Haven't read the whole thread so sorry if i'm repeating other people's ideas but my dd1 used to be a nightmare with toothbrushing, we constantly had to change tactics but some things that worked for us were
Pretending to be different animals with sharp teeth - crocodiles/dinosaurs/wolves/bears and then having a bedtimestory about one fo these animals for a reward.
Me being the mummy animal and her being the baby animal having teeth brushed.
Letting her chose whether to have the top teeth or bottom teeth brushed first.
Buying a flashing toothbrush and brushing for the length of time it flashed.
Counting to ten while brushing,
top teeth 1-10
bottom teeth 1-10
front of teeth 1-5.
Her mouth being the tunnel and the toothbrush being the train (train noises while brushing)
Most recently i've got a tiny travel theramed toothpaste pot which she loves as it;s tiny and special and just for her
She much prefers blue jelly minty toothpaste to anything else.
Hope some of this is useful