arms as much. I kind of got his legs in between mine and held him tightly against my chest whilst my husband tried to clean his teeth. He cried, screamed etc - but at least whilst he cried - his mouth was open so you could get the toothbrush in. I know this sounds brutal and cruel but it had to be done. As I said - we had tried everything!! I would honestly say it took about 3 days of this (we only did it once a day at the time) and he finally allowed us to brush his teeth without being wrapped in a towel. Mind you, there were still tears but no thrashing and better co-operation of mouth opening. We kept the towel by his side (on the lounge) so to remind him that if he didn't co-operate he would be wrapped in the towel again. After about 3 weeks, we no longer needed the towel by his side and now we can get the job done.
We are at the point now where we can make it fun for him by playing little games or singing funny songs or pulling silly faces etc to help him when he doesn't want his teeth cleaned. He is sooo much better now (not perfect - but now we can do it!)
Also, take him to your dentist when you go for a check-up. Let him watch the dentist clean your teeth and dentists usually have a big toy with large teeth and a big toothbrush to demonstrate teeth cleaning. That might help too.
Look out for books or tv programs (or episodes) with teeth cleaning in them.
Also make sure he watches you brush your teeth morning and night so he knows the routine.
I should add the my Child Community nurse suggested not to force the issue but to get him to keep watching us and one day hopefully he will allow us to clean his teeth. We did that but it didn't work.
Best of luck and I do hope your little guy co-operates soon. It's harder on you all as he gets older and more likely to be in situations where he may eat more sugary things that are bad for his teeth.