Man I hope it gets better. I just started brushing Gizmos teeth since he has started to get his adult teeth.
Boy is it a battle! He twists he head back, and squirms around wanting to escape. It eventually turns into me having to lock my legs around him and hold his head tight to he doesn't twist it away. And like some little kid that doesnt want to eat his greens, he shuts his mouth shut. So I have to get my fingers in there, but he will chomp down on them! Ouch!
I tried with the electric toothbrush, but that scarred the crap out of him. So I bought a dog brush that has 2 sides, that way it brushes the inside and outside at the same time.
But I'm not giving up. Gonna do this every night after his last meal. I also give him a "treat" after. Although not a normal treat. It's a chew stick with some added enzymes stuff in it for mouth hygiene and breath.